Aetiology of lateral progression of arthritis following Oxford medial unicompartmental knee replacement: a case-control study

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.

Small change in the arithmetic hip-knee-ankle angle during unicompartmental knee arthroplasty improves early postoperative functional outcomes

INTRODUCTION

The optimal lower-limb alignment after unicompartmental knee arthroplasty (UKA) remains controversial. This study aimed to investigate the optimal lower-limb alignment for functional improvement in the early post-UKA period. We hypothesized that a small change (Δ) in the arithmetic hip-knee-ankle (aHKA) angle during surgery would result in better postoperative knee function.

MATERIALS AND METHODS

This single-centered, retrospective study analyzed 91 patients (91 knees) who underwent UKA from April 2021 and December 2022. Preoperative and postoperative standing whole-leg radiographs were used to evaluate the mechanical HKA angle and aHKA angle. The aHKA angle was calculated from the medial proximal tibial angle (MPTA) and lateral distal femoral angle (LDFA). We defined restored aHKA angle as a postoperative aHKA angle within ± 3° of the preoperative aHKA angle. Functional improvement was evaluated using the preoperative and one-year postoperative Knee Society Scoring 2011 (KSS 2011). A multivariate regression analysis was performed to investigate the optimal lower-limb alignment for functional improvement.

RESULT

Postoperative restored aHKA angle (p = 0.020) was the only significant factor for improved KSS 2011 scores. Postoperative restored aHKA angle was obtained in 64 patients (70%). ΔMPTA (p < 0.001) and ΔLDFA (p = 0.037) were significant factors associated with a postoperative restored aHKA angle.

CONCLUSIONS

UKA restores the native knee, including resurfacing constitutional alignment and medial collateral ligament tension. Minimal change in the aHKA angle during UKA improves the functional outcomes of the knee during the early postoperative period, consistent with the minimally invasive surgical concept of UKA.

Painful Unicompartmental Knee Arthroplasty: Etiology, Diagnosis and Management

Unicompartmental knee arthroplasty (UKA) is an increasingly common procedure. Patients with persistent or new postoperative pain can present a challenge for surgeons to accurately diagnose and treat. The purpose of this study is to provide a comprehensive review of the presentation, diagnosis, and management of the various pathologies contributing to pain after UKA. The most common causes of a painful UKA include aseptic component loosening and progression of osteoarthritis. Both of these conditions may be treated with either revision UKA or conversion to total knee arthroplasty. While technically challenging, these procedures are often associated with favorable outcomes. Other causes of pain after UKA include infection, atraumatic tibial component subsidence, periprosthetic fracture and malalignment. Careful clinical, radiographic, and laboratory evaluation is therefore critical to accurately identify the source of pain and guide appropriate management.

Can bone scintigraphy reflect the progression of osteoarthritis after unicompartmental knee arthroplasty?

BACKGROUND

Bone scintigraphy (BS) has been reported to be a useful predictor of osteoarthritis (OA) progression in primary knee OA. However, no previous studies have explored the relationship between BS and OA progression in the retained compartments after unicompartmental knee arthroplasty (UKA). Thus, we evaluated whether OA progresses to other compartments in patients who undergo UKA and if increased uptake on BS is associated with OA progression in other compartments after UKA.

METHODS

A total of 41 patients with knee BS at least five years after UKA were included. Radiographic OA progression in other compartments was assessed by grading and comparing OA severity in each patient using the Kellgren-Lawrence grading system (K-L grade) and Osteoarthritis Research Society International (OARSI) atlas score. After UKA, the correlation between BS uptake and radiographic OA progression was analyzed in each retained compartment. A correlation analysis was also performed to evaluate the association between BS uptake and OA progression grades.

RESULTS

A significant progression of OA was observed in both contralateral tibiofemoral and patellofemoral compartments after UKA at 98.5 ± 26.0 months of follow-up (all p<0.001). No correlation was found between BS uptake and radiographic OA progression nor between BS uptake and radiographic OA progression grade in the contralateral and patellofemoral compartments.

CONCLUSIONS

Following UKA, OA progresses in the retained contralateral tibiofemoral and patellofemoral compartments over a minimum five-year follow-up period. Thus, BS is ineffective in assessing the progression of OA in these compartments.

Intraoperative sensor technology quantifies inter-prosthesis pressure for predicting lower limb alignment after Oxford unicompartmental knee arthroplasty

