Radiographic evaluation of factors affecting bearing dislocation in the domed lateral Oxford unicompartmental knee replacement

Revision surgery after failure of lateral unicompartmental knee replacement with a mobile-bearing device: a retrospective non -designer case-series

INTRODUCTION

Failure of lateral unicompartmental knee replacement (UKR) with a mobile-bearing (MB) device often occurs due to bearing dislocation. The effectiveness of various treatment options for revision surgery is not clear. Therefore, the purpose of this study was to report on the failure modes in lateral MB-UKR, as well as the results of different revision strategies.

MATERIALS AND METHODS

Patients who experienced failure of lateral MB-UKR and required revision surgery at a single-center between 2008 and 2020 were included in this retrospective study. The aim of the study was to report the reasons for failure and to document all treatment strategies employed. Survivorship analysis was conducted using the Kaplan-Meier estimator, with the endpoint defined as 're-revision for any reason'. Survival rates among various treatment strategies were compared using the log-rank test.

RESULTS

A total of 13 patients were included in the study, with a mean follow-up (FU) period of 94.7 ± 36.4 months. The reasons for failure included bearing dislocation in 69.2%, progression of osteoarthritis (OA) in 23.1%, and periprosthetic joint infection in 7.7%. Treatment options included replacement of the tibial component with a fixed-bearing (FB) device in 23.1% of cases, solitary exchange of the bearing in 53.8%, or conversion to an unconstrained total knee replacement (TKR) in 23.1%. The re-dislocation rate in patients who underwent a bearing exchange as a treatment for bearing dislocation was 100%, with a mean FU period of 8.4 ± 11 months. Therefore, survivorship for the treatment of bearing dislocation differed significantly in these patients compared to those who received an exchange to a FB device (0% vs. 100%, p = 0.014).

CONCLUSIONS

Addressing the recurring issue of bearing dislocation in lateral MB-UKR demands a more comprehensive approach than merely replacing the bearing. Effective solutions include replacing the tibial component with an FB design or converting to an unconstrained TKR.

LEVEL OF EVIDENCE

Retrospective cohort study, Level IV.

Long-term results of lateral unicompartmental knee arthroplasty with a mobile-bearing device

Aims

Unicompartmental knee arthroplasty (UKA) is one option in the treatment of isolated unicompartmental advanced osteoarthritis (OA). While long-term results exist for medial mobile-bearing (MB) UKA, evidence regarding lateral MB-UKA is still limited. The Oxford Domed Lateral (ODL) implant aims to reduce the bearing dislocation rate in lateral MB-UKA through enhanced bearing entrapment. However, the long-term performance of this implant remains unclear. This study evaluated the long-term survival and clinical outcomes of the ODL in a non-designer centre.

Methods

This single-centre retrospective analysis included 115 lateral MB-UKAs using the ODL performed between January 2006 and December 2014. The primary endpoint of the study was implant survival, defined as the time until a revision procedure was required for any reason. Secondary outcomes included Oxford Knee Score (OKS), Forgotten Joint Score (FJS), pain, satisfaction, and Tegner Activity Scale (TAS). Survival was assessed using Kaplan-Meier analysis.

Results

At ten years, the cumulative implant survival rate was 74.8% (95% CI 65.2 to 82.1; number at risk = 71), with bearing dislocation (8.5%) and OA progression (10.4%) as leading revision causes. In 55 non-revised knees with a mean follow-up of 13.4 years (SD 1.8), the mean postoperative OKS improved significantly to 37.8 (SD 9.1) (p < 0.001). Additionally, 85.5% of patients (n = 47) reported satisfaction, with a mean FJS of 65.9 (SD 32.2) and TAS of 2.8 (SD 1.1). However, only 76.4% (n = 42) attained the patient-acceptable symptom state for OKS and FJS.

