The cemented twin-peg Oxford partial knee replacement survivorship: a cohort study

Comparison of cementless twin-peg, cemented twin-peg and cemented single-peg femoral component migration after medial unicompartmental knee replacement: a 5-year randomized RSA study

BACKGROUND

The component design and fixation method of joint arthroplasty may affect component migration and survival. The aim of this study was to compare fixation of cementless twin-peg (CLTP), cemented twin-peg (CTP) and cemented single-peg (CSP) femoral components of medial unicompartmental knee replacement (UKR).

METHODS

Eighty patients (mean age = 63 years, 48 males) with medial knee osteoarthritis were randomized in three ways to CLTP (n = 25), CTP (n = 26) or CSP (n = 29) femoral UKR components. The patients were followed 5 years postoperatively with RSA, bone mineral density (BMD), PROMs and radiological evaluation of radiolucent lines (RLL), femoral component flexion angle and complications.

RESULTS

At the 5-year follow-up, femoral component total translation was comparable between the three groups (p = 0.60). Femoral component internal rotation was 0.50° (95% CI 0.3; 0.69) for the CLTP group, 0.58° (95% CI 0.38; 0.77) for the CTP group and 0.25° (95% CI 0.07; 0.43) for the CSP group (p = 0.01). BMD decreased peri-prosthetically (range - 11.5%; - 14.0%) until 6-month follow-up and increased toward the 5-year follow-up (range - 3.6%; - 5.8%). BMD change did not correlate with component migration. Lower flexion angle was correlated with higher 5-year subsidence, total translation, varus rotation and maximum total point motion (p = 0.01). Two patients (1 CLTP, 1 CTP) had RLL in the posterior zone. There were two revisions.

CONCLUSION

At 5-year follow-up, fixation of UKA femoral components with twin-peg was not superior to the single-peg design. Cementless and cemented twin-peg femoral components had similar fixation. A lower flexion angle was correlated with higher component migration.

Did a New Design of the Oxford Unicompartmental Knee Prosthesis Result in Improved Survival? A Study From the Norwegian Arthroplasty Register 2012-2021

BACKGROUND

Unicompartmental knee arthroplasty (UKA) has generally shown higher revision rates than TKA, and this is particularly true for the femoral component. A twin-peg femoral component (Oxford Partial) has replaced the single-peg version (Oxford Phase III) of the widely used Oxford medial UKA, with the aim of improving femoral component fixation. The introduction of the Oxford Partial Knee also included a fully uncemented option. However, there has been relatively little evidence regarding the effect of these changes on implant survival and revision diagnoses from groups not associated with the implant design.

QUESTIONS/PURPOSES

Using data from the Norwegian Arthroplasty Register, we asked: (1) Has the 5-year implant survival (free from revision for any cause) improved with the medial Oxford unicompartmental knee after the introduction of new designs? (2) Did the causes of revision change between the old and new designs? (3) Is there a difference in risk for specific revision causes between the uncemented and cemented versions of the new design?

METHODS

We performed a registry-based observational study using data from the Norwegian Arthroplasty Register, a nationwide, mandatory and governmental registry with a high reporting rate. Between 2012 and 2021, 7549 Oxford UKAs were performed, and 105 were excluded due to combinations of the three designs, lateral compartment replacement, or hybrid fixation, leaving 908 cemented Oxford Phase III single-peg (used from 2012 to 2017), 4715 cemented Oxford Partial twin-peg (used from 2012 to 2021), and 1821 uncemented Oxford Partial twin-peg (used from 2014 to 2021), UKAs available for the analysis. The Kaplan-Meier method and Cox regression multivariate analysis were used to find the 5-year implant survival and the risk of revision (hazard ratio), when adjusting for age, gender, diagnosis, American Society of Anesthesiologists grade, and time period. The risk of revision for any cause and the risk of revision for specific causes were compared, first for the older with the two new designs, and second for the cemented with the uncemented version of the new design. Revision was defined as any operation exchanging or removing implant parts.

