Minimally invasive lateral unicompartmental knee replacement: Early results from an independent center using the Oxford fixed lateral prosthesis

Unicompartmental knee replacement: controversies and technical considerations

BACKGROUND

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

METHODS

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

RESULT

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

CONCLUSION

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

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

Background

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

Methods

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

Results

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

Conclusions

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

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

INTRODUCTION

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

LEVEL OF EVIDENCE

Retrospective cohort study, level IV.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE

Retrospective case-control study, Level III.

Complications after lateral unicompartmental knee arthroplasty in a fast-track setting: a prospective cohort study of 170 procedures

BACKGROUND AND PURPOSE

In existing studies on fasttrack unicompartmental knee arthroplasty (UKA), the majority of surgeries are medial. There are substantial differences between lateral and medial UKA, which is why outcomes cannot automatically be compared. To gain information on the feasibility and safety of fast-track protocols in lateral UKAs, we investigated length of stay (LOS) and early complications after lateral UKA, performed using a fast-track protocol in well-established fast-track centers.

PATIENTS AND METHODS

We retrospectively evaluated prospectively collected data on patients undergoing lateral UKA in a fast-track setup from 2010 to 2018 at 7 Danish fast-track centers. Data on patient characteristics, LOS, complications, reoperations, and revisions was analyzed using descriptive statistics. Safety and feasibility were defined as complication and reoperation rates within 90 days comparable to non-fast track lateral UKA or fast-track medial UKA.

RESULTS

We included 170 of patients with a mean age of 66 (SD 12) years. Median LOS was 1 day (interquartile range 1-1), which was unchanged from 2012-2018. 18% were discharged on the day of surgery. Within 90 days, 7 patients experienced medical complications and 5 patients experienced surgical complications. 3 patients underwent reoperation, 2 were soft tissue revisions and the third was removal of an exostosis due to catching of the patella. 1 patient was revised due to a bearing dislocation.

CONCLUSION

Our findings suggest that lateral UKA in a fast-track setting is feasible and safe.

[Treatment of unicompartmental osteoarthritis of the knee]

Osteoarthritis of the knee is one of the most important degenerative joint diseases in the clinical routine. The treatment of knee osteoarthritis is not only based on the stage, symptoms and duration of the joint disease, but also depends on the existing arthrosis pattern. In the case of unicompartmental arthrosis, damage typical for osteoarthritis is limited to just one joint compartment. Both the conservative and the surgical treatment of unicompartmental osteoarthritis of the knee have to respect the individual characteristics of the respective forms of osteoarthritis. In the context of this manuscript, the genesis, the diagnostics and the guideline-based stage-adapted conservative and operative treatment of unicompartmental osteoarthritis of the knee are addressed.

Robotic-Arm-Assisted Lateral Unicompartmental Knee Arthroplasty with a Fixed-Bearing Implant

Background

Approximately 5% to 10% of patients with knee arthritis have isolated lateral compartment arthritis; however, lateral unicompartmental knee arthroplasty (UKA) comprises just 1% of all knee arthroplasties1. This low proportion is partly because of the perceived complexity of lateral UKA and concerns over implant longevity and survivorship compared with total knee arthroplasty (TKA)2,3. With an improved understanding of knee kinematics alongside advances in implant design and tools to aid in appropriate restoration of limb alignment, lateral UKA can be an appealing surgical alternative to TKA for certain patients with lateral knee arthritis4,5. In appropriately selected patients, lateral UKA has been associated with reduced osseous and soft-tissue resection, more natural knee kinematics, less pain, shorter hospitalization, decreased blood loss and infection rates, and excellent survivorship and patient-reported outcomes6-9.

Description

This surgical approach and technique described for lateral UKA utilizes robotic-arm assistance and modern fixed-bearing implants10. The specific steps involve appropriate patient evaluation and selection, extensive radiographic and computed-tomography-based preoperative templating, a lateral parapatellar approach, intraoperative confirmation of component position and alignment, and robotic-arm assistance to perform osseous resections to achieve limb alignment and kinematic targets10. Final implants are cemented in place, and patients typically are discharged home on the day of surgery10.

