Comparison of the 10-year outcomes of cemented and cementless unicompartmental knee replacements: data from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man

The effect of fixation type on periprosthetic fractures in high-risk patients who have osteoporosis undergoing total joint arthroplasty

Introduction

Minimizing the burden of periprosthetic fractures (PFF) following total joint arthroplasty (TJA) with regard to morbidity and mortality remains an outcome of interest. Patient and surgical risk factors, including osteoporosis and fixation type, have not truly been optimized in patients undergoing TJA as a means to reduce the risk of PFF. As such, we examined: (1) What percentage of patients who underwent THA and total knee arthroplasty (TKA) met the criteria for osteoporosis screening? (2) How did the 5-year rate of PFF and fragility fracture differ in the high-risk and low-risk groups for osteoporosis between the cemented and cementless cohorts? (3) What percentage of the aforementioned patients received a dual x-ray absorptiometry (DEXA) scan before THA or TKA?

Methods

We queried an all-payer, national database from April 1, 2016 to December 31, 2021, to identify high-risk and low-risk patients who underwent TJA with a cementless or cemented fixation. High-risk patients met at least one of the following criteria: men at least 70 years old, women at least 65 years old, or patients at least 60 years old who have the following: tobacco use, alcohol abuse, body mass index <18.5, prior fragility fracture, chronic systemic corticosteroids, or genetic condition affecting sex hormones or bone mineral density. Exclusion criteria were a diagnosis of malignancy, high-energy events (motor vehicle collision), those who underwent TJA indicated for fracture, patients less than 50 years old, those who had a prior diagnosis of or treatment for osteoporosis, and a minimum follow-up of less than 2 years.

Results

There were 384,783 patients (67.1 %) who underwent cementless TKA and 67,774 patients (11.8 %) who underwent cementless TKA who were considered high risk. Additionally, there were 62,505 patients (10.9 %) who underwent cemented THA and 58,667 patients (10.2 %) who underwent cementless THA and were considered high risk. The cementless cohort had a 5-year periprosthetic fracture risk following TKA of 7.8 % (95 % CI, 5.56 to 10.98) in comparison to 4.30 % in the cemented cohort (85 % CI, 3.98 to 4.65), P < 0.0001. The high-risk cementless cohort had a 5-year periprosthetic fracture risk following THA of 7.9 % (95 % confidence interval (CI), 6.87 to 9.19) in comparison to 7.78 % in the cemented cohort (85 % CI, 6.77 to 8.94), P < 0.0001.

Conclusion

There is an increased risk of PFF at 5 years following TKA in patients at high risk for osteoporosis undergoing cementless fixation in comparison to cemented fixation. There is an increased risk of PFF at 5 years following THA in patients at high risk for osteoporosis for both cementless fixation and cemented fixation, but no clinically meaningful difference between the two groups. Addressing the shortcomings of the underutilization of bone density scans and better selecting appropriate patients for TJA based on bone quality and fracture risk can help expedite the process of improving the current state of practice.

A Matched Comparison of Implant and Functional Outcomes of Cemented and Cementless Unicompartmental Knee Replacements: A Study from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man and the Hospital Episode Statistics Patient Reported Outcome Measures Database

BACKGROUND

Unicompartmental knee replacement (UKR) is an effective treatment for end-stage medial compartment osteoarthritis, but there can be problems with fixation. The cementless UKR was introduced to address this issue. It is unknown how its functional outcomes compare with those of the cemented version on a national scale. We performed a matched comparison of the clinical and functional outcomes of cementless and cemented UKRs.

METHODS

Using the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man (NJR), 14,764 Oxford UKRs with linked data regarding patient-reported outcomes were identified. A total of 6,906 UKRs (3,453 cemented and 3,453 cementless) were propensity score matched on the basis of patient, surgical, and implant factors.

RESULTS

The 10-year cumulative implant survival rate was 93.0% (95% confidence interval [CI], 90.0% to 95.1%) for cementless UKRs and 91.3% (95% CI, 89.0% to 93.0%) for cemented UKRs. The cementless UKR group had a significantly lower revision risk (hazard ratio [HR], 0.74; p = 0.02). Subgroup analyses showed a stronger effect size (HR, 0.66) among UKRs performed by high-caseload surgeons (i.e., surgeons performing ≥30 UKRs/year). In the overall cohort, the postoperative Oxford Knee Score (OKS) in the cementless group (mean and standard deviation, 39.1 ± 8.7) was significantly higher (p = 0.001) than that in the cemented group (38.5 ± 8.6). The cementless group gained a mean of 17.6 ± 9.3 points in the OKS postoperatively and the cemented group gained 16.5 ± 9.6 points, with a difference of 1.1 points between the groups (p < 0.001). The difference in OKS points gained postoperatively was highest among UKRs performed by high-caseload surgeons, with the cementless group gaining 1.8 points more (p < 0.001) than the cemented group.

CONCLUSIONS

The cementless UKR demonstrated better 10-year implant survival and postoperative functional outcomes than the cemented UKR. The difference was largest among UKRs performed by high-caseload surgeons, with the cementless fixation group having an HR for revision of 0.66 and an approximately 2-point greater improvement in the OKS compared with the cemented fixation group.

LEVEL OF EVIDENCE

Prognostic Level III . See Instructions for Authors for a complete description of levels of evidence.

[Research progress on unicompartmental knee arthroplasty for elderly patients with knee osteoarthritis]

Objective

To conclude the research progress of unicompartmental knee arthroplasty (UKA) in the treatment of elderly patients with knee osteoarthritis (KOA).

Methods

The literature on UKA at home and abroad in recent years was reviewed to summarize the clinical characteristics of elderly patients with KOA, perioperative management (including evaluating indications preoperatively, intraoperative prosthesis selection, postoperative complication management, etc).

Results

Through reasonable preoperative evaluation, prosthesis selection, and advanced perioperative management, for elderly patients with KOA who meet the indications, UKA can be considered. Compared with total knee arthroplasty, the incidence of postoperative complications in elderly patients undergoing UKA is lower, joint awareness is reduced, functional improvement and satisfaction are higher. Meanwhile, choosing appropriate prostheses and fixation methods can lead to a good survival rate.

Conclusion

UKA can provide a safe and effective treatment option for elderly patients with KOA within a certain range of indications.

A Comparison of the Periprosthetic Fracture Rate of Cemented and Cementless Mobile Bearing Unicompartmental Knee Arthroplasties: An Analysis of Data From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man

BACKGROUND

Periprosthetic fractures are rare but serious complications of unicompartmental knee arthroplasty (UKA). Although cementless UKA has a lower risk of loosening than cemented, there are concerns that tibial fracture risk may be higher given the reliance on interference fit for primary stability. The risk of fracture and the effect of surgical fixation are currently unknown. We compared the periprosthetic fracture rate following cemented and cementless UKA surgery.

METHODS

A total of 14,122 medial mobile-bearing UKAs (7,061 cemented and 7,061 cementless) from the National Joint Registry and Hospital Episodes Statistics database were propensity score-matched. Cumulative fracture rates were calculated and Cox regressions were used to compare fixation groups.

RESULTS

The three-month periprosthetic fracture rates were similar (P = .80), being 0.10% in the cemented group and 0.11% in the cementless group. The fracture rates were highest during the first three months postoperatively, but then decreased and remained constant between one and 10 years after surgery. The one-year cumulative fracture rates were 0.2% (confidence interval [CI]: 0.1 to 0.3) for cemented and 0.2% (CI: 0.1 to 0.3) for cementless cases. The 10-year cumulative fracture rates were 0.8% (CI: 0.2 to 1.3) and 0.8% (CI: 0.3 to 1.3), respectively. The hazard ratio during the whole study period was 1.06 (CI: 0.64 to 1.77; P = .79).

CONCLUSIONS

The periprosthetic fracture rate following mobile bearing UKA surgery is low, being about 1% at 10 years. There were no significant differences in fracture rates between cemented and cementless implants after matching. We surmise that surgeons are aware of the higher theoretical risk of early fracture with cementless components and take care with tibial preparation.

LEVELS OF EVIDENCE

III.

Periprosthetic tibial fracture as a complication of unicompartmental knee arthroplasty: Current insights

Periprosthetic fracture following knee arthroplasty is a rare but devastating complication associated with significant morbidity. With unicompartmental knee arthroplasty being performed far less frequently than total knee arthroplasty, periprosthetic fracture following unicompartmental knee arthroplasty presents a particular challenge to orthopaedic surgeons, due to clinical unfamiliarity and sparsity of literature. An up-to-date review of the epidemiology, risk factors, and management strategies for PPF after UKA is presented.

Advantages and limitations of mobile-bearing unicompartmental knee arthroplasty: an overview of the literature

INTRODUCTION

Interest in unicompartmental knee arthroplasty (UKA) has recently grown. Mobile bearing UKA, in which the bearing is not fixed but rather perfectly conforms with femoral and tibial components and moves completely passively between the femoral and tibial implant, has now been used for approximately half a century.

AREAS COVERED

Alongside the recognized advantages of UKA, the mobile-bearing variant benefits from an extremely low rate of polyethylene wear and tolerable minor malalignment. Revision rates for UKA have been reported to exceed those of total knee arthroplasty, but long-term survival rates and outcomes from mobile-bearing UKA have been found to be satisfactory. In addition to the lateral osteoarthritis and loosening, which are main complications of UKA, bearing dislocation is a specific complication of mobile bearing UKA. Fractures and valgus subsidence are more prevalent than in the cementless UKA. While these continue to be features to be addressed, they have been partially solved.

EXPERT OPINION

Given the manifold benefits of UKA, its application could be extended to a larger patient population. Successful outcomes rely on careful patient selection and the surgeon's extensive familiarity with the procedure. Looking ahead, the incorporation of robotic surgery, already a feature of some fixed-bearing UKAs, might shape the future trajectory of mobile-bearing UKA.

