Mobile bearing unicompartmental knee replacement

Femoral Coronal Malalignment is Associated With Failure in Mobile-Bearing Medial Unicompartmental Knee Arthroplasty

BACKGROUND

Femur-first (FF) technique for mobile-bearing medial unicompartmental knee arthroplasty (UKA) has been described as an alternative to tibia-first (TF) technique. The aim of this study was to compare the radiographic results in UKAs using FF or TF techniques and their influence on failure rates.

METHODS

We retrospectively reviewed 288 UKAs with a minimum 2-year follow-up. There were 147 knees in the TF and 141 knees in the FF cohorts. Alignment parameters and overhang were assessed as outliers and far outliers. The mean follow-up was 6 years (range, 2 to 16), the mean age was 63 years (range, 27 to 92), and 45% of patients were women. Univariate and multivariate statistical analyses were carried out with Cox regression models.

RESULTS

There were 13 and 6 revisions in the TF and FF cohorts, respectively. The FF had lower rates of femoral coronal alignment (FCA) or femoral sagittal alignment outliers compared to the TF (5.7% versus 19%, P = .011). Tibial coronal alignment and tibial sagittal alignment did not significantly differ between the techniques (22.7% in FF versus 29.9% in TF, P = .119). Overhang outliers did not differ significantly between the groups. Younger age was associated with a higher revision rate (P = .006), while FF versus TF, sex, body mass index, and postoperative mechanical axis did not show statistically significant associations. In multivariate analysis, FCA outliers and younger age were significantly associated with revision.

CONCLUSIONS

The FF technique in mobile-bearing UKA resulted in fewer FCA outliers compared to TF. Despite improved knee alignment with the FF technique, FCA outliers and younger age were associated with a higher revision rate, independent of technique.

Predicting valgus malalignment after mobile-bearing UKA using a new method: the arithmetic HKA of the arthritic knee

BACKGROUND

Valgus malalignment is one of the most common reasons for the progression of osteoarthritis in the lateral compartment of the knee after mobile-bearing unicompartmental knee arthroplasty (UKA). The arithmetic hip-knee-ankle angle (aHKA) of the Coronal Plane Alignment of the Knee (CPAK) classification could reflect the constitutional alignment of the arthritic knee. The purpose of this study was to observe the relationship between the aHKA and valgus malalignment after mobile-bearing UKA.

METHODS

This retrospective study was conducted using 200 knees undergoing UKA from January 1, 2019, to August 1, 2022. These radiographic signs, including preoperative hip-knee-ankle angle (HKA), mechanical proximal tibial angle (MPTA), mechanical lateral distal femoral angle (LDFA), and postoperative HKA, were measured using standardized weight-bearing long-leg radiographs. Patients with postoperative HKA > 180° and postoperative HKA ≤ 180° were classified as the valgus group and non-valgus group, respectively. The aHKA was calculated as 180° + MPTA - LDFA in this study, which had the same meaning as that (aHKA = MPTA - LDFA) in the CPAK classification. The Spearman correlation analysis, the Mann-Whitney U test, the chi-square test, the Fisher's exact test, and multiple logistic regression were used in the study.

RESULTS

Of the 200 knees included in our study, 28 knees were classified as the valgus group, while 172 knees were in the non-valgus group. The mean ± standard deviation (SD) of aHKA (all groups) was 177.04 ± 2.58°. In the valgus group, 11 knees (39.3%) had a value of aHKA > 180°, while 17 knees (60.7%) had a value of aHKA ≤ 180°. In the non-valgus group, 12 knees (7.0%) had a value of aHKA > 180°, while 160 knees (93.0%) had a value of aHKA ≤ 180°. In Spearman correlation analysis, aHKA was positively correlated with postoperative HKA (r = 0.693, p < 0.001). In univariate analysis, preoperative HKA (p < 0.001), LDFA (p = 0.02), MPTA (p < 0.001), and aHKA (p < 0.001) showed significant differences between the valgus and non-valgus groups. Variables with p < 0.1 in univariate analysis were further analyzed using multiple logistic regression analysis, and the variable-aHKA (> 180° vs ≤ 180°, odds ratio (OR) = 5.899, 95% confidence interval (CI) = 1.213 to 28.686, and p = 0.028) was expressed as the risk factor of postoperative valgus malalignment.

CONCLUSION

The aHKA is correlated with the postoperative alignment of mobile-bearing UKA and a high aHKA (> 180°) will increase the risk of postoperative valgus malalignment. Therefore, mobile-bearing UKA should be performed with caution in patients with preoperative aHKA > 180°.

Comparison of Clinical and Radiological Outcomes Between Upper Fibular Curvature and Non-Curvature with Medial Knee Osteoarthritis Following Proximal Fibular Osteotomy: A Retrospective Cohort Study with Minimum 2-Year Follow-up

Objective

To evaluate and compare the clinical and radiographic outcomes of proximal fibular osteotomy (PFO) in treating medial knee osteoarthritis (KOA) patients with upper fibular curvature and non‐curvature.

