No long-term difference between fixed and mobile medial unicompartmental arthroplasty

Altered dynamic joint space in the lateral condyle compartment following medial unicompartmental knee arthroplasty

PURPOSE

The progression of osteoarthritis in lateral compartment has been identified as a primary complication in medial unicompartmental knee arthroplasty (UKA) revisions, irrespective of whether employing fixed bearing (FB) or mobile bearing (MB) designs. Compared to the previous contact point analyses, the tibiofemoral contacts during knee movements are comprehended by a more comprehensive understanding of joint spaces. This study aims to dynamically map the joint spaces in the lateral compartment during the single-leg lunge following FB and MB UKA procedures, and compare them with the respective contralateral native knees. It is hypothesized that the significant change in joint space for post-UKA compared to their native knees.

METHODS

Twelve patients with unilateral medial FB UKA and eleven patients with unilateral medial MB UKA were included and underwent computed tomography scans. The exclusion criteria included anterior cruciate ligament deficiency, postoperative knee pain, any postoperative complications, and musculoskeletal illnesses. A dual fluoroscopic imaging system was utilized to capture the single-leg lunge, and 2D-to-3D registration facilitated the visualization of knee motion. According to the knee motions, joint spaces on tibial and femoral surfaces in the lateral compartments of native, FB, and MB UKA knees were calculated and mapped.

RESULTS

In comparison to the native knees, FB UKA knees exhibited significant increases in medial, lateral, central, and posterior joint spaces in the lateral compartment (p < 0.05), while MB UKA knees showed significant increases only in central and posterior joint spaces (p < 0.05). Moreover, FB UKA demonstrated greater increases in medial, central, and posterior joint spaces compared to MB UKA. Tibial varus and valgus during lunges, as well as the Oxford Knee Score (OKS) and Hip-Knee-Ankle angle (HKA), correlated with joint spaces.

CONCLUSIONS

Dynamic joint space analysis provided a more comprehensive insight into contact dynamics. FB UKA led to an enlargement of joint spaces, whereas MB UKA resulted in joint spaces closer to native knees. These findings contribute to understanding potential postoperative complication in UKAs.

Excellent 10-Year survivorship of robotic-arm-assisted unicompartmental knee arthroplasty

Introduction

Robotic-arm-assisted unicompartmental knee arthroplasty (UKA) is an excellent solution for patients suffering from single-compartment knee arthritis. While outcomes tend to be favorable for UKAs, revision operations, commonly due to component malpositioning and malalignment resulting in accelerated wear, are a major concern. Intraoperative technologies, such as robotic assistance, can help better ensure that implants are positioned based on a patient's specific anatomy and mechanical physiology. However, long-term survivorship and patient-reported satisfaction with robotic-assisted UKAs are limited. Therefore, the purpose of this study was to assess the 10-year outcomes of patients who underwent robotic-arm-assisted unicompartmental knee arthroplasty. Specifically, we evaluated: 1) 10-year survivorships; 2) patient satisfaction scores; and 3) re-operations.

Methods

From a single surgeon and single institution, 185 patients who had a mean age of 65 years (range, 39 to 92) and a mean body mass index of 31.6 (range, 22.4 to 39) at a mean of 10 years follow-up were evaluated (range, 9 to 11). For all patients, the same robotic-assistive device was utilized intraoperatively, and all patients underwent standardized physical therapy and received standardized pain control management. Then 10-year survivorships with Kaplan-Meir curves, patient satisfaction evaluations with a 5-point Likert scale, and re-operations were assessed as primary outcomes.

Results

Overall implant survivorship was 99%, with only two patients requiring revision surgery. There was one patient who was converted to a total knee arthroplasty, while the other patient underwent polyethylene exchange at 5 weeks for an acute infection with successful implant retention. Overall, 97% of the patients were satisfied with their postoperative outcomes, with 81% of patients reporting being very satisfied. There were two other patients who required arthroscopic intervention: one to remove a cement loose body, the other to remove adhered scar from the fat pad and the anterior cruciate ligament.

Conclusion

This study is one of the first to provide longer-term (mean 10-year) survivorship and patient-reported satisfaction outcomes for robotic-assisted UKA patients. These data show strong support for utilizing this surgical technique, as nearly all patients maintained their original prostheses and reported being satisfied after a mean of 10 years. Therefore, based on these results, we recommend the use of robotic assistance when performing UKAs.

Outcomes of fixed versus mobile-bearing medial unicompartmental knee arthroplasty

Aims

The optimal bearing surface design for medial unicompartmental knee arthroplasty (UKA) remains controversial. The aim of this study was to compare outcomes of fixed-bearing (FB) and mobile-bearing (MB) UKAs from a single high-volume institution.

Methods

Prospectively collected data were reviewed for all primary cemented medial UKAs performed by seven surgeons from January 2006 to December 2022. A total of 2,999 UKAs were identified, including 2,315 FB and 684 MB cases. The primary outcome measure was implant survival. Secondary outcomes included 90-day and cumulative complications, reoperations, component revisions, conversion arthroplasties, range of motion, and patient-reported outcome measures. Overall mean age at surgery was 65.7 years (32.9 to 94.3), 53.1% (1,593/2,999) of UKAs were implanted in female patients, and demographics between groups were similar (p > 0.05). The mean follow-up for all UKAs was 3.7 years (0.0 to 15.6).

Results

Using revision for any reason as an endpoint, five-year survival for FB UKAs was 97.2% (95% CI 96.4 to 98.1) compared to 96.0% for MB (95% CI 94.1 to 97.9; p = 0.008). The FB group experienced fewer component revisions (14/2,315, 0.6% vs 12/684, 1.8%; p < 0.001) and conversion arthroplasties (38/2315, 1.6% vs 24/684, 3.5%; p < 0.001). A greater number of MB UKAs underwent revision due to osteoarthritis progression (FB = 21/2,315, 0.9% vs MB = 16/684, 2.3%; p = 0.003). In the MB group, 12 (1.8%) subjects experienced bearing dislocations which required revision surgery. There were 15 early periprosthetic tibia fractures (0.6%) in the FB group compared to 0 for MB (p = 0.035).

Conclusion

In similar patient populations, FB UKAs demonstrated slightly higher survival than a commonly used MB design. Adverse event profiles differed by bearing type, with an increased risk of bearing dislocation and OA progression with MB designs, and early periprosthetic tibia fractures for FB designs.

Long term follow up of 257 consecutive cementless Oxford medial compartment knee arthroplasties at a non-designer centre

AIMS

This study aimed to review the survivorship, indication for revision and patient reported outcomes for 257 consecutive Oxford cementless unicompartmental knee arthroplasties (OUKA's) in 238 patients at 12-14 years post-operatively.

METHODS

Patients underwent surgery between April 2008 and October 2010 by two non-design surgeons including their learning curve. The 5-year clinical and radiological outcomes have already been reported. Oxford knee scores (OKS) were recorded at 1, 5 and 12-14 years with delayed review a result of the COVID-19 pandemic. Revision indication and imaging were reviewed.

RESULTS

Revision was required in 28 OUKA's (10.9%) with a 10-year cumulative survival of 93.0%, reducing to 78.8% at 14 years. 59 patients had died prior to this review and 24 were not contactable. Those not contactable had electronic records reviewed to ensure they did not have a revision elsewhere. Half of the revisions were for progression of lateral compartment arthritis (14/28). Four of 6 cases with a full revision for polyethylene wear may have benefited from a bearing exchange instead. OKSs in non-revised patients were good (median score 38, IQR 30-44) with no significant deterioration noted from 5 to 12-14 years.

CONCLUSIONS

Cementless OUKA in this series had a long-term survival rate comparable to other OUKA's outside of the designer centre. OKSs remain good for those patients not revised. Progression of lateral compartment arthritis was the primary reason for revision with no revisions for component loosening or bearing spinout. Ideally UKA patients who experience problems should be under the care of revisions surgeons who perform UKA. Improving patient selection and understanding of the pathophysiology of lateral disease progression, remain crucial to improve the long-term survivorship of OUKA.

Staged Bi-compartmental Knee Arthroplasty for Contralateral Compartment Failure After Medial Unicompartmental Knee Arthroplasty in Dialysis Patients: Two Case Reports

Unicompartmental knee arthroplasty (UKA) is a minimally invasive surgical technique with good clinical outcomes; however, its outcomes in patients undergoing hemodialysis are unknown. Herein, we report two cases of patients undergoing hemodialysis who underwent staged bi-compartmental UKA (Bi-UKA) for early contralateral compartment failure after medial UKA. We describe the case of early contralateral compartment failure after medial UKA in two women patients aged 71 and 72 years with a dialysis history of seven and 22 years, respectively. Three months after right medial UKA, she had persistent joint edema and arthralgia after minor trauma, with recurrent gait disturbance in the first case. An MRI showed a bone marrow lesion in the contralateral compartment, and a lateral UKA was added. In the second case, the knee pain worsened without any trigger three years after leaving the medial UKA. A subchondral insufficiency fracture (SIF) was diagnosed by a plain radiograph showing a radiolucent area on the lateral femoral condyle. Gait disturbance did not improve, and a lateral UKA was performed. In our hospital, medial UKA was performed on seven knees of dialysis patients in 10 years since 2011, and contralateral compartment failure was observed in two knees at an early stage. In both cases, lumbar bone density was normal and there was no postoperative overcorrection in leg alignment, but a SIF of the contralateral side occurred, suggesting that bone fragility of the contralateral compartment due to long-term dialysis was the underlying cause. Staged Bi-UKA was minimally invasive and useful as a revision surgery.