Purpose: The aim of this study is to quantify inter-prosthetic pressures at different knee angles in Oxford unicompartmental knee arthroplasty (OUKA) and its correlation with postoperative lower limb alignment. Methods: This study included 101 patients (122 knees) who underwent OUKA from March 2022 to July 2022. The previously designed matrix flexible force sensor was used to measure the inter-prosthesis pressure of different knee joint angles during the UKA operation, and the force variation trend and gap balance difference were obtained. The correlation between inter-prosthesis pressure and postoperative lower limb alignment index including hip-knee-ankle angle (HKAA) and posterior tibial slope (PTS) was analyzed. The effect of PTS change (ΔPTS) on the inter-prosthesis pressure and the range of motion (ROM) of the knee joint was analyzed. Radiographic and short-term clinical outcomes of included patients were assessed. Results: The inter-prosthesis pressure of the different knee joint angles during the operation was not consistent. The mean inter-prosthesis pressure and gap balance difference were 73.68.28 ± 41.65N and 36.48 ± 20.58N. The inter-prosthesis pressure at 0° and 20° was positively correlated with postoperative HKAA (p < 0.001). ΔPTS was positively correlated with the pressure at the end of knee extension and negatively correlated with the pressure at the end of knee flexion (p < 0.001). The HKAA, ROM, degree of fixed knee flexion deformity, and knee society score of the included patients were significantly improved compared with those before the operation (p < 0.001). Conclusion: The inter-prosthesis pressure measured at the knee extension position can predict postoperative HKAA to some degree. Changes in PTS will affect the inter-prosthesis pressure at the end of flexion and end of knee extension, but this change is not related to the range of motion of the knee joint.

Coronal tibiofemoral subluxation under valgus stress force radiography is useful for evaluating postoperative coronal tibiofemoral subluxation in mobile-bearing UKA

PURPOSE

Coronal tibiofemoral subluxation (CTFS) is considered a controversial and potential contraindication to unicompartmental knee arthroplasty (UKA) but is less discussed. The study aims to observe the CTFS in a cohort of patients before and after mobile-bearing UKA and to investigate the relationship between preoperative variables (preoperative CTFS and preoperative CTFS under valgus stress) and postoperative CTFS after mobile-bearing UKA.

METHODS

The study retrospectively analyzed 181 patients (224 knees) undergoing mobile-bearing UKA from September 1 2019 to December 31 2021. By using hip-to-ankle anterior-posterior (AP) standing radiographs and valgus stress force radiographs, preoperative CTFS, preoperative CTFS under valgus stress, and postoperative CTFS were measured. CTFS was defined as the distance between the tangent line to the outermost joint edge of the lateral condyle of the femur and the tangent line of the lateral tibial plateau. All patients were divided into two groups based on postoperative CTFS, group A (postoperative CTFS ≤ 5 mm) and group B (postoperative CTFS > 5 mm). The Student's t-test, one-way ANOVA together with Tukey's post hoc test, the chi-square test, the Fisher's exact test, Pearson correlation analysis, simple and multiple linear regression, and univariate and multiple logistic regression were used in the analyses.

RESULTS

The means ± standard deviations (SD) of preoperative CTFS, preoperative CTFS under valgus stress, and postoperative CTFS were 4.96 ± 1.82 mm, 3.06 ± 1.37 mm, and 3.19 ± 1.27 mm. The difference between preoperative CTFS and postoperative CTFS was statistically significant (p < 0.001). The preoperative CTFS (6.35 ± 1.34 mm) in Group B (n = 22) was significantly higher than that (4.81 ± 1.82 mm) in Group A (n = 202) (p < 0.001), so was the variable-preoperative CTFS under valgus stress (5.41 ± 1.00 mm (Group B) > 2.80 ± 1.14 mm (Group A), p < 0.001). In Pearson correlation analysis, there was a correlation between preoperative CTFS and postoperative CTFS (r = 0.493, p < 0.001), while the correlation between preoperative CTFS under valgus stress and postoperative CTFS was stronger (r = 0.842, p < 0.001). In multiple linear regression analysis, preoperative CTFS under valgus stress (β = 0.798, 95% confidence interval (CI) = 0.714-0.883, p < 0.001) was significantly correlated with postoperative CTFS. In multiple logistic regression analysis, preoperative CTFS under valgus stress (OR = 12.412, 95% CI = 4.757-32.384, and p < 0.001) was expressed as the risk factor of postoperative CTFS (> 5 mm).

CONCLUSION

Preoperative CTFS can be improved significantly after mobile-bearing UKA. In addition, postoperative CTFS is correlated with preoperative CTFS under valgus stress and a higher preoperative CTFS under valgus stress will increase the risk of higher postoperative CTFS (> 5 mm).

LEVEL OF EVIDENCE

Level III.

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.

Preoperative uncorrectable tibiofemoral subluxation can worsen clinical outcomes after fixed-bearing unicompartmental knee arthroplasty: a retrospective analysis

INTRODUCTION

The presence of tibiofemoral subluxation (TFS) in patients with unicompartmental arthritis, a potential contraindication to unicompartmental knee arthroplasty (UKA), remains controversial and is not commonly discussed. This study aimed to determine the predictability of postoperative TFS before surgery and the effect of TFS on clinical outcomes after fixed-bearing UKA.

