Lateral Unicompartmental Knee Arthroplasty

Starting Up a Lateral Unicompartmental Knee Arthroplasty Practice - Is Outcome Affected?

INTRODUCTION

In the past, the utilization of lateral unicompartmental knee arthroplasty (UKA) has been limited at national levels, despite the fact that an estimated 10% of patients who have an indication for arthroplasty, present with isolated lateral compartment osteoarthritis (OA). Units dedicated to UKA have reported good outcomes. Identifying patients for the procedure has been less clear, and the procedure has been perceived to be technically more demanding than medial UKA. This may result in a reluctance to start a lateral UKA practice and challenge the early phase. Therefore, this paper aimed to present the outcomes and learning curve when starting up a lateral UKA practice, as this theme remains unelucidated.

METHODS

There were 85 primary fixed-bearing lateral UKAs, with a minimum of 1-year follow-up, performed between 2016 and 2022 by two arthroplasty surgeons with existing UKA practices. The indications were primary (n = 79) or post-traumatic (n = 6) osteoarthritis. Patient-reported outcome measures (PROMs) were assessed at 3, 12, and 24 months. A cumulative sum (CUSUM) analysis was used to evaluate surgical duration and the 12-month Oxford Knee Score (OKS).

RESULTS

Median (Interquartile range (IQR)) 12-month OKS, Activity and Participation Questionnaire (APQ), and Forgotten Joint Score (FJS) were 43 (37.5 to 46), 78 (42.5 to 98.5), and 72 (55 to 90), respectively. The OKS outcomes did not reveal adverse effects from the learning curve. A performance shift in surgical duration was observed around case 33. Kaplan-Meier implant survival reached 95.4% at 7 years for the endpoint "implant revision," and 93.5% for "implant revision/implant addition."

CONCLUSION

Starting up a lateral UKA practice is safe and efficient for surgeons who have prior medial UKA experience, provided strict adherence to indications. While surgical duration indicated a learning curve over approximately 33 cases, PROMs remained stable, suggesting proficient outcomes irrespective of the learning curve.

Unicompartmental knee replacement: controversies and technical considerations

BACKGROUND

Unicompartmental knee replacement (UKR) is one of the effective interventions for the treatment of symptomatic knee osteoarthritis. Moreover, it has multiple advantages over total knee arthroplasty (TKA), including reduced intraoperative blood loss, decreased risk of transfusion, and faster recovery. This study aimed to discuss critical technical considerations regarding UKR and some of the controversies and updates.

METHODS

We conducted a review to provide an overview of the controversies and technical considerations about UKR in several aspects. Only peer-reviewed articles were included, up to December 2023 using PubMed, Google Scholar, ERIC, and Cochrane database for systematic reviews databases.

RESULT

UKR is associated with superior patient-reported clinical and functional outcomes, as well as shorter hospital stays, fewer postoperative complications, and revealed favorable outcomes in patients' return to sport. The choice between mobile- and fixed-bearing prostheses depends, in part, on the surgeon's preference. The mobile-bearing UKR is a less constrained prosthesis and can potentially result in less wear, but it is more technically demanding. While no significant difference between mobile-bearing versus fixed-bearing prostheses, cementless is superior to cemented design. Furthermore, UKR can be a good alternative for high tibial osteotomy (HTO) and still can be considered after a failed HTO. Lastly, recent reviews have shown a revision rate comparable to that of TKA. This is probably influenced by Improved comprehension of the best indications, patient selection criteria, as well as of the design, materials, and technological advances.

CONCLUSION

UKR treatment for unicompartmental knee osteoarthritis is secure and effective. Based on clinical and functional outcomes, decreased morbidity and mortality, and cost-effectiveness, long-term studies suggest that UKR is superior to TKA. Further investigation in this area is warranted.

Lateral UKA can be a safe solution in a young patients' population: a 10-year follow-up report

BACKGROUND

This study aimed to assess the long-term survivorship and functional outcomes of fixed-bearing lateral unicompartmental knee arthroplasty (UKA) in a young patients' population with osteoarthritis limited to the lateral compartment.

METHODS

The study included a cohort of consecutive patients who underwent lateral UKA between January 2008 and December 2014 at a single high-volume surgical center. The surgical procedures were performed by experienced surgeons using a lateral parapatellar approach and fixed-bearing implants. Patient follow-up included a retrospective re-evaluation, clinical assessments, patient-reported outcome measures (PROMs), and X-ray analysis.