Unicompartmental knee arthroplasties: does the type of tibial component selected influence implant survival?

INTRODUCTION

Few information has been published on the survival of unicompartmental knee arthroplasty (UKA) and fixed-bearing tibial components. The aim of this study is to analyze if UKA survival varies according to UKA model used and to analyze the possible risk factors for UKA revision.

MATERIALS AND METHODS

A retrospective study analyzing 301 UKAs (ACCURIS, all-polyethylene tibial component, 152; Triathlon PKR, metal-backed tibial component, 149) was performed. Demographic parameters as well as implant survival and cause of prosthetic revision were analyzed. The Kaplan-Meier survival analysis, the log-rank test and the Cox multiple regression were used for the analysis.

RESULTS

Average follow-up was 8.1 ± 3.08-years. Average age was 68.1 ± 8.6-years; 70.4% of subjects were women. The ACCURIS UKA group had a UKA revision rate higher compared to the Triathlon PKR group (16/152, 10.6% vs 5/149, 3.4%, respectively; p < 0.001). The main cause of prosthetic revision was aseptic loosening (5/21, 23.8%). All aseptic loosening cases and tibial component collapse were reported with the ACCURIS UKA group. Overall UKA survival was 98.01% (95% CI 95.62-99.1) at 1-year, 94.27% (95% CI 90.95-96.4) at 5-years and 92.38% (95% CI 88.48-94.99) at 10-years' follow-up. There were no differences in the Kaplan-Meier survival curves regarding operated side or affected tibiofemoral compartment (log-rank test = 0.614 and 0.763, respectively). However, Kaplan-Meier survival curve according to UKA model used was different (log-rank test = 0.033). The metal-backed component appeared to be a protector factor for UKA revision when adjusted for age, sex, operated side, and affected tibiofemoral compartment (Hazard Ratio 0.32, p = 0.031).

CONCLUSION

Fixed-bearing UKAs showed excellent mid- and long-term survival rates. Aseptic loosening is the main cause of implant failure. PKR group (metal-backed component) seem to be a protector factor to UKA revision when it was compared with ACCURIS UKA group (all-polyethylene tibial component).

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.

Preoperative Bone Marrow Edema Negatively Impacts 10-Year Outcomes After Unicompartmental Knee Arthroplasty

BACKGROUND

The purpose of this study was to investigate the association between the extent of subchondral bone marrow edema (BME), as classified by magnetic resonance imaging, and intermediate to long-term outcomes after unicompartmental knee arthroplasty (UKA) for medial compartment osteoarthritis.

METHODS

We enrolled 150 knees (144 patients) that underwent fixed-bearing UKA between April 2003 and December 2014 with a minimum follow-up of 5 years; the mean overall follow-up duration was 10 years (range, 5-18 years). We divided the patients into 2 groups based on the presence or absence of preoperative BME. Patients were also subdivided into 4 groups according to their BME scores determined by the magnetic resonance imaging Osteoarthritis Knee Score method. Clinical outcomes were assessed using the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Forgotten Joint Score. Furthermore, survival rates and relevant risk factors that affect joint survivorship were analyzed.

RESULTS

The groups with BME demonstrated significantly worse postoperative WOMAC pain and Forgotten Joint Scores at the final follow-up than the group without BME (all P < .05). We also found significant differences among the scores of groups with different BME grades (all P < .05). Post hoc analysis demonstrated differences between groups 1 and 2, 1 and 3, 1 and 4, and 2 and 4 (all P < .05) with a significant correlation between postoperative clinical outcomes and the extent of BME (r = 0.430 [WOMAC pain], r = -0.342 [Forgotten Joint Score]; P < .05). The survival rate was 95.4% for a mean period of 10 years for the UKAs, and the UKA survival was not associated with the presence of BME (P = .232; log-rank test).

CONCLUSION

At a mean of 10 years, preoperative BME negatively impacted the clinical outcomes, especially pain, after UKA. However, UKA contributed to excellent survival rates for the same duration of follow-up, regardless of BME severity. Although this study does not provide any evidence that preoperative BME should be identified as a contraindication, evaluation of BME can provide crucial information about the expected outcomes.

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.

Approximately 41% of knees have a looser gap in full extension than in 20° flexion after Oxford unicompartmental arthroplasty

INTRODUCTION

In Oxford unicompartmental knee arthroplasty (OUKA), the flexion and extension gaps should be adjusted to prevent mobile-bearing dislocation. The extension gap is recommended to be evaluated in the 20° flexion position to avoid underestimation due to tension of the posterior capsule. However, we have become aware of a looser gap in full extension than in 20° flexion in some instances.

MATERIALS AND METHODS

We retrospectively investigated 83 knees in 60 patients who underwent OUKA between January and June 2020. During surgery, the extension gaps were measured in both full extension and 20° flexion. The knees were classified into two groups: the gap was looser in full extension (0° group), and the gap was equal or looser in 20° flexion than in full extension (20° group). The hip-knee-ankle angle (HKAA), the lateral distal femoral angle (LDFA), the medial proximal tibia angle (MPTA), the posterior tibial slope angle (PTSA), and the last spigot size were also measured and compared between the groups.

RESULTS

There was looseness in approximately 41% of knees (34 out of 83 knees) in full extension. In the knees in the 0° group, the last spigot size was significantly smaller (median 1 and 2, P < 0.01). However, there were no significant differences in the HKAA, MPTA, LDFA or PTSA between the groups.

CONCLUSIONS

Approximately 41% of knees have a looser gap in full extension than in 20° flexion after OUKA. Further investigation is needed to better understand which extension gap should be used in such cases, and to find the contributing factors in loose full extension gap other than the size of the last spigot.

Mobile bearing versus fixed bearing medial unicompartmental knee replacement: an independent two center matched-pairs analysis

INTRODUCTION

The aim of the present study was to compare clinical outcome between patients following fixed-bearing (FB) or mobile-bearing (MB) unicompartmental knee replacement (UKR) for antero-medial knee osteoarthrosis (OA) at two independent orthopedic centers.

MATERIALS AND METHODS

Matched-pairs were built between 35 patients receiving FB-UKR and 52 patients following MB-UKR regarding age at time of surgery, body mass index (BMI) and range of motion (ROM) preoperatively. Clinical and functional outcome was measured postoperatively by the American Knee Society Score (AKSS-O/AKSS-F), ROM, Tegner Activity Scale (TAS) as well as the Short Form 36 Health Survey (SF-36).

RESULTS

The average treatment effect of the treated (ATT) after propensity score matching showed a significantly superior ROM in patients following MB-UKR (FB: 118°, MB: 124°). All remaining parameters had no statistically significant differences between both groups involving TAS, AKSS and SF-36.

CONCLUSIONS

The present study suggests that MB-UKR can provide a greater ROM compared to FB-UKR on comparable patients. The authors believe that both designs are suitable for adequate improvement of clinical outcome and ROM for patients suffering from antero-medial osteoarthrosis of the knee joint.

LEVEL OF EVIDENCE

Retrospective cohort study, Level IV.

Supine Knee Positioning Does Not Interfere with Mobile-Bearing Unicompartmental Knee Arthroplasty Performance

The Food and Drug Administration has only approved mobile-bearing unicompartmental knee arthroplasty (MB-UKA) to be performed with a hanging leg holder. The purpose of this study is to evaluate the impact of a supine knee position on MB-UKA performance.In total, 16 cadavers were randomized so that either the right or left knee was placed in the flexed or supine positions. One board-certified orthopaedic surgeon and three adult reconstruction fellows that attended the required Oxford partial knee instructional course performed four operations in each position. The primary outcome was final knee balance. Secondary outcomes included procedure duration, timing of individual surgical steps, implant sizes, range of motion, implant alignment, and fracture. A Students t-test was used to examine differences between positions with significance set at p < 0.05. Secondary analyses using two one-sided tests were conducted to explore equivalence between the two positions.There was no significant difference in mean final balance between supine (1.7 mm ± standard deviation [SD] = 1.5 mm) and flexed (1.3 ± 1.3 mm) positions (p = 0.390). There were also no significant differences between positions for procedure time (p = 0.497), tibia coronal alignment (p = 0.614), tibial slope (p = 0.194), femoral component sagittal alignment (p = 0.091), and fractures (n = 0). Exploratory equivalence analyses indicated that the positions were equivalent for final balance (p = 0.002).MB-UKA performed in the supine position is not significantly different from the flexed position in terms of ligament balance, overall procedure time, and radiographic appearance. These initial safety data warrant further clinical investigations and support the expansion of the surgical technique to include performing MB-UKAs in the supine position.

Evaluation of Safety and Medium-Term Functional Outcomes of a Medial Fixed-Bearing Unicompartmental Knee Arthroplasty with Ultra-Highly Cross-Linked Polyethylene

The primary objective of this study was to evaluate the in vivo safety of a unicompartmental knee arthroplasty design with sequentially annealed cross-linked polyethylene by evaluating reoperation rate, in particular those related to excessive polyethylene wear or breakage. The secondary objective was to examine functional outcomes via standardized questionnaires. This was a 5-year institutional review board-approved prospective single-surgeon case series of the first 152 consecutive patients with symptomatic medial unicompartmental osteoarthritis implanted with a partial knee replacement between May 2010 and December 2014. Study participants were asked to complete the Knee injury and Osteoarthritis Outcome Score (KOOS) and Western Ontario and McMaster Universities Osteoarthrtis Index (WOMAC) questionnaires at preoperation and 2 to 5 years postoperation. Major complications and all reoperations were recorded and we produced Kaplan-Meier survivorship curves with the end point of revision to TKA. Pre- and postoperative differences for KOOS and WOMAC were evaluated by paired t-tests. The median length of follow-up was 7.2 (0-9.72) years. Seven patients required revision surgery to TKA (4.9% of patients): four with progression of arthritis in other compartments, two for infection, and one for loosening of the femoral component and subsequent progression of pain. There were no failures of polyethylene. Survival of cohort was 99.3 and 97.9% at 2 and 5 years, respectively. Patients significantly improved (p-value < 0.001) between preoperative assessment and at 2 years, with no decline at 5 years postoperation. These preliminary midterm results with this fixed-bearing design and cross-linked polyethylene were encouraging with no catastrophic failures of polyethylene. Patient reported outcomes were significantly improved and revision rates were acceptable and lower than registry reported results.