MATERIALS AND METHODS

In total, 70 patients with anteromedial osteoarthritis and osteonecrosis of the knee who underwent fixed-bearing UKA from January 2015 to January 2017 were included. The preoperative TFS was assessed using plain anteroposterior and valgus stress radiographs. The patients were classified into three groups as follows: group A (acceptable TFS, n = 36) comprising patients with preoperative TFS less than 5.0 mm; group C (correctable TFS, n = 17) comprising patients with preoperative TFS of more than 5.0 mm but corrected to less than 5.0 mm under valgus stress; and group U (uncorrectable TFS, n = 17) comprising patients with preoperative TFS of more than 5.0 mm under valgus stress. Patient-derived clinical scores were assessed with the 2011 Knee Society Score preoperatively and 2 years postoperatively. The results were compared among the three groups using analysis of variance.

RESULTS

Group U showed significantly higher postoperative TFS than groups A and C. Improvements in "symptoms" and "patient satisfaction" scores 2 years after surgery were significantly higher in groups A and C than in group U.

CONCLUSION

Preoperative assessment of TFS under valgus stress could be a predictor of postoperative TFS. Furthermore, preoperative uncorrectable TFS could increase pain and decrease patient satisfaction 2 years after undergoing fixed-bearing UKA.

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.

Lateral osteoarthritis progression is associated with a postoperative residual tibiofemoral subluxation in Oxford UKA

PURPOSE

Lateral compartment osteoarthritis progression (LOP) is a major complication after Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study aimed to identify the association between tibiofemoral subluxation (TFS) and LOP after OUKA. Patients whose TFS was uncorrectable according to preoperative stress radiographs were hypothesised to develop residual TFS even after surgery, and thought to be more likely to develop LOP.

METHODS

The study included 201 patients who underwent medial OUKA. Fifteen patients showed increases in LOP of at least two Kellgren-Lawrence grades after surgery [progression (P) group], while the others had no progression (N group, n = 186). TFS was measured on preoperative full leg weight-bearing radiographs, valgus stress radiographs and postoperative plain radiographs. Valgus stress radiographs were obtained using a firm manual valgus force with the knee flexed at 20°. Leg alignment, Oxford knee score (OKS), and revision rates were assessed.

RESULTS

The P group had significantly higher TFS values on preoperative valgus stress (6.8° ± 2.2° vs. 4.5° ± 2.0°; P < 0.001) and postoperative radiographs (6.6° ± 2.3° vs. 4.6° ± 2.9°; P < 0.001) than the N group. Patients with postoperative residual TFS and postoperative valgus alignment were more likely to have LOP, but 9 of the 15 LOP patients did not show postoperative valgus alignment. The P group had significantly poorer postoperative OKS (33.0 ± 10.2 vs. 37.4 ± 6.5, P = 0.017) and a higher rate of revision (6/15 vs 6/186; odds ratio = 19.16; 95% CI = 4.98-76.05, P < 0.001).

CONCLUSION

OA progression in the lateral compartment after medial OUKA might be associated with postoperative residual TFS, but does not always coexist with postoperative valgus alignment. Preoperative assessment of TFS with valgus stress could be a potential predictor of postoperative residual TFS and LOP.

LEVEL OF EVIDENCE

Level III.

Chondrocalcinosis does not affect functional outcome and prosthesis survival in patients after total or unicompartmental knee arthroplasty: a systematic review

PURPOSE

There are contentious data about the role calcium pyrophosphate (CPP) crystals and chondrocalcinosis (CC) play in the progression of osteoarthritis (OA), as well as in the outcomes after knee arthroplasty. Hence, the purpose of this systematic review was to analyse the clinical and functional outcome, progression of OA and prosthesis survivorship after unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) in patients with CC compared to patients without CC.

METHODS

A systematic review of the literature in PubMed, Medline, Embase and Web of Science was performed using the "Preferred Reporting Items for Systematic Reviews and Meta-Analysis" (PRISMA) guidelines. Articles which reported the outcome and survival rates of prosthesis after TKA or UKA in patients with CC were included.

RESULTS

A total of 3718 patient knees were included in eight selected publications, with a median sample sizes of 234 knees (range 78-1000) and 954 knees (range 408-1500) for publications including UKA and TKA, respectively. At time of surgery, the mean age was 69 years and the prevalence for CC ranged from 12.6 to 36%. Chondrocalcinosis did not significantly influence the functional and clinical outcome, the implant survival as well as the radiologic progression of OA disease after UKA and TKA.

CONCLUSION

The presence of CPP crystals in tissue samples, synovial fluid or evidence of calcifications on preoperative radiographs did not significantly influence the postoperative functional and activity scores. It also had no significant influence on prosthesis survival rate, whether it was a UKA or a TKA. This study shows that the impact of a subclinical form of chondrocalcinosis may not be of clinical relevance in the context of arthroplasty.

LEVEL OF EVIDENCE

IV.

[Recommendations for unicondylar knee replacement in the course of time : A current inventory]

BACKGROUND

A higher patient satisfaction stands in contrast to higher revision rates of unicondylar knee joint endoprosthetics (UKE) compared to total knee joint endoprosthetics (TKE). Furthermore, old "dogmas" regarding indications and contraindications persist, which is still reflected in the significantly different case numbers.