Alternatives

Nonoperative treatment for end-stage knee arthritis includes weight loss, activity modification, assistive devices, bracing, nonsteroidal anti-inflammatory medications, and various injections11. Alternative surgical treatments include TKA4 and, in certain patients, an offloading periarticular osteotomy12.

Rationale

Lateral UKA is an appealing surgical option for nonobese patients who have disabling knee pain isolated to the lateral compartment, good preoperative range of motion, and a passively correctable valgus limb deformity10,13.

Expected Outcomes

Patients are typically discharged home on the day of surgery, or occasionally on postoperative day 1 if medical comorbidities dictate hospital monitoring overnight10. Patients return to light activities, including walking, immediately postoperatively. By 3 months postoperatively, patients will generally have returned to all desired activities9. The mid-term outcomes of this procedure, as performed by the corresponding author, have been published recently14,15. The 5-year survivorship of 171 lateral UKAs was 97.7%, with 72.8% of patients reporting that they were very satisfied with their procedure and 19.8%, that they were satisfied14. Only 3.8% of patients reported dissatisfaction with their lateral UKA14. The mean Knee Injury and Osteoarthritis Outcome Score (KOOS) and standard deviation were 85.6 ± 14.314. These outcomes did not differ from those observed in 802 medial UKAs, which showed a survivorship of 97.8% and KOOS of 84.3 ± 15.914. These findings are generally in line with previously published studies, which have demonstrated excellent survivorship and patient-reported outcomes with fixed-bearing lateral UKA16-19.

Important Tips

Component position and alignment are critical to achieve target knee kinematics.Target postoperative alignment is 1° to 4° of valgus.A meticulous cementation technique is required for optimal fixation and avoidance of excess residual cement in the posterior knee.

Acronyms and Abbreviations

ACL = anterior cruciate ligamentAP = anteroposteriorBMI = body mass indexCT = computed tomographyCAT = computed axial tomographyIT = iliotibialKOOS JR = Knee Injury and Osteoarthritis Outcome Score for Joint ReplacementMCL = medial collateral ligamentMRI = magnetic resonance imagingOR = operating roomPFJ = patellofemoral jointpoly = polyethyleneROM = range of motionTKA = total knee arthroplastyUKA = unicompartmental knee arthroplasty.

Physical Activity of Young Patients following Minimally Invasive Lateral Unicompartmental Knee Replacement

Unicompartmental knee replacement (UKR) has increased in popularity in recent years, especially in young patients with high demands on their athletic ability. To date, there are no data available on the physical activity of young patients following lateral UKR. The aim of this study was to demonstrate return-to-activity rate and sporting activity of patients aged 60 years or younger following lateral UKR with a fixed-bearing (FB) prosthesis. Thirty-seven patients aged 60 years or younger after lateral FB-UKR were included. Sporting activities were assessed using the University of California Los Angeles activity scale (UCLA) and the Tegner activity score (TAS). Clinical outcome was measured using the Oxford Knee Score (OKS), range of motion (ROM) and visual analogue scale (VAS). The mean follow-up (FU) was 3.1 ± 1.5 years and the mean age at surgery was 52.8 ± 3.1 years. The return-to-activity rate was 87.5% and 49% of patients were highly active postoperatively as defined by an UCLA score of 7 or higher. All clinical parameters increased significantly postoperatively. We demonstrated a high return-to-activity rate with nearly half of the patients achieving high activity levels. Longer FU periods are necessary to evaluate the effect of activity on implant survival.

A standardized technique for lateral unicompartmental knee arthroplasty

OBJECTIVES

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

METHODS

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

RESULTS

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

CONCLUSION

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

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.

Minimally invasive Oxford medial unicompartmental knee replacement in patients 50 years of age or younger

INTRODUCTION

The aim of the present study was to assess clinical outcome and mid-term survivorship of mobile-bearing unicompartmental knee arthroplasty in patients 50 years of age or younger.