Mobile Bearing versus Fixed Bearing for Unicompartmental Arthroplasty in Monocompartmental Osteoarthritis of the Knee: A Meta-Analysis

Introduction: Whether mobile-bearing (MB) unicompartmental knee arthroplasty (UKA) performs better than fixed-bearing (FB) implants in patients with monocompartmental osteoarthritis (OA) still remains unclear. Therefore, a meta-analysis comparing MB versus FB for UKA was conducted to investigate the possible advantages of MB versus FB in patient-reported outcome measures (PROMs), range of motion (ROM), and complications. We hypothesised that the MB design performs better than FB. Methods: This systematic review was conducted according to the 2020 PRISMA guidelines. In December 2021, PubMed, Web of Science, Google Scholar, and Embase were accessed, with no time constraints. All the clinical investigations comparing MB versus FB bearing for UKA were accessed. Only studies published in peer-reviewed journals were considered. Studies reporting data on revision settings were excluded, as were those combining unicompartmental and total knee arthroplasty. Results: Data from 25 studies (4696 patients) were collected; 58% (2724 of 4696 patients) were women. The mean length of follow-up was 45.8 ± 43.2. The mean age of the patients was 65.0 ± 5.6 years. No difference was found in range of motion (p = 0.05), Knee Scoring System (p = 0.9), function subscale (p = 0.2), and Oxford Knee Score (p = 0.4). No difference was found in the rate of revision (p = 0.2), aseptic loosening (p = 0.9), deep infections (p = 0.99), fractures (p = 0.6), and further extension of OA to the contralateral joint compartment (p = 0.2). Conclusion: The present meta-analysis failed to identify the possible superiority of the MB implants over the FB for UKA in patients with monocompartmental knee osteoarthritis. Long observational investigations are required to evaluate possible long-term complications and implant survivorship. These results should be interpreted within the limitations of the present study.

St Georg Sled medial unicompartmental arthroplasty: survivorship analysis and function at 20 years follow up

PURPOSE

The peri-operative and short-term benefits of unicompartmental knee arthroplasty (UKA) are well supported in the literature. However, there remains concern regarding the higher revision rate when compared with total knee replacement. This manuscript reports the functional outcome and survivorship of a large series of fixed bearing, medial unicompartmental replacements (St Georg Sled), with a minimum of 20 years follow-up.

METHODS

Between 1974 and 1994, 399 patients (496 knees) underwent a medial fixed-bearing UKA. Prospective data were collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan-Meier survival analysis was used to determine survivorship, with revision or need for revision as end point, and differences assessed using Mantel-Cox log rank test.

RESULTS

Functional knee scores improved post-operatively, but demonstrated a slight decline from 10 years of follow-up onwards. Survivorship is estimated as 86% at 10 years, 80% at 15 years, and 78% at 20 years. Sixty knees were revised, with progression of disease in another compartment the commonest reason. Eighty eight percent were revised using a primary prosthesis. For patients over the age of 65 years at the time of index procedure, 93% died with a functioning prosthesis in situ.

CONCLUSION

Medial UKA demonstrates good long-term function and survivorship, and represents an excellent surgical option for patients aged over 65 years of age, where few patients will require a revision procedure.

LEVEL OF EVIDENCE

IV.

Do Fixed or Mobile Bearing Implants Have Better Survivorship in Medial Unicompartmental Knee Arthroplasty? A Study From the Australian Orthopaedic Association National Joint Replacement Registry

BACKGROUND

During the last 5 years, there has been an increase in the use of unicompartmental knee arthroplasty (UKA) to treat knee osteoarthritis in Australia, and these account for almost 6% of annual knee replacement procedures. However, there is debate as to whether a fixed bearing or a mobile bearing design is best for decreasing revision for loosening and disease progression as well as improving survivorship. Small sample sizes and possible confounding in the studies on the topic may have masked differences between fixed and mobile bearing designs.

QUESTIONS/PURPOSES

Using data from the Australian Orthopaedic Association National Joint Replacement Registry (AOANJRR), we selected the four contemporary designs of medial compartment UKA: mobile bearing, fixed modular, all-polyethylene, and fixed molded metal-backed used for the treatment of osteoarthritis to ask: (1) How do the different designs of unicompartmental knees compare with survivorship as measured by cumulative percentage revision (CPR)? (2) Is there a difference in the revision rate between designs as a function of patient sex or age? (3) Do the reasons for revision differ, and what types of revision procedures are performed when these UKA are revised?

METHODS

The AOANJRR longitudinally maintains data on all primary and revision joint arthroplasties, with nearly 100% capture. The study population included all UKA procedures undertaken for osteoarthritis between September 1999 and December 2018. Of 56,628 unicompartmental knees recorded during the study period, 50,380 medial UKA procedures undertaken for osteoarthritis were included in the analysis after exclusion of procedures with unknown bearing types (31 of 56,628), lateral or patellofemoral compartment UKA procedures (5657 of 56,628), and those performed for a primary diagnosis other than osteoarthritis (560 of 56,628). There were 50,380 UKA procedures available for analysis. The study group consisted of 40% (20,208 of 50,380) mobile bearing UKA, 35% (17,822 of 50,380) fixed modular UKA, 23% (11,461 of 50,380) all-polyethylene UKA, and 2% (889 of 50,380) fixed molded metal-backed UKA. There were similar sex proportions and age distributions for each bearing group. The overall mean age of patients was 65 ± 9.4 years, and 55% (27,496 of 50,380) of patients were males. The outcome measure was the CPR, which was defined using Kaplan-Meier estimates of survivorship to describe the time to the first revision. Hazard ratios from Cox proportional hazards models, adjusted for sex and age, were performed to compare the revision rates among groups. The cohort was stratified into age groups of younger than 65 years and 65 years and older to compare revision rates as a function of age. Differences among bearing groups for the major causes and modes of revision were assessed using hazard ratios.

RESULTS

At 15 years, fixed modular UKA had a CPR of 16% (95% CI 15% to 17%). In comparison, the CPR was 23% (95% CI 22% to 24%) for mobile bearing UKA, 26% (95% CI 24% to 27%) for all-polyethylene UKA, and 20% (95% CI 16% to 24%) for fixed molded metal-backed UKA. The lower revision rate for fixed modular UKA was seen through the entire period compared with mobile bearing UKA (hazard ratio 1.5 [95% CI 1.4 to 1.6]; p < 0.001) and fixed molded metal-backed UKA (HR 1.3 [95% CI 1.1 to 1.6]; p = 0.003), but it varied with time compared with all-polyethylene UKA. The findings were consistent when stratified by sex or age. Although all-polyethylene UKA had the highest revision rate overall and for patients younger than 65 years, for patients aged 65 years and older, there was no difference between all-polyethylene and mobile bearing UKA. When compared with fixed modular UKA, a higher revision risk for loosening was shown in both mobile bearing UKA (HR 1.7 [95% CI 1.5 to 1.9]; p < 0.001) and all-polyethylene UKA (HR 2.4 [95% CI 2.1 to 2.7]; p < 0.001). The revision risk for disease progression was higher for all-polyethylene UKA at all time points (HR 1.4 [95% CI 1.3 to 1.6]; p < 0.001) and for mobile bearing UKA after 8 years when each were compared with fixed modular UKA (8 to 12 years: HR 1.4 [95% CI 1.2 to 1.7]; p < 0.001; 12 or more years: HR 1.9 [95% CI 1.5 to 2.3]; p < 0.001). The risk of revision to TKA was higher for mobile bearing UKA compared with fixed modular UKA (HR 1.4 [95% CI 1.3 to 1.5]; p < 0.001).

CONCLUSION

If UKA is to be considered for the treatment of isolated medial compartment osteoarthritis, the fixed modular UKA bearing has the best survivorship of the current UKA designs.

LEVEL OF EVIDENCE

Level III, therapeutic study.

What is the evidence for clinical use of advanced technology in unicompartmental knee arthroplasty?

BACKGROUND

With an aim of improving prosthesis survivorship of unicompartmental knee arthroplasty (UKA), use of computer-assisted technologies (CATs) such as robotics, has been on the rise to reduce intraoperative errors in surgical technique. In light of recent influx of CATs in the UKA, a review of these innovations will help providers to understand their clinical utility.

METHOD

A systematic literature search was performed following Preferred Reporting Items for Systematic Review and Meta-Analysis guidelines.

RESULTS

Among 19 studies comparing robot-assisted UKA with conventional UKA, only 32% were randomized control trials, 47% reported minimum mean follow-up of 2 years, and 21% evaluated prosthesis survival. Similar results were obtained for navigation-assisted UKA and UKA performed with patient-specific instrumentation.