Methods

A retrospective cohort study was performed. From January 2016 to January 2017, a total of 51 patients (nine males and 42 females) at a mean age of 63.7 years (range 48–79 years) with medial KOA who underwent PFO procedure at the Third Hospital of Hebei Medical University were included in the study. The patients were divided into the two groups, namely curvature group (28 patients, six males and 22 females, aged 62.6 ± 7.7 years) and non‐curvature group (23 patients, three males and 20 females, aged 64.5 ± 7.6 years). Perioperative parameters and Kellgren‐Lawrence classification were recorded and analyzed in the two groups, respectively. All patients were followed up at 1, 3, 6, and 12 months at the first year of post‐operation, and then every 6 months from the second year of post‐operation. A telephone survey with standard questionnaire survey, including Visual Analog Scale (VAS) score and Hospital for Special Surgery (HSS) scoring system, was used to evaluate postoperative clinical outcomes. Radiological results were assessed using the femorotibial angle (FTA), hip‐knee‐ankle angle (HKA), and settlement value of medial tibial platform (MTP) in the two groups.

Results

The average follow‐up periods of the curvature group and the non‐curvature group were 34.8 ± 6.1 and 33.9 ± 5.4 months, respectively. There were no significant differences between the two groups of demographic data in terms of number of patients, age, body mass index (BMI), gender, KOA side, and Kellgren‐Lawrence classification (P > 0.05). The VAS scores of the curvature group and non‐curvature group were (3.53 ± 1.62 vs 3.68 ± 1.43 at 1 month, 3.46 ± 0.79 vs 3.57 ± 0.66 at 3 months, and 2.43 ± 0.88 vs 2.83 ± 0.94 at 6 months, both P > 0.05), while significant differences were found from 12 months post‐operation (1.54 ± 0.72 vs 2.03 ± 0.85 at 12 months, and 1.04 ± 0.69 vs 1.74 ± 0.75 at 24 months, both P < 0.05). The HSS scores of the curvature group and non‐curvature group were (79.67 ± 5.14 vs 78.25 ± 6.37 at 1 month, 84.65 ± 3.76 vs 83.18 ± 3.64 at 3 months, and 86.27 ± 3.13 vs 85.49 ± 3.25 at 6 months, both P > 0.05), while significant differences were found from 12 months post‐operation (90.64 ± 4.32 vs 87.71 ± 5.63 at 12 months, and 92.93 ± 2.07 vs 90.06 ± 2.08 at 24 months, both P < 0.05). In addition, the FTA and settlement value of the curvature group were lower than the non‐curvature group (177.18 ± 1.52 vs 178.35 ± 1.86, and 5.29 ± 1.74 vs 6.49 ± 2.09, both P < 0.05) while the HKA were higher than the non‐curvature group (175.32 ± 2.34 vs 173.83 ± 2.64, P < 0.05) at the final follow‐up.

Conclusions

Medial KOA patients with upper fibular curvature is an optimal surgical indication for PFO surgery, with the advantages of pain relief, better functional recovery, and alignment correction.

Medial femoral condyle fracture during an Oxford unicompartmental knee replacement surgery: case report

Oxford unicompartmental knee arthroplasty has been used as a good alternative for medial unicompartmental osteoarthritis due to its association with early rehabilitation and a low rate of intraoperative complications. This case describes a rare complication during the procedure of an intraoperative fracture of the medial condyle that was treated with osteosynthesis with 6.5 mm cannulated screws and a compression technique. The patient followed a non-weight-bearing protocol for 6 weeks and reached full range of motion at 3 months. Complete radiological fusion and good functional outcome were observed. Intraoperative fractures can benefit from stable osteosynthesis that allows free range of motion and does not jeopardise the final surgical result.

High Prevalence of Radiographic Outliers and Revisions with Unicompartmental Knee Arthroplasty

BACKGROUND

Alignment outcomes and their impact on implant survival following unicompartmental knee arthroplasty (UKA) are unclear. The purpose of this study was to assess the implant survival and radiographic outcomes after UKA as well as the impact of component alignment and overhang on implant survival.

METHODS

We performed a retrospective analysis of 253 primary fixed-bearing and mobile-bearing medial UKAs from a single academic center. All UKAs were performed by 2 high-volume fellowship-trained arthroplasty surgeons. UKAs comprised <10% of their knee arthroplasty practices, with an average of 14.2 medial UKAs per surgeon per year. Implant survival was assessed. Femoral coronal (FCA), femoral sagittal (FSA), tibial coronal (TCA), and tibial sagittal (TSA) angles as well as implant overhang were radiographically measured. Outliers were defined for FCA (>±10° deviation from neutral), FSA (>15° of flexion), TCA (>±5° deviation from neutral), and TSA (>±5° deviation from 7°). "Far outliers" were an additional >±2° of deviation. Outliers for overhang were identified as >3 mm for anterior overhang, >2 mm for posterior overhang, and >2 mm for medial overhang.

RESULTS

Among patients with a failed UKA, revision was performed at an average of 3.7 years (range, 0.03 to 8.7 years). The cumulative revision rate was 14.2%. Kaplan-Meier survival analysis demonstrated 5 and 10-year survival rates of 88.0% (95% confidence interval [CI] = 82.0% to 91.0%) and 70.0% (95% CI = 56.0% to 80.0%), respectively. Only 19.0% (48) of the UKAs met target alignment for all 4 alignment measures, and only 72.7% (184) met all 3 targets for overhang. Only 11.9% (30) fell within all alignment and overhang targets. The risk of implant failure was significantly impacted by outliers for FCA (failure rate = 15.4%, p = 0.036), FSA (16.2%, p = 0.028), TCA (17.9%, p = 0.020), and TSA (15.2%, p = 0.034) compared with implants with no alignment or overhang errors (0%); this was also true for far outliers (p < 0.05). Other risk factors for failure were posterior overhang (failure rate = 25.0%, p = 0.006) and medial overhang (38.2%, p < 0.001); anterior overhang was not a significant risk factor (10.0%, p = 0.090).

