The clinical outcome of minimally invasive Phase 3 Oxford unicompartmental knee arthroplasty: a 15-year follow-up of 1000 UKAs

Lateral meniscus extrusion on preoperative MRI and its impact upon mid-term clinical outcomes following mobile-bearing unicompartmental knee arthroplasty

Background

The presence of full-thickness cartilage in the lateral compartment on valgus stress radiography is a criterion for medial mobile-bearing unicompartmental knee arthroplasty (UKA). However, the appropriateness of medial UKA is uncertain when preoperative MRI shows extrusion of the lateral meniscus. We therefore assessed how preoperative MRI-detected lateral meniscus extrusion affects mid-term functional outcomes after mobile-bearing UKA.

Methods

We retrospectively reviewed the records of our patients that underwent mobile-bearing medial UKA between January 2017 and December 2019. Crema's classification system was used to assess MRI of the lateral meniscus, categorizing patients as either grade 0 or ≥ grade 1. We preoperatively evaluated patient-reported outcomes using the Oxford knee score and Knee Society functional score, and then again at the latest follow-up. We also measured range of motion pre- and postoperatively. We compared preoperative individual data with outcome data obtained for at least three years.

Results

The lateral meniscus extrusion group included 19 knees, and the remainder included 98 knees. Clinical outcomes were similar between these groups (p > 0.05). No progression of lateral arthritis was observed in either group during the follow-up period.

Conclusion

Excluding UKA as an option for cases with lateral meniscus extrusion findings on preoperative MRI may require reconsideration.

Impact of intra-articular injection on infection risk and therapeutic effect after unicompartmental knee arthroplasty: a retrospective cohort study

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an effective treatment for single-compartment knee osteoarthritis. However, some patients experience lateral compartment pain after UKA. The impact of lateral compartment intra-articular injection on infection risk of the medial prosthesis and therapeutic outcomes in these patients remains controversial.

OBJECTIVE

This study aims to evaluate the impact of lateral compartment intra-articular injection after UKA on the risk of medial prosthetic joint infection, as well as its therapeutic effect on lateral compartment pain and inflammation. We hypothesized that lateral compartment intra-articular injection in patients with post-UKA lateral pain could provide better pain relief and functional outcomes without increasing the risk of medial prosthetic infection.

METHODS

This retrospective cohort study included patients who experienced lateral compartment pain after UKA at Jinshan Branch of Shanghai Sixth People's Hospital between January 2018 and December 2020. Patients were divided into two groups: those who received lateral compartment intra-articular injection for pain management (injection group) and those who received only oral medication (control group). The primary outcome was medial prosthetic infection rate within 6 months post-injection. Secondary outcomes included pain scores, knee function, and quality of life.

RESULTS

A total of 249 patients with post-UKA lateral compartment pain were included (144 in the injection group, 105 in the control group). There was no significant difference in medial prosthetic infection rates between the two groups (2.1% vs. 2.9%, p = 0.812). The injection group showed significantly better pain relief (VAS score) and knee function (KSS score) at 1 week and 1 month post-injection (p < 0.05). Quality of life measures (SF- 36) also showed improvements in the injection group at these early time points.

CONCLUSION

Intra-articular injection after UKA does not increase the risk of infection and may provide better short-term pain relief and functional outcomes. These findings support the safety and potential efficacy of this approach in managing apparent lateral knee post-operative pain and enhancing early recovery after UKA. However, larger prospective studies are needed to confirm these results and further explore the long-term impact of this intervention.

Long-term outcome of periprosthetic joint infection following unicompartmental knee arthroplasty: A single-centre case series

Purpose

Periprosthetic joint infection (PJI) following unicompartmental knee arthroplasty (UKA) is a rare but serious complication. The data available on this topic are heterogeneous and limited, particularly in regard to long-term survival and patient-reported outcomes (PROs). Therefore, the aim of the present study was to analyse the long-term survival and functional outcome of a case series of PJI following primary UKA at a tertiary referral centre.

Methods

Eighteen knees treated for acute or chronic PJI after primary UKA between 2001 and 2020 with a minimum follow-up of 2 years were retrospectively identified and evaluated in the present study. Surgical treatment included debridement, antibiotics and implant retention (DAIR) in 10 patients, and two-stage arthroplasty in 8 patients. Implant survival analysis was conducted using the Kaplan-Meier estimator. Patient-reported outcome measures (PROMs) were used to assess clinical outcomes.

Results

Overall implant survival free from any revision at 10 years was 83% (95% confidence interval [CI]: 57%-94%). Three DAIR procedures failed due to persistent infection with partially major complications, resulting in a 10-year revision-free implant survival of 73% (95% CI: 37%-90%). No reoperation was required in the group that underwent staged treatment. There were no long-term revisions due to aseptic loosening or degeneration of other compartments in either group. Both groups demonstrated promising median Oxford Knee Scores, with no significant difference (>0.05) between the DAIR (42, range 11-45) and two-stage exchange arthroplasty (43, range 19-46) groups.

Conclusions

Two-stage revision procedure offers excellent long-term survival and high patient satisfaction. The DAIR procedure represents a valid treatment option for acute PJI but carries a certain risk of treatment failure that surgeons should be aware of. Successful treatment of PJI in UKA can provide excellent functional outcomes and long-term survival without an increased risk of low-grade infection and aseptic loosening.

Level of Evidence

Level IV.

Analysis of national real-world data on reoperations after medial unicompartmental knee arthroplasty : insights from a high-usage country

Aims

The aim of this study was to examine the indications for further surgery and the characteristics of the patients within one year of medial unicompartmental knee arthroplasty (mUKA), providing an assessment of everyday clinical practice and outcomes in a high-volume country.

Methods

All mUKAs which were performed between 1 April 2020 and 31 March 2021 and underwent further surgery within one year, from the Danish Knee Arthroplasty Registry (DKAR), were included. For primary procedures and reoperations, we received data on the characteristics of the patients, the indications for surgery, the type of procedure, and the sizes of the components individually, from each Danish private and public arthroplasty centre. All subsequent reoperations were recorded regardless of the time since the initial procedure.

Results

A total of 2,431 primary mUKAs in 2,303 patients were reported to the DKAR during the study period and 55 patients (55 mUKAs; 2.3%; (95% CI 1.7 to 3.0)) underwent further surgery within one year. The most frequent indications for reoperation were periprosthetic fracture (n = 16; 0.7% (95% CI 0.4 to 1.1)), periprosthetic joint infection (PJI) (n = 13; 0.5% (95% CI 0.3 to 0.9)), and bearing dislocation (n = 9; 0.4% (95% CI 0.2 to 0.7)). Six periprosthetic fractures were treated with internal fixation, but five of these patients later underwent revision to a total knee arthroplasty (TKA). Ten PJIs were treated with debridement, antibiotics, and implant retention (DAIR). Due to persistent infection, four of these patients later underwent revision to a TKA. All nine bearing dislocations were treated with exchange of the liner, and seven occurred in patients who, based on their sex and height, probably had undersized femoral components.

Conclusion

Reoperations are rare following mUKA in a high-volume country. The most frequent indications for further surgery were periprosthetic fracture, PJI, and bearing dislocation. Using internal fixation to treat periprosthetic fractures after mUKA gives poor results. Whether DAIR is an appropriate form of treatment for PJI in mUKAs, and how to ensure the effective eradication of infection in these patients, remains uncertain. Undersizing the femoral component might increase the risk of bearing dislocation.

Long-term results of lateral unicompartmental knee arthroplasty with a mobile-bearing device

Aims

Unicompartmental knee arthroplasty (UKA) is one option in the treatment of isolated unicompartmental advanced osteoarthritis (OA). While long-term results exist for medial mobile-bearing (MB) UKA, evidence regarding lateral MB-UKA is still limited. The Oxford Domed Lateral (ODL) implant aims to reduce the bearing dislocation rate in lateral MB-UKA through enhanced bearing entrapment. However, the long-term performance of this implant remains unclear. This study evaluated the long-term survival and clinical outcomes of the ODL in a non-designer centre.

Methods

This single-centre retrospective analysis included 115 lateral MB-UKAs using the ODL performed between January 2006 and December 2014. The primary endpoint of the study was implant survival, defined as the time until a revision procedure was required for any reason. Secondary outcomes included Oxford Knee Score (OKS), Forgotten Joint Score (FJS), pain, satisfaction, and Tegner Activity Scale (TAS). Survival was assessed using Kaplan-Meier analysis.

Results

At ten years, the cumulative implant survival rate was 74.8% (95% CI 65.2 to 82.1; number at risk = 71), with bearing dislocation (8.5%) and OA progression (10.4%) as leading revision causes. In 55 non-revised knees with a mean follow-up of 13.4 years (SD 1.8), the mean postoperative OKS improved significantly to 37.8 (SD 9.1) (p < 0.001). Additionally, 85.5% of patients (n = 47) reported satisfaction, with a mean FJS of 65.9 (SD 32.2) and TAS of 2.8 (SD 1.1). However, only 76.4% (n = 42) attained the patient-acceptable symptom state for OKS and FJS.

Conclusion

This is the first long-term ODL study from a non-designer centre; our results demonstrated high failure rates due to bearing dislocation and OA progression, despite satisfactory clinical outcomes in non-revised patients. The disproportionately high risk of failure suggests that the MB design should be abandoned in favour of a fixed-bearing device for lateral UKA.

Evaluation and Analysis of Outcomes of Unicondylar Knee Arthroplasty in Unicompartmental Knee Osteoarthritis

Background Recent increased interest in less invasive surgical techniques has led to a concurrent resurgence in unicompartmental knee arthroplasty (UKA). UKA is an effective treatment for end-stage, symptomatic unicompartmental osteoarthritis (OA) of the knee. Both clinical outcome and kinematic studies have indicated that successful UKA functions closer to a normal knee. UKA aims to restore the natural alignment of the limb, the original ligament tension, and the joint line. The aim of this study is to evaluate and analyze the outcomes of unicondylar knee arthroplasty performed in patients with unicompartmental OA of the knee joint. Methods This is a prospective study that includes 20 patients of unicompartmental OA knee managed with UKA in the Department of Orthopaedics, Tirunelveli Medical College, Tirunelveli, India. The implant used was JOURNEY UNI unicompartmental knee prosthesis (Smith & Nephew, Watford, England). All patients were evaluated radiologically before and after surgery. Clinical outcome was determined by using the Knee Society Scoring System (KSS) over a two-year follow-up period. Results According to the KSS, the average pre-operative score of 107.25 (95-119) increased to 189.30 (175-205) in the post-operative period. No intra-operative complications were noted in our study. One patient (5%) showed delayed wound healing and healed after a course of antibiotics. There were no additional procedures or revisions for implant-related complications or the occurrence of fractures. Conclusions This prospective study concludes that a fixed-bearing UKA provides an effective solution in treating medial compartment OA of the knee. The fixed-bearing prosthesis has the advantage that it restores the tibial and femoral joint line to the native level and at the same time corrects to previous limb alignment. This procedure also ensures effective functional recovery and pain relief. No major intraoperative or post-operative complications were observed.

Robotic Assistance in Simultaneous Bilateral Medial Unicompartmental Knee Arthroplasty: A Retrospective Cohort Study of 126 Knees Demonstrating Enhanced Radiographic Accuracy and Comparable Safety to Conventional Methods

Background

One-stage bilateral unicompartmental knee arthroplasty (BUKA) is a promising option for patients with bilateral medial knee osteoarthritis. This study aims to compare the safety, early clinical and functional outcomes, and radiological results of conventional vs robotic-assisted medial BUKA.

