Unicompartmental Knee Arthroplasty: Survivorship and Risk Factors for Revision: A Population-Based Cohort Study with Minimum 10-Year Follow-up

Comparative long-term outcomes of unicompartmental and total knee arthroplasty in knee osteoarthritis patients: a systematic review and meta-analysis

Background

Long-term outcomes for knee osteoarthritis patients undergoing unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) remain inconclusive.

Objectives

This study aims to evaluate the long-term outcomes over five years, including Knee Society Pain Scores (KSPS), Knee Society Scores (KSS), Knee Society Function Scores (KSFS), range of motion (ROM), and survival rates-of UKA vs. TKA in knee osteoarthritis patients.

Design

Systematic review using data from randomized controlled and cohort trials, and world databases.

Data sources

Researchers searched Medline, Embase, Cochrane Controlled Register of Trials, and ClinicalTrials.gov from January 1990 to March 2024.

Eligibility criteria for selecting studies

The researchers selected studies based on adult participants with knee osteoarthritis. Eligible studies compare UKA and TKA reports on clinical or surgical outcomes, including KSPS, KSS, KSFS, ROM and survival rates, over 5 years. The researchers excluded the studies fewer than five years, or if English text was unavailable.

Results

Researchers categorized twenty-nine eligible studies into three groups: five randomized controlled trials, 11 registries and database studies, and 13 cohort studies. The analysis revealed that neither TKA nor UKA definitively outperformed the other in terms of pain (SMD (95% CI): -0.06 [-0.41, 0.28], I 2 = 90%) and KSS scores (SMD (95% CI): -0.07 [-0.23, 0.008], I 2 = 81%) over a period of five years. However, KSFS (SMD (95% CI): -0.30 [-0.43, -0.17], I 2 = 74%) and ROM (SMD (95% CI): -0.78 [-1.11, -0.46], I 2 = 92%) tended to favor UKA, and survival rate favor TKA at 5 or over 5-year follow-up periods.

Conclusions

UKA shows a trend towards better outcomes in KSFS and ROM, alongside a more favorable survival rate in TKA at the five-year and beyond follow-up periods.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=517835, PROSPERO (CRD42024517835).

Femoral Coronal Malalignment is Associated With Failure in Mobile-Bearing Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Femur-first (FF) technique for mobile-bearing medial unicompartmental knee arthroplasty (UKA) has been described as an alternative to tibia-first (TF) technique. The aim of this study was to compare the radiographic results in UKAs using FF or TF techniques and their influence on failure rates.

METHODS

We retrospectively reviewed 288 UKAs with a minimum 2-year follow-up. There were 147 knees in the TF and 141 knees in the FF cohorts. Alignment parameters and overhang were assessed as outliers and far outliers. The mean follow-up was 6 years (range, 2 to 16), the mean age was 63 years (range, 27 to 92), and 45% of patients were women. Univariate and multivariate statistical analyses were carried out with Cox regression models.

RESULTS

There were 13 and 6 revisions in the TF and FF cohorts, respectively. The FF had lower rates of femoral coronal alignment (FCA) or femoral sagittal alignment outliers compared to the TF (5.7% versus 19%, P = .011). Tibial coronal alignment and tibial sagittal alignment did not significantly differ between the techniques (22.7% in FF versus 29.9% in TF, P = .119). Overhang outliers did not differ significantly between the groups. Younger age was associated with a higher revision rate (P = .006), while FF versus TF, sex, body mass index, and postoperative mechanical axis did not show statistically significant associations. In multivariate analysis, FCA outliers and younger age were significantly associated with revision.

CONCLUSIONS

The FF technique in mobile-bearing UKA resulted in fewer FCA outliers compared to TF. Despite improved knee alignment with the FF technique, FCA outliers and younger age were associated with a higher revision rate, independent of technique.

Effect of lower limb alignment on outcome after lateral unicompartmental knee arthroplasty: a retrospective study

PURPOSE

The objective of this study was to investigate the correlation between lower limb alignment and patient outcomes after lateral unicompartmental knee arthroplasty (LUKA).