METHODS

This study reports the results of 119 patients (130 knees) following mobile-bearing medial UKA. Primary indication was advanced osteoarthritis or avascular necrosis of the femoral condyle. The anterior cruciate ligament (ACL) as well as the collateral ligaments were functionally intact, the varus deformity was manually correctable and there was no evidence of osteoarthritis in the lateral compartment. Survivorship analysis was performed with different endpoints and clinical outcome was measured using the Oxford Knee Score (OKS), American Knee Society Score and Functional Score (AKSS-O, AKSS-F), range of motion (ROM), Tegner activity score, University of California Los Angeles score (UCLA) and visual analogue scale for pain (VAS).

RESULTS

The survival rate was 96.6% at 6.5 years (95% CI 98.7-91.3%; number at risk: 56) and 91.7% (95% CI 96.7-80%; number at risk: 22) at 10 years for the endpoint device related revisions and 91.5% at 6.5 years (95% CI 95.4-84.5%; number at risk: 56) and 86.8% (95% CI 93-76.2%; number at risk: 22) at 10 years for the endpoint revision for any reason. Outcome scores, VAS and ROM showed significant improvements (p < 0.001). The mean OKS increased from 26.7 (standard deviation (sd): 7.2) preoperatively to 40.9 (sd: 7.6) at final follow-up, the mean AKSS-O from 48.3 (sd: 13.3) to 87.8 (sd: 14.4) and the mean ROM from 118° (sd: 16.7) to 125° (sd: 11.4). The radiological analysis revealed progression of degenerative changes in the lateral compartment in 39.6% of patients without affecting the functional outcome.

CONCLUSIONS

Medial mobile-bearing UKA is a viable surgical treatment option in young patients with significant improvements in knee function and pain. Further follow-up is necessary to evaluate the long-term efficacy.

LEVEL OF EVIDENCE

Retrospective cohort study, Level III.

Early results of fixed-bearing unicompartmental knee replacement designed for the lateral compartment

Background

Isolated lateral compartment knee arthritis is less prevalent than medial. While the reported results of medial unicompartmental knee replacement (UKR) have been good and comparable to total knee replacement, the results of lateral UKR have been mixed. We present the short-term results and survivorship of a fixed-bearing UKR designed specifically for the lateral compartment.

Methods

We report the result of 130 primary fixed-bearing lateral Oxford (FLO) UKRs (123 patients) performed between 2015 and 2019 with a minimum follow-up of 1 year. The indications for lateral UKR were: isolated lateral osteoarthritis (n = 122), post-trauma (n = 5) and osteonecrosis (n = 3). The mean age was 69.1 (± 11.6), mean BMI 28.4 (± 4.9), 66.9% female, 60% right-sided, and mean follow-up 3 (range 1–4.8 years, standard deviation ± 1) years. The primary outcome measure was the Oxford knee score (OKS). Survival analysis was performed with “revision for any reason”, “reoperation”, and “implant failure” as the endpoints.

Results

Six patients died from unrelated reasons. None of the implants failed. One required the addition of a medial UKR for medial arthritis. There were no other reoperations. At 4 years, the survival for implant failure was 100% and for both revision and all reoperations was 99.5% (95% CI 96.7–99.9%). At the last review, at a mean of 3 years, the mean Oxford knee score was 41.

Conclusion

The good survivorship and outcome scores suggest that UKR designed for the lateral compartment is an excellent alternative to total knee replacement in selected patients with isolated lateral tibiofemoral arthritis at short-term follow-up.

High usage of medial unicompartmental knee arthroplasty negatively influences total knee arthroplasty revision rate

PURPOSE

Surgeons with higher medial unicompartmental knee arthroplasty (UKA) usage have lower UKA revision rates. However, an increase in UKA usage may cause a decrease of total knee arthroplasty (TKA) usage. The purpose of this study was to investigate the influence of UKA usage on revision rates and patient-reported outcomes (PROMs) of UKA, TKA, and combined UKA + TKA results.