Methods

A retrospective cohort study was conducted involving patients who underwent medial BUKA as a single-stage procedure between April 2016 and January 2022. The study included both conventional (36 procedures) and robotic-assisted techniques (90 procedures) with a minimum follow-up of 6 months. Conventional procedures were performed either simultaneously by two surgical teams or sequentially by one team. Robotic procedures were exclusively performed sequentially by a single team. Data on surgical outcomes, patient-reported outcome measures (International Knee Society score), and radiographic measurements were collected.

Results

Among the 63 patients analyzed, robotic-assisted procedures took significantly longer (115 ± 22 minutes) compared to conventional approaches (86.9 ± 12 minutes; P < .0001). No significant differences were observed in complications, length of hospital stay, rehospitalizations, patient-reported outcome measures, or overall clinical outcomes. However, radiographic analysis showed superior joint line restoration in the robotic group (-0.2 ± 0.7 mm vs -1.4 ± 1.35 mm, P = .03) and better tibial implant varus control (0.3° ± 0.6 vs 1° ± 1.8 degrees, P = .03).

Conclusions

While robotic-assisted BUKA resulted in longer operative times, clinical outcomes were comparable. Radiographic findings indicated improved implant positioning, suggesting potential benefits in implantation accuracy that warrant further research.

Level of Evidence

IV.

Valgus stress knee radiographs accurately anticipate the bone resection in medial unicompartmental knee arthroplasty: Protocol validation using an image-based robotic system

PURPOSE

The objective of this study was to describe a planning method for medial unicompartmental knee arthroplasty (UKA) implantation using preoperative stress radiographs to measure the thickness of tibial and femoral bone resections and to validate this method with data from an image-based robotic surgery system. Having such method for preoperative planning would be of interest for surgeons performing UKA in order to anticipate optimal bone resection on both tibia and femoral sides.

METHODS

A new planning method for medial UKA based on valgus stress knee radiographs validated it with an image-based robotic surgery system (Restoris MCK, MAKO®, Stryker Corporation) was proposed. This retrospective study involved radiographic measurements of 76 patients who underwent image-based robotic medial UKA between April 2022 and February 2023. Preoperative anteroposterior stress radiographs of the knee were used to simulate UKA implantation. The UKA technique was based on Cartier's angle and aimed at restoring the joint line. The total dimension measured was 14 mm (8 mm for minimal tibial component and polyethylene insert + 4 mm for femoral component + 2 mm for safety laxity). Bone resections were measured in the preoperative valgus stress radiographs and then against the intraoperative bone resection data provided by the robotic system. Inter- and intra-observer reliability was assessed using 25 measurements.

RESULTS

The mean planned tibial resection measured in the radiographs was 4.3 ± 0.4 [2.9-5.8], while the mean robotic resection was 4.2 ± 0.5 [2.7-5.8] (mean difference = 0.15 mm, 95% confidence interval [CI] [-0.27 to 0.57]). There was a strong correlation between these two values (Pearson's rank R = 0.79, p < 0.001). Intra- and inter-observer reliability were also very strong (Pearson's rank R = 0.91, p < 0.001, and Pearson's rank R = 0.82, p < 0.001, respectively). The mean planned femoral bone resection measured in the radiographs was 2.7 ± 0.7 mm [1-4.5], while the mean robotic resection was 2.5 ± 0.9 [1-5] (mean difference = 0.21 mm, 95% CI [-0.66 to 1.08]). There was a strong correlation between these two values (Pearson's rank R = 0.82, p < 0.001). Intra- and inter-observer reliability were also strong (Pearson's rank R = 0.88, p < 0.001, and Pearson's rank R = 0.84, p < 0.001, respectively).

CONCLUSION

This study describes and validates with robotic information a simple and reproducible preoperative planning method to determine femoral and tibial bone resection for medial UKA implantation using antero-posterior valgus stress knee radiographs, leaving a medial safety laxity of 2 mm. It represents a very valuable contribution to the understanding of UKA principles, which can serve to extend its indications and increase reproducibility of the surgical technique.

LEVEL OF EVIDENCE

Level III, retrospective cohort study.

The Estimated Lifetime Risk of Revision After Primary Knee Arthroplasty Is Influenced by Implant Design and Patient Age: Data From the National Joint Registries

BACKGROUND

The aim of this study was to determine the lifetime risk of revision surgery after primary knee arthroplasty (KA) according to implant choice and patient age.

METHODS

The risk of revision according to the implant type (unicondylar, unconstrained, semiconstrained, and fully constrained) was obtained from the National Joint Registry of England and Wales. Mortality risk according to age was estimated from the Scottish Arthroplasty Project (1998 to 2019). The cumulative incidence of revision and death was calculated up to 20 years. The lifetime risk was calculated as a percentage using a multiple decrement life-table methodology.

RESULTS

The lifetime risk of revision varied according to the implant, with unconstrained having the lowest risk and fully constrained and unicondylar having the highest risks, which increased with younger age. For an "average" patient aged between 65 and 69 years, the revision risks for an unconstrained (3.6%, 95% confidence interval [CI] 3.4 to 3.9), semiconstrained (7.2%, 95% CI 3.9 to 13.6), unicondylar (13.7%, 95% CI 12.4 to 15.2), and fully constrained (15.4%, 95% CI 9.2 to 25.7) total KA gradually increased. Relative to an unconstrained KA, the risk of revision for a semiconstrained implant was similar in patients aged < 65 years (relative risk < 2), whereas when this was employed in those ≥ 65 years, the relative risk was more than double (relative risk ≥ 2). Relative to an unconstrained KA, the risk of revision for a fully constrained or a unicondylar KA was more than double in patients aged < 55 years (relative risk > 2) and more than triple (relative risk ≥ 3) in patients ≥ 55 years CONCLUSION: The estimated lifetime risk of revision following KA was dependent on patient age and implant type, with fully constrained and unicondylar KA being associated with a higher lifetime revision risk. There are limitations in the data, and the indication for surgery and the reasons for revision were not assessed.

LEVEL OF EVIDENCE

III.

Revision of unicompartmental knee arthroplasty: a systematic review

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is a surgical procedure for managing osteoarthritis of one joint compartment, most commonly the medial side. This systematic review investigates the causes of UKA revision. The outcomes of interest were establishing the revision rate, time to revision, and the most common causes of revision in the long- and midterm follow-up.

METHODS

This study was conducted according to the 2020 PRISMA statement. In October 2024, the following databases were accessed: PubMed, Web of Science, Google Scholar, and Embase. All the clinical studies investigating the rate and causes of revision in UKA were accessed. Only studies with a minimum of 10 years of follow-up were considered.

RESULTS

Data from 56 studies (13,540 patients) were collected. Of them, 65.6% were women. The mean length of the follow-up was 13.1 ± 3.0 years. The mean age of the patients was 65.6 ± 5.6 years, and the mean BMI was 28.5 ± 2.2 kg/m2. Revisions were performed in 8.8% (2641 of 30,140) of implanted UKAs. The mean time to revision was 6.5 ± 2.6 (range, 2.5 to 13.0) years.

CONCLUSION

8.8% (2641 of 30,140) of UKAs were revised at a mean time of 6.5 ± 2.6 years.

LEVEL OF EVIDENCE

Level IV, systematic review.

The mobile bearing prosthesis: How to know when it's right for my patient and tips for surgical success

Unicompartmental knee arthroplasty (UKA) has seen a revival of popularity in the last thirty years in the United States. The benefits of a medial UKA over the previous 'gold standard' for knee osteoarthritis, the total knee arthroplasty, include increased postoperative range of motion (ROM), maintenance of natural knee mechanics, faster recovery, similar pain relief and decreased morbidity. Mobile-bearing UKA (MB-UKA) implants have been developed to improve polyethylene wear while maintaining normal knee kinematics. In this review, we will cover indications and contraindications for aN MB-UKA, patient selection, and technical tips and tricks.

Cemented versus cementless unicompartmental knee arthroplasty

Unicompartmental knee arthroplasty (UKA) offers a more conservative treatment than total knee arthroplasty when osteoarthritis affects only one tibiofemoral knee compartment. Cemented UKA has become the gold standard due to its good functional outcomes and low revision rates. The most common reasons for revision with cemented UKA include aseptic loss, unexplained pain, and radiolucent lines. Cementless UKA, which adds a porous coating of titanium and hydroxyapatite as well as an additional peg on the femoral component, has been shown to reduce the prevalence of radiolucencies compared to cemented UKAs. National registry data have demonstrated comparable functional outcomes and improved revision rates with cementless UKA. This review aims to summarize various advancements in unicompartmental prostheses, and to highlight how the conceptual advantages of the cementless model lead to superior implant survivorship and functional outcomes.

Influencing factors of kinesiophobia in knee arthroplasty patients under the social cognitive theory: A structural equation model

OBJECTIVE

To analyze the path relationships among influencing factors for kinesiophobia in knee arthroplasty patients through a structural equation model.

BACKGROUND

The occurrence of kinesiophobia significantly impacts the rehabilitation process of knee arthroplasty patients. However, there is still a need to determine factors that contribute to reducing kinesiophobia.

DESIGN

A cross-sectional study was conducted and reported following the STROBE guideline.

METHODS

Between February 2022 to October 2022, 162 total knee arthroplasty (TKA) patients and 81 unicompartmental knee arthroplasty (UKA) patients completed a survey. A structural equation modeling (SEM) approach was utilized to analyze the relationships between kinesiophobia and influencing factors (social support, pain resilience, and rehabilitation self-efficacy). Furthermore, multi-group SEM analysis was conducted to examine whether the model equally fitted patients in different types of knee arthroplasty.

RESULTS

The direct negative effects of rehabilitation self-efficacy (β = -0.535) and pain resilience (β = -0.293) on kinesiophobia were observed. The mediating effect (β = -0.183) of pain resilience and rehabilitation self-efficacy between social support and kinesiophobia was also significant. The SEM model achieved an acceptable model fit (χ2 = 35.656, RMSEA = 0.031, χ2/df = 1.230, GFI = 0.972, NFI = 0.982, IFI = 0.997, CFI = 0.996). In multicohort analysis, no significant differences were observed among knee arthroplasties (TKA, UKA) (Δχ2 = 4.213, p = 0.648).

CONCLUSIONS

Satisfactory social support enhances pain resilience and rehabilitation self-efficacy, so as to reduce kinesiophobia. Future interventions that directly target the assessment and management of kinesiophobia, available social support may help reduce kinesiophobia, and pain resilience and rehabilitation self-efficacy may be critical factors in managing kinesiophobia.

RELEVANCE TO CLINICAL PRACTICE

Reducing kinesiophobia in knee arthroplasty patients requires satisfactory social support, pain resilience, and rehabilitation self-efficacy. Therefore, healthcare organizations may implement initiatives to reduce kinesiophobia by taking these factors into account.

Conversion of UKA to TKA using identical standard implants-How does it compare to primary UKA, primary TKA and revision TKA?

BACKGROUND

UKA is a well-established treatment option for anteromedial osteoarthritis of the knee, resulting in superior functional outcomes but also higher revision rates than TKA. This study aimed to compare the outcomes of UKA, TKA, UKA converted to TKA using identical standard implants and revised TKA to support clinical decision-making.