METHODS

In this retrospective study, the information of 51 patients who underwent lateral UKA was collected after an average of 27months of follow-up (13 to 60 months). Evaluation indicators include the AKS and WOMAC score. The Kellgren-Lawrence grade is used to evaluate the severity of osteoarthritis, while the hip-knee-ankle (HKA) angle is utilized to measure the valgus angle of lower limb alignment.

RESULT

Patients with postoperative valgus (≥ 3°) alignment had the best outcomes, while those with varus (≤-3°) alignment had the worst outcomes (p < 0.001). Furthermore, it was noted that patients with preoperative mild valgus (≤ 4°) alignment had worse postoperative outcomes than those with severe valgus (≥ 7°) alignment (p < 0.05). The study also revealed a positive correlation between postoperative valgus and WOMAC scores (p < 0.001), whereas a negative correlation was observed between the change in valgus angle and WOMAC scores (p = 0.005).

CONCLUSION

During follow-ups, we found that lower limb alignment seems to be an independent predictor of postoperative outcomes. It is recommended that more than 3° of valgus alignment should be maintained after LUKA. Surgeons performing lateral UKA should be cautious of overcorrecting alignment, particularly in patients with preoperative mild valgus alignment.

Unicompartmental knee arthroplasty revised to total knee arthroplasty versus primary total knee arthroplasty: A meta-analysis of matched studies

BACKGROUND

Unicompartmental knee arthroplasty (UKA) offers a less invasive alternative to total knee arthroplasty (TKA), but is accompanied by a high revision risk. The aim of our study was to perform a meta-analysis comparing outcomes of UKA revised to TKA versus primary TKA, to assess if UKA is an effective treatment option, despite its potential need for revision.

METHODS

Studies comparing matched cohorts of patients with UKA revised to TKA versus primary TKA were identified via the PubMed, Ovid EMBASE, and Scopus databases. The following outcome measures were compared between treatment modalities: postoperative reoperation or revision, total complications, range of motion, patient-reported outcome measures, and length of stay.

RESULTS

Ten studies were included with 1,070 patients: 410 UKA to TKA and 660 primary TKA. At an average follow-up of 5.6 years in the UKA to TKA cohort and 5.7 years in the primary TKA cohort, there were no significant difference in risk of revision (p = 0.81), total complications (p = 0.54), range of motion (p = 0.09), or length of stay (p = 0.31). Both objective and functional Knee Society Score were significantly higher in patients with primary TKA (p < 0.01). However, there was no difference in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) or pain scores (p = 0.13 and p = 0.21, respectively).

CONCLUSION

UKA revised to TKA produced comparable clinical and patient-reported outcomes to a primary TKA. UKA may be an effective treatment option in unicompartmental arthritis that would allow for improved functionality and satisfaction without the concern of outcomes deteriorating in patients where a revision becomes necessary.

Malposition is main cause of failure of Oxford mobile-bearing medial unicompartmental knee arthroplasty

Aims

Unicompartmental knee arthroplasty (UKA) is the preferred treatment for anterior medial knee osteoarthritis (OA) owing to the rapid postoperative recovery. However, the risk factors for UKA failure remain controversial.

Methods

The clinical data of Oxford mobile-bearing UKAs performed between 2011 and 2017 with a minimum follow-up of five years were retrospectively analyzed. Demographic, surgical, and follow-up data were collected. The Cox proportional hazards model was used to identify the risk factors that contribute to UKA failure. Kaplan-Meier survival was used to compare the effect of the prosthesis position on UKA survival.

Results

A total of 407 patients who underwent UKA were included in the study. The mean age of patients was 61.8 years, and the mean follow-up period of the patients was 91.7 months. The mean Knee Society Score (KSS) preoperatively and at the last follow-up were 64.2 and 89.7, respectively (p = 0.001). Overall, 28 patients (6.9%) with UKA underwent revision due to prosthesis loosening (16 patients), dislocation (eight patients), and persistent pain (four patients). Cox proportional hazards model analysis identified malposition of the prostheses as a high-risk factor for UKA failure (p = 0.007). Kaplan-Meier analysis revealed that the five-year survival rate of the group with malposition was 85.1%, which was significantly lower than that of the group with normal position (96.2%; p < 0.001).