RESULTS

The 5-year Kaplan-Meier overall implant survival (free from revision for any cause) for the medial Oxford Partial unicompartmental knee did not improve over the study period. The 5-year Kaplan-Meier survival was different (p = 0.03) between the groups: it was 92% (95% confidence interval [CI] 90% to 94%) for the cemented Oxford III, 94% (95% CI 93% to 95%) for the cemented Oxford Partial, and 94% (95% CI 92% to 95%) for the uncemented Oxford Partial. However, the overall risk of revision during the first 5 years was not different between the groups (Cox regression HR 0.8 [95% CI 0.6 to 1.0]; p = 0.09 and 1.0 [95% CI 0.7 to 1.4]; p = 0.89 for the cemented Oxford Partial and the uncemented Oxford Partial, respectively, compared with cemented Oxford III [HR 1]). The uncemented Oxford Partial had a higher risk of revision for infection (HR 3.6 [95% CI 1.2 to 10.5]; p = 0.02) compared with the cemented Oxford III. The uncemented Oxford Partial had a lower risk of revision for pain (HR 0.5 [95% CI 0.2 to 1.0]; p = 0.045) and instability (HR 0.3 [95% CI 0.1 to 0.9]; p = 0.03) compared with the cemented Oxford III. The cemented Oxford Partial had a lower risk of revision for aseptic femoral loosening (HR 0.3 [95% CI 0.1 to 1.0]; p = 0.04) compared with the cemented Oxford III. When comparing the uncemented and cemented versions of the new design, the uncemented Oxford Partial had a higher risk of revision for periprosthetic fracture (HR 15 [95% CI 4 to 54]; p = 0.001) and infection within the first year (HR 3.0 [95% CI 1.5 to 5.7]; p = 0.001) than the cemented Oxford Partial.

CONCLUSION

Considering that we found no difference in overall risk of revision during the first 5 years but we found a higher risk of revision for infection, periprosthetic fracture, and higher per implant cost, we currently would recommend against the use of uncemented Oxford Partial over the cemented Oxford Partial or the cemented Oxford III.

LEVEL OF EVIDENCE

Level III, therapeutic study.

Impact of joint line orientation on clinical outcomes in bilateral Oxford mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

Joint line orientation angle (JLOA) is the angle between the knee joint line and the floor. It has been reported to be related to postoperative outcome after TKA. Regarding unicompartmental knee arthroplasty (UKA), although it can be horizontal after UKA because it is a resurfacing surgery, there are few reports about the JLOA after UKA and its impact on clinical outcomes.

PURPOSE

The purpose of this study was to reveal the relationship between JLOA and clinical outcome after UKA.

METHODS

This study included 106 knees in 53 consecutive patients with osteoarthritis who underwent simultaneous bilateral mobile-bearing UKA. Their pre- and postoperative JLOAs were measured by full-leg-length standing coronal radiographs. We also evaluated the tibial component height (TCH) as the factor which we assumed could influence JLOA. We analyzed the patients' JLOAs, TCHs and clinical outcomes.

RESULTS

Pre- and postoperative JLOA were 0.4 ± 2.4° and 2.7 ± 2.6°, respectively. The JLOA significantly tilted medially (P < 0.0001). The JLOA significantly negatively correlated with the improvement of the clinical outcomes (Oxford Knee Score (OKS): r = 0.40, P < 0.0001, Knee Society Knee Score (KSKS): r = 0.25, P < 0.01, Knee Society Function Score (KSFS): r = 0.22, P = 0.02). The TCH showed a positive correlation with postoperative JLOA and with the postoperative JLOA change (r = 0.45, P < 0.001; r = 0.25, P < 0.01, respectively).

CONCLUSION

The JLOA significantly tilted medially after UKA. An excessive medial tilt of the JLOA was associated with poorer postoperative outcomes of UKA. It is therefore recommended to keep the JLOA horizontal and to avoid a lower tibial cut.