METHODS

In this study, we retrospectively examined 116 patients who underwent UKA, 77 patients who received TKA, 28 patients whose UKA was converted to TKA using identical standard implants, and 21 patients who had a one-stage revision of TKA. The mean age at operation was 66.5 years (39-90 years), with a mean BMI of 28.8 kg/m2 (17.4-58.8) and a mean follow-up period of four years (0.9-9.9 years). We assessed various PROMs, including Oxford Knee Score, UCLA score, KSS score, and a modified WOMAC-Score as well as patient satisfaction and ability to resume daily activities, work, and sports.

RESULTS

The highest patient satisfaction was seen in the UKA. All scores were significantly higher for UKA than for TKA, converted UKA, and revised TKA. None of the scores showed a significant inferiority of converted UKA to TKA. In the case of revision, two scores showed significantly better results for converted UKA than for revised TKA.

CONCLUSIONS

Our results indicated that patients initially treated with UKA did not have significantly worse functional outcomes after conversion to TKA, given the use of identical standard implants. This highlights the effectiveness of UKA as a therapeutic option with outcomes superior to those of primary TKA and the importance of a bone-sparing procedure. Conversely, revision TKA is linked to poorer functional outcomes compared to both primary arthroplasties.

Analysis of correlation between medial joint line change and lower limb coronal alignment after Oxford unicompartmental knee arthroplasty

BACKGROUND

Lower limb coronal alignment was thought to be a predictive factor for Unicompartmental Knee Arthroplasty (UKA) result. The tibial bony resection and implant position lead to joint line change postoperatively. Analysis was done to find out the correlation between these factors.

METHODS

From 2019 to 2021, 90 medial Oxford UKA were implanted by a single surgeon. Hip Knee Ankle Angle (HKAA), Lateral Distal Femoral Angle (LDFA), Medial Proximal Tibial Angle (MPTA), and intraoperative bony resection thickness were measured. The medial joint line change was calculated. The correlation between joint line change and alignment change was evaluated.

RESULTS

The mean tibial resection thickness was 4.3 mm. The mean tibial joint line was elevated by 2.3 mm, while the mean femoral joint line proximalized by 0.8 mm. HKAA changed from 8.4° varus preoperatively to 3.6° varus postoperatively. LDFA changed from 89.0° to 86.7°. MPTA changed from 85.6° to 86.6°. Preoperative HKAA showed a strong correlation with postoperative HKAA (p < 0.001), and preoperative MPTA showed a positive correlation with postoperative HKAA (p < 0.001). While preoperative LDFA had a negative correlation with postoperative HKAA (p < 0.001). The femoral joint line change and LDFA change had a significant correlation with HKAA change (p < 0.05).

CONCLUSION

The change of joint line had no correlation with postoperative HKAA in Oxford UKA. Preoperative HKAA strongly correlated with postoperative HKAA; while preoperative smaller LDFA and larger MPTA had a moderate correlation with postoperative HKAA. The femoral joint line change and LDFA change had a weak to moderate correlation with HKAA change.

Favorable early outcomes of medial unicompartimental knee arthroplasty in active patients presenting a degenerative medial meniscus root tear with meniscal extrusion and mild radiographic osteoarthritis

INTRODUCTION

There is only limited literature available evaluating the preferable treatment for active mid-age or elderly patients presenting with a degenerative medial meniscus root tear (d-MMRT) with medial meniscal extrusion (MME) and early-phase radiographic osteoarthritis (OA), failing to provide solid evidence. The aim of this study was to evaluate early outcomes of medial unicompartimental arthroplasty (mUKA) in active patients presenting a d-MMRT with meniscal extrusion and mild radiographic OA of the knee. To prove this claim we hypothesized that (1) patients with a d-MMRT with initial grade 1-3 KL OA of the medial compartment of the knee present the same pre-operative symptoms as patients with an end-stage grade 4 K-L OA, and that (2) those patients with d-MMRT and low-grade OA achieve the same early clinical and functional outcomes when treated with mUKA compared to patients with end-stage medial OA.

METHODS

We reviewed the prospectively collected data of 185 patients undergoing robotic-assisted image-based mUKA from January 2021 to July 2022 at a single Institution. We identified two different cohorts of non-consecutive patients: a group of 24 patients undergoing mUKA surgery following d-MMRT combined with K-L grades 1-3 OA (group 1), and a group of 161 patients who underwent mUKA but presenting with an end-stage bone-on-bone K-L grade 4 OA (group 2). Preoperative and postoperative clinical assessments at one-year follow-up included the Oxford Knee Score (OKS), 5-level EQ-5D version (EQ-5D-5L score), and a standard weight-bearing X-ray protocol. The paired t-test was used to compare clinical outcomes and radiologic values of the two cohorts and in-between the two cohorts. Statistical significance was set at p < 0.05.

RESULTS

The mean follow-up for group 1 was 16.4 ± 2.5 months, and the mean age at the time of operation was 63 ± 8.6 years with a mean time from diagnosis to intervention of 53 ± 47.5 days. Preoperative impairment was greater in group 1 compared to group 2, but with no significant difference. Postoperatively, both groups showed excellent mean outcomes at 1-year follow-up, with no significant difference. The mean preoperative HKA, mPTA, and LDFA were 176.3 ± 3.1, 88.1 ± 2.3, and 86.6 ± 1.7 respectively. The mean postoperative HKA, coronal femoral component angle, and coronal tibial component angle were 179.1 ± 2.6, 87.2 ± 2.3, and 87.2 ± 3.3. No difference was found between preoperative age, BMI, between the two cohorts.

CONCLUSIONS

Favorable early clinical outcomes were obtained after mUKA in active mid-age and elderly patients presenting with degenerative medial meniscus root tear and mild isolated medial OA. Patients with mild no bone-on-bone OA but with degenerative medial meniscus root tear and medial meniscal extrusion presented the same or worse pre-operative symptoms as patients with end-stage medial OA and benefit the same from mUKA.

Unexpected positive cultures in revision total knee arthroplasty after unicompartmental knee arthroplasty

PURPOSE

Unexpected positive cultures are defined as a single positive culture in intraoperative samples taken during revision surgery after prosthetic joint infection was preoperatively ruled out. This study aims to determine the prevalence of unexpected positive cultures (UPC) in revision total knee arthroplasty (TKA) after unicompartmental knee arthroplasty (UKA). As a secondary objective, this study aims to compare the re-intervention rate in this specific group, between UPC and non-UPC patients. The hypothesis is that the UPC prevalence in patients who undergo a revision TKA after UKA is not higher than in other TKA revision cases and this does not increase the risk of re-intervention.

METHODS

This is a retrospective study where all patients who underwent a UKA revision from January 2016 to February 2023 in a high-volume arthroplasty centre, were analyzed. Unexpected positive culture prevalence in this group of patients was obtained.

RESULTS

During the included period, 270 UKA revision surgeries were performed. Eight cases had at least two positive cultures and were therefore excluded. The final analysis included 262 patients. Of these, 8 (3.05%) patients presented UPCs and the isolated microorganisms were low-virulence organisms. None of the UPC patients received any treatment. No statistical differences were found between UPC and non-UPC groups in the analyzed variables.

CONCLUSION

The prevalence of unexpected positive cultures in patients following revision of unicompartmental knee arthroplasty is lower than in patients who undergo a revision of total knee arthroplasty. In UKA patients a UPC does not seem to increase the risk of a re-intervention, so it can be safely ignored if ICM criteria are not met.

Associated patellofemoral osteoarthritis is not a contraindication for unicompartmental knee replacement. Report of one hundred ten prostheses with an average 6-year follow-up

INTRODUCTION

Associated patellofemoral joint osteoarthritis (APFJ-OA) has typically been considered a contraindication for unicompartmental knee arthroplasty (UKA) in the treatment of femorotibial joint osteoarthritis. However, this contraindication is being challenged. The aim of this study was to assess clinical and functional outcomes, complications, and implant survival in medial or lateral UKA, regardless of clinical symptoms or radiographic signs of APFJ-OA.

METHODS

This retrospective, comparative study included patients treated with medial or lateral UKA regardless of preoperative symptoms or signs of APFJ-OA, with a minimum 2-year follow-up. Intraoperatively, knees were subdivided based on APFJ-OA grade, according to the Outerbridge classification. Clinical and functional outcomes were analyzed using the 2011 Knee Society Score (KSS) at the last follow-up control. APFJ-OA was treated systematically, in a tailored, stepwise fashion according to its severity. Complications and implant survival rates were evaluated. Two-sided paired T-test, ANOVA, and Kruskal-Wallis tests were used with a significance level of 5%.

RESULTS

Finally, 110 UKAs were assessed 81 (73.6%) medial and 29 (26.4%) laterals. The average follow-up was 6 years (2-19.5). According to Outerbridge, 22 knees (20%) were in grade 2, 59 (53.6%) were in grade 3, and 29 (26.4%) were in grade 4. All three groups showed a statistically significant increase in KSS scores and range of motion. There were no significant differences in clinical KSS improvement and flexion contracture between Outerbridge groups (average 35.7 and -4.9, respectively). Group 3 showed statistically significant improvement in functional KSS when compared to group 2 (68.8 vs 61.2). In maximum flexion, groups 3 and 4 did significantly better than group 2 (20° vs 15°). Three prostheses (2.7%) needed revision after 7, 8.6, and 12 years due to aseptic tibial loosening. Implant survival was 100% at 5 (64 of 64), 97% at 7 (30 of 31), 93% at 9 (14 of 15), and 89% at 12 years, respectively (8 of 9).

CONCLUSION

Clinical and functional results, complications, and survival of medial or lateral UKA were not negatively affected by APFJ-OA assessed intraoperatively using the Outerbridge classification after an average follow-up of 6 years. We consider that APFJ-OA is not a contraindication for UKA when treated systematically according to its severity.

LEVEL OF EVIDENCE

IV.

Impact of the sagittal spinopelvic and coronal lower extremity alignments on clinical outcomes after medial unicompartmental knee arthroplasty

Introduction

We evaluated whether the clinical outcomes, including postoperative knee range of motion (ROM), after unicompartmental knee arthroplasty (UKA) were associated with the sagittal spinopelvic parameters and coronal alignment of the full lower extremity.

Methods

Forty-two patients (50 knees: six men, seven knees; 36 women, 43 knees) who underwent medial UKA between April 2015 and December 2022 were included. Preoperative radiographic examinations of the index for sagittal spinopelvic alignment included the sagittal vertical axis (SVA), lumbar lordosis, sacral slope (SS), pelvic tilt (PT), and pelvic incidence. The anteroposterior hip-knee-ankle angle (HKAA) was calculated. The relationship of clinical outcomes and the risk of knee flexion angle ≤125° and knee flexion contracture ≥10° 1-year post-UKA with radiographic parameters were evaluated.