AIM

The aim of this article is to provide an overview of the current literature regarding 1. indication and contraindication (BMI, age, sport, arthrosis of other compartments, ligament status) and 2. the "eternal rival" fixed or mobile bearing for UKE.

RESULTS

The choice of the right patient remains essential, even if all the old "dogmas" of contraindications have been relativized or even outdated. Arthroses of the contralateral (in medial UKE correspondingly lateral) compartment and advanced arthroses of the lateral patella facet remain the only persistent contraindications. In contrast, a high BMI, age, chondrocalcinosis, medial patella facet and a defective (but particularly functionally stable) ACL are not contraindications; however, severe obesity is responsible for a significantly higher complication rate and probably a higher rate of loosening. Rather, the experience and thus the number of UKEs of the individual surgeon is decisive for the outcome, to which the discussion about mobile or fixed inlays must also be completely subordinated.

CONCLUSION

The indications for UKE can, therefore, be extended with a clear conscience on the basis of literature, and the current 1:10 UKE:TKE ratio in Germany can be shifted significantly.

MRI-determined preoperative lateral meniscus degeneration is not associated with adverse mid-term clinical results after mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

One of the conditions constituting surgical indication for medial mobile-bearing unicompartmental knee arthroplasty (UKA) is that there is full-thickness cartilage in the lateral compartment under valgus stress radiography. However, it is unclear whether medial unicompartmental knee arthroplasty should be performed if there is degeneration of the lateral meniscus on preoperative magnetic resonance imaging (MRI).

METHODS

The records of 77 patients (77 knees) who underwent Oxford mobile-bearing UKA were retrospectively reviewed. Based on the status of the lateral meniscus in each knee using preoperative MRI with Stoller's classification system, the patients were divided into two groups; a normal group and a lateral meniscus degenerated group (grades 1-3). The preoperative personal data and the outcome data three years postoperatively were compared.

RESULTS

The normal group contained 31 knees while the lateral meniscus degenerated group comprised 46 knees. There was no difference in clinical outcome or knee function between the groups at three years after UKA. There was no difference in re-operation and revision rate between the groups with no revisions in either group.

CONCLUSIONS

It may not be necessary to exclude UKA indications for cases with degenerative findings in the lateral meniscus on preoperative MRI.

Lateral and patellofemoral compartment osteoarthritis progression after medial unicompartmental knee arthroplasty: A five- to 10-year follow-up study

BACKGROUND

The purpose of the study was to evaluate lateral and patellofemoral osteoarthritis (OA) progression after medial unicompartmental knee arthroplasty (UKA) and identify factors affecting the progression that were not identified previously.

METHODS

We evaluated 146 patients who underwent medial UKA between 2009 and 2014. Kellgren-Lawrence grading of lateral and patellofemoral OA was performed on preoperative and final follow-up knee radiographs. Radiographic and clinical characteristics, SF-36, and Oxford knee scores were compared between the OA progressed and non-progressed groups. Risk factors for lateral and patellofemoral OA progression were evaluated.

RESULTS

The lateral OA progressed and non-progressed groups significantly differed in side, preoperative flexion contracture, preoperative joint line convergence angle, postoperative tibiofemoral angle, insert size, revision status (P < 0.05), and the patellofemoral OA progressed and non-progressed groups significantly differed in age, pre- and postoperative flexion contracture, postoperative tibiofemoral angle and pre- and postoperative patellofemoral OA grade (P < 0.05). At the final follow-up, Visual Analogue Scale, Oxford Knee Scores, and SF-36 sub-scores were significantly better in the lateral OA non-progressed group (P < 0.001). Dominant leg (odds ratio (OR): 2.759), insert size (>4, OR: 2.219), revision status (+, OR: 6.692), and postoperative tibiofemoral angle (>5.5°, OR: 1.177) were independent risk factors for lateral OA progression, whereas age (>60 years, OR: 3.222), preoperative patellofemoral OA grade (>1, OR: 2.085), and postoperative flexion contracture (>10°, OR: 1.919) were those for patellofemoral OA progression.

CONCLUSIONS

Mild radiographic progression of 1 KL grade is frequently seen five to 10 years after medial UKA. Postoperative outcomes are significantly affected by lateral compartment OA progression but not by patellofemoral OA progression.

The three-year survivorship of robotically assisted versus non-robotically assisted unicompartmental knee arthroplasty

AIM

There has been a significant reduction in unicompartmental knee arthroplasty (UKA) procedures recorded in Australia. This follows several national joint registry studies documenting high UKA revision rates when compared to total knee arthroplasty (TKA). With the recent introduction of robotically assisted UKA procedures, it is hoped that outcomes improve. This study examines the cumulative revision rate of UKA procedures implanted with a newly introduced robotic system and compares the results to one of the best performing non-robotically assisted UKA prostheses, as well as all other non-robotically assisted UKA procedures.

