Mobile-bearing unicondylar knee arthroplasty: the Oxford experience

Is unicompartmental knee arthroplasty truly contraindicated in an obese patient? A meta-analysis

BACKGROUND

Obesity has long been considered a relative contraindication to unicompartmental knee arthroplasty (UKA). However, with improved implants and techniques, the criteria for UKAs have been challenged. This paper aims to assess the impact of body mass index (BMI) on revision rates and functional outcomes in UKAs.

METHODS

Databases of Pubmed, EMBASE, MEDLINE, CINHL and the Cochrane registries were systematically searched following the PROSPERO protocol. Studies comparing implant survival and functional outcome scores between obese and non-obese patients after a UKA were included.

RESULTS

Twenty-five articles reported revision rates or functional outcomes in 42,434 UKA surgeries. There was a trend to higher revision rates in patients with BMI > 30 kg/m2 (odds ratio [OR] 0.91 [0.79-1.05]), BMI >35 kg/m2 (OR 0.70 [0.48, 1.01]) or BMI >40 kg/m2 (OR 0.66 [0.41, 1.07]), although the difference was not significant. There was a significant larger improvement in Oxford Knee Scores in obese patients after a UKA (OR 2.68 [1.79, 3.57], p < 0.00001), but no difference in Knee Society Scores or Visual Analogue Scale scores.

CONCLUSION

With no significant increase in revision rates after a UKA, a significantly greater improvement in Oxford Knee Scores and no differences Knee Society Scores or Visual Analogue Scales, obesity should no longer be viewed as a relative contraindication when performing unicompartmental knee replacements.

Impact of lateral meniscus injury detected by preoperative magnetic resonance imaging on midterm results after unicompartmental knee arthroplasty

BACKGROUND

The significance of lateral meniscus injury and its impact on success rates with medial unicompartmental knee arthroplasty (UKA) is still debated among scholars. This study aims to investigate whether preoperative magnetic resonance imaging (MRI) findings of lateral meniscus injury influence midterm outcomes following UKA.

METHODS

This study recruited 104 patients who underwent medial mobile-bearing UKA. Based on the extent of lateral meniscus injury indicated by the preoperative MRI and Stoller's classification system, patients were divided into two groups: the normal group (grade 0), and the lateral meniscus injury group (grade 3). Further, preoperative demographic and clinical outcome data (Hospital for Special Surgery score, lateral knee pain, squatting, and knee extension ability) were compared at least 2 years postoperatively.

RESULTS

No statistically significant difference in knee function or clinical outcome was found between the normal group (n = 59) and the lateral meniscus injury group (n = 45). During the 39.2 months (range: 24-64 months), no patient required any reoperation or revision procedures.

CONCLUSION

In summary, the presence of lateral meniscus injury as determined by preoperative MRI does not affect the midterm results after UKA. Without additional treatment for lateral meniscus injury, UKA can yield desired outcomes regardless of the presence of lateral meniscus injury on preoperative MRI.

Early Outcomes of Modified Technique of Mobile Bearing Unicondylar Knee Replacement

Background

Recent years have seen a resurgence in utilization of partial knee replacement. One such device frequently used is Oxford partial knee implant (OPK). Deeper tibial bone cut while performing OPK replacement may risk early failure.

Methods

We prospectively looked at early outcomes of a modified technique (MT) of OPK replacement adopted by our centre to save tibial bone stock at 24 months of follow up as compared to designer group described technique (DT) as a prospective cohort.

Results

At 2 years follow up New Knee Society Score showed patient satisfaction (38.25 in DT vs 39.02 in MT, p value 0.10), objective (92.77 in DT vs 91.07 in MT, p value 0.21), expectation scores (14.77 in DT vs 14.85 in MT, p value 0.81) and activity (60.72 in DT vs 68.17 in MT, p value 0.79 were similar in MT group as compared to DT. The stair climbing ability (22.46 in MT vs 29.96 in DT, p value < 0.001) and getting up from chair (13.16 in MT vs 19.80 in DT, p value < 0.001), was better with MT group but most other patient performance scores were similar as assessed by DOP (Delaware Osteoarthritis Profile). Both groups had failure rate of 5% at 24 months follow up.

Conclusion

MT resulted in similar early outcomes in terms of patient reported outcomes, satisfaction and performance as compared to DT group. The MT to save tibial bone stock did not compromise early outcomes and can be utilised in certain patients with higher risk of tibial failure.