Results

Preoperative HKA angle affected postoperative knee flexion angle ≤125° (p = 0.017, 95% confidence interval [CI]: 0.473-0.930) in logistic regression analysis. Patients with a knee flexion angle ≤125° had a higher preoperative HKAA (9.8 ± 3.0°), higher SVA (83.8 ± 37.0 mm), and lower SS (23.7 ± 9.0°) than those with a flexion angle >125° (preoperative HKAA: 6.6 ± 4.0°, SVA: 40.3 ± 46.5 mm, SS: 32.0 ± 6.3°) (p = 0.029, 0.012, and 0.004, respectively). PT related to postoperative knee flexion contracture ≥10° (p = 0.010, 95% CI: 0.770-0.965) in the logistic regression analysis. Patients with flexion contracture ≥10° had higher PT (35.0 ± 6.6°) and SVA (82.2 ± 40.5 mm) than those with flexion contracture <10° (PT, 19.3 ± 9.0°; SVA, 42.4 ± 46.5 mm) (p = 0.001 and 0.028, respectively). The postoperative clinical outcome was correlated with the postoperative knee flexion angle and SVA (p = 0.036 and 0.020, respectively).

Conclusions

The preoperative HKAA affected postoperative knee flexion angle, and the knee flexion contracture and clinical outcomes post-UKA were associated with PT and SVA, respectively. To predict outcomes for knee ROM and clinical scores after UKA, radiographic examination, including the sagittal spinopelvic parameters and the coronal view of the full lower extremity, is essential.

In Vivo Kinematics and Cruciate Ligament Tension Are Not Restored to Normal After Bicruciate-Preserving Arthroplasty

BACKGROUND

Whether cruciate ligament forces in cruciate-preserving designs, such as unicompartmental knee arthroplasty (UKA) or bi-cruciate-retaining total knee arthroplasty (BCR-TKA), differ from those in normal knees remains unknown. The purpose of this study was to compare the in vivo kinematics and cruciate ligament force in knees before and after UKA or BCR-TKA to those in normal knees during high-flexion activity.

METHODS

Overall, twenty normal knees, 17 knees with medial UKA, and 15 knees with BCR-TKA were fluoroscopically examined while performing a squatting activity. A 2-dimensional or 3-dimensional registration technique was employed to measure tibio-femoral kinematics. Ligament strains and tensions in the anteromedial bundle of the anterior cruciate ligament and posterolateral bundle of the anterior cruciate ligament and the anterolateral bundle of the posterior cruciate ligament (aPCL) and posteromedial bundle of the posterior cruciate ligament (pPCL) during knee flexion were analyzed.

RESULTS

Tension in both bundles of the anterior cruciate ligament decreased with flexion. At 60° of flexion, anteromedial bundle of the anterior cruciate ligament tension in postoperative UKA knees was greater than that in normal knees. At 30° of flexion, posterolateral bundle of the anterior cruciate ligament tension in postoperative UKA knees was greater than that in normal knees. On the other hand, aPCL and pPCL tensions increased with flexion. From 40 to 110° of flexion, the postoperative aPCL tension in UKA knees was greater than that in normal knees. At 110° of flexion, the preoperative pPCL tension in UKA knees was greater than that in normal knees. In addition, the postoperative pPCL tension in UKA knees was larger than that in normal knees beyond 20° of flexion. Furthermore, the pPCL tension of postoperative BCR-TKA knees was larger than that in normal knees from 20 to 50° and beyond 90° of flexion.

CONCLUSIONS

The cruciate ligament tensions, especially posterior cruciate ligament tension in knees after UKA, were greater than those in the normal knees. Surgeons performing bi-cruciat-preserving knee arthroplasties should therefore balance cruciate ligament tension more carefully in flexion and extension.

Anteromedial knee osteoarthritis (AMOA) evaluated with magnetic resonance imaging (MRI): a cohort study of 100 patients

INTRODUCTION

Magnetic resonance imaging (MRI) scans are increasingly used for knee osteoarthritis evaluation and preoperative planning before unicompartmental knee arthroplasty (UKA), and often patients already have MRI scans before their initial surgeon consultation. This highlights the need for surgeons to understand anteromedial osteoarthritis (AMOA) patterns on MRI. Hence, we aim to describe MRI findings in patients with AMOA meeting current indications for medial UKA.

MATERIALS AND METHODS

We analysed MRI scans from 100 knees evaluated for UKA between 2006 and 2013. Inclusion criteria comprised full-thickness medial compartment loss and intact lateral compartment joint space on preoperative radiographs. Assessment included cartilage lesions, osteophytes, meniscal damage, and anterior-cruciate ligament (ACL) status on tibial and femoral surfaces. Final decision to proceed with UKA relied on intraoperative findings, independent of MRI.

RESULTS

Complete anteromedial tibial and femoral cartilage loss preserved posterior cartilage rims was evident in all cases. Cartilage thinning occurred in the lateral compartment in 34% of cases. While 62% displayed lateral osteophytes, only 6 exhibited small areas of full-thickness cartilage loss. ACL abnormalities varied: 27% normal, 3% ruptured, and 70% had intrasubstance high signal. Larger osteophytes in the medial (p = 0.012) and lateral (p = 0.002) intercondylar notch correlated significantly with ACL damage. All underwent medial UKA, with no evidence of areas with full lateral compartment cartilage loss intraoperatively.

CONCLUSIONS

The MRI findings confirmed the radiographic diagnosis of bone-on-bone medial disease but highlights a range of findings in the ACL, lateral compartment, and patellofemoral joint compartment for patients who met the current x-ray and intraoperative indication for UKA. Further research is required to understand if these MRI changes will affect long-term outcomes.

Enhancing robotic precision in medial UKA: Image-based robot-assisted system had higher accuracy in implant positioning than imageless robot-assisted system across 292 knees

PURPOSE

The objective of this study was to compare the degree of accuracy in implant positioning and limb alignment offered by two robot-assisted (RA) systems: an image-based robot-assisted (IBRA) versus an imageless robot-assisted (ILRA) system for the treatment of medial knee osteoarthritis with unicompartmental knee arthroplasty (UKA).

METHODS

This retrospective radiographic study included medial UKAs performed between 2011 and 2023. Radiographic measurements taken preoperatively and at 1-year postoperative control visit focusing on hip-knee-ankle angle (HKA), posterior tibial slope (PTS), tibial component coronal alignment relative to Cartier's angle and restoration of proper joint line (JL) height were analyzed. Outliers for postoperative measurements were defined as follows: HKA <175° or >180°, PTS <2° or >8°, >3° or <-3° alterations in Cartier's angle and ±2 mm changes in the height of the joint line.

RESULTS

The final sample consisted of 292 medial UKAs: 95 (32.5%) with an IBRA system and 197 (67.5%) with an ILRA system. Implant positioning and limb alignment were more accurate in the group of patients treated with IBRA, HKA (77.9% vs. 67.5%, p = 0.07), PTS (93.7% vs. 82.7%, p = 0.01), restoration of tibial varus relative to Cartier's angle (87.4% vs. 65%, p < 0.001) and restoration of JL height (81.1% vs. 69.5%, p = 0.04).

CONCLUSION

Medial UKA surgery using an IBRA system was associated with a higher degree of accuracy in implant positioning and postoperative limb alignment as compared to an ILRA system. This is a valuable contribution to help communicate the advantages of using this surgical technique and improve its reproducibility.

LEVEL OF EVIDENCE

Level III, Retrospective cohort study.

In Vivo Kinematic Analysis of Mobile-Bearing Unicompartmental Knee Arthroplasty during High Flexion Activities

Mobile-bearing (MB) unicompartmental knee arthroplasty (UKA) has high conformity between the femoral articular surface and the meniscal bearing; therefore, the surface and subsurface contact stress is reduced. Additionally, the survival rate is high. However, the in vivo kinematics of MB UKA knees during high-flexion activities of daily living remain unknown. The aim of this study was to investigate in vivo the three-dimensional kinematics of MB UKA knees during high-flexion activities of daily living. A total of 17 knees of 17 patients who could achieve kneeling after MB UKA were examined. Under fluoroscopy, each patient performed squatting and kneeling motions. To estimate the spatial position and orientation of the knee, a two-dimensional/three-dimensional registration technique was used. We evaluated the femoral rotation and varus-valgus angle relative to the tibia and the anteroposterior translation of the medial sulcus (medial side) and lateral epicondyle (lateral side) of the femur on the plane perpendicular to the tibial mechanical axis in each flexion angle. From 130° to 140° of flexion, the femoral external rotation during squatting was significantly smaller than that during kneeling. Additionally, the medial side of the femur during squatting was significantly more posteriorly located compared with that during kneeling. There was no significant difference between squatting and kneeling in terms of the lateral side of the femur and the varus-valgus position in each flexion angle. At high flexion angle, the kinematics of MB UKA knees may differ depending on the performance.

Early outcomes of the Oxford unicompartmental knee arthroplasty: 140 cases from a single institute in Taiwan

BACKGROUND

The clinical and radiologic outcomes of the Oxford unicompartmental knee arthroplasty utilizing Microplasty® instrumentation have not been extensively investigated in Taiwanese patients. Despite the efficacy of this treatment for unicompartmental knee diseases, its specific impact on this population remains unknown.

METHODS

We retrospectively analyzed prospectively collected data of patients who underwent OUKA with MP between 2018 and 2021, including demographic information, component position, preoperative and postoperative knee range of motion (ROM), numeric rating scale (NRS), and 2011 Knee Society Score-functional activity score (2011 KSS-FAS). We compared preoperative and postoperative data and analyzed the correlation between clinical and radiographic outcomes.

RESULTS

Among 140 patients with an average age of 66.8 years, predominantly female, the majority exhibited components that fell within the radiographically acceptable tolerance ranges. The mean 2.5-year follow-up revealed significant improvements in knee ROM from 102.6° ± 12.9° to 127.3° ± 9.8° ( p < 0.05), pain reduction from 7.7 ± 0.8 to 0.4 ± 0.7 ( p < 0.001), and KSS-FAS from 30.7 ± 10.5 to 94.3 ± 5.2 ( p < 0.001). Notably, a tibial component medial overhang within tolerance predicted shorter hospital stays, and a higher preoperative KSS correlated with lower postoperative NRS. No independent variables were identified as predictors of a higher postoperative KSS.

CONCLUSION

Our study on OUKA with MP in Taiwanese patients reveals promising early clinical and radiographic outcomes. Tibial component medial overhang <3 mm is associated with shorter hospital stays, and a higher preoperative KSS predicts lower NRS at 1 year postoperatively.

Advantages and limitations of mobile-bearing unicompartmental knee arthroplasty: an overview of the literature

INTRODUCTION

Interest in unicompartmental knee arthroplasty (UKA) has recently grown. Mobile bearing UKA, in which the bearing is not fixed but rather perfectly conforms with femoral and tibial components and moves completely passively between the femoral and tibial implant, has now been used for approximately half a century.

AREAS COVERED

Alongside the recognized advantages of UKA, the mobile-bearing variant benefits from an extremely low rate of polyethylene wear and tolerable minor malalignment. Revision rates for UKA have been reported to exceed those of total knee arthroplasty, but long-term survival rates and outcomes from mobile-bearing UKA have been found to be satisfactory. In addition to the lateral osteoarthritis and loosening, which are main complications of UKA, bearing dislocation is a specific complication of mobile bearing UKA. Fractures and valgus subsidence are more prevalent than in the cementless UKA. While these continue to be features to be addressed, they have been partially solved.

EXPERT OPINION

Given the manifold benefits of UKA, its application could be extended to a larger patient population. Successful outcomes rely on careful patient selection and the surgeon's extensive familiarity with the procedure. Looking ahead, the incorporation of robotic surgery, already a feature of some fixed-bearing UKAs, might shape the future trajectory of mobile-bearing UKA.