CONCLUSIONS

The proportions of UKA revisions and alignment outliers were greater than expected, even among high-volume arthroplasty surgeons performing an average of 14.2 UKAs per year (just below the high-volume UKA threshold of 15). Alignment and overhang outliers were significant risk factors for implant failure.

LEVEL OF EVIDENCE

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

A modified technique for tibial bone sparing in unicompartmental knee arthroplasty

Supplemental Digital Content is available in the text

Background:

Previously, the authors modified the surgical technique to preserve tibial bone mass for Oxford unicompartmental knee arthroplasty (UKA). The purpose of this study was to determine the clinical outcomes and values of this modified technique.

Methods:

Clinical data of 34 consecutive patients who underwent the unilateral modified UKA technique (modified group, 34 knees) were retrospectively analyzed. To compare the outcome, a match-paired control group (conventional group, 34 knees) of an equal number of patients using the conventional technique system in the same period were selected and matched with respect to diagnosis, age, pre-operative range of motion (ROM), and radiological grade of knee arthrosis. Clinical outcomes including knee Hospital for Special Surgery (HSS) score, ROM, and complications were compared between the two groups. Post-operative radiographic assessments included hip-knee-ankle angle (HKA), joint line change, implant position, and alignment.

Results:

The mean follow-up time was 38.2 ± 6.3 months. There was no difference in baseline between the two groups. The amount of proximal tibial bone cut in the modified group was significantly less than that of the conventional group (4.7 ± 1.1 mm vs. 6.7 ± 1.3 mm, t = 6.45, P < 0.001). Joint line was elevated by 2.1 ± 1.0 mm in the modified group compared with –0.5 ± 1.7 mm in the conventional group (t = –7.46, P < 0.001). No significant differences were observed between the two groups after UKA with respect to HSS score, VAS score, ROM, and HKA. Additionally, the accuracy of the post-operative implant position and alignment was similar in both groups. As for implant size, the tibial implant size in the modified group was larger than that in the conventional group (χ² = 4.95, P = 0.035).

Conclusions:

The modified technique for tibial bone sparing was comparable with the conventional technique in terms of clinical outcomes and radiographic assessments. It can preserve tibial bone mass and achieve a larger cement surface on the tibial side.

A Technical Tip to Avert Meniscal Rotation and Dislocation in a Mobile Bearing Unicompartmental Knee Arthroplasty

The Oxford (Oxford® partial knee; Biomet) mobile bearing medial unicondylar knee replacement (OUKR) is a preferred choice by surgeons due to minimal blood loss, reduced pain, and better range of motion. Commonly observed complications include aseptic loosening, polyethylene wear, bearing dislocation, and periprosthetic fractures. A bearing dislocation can be prevented by ensuring that there is correct tracking of bearing during the trial reduction as well as no loss of entrapment. We present a case report in a 50-year-old patient undergoing bilateral OUKR wherein it was observed that the meniscal bearing upon the flexion of the knee joint had the tendency to dislocate. Upon revising the vertical tibial recut according to the anterior superior iliac spine, the meniscus was found to have a normal excursion. Mobile bearing dislocation is a unique complication of mobile bearing OUKR. Surgical technique is of paramount importance in ensuring a successful OUKR. The vertical tibial cut is made to accommodate the vertical wall of the tibial component. Meniscal displacement is quite a common complication and can occur due to multiple causes. Inaccurate vertical tibial cut may be one such reason leading to tibial dislocation.

A novel extramedullary technique to guide femoral bone preparation in mobile unicompartmental knee arthroplasty based on tibial cut and overall alignment

Background

The mobile Oxford unicompartmental knee arthroplasty (UKA) implant has been widely used with an intramedullary guide for femoral preparation. We modified the femoral guide technique based on the tibial cut first and spacer block technique. This study was performed to determine the radiographic accuracy and early clinical outcomes of the extramedullary method.

Methods

We retrospectively evaluated 50 consecutive patients who underwent UKA using the extramedullary technique. An equal number of patients who underwent UKA with the conventional technique were matched as the control group. Clinical outcomes were evaluated in terms of the operating time, blood loss, range of motion, and Hospital for Special Surgery score. Radiographic accuracy was evaluated by the implant position and alignment in the coronal and sagittal planes.

Results

The mean follow-up period was 39.76 ± 5.77 months. There were no differences in the postoperative Hospital for Special Surgery score, range of motion, or hip-knee-ankle angle between the two groups. The operating time in the extramedullary group was shorter than that in the conventional group (54.78 ± 7.95 vs. 59.14 ± 10.91 min, respectively; p = 0.025). The drop in hemoglobin after 3 days was only 12.34 ± 4.98 g/L in the extramedullary group which was less than that in the conventional group (p = 0.001). No significant differences were found in the postoperative coronal and sagittal angles between the two groups. Acceptable radiographic accuracy of the implant alignment and position was achieved in 92% of patients in the extramedullary group and 96% of patients in the conventional group.

Conclusions

The radiographic and clinical results of the extramedullary technique were comparable with those of the conventional technique with the advantage of no intramedullary interruption, less blood loss, a shorter operating time, and more rapid recovery. As the technique depends on the accurate tibial cut and overall alignment, we do not recommend it to surgeons without high volume experiences.