Conclusion

UKA constitutes an effective method for treating anteromedial knee OA, with an excellent five-year survival rate. Aseptic loosening caused by prosthesis malposition was identified as the main cause of UKA failure. Surgeons should pay close attention to prevent the potential occurrence of this problem.

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°.

Clinical outcomes, complications, and survivorship for unicompartmental knee arthroplasty versus total knee arthroplasty in patients aged 80 years and older with isolated medial knee osteoarthritis: a matched cohort analysis

PURPOSE

The primary goal of this study is to compare clinical outcomes, complication rate, and survivorship in octogenarians who underwent total knee arthroplasty (TKA) or unicompartmental knee arthroplasty (UKA) by performing a matched cohort analysis.

METHODS

We analyzed 75 medial UKAs performed by a single experienced surgeon. The included cases were matched with 75 TKAs performed during the same study period. Potential TKA matches used identical exclusion criteria. UKAs were age-, gender-, and body mass index (BMI)-matched at the rate of 1 UKA to 1 TKA from our departmental database. Clinical evaluation included the visual analog scale for pain, range of motion (ROM-flexion and extension), Knee Society Score (KSS), and Oxford Knee Score (OKS). Each patient was clinically evaluated on the day before the surgery (T0) and at two follow-ups at least 12 months (T1) and 24 months (T2) after the surgery. For the survivorship, revision was defined as failure of the implant (periprosthetic joint infection, periprosthetic fracture, or aseptic loosening), and survival was based on implant revision or patient death. Undesirable clinical developments that were not present at baseline or that increased in severity after treatment were classified as adverse events.

RESULTS

The mean age at the time of the surgery was 82.1 ± 1.9 years for UKA and 81.5 ± 1.8 years for TKA (p = 0.06). The two groups differed in regard to surgical time (UKA 44.9 ± 7.2 min; TKA 54.4 ± 11.3 min; p < 0.001); furthermore, the UKA group showed better function (ROM; flexion and extension) than the TKA group at each follow-up time point (p < 0.05). Both groups reported a significant improvement in all clinical scores (KSS and OKS) when compared with their preoperative status (p < 0.05), while no differences were found between the groups at each follow-up (p > 0.05). The UKA group reported 7 (9.3%) failures, while TKA reported 6 failures. There were no survival differences between the groups (T1: p = 0.2; T2: p = 0.5). Overall complication rate was 6% in the UKA group versus 9.75% in TKA (p = 0.2).

CONCLUSION

The UKA and TKA patients had similar clinical outcomes, post-operative range of motion, and survivorship in octogenarians with medial knee osteoarthritis, with comparable complication rate. Both the surgical procedures may be considered in this patient population, but further long-term follow-up is needed.

LEVEL OF EVIDENCE

Level III.

Significant correlations between postoperative outcomes and various limb and component alignment strategies in medial unicompartmental knee arthroplasty: a systematic review

PURPOSE

To investigate the correlation between postoperative limb/component alignments and clinical/functional outcomes following medial unicondylar knee arthroplasty (mUKA).

METHODS

Inclusion criteria included peer-reviewed English- or German-language publications assessing postoperative limb or implant alignment and clinical outcomes of mUKA. Methodological Index for Non-Randomized Studies (MINORS) was used to assess article quality.

RESULTS

A total of 2767 knees from 2604 patients were evaluated. Significant correlations were observed between postoperative limb/component alignments and clinical/functional outcomes after mUKA. Inferior outcomes were associated with lower placement and excessive valgus alignment of the tibia component (> 3°). A recommended external rotation of 4°-5° was identified for the tibia component, with specific cut-off values for the femoral and tibia components.

CONCLUSIONS

Optimal outcomes in mUKA were associated with a varus coronal limb alignment. The tibia implant component performed well within a specific alignment range. An exact external rotation value was recommended for the tibia component, while internal rotation correlated negatively with the femoral component.

LEVEL OF EVIDENCE

IV (level IV retrospective case series were included).

Does high activity after total and unicompartmental knee arthroplasty increase the risk for aseptic revision?