Methodological Assessment of the 100 Most-Cited Articles in Total Knee Arthroplasty in the Last Decade Compared to the All-Time List

BACKGROUND

Recent advances in total knee arthroplasty (TKA) have been driven by a growing focus on evidence-based medicine. This transition is reflected in the critical appraisal of both, the quality of work and the potential impact on the orthopedic community. The purpose of our study was to (1) identify the top 100 most-cited articles in TKA in the last decade and from all-time, and (2) compare methodological rigor of the most-cited articles in TKA in the last decade to articles all-time by level of evidence.

METHODS

The top 100 cited articles were recorded for manuscripts from the last decade, January 1, 2012 to December 31, 2022, and manuscripts from all-time for TKA. We collected authors, year of publication, journal of the article, country of origin of authors, article type (basic science article, clinical research article), level of evidence, methodological index for non-randomized studies score, physiotherapy evidence database scale, and citation density (total citations/years published).

RESULTS

The largest number of studies for all-time TKA (53.0%) and decade TKA (42.0%) were Level III. The average methodological index for non-randomized studies score for comparative studies was 18.7 for all-time TKA and 20.7 for decade TKA (P < .001). The average physiotherapy evidence database score was 6.1 for all-time TKA and 8.1 for decade TKA (P > .05). The highest citation density for all-time TKA was 111 and for past decade was 63. The number of level II studies in TKA increased from 19.0% from all time to 38.0% from the last decade (P < .05).

CONCLUSIONS

Our findings of improved methodologies over time reflect positive steps toward evidence-based practice in TKA. A continued focus on producing methodologically sound studies may guide evidence-based clinical decision-making.

Catastrophic Femoral Component Failure of a Unicompartmental Knee Arthroplasty

We report a case of previously undescribed medial unicompartmental knee arthroplasty failure due to femoral component implant fracture. The patient experienced sudden pain and locking while ambulating 8 years postoperatively. Radiographs revealed catastrophic femoral component failure with a transverse break through the metal. The patient underwent revision to total knee arthroplasty. At 1-year follow-up, the patient had no pain and a range of motion of 130 degrees. Particular attention should be paid to obtaining adequate femoral component posterior flange fixation during unicompartmental knee arthroplasty. Patient education regarding maintaining a healthy weight is crucial to preventing this complication.

Propensity of the tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in Oxford unicompartmental knee arthroplasty: retrospective study

PURPOSE

A well-balanced joint gap is necessary in Oxford unicompartmental knee arthroplasty (OUKA) to prevent mobile-bearing dislocation. While the gaps between 20° (extension) and 100° (flexion) are precisely adjusted using the incremental mill system, there has been insufficient evaluation of gaps in other angles. We hypothesized that the gap is not always the same in other angles. This retrospective study aimed to evaluate the gap in full-extension (0°), mid-flexion (60°) and deep flexion (130°) for comparison with those in extension and flexion gaps.

METHODS

We evaluated 119 knees in 83 patients (51 females, 31 males, aged 71.9 years). The full-extension and mid-flexion gaps were compared with the extension gap, and the deep flexion gap was contrasted with the flexion gap. Each gap was classified into isometric, tight or loose, for evaluation of contributing factors.

RESULTS

Although the full-extension gap tended to be isometric (45%), the mid-flexion tended to be tight (48%), whereas the deep-flexion was loose in most knees (84%) (P = 0.002). The tight mid-flexion and loose deep flexion gap pattern accounted for 44% of the total knees, especially so with smaller femoral components (P = 0.004).

CONCLUSION

Our results highlight the propensity of tight mid-flexion and loose flexion gap despite the adjustment of extension and flexion gaps in OUKA. Although the effect of such a minor gap imbalance is still unknown, the pattern was more prevalent in patients with smaller-sized femoral components. Use of a larger femoral component may equalize the gap throughout the motion arc.

[Dealing with early complications in unicondylar knee arthroplasty-what works, what does not?]

Complications in the early postoperative period following the implantation of a unicondylar knee arthroplasty (UKA) are both rare and rarely described in the literature. Often, only small case series or individual case reports are available. In this article, the most common complications of periprosthetic infection, periprosthetic tibial fracture, inlay dislocation and intra-articular cement residue in (loose bone cement body) are described and recommendations for conservative and surgical treatment are presented, including case examples. Ideally, surgical errors or an infection should be recognized at an early stage and revised as soon as possible.

The Femur-First Technique for Oxford Medial Unicompartmental Knee Arthroplasty

Background

Unicompartmental knee arthroplasty (UKA) is a reliable procedure to treat medial compartment knee osteoarthritis (OA). The reported survivorship of UKA has varied in the literature3-7. In part, the higher failure rates of UKA seen in registries could be related to the caseload and experience of the reporting surgeon8. The introduction of techniques that make procedures more reliable, especially in the hands of inexperienced surgeons, can decrease the rate of failure. With the Oxford UKA implant (Zimmer Biomet), the recommended surgical technique involves cutting the tibia first, followed by the femoral preparation. However, a technique that allows for preparation of the femur first, as well as the use of the femoral component as a reference for the tibial cut, may reduce the common technical errors seen with the procedure. We have utilized the femur-first technique in cases of medial Oxford UKA.

Description

The femur-first method outlined in the present article does not require any unique instruments beyond what is supplied by the manufacturer. Before beginning, the femoral positional guide needs to be decoupled from its base. To start, the intramedullary guide is introduced approximately 1 cm anterior and medial to the intercondylar notch. Once the femoral osteophytes are removed, the surgeon identifies the center of the femoral condyle and marks it. The posterior tibial cartilage is then removed with a saw to facilitate the placement of the appropriately sized femoral spherical guide. The size of the femoral component is determined by selecting the implant that aligns best with the width of the femoral condyle. The femoral drill guide is detached from its base because there is not enough space for the base, as the tibia has not yet been resected. The decoupled femoral guide is connected to the intramedullary rod, allowing the precise positioning of the femoral component in approximately 10° of flexion relative to the femoral sagittal plane and drilling of the 2 peg holes. The posterior condylar resection guide is impacted into position, and the osteotomy of the posterior condyle is made. The distal femur is then milled with use of a number-0 spigot, and the femoral component trial is positioned into place. The femoral condyle is "resurfaced" with the femoral component, which restores joint obliquity and the natural height, a critical element of the femur-first technique. Following this, the 1-mm (size-dependent) spherical gauge is placed around the femoral component trial. The tibial guide is secured with the G-clamp and a number-0 resection block, and is pinned into place. We recommend swapping the number-0 cutting guide for a +2 when making the cut in order to avoid over-resection. Recutting is advised if a minimum 3-mm feeler gauge does not adequately occupy the flexion space. The final step is to balance the flexion and extension gaps in the usual fashion.

Alternatives

The alternative technique is a traditional tibia-first approach, in which tibial resection is performed prior to femoral resection. As described in the original manufacturer's manual, the tibial cut is accomplished with use of a number-0 cutting guide, and the tibial rotation is based on the axis formed by the anterior superior iliac spine and knee center, irrespective of the femoral condyle.

Rationale

The femur-first technique is advantageous in several ways. When performing the femoral cut first, the surgeon can better align the drill guide at the center of medial femoral condyle. This will result in the femoral component being positioned more in line with the coronal plane of the femoral condyle. Additionally, the tibial resection is made with the femoral trial in place; therefore, the depth of resection can be more accurate, potentially avoiding excessive bone resection. Finally, with the femoral trial in place, the surgeon can judge the rotation and medial-lateral position of the tibial component more precisely, hence lowering the possibility of bearing spin-out, impingement, and dislocation or unexplained pain.

Expected Outcomes

The femur-first technique is a bone-preserving procedure that results in thinner bearings when compared with a tibia-first approach1. The femur-first approach also improves radiographic outcomes, including femoral coronal, femoral sagittal, and tibial sagittal alignments, while tibial coronal alignment does not differ. There is an early trend toward improved 5-year survivorship with the femur-first (98%) versus tibia-first (94%, p = 0.35) techniques. There has been no significant difference reported in Knee Society Scores between techniques.

Important Tips

Perform a preliminary cut of the posterior tibial cartilage in order to allow insertion of the femoral drill guide under the femoral condyle.Make sure the femoral drill guide lies in the center of the marked medial femoral condyle.Align the tibial sagittal cut with the femoral component trial in order to avoid bearing impingement.Be conservative in the tibial cutting by utilizing a +2 cutting guide (since the coupling is performed with the intramedullary guide in place, which drives the tibial guide distally).

Acronyms and Abbreviations

UKA = unicompartmental knee arthroplastyFF = femur-firstM-L = medial-lateralAP = anteroposteriorPA = posteroanteriorASA = acetylsalicylic acid (aspirin)BID = bis in die, twice a dayPT = physical therapyTF = tibia-firstFCA = femoral coronal angleFSA = femoral sagittal angleTSA = tibial sagittal angleIM = intramedullaryOA = osteoarthritis.

Factors predicting lower limb alignment after Oxford medial unicompartmental knee arthroplasty

This study aimed to identify the factors affecting hip-knee-ankle (HKA) angle following Oxford medial unicompartmental knee arthroplasty (MUKA). A retrospective analysis of 200 patients who underwent Oxford MUKA from June 2018 to October 2020 was conducted. Univariate and multivariate analyses were performed to investigate the impact of surgical and radiographic characteristics on the postoperative HKA angle. The mean HKA angle was 9.5 ± 4.3° before surgery and 3.6 ± 3.7° after surgery (p < 0.001). The postoperative HKA angle significantly correlated with the preoperative HKA angle, bearing size, tibial component alignment angle, and BMI (r = 0.71, p < 0.001; r =  - 0.24, p = 0.001; r = 0.21, p = 0.004; r =  - 0.18, p = 0.011). Multiple linear regression analysis revealed that the preoperative HKA angle (β = 0.68, p < 0.001), bearing size (β =  - 0.31, p < 0.001), tibial component alignment angle (β = 0.14, p = 0.003), and BMI (β =  - 0.09, p = 0.047) significantly affected the postoperative HKA angle. In conclusion, larger preoperative varus deformity, smaller bearing size, greater varus alignment of the tibial component, and lower BMI lead to greater postoperative varus alignment of the lower limb in Oxford MUKA. With this concept, surgeons can more accurately predict postoperative lower limb alignment and avoid malalignment in Oxford MUKA.

Regional Trends in Unicondylar and Patellofemoral Knee Arthroplasty: An Analysis of the American Joint Replacement Registry

BACKGROUND

As the popularity of unicondylar knee arthroplasty (UKA) and patellofemoral arthroplasty (PFA) have expanded, more patients who have limited arthritis are undergoing partial knee arthroplasty. No studies have evaluated if any regional differences in the United States (U.S.) exist between partial versus total knee arthroplasty (TKA). The purpose of this study was to utilize the American Joint Replacement Registry to evaluate regional differences in UKA, PFA, and TKA.

METHODS

The American Joint Replacement Registry was queried for all TKA, PFA, and UKA procedures between 2012 and 2021. Surgical volume was compared between the Midwest (MW), Northeast (NE), South, and West (W) regions. Trends were compared using multivariate logistic regression analyses and least squared mean logistic regression models.