Trial registration

Retrospectively registered

Level of evidence

IV, retrospective study

Risk factors of postoperative valgus malalignment in mobile-bearing medial unicompartmental knee arthroplasty

OBJECTIVE

The aim of this observational study was to investigate the risk factors of postoperative valgus malalignment after mobile-bearing medial unicompartmental knee arthroplasty (UKA).

METHODS

We retrospectively evaluated radiographic and surgical characteristics in 122 consecutive Oxford phase 3 UKAs. According to postoperative hip-knee-ankle angle (HKAA), 24 knees were sorted into group valgus with HKAA > 180° and 98 knees were sorted into group non-valgus with HKAA ≤ 180°. Logistic regression was performed to analyze risk factors including age, gender, BMI, side, preoperative limb alignment HKAA, preoperative LDFA, MPTA, FTFA, thickness of polyethylene bearing insert, tibial prothesis size, femoral prothesis size, medial tibial cut thickness, thickness of distal femoral mill, prothesis angle of coronal, and sagittal plane.

RESULTS

The mean mechanical preoperative HKAA of 174.39°±4.23° was corrected to 178.18°±3.49° postoperatively (t = - 13.45, p = 0.000). The mean of postoperative HKAA in valgus group and non-valgus group was 183.45 ± 2.21° and 176.88 ± 2.35°, respectively (t = 12.44, p = 0.000). After statistical analysis with univariate analysis, eight risk factor variables among 16 independent variables were identified as potential predictors with p value ≤ 0.1. Multivariate logistic regression analysis for these eight potential predictors revealed that tibial cut (p = 0.046), LDFA (p = 0.003), MPTA (p = 0.011), and FTFA (p = 0.008) were significant risk factors predicting postoperative valgus malalignment after mobile-bearing UKA.

CONCLUSIONS

Preoperative smaller LDFA, FTFA, larger MPTA and less medial tibial cut thickness were significantly associated with postoperative valgus malalignment in mobile-bearing UKA.

Patterns of Compartment Involvement in End-stage Knee Osteoarthritis in a Chinese Orthopedic Center: Implications for Implant Choice

OBJECTIVES

Knee osteoarthritis (OA) is a prevalent disease in the elderly, causing pain and contributing to poor quality of life. Surgical intervention, such as knee arthroplasty, can be used in those with end-stage knee OA. Total knee arthroplasty (TKA) is one of the most common surgical procedures for end-stage knee OA, with promising clinical outcomes. However, a large proportion of patients with isolated compartment OA can be treated with unicompartmental knee arthroplasty (UKA) instead. UKA has shown better patient-reported functional outcomes, and lower mortality and major complication rates than TKA. The percentage of UKA in knee arthroplasty varied in different orthopedic centers, and we believed that the requirement for UKA was underestimated in many centers. A retrospective study was carried out on our Chinese patient population presenting for knee arthroplasty; it aimed to identify the proportion of patients that might be suitable for UKA.

METHODS

A retrospective cross-sectional study of 155 consecutive patients (168 knees) awaiting TKA for end-stage primary OA was performed. The pattern and grade of OA was recorded from preoperative weight-bearing anteroposterior and non-weight-bearing lateral radiographs. The medial, lateral, patellofemoral compartment was given an individual Kellgren-Lawrence grade on the radiographs, and those grade ≥3 were defined as end-stage OA. The compartments involvement was established then. The integrity of the anterior cruciate ligament (ACL) was determined by the modified Keyes classification on lateral radiographs. The applicability for total or partial knee arthroplasty was determined according to the compartments involvement.

RESULTS

Medial compartment involvement was found in 154 (91.7%) knees, while the involvement of the lateral compartment and patellofemoral joint was found in 54 (32.1%) and 57 (33.9%) knees, respectively. Eighty-one (48.2%) of the knees showed medial compartment OA with or without patellofemoral joint involvement, and modified Keyes classification grade 1, indicating an intact ACL, and, hence, potential suitability for medial UKA. Isolated lateral OA indicating possible suitability for lateral UKA was identified in 11 knees (6.5%). No patients showed isolated patellofemoral joint OA. The other 76 (45.2%) knees could be treated by TKA.

CONCLUSIONS

The medial compartment was the most commonly affected in our Chinese patients indicated for knee arthroplasty. More than half of the patients in this group could be treated by either medial or lateral UKA.

FTFA change under valgus stress force radiography is useful for evaluating the correctability of intra-articular varus deformity in UKA

OBJECTIVE

The aim of this observational study was to investigate the postoperative alignment change with Oxford unicompartmental knee arthroplasties (UKA), and clarify whether femoro-tibial facet angle (FTFA) is useful for evaluating alignment correctability with UKA.

METHODS

This study evaluated 79 knees consecutive minimally invasive Oxford phase 3 UKAs performed between 2013 and 2014. Full-length weight-bearing radiographs of the lower limbs were obtained pre- and postoperatively to assess varus angle. Preoperative valgus stress radiography in the supine position was also performed. FTFA was measured on weight-bearing anteroposterior radiography and valgus stress radiography.