CONCLUSION

While CATs seem to reduce the surgical errors in UKA, the evidence on the efficacy of any of the studied CATs to improve survivorship remains limited and there are issues related to cost-effectiveness, learning curve, and increase in operating time.

Robotic arm-assisted versus conventional medial unicompartmental knee arthroplasty: five-year clinical outcomes of a randomized controlled trial

Aims

Unicompartmental knee arthroplasty (UKA) is a bone-preserving treatment option for osteoarthritis localized to a single compartment in the knee. The success of the procedure is sensitive to patient selection and alignment errors. Robotic arm-assisted UKA provides technological assistance to intraoperative bony resection accuracy, which is thought to improve ligament balancing. This paper presents the five-year outcomes of a comparison between manual and robotically assisted UKAs.

Methods

The trial design was a prospective, randomized, parallel, single-centre study comparing surgical alignment in patients undergoing UKA for the treatment of medial compartment osteoarthritis (ISRCTN77119437). Participants underwent surgery using either robotic arm-assisted surgery or conventional manual instrumentation. The primary outcome measure (surgical accuracy) has previously been reported, and, along with secondary outcomes, were collected at one-, two-, and five-year timepoints. Analysis of five-year results and longitudinal analysis for all timepoints was performed to compare the two groups.

Results

Overall, 104 (80%) patients of the original 130 who received surgery were available at five years (55 robotic, 49 manual). Both procedures reported successful results over all outcomes. At five years, there were no statistical differences between the groups in any of the patient reported or clinical outcomes. There was a lower reintervention rate in the robotic arm-assisted group with 0% requiring further surgery compared with six (9%) of the manual group requiring additional surgical intervention (p < 0.001).

Conclusion

This study has shown excellent clinical outcomes in both groups with no statistical or clinical differences in the patient-reported outcome measures. The notable difference was the lower reintervention rate at five years for roboticarm-assisted UKA when compared with a manual approach.

Cite this article: Bone Joint J 2021;103-B(6):1088–1095.

Medial Unicompartmental Knee Arthroplasty with a Mobile-Bearing Implant

Background

For patients with isolated medial knee arthritis, unicompartmental knee arthroplasty (UKA) is an appealing surgical option. Compared with total knee arthroplasty (TKA), UKA is less invasive, preserves more native bone stock, has lower perioperative morbidity and mortality^1,2, allows for quicker recovery^1,2, and has higher patient satisfaction^2,3. It also allows for more dynamic proprioception and postural control, allowing for function more similar to a native knee⁴. Proper surgical technique and patient selection are critical to the growing success of UKA.

Description

The general principles of UKA are to remove and replace the diseased femoral and tibial joint surfaces while restoring limb alignment. The key steps of this procedure are demonstrated in the video article: (1) patient evaluation, (2) patient positioning, (3) surgical exposure, (4) tibial guide placement and resection, (5) femoral guide placement and resection, (6) knee balancing and implant trialing, (7) preventing impingement, (8) final tibial preparation, (9) final component placement, and (10) closure and postoperative course.

Alternatives

Patients should first exhaust all nonoperative treatments before considering UKA. For those patients who do not meet the appropriate indications for UKA, TKA is the most acceptable alternative treatment. In active patients <55 years old without bone-on-bone osteoarthritis, a high tibial osteotomy may be considered. When considering UKA, options include both mobile-bearing and fixed-bearing designs.

Rationale

The potential advantages of UKA over TKA make it an attractive option for the appropriate patient. Recently, indications for UKA have expanded to include (1) isolated noninflammatory bone-on-bone arthritis in the medial compartment; (2) retained full-thickness cartilage in the lateral compartment, best visualized on valgus-stress radiographs; (3) a functionally normal medial collateral ligament; and (4) a functionally normal anterior cruciate ligament⁵. Mobile-bearing UKA designs consist of a dual articulation between the concave polyethylene insert and the metallic tibial and spherical femoral components, which allows for distribution of contact forces over a large surface area⁶. In contrast, fixed-bearing designs have a flat polyethylene insert that does not conform to the femur. Current data do not demonstrate a clear difference in clinical performance between the 2 bearings. However, a recent systematic review has shown lower polyethylene wear rates in mobile-bearing implants⁷.

Expected Outcomes

The survivorship of mobile-bearing UKA ranges from 85% to 98% at 10 years^8-12 and from 79% to 94% at 15 years^8,13,14. The most common indications for revision include aseptic loosening (36%), progression of osteoarthritis (20%), and unexplained pain (11%)⁷. Bearing dislocation is a unique complication for mobile-bearing UKAs, with reported rates between 0.3% to 4.2%^6,10,12.

Important Tips

Always inspect all compartments of the knee for evidence of substantial degenerative changes prior to proceeding with UKA. If there is advanced arthritis in other compartments, the decision should be made to proceed with TKA instead. Therefore, preoperatively, all patients indicated for UKA should also sign a consent form for TKA, and TKA implants should be available in case they are needed.When assessing bearing size, it is important that there is no axial loading through the heel to properly assess the flexion gap. Intraoperatively, this can be done by elevating the thigh so that the foot hangs freely. The trial spoon should fit into the joint without substantial resistance or effort.Spigots do not reference the end of the bone. Rather, they reference the end of the spigot hole that was drilled using the initial 0 spigot.Spigot number represents the total thickness of additional bone that will be removed from the first mill cut.Confirm the amount of bone that was resected by inspecting the small rim of bone that remains around the spigot hole after milling.

A Comparison of Mobile- and Fixed-Bearing Unicompartmental Knee Arthroplasties in the Treatment of Medial Knee Osteoarthritis: A Systematic Review and Meta-analysis of 1,861 Patients

Many studies have compared mobile-bearing (MB) and fixed-bearing (FB) unicompartmental knee arthroplasties (UKAs) in patients with unicompartmental knee osteoarthritis (OA). The present systematic review and meta-analysis examined the differences in the clinical and radiological outcomes of MB UKA and FB UKA. PubMed, EMBASE, and Cochrane databases, as well as Google Scholar were searched for relevant studies. Randomized controlled trials (RCTs) and cohort studies that compared MB UKA and FB UKA were included. The weighted mean difference in the knee scores and range of motion (ROM) as well as the summary odds ratio of postoperative mechanical axis alignment, radiolucency, revision rate, and complications were calculated in the MB UKA and FB UKA groups. Finally, 2 RCTs and 11 cohort studies that involved 1,861 patients (1,996 knees) were included. The FB UKA group showed better postoperative Knee Society score (KSS), Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and ROM than the MB UKA group. However, the MB UKA group had more knees with a neutral limb alignment and a lower incidence of polyethylene wear than the FB UKA group. No significant differences were observed between the groups with respect to radiolucency, revision rate, and complications, such as arthritis progression, aseptic loosening, and postoperative pain. This meta-analysis has demonstrated that both prostheses provided excellent clinical outcomes and survivorship in patients with unicompartmental knee OA. The MB UKA group achieved the expected postoperative neutral limb alignment as compared with the FB UKA group, while the FB UKA group showed higher knee scores and superior ROM than the MB UKA group. Limited evidence is currently available; therefore, the results of our meta-analysis should be interpreted with caution.

Finite element analysis of the influence of the posterior tibial slope on mobile-bearing unicompartmental knee arthroplasty

BACKGROUND

The most common modes of failure reported in unicompartmental knee arthroplasty (UKA) in its first two decades were wear on the polyethylene (PE) insert, component loosening, and progressive osteoarthritis in the other compartment. The rates of implant failure due to poor component positioning in patients who have undergone UKA have been reported. However, the effect of the posterior tibial slope on the biomechanical behavior of mobile-bearing Oxford medial UKA remains unknown.

METHODS

We applied finite element (FE) analysis to evaluate the effects of the posterior tibial slope in mobile-bearing UKA on the contact stresses in the superior and inferior surfaces of PE inserts and articular cartilage as well as the forces exerted on the anterior cruciate ligament (ACL). Seven FE models for posterior tibial slopes of -1°, 1°, 3°, 5°, 7°, 9°, and 11° were developed and analyzed under normal-level walking conditions based on this approach.

RESULTS

The maximum contact stresses on both the superior and inferior surfaces of the PE insert decreased as the posterior tibial slope increased. However, the maximum contact stress on the lateral articular cartilage and the force exerted on the ACL increased as the posterior tibial slope increased.

CONCLUSIONS

Increasing the tibial slope led to a reduction in the contact stress on the PE insert. However, a high contact stress on the other compartment and increased ACL force can cause progressive osteoarthritis in the other compartment and failure of the ACL.

Fixed bearing, all-polyethylene tibia, lateral unicompartmental arthroplasty - A final outcome study with up to 28 year follow-up of a single implant

BACKGROUND

Lateral unicompartmental arthroplasty (UKA) constitutes only 5-10% of all unicompartmental replacements performed. Whilst the short and medium term benefits are well documented, there remains concern regarding the higher revision rate when compared with total knee replacement. We report the long term clinical outcome and survivorship of a large series of lateral UKA.

PATIENTS AND METHODS

Between 1974 and 1994, 71 patients (82 knees) underwent a lateral fixed-bearing St Georg Sled UKA. Prospective data was collected pre-operatively and at regular intervals post-operatively using the Bristol Knee Score (BKS), with later introduction of the Oxford Knee (OKS) and Western Ontario MacMaster (WOMAC) scores. Kaplan Meier survival analysis was used, with revision, or need for revision, as end point. 85% of the patients were female. No patients were lost to follow-up.