A Comparison of the Periprosthetic Fracture Rate of Cemented and Cementless Total Knee Arthroplasties: An Analysis of Data From the National Joint Registry

BACKGROUND

Periprosthetic fractures are serious complications of knee arthroplasty often requiring complex surgery. There is concern of increased periprosthetic fracture risk with cementless components given the reliance on interference fit for primary stability. It is unknown how the periprosthetic fracture risk compares between cemented and cementless total knee arthroplasties (TKAs).

METHODS

A total of 22,477 cemented and 22,477 cementless TKAs from the National Joint Registry and Hospital Episodes Statistics database were propensity score matched on patient and surgical factors. Cumulative periprosthetic fracture rates were calculated using Kaplan-Meier analyses and compared with Cox regressions. Subgroup analyses were performed in different age, body mass index, and sex groups.

RESULTS

The 3-month fracture rate in the cemented and cementless TKA groups were 0.02% and 0.04%, respectively. At 10 years, the cumulative fracture rate after cemented TKA was 1.2%, and after cementless was 1.4%. During the study period, there were no significant differences in fracture rates between cemented and cementless TKAs with a hazards ratio 1.14 (confidence interval 0.94 to 1.37, P = .20) at 10 years postoperatively. There were no significant differences in fracture rates between fixation types on subgroup analyses of sex, body mass index, and age groups. Female sex was a risk factor for fracture in both cemented (odds ratio 2.35, P < .001) and cementless TKAs (odds ratio 2.97, P < .001).

CONCLUSIONS

The periprosthetic fracture rates following cemented and cementless TKA surgery are low being approximately 1.2% and 1.4%, respectively at 10 years. There were no significant differences in periprosthetic fracture rates requiring readmission between cemented and cementless TKAs.

LEVEL OF EVIDENCE

III.

Comparison of the early postoperative outcomes of cementless and cemented medial unicompartmental knee arthroplasty

Aims

The primary objective of this registry-based study was to compare patient-reported outcomes of cementless and cemented medial unicompartmental knee arthroplasty (UKA) during the first postoperative year. The secondary objective was to assess one- and three-year implant survival of both fixation techniques.

Methods

We analyzed 10,862 cementless and 7,917 cemented UKA cases enrolled in the Dutch Arthroplasty Registry, operated between 2017 and 2021. Pre- to postoperative change in outcomes at six and 12 months' follow-up were compared using mixed model analyses. Kaplan-Meier and Cox regression models were applied to quantify differences in implant survival. Adjustments were made for patient-specific variables and annual hospital volume.

Results

Change from baseline in the Oxford Knee Score (OKS) and activity-related pain was comparable between groups. Adjustment for covariates demonstrated a minimally greater decrease in rest-related pain in the cemented group (β = -0.09 (95% confidence interval (CI) -0.16 to -0.01)). Cementless fixation was associated with a higher probability of achieving an excellent OKS outcome (> 41 points) (adjusted odds ratio 1.2 (95% CI 1.1 to 1.3)). The likelihood of one-year implant survival was greater for cemented implants (adjusted hazard ratio (HR) 1.35 (95% CI 1.01 to 1.71)), with higher revision rates for periprosthetic fractures of cementless implants. During two to three years' follow-up, the likelihood of implant survival was non-significantly greater for cementless UKA (adjusted HR 0.64 (95% CI 0.40 to 1.04)), primarily due to increased revision rates for tibial loosening of cemented implants.

Conclusion

Cementless and cemented medial UKA led to comparable improvement in physical function and pain reduction during the initial postoperative year, albeit with a greater likelihood of achieving excellent OKS outcomes after cementless UKA. Anticipated differences in early physical function and pain should not be a decisive factor in the choice of fixation technique. However, surgeons should consider the differences in short- and long-term implant survival when deciding which implant to use.

Unicompartmental knee replacement: controversies and technical considerations

BACKGROUND

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

METHODS

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

RESULT

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

CONCLUSION

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

Undersizing of the tibial component in Oxford unicompartmental knee arthroplasty (UKA) increases the risk of periprosthetic fractures

INTRODUCTION

Tibial periprosthetic fractures (TPF) after unicompartmental knee arthroplasty (UKA) are a rare condition that affects about 1% of cases. Known risk factors include age, sex, body mass index (BMI), and bone density, as well as surgical technique and prosthesis design. The purpose of the study was to determine if undersizing of the tibial component in relation to the femoral component increases the risk of tibial periprosthetic fractures.

MATERIAL AND METHODS

Over a 6-year-period 1542 patients with cemented (n = 363) and uncemented (n = 1179) medial UKA were retrospectively evaluated. Tibial periprosthetic fractures were identified and classified, and epidemiologic data were documented at follow-up. Undersizing was defined as a smaller tibial component compared to the femoral implant. The association of potential risk factors for TPF with the incidence of TPF was investigated with binominal logistic regression.

RESULTS

Fourteen patients (0.9%) suffered from TPF at a median of 1 month after surgery. The mean follow-up period was 5.9 ± 1.7 years. Fractures were more common in cases with undersized tibial components [odds ratio (OR) 3.2, p < 0.05]. Furthermore, older age (OR 1.1, p < 0.05) and female sex (OR 6.5, p < 0.05) were identified as significant risk factors, while BMI (p = 0.8) and cemented implantation (p = 0.2) had no effect on fracture rate. Revision surgery included open reduction and internal fixation or conversion to total knee arthroplasty.

CONCLUSIONS

Undersizing of implant sizes in UKA increases the risk for TPF especially in patients with small tibial implants. Therefore, mismatched implants should be avoided for UKA particularly when risk factors like obesity, older age, or female gender are present. Tibial periprosthetic fractures were successfully treated by open reduction and internal fixation or conversion to total knee arthroplasty.

A finite element model for investigating the influence of keel design and position on unicompartmental knee replacement cementless tibial component fixation

OBJECTIVES

The cementless Oxford Unicompartmental Knee Replacement (OUKR) tibial component relies on an interference fit to achieve initial fixation. The behaviour at the implant-bone interface is not fully understood and hence modelling of implants using Finite Element (FE) software is challenging. With a goal of exploring alternative implant designs with lower fracture risk and adequate fixation, this study aims to investigate whether optimisation of FE model parameters could accurately reproduce experimental results of a pull-out test which assesses fixation.

MATERIALS AND METHODS

Finite element models of implants with three methods of fixation (standard keel, small keel, and peg) in a bone analogue foam block were created, in which implants were modelled using an analytical rigid definition and the foam block was modelled as a homogenous linear isotropic material. The total interference and elastic slip were varied in these models and optimised by comparing simulated and experimental results of pull-out tests for two (standard and peg) implant geometries. Then the optimised interference and elastic slip were validated by comparing simulated and experimental data of a third (small keel) implant geometry.

RESULTS

The optimisation of parameters established an interference of 0.16 mm and an elastic slip of 0.20 mm as most suitable for modelling the experimental force-displacement plots during pull-out. This combination of parameters accurately reproduced the experimental results of the small keel geometry. The maximum pull-out forces from the FE models were consistent with experimental data for each implant design.

CONCLUSIONS

This study shows that experimental pull-out tests can be accurately modelled using adjusted interference values and non-linear friction and outlines a method for determining these parameters. This study demonstrates that complex problems in modelling implant behaviour can be addressed with relatively simple models. This can potentially lead to the development of implants with reduced risk of failure.

Polyethylene bearing wear is comparable for cemented and cementless Oxford unicompartmental knee replacements: Ten-year results of a randomized controlled trial

PURPOSE

There is concern that using cementless components may increase polyethylene wear of the Oxford unicompartmental knee replacement (OUKR). Therefore, this study aimed to measure bearing wear at 10 years in patients from a randomized trial comparing Phase 3 cemented and cementless OUKRs and to investigate factors that may affect wear. It was hypothesized that there would be no difference in wear rate between cemented and cementless OUKRs.

METHODS

Bearing thickness was determined using radiostereometric analysis at postoperative, 3-month, 6-month, 1-year, 2-year, 5-year and 10-year timepoints. As creep occurs early, wear rate was calculated using linear regression between 6 months and 10 years for 39 knees (20 cemented, 19 cementless). Associations between wear and implant, surgical and patient factors were analysed.

RESULTS

The linear wear rate of the Phase 3 OUKR was 0.06 mm/year with no significant difference (p = 0.18) between cemented (0.054 mm/year) and cementless (0.063 mm/year) implants. Age, Oxford Knee Score, component size and bearing thickness had no correlation with wear. A body mass index ≥ 30 was associated with a significantly lower wear rate (p = 0.007) as was having ≥80% femoral component contact area on the bearing (p = 0.003). Bearings positioned ≥1.5 mm from the tibial wall had a significantly higher wear rate (p = 0.002).

CONCLUSIONS

At 10 years, the Phase 3 OUKR linear wear rate is low and not associated with the fixation method. To minimize the risk of wear-related bearing fracture in the very long-term surgeons should consider using 4 mm bearings in very young active patients and ensure that components are appropriately positioned, which is facilitated by the current instrumentation.

LEVEL OF EVIDENCE

Level III, retrospective comparative study.

A Comparison of the Periprosthetic Fracture Rate of Unicompartmental and Total Knee Replacements: An Analysis of Data of >100,000 Knee Replacements from the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man and Hospital Episode Statistics

BACKGROUND

Periprosthetic fractures are rare but devastating complications of knee replacement, often requiring complex surgery with substantial morbidity and mortality. It is not known how the fracture rates after total knee replacement (TKR) and unicompartmental knee replacement (UKR) compare. We performed the first matched study comparing TKR and UKR periprosthetic fracture rates.

METHODS

This study involved 54,215 UKRs and 54,215 TKRs, identified in the National Joint Registry and Hospital Episodes Statistics database, which were propensity score-matched on patient and surgical factors. The International Classification of Diseases, Tenth Revision, (ICD-10) code M96.6 was used to identify periprosthetic fractures at ≤3 and >3 months postoperatively, as well as estimate rates at up to 10 years. Subgroup analyses were performed in different age groups (<55, 55 to 64, 65 to 74, and ≥75 years), body mass index (BMI) categories (normal, 18.5 to <25 kg/m 2 ; overweight, 25 to <30 kg/m 2 ; obese, 30 to <40 kg/m 2 ; and morbidly obese, ≥40 kg/m 2 ), and sexes.