METHODS

Using the New Zealand Registry Database, surgeons were divided into six groups based on their medial UKA usage: < 1%, 1-5%, 5-10%, 10-20%, 20-30% and > 30%. A comparison of UKA, TKA and UKA + TKA revision rates and PROMs using the Oxford Knee Score (OKS) was performed.

RESULTS

A total of 91,895 knee arthroplasties were identified, of which 8,271 were UKA (9.0%). Surgeons with higher UKA usage had lower UKA revision rates, but higher TKA revision rates. The lowest TKA and combined UKA + TKA revision rates were observed for surgeons performing 1-5% UKA, compared to the highest TKA and UKA + TKA revision rates which were seen for surgeons using > 30% UKA (p < 0.001 TKA; p < 0.001 UKA + TKA). No clinically important differences in UKA + TKA OKS scores were seen between UKA usage groups at 6 months, 5 years, or 10 years.

CONCLUSION

Surgeons with higher medial UKA usage have lower UKA revision rates; however, this comes at the cost of a higher combined UKA + TKA revision rate that is proportionate to the UKA usage. There was no difference in TKA + UKA OKS scores between UKA usage groups. A small increase in TKA revision rate was observed for high-volume UKA users (> 30%), when compared to other UKA usage clusters. A significant decrease in UKA revision rate observed in high-volume UKA surgeons offsets the slight increase in TKA revision rate, suggesting that UKA should be performed by specialist UKA surgeons.

LEVEL OF EVIDENCE

III, Retrospective therapeutic study.

High survivorship rate and good clinical outcomes at mid-term follow-up for lateral UKA: a systematic literature review

PURPOSE

The purpose of this paper is to systematically review the available literature to understand the effectiveness, the survivorship, the clinical outcomes and the complications of lateral UKA.

METHODS

A review of the current literature available about lateral UKA was performed in March 2020, according to the PRISMA guidelines. Selection was based on the following inclusion criteria: (1) clinical reports of any level of evidence, (2) written in English language, (3) published from 1996 to 2020, (4) dealing with clinical data on lateral UKA. A total of 47 articles, published between 1996 and 2020, were included in the review. Quality of every article was assessed using the Modified Coleman Methodology Score.

RESULTS

A total of 47 studies were included. Mean mCMS was 45.27 (range 30-62). Mean age at surgery was 64.5 years (range 34.1-88.0 years). In 1741 patients (65.5%) a metal back implant was used and in 421 patients (15.8%) an all poly design was used. Several scores were used to evaluate clinical results (OKS, AKSS, IKS, KOOS, WOMAC, VAS). Range of motion improved with an overall mean value of 120.3° (range: 105.9°-143.3°). The mean follow-up was 60.7 months (range, 7-204 months), mean survivorship (absence of a revision) with a minimum 60 months of follow-up was 88.6% (range 74.5-100) and mean satisfaction of patients was 78.5% (range 41.0-97.9).

CONCLUSIONS

Lateral UKA seems to be an effective solution to manage lateral osteoarthritis (OA), based on preliminary results, with survivorship and satisfaction rate comparable to medial UKA and total knee arthroplasty (TKA). Nonetheless, this review highlights that the quality of studies available in current literature is low.

LEVEL OF EVIDENCE

Systematic review of level IV studies.

Systematic review and meta-analysis of bearing dislocation in lateral meniscal bearing unicompartmental knee replacement: Domed versus flat tibial surface

BACKGROUND

Bearing dislocation is a problem following mobile bearing Oxford lateral Unicompartmental Knee Replacement (UKR). Therefore, the design of the tibial component was changed from a flat tibial surface to a domed tibial surface with a biconcave bearing to increase bearing entrapment. This systematic review compared the dislocation and revision rates of the two designs.