Satisfaction and Functional Outcomes in Unicompartmental Compared with Total Knee Arthroplasty: Radiographically Matched Cohort Analysis

Unicompartmental and total knee arthroplasty (UKA and TKA) have demonstrated excellent mid- and long-term outcomes and have been compared in clinical series for decades; however, to our knowledge, no study has sufficiently matched UKA and TKA cohorts on preoperative osteoarthritis severity. The purpose of this study was to evaluate patient-reported outcomes of radiographically and demographically matched UKA and TKA cohorts.

A matched comparison of revision rates of cemented Oxford Unicompartmental Knee Replacements with Single and Twin Peg femoral components, based on data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man

Background and purpose - Registries report high revision rates after unicompartmental knee replacement (UKR) due, in part, to aseptic loosing. In an attempt to improve Oxford UKR femoral component fixation a new design was introduced with a Twin rather than a Single peg. We used the National Joint Registry (NJR) to compare the 5-year outcomes of the Single and Twin Peg cemented Oxford UKRs.Patients and methods - We performed a retrospective observational study using NJR data on propensity score matched Single and Twin Peg UKRs (matched for patient, implant and surgical factors). Data on 2,834 Single Peg and 2,834 Twin Peg were analyzed. Cumulative implant survival was calculated using the Kaplan-Meier method and comparisons between groups performed using Cox regression models.Results - In the matched cohort, the mean follow up for both Single and Twin Peg UKRs was 3.3 (SD 2) and 3.4 years (SD 2) respectively. The 5-year cumulative implant survival rates for Single Peg and Twin Peg were 94.8% (95% CI 93.6-95.8) and 96.2% (CI 95.1-97.1) respectively. Implant revision rates were statistically significantly lower in the Twin Peg (hazard ratio [HR)] = 0.74; p = 0.04). The revision rate for femoral component aseptic loosening decreased significantly (p = 0.03) from 0.4% (n = 11) with the Single Peg to 0.1% (n = 3) with the Twin Peg. The revision rate for pain decreased significantly (p = 0.01) from 0.8% (n = 23) with the Single Peg to 0.3% (n = 9) with the Twin Peg. No other reasons for revision had significant differences in revision rates.Interpretation - The revision rate for the cemented Twin Peg Oxford UKR was 26% less than the Single Peg Oxford UKR. This was mainly because the revision rates for femoral loosening and pain more than halved. This suggests that the Twin Peg component should be used in preference to the Single Peg design.

Isolated medial patellofemoral ligament reconstruction significantly improved quality of life in patients with recurrent patella dislocation

PURPOSE

The purpose of this study was to measure the improvement in quality of life (QoL) following isolated anatomical double-bundle medial patellofemoral ligament reconstruction.

METHODS

This is a single-centre, prospective study of 56 consecutive patients (57 knees) who underwent isolated MPFL reconstruction between 2014 and 2017. Functional outcome and QoL were assessed with the Kujala score and the EQ-5D-3L questionnaire, respectively. Objective outcomes were obtained through clinical examination at the latest follow-up assessing redislocation rate, patella apprehension test, patellar tilt, pain and range of motion.

RESULTS

The median Kujala score increased from 60 (range 31-96) to 92 (range 34-100) at latest follow-up (p < 0.001). The median EQ-5D index also increased, from 0.69 (range 0.10-1) at baseline to 1 (range 0.16-1) at latest follow-up (p < 0.001), as well as the median EQ-5D VAS from 75 (range 20-95) to 92 (range 40-100) (p < 0.001). Four dimensions of the EQ-5D were significantly improved except for the anxiety/depression scores. Female patients reported lower scores at baseline and at latest follow-up, for all three outcomes (Kujala, EQ-5D index, EQ-5D VAS), however there was no evidence that gender negatively impacted on the benefit of surgery. The re-dislocation rate was 0%. Apprehension and patellar tilt test were negative in all patients and no flexion deficit was identified at latest follow-up. Two patients had tenderness along the reconstruction requiring femoral screw removal in one of them.