Conclusion

This is the first long-term ODL study from a non-designer centre; our results demonstrated high failure rates due to bearing dislocation and OA progression, despite satisfactory clinical outcomes in non-revised patients. The disproportionately high risk of failure suggests that the MB design should be abandoned in favour of a fixed-bearing device for lateral UKA.

Insights into complications after unicompartmental knee arthroplasty

Zhao's study, offers a comprehensive analysis of unicompartmental knee arthroplasty (UKA) revision indications. The study provides a detailed, case-by-case analysis of the factors leading to knee revision surgery in 13 patients. Not only elucidates the complexities of UKA revisions but also underscores the importance of continuous improvement in surgical techniques and the adoption of innovative technologies.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

LEVEL OF EVIDENCE

Retrospective case-control study, Level III.

Cemented Lateral Unicompartmental Knee Replacement: A retrospective single centre independent series

Background

Unicompartmental knee replacement (UKR) has functional and economic benefits when compared with total knee replacement, however it is technically demanding and may be associated with higher failure rates. The primary aim of this independent series study was to evaluate the survival of lateral UKRs implanted in our institution and their clinical outcomes. The secondary outcome was to compare the results of mobile and fixed-bearing prostheses.

Methods

This is a retrospective series study of 183 cemented lateral UKRs implanted in 170 patients, for advanced isolated lateral compartment arthritis, under the care of two senior surgeons. Fixed or mobile-bearing prostheses were used according to the surgeon's preference. Kaplan Meier analysis was used to evaluate prosthesis survival with the endpoint being revision for any reason. A subgroup analysis of survival was also done for each bearing type. Functional outcomes were evaluated using the Oxford knee score (OKS) at final follow-up.

Results

This series included 103 Fixed-bearing and 80 mobile-bearing prostheses. Median follow-up was 6.9 years. 9 knees required revision. The commonest reason for revision was progression of arthritis to the medial compartment. Dislocation was the commonest cause of revision in the mobile-bearing group. Survival at 10 years was 91.9% with no significant difference ( p = 0.083) between bearing types (fixed-bearing 93.8% and mobile-bearing 90.6%). The OKS were comparable in both groups, the mean OKS was 44/48.

Conclusion

Good survival and functional outcomes can be achieved using cemented lateral UKRs with both bearing types. There was a trend towards superior outcomes in the fixed-bearing group.

Can accuracy of component alignment be improved with Oxford UKA Microplasty® instrumentation?

Background

One factor in the long-term survivorship of unicompartmental knee arthroplasty is the accuracy of implantation. In addition to implant designs, the instrumentation has also evolved in the last three decades to improve the reproducibility of implant placement. There have been limited studies comparing mobile bearing unicompartmental knee arthroplasty with contemporary instrumentation and fixed bearing unicompartmental knee arthroplasty with conventional instrumentation. This study aims to determine whether the Microplasty instrumentation in Oxford unicompartmental knee arthroplasty allows the surgeon to implant the components more precisely and accurately.

Methods

A total of 150 patients (194 knees) were included between April 2013 and June 2019. Coronal and sagittal alignment of the tibial and femoral components was measured on postoperative radiographs. Component axial rotational alignment was measured on postoperative computer tomography. The knee rotation angle was the difference between the femoral and tibial axial rotation. A rotational mismatch was defined as a knee rotation angle of > 10°. Statistical analysis was performed using Student t test and Mann-Whitney nonparametric test. A p value < 0.05 was considered statistically significant in each analysis.

Results

Between April 2013 to June 2019, 112 patients (150 knees) received Oxford unicompartmental knee arthroplasty, one patient (2 knees) had Journey unicompartmental knee arthroplasty, and 37 patients (42 knees) received Zimmer unicompartmental knee arthroplasty. All femoral components in the Oxford group were implanted within the reference range, compared with 36.6% in the fixed bearing group (p < 0.001). 88.3% of Oxford knees had tibial component falling within the reference range, whereas 56.1% of knees in the fixed bearing group fell within the reference range (p < 0.001). 97.5% of Oxford knees had tibial slope that fell within reference range, whereas 53.7% fell within range for fixed bearing group (p < 0.001). Femorotibial rotational mismatch of more than 10° was noted in 13.8% in Oxford group and 20.5% in fixed bearing group (p = 0.04).