INTRODUCTION

It has been suggested that high activity might negatively impact implant survival following total and unicompartmental knee arthroplasty (TKA/UKA) and many surgeons advise their patients to only participate in moderate level sport activities. To date, it remains unclear whether such restraints are necessary to assure longevity of the implants.

MATERIALS AND METHODS

We conducted a retrospective study on 1906 knees (1745 TKA, 161 UKA) in 1636 patients aged 45-75 years who underwent primary arthroplasty for primary osteoarthritis. Lower extremity activity scale (LEAS) at a two year follow-up was assessed to define the activity level. Cases were grouped in low (LEAS ≤ 6), moderate (LEAS 7-13) and high activity (LEAS ≥ 14). Cohorts were compared with Kruskal-Wallis- or Pearson-Chi2-Test. Univariate logistic regression was conducted to test for association between activity level at two years and later revisions. Odds ratio was reported and converted to predicted probability. A Kaplan-Meier curve was plotted to predict implant survival.

RESULTS

The predicted implant survival for UKA was 100.0% at two years and 98.1% at five years. The predicted implant survival for TKA was 99.8% at two years, 98.1% at five years. The difference was not significant (p = 0.410). 2.5% of the UKA underwent revision, one knee in the low and three knees in the moderate activity group, differences between the moderate and high activity group were not significant (p = 0.292). The revision rate in the high activity TKA group was lower than in the low and moderate activity groups (p = 0.008). A higher LEAS two years after surgery was associated with a lower risk for future revision (p = 0.001). A one-point increase in LEAS two years after surgery lowered the odds for undergoing revision surgery by 19%.

CONCLUSIONS

The study suggests that participating in sports activity following both UKA and TKA is safe and not a risk factor for revision surgery at a mid-term follow-up. Patients should not be prevented from an active lifestyle following knee replacement.

How to Perform Better on Oxford UKA? A Technical Note from over 500 Surgical Experiences

Oxford unicompartmental knee arthroplasty (UKA) has been particularly prevalent because the concept of knee preservation is deeply rooted in people's minds. Mobile bearing UKA is a surgical type of UKA with considerable advantages. This note describes some surgical techniques, including patient position, surgical field exposure, selection of the size of the prosthesis, sagittal tibial osteotomy, placement of the femoral prosthesis and gap balance, to assist surgeons with less experience in performing these operations successfully. The techniques described in this note have been used in over 500 Oxford UKA cases, and nearly 95% patients achieved good prosthesis position and satisfactory postoperative outcome. We hope that the empirical summaries from numerous cases will help surgeons to learn Oxford UKA quickly and effectively, driving the spread of the technique and benefiting more patients.

Favourable mid-term outcomes following unicompartmental knee arthroplasty with wider patient selection: A single-centre experience

OBJECTIVE

The purpose of this study was to determine surgical outcomes of robotic-assisted UKAs utilizing a wider set of indications than traditionally utilized. Additionally, we seek to determine alternate predictive factors as potential surgical indications and contraindications.

METHODS

A prospectively maintained institutional joint registry was queried at a single academic centre for all patients that underwent robotic-assisted UKA between January 2010-December 2016. Surgical indication included isolated medial or lateral compartment degenerative disease with a stable knee based on physical exam. In 2013, haemoglobin A1C levels over 7.5% were considered contraindications, which was lowered to 7.0% in 2015. Preoperative alignment, age, activity level and degree of pain were not contraindications for surgery. Preoperative demographics, Oxford scores, radiographic (joint space), comorbidities and operative data were collected and reviewed to determine factors related to conversion to TKA and survivorship of the primary implant.