RESULTS

Functional knee scores improved post-operatively up to 10 years, at which point they demonstrated a steady decline. Survivorship was 72% at 15 years, and 68% at 20 and 25 years. Nineteen knees were revised, with progression of disease in another compartment the commonest reason. There were two revisions due to implant fracture. In patients aged over 70 years at time of index procedure, 81% died with a functioning prosthesis in situ.

CONCLUSION

This represents the longest follow-up of a large series of lateral UKA. Results of this early design of fixed bearing UKA demonstrate satisfactory long term survivorship. In elderly patients, further intervention is rarely required. More contemporary designs or techniques may show improved long term survivorship in time.

[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.

One stage bilateral unicompartmental knee replacement: Similar early clinical outcome with shorter rehabilitation and better resources utilization compared with two stage

Introduction:

There are a lot of debates on the advantages and safety profile of one stage bilateral knee arthroplasty. Most of the studies focus on total knee replacement, and it may not be applied directly to unicompartmental knee replacement (UKR). We would like to compare the early results of one and two stage bilateral UKR in our center.

Methods:

This is a retrospective review of all the bilateral medial UKR done in our center in 2018–2019. Patients’ demographic data, operative time, postoperative blood, length of stay (LOS) and complications were recorded. The number of admissions, pre-operative assessment sessions (PAS), and weeks of post-operative physiotherapy were analyzed. Clinical outcome was measured by Knee society knee score and range of motion (ROM).

Results:

Our center performed 97 UKR in 2018–2019, with 50 UKR performed in 25 patients, among which 16 received one stage while 9 received two stage bilateral UKR. Both groups had similar mean age, BMI, sex ratio, ASA grading, pre-operative knee score and ROM. Patient in the one stage group required only 1 PAS/admission/operation to treat both knees with a mean LOS of 7.3 days and 7.8 weeks of physiotherapy, while those in the two stage group required 2 PAS/admissions/operations with a mean cumulative LOS of 9.8 days and 14.1 weeks of physiotherapy. The mean cumulative operative time was similar for both groups but the one stage group only required 1 operative session. There was no difference in blood loss and there was no transfusion or complication. The post-operative knee score and ROM at 3 and 6 months were similar for both groups.

Conclusion:

In suitable patients with bilateral medial OA knee, one stage bilateral UKR offers simliar early clinical outcome with shorter rehabilitation duration but without increasing complications compared with two stage. Resources can therefore be better utilized.

Effects of contact stress on patellarfemoral joint and quadriceps force in fixed and mobile-bearing medial unicompartmental knee arthroplasty

Background

Unicompartmental knee arthroplasty (UKA) is an effective treatment for end-stage, symptomatic unicompartmental osteoarthritis of the knee joint. However, patellofemoral joint degeneration is a contraindication to medial UKA. Therefore, the objective of this study was to evaluate the biomechanical effect of medial UKA using fixed-bearing (FB) and mobile-bearing (MB) design prostheses on the patellofemoral joint.

Methods

A three-dimensional finite-element model of a normal knee joint was developed using medical image data. We performed statistical analysis for each model. The differences in contact stress on the patellofemoral joint and the quadriceps force between the FB and MB designs were evaluated under a deep-knee-bend condition.

Results

At an early flexion angle, the results of contact stress showed no significant difference between the FB and MB medial UKA models compared with the intact model. However, at high flexion angles, we observed a significant increase in contact stress with the FB models compared with the intact model. On the contrary, in the case of the MB models, we found no statistically significant increment compared with the intact model. A larger quadriceps force was needed to produce an identical flexion angle for both the FB and MB UKA designs than for the intact model. At high flexion angles, a significant increase quadriceps force whit the FB model compared with the intact model.

Conclusions

Our results indicate that with medial UKA, the contact stress increased and greater quadriceps force was applied to the patellofemoral joint. However, performing UKA on a patellofemoral joint with osteoarthritis should not be difficult, unless anterior knee pain is present, because the increase in contact stress is negligible.

Fixed- versus mobile-bearing unicompartmental knee arthroplasty: a meta-analysis

Unicompartmental knee arthroplasty (UKA) can be either a fixed bearing (FB) or a mobile bearing (MB) construct with controversy as to which design is superior. This question is addressed with a systematic review and meta-analysis. A literature search was performed using PubMed, Embase and the Cochrane Library. Studies were reviewed according to the inclusion and exclusion criteria developed in advance. We compared the differences in clinical and radiological outcomes between the FB and MB UKAs. Analyses were performed with the Review Manager and STATA software. A total of 17 studies involving 2612 knees were included. No significant differences were presented between the FB and MB prostheses in clinical and radiological outcomes. However, it was evident that there were differences in the modes and timing of the failures, bearing dislocation led to earlier failures in the MB prosthesis, while the FB prosthesis failed later due to polyethylene wear. There was no evidence of publication bias using the incidence of revisions. There is no significant difference between the FB and MB UKAs; however, there are differences in the modes and timing of failures.

Clinical outcome of bi-unicompartmental knee arthroplasty for both medial and lateral femorotibial arthritis: a systematic review-is there proof of concept?

INTRODUCTION

Unicompartmental knee arthroplasty (UKA) is a well-accepted treatment for isolated unicompartmental osteoarthritis (OA) of the knee. In previous literature, it has been suggested that bi-unicompartmental knee arthroplasty (bi-UKA) which uses two UKA implants in both the medial and lateral compartments of the same knee is a feasible and viable option for the treatment of knee OA. Given the advantages of UKA treatment, it is warranted to review the literature of bi-UKA and discuss the evidence in terms of implant selection, indications, surgical techniques, and outcomes, respectively.

MATERIALS AND METHODS

Following the PRISMA guidelines, PubMed, Medline, Embase, CINAHL, Web of Science, and Cochrane Library were searched for studies presenting outcome of bi-UKA. Studies were included if they reported clinical outcomes using two unicompartmental prostheses for both medial and lateral femorotibial arthritis. Studies with the addition of patellofemoral arthroplasty or concomitant soft-tissue reconstruction and those not published in English were excluded.

RESULTS

In the early literature, the procedure of bi-UKA were performed for very severe OA and rheumatoid arthritis, but indications have evolved to reflect a more contemporary case-mix of knee OA patients. Both mobile and fixed bearing implants have been used, with the latter being the most frequent choice. A medial parapatellar approach for incision and arthrotomy has been the most frequently used technique. The present review found a promising clinical outcome of both simultaneous and staged bi-UKA although the number of long-term follow-up studies was limited.

CONCLUSIONS

Both simultaneous and staged bi-UKA has demonstrated good functional outcomes. However, the volume and level of evidence in general is low for studies captured in this review, and the data on long-term outcomes remain limited. The present review indicates that bi-UKA is a feasible and viable surgical option for bicompartmental femorotibial OA in carefully selected patients.

Unicompartmental knee arthroplasty, an enigma, and the ten enigmas of medial UKA

Unicompartmental knee arthroplasty (UKA) is a bone- and ligament-sparing alternative to total knee arthroplasty in the patients with end-stage single-compartment degeneration of the knee. Despite being a successful procedure, the multiple advantages of UKA do not correlate with its usage, most likely due to the concerns regarding prosthesis survivability, patient selection, ideal bearing design, and judicious use of advanced technology among many others. Therefore, the purpose of this study is to review and summarize the debated literature and discuss the controversies as “Ten Enigmas of UKA.”

Comparison of implant position and joint awareness between fixed- and mobile-bearing unicompartmental knee arthroplasty: a minimum of five year follow-up study

PURPOSE

To compare the implant position and patient-reported outcomes (PROs) regarding joint awareness using the Forgotten Joint Score (FJS) following between fixed-bearing (FB) and mobile-bearing (MB) unicompartmental knee arthroplasty (UKA) with a minimum of five years' follow-up.

METHODS

One hundred fifteen consecutive UKAs (58 FB UKAs and 57 MB UKAs) performed were retrospectively evaluated. We compared the radiographic parameters including component positions and relationships as well as lower extremity alignment. Post-operative clinical outcomes were assessed using Knee Society Score (KSS), the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) score, Tegner activity score, and FJS.

RESULTS

The MB UKA group showed more convergent componentry relationship between femoral and tibial components (p < 0.001). The joint line of the MB UKA group was restored significantly better (p < 0.05). In addition, the positioning of femoral and tibial components of the MB UKA group showed less deviation from the weight-bearing line (WBL) (p < 0.05). Although there were no differences in KSS, WOMAC, and Tegner activity scores between the groups, the MB UKA group showed significantly better FJS than did the FB UKA group at five years post-operatively (p < 0.05).

CONCLUSION

The MB UKA group had a more convergent componentry relationship, less deviation from WBL, better joint-line restoration, and reduced joint awareness than did the FB UKA group at five years follow-up.

Is Mobile-Bearing Medial Unicompartmental Knee Arthroplasty Appropriate for Asian Patients With the Risk of Bearing Dislocation?

BACKGROUND

Mobile-bearing unicompartmental knee arthroplasty (UKA) is an attractive operation for medial unicompartmental knee arthritis, but unexpected bearing dislocation is a drawback. Bearing dislocation occurs more frequently in Asians, whose lifestyle involves deeper knee flexion than Westerners. This study investigated whether mobile-bearing medial UKA is appropriate for Asians by analyzing (1) the rate of bearing dislocation and (2) the results of patients with bearing dislocation.

METHODS

We retrospectively reviewed 531 consecutive mobile-bearing medial UKA in the previous 15 years, including 22 patients with bearing dislocation who had at least 2 years of follow-up. The entire patient cohort was divided into 2 groups: the symmetrical bearing (187 knees) and the anatomic bearing (344 knees) groups. In the anatomic bearing group, patients who underwent surgery using the conventional phase III (283 knees) vs the Microplasty (61 knees) instrumentation systems were compared.