RESULTS

Since 2012, there has been a steady increase in the amount of UKAs performed across the U.S., except during the COVID-19 pandemic when numbers decreased. Logistic regression analyses demonstrated a higher likelihood of receiving a UKA compared to TKA in the NE compared to other regions, and higher likelihood of receiving a PFA in the NE and W compared to other regions over the study period. Other factors that increased the likelihood of having a UKA nationally were men, the procedure being performed at a teaching hospital, and having surgery in urban areas. Patients were more likely to have a PFA in the NE compared to the S and MW, and higher odds in the South and W compared to the MW, with rates of PFA consistently lower in the MW compared to other regions.

CONCLUSIONS

Patients were more likely to have a UKA in the NE compared to other regions of the country. Patients had higher odds of having a PFA in the NE and W regions relative to the MW. Men had higher odds of having either UKA or PFA than women across the nation.

The outcomes of acute periprosthetic joint infection following unicompartmental knee replacement managed with early debridement, Antibiotics, and implant retention

BACKGROUND

Periprosthetic joint infection (PJI) following unicompartmental knee replacement (UKR) is an uncommon, yet serious, complication. There is a paucity of evidence regarding the effectiveness of Debridement-Antibiotics-and-Implant-Retention (DAIR) in this setting. The aim of this study is to investigate the effectiveness of DAIR for acute UKR PJI.

METHOD

Between 2006 and 2019, 5195 UKR were performed at our institution. Over this period, sixteen patients underwent DAIR for early, acute PJI. All patients met MSIS PJI diagnostic criteria. The median age at DAIR was 67 years (range 40-73) and 12 patients were male (75.0%). The median time to DAIR was 24 days (range 6-60). Patients were followed up for a median of 6.5 years (range1.4-10.5) following DAIR.

RESULTS

0.3% (16/5195) of UKR in our institution had a DAIR within 3 months. 15 of 16 patients (93.8%) were culture positive, with the most common organism MSSA (n = 8, 50.0%). Patients were treated with an organism-specific intravenous antibiotic regime for a median of 6 weeks, followed by oral antibiotics for a median duration of 6 months. The Kaplan-Meier survivor estimate for revision for PJI was 57% (95%CI: 28-78%) at five years, and survivor estimate for all cause revision 52% (95%CI: 25-74%).The median Oxford Knee Score for patients with a viable implant at final follow-up was 45 points (range 39-46).

CONCLUSION

Early, acute PJI after UKR is rare. DAIR had a moderate success rate, with infection-free survivorship of 57% at 5 years. Those successfully treated with DAIR had excellent functional outcome and implant survival.

Polyethylene bearing wear is comparable for cemented and cementless Oxford unicompartmental knee replacements: Ten-year results of a randomized controlled trial

PURPOSE

There is concern that using cementless components may increase polyethylene wear of the Oxford unicompartmental knee replacement (OUKR). Therefore, this study aimed to measure bearing wear at 10 years in patients from a randomized trial comparing Phase 3 cemented and cementless OUKRs and to investigate factors that may affect wear. It was hypothesized that there would be no difference in wear rate between cemented and cementless OUKRs.

METHODS

Bearing thickness was determined using radiostereometric analysis at postoperative, 3-month, 6-month, 1-year, 2-year, 5-year and 10-year timepoints. As creep occurs early, wear rate was calculated using linear regression between 6 months and 10 years for 39 knees (20 cemented, 19 cementless). Associations between wear and implant, surgical and patient factors were analysed.

RESULTS

The linear wear rate of the Phase 3 OUKR was 0.06 mm/year with no significant difference (p = 0.18) between cemented (0.054 mm/year) and cementless (0.063 mm/year) implants. Age, Oxford Knee Score, component size and bearing thickness had no correlation with wear. A body mass index ≥ 30 was associated with a significantly lower wear rate (p = 0.007) as was having ≥80% femoral component contact area on the bearing (p = 0.003). Bearings positioned ≥1.5 mm from the tibial wall had a significantly higher wear rate (p = 0.002).

CONCLUSIONS

At 10 years, the Phase 3 OUKR linear wear rate is low and not associated with the fixation method. To minimize the risk of wear-related bearing fracture in the very long-term surgeons should consider using 4 mm bearings in very young active patients and ensure that components are appropriately positioned, which is facilitated by the current instrumentation.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

Patients With Significant Medical Comorbidities May Benefit from Unicompartmental Knee Arthroplasty Over Total Knee Arthroplasty

Many studies have compared outcomes in total knee arthroplasty (TKA) versus unicompartmental knee arthroplasty (UKA); however, to the authors' knowledge, there is no study evaluating complication rates in patients with significant comorbidities. The purpose of this retrospective study was to compare the incidence of postoperative complications, readmission and reoperation rates, length of stay (LOS), and discharge location for patients with significant medical comorbidities undergoing TKA versus UKA. Using the NSQIP database from 2008 to 2018, patients were identified by CPT code (27447 or 27446) and admission diagnostic code of primary osteoarthritis and included in the study if they had an American Society of Anesthesia score greater than or equal to 3. Chi-square test was used to compare categorical variables and t-test for continuous variables. Multivariate regression was used to compare outcomes of interest between groups. A total of 167,054 patients were analyzed with 97.3% undergoing TKA. TKA patients had a greater overall complication rate than those undergoing UKA (p < 0.001). Readmission rates were approximately 1.5 times higher in TKA compared with UKA (p = 0.002), while no statistically significant difference was discovered in reoperation rates (p = 0.868). TKA was also associated with decreased rates of same day discharge, discharge within 24 hours of surgery, and discharge home (p < 0.001, <0.001, and <0.001, respectively). This study found an increase in complication rates, readmission rates, and LOS, along with a lower likelihood of discharge home when undergoing a TKA. These findings suggest that patients with significant medical comorbidities at baseline may benefit from UKA over TKA when anatomically indicated.

Image-based robotic-arm assisted unicompartmental knee arthroplasty provides high survival and good-to-excellent clinical outcomes at minimum 10 years follow-up

PURPOSE

The purpose of the present study was to determine the incidence of revision and report on clinical outcomes at a minimum of 10 years follow-up in patients who had received a medial unicompartmental knee arthroplasty (UKA) with an three-dimensional image-based robotic system.

METHODS

A total of 239 patients (247 knees), who underwent medial robotic-arm assisted (RA)-UKA at a single center between April 2011 and June 2013, were assessed. The mean age at surgery was 67.0 years (SD 8.4). Post-operatively, patients were administered the Forgotten Joint Score-12 (FJS-12) and asked about their satisfaction (from 1 to 5). Post-operative complications were recorded. Failure mechanisms, revisions and reoperations were collected. Kaplan-Meier survival curves were calculated, considering revision as the event of interest.

RESULTS

A total of 188 patients (196 knees) were assessed at a mean follow-up of 11.1 years (SD 0.5, range 10.0-11.9), resulting in a 79.4% follow-up rate. Seven RA-UKA underwent revision, resulting in a survivorship rate of 96.4% (CI 94.6%-99.2%). Causes of revision included aseptic loosening (2 cases), infection (1 case), post-traumatic (1 case), and unexplained pain (3 cases). The mean FJS-12 and satisfaction were 82.2 (SD 23.9) and 4.4 (SD 0.9), respectively. Majority of cases (174/196, 88.8%) attained the Patient Acceptable Symptoms State (PASS, FJS-12 > 40.63). Male subjects had a higher probability of attaining a "forgotten joint" (p < 0.001) and high satisfaction (equal to 5, p < 0.05), when compared to females.

CONCLUSIONS

Three-dimensional image-based RA-UKA demonstrated high implant survivorship and good-to-excellent clinical outcomes at minimum 10 years follow-up. Pain of unknown origin represented the most common reason for RA-UKA revision.

LEVEL OF EVIDENCE

III.

Fixed lateral unicompartmental knee replacement is a reliable treatment for lateral compartment osteoarthritis after mobile-bearing medial unicompartmental replacement

PURPOSE

Lateral osteoarthritis following medial unicompartmental knee replacement (UKR) is usually treated with total knee replacement, however, lateral UKR is a less invasive option that preserves a well-functioning medial UKR. This study aimed to determine the 5-year outcome of the cemented Fixed Lateral Oxford UKR (FLO) when used for the treatment of severe lateral disease after medial Oxford unicompartmental knee replacement.

METHODS

Forty-four knees with lateral bone-on-bone osteoarthritis (n = 43) and avascular necrosis (n = 1) treated with the FLO following medial Oxford UKR were followed up prospectively. The Oxford Knee Score (OKS) and Tegner Activity Score (TAS) were collected pre- and post-operatively. Life-table analysis was used to determine survival rates.

RESULTS

The mean patient age at the time of FLO surgery was 74.4 years with a mean time of 12.1 years between the primary medial UKR and the conversion to a bi-UKR with a FLO. Mean follow-up of the FLO was 3.5 years. After FLO no intra-operative or medical complications, re-admissions, or mortality occurred. There was one reoperation in which a bearing was exchanged for a medial bearing dislocation. There were no revisions of the FLO, so the FLO survival rate at 5 years was 100% (24 at risk). The mean pre-operative OKS was 22, which significantly (p < 0.0001) improved to a mean of 42, 42, and 40 at 1, 2, and 5 years, respectively. The median TAS had a non-significant improvement from 2.5 (Range 0-8) pre-operatively to 2 (Range 1-6) at 5 years postoperatively.

CONCLUSION

The FLO is a reliable treatment for lateral osteoarthritis following medial UKR. At 5 years there was a 100% survival of the FLO with a mean OKS of 40.

LEVEL OF EVIDENCE

IV, Prospective Case Series.

Combination of a High Residual Varus and Joint-Line Lowering Strongly Increases the Risk of Early Implant Failure in Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Outliers in implant positioning, malalignment, and joint line height change are risk factors for unicompartmental knee arthroplasty (UKA) failure. However, their relationships and patterns in large datasets remain unexplored. This study assessed medial UKA survival in a large cohort and explored associated risk factors.

METHODS

This was a retrospective cohort study on medial UKA patients (2011 to 2019). Radiological outcomes included tibial implant positioning in the coronal plane, posterior tibial slope, residual knee deformity, and joint line restitution. Survival rate at last follow-up was recorded. Multinomial logistic regression analyzed risk factors, incorporating demographic and univariate analysis data.

RESULTS

Three hundred and sixty-six knees met inclusion criteria, with 10 lost to follow-up (2.7%). Mean follow-up was 61.3 months [24.1 to 135.1]. 5- and 10-year implant survival rates were 92% ± 1.6 and 88.4% ± 3.8, respectively. Multivariate analysis identified post-operative hip-knee-ankle angle (HKA) ≤ 175° (OR = 5.30 [1.64 to 17.13], P = .005) and joint line lowering ≥2 mm (OR = 8.86 [2.06 to 38.06]) as significant risk factors for tibial implant failure. Their combination carried a significantly high risk of failure (OR = 10.3 [3.1 to 34.3]). Post-operative HKA < 175° was common in knees with pre-operative HKA < 172°.

CONCLUSION

This study reports encouraging 5- and 10-year survival outcomes for medial UKA. Tibial loosening was the main reason for revision. Patients with joint line lowering ≥ 2 mm and post-operative HKA ≤ 175° were at high risk of tibial implant failure. Surgeons should carefully restore the joint line in cases of pre-operative HKA < 172°.

Severe patellofemoral arthritis does not compromise 6-month post-operative range of motion or function following unicondylar knee arthroplasty

BACKGROUND

The presence of significant patellofemoral arthritis (PFA) is still considered a contraindication for unicondylar knee arthroplasty (UKA) by many surgeons. The purpose of this study was to determine if the presence of severe PFA at the time of UKA compromised early (< 6 months) post-operative knee range of motion or functional outcomes.