CONCLUSIONS

Isolated anatomical double-bundle aperture MPFL reconstruction, offered significantly improved short-term QoL along with excellent functional outcome. Female patients scored lower, but this did not affect the overall outcome. Including QoL tools in the assessment of ligament reconstruction operations, such as the MPFL, can provide more accurate understanding of the overall patient benefit.

LEVEL OF EVIDENCE

II.

Improving Estimates of Annual Survival Rates for Medial Unicompartmental Knee Arthroplasty, a Meta-Analysis

BACKGROUND

Medial unicompartmental knee arthroplasty (mUKA) is an increasingly popular treatment option for medial compartment knee osteoarthritis. Published mUKA survival rates have varied. The purpose of this meta-analysis was to provide pooled estimates of mUKA survival 5 and 10 years postoperatively.

METHODS

We included studies in English within the last 15 years with a clear description of mUKA failure. Random-effects models were used to pool complementary log-log transformed implant survival estimates at 5 and 10 years postoperatively. Between-study variance was estimated using the restricted maximum likelihood method. Between-study heterogeneity was tested using the χ2 test and quantified using the I² statistic. I² values <25%, 25%-75%, and >75% were considered low, moderate, and high, respectively. Multivariable meta-regression was used to assess the potential association of mean patient age and study start year with survival estimates at 5 and 10 years. All analyses were performed using the metafor and meta packages implemented in R software version 3.3.4 (R Foundation for Statistical Computing, Vienna, Austria).

RESULTS

Twenty-six studies met inclusion criteria, representing 42,791 knees. Study-level and pooled 5- and 10-year mUKA survival estimates were 95.3% (95% confidence interval, 93.6-96.6) and 91.3% (88.9-93.3), respectively. Between-study heterogeneity was high (>88%) for all years. Mean patient age and study start year explained only 12.3% and 30.7% of between-study heterogeneity at 5 and 10 years, respectively.

CONCLUSION

Five- and 10-year pooled mUKA survival estimates were 95.3% and 91.3%, respectively. These data establish better estimates of mUKA survivorship and can help when counseling patients considering mUKA.

Patient reported outcomes and implant survivorship after Total knee arthroplasty with the persona knee implant system: two year follow up

Background

More personalized implant designs for total knee arthroplasty might optimize the clinical outcome after surgery. One of these personalized implant designs is the Persona knee implant system (Zimmer Biomet, Warsaw, Indiana, USA). The primary objective of this study was to determine patient reported outcomes and implant survivorship of the Persona Knee system used in primary total knee arthroplasty, up to two years after surgery.

Methods

From November 2013 to July 2016 consecutive patients undergoing primary total knee arthroplasty were enrolled in a prospective observational cohort study at three centers. Preoperatively, at 6 weeks, 6 months, 1 and 2 years after surgery, patients completed the Knee Injury and Osteoarthritis Outcome Score (KOOS), the Oxford Knee Score (OKS), the Knee Society Score (KSS, 2011, modified version) and the EQ-5D. Adverse Events were captured, assessed for relationship to device, and recorded in the study database. Furthermore, physical functioning was assessed by the orthopedic surgeon.

Repeated measures analyses were performed on PROM scores. Kaplan Meier was used to calculate survivorship of the Persona Knee Implant System.

Results

A total of 146 total knee arthroplasties were performed. 61% (89/146) of the patients were female and mean age was 64.7 (± 6.9) years. Two years after surgery, one patient had a revision of the polyethylene insert because of a periprosthetic joint infection. Therefore, the Kaplan-Meier survival estimate at 2 years was 0.99 (0.95–1.00 95% CI).

OKS increased from 22.1 (95% CI 20.9–23.3) to 41.8 (95% CI 40.6–43.1) two years after surgery. Furthermore, all other PROMs also increased from before surgery to 2 year postoperatively.

Conclusion

The Persona Knee implant is safe and effective and the clinical results up to two years after surgery are promising. PROMs results are very good; pain, function and quality of life all improved greatly after TKA. Further studies are needed to determine the long term clinical performance of the Persona prosthesis.