RESULTS

The preoperative varus angle of 4.6° ± 3.1° reduced to 1.7° ± 2.6° postoperatively. Preoperative varus angle and postoperative varus angle change strongly correlated with the FTFA value and its change on the valgus stress radiographs, respectively (p < 0.01). Based on preoperative FTFA under valgus stress radiography, intra-articular varus corrected group (37 knees) with preoperative varus angle 2.9° ± 2.4° was corrected to - 0.3° ± 2.0° after UKA. However, intra-articular varus uncorrected group (42 knees) with preoperative varus angle 6.0° ± 3.0° was only corrected to 3.5° ± 1.7°. Thirteen knees (16.5%) were overcorrected to valgus after UKA, with a mean FTFA of - 1.2° ± 0.4° under valgus stress force, which related with a postoperative valgus angle 0.8° ± 1.2°.

CONCLUSION

FTFA change under valgus stress force was useful for evaluating the correctability of UKA. It could reflect intra-articular varus deformity. Intra-articular varus deformity not corrected under valgus stress would result in varus after UKA. However, intra-articular deformity which could be overcorrected under valgus stress would have a tendency to valgus after Oxford UKA.

Intentionally Increased Flexion Angle of the Femoral Component in Mobile Bearing Unicompartmental Knee Arthroplasty

Purpose

The purpose of this study was to determine the results of mobile bearing unicompartmental knee arthroplasty (UKA) with an intentionally increased flexion angle of the femoral component in patients requiring high flexion.

Materials and Methods

We investigated 45 knees treated by UKA. Clinically, we measured the range of motion (ROM) and the American Knee Society (AKS) score preoperatively and at final follow-up and investigated complications. Radiologically, we measured the flexion angle of the femoral component, the posterior slope angle of the tibial component, the femorotibial angle and mechanical axis of the limb postoperatively.

Results

The ROM was increased from 123° preoperatively to 139° at the final follow-up. The AKS knee and function scores increased from 59 and 68, respectively, preoperatively to 94 and 96, respectively, at the final follow-up. The flexion angle of the femoral component was 9.1°, and the posterior slope angle of the tibial component was 8.6°. There was one case of bearing dislocation in the largest femoral flexion angle case.

Conclusions

The results might reflect the positive effect of an increased flexion angle of the femoral component up to 10° on ROM in mobile bearing UKA, which would contribute to better quality of life after UKA especially in populations requiring deep knee flexion.

Long-Term Clinical Results of Unicompartmental Knee Arthroplasty in Patients Younger than 60 Years of Age: Minimum 10-Year Follow-up

Purpose

To evaluate the long-term clinical results and survivorship of unicompartmental knee arthroplasty (UKA) in patients younger than 60 years of age.

Materials and Methods

One hundred and six cases of medial UKA with a minimum follow-up of 10 years were selected for this study. There were 80 patients and the preoperative diagnosis was osteoarthritis in all cases. The mean age of the patients was 54.2 years and the mean duration of follow-up was 12.1 years. Clinical assessments were performed using the Knee Society clinical rating system, and a survival analysis was performed using the Kaplan-Meier method.

Results

The mean knee and function scores improved from 52.8±8.4 points and 56.6±10.6 points preoperatively to 85.4±9.1 points and 84.7±10.4 points at the last follow-up, respectively (p<0.001). The mean range of motion was recovered from 130.7° to 132.8° at the last follow-up. Complications occurred in 20 cases (16.7%) and the most prevalent complication was mobile bearing dislocation (n=9, 7.5%). The 10-year survival rate was 92.8% when conversion to total knee arthroplasty was defined as failure, whereas 89.3% when failure was defined as all revision surgeries.

Conclusions

The long-term clinical results of UKA were satisfactory in patients under 60 years of age. Therefore, UKA could be a useful method for the treatment of medial compartment osteoarthritis of the knee in patients younger than 60 years of age.

Midterm Results of Cementless and Cemented Unicondylar Knee Arthroplasty with Mobile Meniscal Bearing: A Prospective Cohort Study

Background:

Cemented unicompartmental knee arthroplasty (UKA) yields good clinical outcome but common revision reasons are loosening and pain. Cementless UKA may reduce the revision rate.

Objective:

The current study was designed to assess clinical and radiographic outcome of cemented and cementless UKA, using bone quality as determined by the Bone Hardness Test (BHT) as selection criterion for cementless implantation.

Methods:

In this prospective comparative cohort study we analyzed 50 cementless and 29 Oxford consecutive UKA cases. Patients with sufficient bone quality were eligible for cementless UKA. Bone quality was assessed with the BHT, which consisted of exercising pressure with the thumb on the bone surface created after resection of the tibia.

Results:

The average surgical times were 62.5 ± 12.6 and 78 ± 16 minutes in the cementless and the cemented group, respectively (p < 0.01). The average thickness of the polyethylene insert was 4.3 ± 1.2 (range, 3 – 9) and 3.7 ± 0.8 (range, 3 – 6) mm, respectively (p = 0.02). Both types of implants yielded excellent clinical and functional results. At an average follow-up time of seven years, we found non-significant differences between clinical results of cementless versus cemented implants.

Conclusion:

Shorter surgical time makes cementless implantation more attractive to surgeons when considering UKA options for their patients. The average thickness of the polyethylene insert in cementless group was 0.6 mm thinner than in the cemented group. The BHT is a simple and useful test to assess whether patients are eligible for cementless UKA.

The influence of different sets of surgical instrumentation in Oxford UKA on bearing size and component position

INTRODUCTION

The Oxford unicompartmental knee arthroplasty (OUKA) has been proven to be an effective treatment for anteromedial osteoarthritis of the knee joint. New instrumentation has been introduced to improve the reproducibility of implant positioning and to minimize bone loss during tibial resection (Oxford Microplasty; Zimmer Biomet, Warsaw, Indiana, USA).