RESULTS

The overall incidence of bearing dislocation was 4.1% (22/531). Patients with the symmetrical bearing displayed a relatively high dislocation rate of 9.6% (18/187), which significantly decreased to 1.1% (4/344) after changing to the anatomic bearing (P < .001). In the anatomic bearing group, the dislocation rate with the conventional phase III system was 1.4% (4/283). There were no bearing dislocations in the Microplasty system group (0%, 0/61) after at least 2 years of follow-up.

CONCLUSION

Although mobile-bearing medial UKA was reported to have a high incidence of bearing dislocation in Asians, this frequency of dislocation is drastically decreased by bearing design and implantation system improvements. We consider mobile-bearing medial UKA appropriate for Asians.

The Effect of Bone Quality on Tibial Component Migration in Medial Cemented Unicompartmental Knee Arthroplasty. A Prospective Cohort Study Using Dual X-Ray Absorptiometry and Radiostereometric Analysis

BACKGROUND

Periprosthetic bone mineral density (BMD) may influence implant fixation and subsequent loosening. Unicompartmental knee arthroplasty (UKA) restores normal knee kinematics and load distribution to the surrounding bone. We studied the influence of systemic and periprosthetic BMD of the proximal tibia on migration of the tibial component of cemented medial UKA.

METHODS

The cohort was dichotomized into a normal BMD group (T-score ≥ -1; n = 37) and a low BMD group (T-score < -1; n = 28) according to World Health Organization criteria. BMD of the proximal tibia and migration of the tibial component were measured with dual X-ray absorptiometry scans and stereoradiographs with 2-year follow-up.

RESULTS

Patients with normal systemic BMD had an 11% to15% higher BMD in all regions of interest (ROIs) compared to patients with low systemic BMD throughout follow-up. Over time, a decrease in periprosthetic BMD in ROI 1-3 was seen for both groups. The operated knees and contralateral knees showed a similar reduction in BMD in all ROIs between preoperative and 24 months. Between 12 and 24 months, the normal BMD group migrated (maximal total point motion) 0.03 mm (95% confidence interval, -0.01, 0.08) and the low BMD group migrated 0.02 mm (95% confidence interval, -0.03, 0.07). Migration over time was not influenced by change in periprosthetic BMD.

CONCLUSION

Migration of cemented medial tibial UKA was low until 24 months and was neither affected by preoperative systemic BMD nor affected by postoperative change in periprosthetic BMD. This suggests good long-term fixation despite an index difference in proximal tibial BMD.

Arthroscopy combined with unicondylar knee arthroplasty for treatment of isolated unicompartmental knee arthritis: A long-term comparison

BACKGROUND

Knee osteoarthritis is the most prevalent form of osteoarthritis and is becoming the main reason for progressive pain in knee joints. Arthroscopy combined with unicondylar knee arthroplasty (UKA) is one of the effective methods for the treatment of severe unicompartmental knee arthritis. This surgical approach gives us the capacity to explore all the articular cavities and plays a vital role in UKA patient selection. However, some scholars think that the surgical procedure is traumatic and may increase the rate of surgical infection, and its clinical efficacy needs further study.

AIM

To compare the clinical effect of arthroscopy combined with UKA and UKA alone for patients suffering from unicompartmental osteoarthritis (OA).

METHODS

A retrospective study was conducted on patients who were diagnosed with unicompartmental OA (Kellgren–Laurence grade ≥ III) and underwent UKA between October 2012 and November 2006. The patients were followed at 3, 6, and 12 mo and every 2 years thereafter. During each follow-up, the radiographic materials, the range of motion of knee and hospital for special surgery (HSS) score, knee society score and knee function score as recorded, and the modes and time of failure and revision details were collected as well.

RESULTS

Data on 104 patients (118 knees), including 54 patients (60 knees) in the arthroscopy combined with UKA group (group A) and 51 (58 knees) in UKA alone group (group B) were collected during an average follow-up duration of 7.25 years, excluding the cases who were lost to follow-up. At the final follow-up, 3 (5.0%) of 60 knees in group A compared with 4 (6.9%) of 58 knees in group B failed and converted to total knee arthroplasty, with no statistically significant difference between the two groups (P = 0.933). The percentage of patients receiving blood transfusion was 40% in group A, significantly lower than that in group B (67.2%; P = 0.003). Total volume of blood transfusion in group A was also significantly lower than that of group B (P = 0.001). Both groups improved significantly after operation in clinical symptoms and functions. HSS score, knee society score, and knee function score increased significantly at the latest follow-up compared to pre-operation in group A, from 59.6 ± 10.9 to 82.7 ± 9.3 (mean difference [MD], 23.2; 95%CI: 19.3-27.0; P = 0.000), 47.3 ± 6.3 to 76.2 ± 13.1 (MD, 28.9; 95%CI: 25.1-32.7; P = 0.000), and 57.5 ± 6.3 to 75.1 ± 19.6 (MD, 17.5; 95% CI: 12.1-23.0; P = 0.000); and in group B, from 59.3 ± 15.6 to 84.3 ± 10.1 (MD, 23.7; 95%CI: 18.9-28.5; P = 0.000), 49.1 ± 9.2 to 75.1 ± 13.2 (MD, 24.7; 95%CI: 19.9-29.5; P = 0.000), and 59.3 ± 9.0 to 77.4 ± 13.8 (MD, 17.2; 95%CI: 12.8-21.6; P = 0.000).

CONCLUSION

Arthroscopy combined with UKA and UKA alone both provide benefits in clinical symptom improvement and alignment correction. Arthroscopy combined with UKA does not increase the infection probability and surgical complications, and has an advantage in reducing the total volume of blood transfusion and the percentage of patients receiving blood transfusion.

Comparison of Fixed-Bearing and Mobile-Bearing Unicompartmental Knee Arthroplasty: A Systematic Review and Meta-Analysis

BACKGROUND

Prior studies have compared fixed-bearing unicompartmental knee arthroplasty (FB-UKA) with mobile-bearing UKA (MB-UKA), suggesting that both procedures have good clinical outcomes. However, which treatment is more beneficial for patients is controversial. The purpose of our study is to evaluate the postoperative outcomes, including the revision rate, complications, functional results, range of motion, and femoral-tibial angle, between the 2 procedures.

METHODS

We searched the MEDLINE, EMBASE, Cochrane Library, and Web of Science databases starting from August 2017 to May 2018. The publication date of articles was not restricted. Before we submit our contribution, we have re-searched it again. Articles that directly compared the postoperative outcomes of the 2 prosthesis type were included.

RESULTS

A total of 15 comparative studies were included in our meta-analysis. The pooled data indicated no differences between the 2 operation modes in terms of revision rates, complications, and knee function, but earlier failure occurred more frequently with the MB design.

CONCLUSION

Both the arthroplasty types provided satisfactory clinical results for patients with classic indications. However, MB-UKA tended to fail in early postoperative years whereas fixed-bearing UKA in later postoperative years. Therefore treatment options should be carefully considered for each patient, and surgeons should still use their personal experience when deciding between these options.

Long-term outcomes of unicompartmental knee arthroplasty in patients requiring high flexion: an average 10-year follow-up study

INTRODUCTION

To evaluate the long-term survival of unicompartmental knee arthroplasty (UKA) in the Asian population and assess differences in clinical outcomes between mobile- and fixed-bearing UKA.

MATERIALS AND METHODS

Among 111 cases of UKA that were performed by 1 surgeon from January 2002 to December 2009, we retrospectively reviewed 96 cases (36 mobile-bearing, 62 fixed-bearing) for this study. We examined cause of revision or failure, type of reoperation/revision, and duration from the surgery date to the revision upon reviewing the medical record. Survival analysis was conducted using the Kaplan-Meier method. Functional outcomes were evaluated based on range of motion and patient-reported outcome (PRO) measures (Knee Injury and Osteoarthritis Outcome Score) for cases with at least 8 years of follow-up (average, 10.2 years).

RESULTS

Overall, the 10-year survival was 88% [95% confidence interval (CI) 0.81-0.95], and the estimated mean survival time was 13.4 years (95% CI 12.5-14.2). In a comparison of survival between the mobile- and fixed-bearing groups, the former had a 10-year survival of 85% (95% CI, 0.72-0.97) and an estimated mean survival time of 13.5 years (95% CI 12.2-14.7) and the latter had a 10-year survival of 90% (95% CI 0.82-0.99) and an estimated mean survival time of 13.4 years (95% CI 12.3-14.4). Thus, there was no significant difference in survival between the two groups (log-rank test, p = 0.718). In addition, no significant difference in functional outcomes was observed between the two groups (p > 0.05 for all).

CONCLUSIONS

UKA performed in the Asian population showed a relatively good functional outcome and survival rate at an average 10-year follow-up. No difference in survival and PROs was observed according to the bearing type. Although the present study demonstrated a good survival rate, similar to that in other Western studies, further studies investigating the impact of the Asian lifestyle on the long-term survival of UKA is necessary.

Differences in Risk of Revision and Mortality Between Total and Unicompartmental Knee Arthroplasty. The Influence of Hospital Volume

BACKGROUND

The volume of arthroplasties performed in a hospital by year has an influence on the outcomes of total knee arthroplasty (TKA) and unicompartmental knee arthroplasty (UKA). The aims of this study are (1) to evaluate and compare the risk of revision and mortality of TKA and UKA and (2) to assess whether hospital volume is related to differences in revision risk and mortality.