RESULTS

The 3-month fracture rate was 0.09% (n = 50) in the UKR group and 0.05% (n = 25) in the TKR group, with this difference being significant (odds ratio [OR], 2.0; p = 0.004). The rate of fractures occurring at >3 months was 0.32% (n = 171) in the UKR group and 0.61% (n = 329) in the TKR group (OR, 0.51; p < 0.001). At 10 years, the cumulative incidence of fractures was 0.6% after UKR versus 1% after TKR (OR, 0.68; p < 0.001). Fracture rates increased with increasing age, decreasing BMI, and female sex for both UKRs and TKRs.

CONCLUSIONS

The fracture risk was small after both UKR and TKR, with small absolute differences between implant types. During the first 3 postoperative months, the fracture rate after UKR was 0.1% and was about twice as high as that after TKR. However, over the first 10 years, the cumulative fracture rate after TKR was 1% and was almost twice as high as that after UKR. Fracture rates after both UKR and TKR were higher in women, patients ≥75 years of age, and patients with normal weight.

LEVEL OF EVIDENCE

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

Does changes in unicompartmental knee arthroplasty practice pattern influence reasons for revision?

Aims

The aim of this study was to describe the pattern of revision indications for unicompartmental knee arthroplasty (UKA) and total knee arthroplasty (TKA) and any change to this pattern for UKA patients over the last 20 years, and to investigate potential associations to changes in surgical practice over time.

Methods

All primary knee arthroplasty surgeries performed due to primary osteoarthritis and their revisions reported to the Danish Knee Arthroplasty Register from 1997 to 2017 were included. Complex surgeries were excluded. The data was linked to the National Patient Register and the Civil Registration System for comorbidity, mortality, and emigration status. TKAs were propensity score matched 4:1 to UKAs. Revision risks were compared using competing risk Cox proportional hazard regression with a shared γ frailty component.

Results

Aseptic loosening (loosening) was the most common revision indication for both UKA (26.7%) and TKA (29.5%). Pain and disease progression accounted for 54.6% of the remaining UKA revisions. Infections and instability accounted for 56.1% of the remaining TKA revision. The incidence of revision due to loosening or pain decreased over the last decade, being the second and third least common indications in 2017. There was a decrease associated with fixation method for pain (hazard ratio (HR) 0.40; 95% confidence interval (CI) 0.17 to 0.94) and loosening (HR 0.29; 95% CI 0.10 to 0.81) for cementless compared to cemented, and units UKA usage for pain (HR 0.67, 95% CI 0.50 to 0.91), and loosening (HR 0.51; 95% CI 0.37 to 0.70) for high usage.

Conclusion

The overall revision patterns for UKA and TKA for the last 20 years are comparable to previous published patterns. We found large changes to UKA revision patterns in the last decade, and with the current surgical practice, revision due to pain or loosening are significantly less likely.

Reduced 5-Year Risk for Revision of the Oxford UKA Using New Instrumentation versus Conventional Instrumentation: A Registry Study of 12,867 UKAs

Microplasty instrumentation was introduced for a more consistent surgical implantation technique, especially component alignment and tibial resection level, of the Oxford medial unicompartmental knee arthroplasty (UKA) and thereby aims to improve UKA survival. This study aimed to assess the 5-year risk for revision and reasons for revision of the Oxford medial UKA using the new instrumentation (Microplasty) with its predecessor, that is, conventional instrumentation (Phase 3). Data of all medial UKAs from the Dutch Arthroplasty Register (Landelijke Registratie Orthopedische Implantaten) between 2007 and 2019 were collected. Type of instrumentation was divided into new (Microplasty) and conventional instrumentation. Kaplan-Meier analysis was performed to calculate 5-year cumulative revision percentage with any reason for revision as end point. A multivariable Cox regression with outcome revision of UKA adjusted for age, gender, American Society of Anesthesiologists score, surgical history, and type of fixation was performed. Additionally, reasons for revision at 3-year were assessed and tested through Fisher's exact tests. A total of 12,867 Oxford medial UKAs, 8,170 using new and 4,697 using conventional instrumentation, were included. The 5-year revision percentage was 9.2% (95% confidence interval [CI]: 8.4-10.1%) for UKAs using the conventional and 6.1% (95% CI: 5.4-6.7%) for new instrumentation. The adjusted hazard ratio for revision at 5-year follow-up was 0.74 (95% CI: 0.63-0.87) in favor of UKAs using the new instrumentation. Malalignment was more frequently registered as reason for revision in UKAs using the conventional compared with the new instrumentation (16% versus 7.5%; p = 0.001). Our results show a reduced 5-year risk for revision of the medial Oxford UKAs using the new compared with the conventional instrumentation. This might be the result of a lower revision rate for malalignment in UKAs using the new instrumentation.

Advantages of Simultaneous Cementless Bilateral Unicondylar Knee Arthroplasty Compared to Staged Surgery

Background

Unicondylar knee arthroplasty (UKA) is an effective procedure, which reduces pain, increases range of motion, and improves function. UKA could be performed simultaneously or in staged sessions. This study aimed to compare bilateral cementless UKA performed simultaneously and in staged sessions in terms of complications, hemoglobin levels, transfusions, and functional outcomes.

Methods

Patients undergoing bilateral UKA for symptomatic medial compartment osteoarthritis were retrospectively analyzed. Of the 73 patients who met the inclusion criteria, 40 underwent surgery simultaneously and 33 underwent surgery in separate sessions. Operative time, length of hospital stay, change in hemoglobin, need for blood transfusion, complications, and functional outcomes were assessed.

Results

There was no statistically significant difference between the two groups in demographic data. Simultaneously operated patients had a significantly shorter hospital stay and shorter operative time. Statistically significant improvements in clinical scores were noted in both groups. The degree of improvement in functional scores did not differ between the groups. There was no difference between the two groups in terms of complication rates, but the number of periprosthetic tibial fractures was higher in the simultaneous group.

Conclusions

Simultaneous bilateral cementless UKA was more advantageous in terms of cumulative hospital stay and total operation time with similar clinical results when compared to a staged procedure. While the overall complication rate was similar, the rate of periprosthetic fractures was 5% in the simultaneous group.

Cementless versus cemented unicompartmental knee arthroplasty: a systematic review of comparative studies

There are still some controversies regarding the clinical use of cementless UKAs. The aim of this systematic review was to determine whether cementless medial UKA leads to similar outcomes compared to cemented medial UKA. This search was conducted in accordance with the Preferred Reporting Items for Systematic Reviews guidelines (PRISMA). The random effects model with 95% confidence interval (CI) was applied to the analysis. The I2 statistic was used to assess study heterogeneity. Six studies were eligible for inclusion (4784 UKAs, 4776 patients): 2947 cemented UKAs (61.6%) and 1837 cementless UKAs (38.4%). The overall mean follow-up was 4.9 years. The all-cause reoperation rate was 11.3% (80 of 706) at mean 5.7-year follow-up for cemented UKA and 6.9% (57 of 824) at mean 4.1-year follow-up for the cementless. The overall revision rate was 10.2% (303 of 2947) for the cemented and 5.8% (108 of 1837) for the cementless. Aseptic loosening was the most frequent reason of revision (2.3% cemented vs 0.5% cementless). The overall rate of radiolucent lines (RLL) was 28.3% (63 of 223) in the cemented cohort and 11.1% in the cementless (26 of 234). All the studies reported improved functional outcomes. Cementless UKA provides at least equivalent if not better results compared to cemented UKA. Despite the use of cemented UKA outnumber cementless fixation, available data shows that cementless UKA had a reduced midterm revision rate, while providing similar functional outcomes.

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

BACKGROUND

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

QUESTIONS/PURPOSES

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

METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE

Level III, therapeutic study.

Assessing lateral femoral condyle cartilage prior to medial UKA: MRI vs. Valgus stress radiograph

BACKGROUND

The cartilage quality of the lateral compartment needs to be clarified prior to medial unicompartmental knee arthroplasty (UKA). Valgus stress radiograph has been recommended as the preferred tool. Some studies also show that magnetic resonance imaging (MRI) has a higher diagnostic value. So, we conducted this study to compare whether valgus stress radiographic lateral joint space width (LJSW) and MRI grading can accurately reflect cartilage quality and its screening value for UKA-suitable patients.

METHODS

One hundred and thirty eight knees proposed for UKA were enrolled prospectively. Valgus stress radiograph was taken to measure LJSW. LJSW > 4 mm was considered normal and suitable for UKA. For weight-bearing area cartilage of lateral femoral condyle, Recht grade was assessed by MRI preoperatively. Recht grades ≤ 2 were treated as non-high-grade injuries while Recht grades > 2 were treated as high-grade injuries. Outerbridge grade was the gold standard and was assessed intraoperatively. Patients with Outerbridge grades 0-2 (non-high-grade injuries) underwent UKA, and patients with Outerbridge grades 3-4 (high-grade injuries) underwent total knee arthroplasty (TKA). The diagnostic parameters of valgus stress radiograph and MRI for the selection of UKA candidates were calculated, and receiver operating characteristic curves were drawn. P < 0.05 was considered significant.

RESULTS

Of 138 knees, 120 underwent UKAs, and 18 underwent TKAs. In terms of selecting UKA candidates, the sensitivity was close between MRI (95.0%) and valgus stress radiograph (96.7%), and the specificity, accuracy, positive predictive value and negative predictive value of MRI (94.4%, 94.9%, 99.1%, 73.9%, respectively) were higher than that of valgus stress radiograph (5.9%, 85.5%, 88.0%, 20.0%, respectively). The difference in area under the curve (AUC) between MRI (0.950) and LJSW (0.602) was significant (P = 0.001).