METHODS

Data from the Australian Orthopaedic Association National Joint Arthroplasty Registry (AOANJRR) for all UKA procedures performed for osteoarthritis (OA) between 2015 and 2018 were analyzed. Procedures using the Restoris MCK UKA prosthesis implanted using the Mako Robotic-Arm Assisted System were compared to non-robotically assisted Zimmer Unicompartmental High Flex Knee System (ZUK) UKA, a commonly used UKA with previously reported good outcomes and to all other non-robotically assisted UKA procedures using Cox proportional hazard ratios (HRs) and Kaplan-Meier estimates of survivorship.

RESULTS

There was no difference in the rate of revision when the Mako-assisted Restoris UKA was compared to the ZUK UKA (zero to nine months: HR 1.14 (95% CI 0.71 to 1.83; p = 0.596) vs nine months and over: HR 0.66 (95% CI 0.42 to 1.02; p = 0.058)). The Mako-assisted Restoris had a significantly lower overall revision rate compared to the other types of non-robotically assisted procedures (HR 0.58 (95% confidence interval (CI) 0.42 to 0.79); p < 0.001) at three years. Revision for aseptic loosening was lower for the Mako-assisted Restoris compared to all other non-robotically assisted UKA (entire period: HR 0.34 (95% CI 0.17 to 0.65); p = 0.001), but not the ZUK prosthesis. However, revision for infection was significantly higher for the Mako-assisted Restoris compared to the two comparator groups (ZUK: entire period: HR 2.91 (95% CI 1.22 to 6.98; p = 0.016); other non-robotically assisted UKA: zero to three months: HR 5.57 (95% CI 2.17 to 14.31; p < 0.001)).

CONCLUSION

This study reports comparable short-term survivorship for the Mako robotically assisted UKA compared to the ZUK UKA and improved survivorship compared to all other non-robotic UKA. These results justify the continued use and investigation of this procedure. However, the higher rate of early revision for infection for robotically assisted UKA requires further investigation. Cite this article: Bone Joint J 2020;102-B(3):319-328.

Mid-term survivorship and patient-reported outcomes of robotic-arm assisted partial knee arthroplasty

Aims

Limited evidence is available on mid-term outcomes of robotic-arm assisted (RA) partial knee arthroplasty (PKA). Therefore, the purpose of this study was to evaluate mid-term survivorship, modes of failure, and patient-reported outcomes of RA PKA.

Methods

A retrospective review of patients who underwent RA PKA between June 2007 and August 2016 was performed. Patients received a fixed-bearing medial or lateral unicompartmental knee arthroplasty (UKA), patellofemoral arthroplasty (PFA), or bicompartmental knee arthroplasty (BiKA; PFA plus medial UKA). All patients completed a questionnaire regarding revision surgery, reoperations, and level of satisfaction. Knee Injury and Osteoarthritis Outcome Scores (KOOS) were assessed using the KOOS for Joint Replacement Junior survey.

Results

Mean follow-up was 4.7 years (2.0 to 10.8). Five-year survivorship of medial UKA (n = 802), lateral UKA (n = 171), and PFA/BiKA (n = 35/10) was 97.8%, 97.7%, and 93.3%, respectively. Component loosening and progression of osteoarthritis (OA) were the most common reasons for revision. Mean KOOS scores after medial UKA, lateral UKA, and PFA/BiKA were 84.3 (SD 15.9), 85.6 (SD 14.3), and 78.2 (SD 14.2), respectively. The vast majority of the patients reported high satisfaction levels after RA PKA. Subgroup analyses suggested tibial component design, body mass index (BMI), and age affects RA PKA outcomes. Five-year survivorship was 98.4% (95% confidence interval (CI) 97.2 to 99.5) for onlay medial UKA (n = 742) and 99.1% (95% CI 97.9 to 100) for onlay medial UKA in patients with a BMI < 30 kg/m2 (n = 479).

Conclusion

This large single-surgeon study showed high mid-term survivorship, satisfaction levels, and functional outcomes in RA UKA using metal-backed tibial onlay components. In addition, favourable results were reported in RA PFA and BiKA. Cite this article: Bone Joint J 2020;102-B(1):108–116

Reduced bone activity in the native compartments after medial mobile-bearing unicompartmental knee arthroplasty. A prospective SPECT/CT study

AIMS

Altered alignment and biomechanics are thought to contribute to the progression of osteoarthritis (OA) in the native compartments after medial unicompartmental knee arthroplasty (UKA). The aim of this study was to evaluate the bone activity and remodelling in the lateral tibiofemoral and patellofemoral compartment after medial mobile-bearing UKA.

PATIENTS AND METHODS

In total, 24 patients (nine female, 15 male) with 25 medial Oxford UKAs (13 left, 12 right) were prospectively followed with sequential 99mTc-hydroxymethane diphosphonate single photon emission CT (SPECT)/CT preoperatively and at one and two years postoperatively, along with standard radiographs and clinical outcome scores. The mean patient age was 62 years (40 to 78) and the mean body mass index (BMI) was 29.7 kg/m2 (23.6 to 42.2). Mean osteoblastic activity was evaluated using a tracer localization scheme with volumes of interest (VOIs). Normalized mean tracer values were calculated as the ratio between the mean tracer activity in a VOI and background activity in the femoral diaphysis.