RESULTS

A total of 40 lateral UKAs were analyzed, with 19 performed on the left and 21 on the right knee. The mean age of the patients at the time of surgery was 57.6 years, and the mean BMI was 24.8. At the final follow-up, 80% of patients achieved excellent outcomes (OKS > 41), and 20% had good outcomes (OKS: 34-41). No patients exhibited fair or poor outcomes. The mean FJS at the final follow-up was 82.8. The mean WOMAC was 10.5. Kaplan-Meier survival analysis revealed a survivorship rate of 93.1% at 10 years, considering revision for any reason as endpoint.

CONCLUSIONS

Lateral UKA proved to be an effective treatment option for osteoarthritis affecting the lateral compartment of the knee. The study demonstrated a high survivorship rate and favorable functional outcomes at a mean follow-up of 132.7 months. These findings highlight the potential benefits of fixed-bearing lateral UKA in selected patients with lateral compartment knee pathology.

Preoperative valgus-corrected hip-knee-ankle angle and medial meniscal extrusion are useful for evaluating postoperative alignment in mobile-bearing UKA

Purpose

The purposes of the study were to analyze the correlation between preoperative variables (valgus corrected hip-knee-ankle angle (vcHKA), medial osteophyte areas of the tibia and femur, and medial meniscus extrusion (MME)) and the postoperative alignment in mobile-bearing unicompartmental knee arthroplasty (UKA).

Methods

This study enrolled 109 patients (118 knees) who underwent mobile-bearing UKA between January 1, 2019 and January 1, 2023, retrospectively. Radiographic parameters, including the HKA, hip-knee-shaft angle (HKS), and valgus-corrected femorotibial angle (vcFTA), were measured using preoperative radiographs. The vcHKA was calculated as vcFTA - HKS. The medial osteophyte areas of the tibia and femur and MME were measured using knee magnetic resonance imaging (MRI). Simple and multiple linear regression analyses, univariate and multivariate logistic regression analyses, and receiver operating characteristic (ROC) curves were performed.

Results

In total, 109 patients (118 knees) were enrolled in this study. In the multiple linear regression analysis, vcHKA (β = 0.732, 95 % confidence interval (95%CI) = 0.582 to 0.881; p < 0.001) and MME (β = 0.203, 95%CI = 0.001 to 0.405; p = 0.049) were positively correlated with postoperative HKA, and postoperative HKA was modeled according to the following equation: 45.420 + (0.732° * vcHKA) + (0.203 mm × MME). In the multivariate logistic regression analysis, vcHKA (odds ratio (OR) = 2.007, 95 % CI = 1.433 to 2.810, p < 0.001) was associated with postoperative valgus malalignment independently. In the ROC curve, vcHKA (cutoff value: 180°) was predictive of postoperative valgus malalignment, with an accuracy (95%CI) of 0.862 (0.780-0.944).

Conclusion

Overcorrection of a varus knee under valgus stress radiograph (VSR) and excessive MME on preoperative MRI increase the possibility of overcorrection of postoperative alignment in mobile-bearing UKA.

Fixed-Bearing Unicompartmental Knee Arthroplasty of the Lateral Compartment: A Series of 246 Cases

Background

Isolated osteoarthritis of the lateral compartment of the knee is less common than that of the medial compartment, resulting in significantly fewer lateral unicompartmental knee arthroplasties (UKAs) being performed. This study aimed to evaluate results of a fixed-bearing UKA for the treatment of lateral compartment osteoarthritis of the knee.

Methods

A prospectively collected cohort of 255 patients undergoing fixed-bearing UKA of the lateral compartment using the Triathlon PKR (Stryker, Warsaw, IND) implant with a minimum 2-year follow-up was reviewed. The Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, radiographic alignment, complications, reoperations, and revisions were recorded. Patient factors and pre- and post-surgical alignment were assessed for their association with a minimum important change (MIC) of the total WOMAC score.

Results

A total of 246 implants with a mean follow-up of 6.6 years (2-10.8 years) were included (4% lost to follow-up). The total WOMAC score increased from 61.3 ± 3.5 to 85.3 ± 7.5, exceeding the MIC in 215 patients (88%). Exceeding the MIC was not associated with age, body mass index, or alignment. The 5-year implant revision rate was 1.6% (3/187).