CONCLUSION

Compared with valgus stress radiograph, MRI has excellent evaluation value in diagnosing lateral weight-bearing cartilage injuries and can be used as a reliable tool for selecting suitable UKA patients.

An ACS-NSQIP Analysis of Unicompartmental Knee Arthroplasty Trends from 2013 to 2018

Unicompartmental knee arthroplasty (UKA) volume has increased with advances in implant design, perioperative protocols, and patient selection. This study analyzed national trends of UKA from 2013 to 2018 and the relationship between patient demographics and postoperative outcomes. Data on UKA (CPT 27446) from 2013 to 2018 was collected from the National Surgical Quality Improvement Program (NSQIP). Variables collected included patient demographics, American Society of Anesthesiology classification, functional status, NSQIP morbidity probability, operative time, length of stay, 30-day reoperation, and readmission rates. There was an increase in outpatient UKAs performed (920 in 2013; 11,080 in 2018) (p < 0.0001). Analysis of variance from 2013 to 2018 revealed significant decrease in patient body mass index (BMI) (32.5 in 2013; 31.5 in 2018) (p < 0.01) and NSQIP morbidity probability (0.014 in 2013; 0.011 in 2018) (p < 0.0001). Operative time increased (79.1 minutes in 2013; 84.4 minutes in 2018) (p < 0.01), but length of stay decreased (0.9 days in 2013; 0.5 days in 2018) (p < 0.0001). The number of all-cause and related readmissions decreased significantly (p < 0.045; p < 0.01). Age, male gender, BMI >40 and chronic obstructive pulmonary disease (COPD) were significant predictors for 30-day readmission. BMI >40 was a significant predictor for discharge destination. UKA has seen a rise in incidence from 2013 to 2018 with an increasing number of outpatient UKAs. Operative times and 30-day readmissions have both decreased in this time. BMI > 40 is predictive for discharge destination after UKA, while age, male gender, BMI >40, and COPD are independent risk factors for 30-day readmission.

The effect of activity on the outcome of cementless mobile bearing unicompartmental knee replacements

BACKGROUND

Many surgeons consider high activity levels a contraindication to Unicompartmental Knee Replacement (UKR). Cementless fixation is of particular concern given the lack of cement to augment primary stability. We assessed the effect of pre and post-operative activity levels on the outcomes of cementless UKRs.

METHODS

A prospective cohort of 1000 medial cementless mobile bearing UKR were analysed. Patients were categorised by their pre-operative and highest post-operative Tegner Activity Score (TAS) and results compared between groups. Outcomes of interest included implant survival, Oxford Knee Score (OKS) and the American Knee Society Score - Objective/Functional (AKSS-O/F).

RESULTS

Increasing post-operative activity were not associated with higher revision rates. The 10-year survival of the high activity group (TAS ≥ 5, 96.7% (CI 91.3-98.8), and low/medium activity group (TAS ≤ 4, 98.1% (CI 96.5-99.0)) were not significantly different (p = 0.57). The mean 10-year OKS of the high activity group (46.5, SD 3.1) was significantly (p < 0.001) higher than that of the low/medium activity group (41.3, SD 7.7). There was a significant trend for increasing activity being associated with increasing AKSS-F at 5-years (p < 0.001) and 10 years (p = 0.01) and increasing AKSS-O at 5 years (p < 0.001). Higher pre-operative activity did not significantly increase revision rates and resulted in significantly higher 5-year post-operative scores.

CONCLUSIONS

Neither higher pre-operative nor post-operative activity were associated with increased revision rates, but both were associated with better post-operative function. Therefore activity should not be considered a contraindication to cementless mobile bearing UKR and not be restricted post-operatively.

Survivorship, clinical outcomes and indications for revision in uncemented unicompartmental knee arthroplasty: systematic review

Modern uncemented unicompartmental knee arthroplasty (UKA) relies on the mechanics of the implant design and a biological bond at the bone-implant interface to create a secure fixation of its components. The aim of this systematic review was to determine implant survivorship, clinical outcomes and indications for revision in uncemented UKAs. A search strategy was employed using keywords related to UKAs and uncemented fixation to identify suitable studies. Both prospective and retrospective studies with a minimum of two year mean follow-up were included. Data was gathered on study design, implant type, patient demographics, survivorship, clinical outcome scores and the indications for revision. Methodological quality was assessed using a ten-point risk of bias scoring tool. Eighteen studies were included in the final review. The mean follow-up of studies ranged between 2-11 years. The primary outcome of survival demonstrated 5 year survivorship ranged between 91.7-100.0% and 10-year survivorship between 91.0-97.5%. Clinical and functional outcome scores were found to be excellent in the majority of studies with the remaining reporting good results. Revisions represented 2.7% of the total operations performed. There were 145 revisions with an overall revision rate of 0.8 per 100 observed component years. Osteoarthritis disease progression (30.2%) and bearing dislocations (23.8%) were the most common causes of implant failure. This review finds uncemented UKAs demonstrate comparable survivorship, clinical outcomes and safety profile to cemented UKAs to consider this fixation a suitable alternative in clinical use.

The Influence of Surgeon Caseload and Usage on the Long-Term Outcomes of Mobile-Bearing Unicompartmental Knee Arthroplasty: An Analysis of Data From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man

BACKGROUND

Unicompartmental knee arthroplasty (UKA) revision rates are variable and known to be influenced by a surgeon's caseload (number of UKAs performed annually) and usage (UKA as a proportion of overall knee arthroplasty practice). It is not known which is more important. We explored the influence of caseload and usage on cemented and cementless UKA.

METHODS

A total of 34,277 medial Oxford UKAs (23,707 cemented and 10,570 cementless) from the National Joint Registry were analyzed. UKAs were subdivided by the following: (1) surgeon caseload, into low (<10 UKAs/y) and high (≥10 UKAs/y) categories; and (2) usage, into low (<20%) and high (≥20%) categories. The 10-year revision rates were compared.

RESULTS

The 10-year survival of the low-caseload/low-usage cemented and cementless UKA was 82.8% (CI 81.6-83.9) and 86.2% (CI 72.1-93.4), respectively. The 10-year survival of the high-caseload/high-usage cemented and cementless UKA was 90.0% (CI 89.2-90.6) and 93.3% (CI 91.3-94.8), respectively. For cemented UKA, the high-caseload/high-usage group had lower revision rates (hazard ratio [HR] 0.57, CI 0.52-0.63, P < .001) compared to the low-caseload/low-usage group. The high-caseload/low-usage (HR 0.74, CI 0.66-0.83, P < .001) and the low-caseload/high-usage (HR 0.86, CI 0.74-0.99, P = .04) groups also had lower revision rates than the low-caseload/low-usage group.

CONCLUSION

Mobile-bearing UKA revision rates improve with both increasing surgeon UKA caseload and usage. Surgeons using cemented UKA who have usage ≥20% and caseload ≥10/year had a 10-year survival of 90%. Higher survivorship was associated with higher caseload, higher usage, and cementless fixation.

LEVELS OF EVIDENCE

III.

The Effect of Age on the Relative Outcomes of Cemented and Cementless Mobile-Bearing Unicompartmental Knee Arthroplasty, Based on Data From National Databases

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an effective treatment for medial compartment arthritis. A challenge is that patients requiring knee arthroplasty are becoming younger. It is currently unknown what the relative performances of cemented and cementless UKAs are, in different age groups.

METHODS

A total of 12,882 cemented and cementless UKAs from the National Joint Registry and Hospital Episodes Statistics databases were matched on patient and surgical factors. Patients were stratified into 3 groups: (1) <60 years; (2) 60-69 years; and (3) ≥70 years. Revision and reoperation rates were compared using Cox regression analyses.

RESULTS

The 10-year implant survival for the matched cemented and cementless UKAs for (1) <60 years were 81.4% (CI 73.6-87.0) and 86.7% (CI 80.7-90.9) (hazard ratio [HR] 0.73, CI 0.56-0.94, P = .02); (2) for 60-69 years were 91.8% (CI 88.9-94.0) and 94.5% (CI 92.9-95.7) (HR 0.90, CI 0.67-1.22, P = .51); and (3) ≥70 years were 93.5% (CI 91.1-95.3) and 94.2% (CI 92.0-95.8) (HR 1.0, CI 0.71-1.40, P = .99). The same trend was observed for reoperations. In the <60 years and 60-69 years groups there were significantly fewer revisions for aseptic loosening in the cementless group (0.5% versus 1.6% [P < .001] and 0.4% versus 1.3% [P = .002], respectively).

CONCLUSION

Younger ages were associated with higher revision rates in both cemented and cementless UKA groups. Cementless fixation has reduced long-term revision rates compared to cemented fixation in the <60 years group with aseptic loosening rates 3 times lower.

LEVEL OF EVIDENCE

III.

Hybrid fixation of unicompartmental knee arthroplasty shows equivalent short-term implant survivorship and clinical scores compared to standard fixation techniques

INTRODUCTION

There is a paucity of data regarding hybrid-fixated unicompartmental knee arthroplasty (UKA), and no study directly compared all three available fixation techniques (cementless, cemented, and hybrid). The hypothesis was that hybrid fixation might have a lower incidence of radiolucent lines (RLL) than cemented UKA, with equivalent outcomes to uncemented UKA.

MATERIALS AND METHODS

A total of 104 UKA with a minimal follow-up of 1 year were retrospectively included, of which 40 were cemented, 41 cementless, and 23 hybrid prostheses. The functional outcomes scores included the Oxford Knee (OKS), Subjective Knee (SKS), and Forgotten Joint scores (FJS). RLLs, subsidence, and component positioning were assessed on radiographs.

RESULTS

At a mean follow-up of 28 months, the survival rate was 95% for cemented UKA and 100% for the cementless and hybrid UKA (n.s.), respectively. Postoperative FJS (93 vs. 82 points, p = 0.007) and SKS (4.7 vs. 4.1 points, p = 0.001) were better in cementless than cemented UKA, with hybrid-fixated UKA in between the two (90 and 4.4 points, n.s.). Improvement of OKS preoperatively to postoperatively did not differ between the groups (n.s.). RLLs were more frequent in cemented (23%) compared to cementless (5%, p = 0.021) and hybrid UKA (9%, n.s.). With an incidence of 12%, subsidence occurred more commonly in cementless UKA compared to cemented (5%) and hybrid (0%) (n.s.) UKA.