RESULTS

Significant reduction of normalized tracer activity was observed one year postoperatively in tibial and femoral VOIs adjacent to the joint line in the lateral compartment. Patellar VOIs and remaining femoral VOIs demonstrated a significant, diminished normalized tracer activity at final follow-up.

CONCLUSION

The osteoblastic bone activity in the native compartments decreased significantly after treatment of medial end-stage OA with a UKA, implying reduced stress to the subchondral bone in the retained compartments after a UKA. Cite this article: Bone Joint J 2019;101-B:915-921.

Association between chondrocalcinosis and osteoarthritis: A systematic review and meta-analysis

AIM

To systematically examine the existing literature on the associations between chondrocalcinosis (CC) and osteoarthritis (OA) at different joints, and to quantify such associations through meta-analysis.

METHODS

PubMed, Embase and Scopus databases were searched through from inception to June 2017. Cohort, case-control or cross-sectional studies were included if they examined the association between CC and OA. Data on the odds ratios (OR) and their 95% confidence intervals (CI) of the prevalence or progression of OA between the CC group and non-CC group with respect to the same joint were extracted.

RESULTS

A total of 14 studies were identified. Twelve studies were eligible for assessing the association between knee CC and knee OA. The combined data showed a positive association between them (OR = 2.84; 95% CI, 2.12-3.81; P < 0.001). Three studies were eligible for assessing the association between hip CC and hip OA. The data on the OR could only be extracted from one study (OR = 0.92; 95% CI, 0.68-1.24; P = 0.59). Two studies were eligible for assessing the association between hand CC and hand OA, and the data on the OR could only be extracted from one study which reported significant associations between CC and OA at the metacarpophalangeal joint (OR = 4.75; 95% CI, 2.12-10.64; P < 0.001) and the wrist joint (OR = 4.44; 95% CI, 3.56-5.54; P < 0.001).

CONCLUSION

This study established a strong association between knee CC and knee OA. However, the associations between CC and OA at the hip or hand still remain controversial and warrant further study.

Patient relevant outcomes of unicompartmental versus total knee replacement: systematic review and meta-analysis

OBJECTIVE

To present a clear and comprehensive summary of the published data on unicompartmental knee replacement (UKA) or total knee replacement (TKA), comparing domains of outcome that have been shown to be important to patients and clinicians to allow informed decision making.

DESIGN

Systematic review using data from randomised controlled trials, nationwide databases or joint registries, and large cohort studies.

DATA SOURCES

Medline, Embase, Cochrane Controlled Register of Trials (CENTRAL), and Clinical Trials.gov, searched between 1 January 1997 and 31 December 2018.

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Studies published in the past 20 years, comparing outcomes of primary UKA with TKA in adult patients. Studies were excluded if they involved fewer than 50 participants, or if translation into English was not available.

RESULTS

60 eligible studies were separated into three methodological groups: seven publications from six randomised controlled trials, 17 national joint registries and national database studies, and 36 cohort studies. Results for each domain of outcome varied depending on the level of data, and findings were not always significant. Analysis of the three groups of studies showed significantly shorter hospital stays after UKA than after TKA (-1.20 days (95% confidence interval -1.67 to -0.73), -1.43 (-1.53 to -1.33), and -1.73 (-2.30 to -1.16), respectively). There was no significant difference in pain, based on patient reported outcome measures (PROMs), but significantly better functional PROM scores for UKA than for TKA in both non-trial groups (mean difference -0.58 (-0.88 to -0.27) and -0.32 (-0.48 to -0.15), respectively). Regarding major complications, trials and cohort studies had non-significant results, but mortality after TKA was significantly higher in registry and large database studies (risk ratio 0.27 (0.16 to 0.45)), as were venous thromboembolic events (0.39 (0.27 to 0.57)) and major cardiac events (0.22 (0.06 to 0.86)). Early reoperation for any reason was higher after TKA than after UKA, but revision rates at five years remained higher for UKA in all three study groups (risk ratio 5.95 (1.29 to 27.59), 2.50 (1.77 to 3.54), and 3.13 (1.89 to 5.17), respectively).

CONCLUSIONS

TKA and UKA are both viable options for the treatment of isolated unicompartmental osteoarthritis. By directly comparing the two treatments, this study demonstrates better results for UKA in several outcome domains. However, the risk of revision surgery was lower for TKA. This information should be available to patients as part of the shared decision making process in choosing treatment options.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO number CRD42018089972.

Functional Outcome and Revision Rate Are Independent of Limb Alignment Following Oxford Medial Unicompartmental Knee Replacement

BACKGROUND

There is controversy about optimal limb alignment following knee replacement. An aim of using Oxford medial unicompartmental knee replacement (UKR) implants is to accurately restore normal ligament tension in the knee, thereby restoring normal kinematics. This return to normal tension typically results in a return to prearthritic alignment, which is frequently varus. The aim of this study was to investigate the relationship between postoperative limb alignment and postoperative patient-reported outcome and implant revision rate.