Conclusions

The fixed-bearing Stryker Triathlon PKR implant for lateral UKA resulted in good clinical outcomes with a low revision rate at midterm follow-up. Body mass index, age, and pre- and post-surgical alignment did not correlate with the clinical outcome. Long-term follow-up is necessary to determine if the clinical improvement and low revision rate can be maintained.

Impact of lateral meniscus injury detected by preoperative magnetic resonance imaging on midterm results after unicompartmental knee arthroplasty

BACKGROUND

The significance of lateral meniscus injury and its impact on success rates with medial unicompartmental knee arthroplasty (UKA) is still debated among scholars. This study aims to investigate whether preoperative magnetic resonance imaging (MRI) findings of lateral meniscus injury influence midterm outcomes following UKA.

METHODS

This study recruited 104 patients who underwent medial mobile-bearing UKA. Based on the extent of lateral meniscus injury indicated by the preoperative MRI and Stoller's classification system, patients were divided into two groups: the normal group (grade 0), and the lateral meniscus injury group (grade 3). Further, preoperative demographic and clinical outcome data (Hospital for Special Surgery score, lateral knee pain, squatting, and knee extension ability) were compared at least 2 years postoperatively.

RESULTS

No statistically significant difference in knee function or clinical outcome was found between the normal group (n = 59) and the lateral meniscus injury group (n = 45). During the 39.2 months (range: 24-64 months), no patient required any reoperation or revision procedures.

CONCLUSION

In summary, the presence of lateral meniscus injury as determined by preoperative MRI does not affect the midterm results after UKA. Without additional treatment for lateral meniscus injury, UKA can yield desired outcomes regardless of the presence of lateral meniscus injury on preoperative MRI.

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°.

Robotic-Assisted Conversion of a Failed Medial Unicompartmental Knee Arthroplasty to Total Knee Arthroplasty: A Case Report

CASE

An 81-year-old man with a history of left medial unicompartmental knee arthroplasty (mUKA) 8 years prior presented to the outpatient clinic with gradually increasing medial left knee pain of 6 years of duration. He underwent left conversion robotic-assisted total knee arthroplasty (RA TKA). At 1-year follow-up, the patient reported satisfactory clinical outcomes and excellent component alignment on x-rays.

CONCLUSION

This case highlights using RA TKA for failed mUKA as a viable and promising conversion arthroplasty alternative technique that may improve surgical outcomes by enhancing implant alignment and positioning, protecting the soft tissues, and preserving bone stock.

Survival of Patient-Specific Unicondylar Knee Replacement

Unicompartmental knee arthroplasty (UKA) in isolated medial or lateral osteoarthritis leads to good clinical results. However, revision rates are higher in comparison to total knee arthroplasty (TKA). One reason is suboptimal fitting of conventional off-the-shelf prostheses, and major overhang of the tibial component over the bone has been reported in up to 20% of cases. In this retrospective study, a total of 537 patient-specific UKAs (507 medial prostheses and 30 lateral prostheses) that had been implanted in 3 centers over a period of 10 years were analyzed for survival, with a minimal follow-up of 1 year (range 12 to 129 months). Furthermore, fitting of the UKAs was analyzed on postoperative X-rays, and tibial overhang was quantified. A total of 512 prostheses were available for follow-up (95.3%). Overall survival rate (medial and lateral) of the prostheses after 5 years was 96%. The 30 lateral UKAs showed a survival rate of 100% at 5 years. The tibial overhang of the prosthesis was smaller than 1 mm in 99% of cases. In comparison to the reported results in the literature, our data suggest that the patient-specific implant design used in this study is associated with an excellent midterm survival rate, particularly in the lateral knee compartment, and confirms excellent fitting.

A standardized technique for lateral unicompartmental knee arthroplasty

OBJECTIVES

We developed a new standardized procedure for lateral unicompartmental knee arthroplasty (UKA) to maximize the benefits and minimize the risks of surgery in patients with osteoarthritis (OA).

METHODS

This retrospective study recruited patients who underwent lateral UKA at our hospital between January 2014 and January 2016. Demographic characteristics and preoperative and postoperative American Knee Society (AKS) clinical scores (including pain, clinical, and knee mobility scores) were collected.