CONCLUSION

Hybrid fixation achieves equivalent results to standard UKA fixation techniques regarding implant survival and functional and radiological outcomes. Therefore, the hybrid fixation technique seems to be a valuable alternative as it combines the advantages of cemented tibial components with those of uncemented femoral components.

LEVEL OF EVIDENCE

III.

Knee registries: state of the art

Sports injuries, trauma and the globally ageing and obese population require increasing levels of knee surgery. Shared decision making has replaced the paternalistic approach to patient management. Evidence-based medicine underpins surgical treatment strategies, from consenting an individual patient to national healthcare system design. The evolution of successful knee-related registries starting from specific arthroplasty registries has given rise to ligament reconstruction, osteotomy and cartilage surgery registries developing as platforms for surgical outcome data collection. Stakeholders include surgeons and their patients, researchers, healthcare systems, as well as the funding insurers and governments. Lately, implant manufacturers have also been mandated to perform postmarket surveillance with some hoping to base that on registry data. Aiming to assess the current status of knee-related registries, we performed a comprehensive literature and web search, which yielded 23 arthroplasty, 8 ligament, 4 osteotomy and 3 articular cartilage registries. Registries were evaluated for their scope, measured variables, impact and limitations. Registries have many advantages as they aim to increase awareness of outcomes; identify trends in practice over time, early failing implants, outlier surgeon or institution performance; and assist postmarketing surveillance. International collaborations have highlighted variations in practice. The limitations of registries are discussed in detail. Inconsistencies are found in collected data and measured variables. Potential measurement and selection biases are outlined. Without mandated data collection and with apparent issues such as unverified patient reporting of complications, registries are not designed to replace adverse event recording in place of a proper safety and efficacy study, as demanded by regulators. Registry 'big data' can provide evidence of associations of problems. However, registries cannot provide evidence of causation. Hence, without careful consideration of the data and its limitations, registry data are at risk of incorrectly drawn conclusions and the potential of misuse of the results. That must be guarded against. Looking at the future, registry operators benefit from a collective experience of running registries as they mature, allowing for improvements across specialties. Large-scale registries are not only of merit, improving with stakeholder acceptance, but also are critical in furthering our understanding of our patients' outcomes. In doing so, they are a critical element for our future scientific discourse.

Medium term results of the cementless Oxford mobile bearing medial unicompartmental knee replacement

BACKGROUND

Medial Unicompartmental Knee Replacement (UKR) has well-documented benefits over Total Knee Replacement in the treatment of anteromedial osteoarthritis of the knee. There has been an increasing move from cemented to cementless UKR over the last decade. This non-design centre study assesses the initial experience using the cementless Oxford medial partial knee replacement and provides medium term revision data, as well as Patient Reported Outcome Measures (PROMs).

METHODS

A cohort of 200 consecutive patients undergoing medial UKR using the cementless Oxford were identified from our knee groups prospectively collected database. Cases were performed in a single centre under the care of one of four surgeons. All patients were beyond the 5-year minimum timepoint following UKR surgery in order to produce medium term results, at a mean of 7.9 years. Eligible patients completed a postal questionnaire to collect PROMs: Oxford Knee Score, WOMAC and modified American Knee Society Score questionnaires in January 2020 and had their clinical records reviewed.

RESULTS

The survivorship in our cohort was 94.5% at a mean follow up of 7.9 years following surgery. There were 11 re-operations in total with a three percent risk of re-operation within the first 18 months following surgery. There was a sustained improvement in Oxford Knee Score with a near 20 points improvement on pre-operative scores.

CONCLUSIONS

Our results provide further evidence that partial knee replacements using the cementless Oxford produce good clinical outcomes. Revision rates are similar to those published in the National Joint Registry.

LEVEL OF EVIDENCE

III.

A matched comparison of cementless unicompartmental and total knee replacement outcomes based on the National Joint Registry for England, Wales, Northern Ireland and the Isle of Man

BACKGROUND AND PURPOSE

The main treatments for severe medial compartment knee arthritis are unicompartmental (UKR) and total knee replacement (TKR). UKRs have higher revision rates, particularly for aseptic loosening, therefore the cementless version was introduced. We compared the outcomes of matched cementless UKRs and TKRs.

PATIENTS AND METHODS

The National Joint Registry was linked to the English Hospital Episode Statistics and Patient Reported Outcome Measures (PROMs) databases. 10,552 cementless UKRs and 10,552 TKRs were propensity matched and regression analysis used to compare revision/reoperation risks. 6-month PROMs were compared. UKR results were stratified by surgeon caseload into low- (< 10 UKRs/year), medium- (10 to < 30 UKRs/year), and high-volume (≥ 30 UKRs/year).

RESULTS

8-year cementless UKR revision survival for the 3 respective caseloads were 90% (95% CI 87-93), 93% (CI 91-95), and 96% (CI 94-97). 8-year reoperation survivals were 76% (CI 71-80), 81% (CI 78-85), and 84% (CI 82-86) respectively. For TKR the 8-year implant survivals for revision and reoperation were 96% (CI 95-97) and 81% (CI 80-83). The HRs for the 3 caseload groups compared with TKR for revision were 2.0 (CI 1.3-2.9), 2.0 (CI 1.6-2.7), and 1.0 (CI 0.8-1.3) and for reoperation were 1.2 (CI 1.0-1.4), 0.9 (CI 0.8-1.0), and 0.6 (CI 0.5-0.7). 6-month Oxford Knee Score (OKS) (39 vs. 37) and EQ-5D (0.80 vs. 0.77) were higher (p < 0.001) for the cementless UKR.

INTERPRETATION

Cementless UKRs have higher revision and reoperation rates than TKR for low-volume UKR surgeons, similar reoperation but higher revision rates for mid-volume surgeons, and lower reoperation and similar revision rates for high-volume surgeons. Cementless UKR also had better PROMs.

Optimized medial unicompartmental knee arthroplasty outcome: learning from 20 years of propensity score matched registry data

BACKGROUND AND PURPOSE

Unicompartmental knee arthroplasty (UKA) has increased in use. We investigated changes to UKA revision risk over the last 20 years compared with total knee arthroplasty (TKA), examined external and patient factors for correlation to UKA revision risk, and described the survival probability for current UKA and TKA practice.

PATIENTS AND METHODS

All knee arthroplasties reported to the Danish Knee Arthroplasty Register from 1997 to 2017 were linked to the National Patient Register and the Civil Registration System for comorbidity, emigration, and mortality information. All primary UKA and TKA patients with primary osteoarthritis were included and propensity score matched 4 TKAs to 1 UKA. Revision and mortality were analyzed using competing risk cox regression with a shared gamma frailty component.

RESULTS

The matched cohort included 48,195 primary knee arthroplasties (9,639 UKAs). From 1997-2001 to 2012-2017 the 3-year hazard ratio decreased from 5.5 (95% CI 2.7-11) to 1.5 (CI 1.2-1.8) due to increased UKA survival. Cementless fixation, a high percentage usage of UKA, and increased surgical volume decreased UKA revision risk, and increased in occurrence parallel to the decreasing revision risks. Current UKA practice using cementless fixation at a high usage unit has a 3-year implant survival of 96% (CI 97-95), 1.1% lower than current TKA practice.

INTERPRETATION

UKA revision risk has decreased over the last 20 years, nearing that of TKA surgery. High usage rates, surgical volume, and the use of cementless fixation have increased during the study and were associated with decreased UKA revision risks.

Short distance from the keel to the posterior tibial cortex is associated with fracture after cementless Oxford UKA in Asian patients

PURPOSE

Tibial plateau fractures are serious complications of Oxford mobile-bearing unicompartmental knee arthroplasty (OUKA). This study examined where the fracture lines arises and evaluated the keel-cortex distances (KCDs) using three-dimensional computed tomography (3D-CT) and the effects of technical error (assessed by tibial component positions) and proximal tibial morphology on the KCDs.

METHODS

This retrospective study included 217 OUKAs with cementless tibial components. Fifteen patients had tibial fractures after surgery. Anterior and posterior KCDs and fracture line origins were assessed using 3D-CT postoperatively. Proximal tibial morphology was assessed using the medial eminence line (MEL), which runs parallel to the tibial axis and passes through the tip of the medial intercondylar eminence of the tibia on long-leg anteroposterior radiograph. Knees had overhanging medial tibial condyle if the MEL passed medially to the medial tibial cortex. KCDs were compared between patients with/without fractures. Tibial component positions were evaluated, considering effects of tibial morphologies and component positions on fracture prevalence and KCDs.

RESULTS

Fracture lines were found between the keel and posterior cortex in 12/15 patients. Posterior KCDs were significantly shorter in patients with fractures than in patients without (2.7 ± 1.6 mm vs 5.2 ± 1.7 mm, P < 0.001). Patients with medial overhanging condyles were more likely to have fracture (10/51 vs 5/166, P < 0.001) and had significantly shorter posterior KCD than those without (3.6 ± 1.5 mm vs 5.5 ± 1.8 mm, P < 0.001). Patients with tibial component that was set too medial, low, and valgus had higher rates of fracture than those without (7/39 vs 8/178, P = 0.008). Medial (r = 0.30, P < 0.001), low (r = -0.33, P < 0.001), and valgus implantations (r = 0.35, P < 0.001) of tibial components were related to shorter posterior KCDs.

CONCLUSION

Short posterior KCD after OUKA is a risk factor for postoperative tibial fracture. Patients with either malposition of the tibial component (too medial, low, and valgus) and/or a medial overhanging condyle exhibit a shorter distance of posterior KCD and higher rate of fracture.

LEVEL OF EVIDENCE

Level III.