Medial unilateral knee arthroplasty after high tibial osteotomy: A retrospective study of 41 cases

INTRODUCTION

When medial knee osteoarthritis continues to get worse after a high tibial osteotomy (HTO) procedure, a subsequent total knee arthroplasty (TKA) is typically warranted. Medial unilateral knee arthroplasty (UKA) is not recommended. The aim of this study was to evaluate the outcomes of patients who underwent medial UKA after HTO.

HYPOTHESIS

Good results can be obtained with this procedure, as long as the postoperative valgus is not excessive.

MATERIALS AND METHODS

This was a retrospective, single-center study of patients operated between January 2005 and June 2019. The primary endpoint was the Oxford Knee Scale (OKS). The Knee injury and Osteoarthritis Outcome Score (KOOS) and the Western Ontario and McMaster Universities osteoarthritis index (WOMAC), range of motion and complications were the secondary endpoints. The average follow-up was 79 months.

RESULTS

Forty-one knees in 38 patients were analyzed. Four revisions with implant exchange (10%) were needed. Thirty-seven knees had a mean OKS of 20/60±8 (12-39). The mean flexion and extension amplitude were 123°±8° (110-140) and -1.5°±4 (-15-0), respectively. Eight patients had flexion and/or extension contractures.

DISCUSSION

Good functional and clinical outcomes in the medium term were achieved for the patients in this study who underwent UKA after HTO. These findings reinforce the good results reported in recent studies of UKA after HTO.

LEVEL OF EVIDENCE

IV, Retrospective study.

The effect of BMI on the mid-term clinical outcomes of mobile-bearing unicompartmental knee arthroplasty

Objective

To evaluate the impact of body mass index (BMI) on the mid-term clinical outcomes and survival in patients receiving a mobile-bearing unicompartmental knee arthroplasty (UKA).

Methods

We retrospectively collected data from 355 patients who underwent UKA from June 2006 to June 2015, with a mean follow-up of 106.5 ± 22.5 months. Patients were assigned into four groups based on their BMI before surgery: normal weight group (BMI 18.5 ~ 22.9 kg/m²), overweight group (23 ~ 24.9 kg/m²), obesity group (25 ~ 29.9 kg/m²), and severe obesity group (≥ 30 kg/m²). The knee society score (KSS), knee society function score (KSFS), hospital for special surgery score (HSS), and range of motion (ROM) were assessed before the operation and at the last follow-up. The femorotibial angle (FTA) was assessed after the operation immediately and at the last follow-up. Kaplan–Meier survival analysis was performed among the four groups.

Results

The KSS, KSFS, and HSS in all groups were markedly improved compared with the preoperative values (p<0.001), but the ROM score was not significantly different (p>0.05). There were significant differences in KSS (p<0.001) and HSS (p = 0.004) across the four BMI groups, and these differences were due to the severe obesity group. All groups exhibited an inclination of knee varus deformity at the last follow-up (p < 0.05). Moreover, no marked difference in the implant survival rate was found among the different groups (p = 0.248), or in the survival curves (p = 0.593).

Conclusions

BMI does not influence the implant survival rate. The postoperative functional and quality-of-life scores were significantly improved in all groups. Obese (BMI ≥30 kg/m²) individuals should not be excluded from UKA.

A novel radiographic technique to assess 180° rotational spin of the Oxford unicompartmental knee mobile bearing

INTRODUCTION

The recognition of anteromedial knee arthritis as a distinct early clinicopathological entity has led to a resurgence in medial unicompartment knee arthroplasty (UKA). Symptomatic knee pain caused by 180° rotational spin of the mobile bearing of the Oxford Knee is an unrecognized and therefore under-reported complication of UKA. Whilst the post-operative radiographic criteria for optimal positioning of UKA is well described in the available literature, this isn't the case for assessing antero-posterior (AP) orientation of the mobile-bearing.

METHODS

Following a literature review, we describe a novel radiographic technique that can consistently assess AP orientation, and as a result, diagnose 180° rotational spin of the mobile-bearing. This technique overcomes the radiological challenge of superimposition of the radiopaque markers with the lateral edge of the tibial tray.

RESULTS

The modified oblique view results in clear visualization of the metallic rod embedded in the polyethylene, away from the lateral edge of the tibial tray. An anteriorly viewed metallic rod would indicate a well oriented mobile bearing. However, if the metallic beads are visualized anteriorly without dislocation, the component would have spun 180°.

CONCLUSION

Clinicians should have a high index of suspicion for 180° spin to have occurred in patients with posterior dislocation with or without spontaneous reduction. We recommend bearing exchange ± revision arthroplasty for symptomatic patients. The modified oblique view is now part of our immediate post-operative XR protocol and repeated for any patient who re-presents symptomatically at any stage following the index procedure.