RESULTS

A total of 158 patients (35 male and 123 female) who underwent 160 lateral UKAs were analyzed. Their AKS clinical scores (0-100 points) improved from 53.1 ± 4.1 (range 45-62) preoperatively to 97.0 ± 1.7 (range 92-99) (p < 0.001) postoperatively with additional improvements of 9.1 ± 1.8 (range 3-14) to 47.3 ± 1.5 (range 45-49) (p < 0.001) for pain, 49.7 ± 9.7 (range 35-70) to 97.1 ± 4.1 (range 90-100) (p < 0.001) for function, and 105.0 ± 4.4° (equivalent to ∼100-115°) to 125.5 ± 5.3° (∼110-135°) (p < 0.001) for a range of motion (ROM). No patients required reoperations or revisions. Two patients were readmitted within 60 days due to severe knee swelling.

CONCLUSION

The lateral UKA protocol was reproducible and the patients had a good postoperative outcomes. Yet, large-scale, multi-center, prospective studies are needed to further confirm our findings.

Similar survivorship at the 5-year follow-up comparing robotic-assisted and conventional lateral unicompartmental knee arthroplasty

PURPOSE

This retrospective study aims to analyse the survivorship and functional outcomes of two samples with similar preoperative clinical and demographic data of lateral unicompartmental knee arthroplasty (UKA) performed with robotic and conventional surgery at a minimum 5-year follow-up.

METHODS

In this retrospective study, the clinical records of two cohorts for 95 lateral UKA implants were analysed. The first cohort consisted of 43 patients with cemented lateral UKA performed with the conventional procedure (Conventional group). The second cohort consisted of 52 patients who received robot-assisted cemented lateral UKA (Robotic group). Clinical evaluation of the two samples entailed evaluating the Knee Injury and Osteoarthritis Outcome Score divided into subscales (symptoms and stiffness, pain, function in daily living, function in sport and recreation and quality of life) for each patient. Revision was defined as the failure of the implant (periprosthetic joint infection, periprosthetic fracture or aseptic loosening), and survival was based on implant revision.

RESULTS

The mean follow-up time was 90.3 ± 9.1 months for the Conventional Group and 95.4 ± 11.0 months for the Robotic Group (n.s.). Each patient was clinically evaluated on the day before surgery (T₀), at a minimum 1-year follow-up (T₁) and at a minimum 5-year follow-up (T₂). In both groups, all clinical scores improved between T₀ and T₁ and between T₀ and T₂ (p < 0.05); for both groups, no differences were noted in any clinical scores between T₁ and T₂ (n.s.). No significant differences in any clinical score were found between the two groups at each follow-up (n.s.). Survival analysis reported no differences between the two groups at the final 1-year follow-up, with three failures (2 aseptic loosening and 1 periprosthetic fracture) in the Conventional group and two failures (1 patellofemoral osteoarthritis and 1 inexplicable pain) in the Robotic group (n.s.).

CONCLUSIONS

This study shows excellent clinical outcomes and revision rates in robotic arm-assisted and manual techniques for lateral UKA, with no clinical differences at medium- to long-term follow-up.

LEVEL OF EVIDENCE

Level III-comparative study.

Insufficient evidence to confirm benefits of custom partial knee arthroplasty: a systematic review

PURPOSE

The purpose of this systematic review was to synthesise the available literature and critically appraise current evidence on the functional and radiographic outcomes as well as reoperation and revision rates of custom partial knee arthroplasty, i.e., unicompartmental knee arthroplasty (UKA), bicompartmental knee arthroplasty (BKA), and patellofemoral arthroplasty (PFA).

MATERIAL AND METHODS

This systematic review was performed in accordance with the guidelines of Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA), and a protocol was registered with Prospero. On 25 May 2021, two authors independently searched and screened Level I-IV studies that reported on outcomes of custom partial knee arthroplasty using the databases of MEDLINE^®, EMBASE^®, and the Cochrane Library without restriction on date of publication. Findings from eligible articles were synthesised and tabulated, and quality assessments were done according to the guidelines of the Joanna Briggs Institute (JBI) Checklists.