METHODS

This retrospective review evaluated unilateral and bilateral UKA (323 patients; 418 knees) between 2015 and 2019. Procedures were grouped by degree of PFA present at the time of surgery, including mild PFA (Group 1; N = 266), moderate to severe PFA (Group 2; N = 101), and severe PFA with lateral compartment bone-on-bone contact (Group 3; N = 51). Knee range of motion and Knee Society Knee (KSS-K) and Function (KSS-F) scores were collected both before and at 6 months following surgery. Group differences were evaluated with Kruskal-Wallis and Chi-square tests for continuous and categorical variables, respectively. Univariate and multivariable logistic regressions were performed to determine influential variables associated with post-operative knee flexion being ≤ 120° and presented as odds ratios (OR) and 95% confidence intervals (CI).

RESULTS

Pre-operative flexion was lowest in Group 3 (p = 0.010) with 17.6% of knees having flexion ≤ 120°. Post-operative flexion was lowest in Group 3 (119.1° ± 8.4°, p = 0.003) with 19.6% knees having flexion ≤ 120° compared to 9.8% and 8.9% in Groups 1 and 2, respectively. No significant difference in KSS-F following surgery was found; all three groups demonstrated similar clinical improvement. Increased age (OR 1.089, CI 1.036-1.144; p = 0.001) and body mass index (OR 1.082, CI 1.006-1.163; p = 0.034) were found to be associated with post-operative knee flexion ≤ 120°, while high pre-operative flexion (OR 0.949, CI 0.921-0.978; p = 0.001) was found to be inversely associated with poor knee flexion following surgery.

CONCLUSION

Patients with severe PFA demonstrate similar clinical improvement following UKA at 6 months as patients with less severe PFA.

Predicting valgus malalignment after mobile-bearing UKA using a new method: the arithmetic HKA of the arthritic knee

BACKGROUND

Valgus malalignment is one of the most common reasons for the progression of osteoarthritis in the lateral compartment of the knee after mobile-bearing unicompartmental knee arthroplasty (UKA). The arithmetic hip-knee-ankle angle (aHKA) of the Coronal Plane Alignment of the Knee (CPAK) classification could reflect the constitutional alignment of the arthritic knee. The purpose of this study was to observe the relationship between the aHKA and valgus malalignment after mobile-bearing UKA.

METHODS

This retrospective study was conducted using 200 knees undergoing UKA from January 1, 2019, to August 1, 2022. These radiographic signs, including preoperative hip-knee-ankle angle (HKA), mechanical proximal tibial angle (MPTA), mechanical lateral distal femoral angle (LDFA), and postoperative HKA, were measured using standardized weight-bearing long-leg radiographs. Patients with postoperative HKA > 180° and postoperative HKA ≤ 180° were classified as the valgus group and non-valgus group, respectively. The aHKA was calculated as 180° + MPTA - LDFA in this study, which had the same meaning as that (aHKA = MPTA - LDFA) in the CPAK classification. The Spearman correlation analysis, the Mann-Whitney U test, the chi-square test, the Fisher's exact test, and multiple logistic regression were used in the study.

RESULTS

Of the 200 knees included in our study, 28 knees were classified as the valgus group, while 172 knees were in the non-valgus group. The mean ± standard deviation (SD) of aHKA (all groups) was 177.04 ± 2.58°. In the valgus group, 11 knees (39.3%) had a value of aHKA > 180°, while 17 knees (60.7%) had a value of aHKA ≤ 180°. In the non-valgus group, 12 knees (7.0%) had a value of aHKA > 180°, while 160 knees (93.0%) had a value of aHKA ≤ 180°. In Spearman correlation analysis, aHKA was positively correlated with postoperative HKA (r = 0.693, p < 0.001). In univariate analysis, preoperative HKA (p < 0.001), LDFA (p = 0.02), MPTA (p < 0.001), and aHKA (p < 0.001) showed significant differences between the valgus and non-valgus groups. Variables with p < 0.1 in univariate analysis were further analyzed using multiple logistic regression analysis, and the variable-aHKA (> 180° vs ≤ 180°, odds ratio (OR) = 5.899, 95% confidence interval (CI) = 1.213 to 28.686, and p = 0.028) was expressed as the risk factor of postoperative valgus malalignment.

CONCLUSION

The aHKA is correlated with the postoperative alignment of mobile-bearing UKA and a high aHKA (> 180°) will increase the risk of postoperative valgus malalignment. Therefore, mobile-bearing UKA should be performed with caution in patients with preoperative aHKA > 180°.

Prevalence of osteoporosis in patients awaiting unicompartmental knee arthroplasty: a cross-sectional study

Objectives

Osteoporosis may contribute to failure of unicompartmental knee arthroplasty (UKA), yet the prevalence of osteoporosis in the population awaiting UKA has not been adequately studied. The objectives of this study were to report the prevalence of osteoporosis in people awaiting UKA and the rate of anti-osteoporosis treatment, and to explore factors associated with osteoporosis prevalence in people awaiting UKA.

Methods

Participants awaiting UKA from January 2019 to May 2023 were consecutively enrolled. Participants ' age, gender, BMI, knee K-L score, VAS score, history of previous DXA testing, history of anti-osteoporosis treatment, and possible underlying risk factors were recorded. All participants were given a dual-energy x-ray absorptiometry (DXA) test after the visit. The diagnosis of osteoporosis was made according to the World Health Organization criteria. Compare the prevalence of osteoporosis between people waiting for UKA and the general population. Risk factors associated with osteoporosis were analyzed using multiple linear regression and binary logistic regression models.

Results

A total of 340 participants were included in the study, 259 in female and 81 in male, with a mean age of 63.53 years (range: 41-84 years), and all participants completed UKA and had DXA prior to UKA. The prevalence of osteoporosis was 40.88% (44.79% in female and 28.40% in male). The prevalence of osteoporosis was higher in female than in male (p<0.001). The prevalence of osteoporosis in the population waiting for UKA was significantly higher than that in the general population (p < 0.001). DXA testing was performed in 12.06% within 1 year prior to the visit. The percentage of those who had received anti-osteoporosis treatment was 20.59% (20.86% in osteoporosis, 22.39% in Osteopenia and 16.42% in normal bone mass). The correlation between age, gender, body mass index, visual analogue scale score and osteoporosis was statistically significant.

Conclusion

Osteoporosis is common in people waiting for UKA, but screening and treatment rates are low. Female patients of advanced age and low weight combined with significant pain should be considered for osteoporosis screening and appropriate treatment before UKA.

Short- to mid-term results of minimally invasive lateral unicompartmental knee replacement: 133 cases in a non-designer series

INTRODUCTION

The aim of the current study was to demonstrate short- to mid-term survivorship as well as clinical outcome of lateral unicompartmental knee replacement (UKR) with a fixed-bearing (FB) design from a non-designer center using the Oxford Fixed Lateral prosthesis.

MATERIALS AND METHODS

This single-center retrospective cohort study reports the results of 133 consecutive lateral FB-UKR. Survivorship analysis was performed with different endpoints and clinical outcome was measured using the Oxford-Knee-Score (OKS), American-Knee-Society-Score (AKSS-O), range-of-motion (ROM) and visual-analog-scale for pain (VAS).

RESULTS

There were two revision surgeries with conversion to total knee replacements (TKR) due to persistent pain resulting in a survival rate of 98.5% (95% CI 93.5-99.6) with a mean follow-up (FU) of 3.3 ± 1.8 years (range 1-8.5). All outcome scores, VAS and ROM showed a significant improvement at final FU (p < 0.001). The OKS improved from 26 ± 7.8 (range 11-45) preoperatively to 39 ± 8.3 (range 13-48), the AKSS-O from 49.2 ± 14.6 (range 18-90) to 81.8 ± 15.1 (range 40-100), the AKSS-F from 53 ± 23.7 (range 0-100) to 80.4 ± 21.4 (range 5-100) and the ROM from 118 ± 17 (range 90-160) to 134 ± 9.5 (range 100-155).

CONCLUSIONS

The short- to mid-term results following lateral FB-UKR demonstrate a high survivorship and good clinical outcome from an independent series. We, therefore, suggest that FB-UKR is a safe treatment option for isolated lateral OA if sufficient surgical experience is provided.

LEVEL OF EVIDENCE

Retrospective cohort study, level IV.

Fixed-bearing is superior to mobile-bearing in lateral unicompartmental knee replacement: a retrospective matched-pairs analysis

PURPOSE

Due to low incidence of isolated lateral osteoarthritis (OA), there are limited data on whether a fixed-bearing (FB) or a mobile-bearing (MB) design is superior for lateral unicompartmental knee replacement (UKR). The aim of this matched-pairs analysis was to compare both designs in terms of implant survival and clinical outcome.

METHODS

Patients who received MB-UKR (Group A) and FB-UKR (Group B) at a single centre were matched according to gender, age at time of surgery and body mass index (BMI). Survivorship analysis was performed with the endpoint set as "revision for any reason". Clinical outcome was assessed using the Oxford knee score (OKS), visual analogue scale for pain (VAS), patients' satisfaction, University of California Los Angeles activity scale (UCLA) and the Tegner activity score (TAS).

RESULTS

A total of 60 matched pairs were included with a mean follow-up (FU) of 3.4 ± 1.3 (range 1.2-5.0) years in Group A and 2.7 ± 1.2 (range 1.0-5.0) years in Group B. Survivorship between both groups differed significantly (Group A: 78.7%; Group B: 98.3%, p = 0.003) with bearing dislocation being the most common reason for revision in Group A (46.2%). The relative and absolute risk reduction were 92.2% and 20%, respectively, with 5 being the number needed to treat. There were no differences in OKS (Group A: 41.6 ± 6.5; Group B: 40.4 ± 7.7), VAS (Group A: 2.9 ± 3.2; Group B: 1.6 ± 2.2), UCLA (Group A: 5.7 ± 1.3; Group B: 5.9 ± 1.8) and TAS (Group A: 3.0 ± 1.0; Group B: 3.1 ± 1.2) between both groups on follow-up.

CONCLUSION

Despite modern prosthesis design and surgical technique, implant survival of lateral MB-UKR is lower than that of FB-UKR on the short- to mid-term due to bearing dislocation as the most common cause of failure. Since clinical results are equivalent in both groups, FB-UKR should be preferred in treatment of isolated lateral OA.

LEVEL OF EVIDENCE

Retrospective case-control study, Level III.

Early Outcomes of Modified Technique of Mobile Bearing Unicondylar Knee Replacement

Background

Recent years have seen a resurgence in utilization of partial knee replacement. One such device frequently used is Oxford partial knee implant (OPK). Deeper tibial bone cut while performing OPK replacement may risk early failure.

Methods

We prospectively looked at early outcomes of a modified technique (MT) of OPK replacement adopted by our centre to save tibial bone stock at 24 months of follow up as compared to designer group described technique (DT) as a prospective cohort.