Conclusion

In conclusion, Microplasty instrumentation for Oxford mobile bearing unicompartmental knee arthroplasty is more accurate and precise compared to conventional fixed bearing unicompartmental knee arthroplasty in sagittal, coronal, and axial alignment. Prospective studies with long-term follow-up are warranted to investigate the clinical implications.

A Comprehensive Evaluation of Lateral Unicompartmental Knee Arthroplasty Short to Mid-Term Survivorship, and the Effect of Patient and Implant Characteristics: An Analysis of Data From the Dutch Arthroplasty Register

BACKGROUND

The rarity of lateral unicompartmental knee arthroplasty (UKA) results in a lack of large cohort studies and understanding. The aim of this study is to comprehensively evaluate survivorship of lateral UKA with registry data and compare this to medial UKA.

METHODS

Lateral (n = 537) and medial UKAs (n = 19,295) in 2007-2017 were selected from the Dutch Arthroplasty Register. Survival analyses were performed with revision for any reason as primary endpoint. Adjustments were made for patient and implant characteristics. Stratified analyses according to patient and implant characteristics were performed. Reasons and type of revision were grouped according to laterality and bearing design.

RESULTS

The 5-year revision rate was 12.9% for lateral UKA and 9.3% for medial UKA. Multivariable regression analyses showed no significant increased risk for revision for lateral UKA (hazard ratio 0.87, 95% confidence interval 0.66-1.15). Stratified analyses showed that the effect of patient characteristics on revision was comparable between lateral and medial UKA; however, the use of mobile-bearing design for lateral UKA was associated with increased revision rate. Progression of osteoarthritis was the main reason for revision on both sides accompanied by tibia component loosening for medial UKA. Reasons and type of revision varied depending on bearing design.

CONCLUSION

Similar survivorship of lateral and medial UKA was reported. Specifically, there is a notable risk for revision when using mobile-bearing designs for lateral UKA. Failure modes and type of revision depends on laterality and bearing design. These findings emphasize that surgical challenges related to anatomy and kinematics of the lateral and medial knee compartment need to be considered.

Unicompartmental Knee Arthroplasty: US and Global Perspectives

Unicompartmental knee arthroplasty (UKA) is a treatment option for anteromedial osteoarthritis. Compared with total knee arthroplasty (TKA), UKA offers improved knee range of motion, functional recovery and decreased medical complications. Revision rates continue to be higher with UKA compared with TKA. With current UKA implants, there is no significant difference in mobile bearing or fixed bearing, or between cemented and cementless implants. Enabling technology, such as robotic-assisted surgery, has demonstrated improvements in component positioning, but no long-term difference in survival compared with traditional manual instruments.

Posterior Bearing Overhang Following Medial and Lateral Mobile Bearing Unicompartmental Knee Replacements

This study explores the extent of bearing overhang following mobile bearing Oxford unicompartmental knee replacement (OUKR) (Oxford Phase 3, Zimmer Biomet). The Oxford components are designed to be fully congruent, however knee movements involve femoral rollback, which may result in bearing overhang at the posterior margin of the tibial implant, with potential implications for; pain, wear, and dislocation. Movement is known to be greater, and therefore posterior overhang more likely to occur, with; lateral compared to medial implants, anterior cruciate ligament (ACL) deficiency (ACLD) compared to ACL intact (ALCI), and at extremes of movement. Twenty-four medial, and 20 domed lateral, OUKRs underwent sagittal plane knee fluoroscopy during step-up and forward lunge exercises. The bearing position was inferred from the relative position of the femoral and tibial components. On the basis of the individual component sizes and geometry the extent the posterior part of the bearing which overhung the posterior part of the tibial component was calculated. There was no significant posterior overhang in knees with medial implants. Knees with lateral domed implants exhibited overhang at flexion angles beyond 60°, the magnitude of which increased with increasing flexion angle, reaching a maximum of 50% of the bearing length at 140° (range 0-140°). This demonstrates a clear difference between the kinematics, and prevalence and extent of posterior bearing overhang between medial and lateral OUKRs. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 37:1938-1945, 2019.