RESULTS

Fifteen articles were eligible for data extraction, of which two comparative and four case series were on custom UKA (follow-up, 0-9 months), one comparative and five case series on custom BKA (follow-up, 0.25-72 months), and three case series on custom PFA (follow-up, 2-119 months). Three studies on custom UKA reported mean Knee Society Score (KSS) Knee of 86-94 and mean KSS Function of 94-95, and two studies on custom BKA reported mean KSS Knee of 90-94 and KSS function of 81, whereas one study on custom PFA reported KSS Knee of 91 and KSS Function of 89. Custom implants tended to have less bone-implant mismatch compared to off the shelf (OTS) implants. Revision rates were 3-25% for custom UKA (at 0-109 months), 3-5% for custom BKA (at 12-72 months), and 0-14% for custom PFA (at 2-119 months).

CONCLUSION

Due to the small number of comparative studies and lack of consistency in reported outcomes, it remains difficult to ascertain the benefits of custom partial knee arthroplasty. Anecdotal evidence suggests that, compared to OTS implants, custom implants result in less bone-implant mismatch and that 78-91% of patients are either satisfied or very satisfied after custom partial knee arthroplasty.

LEVEL OF EVIDENCE

IV.

Disease progression, aseptic loosening and bearing dislocations are the main revision indications after lateral unicompartmental knee arthroplasty: a systematic review

IMPORTANCE

Lateral unicompartmental knee arthroplasty (UKA) is a surgical option for patients with isolated lateral osteoarthritis however, the procedure has higher revision rates than medial UKA. The reason for this remains unclear; therefore, a better understanding of the indications for lateral UKA revision is needed.

AIM

The primary aim of this systematic review was to identify revision indications for lateral UKA. Secondary aims were to further investigate if revision indications were influenced by implant design and time from surgery.

EVIDENCE REVIEW

A systematic literature review was performed according to the PRISMA 2020 guidelines. Search was performed in January 2022 in MedLine, EMBASE, CINAHL and the Cochrane Library using the keywords "knee arthroplasty", "unicompartmental", "reoperation", synonyms and abbreviations. Articles published in 2000-2021 that were at least level III retrospective cohort studies with at least 10 lateral UKAs and reported all failure modes were included. Risk of bias was assessed using the ROBINS-I tool. Revision indications, patient characteristics, study design, implant types and time to failure were extracted from the selected studies. Collated data were tabulated and differences were tested using Chi-square or Fisher's exact test.

FINDINGS

A total of 29 cohort and 4 registry studies that included 7,668 UKAs met the inclusion criteria. Studies were judged as having moderate or severe risk of bias; this was associated with the retrospective nature of studies required to investigate long-term outcomes of knee arthroplasty. The main indications for lateral UKA revision were OA progression (35%), aseptic loosening (17%) and bearing dislocation (14%). The incidence of revision was similar for mobile-bearing implants (7.6%) and fixed-bearing (6.4%). For mobile-bearing implants, there was introduction of bearing dislocations as an additional mode of failure (24% cf. 0%, p < 0.001). For fixed-bearing implants, the incidence of revision was higher for all-poly-ethylene (13.9%) than metal-backed (1.8%) tibial components. Early lateral UKA failures were associated with bearing dislocations (sequential decrease from 69% under 6 months to 0% 10+ years, p < 0.001), whereas late failures were associated with OA progression (sequential increase from 0% under 6 months to 100% > 10+ years, p < 0.01). Compared with medial UKA, OA progression (41% cf. 30%, p = 0.004), malalignment (2.7% cf. 0.8%, p = 0.02), instability (4% cf. 1%, p = 0.02) and bearing dislocations (20% cf. 10%, p < 0.001) were more common for lateral UKA.

CONCLUSIONS AND RELEVANCE

OA progression, aseptic loosening and bearing dislocation were the three main revision indications for lateral UKA. Compared to medial UKA, OA progression, malalignment, instability and bearing dislocations were more common revision indications for lateral UKA. Higher survivorship of metal-backed fixed-bearing implants was found. The findings suggest that the outcomes of lateral UKA may be improved with more optimal alignment, gap balancing and patient selection.

LEVEL OF EVIDENCE

Level III systematic review.

Isolated Lateral Tibiofemoral Compartment Osteoarthritis: Survivorship and Patient Acceptable Symptom State After Lateral Fixed-Bearing Unicompartmental Knee Arthroplasty at Mean 10-Year Follow-up

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) is an excellent option to alleviate disability and restore function in patients with lateral compartment knee osteoarthritis (OA). The purpose of the present study was to determine the survivorship and long-term outcomes in both younger/middle-aged and older patients with lateral compartment OA following non-robotically-assisted, fixed-bearing lateral UKA and to determine if an acceptable symptom state can be achieved.