METHODS

To assess the effect of the new instrumentation, we retrospectively evaluated the postoperative radiographs and surgical records of 300 OUKAs in three consecutive cohorts of patients. The first cohort consists of the first 100 minimal invasive implantations of the OUKA using the conventional phase III instrumentation, the second cohort consists of the 100 most recent minimal invasive OUKA with the conventional phase III instrumentation and the third cohort consists of the first 100 minimal invasive OUKA using the new Oxford Microplasty instrumentation.

RESULTS

Mean bearing thickness was statistically significant and lower in OUKA with use of the updated instrumentation than with the conventional instrumentation (p = 0.01 and p = 0.04). Additionally, statistically significant and more femoral components were aligned within the accepted range of tolerance in both the coronal and the sagittal plane with use of the updated instrumentation compared to the conventional phase III instrumentation in group A (p = 0.029 and p = 0.038) and in the sagittal plane with use of the updated instrumentation compared to the conventional phase III instrumentation in group B (p = 0.002).

CONCLUSION

The new modified instrumentation seems to be an effective tool to reduce the risk of malalignment of the femoral component in the coronal and in the sagittal plane compared to the conventional phase III instrumentation. Furthermore, the instrumentation is also effective in determining an adequate level of tibial resection and thus avoiding unnecessary bone loss.

Medial femoral condyle fracture as an intraoperative complication of Oxford unicompartmental knee replacement

Oxford unicompartmental knee replacement (OUKR) is associated with a low perioperative complication rate. This case report describes a periprosthetic fracture of the medial femoral condyle that occurred during an OUKR. The patient was treated with a non-weight-bearing long leg cast for 6 weeks. Afterwards, the fracture had healed, and 3 months postoperatively, there was a full range of motion. Factors leading to this complication could be the impaction force or direction, or a diminished load resistance of the distal femur. Minimally displaced coronal periprosthetic fractures after OUKR can be managed conservatively without residual functional impairment.

LEVEL OF EVIDENCE

Case report, Level IV.

Fixed- versus mobile-bearing UKA: a systematic review and meta-analysis

PURPOSE

Two design concepts are currently used for unicondylar knee arthroplasty (UKA) prostheses: fixed bearing (FB) and mobile bearing (MB). While MB prostheses have theoretical advantages over their FB counterparts, it is not clear whether they are associated with better outcomes. A systematic review was conducted to examine survivorship differences and differences in failure modes of between FB and MB designs.

METHODS

PubMed, Scirus and Cochrane library databases were searched for medial UKA outcome studies. A total of 44 papers, involving 9,463 knees, were eligible. Outcomes examined included knee function, survivorship and the reasons for, and incidence of, revision for FB and MB prostheses. Random effects meta-analysis was employed to obtain pooled revision rate estimates. Where available, cause-specific time to revision was extracted.

RESULTS

Mean follow-up was 8.7 years for FB and 5.9 years for MB prostheses. There were no other relevant baseline differences. The overall crude revision rate for FB and for MB prostheses was 0.90 (95 % confidence interval (CI) 0.65-1.21) and 1.51 (95 % CI 1.11-1.93) per 100 component years, respectively. After stratification on follow-up time and age, the revision rates were not substantially different, aside for younger patients in short term from studies with short-term follow-up.

CONCLUSION

No essential differences between the two designs were observed. MB and FB UKA designs have comparable revision rates. As our study is based on predominantly observational data, with large variations in reporting standards, inferences should be drawn with caution.

LEVEL OF EVIDENCE

IV.

Mid-term Results of Oxford Phase 3 Unicompartmental Knee Arthroplasties at a Small-Volume Center

BACKGROUND AND AIMS

Unicompartmental knee arthroplasty is considered as an alternative to total knee arthroplasty for patients who have osteoarthritis limited to the medial compartment of the knee. The aim of this retrospective study was to find out clinical and radiological outcomes and related complications using the Oxford phase 3 prosthesis at a small-volume center.

MATERIAL AND METHODS

In all, 95 Oxford unicompartmental knee arthroplasties (87 patients) were performed between 2000 and 2010 in North Karelia Central Hospital. Of these, five patients had undergone revision surgery. In all, 52 unicompartmental knee arthroplasties (46 patients) participated in this study. The mean age of patients was 61.4 years, and 78.2% of patients were females. Pain and function levels were evaluated by using the Knee Society score. Radiographic analyses were performed on preoperative and postoperative and follow-up radiographs.

RESULTS AND CONCLUSIONS

The mean follow-up time was 6.5 years, and the Kaplan-Meier estimated 9-year implant survival rate was 88.9% (95% confidence interval = 78.7%-99.1%). The median Knee Society score of 77 (range: 18-93) at follow-up was considered good (range: 70-79). In this study, we found out that medial knee pain remains in 10% of unicompartmental knee arthroplasties several years after surgery, although the reason for the pain remained unclear. These mid-term results are promising, and good results can be achieved also at a small-volume center when strict patient selection is followed.

Femoral component failure in the Oxford unicompartmental knee arthroplasty: a case report

INTRODUCTION

The present case report describes a patient who presented with an early complication after a unicompartmental knee arthroplasty. It is not the first case in this subject but the unique aspect of this case report rests on the timing in which the failure occurred.