Trial registration

Clinicaltrials.gov (NCT02337244). Registered June 1st, 2015. Retrospectively registered.

Two pegs are better than one: rare mode of femoral component failure in unicompartmental arthroplasty requiring revision to total knee arthroplasty

Femoral component fracture is a rare complication in unicompartmental knee arthroplasty, especially in cemented prostheses. We present a 75-year-old man who presented with a fractured single-peg Vanguard component 9 years postoperatively. He was revised to a total knee arthroplasty with an excellent functional outcome at 1 year. The components were additionally examined at an outside biomechanical engineering laboratory. Theories as to the cause of the component fracture include aseptic loosening due to a thin anterior cement mantle and the single-peg Oxford design.

The Oxford Medial Unicompartmental Knee Arthroplasty: The South African Experience

BACKGROUND

The Oxford unicompartmental knee arthroplasty (OUKA) is a successful treatment for endstage, symptomatic anteromedial osteoarthritis. This study reports the results of a cohort of consecutive cemented and cementless medial OUKAs from an independent center and aims to answer the following questions: what is the survival of OUKA in the hands of a nondesigner surgeon? Are there any differences in the survival of cementless and cemented OUKA? Are the failure modes any different with the cementless and cemented OUKA?

METHODS

One thousand one hundred twenty consecutive OUKAs were implanted in a single center for the recommended indications. Patients were prospectively identified and followed up. Survival was calculated with revision as the end point.

RESULTS

There were 522 cemented and 598 cementless implants. The mean follow-up was 8.3 years for cemented implants (range 0.5-17, standard deviation [SD] 2.9) and 2.7 years (range 0.5-7, SD 1.8) for cementless implants. The Oxford knee score improved from a preoperative mean of 22 (SD 8.1) to 40 (SD 7.9) at the last follow-up (P < .001). There were 59 failures requiring revision surgery, with a 5.3% cumulative revision rate. The most common reason for failure was progression of osteoarthritis in the lateral compartment, occurred in 26 cases (2.3%). The cumulative 10-year survival was 91% (95% confidence interval 87.3-95.2).

CONCLUSION

The results of this prospective, consecutive case series from the African continent demonstrated that excellent results are achievable with the OUKA in independent centers if the correct indications and surgical technique are used.

The influence of the twin peg design on femoral Interface temperature and maximum load to failure in cemented Oxford unicompartmental knee arthroplasty

BACKGROUND

The twin peg femoral component was introduced for the cemented Oxford unicondylar knee to increase implant stability. The aim of this experimental study was to investigate the influence of the twin peg design on femoral interface temperature and maximum load to failure in comparison to the single peg design.

METHODS

In this experimental study medial Oxford unicompartmental knee arthroplasty was performed in 12 pairs of fresh-frozen human knees. A cemented femoral single peg component was implanted on the one side (group A) and a cemented twin peg component on the other side (group B). Cement interface temperature was continuously monitored during the procedure. Maximum tensile forces of the femoral components were measured by pull-out tests.

FINDINGS

Maximum femoral interface temperatures did not reach critical values for heat necrosis of the bone in group A (mean 28.4, SD 1.2 °C) or group B (mean 27.6, SD 0.5 °C). The maximum load to failure was significantly higher in the twin peg group (mean 3628.41, SD 650.92 N) compared to the single peg group (mean 2979, SD 781 N) (P = 0.016).

INTERPRETATION

Our experiments showed higher load to failure for the twin peg design compared to the single peg design without raising the risk of heat necrosis at the interfacial bone. The twin peg component offers a save alternative to the single peg component in a cadaveric setting.