Bearing design influences short- to mid-term survivorship, but not functional outcomes following lateral unicompartmental knee arthroplasty: a systematic review

PURPOSE

To determine survivorship and functional outcomes of fixed and mobile-bearing designs in lateral unicompartmental knee arthroplasties (UKA).

METHODS

Medline, EMBASE and Cochrane databases were searched. Annual revision rate and functional outcomes were assessed for both fixed and mobile-bearing designs.

RESULTS

A total of 28 studies, of which 19 fixed-bearing and 9 mobile-bearing, representing 2265 lateral UKAs were included for survivorship and functional outcome analyses. The mean follow-up of fixed and mobile-bearing studies was 7.5 and 3.9 years, respectively. Annual revision rate of fixed-bearing designs was 0.94 (95% CI 0.66-1.33) compared to 2.16 (95% CI 1.54-3.04) for mobile-bearing. A subgroup analysis of the domed shaped mobile-bearing design noted an annual revision rate of 1.81 (95% CI 0.98-3.34). Good-to-excellent functional outcomes were observed following fixed and mobile-bearing lateral UKAs; no significant differences were found.

CONCLUSION

Mobile-bearing lateral UKAs have a higher rate of revision compared to fixed-bearing lateral UKAs with regard to short- to mid-term survivorship; however, the clinical outcomes are similar. Despite the introduction of the domed shaped mobile-bearing design, findings of this study suggest fixed-bearing implant design is preferable in the setting of isolated lateral osteoarthritis (OA). This systematic review was based on low to moderate evidence, therefore, future registry data are needed to confirm these findings. However, this study included a large number of patients, and could provide information regarding risk of revision and functional outcomes of mobile and fixed-bearing type lateral UKA.

LEVEL OF EVIDENCE

IV.

[Imaging study on effect of femoral intramedullary guide on the alignment of femoral prosthesis in unicompartmental knee arthroplasty]

Objective

To explore the imaging features of intramedullary guide rod and its influence on the alignment of the femoral prosthesis in unicompartmental knee arthroplasty (UKA).

Methods

Between August 2016 and November 2016, 50 patients (50 knees) with primary anteromedial osteoarthritis were treated with UKA by Oxford MicroPlasty minimally invasive replacement system. There were 10 males and 40 females. The age ranged from 62 to 77 years with an average of 68.8 years. Preoperative varus and flexion deformity angles were (5.22±3.46)° and (7.42±2.65)°, respectively. The knee range of motion (ROM) was (106.85±7.62)°. The Hospital for Special Surgery (HSS) score was 68.26±4.65. The angles between the femoral intramedullary guide rod and the anatomical axis of femur on the coronal and sagittal planes, the femoral component valgus/varus angle (FCVA), the femoral component posterior slope angle (FCPSA), knee varus deformity angle, and knee flexion deformity angle were measured by intra- and post-operative X-ray films. The postoperative ROM and HSS score were measured.