METHODS

Two authors independently searched MEDLINE, EMBASE and ISI Web of Science, reference lists of retrieved articles, and the internet. Randomised, cohort, case-control and case studies of adult patients with lateral knee osteoarthritis treated with flat or domed Oxford lateral UKR and their outcomes were included. The overall dislocation rate and the annual revision rate (per 100 component years) were determined.

RESULTS

Nine studies (937 knees) met the inclusion criteria (3 flat, 6 domed). Four studies (all domed) had a low risk of bias and five had a high risk (3 flat, 2 domed), so data should be interpreted with caution. The bearing dislocation rate decreased from 17% (flat) to 3.7% (domed). Dislocations occurred on average at 16 months and medial dislocations were most common. The revision rate excluding dislocation decreased from 1.1%pa to 0.7%pa. PROSPERO registration: CRD42019139250.

CONCLUSION

Modifying the tibial component from a flat to a domed shape decreased the bearing dislocation rate to 3.7% and increased the 10 year survival rate excluding dislocation to 93%. The dislocation rate is still relatively high so bearing stability should be assessed intra-operatively and if unacceptable, a fixed bearing version of the Oxford lateral tibial component can be inserted.

Sports activity and patient-related outcomes after fixed-bearing lateral unicompartmental knee arthroplasty

BACKGROUND

Unicompartmental osteoarthrosis increasingly affects younger patients who have high expectations concerning their postoperative level of activity. However, there is no available data on the activity level after fixed-bearing lateral unicompartmentalkneearthroplasty (UKA). The aim of this study was to report sports activity after fixed-bearing lateral UKA with a minimum two-year follow up.

METHODS

Nineteen patients were surveyed to determine their sporting activities at a mean follow up of 4.6 years (range 2.0-9.7 years) after fixed-bearing lateral UKA. We also assessed the Knee Injury and Osteoarthritis Outcome Score Joint Replacement (KOOS JR) Score and the University of California, Los Angeles activity scale (UCLA scale) at baseline and latest follow up.

RESULTS

Before the onset of the first symptoms, 15 of 19 patients were active in at least one sport compared with 13 of 19 patients after surgery. Eighty-six per cent of the patients returned to activity. Within 6 months, 68% returned to their activities after surgery. The mean postoperative UCLA score was 6.4 (±1.3). Half of the patients reached a high activity level (UCLA ≥ 7). Most common activities after surgery were long walks, biking and hiking. High-impact activities showed a significant decrease.

CONCLUSION

Eighty-six per cent of the patients were able to return to regular recreational and sporting activities. In general, a shift from high-impact to low-impact activities was observed. There was no difference in the number of disciplines performed. Overall, the session length and frequency remained unchanged. However, male patients and younger patients participated in sports less frequently compared with preoperative levels.

Bilateral unicompartmental knee arthroplasty for windswept knee osteoarthritis: A report of 13 cases

BACKGROUND

Windswept deformity is a condition of the lower limbs with a valgus knee on one side and a varus knee on the other. We present a case series of bilateral unicompartmental knee arthroplasty (UKA) for windswept knee osteoarthritis (WSKO).

METHODS

We analysed the outcomes of 26 knees of 13 consecutive patients with WSKO treated with bilateral UKA. The mean age was 73.0 years and the mean follow up period was 2.6 years. Pre- and postoperative Oxford Knee Score (OKS) and Japanese Orthopaedic Association (JOA) score, radiological measurements and postoperative complications were evaluated. No knees required revision for either infection or loosening.

RESULTS

The mean preoperative OKS was 25.3 ± 9.7, which increased to 34.9 ± 5.8 at the latest follow up. The mean preoperative JOA scores for the varus and the valgus sides were 64.6 ± 12.5 and 66.9 ± 14.1, which increased to 85.0 ± 11.3 and 84.6 ± 11.2, respectively, after operation.

CONCLUSIONS

Our results show that good short-term clinical results can be achieved by bilateral UKA in cases of WSKO. Bilateral UKA may be an effective treatment for WSKO if indications are met.