CASE PRESENTATION

A 64-year-old Caucasian man received a medial unicompartmental knee arthroplasty (Oxford® Partial Knee) due to isolated anteromedial osteoarthritis of his right knee. His initial recovery was good, however, after 3 months he presented with acute pain and a locked knee. Radiographs showed a complete loosening and migration of the femoral component. During revision surgery no clear explanation was found for failure of the femoral component.

CONCLUSIONS

The most likely explanation for loosening is the combination of peak stresses on the posterior facet of the femoral components of a unicompartmental knee arthroplasty in a patient in a cross-legged knee position causing bone-cement or cement-implant interface failure. Further research is necessary in prosthetic designs and applications of the unicompartmental knee arthroplasty to determine the origin of this early complication.

The learning curve for minimally invasive Oxford phase 3 unicompartmental knee arthroplasty: cumulative summation test for learning curve (LC-CUSUM)

BACKGROUND

The minimally invasive Oxford unicompartmental knee arthroplasty (UKA) is a demanding procedure but has many advantages compared with total knee arthroplasty (TKA). The aim of this observational study was to investigate the learning curve of one experienced surgeon introducing minimally invasive Oxford phase 3 UKA into his routine clinical practice.

METHODS

The first 50 consecutive cases of minimally invasive Oxford phase 3 UKA performed by one surgeon were evaluated to determine whether there was an association between outcomes and the cumulative number of cases performed, indicating the presence of learning curve. The cohort was divided into two groups: group A comprised the first 25 cases and group B cases 26-50. Duration of surgery, blood loss, Hospital for Special Surgery score, range of motion, complications, and the radiographical position of the implant were compared between the groups. The cumulative summation test for learning curve (LC-CUSUM) was then used to further analyze the learning curve.

RESULTS

The mean age and follow-up were 64.4 years and 50.9 months, respectively. The duration of surgery and blood loss were significantly more favorable in group B. The length of incision gradually reduced from 9.7 ± 1.3 to 8.5 ± 1.1 cm. Failures were identified in nine patients (18%). Two revisions and two dislocations were encountered in group A; one revision was performed 4 years after surgery for a patient in group B because of a fracture. One case of lateral compartment osteoarthritis was identified in group A. Two patients in each group reported continuing unexplained pains. CUSUM analysis showed that failure rates diminished rapidly after 16 cases and reached an acceptable rate after 29 cases.

CONCLUSIONS

Minimally invasive Oxford phase 3 UKA for anteromedial osteoarthritis is a demanding procedure, but satisfactory outcomes can be achieved after approximately 25 cases.

Medial femoral condyle fracture after cementless unicompartmental knee replacement: a rare complication

This case report describes a rare complication of unicompartmental knee arthroplasty. Femoral fracture after TKR is a serious and relatively common problem, but to the best of our knowledge, only one case of femoral condylar fracture after UKA has been reported thus far.

Oxford unicompartmental knee arthroplasty: medial pain and functional outcome in the medium term

BACKGROUND

In our experience results of the Oxford unicompartmental knee replacement have not been as good as had been expected. A common post operative complaint is of persistent medial knee discomfort, it is not clear why this phenomenon occurs and we have attempted to address this in our study.

METHODS

48 patients were retrospectively identified at a mean of 4.5 years (range = 3 to 6 years) following consecutive Oxford medial Unicompartmental Knee arthroplasties for varus anteromedial osteoarthritis. The mean age at implantation was 67 years (range 57-86). Of these 48 patients, 4 had died, 4 had undergone revision of their unicompartmental knee replacements and 2 had been lost to follow up leaving 38 patients with 40 replaced knees available for analysis using the 'new Oxford Knee Score' questionnaire. During assessment patients were asked specifically whether or not they still experienced medial knee discomfort or pain.

RESULTS

The mean 'Oxford score' was only 32.7 (range = 16 to 48) and 22 of the 40 knees were uncomfortable or painful medially.The accuracy of component positioning was recorded, using standard post operative xrays, by summing the angulation or displacement of each component in two planes from the ideal position (according to the 'Oxford knee system radiographic criteria'). No correlation was demonstrated between the radiographic scores and the 'Oxford scores', or with the presence or absence of medial knee discomfort or pain.

CONCLUSION

In our hands the functional outcome following Oxford Unicompartmental knee replacement was variable, with a high incidence of medial knee discomfort which did not correlate with the postoperative radiographic scores, pre-op arthritis and positioning of the prosthesis.

Factors associated with reduced early survival in the Oxford phase III medial unicompartment knee replacement

The aim of this study was to determine the prognostic value of preoperative patellofemoral osteoarthritis, BMI and age for implant survival of unicompartmental knee arthroplasty (UKA) performed in patients meeting strict admission criteria. The data and radiographs of 437 unilateral Oxford phase III procedures (Biomet, Bridgend, UK) were analysed. All procedures were carried out or supervised by 13 specialised knee surgeons in three different hospitals. The study group comprised 437 patients with a median follow of 2.6 years (0.1-7.9). The cumulative standard case survival rate at 5 years, when there were still 101 patients at risk, was 84.7% (CI-95%: 80.1-89.3%). Young age (<60 years) was associated with a 2.2-fold increased adjusted risk of revision (CI: 1.08-4.43; p=0.03). The preoperative presence of radiological features of patellofemoral osteoarthritis was associated with a 0.3-fold reduced adjusted risk of revision (CI: 0.11-0.89; p=0.03). BMI>30 kg/m(2), gender, the surgeon performing the operation (either as an individual or categorised by annual surgical UKA caseload, i.e., more or less than 10 UKAs) and the hospital in which surgery took place did not predict implant survival of UKA. We conclude that young patients (<60 years) experience an increased early risk of revision for UKA when compared to older patients (>60 years). Obesity (BMI>30 kg/m(2)) and preoperative patellofemoral osteoarthritis are not associated with a decreased implant survival and therefore should not be considered risk factors in this context.