METHODS

All patients were managed with fixed-bearing lateral UKA by a single surgeon utilizing a lateral parapatellar approach without robotic assistance. The primary outcome variables were the Knee injury and Osteoarthritis Outcome Score (KOOS) Activities of Daily Living (ADL) and Sport subscale scores. In addition, the other KOOS subscores, the Lysholm score, the achievement of the Patient Acceptable Symptom State (PASS), and the Veterans RAND (VR-12) Physical Component Summary score (PCS) and Mental Component Summary score (MCS) were collected. Failure was defined as conversion to total knee arthroplasty (TKA). Patients were divided into 2 cohorts: younger/middle-aged patients (<60 years of age) and older patients (≥60 years of age).

RESULTS

A cohort of 256 patients underwent medial (n = 193) or lateral (n = 63) UKA. Sixty-one patients met the inclusion criteria. At mean of 10 years (range, 4 to 17 years) of follow-up, there were no significant differences between the groups in terms of any patient-reported outcome measures (p > 0.05). The percentage of patients in whom PASS was achieved on the KOOS ADL and Sport subscores was 82% and 88%, respectively, in the younger cohort and 80% and 80%, respectively, in the older cohort. The mean survival estimate of the prothesis was 15.3 years (95% confidence interval [CI], 14.5 to 16.2 years) for the entire cohort. The estimated rate of implant survival in the younger cohort was 100% at 5 and 10 years, and the estimated rate of implant survival in the older cohort was 98% at 5 years and 96% at 10 years.

CONCLUSIONS

Lateral fixed-bearing, non-robotic UKA for the treatment of isolated lateral compartment OA resulted in >80% of patients reaching an acceptable symptom state in terms of both activities of daily living and sporting activities. UKA provides an excellent option that provides longevity with high PASS rates and return to activities with a low risk of complications and failure.

LEVEL OF EVIDENCE

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

The Lawrence D. Dorr Surgical Techniques & Technologies Award: Patient Acceptable Symptom State (PASS) in Medial and Lateral Unicompartmental Knee Arthroplasty: Does the Status of the ACL Impact Outcomes?

BACKGROUND

The aim of this study is to determine if there is a difference in the percentage of patients who reach Patient Acceptable Symptom State (PASS) when comparing anterior cruciate ligament (ACL)-deficient and ACL-intact knees following fixed-bearing medial and lateral unicompartmental knee arthroplasty (UKA).

METHODS

A consecutive series of 215 knees that underwent UKA (medial = 158, lateral = 57) were included in the study. The Knee Osteoarthritis Outcome Score functional score [KOOS activities of daily living (ADL)] and KOOS Sport were used as the primary outcome variables. A KOOS ADL PASS of 87.5 and KOOS Sport PASS of 43.8 were previously described for total knee arthroplasty (TKA). Failure was defined as conversion to TKA.

RESULTS

There were 157 in the ACL-intact group and 58 in the ACL-deficient group. Conversion to TKA was 3.7%. The failure rate in the ACL-deficient group was 5% (3/58) and 3% (5/157) in the ACL-intact group (P = .447). The mean survival for the entire group was 18.1 years (95% confidence interval 17.6-18.6). At 10 years, the survival was 94.3% (standard error = 0.028) in the ACL-deficient group and 97.6% (standard error = 0.014) in the ACL-intact group. At a mean 10 ± 3.5 years, with 93% follow-up, 83% in the ACL-deficient group and 80% in the ACL-intact group reached PASS for KOOS ADL (P = .218). For KOOS Sport, 85% of the ACL-deficient group compared to 81% in the ACL-intact group (P = .374) reached PASS.

CONCLUSION

The ACL-deficient cohort results were not significantly different compared to ACL-intact knees in both medial and lateral compartment UKA. Fixed-bearing medial and lateral UKA resulted in low failure rate and excellent long-term outcomes.

Midterm Survivorship of Robotic-Assisted Lateral Unicompartmental Knee Arthroplasty

BACKGROUND

Lateral unicompartmental knee arthroplasty (UKA) is a popular alternative to total knee arthroplasty (TKA) for patients with isolated lateral compartment osteoarthritis. Few studies have investigated outcomes following robotic-assisted lateral UKA. The purpose of this study is to evaluate mid-term survivorship and patient-reported outcomes of robotic-assisted lateral UKA.