Results

Intraoperative X-ray films measurement showed that the lateral side angles between femoral intramedullary guide rod and femoral anatomical axis were observed on coronal plane, and the angles ranged from 0.28 to 2.06° with an average of 0.96°. While the posterior side angles were observed on sagittal plane, and the angles ranged from 0.09 to 0.48° with an average of 0.23°. The angulations (>1°) between femoral intramedullary part guide rod and outside part of the rod were confirmed in 12 cases (24%) on coronal plane. Postoperative femoral prosthesis were mild varus in 38 patients (76%). The FCVA ranged from -1.76 to 4.08° with an average of 2.21°. The FCPSA ranged from 7.12 to 13.86° with an average of 9.16°. All patients were followed up 22-26 months, with an average of 24.5 months. The incisions healed by first intention. At last follow-up, the varus and flexion deformity angles were (1.82±1.05) and (2.54 ± 1.86)°, respectively. ROM was (124.62±5.85)° and HSS score was 91.58±3.65. There were significant differences between pre- and post-operative parameters ( P<0.05). No complication such as dislocation or aseptic loosening of the prosthesis occurred during the follow-up.

Conclusion

UKA by Oxford MicroPlasty minimally invasive replacement system can obtain accurate femoral prosthesis position with the help of intramedullary guide system, and the effectiveness is excellent.

Superior femoral component alignment can be achieved with Oxford microplasty instrumentation after minimally invasive unicompartmental knee arthroplasty

PURPOSE

Oxford microplasty (MP) instrumentation has been developed to facilitate the reproducible and consistent performance of minimally invasive unicompartmental knee arthroplasty (MI-UKA) operation. The aim of this study was to compare the clinical and radiographic results of two groups of patients implanted using either a conventional instrumentation technique or an MP technique.

METHODS

A prospective cohort study of 108 knees in 108 patients who underwent an MI-UKA procedure using either conventionally instrumented UKA (CI-UKA) (52 knees of 52 patients) or MP-assisted UKA (MP-UKA) (56 knees of 56 patients). The clinical assessment included the Oxford Knee Score (OKS), the Knee Society Score (KSS), a visual analogue scale (VAS) for pain, and range of motion (ROM). Complications were also recorded.

RESULTS

No significant differences were observed between the two groups regarding OKS, KSS, VAS, and ROM. There were also no significant differences in terms of mechanical limb alignment and tibia implant alignment. However, the MP-UKA group showed significantly more accurate positioning of the femoral component than the CI-UKA group. Additionally, the MP-UKA group had more femoral prostheses implanted in the "satisfactory" range and fewer "outliers" than the CI-UKA group. No significant difference in complications was noted between the two groups.

CONCLUSION

This study suggested that compared with CI-UKA, MP-UKA provides significant improvements in increasing the accuracy of sagittal and coronal implantation of the femoral component and in reducing the numbers of outliers for femoral prosthetic alignment. It is advocated that the MP system should be considered when MI-UKA is performed.

LEVEL OF EVIDENCE

Therapeutic study, Level IV.

Does 3-Dimensional In Vivo Component Rotation Affect Clinical Outcomes in Unicompartmental Knee Arthroplasty?

BACKGROUND

Unicompartmental knee arthroplasty (UKA) is an effective treatment for single-compartment osteoarthritis. Limited studies have examined the relationship between component rotation and functional outcomes, with no existing consensus to guide "optimal" UKA component rotation. Our study aims to study the effect of 3-dimensional (3D) in vivo UKA component axial rotation on functional outcomes by determining (1) how much component axial rotation variability exists in UKA? and (2) does 3D in vivo UKA component axial rotation affect functional outcomes?

METHODS

Sixty-six UKAs from 58 consecutive patients (36 male [62.1%], age 63.7 ± 9.2 years, body mass index 28.2 ± 4.9 kg/m(2), and mean follow-up time 49.2 months) were imaged in weight-bearing standing position using biplanar radiography. We performed multiple comparisons to analyze the relationship between 3D UKA component alignment and European Quality of Life - 5 Dimensions (EQ-5D), UCLA activity score, and Knee Injury and Osteoarthritis Outcome Scores.