METHODS

We used a consecutive cohort of 891 knees with cemented Oxford medial UKR implants with a mean 10-year follow-up and recorded alignment. We grouped knees according to postoperative mechanical alignment as marked varus (estimated at 10°), mild varus (estimated at 5°), neutral, and valgus. The mean Oxford Knee Score (OKS) was calculated at 5 and 10 years postoperatively. Revision risk was assessed by survival analysis and component-time incidence rates.

RESULTS

Postoperatively, 67 (8%) of the 891 knees were in marked varus; 308 (35%), in mild varus; 508 (57%), in neutral; and 8 (1%), in valgus. The valgus group (8 knees) was too small for further analysis. The mean OKS (and standard deviation [SD]) at 10 years postoperatively was 41.7 ± 7 for marked varus, 40.5 ± 8 for mild varus, and 39.4 ± 9 for neutral alignment (p = 0.28). At 10 years, 92%, 85%, and 76% achieved a good or excellent OKS outcome, respectively (p = 0.02). Twelve-year survival rates were 93.3% for marked varus, 93.2% for mild varus, and 93.6% for neutral alignment, respectively (p = 0.53). Revision incidence rates per 100 component-years were 0.49 (95% confidence interval [CI], 0.2 to 1.5), 0.36 (95% CI, 0.2 to 0.7), and 0.54 (95% CI, 0.4 to 0.8), respectively, and were not significantly different (p = 0.53).

CONCLUSIONS

Marked postoperative varus mechanical alignment of an estimated 10° was present in 8%, and mild varus of about 5° was present in 35%. Increasing varus alignment was associated with an increasing percentage of good or excellent OKS outcomes, but otherwise there were no significant differences between alignment groups in patient-reported outcome or revision rate. These data support the standard operative technique for the Oxford UKR, which aims to restore ligament tension and therefore prearthritic alignment rather than neutral mechanical alignment.

LEVEL OF EVIDENCE

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

Patterns of Compartment Involvement in End-stage Knee Osteoarthritis in a Chinese Orthopedic Center: Implications for Implant Choice

OBJECTIVES

Knee osteoarthritis (OA) is a prevalent disease in the elderly, causing pain and contributing to poor quality of life. Surgical intervention, such as knee arthroplasty, can be used in those with end-stage knee OA. Total knee arthroplasty (TKA) is one of the most common surgical procedures for end-stage knee OA, with promising clinical outcomes. However, a large proportion of patients with isolated compartment OA can be treated with unicompartmental knee arthroplasty (UKA) instead. UKA has shown better patient-reported functional outcomes, and lower mortality and major complication rates than TKA. The percentage of UKA in knee arthroplasty varied in different orthopedic centers, and we believed that the requirement for UKA was underestimated in many centers. A retrospective study was carried out on our Chinese patient population presenting for knee arthroplasty; it aimed to identify the proportion of patients that might be suitable for UKA.

METHODS

A retrospective cross-sectional study of 155 consecutive patients (168 knees) awaiting TKA for end-stage primary OA was performed. The pattern and grade of OA was recorded from preoperative weight-bearing anteroposterior and non-weight-bearing lateral radiographs. The medial, lateral, patellofemoral compartment was given an individual Kellgren-Lawrence grade on the radiographs, and those grade ≥3 were defined as end-stage OA. The compartments involvement was established then. The integrity of the anterior cruciate ligament (ACL) was determined by the modified Keyes classification on lateral radiographs. The applicability for total or partial knee arthroplasty was determined according to the compartments involvement.

RESULTS

Medial compartment involvement was found in 154 (91.7%) knees, while the involvement of the lateral compartment and patellofemoral joint was found in 54 (32.1%) and 57 (33.9%) knees, respectively. Eighty-one (48.2%) of the knees showed medial compartment OA with or without patellofemoral joint involvement, and modified Keyes classification grade 1, indicating an intact ACL, and, hence, potential suitability for medial UKA. Isolated lateral OA indicating possible suitability for lateral UKA was identified in 11 knees (6.5%). No patients showed isolated patellofemoral joint OA. The other 76 (45.2%) knees could be treated by TKA.

CONCLUSIONS

The medial compartment was the most commonly affected in our Chinese patients indicated for knee arthroplasty. More than half of the patients in this group could be treated by either medial or lateral UKA.

Single-stage bilateral medial Oxford Unicompartmental Knee Arthroplasty: A case-control study of perioperative blood loss, complications and functional results

BACKGROUND

The benefits and risks of a single-stage medial UKA remains a subject of debate because of the theoretically higher risk of complications and specifically blood loss. The aim of this study was to evaluate the perioperative blood loss, risks and the functional results of single-stage bilateral medial Oxford Unicompartmental Knee Arthroplasty (OUKA) compared to a standard unilateral medial OUKA procedure (control group).

HYPOTHESIS

The blood loss observed during bilateral single-stage medial Oxford UKA is not different from that of the control group.