METHODS

A retrospective case series was conducted on all robotic-assisted lateral UKAs performed by a single surgeon between 2013 and 2019. Patient demographics, surgical variables, and Kozinn and Scott criteria were collected. Implant survivorship was estimated using the Kaplan-Meier method with all-cause reoperation and conversion to TKA as endpoints. Participating patients were assessed for patient satisfaction and the Forgotten Joint Score-12. Correlations between patient demographics and patient outcome scores were investigated.

RESULTS

In total, 120 lateral UKAs were identified, 84 of which met inclusion criteria, with a mean follow-up of 4.0 years (range 2.0-7.0). Five-year survivorship was 92.9% (95% confidence interval [CI] 84.5-96.7) with all-cause reoperation as the endpoint, and 100% (95% CI 95.0-100) with conversion to TKA as the endpoint. One patient was converted to TKA after the 5-year mark, resulting in a 6-year survival for conversion to TKA of 88.9% (95% CI 44.9-98.5). Average Forgotten Joint Score-12 score was 82.7/100, and patient satisfaction 4.7/5. Mean coronal plane correction was 2.5° ± 1.9° toward the mechanical axis. Neither final postoperative alignment nor failure to meet classic Kozinn and Scott criteria for UKA resulted in differences in patient-reported outcomes.

CONCLUSION

The current study demonstrates high mid-term survivorship and excellent patient-reported outcomes with robotic-assisted lateral UKA. Robotic-assisted lateral UKA is a viable treatment option for isolated lateral compartment arthritis even in patients who do not meet classic indications.

Midterm Outcomes in Lateral Unicompartment Knee Replacement: The Effect of Patient Age and Bearing Choice

Isolated lateral compartment knee osteoarthritis (OA) affects between 7 and 10% of patients with knee OA. Although lateral unicompartmental knee arthroplasty (UKA) is an accepted treatment to manage this condition, it is performed relatively infrequently. The aim of this study was to evaluate the mid-term survivorship, radiographic outcomes, and patient-reported outcome measures (PROMs). We performed a retrospective review of a prospectively maintained database of consecutive isolated lateral UKAs performed by a single surgeon at an academic institution between September 2007 and December 2015. Our primary outcome was failure defined as revision surgery to total knee arthroplasty (TKA). Secondary outcomes included any additional surgery for any other reason. Forty-nine consecutive patients (27 females) with median age of 54.7 years (45.2-82.2) met the inclusion criteria. The survival rate for the whole cohort was 86.1% (95% confidence interval [CI]: 73.2-99.0) at 10 years as defined by conversion to TKA. There were a total of four lateral UKAs (all mobile bearings) revised to TKAs. The entire cohort demonstrated statistically significant improvements from preoperative PROMs compared with the most recent postoperative PROMs including the Western Ontario and McMaster Universities Osteoarthritis Index, Knee injury and Osteoarthritis Outcome Score, and Tegner activity scale at a median 8.8 (1.7-12.2) years follow-up. Patients with mobile bearing underwent higher revision to TKA and reoperation for all indications compared with fixed-bearing lateral UKA. In this relatively young cohort, lateral UKA yielded acceptable long-term survival and satisfactory improvement in functional outcomes. Patients who had fixed-bearing implants had similar improvement and trended toward lower revision rates than those with mobile-bearing implants. Level III therapeutic: retrospective Study was performed.

No difference in return to amateur sports after medial and lateral unicompartmental knee arthroplasty in patients younger than 65 years

PURPOSE

The aim of this study was to assess the return to amateur sports of patients under 65 years, following medial unicompartmental knee arthroplasty (mUKA) versus lateral unicompartmental knee arthroplasty (lUKA). It was hypothesized that patients younger than 65 years who underwent lateral or medial unicondylar knee replacement will result in similar rates to amateur sports, at a minimum follow-up of 2 years.

METHOD

Patients who underwent medial or lateral UKA participated in a 2-year follow-up program, where they were clinically evaluated for their return to amateur sports, using the University of California, Los Angeles (UCLA) activity scale and the High-Activity Arthroplasty Score (HAAS). Furthermore, subgroup analyses by gender and age were performed. Power analysis was performed to ensure sample size considering that lUKA is implanted ten times less frequently than its medial counterpart.