RESULTS

Significant improvements in EQ-5D, EQ-5D (United States adjusted), and Knee Injury and Osteoarthritis Outcome Scores (Sport/Rec) scores were noted postoperatively. However, high variability in 3D UKA femoral (6.2° ± 6.5°) and tibial (4.6° ± 6.4°) component positioning was observed. A trend toward better outcome scores in lower angles of femoral (<2.7° external rotation [ER]) and tibial (2.7° ER to 2.4° internal rotation [IR]) component rotation was noted, with better functional scores observed at mean femoral and tibial rotation angles of 3° ER to 3° IR.

CONCLUSION

Patients with UKA femoral and/or tibial component rotation angles within 3° ER to 3° IR of neutral component alignment reported better functional outcomes. Surgeons should be cognizant of the high variability noted in UKA component axial rotation and its potential correlation with functional scores.

Three-Dimensional Imaging Analysis of Unicompartmental Knee Arthroplasty Evaluated in Standing Position: Component Alignment and In Vivo Articular Contact

BACKGROUND

Component malalignment in unicompartmental knee arthroplasty (UKA) has been associated with contact stress concentration and poor clinical outcomes. However, there is a paucity of data regarding UKA component alignment and in vivo articular contact in weight-bearing position. This study aims to (1) quantify three-dimensional UKA component alignment and (2) evaluate the association between the component alignment and in vivo articular contact in standing position.

METHODS

Seventy-seven UKAs in 68 consecutive patients were imaged in standing position using a biplanar X-ray imaging acquisition system. The UKA models were imported into a virtual imaging environment and registered with component silhouette on X-ray image for determination of component position and contact location. Anatomic bony landmarks of the lower limb were digitized for quantification of the bone alignment.

RESULTS

The femoral component (FC) showed 1.6° ± 3.3° valgus, 6.5° ± 6.4° external rotation, and 2.4° ± 4.6° flexion. The tibial component (TC) showed 3.9° ± 4.5° varus, 4.4° ± 6.7° internal rotation, and 10.1° ± 4.6° tibial slope. The average contact point was located medially and posteriorly by 7.8 ± 7.6% and 0.7 ± 7.7% of TC dimensions to its center. Multiple regression analysis identified FC flexion as a significant variable affecting UKA anterior and/or posterior contact position (R = 0.549, P < .001).

CONCLUSION

This study demonstrated the highest variability of UKA component positioning in axial plane rotation for FC and TC. The association between FC flexion and anterior contact position suggests accurate implant positioning may be important in optimizing in vivo UKA contact behavior. Further studies are required to gain understanding of the influence of axial rotation variability on in vivo UKA contact kinematics during functional activities.

Are the Oxford(®) medial unicompartmental knee arthroplasty new instruments reducing the bearing dislocation risk while improving components relationships? A case control study

INTRODUCTION

The recently introduced Microplasty(®) system is an upgrade of conventional phase III instrumentation. However, little is known of its impact on the position of the implant following the Oxford(®) mobile-bearing unicompartmental knee arthroplasty (UKA). This study investigated whether the Microplasty(®) instrumentation system can improve the positioning of the implant and reduce the rate of early failure.

HYPOTHESIS

Microplasty(®) provides a better positioning and decreases the rate of dislocation.

MATERIALS AND METHODS

The medical records and radiographs of 82 consecutive Oxford(®) UKAs were reviewed retrospectively. The radiographic parameters and prevalence of early failure of 41 UKAs performed with the Microplasty(®) system and 41 UKAs using the conventional instrumentation system were compared. Both groups were comparable in terms of demographics and preoperative status.

RESULTS

The femoral components in the Microplasty(®) group were more contiguously placed and more convergent in relation to the tibial components compared to the conventional instrumentation system (P<0.01). The frequency of bearing dislocation was lower in the Microplasty(®) group (P=0.04). A wide gap and the angle between components were associated with an increased risk of bearing dislocation.

CONCLUSION

The Microplasty(®) instrumentation system consistently placed the femoral and tibial components in more contiguous and convergent positions. Such changes in position decreased the risk of bearing dislocations by reducing the space available for bearing rotation.

LEVEL OF EVIDENCE

Level III, case control study.