Correlation of positioning and clinical results in Oxford UKA

In a prospective clinical study, 59 patients with anteromedial osteoarthritis of the knee (61 knee joints) underwent minimally invasive medial Oxford unicompartmental arthroplasty phase 3. Clinical and radiographic examinations of 56 knees were carried out at five (4-7) years. American Knee Society (AKS) scores improved from mean 45.5 (20-80) points (knee score) and 55 (15-100) points (function score) before surgery to 90 (30-100) points in both scores after surgery. The position of each implant was determined on screened radiographs using an image intensifier. The implant position was analysed according to the Oxford X-ray rating system. We evaluated nine measures, and there was no detectable correlation between implant position and clinical result. However, long-term studies are needed before it is possible to elaborate an evidence-based guideline on positioning.

Fracture of the medial femoral condyle after unicompartmental knee arthroplasty

Periprosthetic fracture is a relatively rare but well-recognized complication after knee joint arthroplasty. We experienced a case of medial femoral condylar fracture among 700 cases of unicompartmental knee arthroplasty (UKA). The patient was a 56-year-old woman who underwent minimally invasive UKA for medial osteoarthritis of the knee. A displaced medial femoral condylar fracture occurred 3 years after UKA. A closed reduction and percutaneous fixation using 3 cannulated cancellous screws was performed. Union of the fracture was achieved, and a full recovery of knee motion was gained after 3 months. The Knee Society knee and function scores were 87 and 80, respectively, at the 2-year follow-up. They were the same as the scores before the fracture took place, and there was no evidence of component loosening or ligament instability.

Bi-unicompartmental versus total knee arthroplasty: a matched paired study with early clinical results

INTRODUCTION

The authors performed a matched paired study between two groups: bi-unicompartmental (Bi-UKR) versus total knee replacements (TKR) for the treatment of isolated bicompartmental tibio-femoral knee arthritis with an asymptomatic patello-femoral joint. The Authors believe that Bi-UKR could achieve comparable outcomes than TKR, but with a real less invasive surgery and maintaining a higher joint function.

MATERIALS AND METHODS

A total of 22 patients with bicompartmental tibio-femoral knee arthritis, who underwent Bi-UKR between January 1999 and March 2003, were included in the study (group A). In all the knees the arthritic changes were graded according to the classification of Alback. All patients had an asymptomatic patello-femoral joint. All patients had a varus deformity lower than 8 degrees , a body-mass index lower than 34, no clinical evidence of ACL laxity or flexion deformity and a preoperative range of motion of a least 110 degrees . At a minimum follow-up of 48 months, every single patient in group A was matched with a patient who had undergone a computer assisted TKR between August 1999 and September 2002 (group B). In the Bi-UKR group, in two cases we registered intraoperatively the avulsion of the treated tibial spines, requiring intra-operative internal fixation and without adverse effects on the final outcome. Statistical analysis of the results was performed.

RESULTS

At a minimum follow-up of 48 months there were no statistical significant differences in the surgical time while the hospital stay was statistically longer in TKR group. No statistically significant difference was seen for the Knee Society, Functional and GIUM scores between the two groups. Statistically significant better WOMAC Function and Stiffness indexes were registered for the Bi-UKR group. TKR implants were statistically better aligned with all the implants positioned within 4 degrees of an ideal hip-knee-ankle (HKA) angle of 180 degrees .

CONCLUSIONS

The results of this 48 months follow-up study suggest that Bi-UKR is a viable option for bicompartmental tibio-femoral arthritis at least as well as TKR but maintaining a higher level of function.

Analysis of Oxford medial unicompartmental knee replacement using the minimally invasive technique in patients aged 60 and above: an independent prospective series

We present the outcome of an independent prospective series of phase-3 Oxford medial mobile-bearing unicompartmental knee replacement surgery. Eight surgeons performed the 154 procedures in a community-based hospital between 1998 and 2003 for patients aged 60 and above. Seventeen knees were revised; in 14 cases a total knee replacement was performed, in 3 cases a component of the unicompartmental knee prosthesis was revised, resulting in a survival rate of 89% during these 2-7 years follow-up interval. This study shows that mobile-bearing unicompartmental knee replacement using a minimally invasive technique is a demanding procedure. The study emphasises the importance of routine in surgical management and strict adherence to indications and operation technique used to reduce outcome failure.

The Oxford phase III unicompartmental knee replacement in patients less than 60 years of age

Treatment of younger patients with medial unicompartmental disease of the knee joint remains a challenging therapeutic dilemma. With the refinement of implant design, fixation and the minimally invasive techniques employed with unicompartmental knee replacement, indications have expanded to include its use in young patients. A prospective cohort of 46 unicompartmental knee procedures were performed with a 2-year minimum and 6-year maximum follow-up, using the Oxford phase III unicompartmental knee arthroplasty, in the younger patient group (age 60 or younger). We conclude that the unicompartmental knee arthroplasty is an important option for the treatment of medial compartment disease for patients 60 years or younger. Obesity can cause technical difficulties, increased risk of complications and early failure of this prosthesis.