The twin peg Oxford knee - Medium term survivorship and surgical principles

BACKGROUND

A multicentre study of single peg Oxford knees reported failure associated with osteoarthritis progression, femoral component loosening, unexplained pain and meniscal bearing dislocation. Suboptimally positioned femoral components and intraoperative MCL damage could explain these problems. We hypothesised that modifying implantation technique to optimise femoral component positioning and MCL preservation, and introducing the twin peg Oxford knee would address these problems and improve longer term survival. Moreover, its better congruency in high flexion could reduce wear. This study aims to investigate this hypothesis by asking 1) Is the 98% survivorship up to nine years found in an earlier study sustained at longer term (up to 13 years)? 2) What are the remaining causes of failure?

METHODS

We described our modified implantation technique. A cohort of all patients treated by the senior author using this modified technique and the Oxford twin peg cemented knee replacement between September 2003 and August 2013 was investigated. A survival analysis was performed and the causes of failure were analysed.

RESULTS

The cohort consisted of 468 patients with 554 medial cemented implants. In all, 16 implants were revised and the 12-year survivorship was 95%. Patients with extended indications had a lower survivorship than those with anteromedial osteoarthritis (10-year survival rate 78% vs 97%, p<0.001). There were no failures due to femoral loosening.

CONCLUSIONS

Using our surgical principles the cemented twin peg Oxford knee can result in good medium to long-term implant survival, comparable to those obtained by the originating centre for the single peg Oxford knee.

Eight Hundred Twenty-Five Medial Mobile-Bearing Unicompartmental Knee Arthroplasties: The First 10-Year US Multi-Center Survival Analysis

BACKGROUND

FDA approval for the Oxford phase III device was approved for use in the United States in 2004. This study seeks to provide the first long-term, large patient sample size, Oxford phase III multi-site survivorship study in the United States, investigating patient reported outcomes of pain and function, while also providing an in-depth analysis of causes for revision, and finally addressing recent advancements that can help aid the unicompartmental knee arthroplasty (UKA) process and further improve partial knee survivorship.

METHODS

Between July 2004 and December 2006, 5 surgeons from around the United States performed medial UKA through the minimally invasive surgical approach, on 825 knees in 695 patients. This was a consecutive series of primary UKAs using the phase III mobile bearing; cemented Oxford Knee (Zimmer Biomet, Warsaw, IN), implanted utilizing phase III instrumentation. UKA survivorship considered all revisions as the end point. Implant survivorship eliminated revisions at which the original Oxford implant was determined to be well fixated and functional intra-operatively.

RESULTS

A total of 93 knees were revised in this study. Mean follow-up was 9.7 years (6-12). Implant survivorship at year 10 was 90% (confidence interval 2.7%). UKA survivorship at year 10 was 85% (confidence interval 3.8%). Average preoperative American Knee Society Score (knee score) was 49 and rose to 90 postoperatively (standard deviations 16 and 18, respectively). Average preoperative American Knee Society Score (function score) was 55 and rose to 77 postoperatively (standard deviations 15 and 28, respectively).

CONCLUSION

This was the first large-scale, 10-year, multi-site follow-up of the Oxford mobile-bearing medial UKA undertaken in the United States, displaying good survivorship and excellent patient outcomes.

Annual revision rates of partial versus total knee arthroplasty: A comparative meta-analysis

BACKGROUND

Utilization of unicompartmental knee arthroplasty (UKA) and patellofemoral arthroplasty (PFA) as alternatives to total knee arthroplasty (TKA) for unicompartmental knee osteoarthritis (OA) has increased. However, no single resource consolidates survivorship data between TKA and partial resurfacing options for each variant of unicompartmental OA. This meta-analysis compared survivorship between TKA and medial UKA (MUKA), lateral UKA (LUKA) and PFA using annual revision rate as a standardized metric.

METHODS

A systematic literature search was performed for studies quantifying TKA, MUKA, LUKA and/or PFA implant survivorship. Studies were classified by evidence level and assessed for bias using the MINORS and PEDro instruments. Annual revision rates were calculated for each arthroplasty procedure as percentages/observed component-year, based on a Poisson-normal model with random effects using the R-statistical software package.