The effect of age on the outcomes of cementless mobile bearing unicompartmental knee replacements

PURPOSE

Unicompartmental Knee Replacements (UKR) are being performed in patients with increasing demands and life expectancies with surgical concerns that cemented fixation will not last. Cementless fixation may offer a solution, but the results in different age groups have not been assessed. The effect of age at surgery on the outcomes of cementless UKRs was investigated.

METHODS

A prospective cohort of 1000 medial cementless mobile bearing UKR were analysed. Patients were categorised into four age groups (< 55, 55 to < 65, 65 to < 75 and ≥ 75 years). Implant survival was assessed using endpoints reoperation, revision and major revision requiring revision knee replacement components. Functional outcomes were assessed.

RESULTS

10 year cumulative revision rate for the < 55, 55 to < 65, 65 to < 75 and ≥ 75 groups were 2.1% (CI 0.6-6.1), 1.8% (CI 0.6-5.3), 3.2% (CI 1.5-6.5) and 4.1% (1.7-9.6) with no differences between groups (p = 0.52). Two of the 22 revisions were considered major. The 10 year cumulative reoperation rates were 4.5% (CI 2.0-10.0), 3.0% (CI 1.3-6.5), 3.8% (CI 2.0-7.1) and 4.1% (CI 1.7-9.6) with no differences between groups (p = 0.81). The 10 year median Oxford Knee Scores were 42.5, 46.5, 45 and 42.5, respectively. The 10 year median Objective American Knee Society Scores were 95 for all age groups.

CONCLUSION

The cementless mobile bearing UKR has low reoperation and revision rates and similar functional outcomes in all age groups. Cementless UKR should be used in all age groups and age should not be considered a contraindication.

LEVEL OF EVIDENCE

III.

A Matched Comparison of Long-Term Outcomes of Total and Unicompartmental Knee Replacements in Different Ages Based on National Databases: Analysis of Data From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man

BACKGROUND

The 2 main treatment options for end-stage single compartment knee arthritis are unicompartmental (UKR) or total knee replacement (TKR). We compared the long-term outcomes in different age groups.

METHODS

In total, 54,215 UKRs and 54,215 TKRs from the National Joint Registry and Hospital Episode Statistics database were propensity score matched and Kaplan-Meier and regression analysis used to compare revision, reoperation, mortality, and 3-month complications.

RESULTS

UKR had higher 10-year revision rates (12% vs 5%, hazard ratio [HR] 2.31, P < .001) and 10-year reoperation rates (25% vs 21%, HR 1.12, P < .001). UKR had lower 10-year mortality rates (13.6% vs 15.5%, HR 0.86, P < .001). UKR had lower rates of medical (P < .001) and procedure related (P < .001) complications and deaths (HR 0.61, P = .02). If 100 patients had a UKR instead of a TKR then over 10 years, if they were <55 years old there would be 7 more reoperations and 1 less death; if they were 55-64 years old there would be 6 more reoperations and 2 more deaths; if they were 65-74 years old there would be 4 more reoperations and 2 less deaths; and if they were ≥75 years old there would be 3 more reoperations and 4 less deaths.

CONCLUSION

UKR has higher revision and slightly higher reoperation rates but lower mortality rates than matched TKR. The decision to do a UKR should, in part, be based on the balance of these risks, which are influenced by patient age. In the elderly group (>75 years) the data suggests that UKR compared to TKR has a greater absolute reduction in mortality than the increase in reoperation rate.

LEVELS OF EVIDENCE

III.

Good mid- to long-term results of the cemented oxford phase 3 unicompartmental knee arthroplasty in a non-designer centre

PURPOSE

Unicompartmental knee arthroplasty (UKA) provides patients with an alternative treatment to TKA in isolated medial compartment osteoarthritis providing better functional outcomes and faster recovery in the short term. Our aim was to quantify revision rates, predictors of revision, mortality rate and functionality of the Oxford Phase 3 UKA in a non-designer institution.

METHODS

This was a retrospective review of prospectively collected regional registry data. All Oxford Phase 3 UKAs performed for medial tibio-femoral osteoarthritis of the knee joint were included from a single academic institution between the period of January 1st 2006 and December 30th 2009. Kaplan-Meier survivorship curves adjusting for loss to follow-up and deceased patients were generated. Primary outcome variables included all-cause and aseptic revision. Secondary outcome variables included functional outcome scores. Patients were reviewed at 6 months, 2 years, 5 years, 10 years and 15 years.

RESULTS

A total of 64 cemented Oxford phase 3 UKAs were performed between January 2006 and November 2009. Fifteen-year follow-up data were available for 51 patients, of these 12 required revision. Survival rates, adjusting for patients that were either lost to follow-up or deceased, were 87.5% at 5 years, 81.4% at 10 years and 76.4% at 15 years. The overall aseptic revision rate at the time of review was 18.75% (n = 12). The only significant predictor of postoperative WOMAC score at 15 years was the preoperative WOMAC score (p = 0.03).

CONCLUSION

The Oxford Phase 3 UKA for medial tibio-femoral arthritis has promising outcomes at 15-year follow-up with a survival rate of 76.4% in a non-designer centre.

LEVEL OF EVIDENCE

III.

Comparable incidence of periprosthetic tibial fractures in cementless and cemented unicompartmental knee arthroplasty: a systematic review and meta-analysis

PURPOSE

(I) To determine the incidence of periprosthetic tibial fractures in cemented and cementless unicompartmental knee arthroplasty (UKA) and (II) to summarize the existing evidence on characteristics and risk factors of periprosthetic fractures in UKA.

METHODS

Pubmed, Cochrane and Embase databases were comprehensively searched. Any clinical, laboratory or case report study describing information on proportion, characteristics or risk factors of periprosthetic tibial fractures in UKA was included. Proportion meta-analysis was performed to estimate the incidence of fractures only using data from clinical studies. Information on characteristics and risk factors was evaluated and summarized.

RESULTS

A total of 81 studies were considered to be eligible for inclusion. Based on 41 clinical studies, incidences of fractures were 1.24% (95%CI 0.64-2.41) for cementless and 1.58% (95%CI 1.06-2.36) for cemented UKAs (9451 UKAs). The majority of fractures in the current literature occurred during surgery or presented within 3 months postoperatively (91 of 127; 72%) and were non-traumatic (95 of 113; 84%). Six different fracture types were observed in 21 available radiographs. Laboratory studies revealed that an excessive interference fit (press fit), excessive tibial bone resection, a sagittal cut too deep posteriorly and low bone mineral density (BMD) reduce the force required for a periprosthetic tibial fracture to occur. Clinical studies showed that periprosthetic tibial fractures were associated with increased body mass index and postoperative alignment angles, advanced age, decreased BMD, female gender, and a very overhanging medial tibial condyle.

CONCLUSION

Comparable low incidences of periprosthetic tibial fractures in cementless and cemented UKA can be achieved. However, surgeons should be aware that an excessive interference fit in cementless UKAs in combination with an impaction technique may introduce an additional risk, and could therefore be less forgiving to surgical errors and patients who are at higher risk of periprosthetic tibial fractures.

LEVEL OF EVIDENCE

V.

Comparison of five-year clinical outcomes of 524 cemented and cementless medial unicompartmental knee replacements

AIM

To compare the outcomes of cemented and cementless Unicompartmental Knee Replacements (UKR) at 5 years after surgery.

METHODS

262 cemented and 262 cementless medial mobile-bearing UKR, implanted by four high-volume surgeons using identical indications and surgical techniques, were reviewed by independent physiotherapists at 5 years. Survival, Oxford Knee Score (OKS), American Knee Society Score (AKSS), and EQ-5D-5L were assessed. The cementless cohort was mainly implanted after the cemented. Each cohort was divided into early and late sub-groups and compared, to assess if any differences were due to progressive improvement in surgical practice over time.

RESULTS

There were no significant differences between the cohorts for demographics, pre-operative scores, and 5-year revision (0.8%), re-operation (1.5%), and complication rates (5%). The cementless cohort had significantly better 5-year OKS (43v41, p = 0.008), AKSS-Objective (94v90, p = 0.049) and EQ-5D-5L (0.81v0.87, p = 0.0001). Pain sub-scores within OKS, AKSS, and EQ-5D-5L were also significantly better in the cementless cohort, and the differences were proportionally much greater and more significant than differences in their respective overall scores. There was no significant improvement in scores between the early and late subgroups of the cohorts, whereas the 'early-cementless' cohort had significantly better scores than the contemporaneously implanted 'late-cemented' cohort. This suggests that differences found were due to implant type, instead of improved surgical practice over time.

CONCLUSION

Cementless UKR is associated with better clinical outcomes than cemented UKR, which is primarily due to improved pain relief. Both cemented and cementless UKR are safe with low reoperation and complication rates, and a 5-year survival of 99%.

A Matched Comparison of the Long-Term Outcomes of Cemented and Cementless Total Knee Replacements: An Analysis from the National Joint Registry of England, Wales, Northern Ireland and the Isle of Man

BACKGROUND

Total knee replacements (TKRs) can be implanted with or without the use of cement. It is currently uncertain how cemented and cementless TKRs compare overall and in different age groups of the population in the long term.

METHODS

The National Joint Registry collects information on knee replacements inserted in England, Wales, Northern Ireland, and the Isle of Man and was linked for multiple confounders to the National Health Service Hospital Episode Statistics database. With use of propensity score matching techniques, 44,954 cemented and cementless TKRs were compared. Regression models were used to compare the outcomes of revision, reoperation, and mortality both overall and in different age strata.

RESULTS

The 10-year implant survival rate with revision as the end point for cemented and cementless TKRs was 96.0% and 95.5%, respectively (hazard ratio [HR] = 1.14; p = 0.01). The 10-year survival rate with reoperation as the end point was 82.7% and 81.4%, respectively (HR = 1.08; p = 0.001). The rate of revision for pain was higher for cementless TKRs (0.5% [cemented] compared with 0.7% [cementless]; p = 0.002), but the rate of revision for infection was lower (0.7% [cemented] compared with 0.5% [cementless]; p = 0.003). No significant interactions with age existed for the outcomes of revision (p = 0.24), reoperation (p = 0.30), or mortality (p = 0.58).