METHODS

All individuals recorded in the Catalan Arthroplasty Register between 1/1/2005 and 31/12/2016, diagnosed with osteoarthritis, undergoing cemented TKA and UKA were included. A propensity score matching method was used to obtain comparable cohorts, including 2374 matched prostheses overall. Hospital volume was considered as a dichotomous variable (lower/higher). Descriptive analyses were done before and after matching. Risks of revision and mortality at 30 days, 90 days, 1, 3, and 5 years were calculated and competing risks models and Cox models were fitted.

RESULTS

For the population as a whole, higher risk of revision (sub-hazard ratio, 1.98; 95% confidence interval, 1.25-3.17) was found in UKA than in TKA but higher mortality was not. Considering the volume groups, significantly higher risk of revision in UKA than TKA was found in the lower-volume group only (sub-hazard ratio, 1.95; 95% confidence interval, 1.11-3.44). No differences in mortality between TKA and UKA were found in either group.

CONCLUSION

Mortality and revision rates after TKA and UKA at higher-volume hospitals are similar. UKAs performed at lower-volume hospitals have higher revision rates. Volume-dependent specialization thus might help to reduce revision and mortality after surgery.

Medial Unicompartmental Arthroplasty of the Knee

Indications for medial unicompartmental knee arthroplasty (UKA) have expanded over the past two decades. Proposed advantages include faster recovery, improved kinematics, and better functional outcomes compared with total knee arthroplasty (TKA) in age-matched control subjects. A focused preoperative examination and imaging is essential to identify appropriate surgical candidates. No difference has been demonstrated between fixed- and mobile-bearing implants for implant survivorship or patient-reported outcomes. The most common reasons for conversion to a TKA are aseptic loosening and progression of osteoarthritis. Ten-year survival for UKA in cohort studies has shown to be >90% with outcomes after conversion to TKA being similar to outcomes for revision TKA. Registries have consistently shown lower implant survival for UKA compared with that for TKA, which is likely secondary to use of several different implants by surgeons of varying levels of experience. UKA has the potential to be a cost-effective alternative to TKA in certain patient populations when performed at high-volume centers with advanced surgical techniques.

How long does a knee replacement last? A systematic review and meta-analysis of case series and national registry reports with more than 15 years of follow-up

BACKGROUND

Knee replacements are the mainstay of treatment for end-stage osteoarthritis and are effective. Given time, all knee replacements will fail and knowing when this failure might happen is important. We aimed to establish how long a knee replacement lasts.

METHODS

In this systematic review and meta-analysis, we searched MEDLINE and Embase for case series and cohort studies published from database inception until July 21, 2018. Articles reporting 15 year or greater survival of primary total knee replacement (TKR), unicondylar knee replacement (UKR), and patellofemoral replacements in patients with osteoarthritis were included. Articles that reviewed specifically complex primary surgeries or revisions were excluded. Survival and implant data were extracted, with all-cause survival of the knee replacement construct being the primary outcome. We also reviewed national joint replacement registry reports and extracted the data to be analysed separately. In the meta-analysis, we weighted each series and calculated a pooled survival estimate for each data source at 15 years, 20 years, and 25 years, using a fixed-effects model. This study is registered with PROSPERO, number CRD42018105188.

FINDINGS

From 4363 references found by our initial search, we identified 33 case series in 30 eligible articles, which reported all-cause survival for 6490 TKRs (26 case series) and 742 UKRs (seven case series). No case series reporting on patellofemoral replacements met our inclusion criteria, and no case series reported 25 year survival for TKR. The estimated 25 year survival for UKR (based on one case series) was 72·0% (95% CI 58·0-95·0). Registries contributed 299 291 TKRs (47 series) and 7714 UKRs (five series). The pooled registry 25 year survival of TKRs (14 registries) was 82·3% (95% CI 81·3-83·2) and of UKRs (four registries) was 69·8% (67·6-72·1).

INTERPRETATION

Our pooled registry data, which we believe to be more accurate than the case series data, shows that approximately 82% of TKRs last 25 years and 70% of UKRs last 25 years. These findings will be of use to patients and health-care providers; further information is required to predict exactly how long specific knee replacements will last.

FUNDING

The National Joint Registry for England, Wales, Northern Ireland, and Isle of Man and the Royal College of Surgeons of England.

A Comparison of Mobile and Fixed-Bearing Unicompartmental Knee Arthroplasty at a Minimum 10-Year Follow-up

BACKGROUND

The long-term survivorship and functional outcomes of the mobile-bearing (MB) compared to the fixed-bearing (FB) unicompartmental knee arthroplasty (UKA) implant design remain a topic of debate. The aim of the current study was to compare the survivorship and functional outcomes of MB and FB UKA at a minimum 10-year follow-up.

METHODS

We retrospectively reviewed 106 consecutive medial UKAs (89 patients) from our institution with a minimum 10-year follow-up. The 38 MB and 68 FB knees had follow-up of 14.2 years (12.9-15.5) and 11.5 years (10.2-15.1), respectively. Validated patient-reported outcomes and radiographs were evaluated as were etiology, timing, and complexity of revision. Kaplan-Meier 10-year survival was calculated with revision to total knee arthroplasty as the end point.

RESULTS

The 10-year survival was 82.9% (95% confidence interval [CI] 65.8-91.9) for MB and 90.9% (95% CI 79.4-96.2) for FB UKA (P = .102), and 88.0% (95% CI 79.3-93.2) for the entire cohort. Patient outcomes were similar between groups, as were timing and etiologies for revision to total knee arthroplasty. One-third of revisions required either stems or tibial augments, and of these, all were of MB design.

CONCLUSION

Survival and functional outcomes were similar between MB and FB designs. One-third of revisions required either stems or augments, all were of MB design.

Larger range of motion and increased return to activity, but higher revision rates following unicompartmental versus total knee arthroplasty in patients under 65: a systematic review

PURPOSE

Due to the lack of comparative studies, a systematic review was conducted to determine revision rates of unicompartmental and total knee arthroplasty (UKA and TKA), and compare functional outcomes, range of motion and activity scores in patients less than 65 years of age.

METHODS

A literature search was performed using PubMed, Embase, and Cochrane systems since 2000. 27 UKA and 33 TKA studies were identified and included. Annual revision rate (ARR), functional outcomes, and return to activity were assessed for both types of arthroplasty using independent t tests.

RESULTS

Four level I studies, 12 level II, 16 level III, and 29 level IV were included, which reported on outcomes in 2224 UKAs and 4737 TKAs. UKA studies reported 183 revisions, yielding an ARR of 1.00 and extrapolated 10-year survivorship of 90.0%. TKA studies reported 324 TKA revisions, resulting in an ARR of 0.53 and extrapolated 10-year survivorship of 94.7%. Functional outcomes scores following UKA and TKA were equivalent, however, following UKA larger ROM (125° versus 114°, p = 0.004) and higher UCLA scores were observed compared to TKA (6.9 versus 6.0, n.s.).

CONCLUSION

These results show that good-to-excellent outcomes can be achieved following UKA and TKA in patients less than 65 years of age. A higher ARR was noted following UKA compared to TKA. However, improved functional outcomes, ROM and return to activity were found after UKA than TKA in this young population. Comparative studies are needed to confirm these findings and assess factors contributing to failure at the younger patient population. Outcomes of UKA and TKA in patients younger than 65 years are both satisfying, and therefore, both procedures are not contraindicated at younger age. UKA has several important advantages over TKA in this young and frequently more active population.

LEVEL OF EVIDENCE

IV.

Midterm Survivorship and Patient Satisfaction of Robotic-Arm-Assisted Medial Unicompartmental Knee Arthroplasty: A Multicenter Study

BACKGROUND

Studies have showed improved accuracy of lower leg alignment, precise component position, and soft-tissue balance with robotic-assisted unicompartmental knee arthroplasty (UKA). No studies, however, have assessed the effect on midterm survivorship. Therefore, the purpose of this prospective, multicenter study was to determine midtem survivorship, modes of failure, and satisfaction of robotic-assisted medial UKA.

METHODS

A total of 473 consecutive patients (528 knees) underwent robotic-arm-assisted medial UKA surgery at 4 separate institutions between March 2009 and December 2011. All patients received a fixed-bearing, metal-backed onlay tibial component. Each patient was contacted at minimum 5-year follow-up and asked a series of questions to determine survival and satisfaction. Kaplan-Meier method was used to determine survivorship.

RESULTS

Data were collected for 384 patients (432 knees) with a mean follow-up of 5.7 years (5.0-7.7). The follow-up rate was 81.2%. In total, 13 revisions were performed, of which 11 knees were converted to total knee arthroplasty and in 2 cases 1 UKA component was revised, resulting in 97% survivorship. The mean time to revision was 2.27 years. The most common failure mode was aseptic loosening (7/13). Fourteen reoperations were reported. Of all unrevised patients, 91% was either very satisfied or satisfied with their knee function.

CONCLUSION

Robotic-arm-assisted medial UKA showed high survivorship and satisfaction at midterm follow-up in this prospective, multicenter study. However, in spite of the robotic technique, early fixation failure remains the primary cause for revision with cemented implants. Comparative studies are necessary to confirm these findings and compare to conventional implanted UKA and total knee arthroplasty.

Predictors of Midterm Outcomes after Medial Unicompartmental Knee Arthroplasty in Asians

Background

This study was designed to evaluate predictors of good outcomes following medial unicompartmental knee arthroplasty (UKA) in Asian patients.