RESULTS

One hundred and twenty-four studies (113 cohort and 11 registry-based studies) met inclusion/exclusion criteria, providing data for 374,934 arthroplasties and 14,991 revisions. The overall evidence level was low, with 96.7% of studies classified as level III-IV. Annual revision rates were lowest for TKA (0.49%, CI 0.41 to 0.58), followed by MUKA (1.07%, CI 0.87 to 1.31), LUKA (1.13%, CI 0.69 to 1.83) and PFA (1.75%, CI 1.19 to 2.57). No difference was detected between revision rates for MUKA and LUKA (p=0.222).

CONCLUSIONS

Revisions of MUKA, LUKA and PFA occur at an annual rate of 2.18, 2.31 and 3.57-fold that of TKA, respectively. These estimates may be used to inform clinical decision-making, guide patient expectations and evaluate the cost-effectiveness of total versus partial knee replacement in the setting of unicompartmental OA.

Early outcomes of twin-peg mobile-bearing unicompartmental knee arthroplasty compared with primary total knee arthroplasty

Aims

Since redesign of the Oxford phase III mobile-bearing unicompartmental knee arthroplasty (UKA) femoral component to a twin-peg design, there has not been a direct comparison to total knee arthroplasty (TKA). Thus, we explored differences between the two cohorts.

Patients and Methods

A total of 168 patients (201 knees) underwent medial UKA with the Oxford Partial Knee Twin-Peg. These patients were compared with a randomly selected group of 177 patients (189 knees) with primary Vanguard TKA. Patient demographics, Knee Society (KS) scores and range of movement (ROM) were compared between the two cohorts. Additionally, revision, re-operation and manipulation under anaesthesia rates were analysed.

Results

The mean follow-up for UKA and TKA groups was 5.4 and 5.5 years, respectively. Six TKA (3.2%) versus three UKAs (1.5%) were revised which was not significant (p = 0.269). Manipulation was more frequent after TKA (16; 8.5%) versus none in the UKA group (p < 0.001). UKA patients had higher post-operative KS function scores versus TKA patients (78 versus 66, p < 0.001) with a trend toward greater improvement, but there was no difference in ROM and KS clinical improvement (p = 0.382 and 0.420, respectively).

Conclusion

We found fewer manipulations, and higher functional outcomes for patients treated with medial mobile-bearing UKA compared with TKA. TKA had twice the revision rate as UKA although this did not reach statistical significance with the numbers available.

Cite this article: Bone Joint J 2016;98-B(10 Suppl B):28–33.

Predictors of Subjective Outcome After Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Unexplainable pain after medial unicompartmental knee arthroplasty (UKA) remains a leading cause for revision surgery. Therefore, the aim of this study is to identify the patient-specific variables that may influence subjective outcomes after medial UKA to optimize results.

METHODS

Retrospectively, we analyzed 104 consecutive medial UKA patients. The evaluated parameters consisted of age, body mass index, gender, preoperative radiographic severity of the various knee compartments, and preoperative and postoperative mechanical axis alignments.

RESULTS

At an average of 2.3-year follow-up, our data demonstrate that body mass index, gender, and preoperative severity among the various knee compartments do not influence Western Ontario and McMaster Universities Arthritis Index (WOMAC) results. Preoperatively, patients aged <65 years had inferior WOMAC stiffness (4.6 vs 2.9, P = .001), pain (9.7 vs 7.6, P = .041), and total (37.2 vs 47.6, P = .028) scores vs patients aged ≥65 years. Postoperatively, only the difference on the WOMAC stiffness subscale remained significant between both age groups, in favor of patients aged ≥65 years (1.0 vs 1.5, P = .035). A postoperative varus mechanical axis alignment of 1°-4° correlated to significantly superior WOMAC pain (P = .03), function (P = .04), and total (P = .04) scores compared to a varus of ≤1° or ≥4°.

CONCLUSION

Our data suggest that greater pain relief can be expected in patients aged <65 years and that a postoperative lower limb alignment of 1°-4° varus should be pursued. Taking these factors into consideration will help to maximize clinical outcomes, fulfill patient expectations after medial UKA, and subsequently minimize revision rates.