CONCLUSIONS

We found that matched cemented and cementless TKRs both have 10-year implant survival rates of >95%. Cementless TKRs had a higher revision rate (absolute difference, 0.5%) and reoperation rate (absolute difference, 1.3%). The rate of revision for infection was lower in the cementless group, although the rate of revision for pain was higher. Age did not significantly affect the relative performances.

LEVEL OF EVIDENCE

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

A matched comparison of the patient-reported outcome measures of 38,716 total and unicompartmental knee replacements: an analysis of linked data from the National Joint Registry of England, Northern Ireland and Isle of Man and England's National PROM collection programme

Background and purpose - The surgical treatment options for severe knee osteoarthritis are unicompartmental (UKR) and total knee replacement (TKR). For patients, functional outcomes are more important than revision rate. We compared the patient-reported outcome measures (PROMs) of both implant types using a large PROMs dataset.Patients and methods - We analysed a propensity-matched comparison of 38,716 knee replacements (19,358 UKRs and 19,358 TKRs) enrolled in the National Joint Registry and the English National PROM collection programme. Subgroup analyses were performed in different age groups.Results - 6-month postoperative Oxford Knee Score (OKS) for UKR and TKR were 38 (SD 9.4) and 36 (SD 9.4) respectively. A higher proportion of UKRs had an excellent OKS (≥ 41) compared with TKR (47% vs 36%) and a lower proportion of poor OKS (< 27) scores (13% vs. 16%). The 6-month OKS was higher in all age groups for UKR compared with TKR, with the difference increasing in older age groups. The mean 6-month EQ-5D score was 0.78 (SD 0.25) and 0.75 (SD 0.25) respectively. The improvement in EQ-5D resulting from surgery was higher for UKR than TKR both overall and in all age groups. All comparisons were statistically significant (p < 0.05).Interpretation - UKR had a greater proportion of excellent OKS scores and lower proportion of poor scores than TKR. Additionally, the quality of life was higher for UKR compared with TKR. These factors should be balanced against the higher revision rate for UKR when choosing which procedure to perform.

Cementless unicompartmental knee replacement achieves better ten-year clinical outcomes than cemented: a systematic review

PURPOSE

The aim of this study was to report and compare the long-term revision rate, revision indications and patient reported outcome measures of cemented and cementless unicompartmental knee replacements (UKR).

METHODS

Databases Medline, Embase and Cochrane Central of Controlled Trials were searched to identify all UKR studies reporting the ≥ 10 year clinical outcomes. Revision rates per 100 component years [% per annum (% pa)] were calculated by fixation type and then, subgroup analyses for fixed and mobile bearing UKRs were performed. Mechanisms of failure and patient reported outcome measures are reported.

RESULTS

25 studies were eligible for inclusion with a total of 10,736 UKRs, in which there were 8790 cemented and 1946 cementless knee replacements. The revision rate was 0.73% pa (CI 0.66-0.80) and 0.45% pa (CI 0.34-0.58) per 100 component years, respectively, with the cementless having a significantly (p < 0.001) lower overall revision rate. Therefore, based on these studies, the expected 10-year survival of cementless UKR would be 95.5% and cemented 92.7%. Subgroup analysis revealed this difference remained significant for the Oxford UKR (0.37% pa vs 0.77% pa, p < 0.001), but for non-Oxford UKRs there were no significant differences in revision rates of cemented and cementless UKRs (0.57% pa vs 0.69% pa, p = 0.41). Mobile bearing UKRs had significantly lower revision rates than fixed bearing UKRs in cementless (p = 0.001), but not cemented groups (p = 0.13). Overall the revision rates for aseptic loosening and disease progression were significantly lower (p = 0.02 and p = 0.009 respectively) in the cementless group compared to the cemented group (0.06 vs 0.13% pa and 0.10 vs 0.21% pa respectively).

CONCLUSIONS

Cementless fixation had reduced long-term revision rates compared to cemented for the Oxford UKR. For the non-Oxford UKRs, the revision rates of cementless and cemented fixation types were equivalent. Therefore, cementless UKRs offer at least equivalent if not lower revision rates compared to cemented UKRs.

LEVEL OF EVIDENCE

III.

Hybrid Oxford unicompartmental knee arthroplasty has lower residual cement extrusion than cemented arthroplasty in treating end-stage unicompartmental knee osteoarthritis

Background

Hybrid Oxford unicompartmental knee arthroplasty (OUKA) consists of cementless femoral prostheses and cemented tibial prostheses. Although a hybrid OUKA has been used in clinical practice, the clinical outcome has not been reported. The purpose of this study was to compare the short-term clinical outcomes and rate of residual bone cement extrusion between hybrid and cemented prostheses and analyse the possible reasons for differences between outcomes.

Methods

A total of 128 knees (118 patients) with end-stage osteoarthritis were included in this study, of which underwent consecutive operations using unicondylar Oxford phase 3 implants from July 2017 and September 2019 in our centre. Follow-up was performed at 6 weeks, 3 and 6 months, 1 year and every year after operation, and complications and changes in the Oxford knee score (OKS) were recorded. The OKS of the two groups was analysed by the generalized estimating equation approach. Prosthesis-based standard fluoroscopy was performed in a timely manner after each operation, and the rate of residual cement extrusion of the two groups was estimated using T-tests and a multivariate regression analysis.

Results

Excluding the cases that lost follow-up, a total of 120 knees (65 in hybrid group and 55 in cemented group) were included in the analysis. There was no statistically significant difference in patient characteristics between the two groups (p > 0.05). The average follow-up time was 23.4 months (and ranged from 12 to 38 months). As of the last follow-up, there were no complications, such as dislocation, fracture, prosthesis loosening and subsidence, but one patient in the cemented group experienced symptoms caused by residual loose cement. Postoperative OKS in both groups improved significantly (p < 0.001). There was no significant difference in the OKS at any point during the follow-up or in the improvement of the OKS between the two groups (p > 0.05). Residual cement was mainly extruded behind the tibial prosthesis. The rate of hybrid periprosthetic residual cement extrusion was significantly lower in the hybrid group than in the cemented group, and the difference was statistically significant (OR = 3.38; p = 0.014).

Conclusions

Hybrid OUKA is as effective as cemented OUKA in the short term after operation and can significantly reduce the residual cement extrusion rate around the tibial prosthesis.

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

BACKGROUND

Operative management for end-stage knee osteoarthritis (OA) primarily consists of arthroplasty. Total knee arthroplasty (TKA) is the so-called gold standard for multicompartmental OA. In selected patients, specifically those with unicompartmental OA and no definite contraindications, realignment osteotomies and unicompartmental knee arthroplasty (UKA) are viable options. UKA offers several advantages over TKA, including preservation of both cruciate ligaments, faster recovery, and less osseous resection. The purpose of this study was to determine the survivorship of UKAs and risk factors for all-cause revision surgery in patients with a minimum follow-up of 10 years in a large population-based database.

METHODS

We performed a population-based cohort study using linked administrative databases in Ontario, Canada. We identified all UKAs performed from January 2002 through December 2006. All patients had a minimum 10-year follow-up. Demographic data and outcomes were summarized using descriptive statistics. We used a Cox proportional hazards model with the Fine and Gray method accounting for competing risks such as death to analyze the effect of surgical and patient factors on the risk of revision of UKA.

RESULTS

A total of 4,385 patients were identified as having undergone primary UKA from 2002 through 2006 in Ontario. Of these patients, 779 underwent revision surgery, for a cumulative risk for all-cause revision of 16.5% at 10 years (95% confidence interval [CI]: 15.4% to 17.7%). Mechanical loosening was the reason for 83.4% of all revisions. Male sex, diabetes, an age younger than 50 years, and cementless implants were significant risk factors for revision surgery. Residence in a rural or urban setting, income quintile, discharge destination, and type of OA were not associated with the risk of revision. Survivorship at 1, 5, 10, and 15 years was 97.2%, 90.5%, 83.5%, and 81.9%, respectively.

CONCLUSIONS

This study demonstrated a >80% long-term survivorship for UKA based on a large administrative database sample and identified important risk factors for failure including male sex, younger age, diabetes, and cementless fixation. This study found rates of survivorship similar to those previously reported in the literature, while identifying key risk factors for failure. Patient selection has always been identified as a key factor in ensuring successful UKA, and the risk factors identified in this study may help guide decision-making for surgeons and patients dealing with unicompartmental knee OA.

LEVEL OF EVIDENCE

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

The Impact of the Largest National Joint Registry on Current Knee Replacement Longevity Estimates: An Analysis and Review of Knee Prosthesis Brand and Fixation Technique

BACKGROUND

The UK National Joint Registry is the single largest joint registry in the world enrolling 1.3 million patients and recently reaching 17 years of follow-up data. Current knee prosthesis longevity estimates are based off smaller sized international registries and the impact of fixation type on prosthesis survival remains unclear.

METHODS

We used the UK National Joint Registry 17th annual report to calculate pooled mean survival estimates of total knee replacements (TKRs), unicondylar knee replacements (UKRs), and patellofemoral knee replacements at 10 and 15 years based on both construct brand and fixation technique (cemented vs uncemented). Independent t-testing was performed for significance.

RESULTS

All-cause survivorship of TKRs at 10 and 15 years is 96.7% and 95.4%, respectively. For UKRs it is 89.8% and 80.7% and for patellofemoral knee replacements it is 81.6% and 76.5%. In regard to fixation technique, cemented and uncemented TKRs show similar survivorship at both time points. For UKRs uncemented constructs showed improved survivorship compared to cemented at 10 years (92.7% vs 88.2%, P < .001). This was greatest among those <65 years of age. In fact, all construct types regardless of fixation showed increased rate of revision in those <65 years vs those ≥65 years.

CONCLUSION

We provide more accurate estimations for knee prosthesis survival and highlight that younger patients, particularly those receiving UKRs, are prone to greater revision risks. This data also suggests that uncemented fixation may offer improved joint survival in these patients.