RESULTS

In total, 1878 cases were performed; however, excluding multi-joint knees, there were a total of 1186 knees in 1014 patients with a minimum 4-year follow-up. The mean age was 63.4 ​± ​10.7 years and mean follow-up was 76.4 ​± ​17.4 months. Mean BMI was 32.3 ​± ​6.5 ​kg/m2. (52.9% females, 47.1% males). There were 901 patients undergoing medial UKA, 122 patients undergoing lateral UKA and 69 patients undergoing patellofemoral UKA. In total, 85 (7.2%) knees underwent conversion to TKA. Preoperative factors such as the degree of preoperative valgus deformity (p ​= ​0.01), greater operative joint space (p ​= ​0.04), previous surgery (p ​= ​0.01), inlay implant (p ​= ​0.04) and pain syndrome (p ​= ​0.01) were associated with increased risk of revision surgery. Factors associated with decreased implant survivorship included patients with history of previous surgery (p ​< ​0.01), history of pain syndrome (p ​< ​0.01) and greater preoperative joint space (>2 ​mm) (p ​< ​0.01). There was no association of BMI to conversion to TKA.

CONCLUSION

Robotic-assisted UKA with wider patient selection demonstrated favourable outcomes at 4 years with survivorship greater than 92%. The present series agree with emerging indications that do not exclude patients based on age, BMI, or degree of deformity. However, increased operative joint space, inlay design, history of surgery and coexistence of pain syndrome are factors that increase risk of conversion to TKA.

LEVEL OF EVIDENCE

Level III.

Effect of tibial component overhang on survivorship in medial mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

Some studies have shown that the position of the tibial component in Oxford unicompartmental knee arthroplasty with a mobile bearing will affect the clinical outcome of patients. Hence, our study aimed to investigate the relationship between the overhang distance of the tibial component and the survival of the implant.

METHODS

A retrospective analysis of patients who underwent unicompartmental knee arthroplasty at the same institution from 2014 to 2018 was presented. The study was divided into three groups: minor underhang group (underhang between -3 and 0 mm); minor overhang group (overhang 0-3 mm); and major overhang group (overhang ≥ 3 mm). Demographic and clinical profile characteristics of each group were compared, and survival curves of each group were also compared using Kaplan-Meier and modeled using multivariate Cox regression.

RESULTS

A total of 351 knees were included in this study with a minimum follow up of three years and a mean follow up of 4.8 ± 1.5 years. The revision rates in each group were 3.6% (minor underhang group), 2.7% (minor overhang group), and 20.9% (major overhang group) (P < 0.001). From the three groups' cumulative survival rates, the major overhang group was significantly lower than the other two groups (log rank P < 0.001). Multivariate Cox regression showed an association between the major overhang group and implant survival rate (hazard ratio = 7.515, 95% confidence interval = 2.500-22.593, P < 0.001) CONCLUSION: The risk of revision will increase if the tibial component overhangs more than 3 mm medially. Moreover, the reasons for revision are generally bearing dislocation and aseptic loosening.

Minimum 10-Year Survivorship of Mobile-Bearing Unicompartmental Arthroplasty: Single Surgeon, North American Non-Designer Consecutive Series

BACKGROUND

Mobile-bearing unicompartmental knee arthroplasty (UKA) provides a durable option for the surgical treatment of monocompartmental knee arthritis. Despite its availability in the United States since 2004, there is only 1 published North American series reporting on the minimum 10-year results of mobile-bearing UKA. The purpose of this study is to determine the survivorship, reasons for failure, and patient-reported outcomes of the Oxford mobile-bearing UKA at minimum 10-year follow-up.

METHODS

One hundred fifty-seven knees were eligible for inclusion in this study based on the date of their index surgery allowing for a minimum 10-year follow-up. The mean follow-up from implantation was 11.4 years (range 10.0-13.8). Failures were reviewed for potential etiologic factors. Survivorship free of reoperation for any reason and free of revision was determined using Kaplan-Meier curves. Functional outcomes were assessed using the Knee Society Knee and Function scores.

RESULTS

There were 17 revisions (10.6%). Six were secondary to progression of lateral compartment arthritis, 5 for persistent pain, 3 for femoral component aseptic loosening, 2 polyethylene dislocations, and 1 deep infection. The mean time to revision was 4 years (range 0.1-11). The survivorship free from revision at minimum 10-year follow-up was 85%. At final follow-up, the mean Knee Society Knee Score was 93 (range 66-100) and the mean functional score was 80 (range 30-100).

CONCLUSION

This single surgeon series demonstrated a survivorship of 85% at minimum 10-year follow-up. These results are comparable to published data from North America, but survivorship is lower than European series.