Results

At 2 years follow up New Knee Society Score showed patient satisfaction (38.25 in DT vs 39.02 in MT, p value 0.10), objective (92.77 in DT vs 91.07 in MT, p value 0.21), expectation scores (14.77 in DT vs 14.85 in MT, p value 0.81) and activity (60.72 in DT vs 68.17 in MT, p value 0.79 were similar in MT group as compared to DT. The stair climbing ability (22.46 in MT vs 29.96 in DT, p value < 0.001) and getting up from chair (13.16 in MT vs 19.80 in DT, p value < 0.001), was better with MT group but most other patient performance scores were similar as assessed by DOP (Delaware Osteoarthritis Profile). Both groups had failure rate of 5% at 24 months follow up.

Conclusion

MT resulted in similar early outcomes in terms of patient reported outcomes, satisfaction and performance as compared to DT group. The MT to save tibial bone stock did not compromise early outcomes and can be utilised in certain patients with higher risk of tibial failure.

Ten-Year Survivorship and Patient Satisfaction Following Robotic-Arm-Assisted Medial Unicompartmental Knee Arthroplasty: A Prospective Multicenter Study

BACKGROUND

Robotic-arm-assisted unicompartmental knee arthroplasty (UKA) has been shown to result in high short- and mid-term survivorship. However, it is not known whether these outcomes are maintained at long-term follow-up. This study aimed to evaluate long-term implant survivorship, modes of failure, and patient satisfaction following robotic-arm-assisted medial UKA.

METHODS

A prospective multicenter study of 474 consecutive patients (531 knees) undergoing robotic-arm-assisted medial UKA was conducted. A cemented, fixed-bearing system with a metal-backed onlay tibial implant was used in all cases. Patients were contacted at 10-year follow-up to determine implant survivorship and satisfaction. Survival was analyzed using Kaplan-Meier models.

RESULTS

Data were analyzed for 366 patients (411 knees) with a mean follow-up of 10.2 ± 0.4 years. A total of 29 revisions were reported, corresponding to a 10-year survivorship of 91.7% (95% confidence interval, 88.8% to 94.6%). Of all revisions, 26 UKAs were revised to total knee arthroplasty. Unexplained pain and aseptic loosening were the most commonly reported modes of failure, accounting for 38% and 35% of revisions, respectively. Of patients without revision, 91% were either satisfied or very satisfied with their overall knee function.

CONCLUSIONS

This prospective multicenter study found high 10-year survivorship and patient satisfaction following robotic-arm-assisted medial UKA. Pain and fixation failure remained common causes for revision following cemented fixed-bearing medial UKA, despite the use of a robotic-arm-assisted technique. Prospective comparative studies are needed to assess the clinical value of robotic assistance over conventional techniques in UKA.

LEVEL OF EVIDENCE

Prognostic Level II. See Instructions for Authors for a complete description of levels of evidence.

Incidence and severity of radiological lateral osteoarthritis 15 years following medial unicompartmental knee arthroplasty

To assess the incidence of radiological lateral osteoarthritis (OA) at 15 years after medial unicompartmental knee arthroplasty (UKA) and assess the relationship of lateral OA with symptoms and patient characteristics. Cemented Phase 3 medial Oxford UKA implanted by two surgeons since 1998 for the recommended indications were prospectively followed. A 15-year cumulative revision rate for lateral OA of 5% for this series was previously reported. A total of 163 unrevised knees with 15-year (SD 1) anterior-posterior knee radiographs were studied. Lateral joint space width (JSWL) was measured and severity of lateral OA was classified as: nil/mild, moderate, and severe. Preoperative and 15-year Oxford Knee Scores (OKS) and American Knee Society Scores were determined. The effect of age, sex, BMI, and intraoperative findings was analyzed. Statistical analysis included one-way analysis of variance and Kruskal-Wallis H test, with significance set at 5%. The mean age was 80.6 years (SD 8.3), with 84 females and 79 males. The mean JSWL was 5.6 mm (SD 1.4), and was not significantly related to age, sex, or intraoperative findings. Those with BMI > 40 kg/m2 had a smaller JSWL than those with a 'normal' BMI (p = 0.039). The incidence of severe and moderate lateral OA were both 4.9%. Overall, 2/142 (1.4%) of those with nil/mild lateral OA, 1/8 (13%) with moderate, and 2/8 (25%) with severe subsequently had a revision. Those with severe (mean OKS 35.6 (SD 9.3)) and moderate OA (mean OKS 35.8 (SD 10.5)) tended to have worse outcome scores than those with nil/mild (mean OKS 39.5 (SD 9.2)) but the difference was only significant for OKS-Function (p = 0.044). This study showed that the rate of having severe or moderate radiological lateral OA at 15 years after medial UKA was low (both 4.9%). Although patients with severe or moderate lateral OA had a lower OKS than those with nil/mild OA, their mean scores (OKS 36) would be classified as good.

Comparing Unicompartmental Knee Arthroplasty and High Tibial Osteotomy for Isolated Medial Compartment Knee Osteoarthritis

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Both unicompartmental knee arthroplasty (UKA) and high tibial osteotomy (HTO) allow for compartment-specific intervention on an arthritic knee joint that preserves bone stock and native soft tissue compared to a total knee arthroplasty (TKA). Both operations give a more natural feeling with native proprioception compared with a TKA.

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HTO is better suited in patients who are younger (<55 years-of-age), have a body mass index (BMI) <30 kg/m2, high activity requirements, mechanical malalignment, asymmetric varus, isolated anterior cruciate ligament insufficiency, need for multiplanar correction, and a preference for joint preserving interventions. Recent data suggest that age (>55 years-of-age) should not solely contraindicate a HTO.

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UKA may be chosen in patients who are older (>55 years-of-age), low activity requirements, have a BMI <40 kg/m2, severe osteoarthritis with significant joint space narrowing, acceptable coronal alignment, symmetric varus, and patient preference for arthroplasty.

Pulsatile Lavage Improves Tibial Cement Penetration and Implant Stability in Medial Unicompartmental Arthroplasty: A Cadaveric Study

Cemented unicompartmental knee arthroplasty (UKA) shows good survivorship and function. However, implant failure, causing the need for revision, can occur. Aseptic loosening is still among the most common reasons for revision. The purpose of this study was to assess the influence of preimplantation lavage technique on tibial cement penetration depth, tibial cement volume, and load to fracture in the tibial component of mobile-bearing UKA. In 10 pairs of fresh frozen human tibiae, cemented UKA was implanted by an experienced surgeon. Tibial components were then implanted, left and right tibiae were randomly allocated to group A or B. Prior to implantation, irrigation was performed with either syringe lavage or pulsatile jet lavage in a standardized manner. Cement surface was 4170.2 mm² (3271.6-5497.8 mm²) in the syringe lavage group, whereas the jet lavage group showed 4499.3 mm² (3354.3-5809.1 mm²); cement volume was significantly higher as well (4143.4 mm³ (2956.6-6198.6 mm³) compared with 5936.9 mm³ (3077.5-8183.1 mm³)). Cement penetration depth was 2.5 mm (1.7-3.2 mm) for the jet lavage, and 1.8 mm (1.2-2.4 mm) for the syringe lavage. The mean fracture load was 4680 N in the jet lavage group and 3800 N in the syringe lavage group (p = 0.001). Subsidence was significantly higher for syringe lavage. This study suggests a correlation of cement penetration depth and cement volume to implant failure in the tibial component of a UKA using a cadaveric model. The type of bone lavage most likely influences these two key parameters.

Unicompartmental knee arthroplasty in patients under the age of 60 years provides excellent clinical outcomes and 10-year implant survival: a systematic review : A study performed by the Early Osteoarthritis group of ESSKA-European Knee Associates section

PURPOSE

The purpose of the present study was to systematically review the clinical and functional outcomes following medial unicompartmental knee arthroplasty (UKA) in patients under the age of 60 years old.

METHODS

Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, studies between 2012 and April 2022, on patients 18-60 years old who have had a unicompartmental knee replacement evaluating patient-reported outcomes measures (PROMs), were included. The Knee Society Scores (KSS) clinical score was considered the primary outcome. Pre- and post-operative range of motion (ROM), PROMs, complications and survival were recorded. Paired sample t testing was performed to compare the pre-operative with post-operative KSS.

RESULTS

Seventeen articles comprising 2083 unicompartmental arthroplasties were included. The follow-up range was between 1 and 15 years. In eligible studies, all reported outcomes were improved following UKA. The mean KSS clinical was significantly improved from 45.5 (SD: 9.6) pre-operatively to 89.4 (SD: 4.4) post-operatively (p = 0.0001). Mean implant survival ranged 86-96.5% at 10 years follow-up. There was no significant difference between mobile and fixed bearing in terms of ROM and KSS clinical. In total, 92 revisions and 7 re-operations with implant retention were reported.

CONCLUSION

Unicompartmental knee arthroplasty for medial osteoarthritis is a safe, reliable and effective treatment option for patients of 60 years or younger. It provides pain relief, satisfactory activity level, excellent clinical outcomes, and up to 96.5% implant survival at 10-year follow-up.

LEVEL OF EVIDENCE

IV.

Similar Survivorship but Different Revision Reasons for Uncemented Mobile-Bearing and Cemented Fixed-Bearing Medial UKA: A Long-Term Population-Based Cohort Study of 2,015 Patients

BACKGROUND

Long-term survivorship and accurate characterization of revision reasons in unicompartmental knee arthroplasty (UKA) are limited by a lack of long-term data and standardized definitions of revision. The aim of this study was to identify survivorship, risk factors, and reasons for revision in a large cohort of medial UKAs with long-term follow-up (up to 20 years).

METHODS

Patient, implant, and revision details for 2,015 primary medial UKAs (mean follow-up, 8 years) were recorded following systematic clinical and radiographic review. Survivorship and risk of revision were analyzed using Cox proportional hazards. Reasons for revision were analyzed using competing-risk analysis.

RESULTS

Implant survivorship at 15 years was 92% for cemented fixed-bearing (cemFB), 91% for uncemented mobile-bearing (uncemMB), and 80% for cemented mobile-bearing (cemMB) UKAs (p = 0.02). When compared with cemFB, the risk of revision was higher for cemMB implants (hazard ratio [HR] = 1.9, 95% confidence interval [CI] = 1.1 to 3.2; p = 0.03). At 15 years, cemented implants had a higher cumulative frequency of revision due to aseptic loosening (3% to 4%, versus 0.4% for uncemented; p < 0.01), cemMB implants had a higher cumulative frequency of revision due to osteoarthritis progression (9% versus 2% to 3% for cemFB/uncemMB; p < 0.05), and uncemMB implants had a higher cumulative frequency of revision due to bearing dislocation (4% versus 2% for cemMB; p = 0.02). Compared with the oldest patients (≥70 years), younger patients had a higher risk of revision (<60 years: HR = 1.9, 95% CI = 1.2 to 3.0; 60 to 69 years: HR = 1.6, 95% CI = 1.0 to 2.4; p < 0.05 for both). At 15 years, there was a higher cumulative frequency of revision for aseptic loosening in these younger groups (3.2% and 3.5% versus 2.7% for ≥70 years; p < 0.05).

CONCLUSIONS

Implant design and patient age were risk factors for revision of medial UKA. The findings from this study suggest that surgeons should consider using cemFB or uncemMB designs because of their superior long-term implant survivorship compared with cemMB designs. Additionally, for younger patients (<70 years), uncemMB designs had a lower risk of aseptic loosening than cemFB designs at the expense of a risk of bearing dislocation.

LEVEL OF EVIDENCE

Prognostic Level III. See Instructions for Authors for a complete description of levels of evidence.