Incidence, temporal trends and potential risk factors for aseptic loosening following primary unicompartmental knee arthroplasty: A meta-analysis of 96,294 knees

BACKGROUND

Aseptic loosening (AL) is among the major reasons for revision of failed primary unicompartmental knee arthroplasty (UKA). There is an ongoing temporal increase in the use of UKA with a resultant increase in the revision burden. We aimed to evaluate the incidence of, temporal trends and risk factors for AL.

METHODS

Longitudinal studies reporting the incidence of AL following primary UKA were sought from MEDLINE, Embase, Web of Science and Cochrane Library up to 6th April 2020. Incidence and relative risks (RR) (with 95% confidence intervals) were calculated.

RESULTS

We identified 62 studies for inclusion. Overall, 96,294 primary UKA procedures accounting for 1752 AL cases were included. AL incidence ranged from 0.00% to 22.70% over a 7.7 year weighted mean follow-up. The pooled random effects incidence (95% CI) was 1.77% (1.34-2.25) in the same follow-up period. The annual rate of AL was 0.10% (0.02-0.22). AL incidence increased with length of follow-up, but there was a temporal decrease from the 1970s onwards. Tibial loosening was more common than femoral component loosening: incidence (95% CI) of 1.63% (0.96-2.44) and 0.58% (0.20-1.09) respectively over a weighted follow-up of 6.6 years. Fixed bearing implant design and cemented fixation were both associated with increased AL risk, whereas robotic-assisted surgery was associated with decreased risk.

CONCLUSION

The overall incidence of AL following primary UKA is primarily driven by tibial component loosening and there is a temporal decline in rates. The use of mobile bearing, uncemented implants inserted with robotic assisted surgery may reduce the risk of AL.

Risk of revision for medial unicompartmental knee arthroplasty according to fixation and bearing type : short- to mid-term results from the Dutch Arthroplasty Register

AIMS

Uncemented mobile bearing designs in medial unicompartmental knee arthroplasty (UKA) have seen an increase over the last decade. However, there are a lack of large-scale studies comparing survivorship of these specific designs to commonly used cemented mobile and fixed bearing designs. The aim of this study was to evaluate the survivorship of these designs.

METHODS

A total of 21,610 medial UKAs from 2007 to 2018 were selected from the Dutch Arthroplasty Register. Multivariate Cox regression analyses were used to compare uncemented mobile bearings with cemented mobile and fixed bearings. Adjustments were made for patient and surgical factors, with their interactions being considered. Reasons and type of revision in the first two years after surgery were assessed.

RESULTS

In hospitals performing less than 100 cases per year, cemented mobile bearings reported comparable adjusted risks of revision as uncemented mobile bearings. However, in hospitals performing more than 100 cases per year, the adjusted risk of revision was higher for cemented mobile bearings compared to uncemented mobile bearings (hazard ratio 1.78 (95% confidence interval 1.34 to 2.35)). The adjusted risk of revision between cemented fixed bearing and uncemented mobile bearing was comparable, independent of annual hospital volume. In addition, 12.3% of uncemented mobile bearing, 20.3% of cemented mobile bearing, and 41.5% of uncemented fixed bearing revisions were for tibial component loosening. The figures for instability were 23.6%, 14.5% and 11.7%, respectively, and for periprosthetic fractures were 10.0%, 2.8%, and 3.5%. Bearing exchange was the type of revision in 40% of uncemented mobile bearing, 24.3% of cemented mobile bearing, and 5.3% cemented fixed bearing revisions.

CONCLUSION

The findings of this study demonstrated improved survival with use of uncemented compared to cemented mobile bearings in medial UKA, only in those hospitals performing more than 100 cases per year. Cemented fixed bearings reported comparable survival results as uncemented mobile bearings, regardless of the annual hospital volume. The high rates of instability, periprosthetic fractures, and bearing exchange in uncemented mobile bearings emphasize the need for further research. Cite this article: Bone Joint J 2021;103-B(7):1261-1269.

[Focal femoral resurfacing and unicompartmental knee replacement : Between osteotomy and total knee replacement]

Unicompartmental knee arthroplasty, especially for both femorotibial compartments of the knee, is an established partly joint-saving treatment option for osteoarthritis of the knee if the disease is limited to one compartment. Even smaller implants or resurfacing of the patellofemoral joint have been shown-in smaller patient collectives-to have the potential to yield good clinical results.

Regional five-year clinical outcomes of 289 consecutive cementless oxford uni-compartmental knee replacements at a non-inventor centre

INTRODUCTION

Uncemented unicompartmental knee replacement offers a minimally invasive approach, faster rehabilitation and good levels of function, supported by evidence reporting low intra-operative fracture rate and mid-term stability with no implant migration at 5-years. Our aim was to examine the clinical outcomes in 289 consecutive Oxford unicompartmental knee arthroplasties (257 patients), five years post-operatively.

METHODS

A retrospective study of patients treated between 2008 and 2014 in a non-inventor centre by a single surgeon was performed. Patients with anteromedial bone on bone uni-compartmental arthritis were included. Oxford Knee Scores (OKSs) at last follow-up were recorded, intra-operative complications reported with commentary on revision cases.

RESULTS

Mean age of patients was 66 years (SD 9.6, 45-88 years). 122 (42%) patients were female and 135 (58%) were male. Patient in our study were ASA 1 (36%), ASA 2 (62%) and ASA 3 (01%). There were no intra-operative complications, particularly tibia fractures during impaction. The average oxford knee score was 40.1 (n = 232, Range 06 to 48, SD 8.46) at an average 6 years and 3 months from surgery, including revised patients. Six patients had their prosthesis revised within five-years of the index surgery. Five-year cumulative implant survival rate was 97.8% (95% CI 97.62 to 97.98, SE 0.09). Indications for revision were: lateral side wear (n = 1); dislocated spacer (n = 4); instability and spacer subluxation (n = 1). Thirteen patients died within five years of surgery Five-year cumulative survival rate was 94.9% (95% CI 94.87 to 94.925, SE 0.013).

CONCLUSION

The proportion of patients requiring revision at five-years is lower than that generally reported for UKR. These findings add support for the use of the cementless oxford UKR outside the design centre.

The Mid- to Long-Term Outcomes of the Lateral Domed Oxford Unicompartmental Knee Replacement: An Analysis From the National Joint Registry for England, Wales, Northern Ireland, and the Isle of Man

BACKGROUND

Lateral unicompartmental knee replacement (UKR) is an alternative to total knee replacement for isolated lateral unicompartmental knee arthritis. The geometry and mechanics of the lateral compartment differ to the medial compartment with the Lateral Domed Oxford UKR designed to address this. We used the National Joint Registry (NJR) data to report the mid- to long-term outcomes of this device.

METHODS

We performed a retrospective observational study using NJR data on 992 Lateral Domed Oxford UKRs implanted between 1st January 2005 and 31st December 2017. Outcomes of interest were implant survival and revision indications.

RESULTS

The 10 year cumulative implant survival rates were 88.6% (CI 85.3-91.2). When compared with <55 year age group, the 55-64, 65-74 and ≥75 groups had significantly lower revision rates (hazard ratio (HR) = 0.56 (CI 0.32-0.98, P = .04), HR 0.40 (CI 0.22-0.72, P = .003), and HR 0.27 (CI 0.12-0.58, P = .001), respectively). The obese group had significantly (P = .04) increased revision risk compared with normal BMI (HR 2.33, CI 1.06-5.12). The commonest reasons for revision surgery were dislocation (n = 23, 2.3%), pain (n = 15, 1.5%), and aseptic loosening (n = 14, 1.4%).

CONCLUSION

The Lateral Domed Oxford UKR provides a good option for isolated lateral compartment osteoarthritis. However, dislocation of the mobile bearing remains a problem, occurring in 2.3% of the patients and accounting for 30% of the revisions. To help prevent dislocation, it is now possible to assess bearing stability intraoperatively and if very unstable to implant a compatible fixed bearing tibial component, without the need for further bone preparation.

Revision Following Cemented and Uncemented Oxford-III Primary Medial Unicompartmental Knee Replacements: A 19-Year Analysis from the New Zealand Joint Registry

BACKGROUND

Oxford-III unicompartmental knee replacements (UKRs) are among the most commonly used prostheses to treat isolated medial compartment osteoarthritis (OA). However, the best mode of implant fixation for primary UKRs remains a source of debate. The hypothesis of this study was that the biologically superior fixation of uncemented Oxford-III primary UKRs would translate into a lower revision rate when compared with cemented Oxford-III primary UKRs used to treat isolated medial compartment OA.

METHODS

Data on all Oxford-III primary UKRs (n = 8,733) completed for isolated medial compartment OA from January 2000 to December 2018 were obtained from the New Zealand Joint Registry (NZJR). Revision rates were documented for each fixation type and analyzed for associations with patient sex and age at surgery. A multivariate Cox proportional-hazards analysis was completed to determine if type of fixation was an independent risk factor for revision of Oxford-III UKRs.

RESULTS

Statistical analysis revealed a >1.8-fold greater revision risk for cemented Oxford-III UKRs compared with uncemented Oxford-III UKRs (p = 0.001) when considered independently of other risk factors. Furthermore, compared with uncemented fixation, cemented fixation was associated with a 2.9-fold (p < 0.001) increase in revision risk for women <65 years old and a 1.7-fold (p = 0.008) increase in revision risk for men 55 to 74 years old. There was no significant difference in the risk of revision between fixation methods for women ≥65 years old and men ≥75 years old.

CONCLUSIONS

We found that the type of fixation was an independent risk factor for revision of Oxford-III UKRs used in the treatment of isolated medial compartment OA. Uncemented Oxford-III primary UKRs had superior implant survivorship in women <65 years old and men 55 to 74 years old. Age and sex are important factors to consider when determining the type of fixation for Oxford-III primary UKRs used to treat isolated medial compartment OA.

LEVEL OF EVIDENCE

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

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

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