RESULTS

There were 85 patients who completed the entire minimum 2-year follow-up of which 73 belonged to the mUKA group and 12 to the lUKA group. No preoperative differences were found between the groups regarding the gender, the affected side, age, and mean follow-up. Both groups showed statistically significant improvement (p < 0.05) in their return to amateur sports in all parameters (UCLA and HAAS). No differences among the two groups were found at T₀ and T₁ (n.s.)_. All subgroups showed a statistically significant improvement (p < 0.05) with respect to the preoperative value, except for UCLA for lUKA with less than 60 years and HAAS for males in the lUKA group (n.s.). No differences were found among subgroups both at T_o and T₁ (n.s.).

CONCLUSION

Both mUKA and lUKA procedures enabled all young and active patients a certain return to amateur sports 2 years after surgery, regardless of age and gender. UKA, medial or lateral, should always be considered for the treatment of isolated osteoarthritis in young and active patients with high functional demands.

LEVEL OF EVIDENCE

Cohort Study, Level of Evidence III.

REGISTRATION

Researchregistry6221 - Research Registry www.researchregistry.com .

A 180° Spin of the Femoral Component in Unicompartmental Knee Arthroplasty: A Report of 2 Cases

CASE

We report 2 cases of undescribed lateral unicompartmental knee arthroplasty failure: a 180° rotation of the femoral component. The patients experienced a locking event several years after arthroplasty, and radiographs revealed a perfect 180° rotation of the implant. Each patient underwent revision surgery to a total knee arthroplasty. At the 13-year follow-up, the first patient had no pain and a range of motion of 140°. The second patient, at 3 months, could walk without crutches with a flexion at 145°.

CONCLUSION

Excessive laxity, coronal or sagittal, might be associated with this complication.

A Medial Subvastus Approach for Lateral Unicompartmental Knee Arthroplasty: Technique Description and Early Outcome Results

Background

Unicompartmental knee arthroplasty (UKA) treats arthritis involving only one compartment of the knee. Lateral UKA is mainly performed through medial parapatellar or lateral parapatellar approaches to the knee. This technique article introduces a medial subvastus approach to lateral UKA, discusses the clinical rationale behind its use, and offers a preliminary retrospective study on short-term outcomes of lateral UKAs using the lateral vs medial subvastus approaches.

Methods

A description of the medial subvastus approach is included. In addition, we reviewed 32 and 30 lateral UKAs performed using the lateral and medial subvastus approaches, respectively. Minimum follow-up duration was 1 year. Knee injury and osteoarthritis outcome score for joint replacement (KOOS, JR) knee scores were used for comparison.

Results

Age and body mass index were similar between the 2 cohorts. Mean KOOS, JR. scores for the subvastus approach group were significantly higher than those for the lateral approach group at 81.41 ± 2.0 for medial subvastus and 74.19 ± 2.9 for lateral (P = .02). One deep infection and 2 revision total knee arthroplasties occurred in the lateral approach group. Neither occurred in the subvastus group. The mean follow-up duration was significantly longer for the lateral approach group than that for the subvastus group at 749 vs 410 days (P < .001). Literature on time-dependence of patient-reported outcomes supports usage of the data, despite follow-up discrepancies.

Conclusions

A subvastus approach for lateral UKA may offer improved visualization, easier conversion to total knee arthroplasty, and faster recovery, based on clinical observation. Preliminary results suggest improved short-term knee scores compared to a lateral approach.

Lower limb kinematics of unicompartmental knee arthroplasty individuals during stair ascent

Objective

Purpose of the study was to compare lower-limb kinematics and interlimb asymmetry during stair ascent in individuals post-medial or lateral unicompartmental knee arthroplasty (UKA).

Methods

60 patients (20 medial; 10 lateral) post-UKA and 30 matched healthy controls performed stair ascent. Spatio-temporal, lower-limb kinematics and interlimb asymmetries during stair ascent were compared.

Results

Medial-UKA group displayed 5° less knee extension of the UKA limb than controls (p = 0.005) and 2° less than the contralateral limb during stance phase. No interlimb asymmetries were found for lateral-UKA.

Conclusion

Patients post-UKA demonstrate satisfactory lower-limb kinematics and minimal interlimb asymmetry during stair ascent compared to healthy individuals.