METHODS

In this case-control prospective study, fifty patients (100 knees) who underwent single-stage bilateral medial OUKA (study group) were compared to a hundred patients (100 knees) with unilateral medial OUKA (control group), performed by the same surgeon. The real blood loss (in mL of hematocrit at 100%), incidence of blood transfusions, and complication rates were compared. Clinical results were assessed at 6 month and at a two-year minimum follow-up (FU) using IKS, KOOS and OKS scores, in addition to a satisfaction questionnaire.

RESULTS

Groups were deemed comparable. Concerning blood loss, no significant difference was observed compared to the control group (465mL±225 vs. 396±190; p=0.07). No difference was found, either, between groups regarding the complication rates (p=0.36), nor the clinical results (p=0.61) and patient satisfaction (p=0.23) at last FU.

CONCLUSION

Single-stage bilateral procedure does not cause increased blood loss compared with controls. Moreover, clinical results were deemed good and excellent in spite of a slightly greater complication rate than those found in the literature but similar to controls.

LEVEL OF EVIDENCE

Case-control study, level III.

Oxford medial unicompartmental knees display contact-loss during step-cycle motion and bicycle motion: A dynamic radiostereometric study

The Oxford medial unicompartmental knee is designed fully congruent, with the purpose of maintaining a large contact-area throughout motion and minimize wear. No other study has investigated this design feature in-vivo. We aimed to evaluate if contact-loss was introduced between the articulating surfaces of the Oxford medial unicompartmental knee during bicycle- and step-cycle motion, and whether this correlated with essential implant parameters, such as polyethylene (PE) wear, knee-loadings, and clinical outcome. To study contact-loss, 15 patients (12 males, mean age 69 years) with an Oxford medial unicompartmental knee (7 cemented, mean follow-up 4.4 years) were examined with use of dynamic radiostereometry (RSA) (10 frames/s). PE wear was measured from static RSA and clinical outcome was evaluated with American Knee Society Score (AKSS) and Oxford Knee Score (OKS). Data on knee-loadings were acquired from the literature. Contact-loss was deteced in all patients during both exercises, and the trend of contact-loss correlated with the knee-loadings. Median contact-loss was 0.8 mm (95%PI: 0.3; 1.5) for bicycle motion and 0.3 mm (95%PI: 0.24; 0.35) for step-cycle motion, and did not correlate with the PE wear rate of mean 0.06 mm/year. Possible in-congruency was seen in three patients. Clinical outcome scores correlated with contact-loss during step-cycle motion. In conclusion, contact-loss was seen in all patients indicating a clinical tolerance during load. Contact-loss followed the knee-loadings, which could explain why no correlation was seen with PE wear, as an increase in load was acommadated by an increase in contact-area (contact-loss reduction). The size of contact-loss may reflect clinical outcome. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:357-364, 2018.

All-polyethylene versus metal-backed tibial component in total knee arthroplasty

PURPOSE

The aim of this systematic review was to evaluate the clinical outcomes, rate of revisions and complications of all-polyethylene tibial and metal-backed tibial components in patients treated with knee arthroplasty for primary or secondary osteoarthritis.

METHODS

A systematic review of the literature according to the PRISMA guidelines was performed. A comprehensive search of PubMed, Medline, CINAHL, Cochrane, Embase, and Google Scholar databases using various combinations of the keywords such as "knee", "arthroplasty", "metal-backed", and "all-polyethylene", since inception of databases to 2016, was performed.

RESULTS

Thirty-two articles, describing patients with all-polyethylene tibial or metal-backed tibial components in the setting of osteoarthritis, were included. A total of 68,202 knees in 58,942 patients were included, with an average age at surgery of 69.3 years, ranging from a mean age of 57.9-82 years. The mean KSS was 82.4 and 81.3 (n.s.), the mean KSS(F) was 73.6 and 74.9 (p = 0.04), the mean ROM was 104.5 and 104.6 (n.s.), and the mean HSS was 87 and 86, each, respectively, for the metal-backed tibial components group and all-polyethylene tibial components group. The overall rate of revisions was 1.90 %. The rate of revision in the metal-backed tibial components group was 1.85 %, whilst the rate of revision in the all-polyethylene tibial components group was 2.02 % (p < 0.00001).

CONCLUSION

Metal-backed tibial and all-polyethylene tibial components did not show any significant difference in most of the included outcome scores, but statistical differences were found in terms of complications and revision rate. These items have a negative impact on the cost-effectiveness of all-polyethylene tibial components. Even if all-polyethylene tibial components show similar clinical outcome score, equivalent range of knee motion, and long-term survival compared to metal-backed tibial components, complications and revision rate seem to lead the surgeon to prefer the last ones. The clinical relevance of this study is that metal-backed tibial components should be preferred in TKA surgery because complications are higher using all-polyethylene tibial components. On the other hand, the quality of evidence, according to GRADE system, is low underling the necessity of more randomised study to clarify these items.

LEVEL OF EVIDENCE

III.