Methods

Registry data of patients who underwent primary unilateral medial UKA from 2006 to 2011 were collected. Outcomes studied were the Oxford Knee Score (OKS) and the Physical Component Score (PCS) of the Short Form 36 (SF-36) questionnaire. These outcome scores were collected prospectively, pre- and postoperatively up to 5 years. Good outcome was defined as an overall improvement in score greater than or equal to the minimal clinically important difference (MCID). The MCID for the OKS was 5 while the MCID for the PCS was 10. Regression analysis was used to identify predictors of good outcomes following medial UKA.

Results

Primary medial UKA was performed in 1,075 patients. Higher (poorer) preoperative OKS (odds ratio [OR], 1.27; p < 0.001), lower (poorer) preoperative PCS (OR, 1.08; p < 0.001), lower (poorer) preoperative Knee Society Knee Score (KSKS; OR, 1.02; p < 0.001) and higher (better) preoperative SF-36 Mental Component Score (MCS; OR, 1.02; p < 0.001) were significant predictors of good outcomes.

Conclusions

Patients with poorer OKS, PCS and KSKS and better SF-36 MCS preoperatively tended to achieve good outcomes by the MCID criterion at 5 years following the index surgery.

The Interaction of Caseload and Usage in Determining Outcomes of Unicompartmental Knee Arthroplasty: A Meta-Analysis

BACKGROUND

Outcomes after unicompartmental knee arthroplasty (UKA) are variable and influenced by caseload (UKA/y) and usage (percentage of knee arthroplasty that are UKA), which relates to indications. This meta-analysis assesses the relative importance of these factors.

METHODS

MEDLINE (Ovid), Embase (Ovid), and Web of Science (ISI) were searched for consecutive series of cemented Phase 3 Oxford medial UKA. The primary outcome was revision rate/100 observed component years (% pa) with subgroup analysis based on caseload and usage.

RESULTS

Forty-six studies (12,520 knees) with an annual revision-rate ranging from 0% to 4.35% pa, mean 1.21% pa (95% confidence interval [CI], 0.97-1.47), were identified. In series with mean follow-up of 10-years, the revision-rate was 0.63% pa (95% CI, 0.46-0.83), equating to a 94% (95% CI, 92%-95%) 10-year survival. Aseptic loosening, lateral arthritis, bearing dislocation, and unexplained pain were the predominant failure mechanisms with revision for patellofemoral problems and polyethylene wear exceedingly rare. The lowest revision-rates were achieved with caseload >24 UKA/y (0.88% pa; 95% CI, 0.63-1.61) and usage >30% (0.69% pa; 95% CI, 0.50-0.90). Usage was more important than caseload; with high usage (≥20%), the revision-rate was low, whether the caseload was high (>12 UKA/y) or low (≤12 UKA/y; (0.94% pa; 95% CI, 0.69-1.23 and 0.85% pa; 95% CI, 0.65-1.08), respectively); with low usage (<20%), the revision-rate was high, whether the caseload was high or low (1.58% pa; 95% CI, 0.57-3.05 and 1.76% pa; 95% CI, 1.21-2.41, respectively).

CONCLUSION

To achieve optimum results, surgeons, whether high or low caseload, should adhere to the recommended indications such that ≥20%, or ideally >30% of their knee arthroplasties are UKA. If they do this, then they can expect to achieve results similar to those of the long-term series, which all had high usage (>20%) and an average 10-year survival of 94%.

Does new instrumentation improve radiologic alignment of the Oxford® medial unicompartmental knee arthroplasty?

BACKGROUND

A new instrument system has been introduced to improve the accuracy and reproducibility of implant positioning in Oxford® unicompartmental knee arthroplasty (UKA). This study aimed to determine if the new instrumentation could improve postoperative implant positioning and limb alignment, and reduce the occurrence of outliers in Oxford® UKA.

METHODS

A total of 77 cases of Oxford® UKA with the new instrumentation were included. Individual matching for the conventional instrument group was performed according to age, sex, and body mass index. Postoperative radiological variables, including the hip-knee-ankle angle and the varus/valgus and flexion/extension angles of the femoral and tibial implants, were measured and compared between the new instrumentation group and the conventional group. The outliers in implant positions and postoperative complications were also compared.

RESULTS

No significant between-group differences were observed in terms of lower limb alignment and tibial implant alignment. However, statistically significant differences were identified in the varus/valgus and flexion/extension angles of the femoral implant (P=0.01 and P<0.001, respectively). More outliers were observed in the flexion/extension angles of the femoral and tibial implants in the new instrumentation group. Eight meniscal bearing dislocations and three lateral compartmental degenerative changes were found in the conventional group, while there were two meniscal bearing dislocations in the new instrumentation group during the study period.

CONCLUSION

The present study did not confirm any benefit of the new instrument system in terms of postoperative limb alignment, positioning of the implant, or reducing outliers beyond the use of the conventional instruments.

Comparison of articular and backside polyethylene wear in mobile bearing unicompartmental knee replacement

BACKGROUND

Unicompartmental knee replacement (UKR) is an alternative to total knee replacement for selected patients with isolated medial or lateral compartment osteoarthritis. One of the most popular UKR implants was introduced as a mobile-bearing design in part to reduce polyethylene wear. However, backside wear of the mobile-bearing implant has not been examined independently from the articular surface.

METHODS

Sixteen retrieved polyethylene inserts from a medial mobile-bearing UKR from 16 patients were examined after an average of 4.2years implantation (range 1.5 to 10.0years). Reasons for revision included aseptic loosening, pain, and progression of osteoarthritis. Each retrieved insert was evaluated using visual damage scoring across the articular and backside surfaces. Inserts were also micro-CT scanned and compared to a reference insert of the same size, to measure wear on the articular and backside surfaces.

RESULTS

The total damage scores were greater (p=0.01) on the articular surface (27.2±5.7 (standard deviation)) than the backside surface (23.8±6.2). Burnishing, abrasions, and pitting were the most common damage modes on both surfaces, with only pitting greater (p=0.03) on the articular surface than the backside surface. There was no difference (p=0.46) in wear rate between the articular surface (0.028±0.025mm/year) and backside surface (0.029±0.017mm/year).

CONCLUSIONS

The retrieved mobile-bearing UKR polyethylenes demonstrated good overall wear resistance, with no evidence of severe damage. However, backside wear was equal to articular wear, suggesting that the backside surface is a potential source of polyethylene wear debris.

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.

[Fixed bearing unicondylar arthroplasty in medial osteoarthritis of the knee]

OBJECTIVE

The unicondylar prosthesis replaces the medial femerotibial compartment only, the part presenting with osteoarthritic changes. The remaining compartments of the knee present less osteoarthritic changes and thus can be preserved.

INDICATIONS

Osteoarthritis of the medial femorotibial compartment is the ideal indication for unicondylar arthroplasty. The knee should show an intraarticular deformity, which means the malalignment is caused by the osteoarthritic changes of the medial compartment.

CONTRAINDICATIONS

Malalignment of >5°, flexion contracture of >10°, mediolateral instability and symptomatic osteoarthritis of a second compartment should be considered as contraindications for unicondylar arthroplasty.

SURGICAL TECHNIQUE

In the current article, implantation of the BalanSys® system is presented. Femoral bony resection is solely ligament balanced. The technique allows creation of an optimal extension and flexion gap. Bone cuts were performed using a soft tissue tension device for measuring the extension and flexion gap.

POSTOPERATIVE MANAGEMENT

Full weight bearing on crutches is allowed immediately after surgery without restriction in flexion. Crutches are recommended for 4 weeks in order to compensate for neuromuscular deficits. Anticoagulation is recommended for 11-14 days according to the AWMF guidelines (S3 guidelines, Release:15 October 2015).

RESULTS

The clinical follow-up after 2 years showed 87 ± 13 points in the knee score and 80 ± 10 points in the function score. The mean range of motion increased from 113°±24° prior to surgery to 122°±23° after surgery. A preoperative extension deficit of 10° was observed in 9 patients and reduced postoperatively in 3 patients.

A survival analysis of 1084 knees of the Oxford unicompartmental knee arthroplasty: a comparison between consultant and trainee surgeons

Aims

The aim of this to study was to compare the previously unreported long-term survival outcome of the Oxford medial unicompartmental knee arthroplasty (UKA) performed by trainee surgeons and consultants.

Patients and Methods

We therefore identified a previously unreported cohort of 1084 knees in 947 patients who had a UKA inserted for anteromedial knee arthritis by consultants and surgeons in training, at a tertiary arthroplasty centre and performed survival analysis on the group with revision as the endpoint.

Results

The ten-year cumulative survival rate for revision or exchange of any part of the prosthetic components was 93.2% (95% confidence interval (CI) 86.1 to 100, number at risk 45). Consultant surgeons had a nine-year cumulative survival rate of 93.9% (95% CI 90.2 to 97.6, number at risk 16). Trainee surgeons had a cumulative nine-year survival rate of 93.0% (95% CI 90.3 to 95.7, number at risk 35). Although there was no differences in implant survival between consultants and trainees (p = 0.30), there was a difference in failure pattern whereby all re-operations performed for bearing dislocation (n = 7), occurred in the trainee group. This accounted for 0.6% of the entire cohort and 15% of the re-operations.

Conclusion

This is the largest single series of the Oxford UKA ever reported and demonstrates that good results can be achieved by a heterogeneous group of surgeons, including trainees, if performed within a high-volume centre with considerable experience with the procedure.

Cite this article: Bone Joint J 2016;(10 Suppl B):22–7.