Effect of vertical cut on coronal coverage and rotation of tibial component in Oxford unicompartmental knee arthroplasty

Objective

This study was performed to investigate the influence of a standard Oxford vertical cut on the coronal coverage and rotation of the tibial component and determine whether a relationship exists between coverage and rotation.

Methods

We retrospectively analyzed 71 patients with anteromedial osteoarthritis of the knee treated by Oxford unicompartmental knee arthroplasty in one center from October 2016 to October 2017. The distance of coronal coverage was measured on a postoperative anteroposterior view of the tibial component. Two different reference lines between the lateral wall of the tibial component were defined as rotation angle α and β, respectively, on a computed tomography scan.

Results

The mean distance was 0.3 ± 1.1 mm. The mean angle α and β were 5.7° ± 4.6° and 8.4° ± 4.6°, respectively. There were no significant differences in the distance according to the tibial component rotation or in the α and β angles according to the coronal coverage. No significant correlation was found between the α and β angles and the distance.

Conclusion

A standard tibial vertical cut caused various changes in coronal coverage and rotation of the tibial component. The rotation of the tibial component did not affect coverage within a certain range.

High Failure Rates for Unicompartmental Knee Arthroplasty in Morbidly Obese Patients: A Two-Year Minimum Follow-Up Study

BACKGROUND

Several recent studies have recommended offering unicompartmental knee arthroplasty (UKA) to all patients regardless of body mass index (BMI). The aim of this investigation was to evaluate the proposition that UKA can indeed be offered to the morbidly-obese and super-obese (morbidly-obese, BMI ≥ 40 kg/m²) without compromising results or survivorship.

METHODS

We retrospectively reviewed mobile-bearing medial UKA procedures performed at our facility from January 2012 to May 2015 with a minimum of 2-year follow-up. The study cohort was divided into patients with morbid obesity (BMI ≥ 40 kg/m²) and those without morbid obesity (BMI < 40 kg/m²). A detailed medical record review was performed. Extracted outcome data included the frequency of (1) major revision procedures (components revised), (2) minor secondary procedures (components not revised), (3) infection procedures, and (4) recommendations for revision.

RESULTS

We found 152 patients (190 knees) who met criteria for inclusion. Mean follow-up duration was 3.4 years (range: 2.0-6.8 years). Major revision surgery occurred more frequently in the morbid-obesity UKA group (15.7% vs 3.0%, P < .01). Rates of minor secondary surgery and infection were comparable for both groups. Most failures in the morbid-obesity UKA group (85.7%) were due to disease progression involving other compartments or mobile-bearing instability.

CONCLUSION

We found the rate of early major revision surgery in morbidly-obese patients undergoing UKA to be over 5-times greater than that of other patients. Failure was predominantly due to disease progression in other compartments or mobile-bearing instability. Further study is warranted and needed before expanding UKA indications to the morbidly-obese population.

[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.

Eight Hundred Twenty-Five Medial Mobile-Bearing Unicompartmental Knee Arthroplasties: The First 10-Year US Multi-Center Survival Analysis

BACKGROUND

FDA approval for the Oxford phase III device was approved for use in the United States in 2004. This study seeks to provide the first long-term, large patient sample size, Oxford phase III multi-site survivorship study in the United States, investigating patient reported outcomes of pain and function, while also providing an in-depth analysis of causes for revision, and finally addressing recent advancements that can help aid the unicompartmental knee arthroplasty (UKA) process and further improve partial knee survivorship.

METHODS

Between July 2004 and December 2006, 5 surgeons from around the United States performed medial UKA through the minimally invasive surgical approach, on 825 knees in 695 patients. This was a consecutive series of primary UKAs using the phase III mobile bearing; cemented Oxford Knee (Zimmer Biomet, Warsaw, IN), implanted utilizing phase III instrumentation. UKA survivorship considered all revisions as the end point. Implant survivorship eliminated revisions at which the original Oxford implant was determined to be well fixated and functional intra-operatively.

RESULTS

A total of 93 knees were revised in this study. Mean follow-up was 9.7 years (6-12). Implant survivorship at year 10 was 90% (confidence interval 2.7%). UKA survivorship at year 10 was 85% (confidence interval 3.8%). Average preoperative American Knee Society Score (knee score) was 49 and rose to 90 postoperatively (standard deviations 16 and 18, respectively). Average preoperative American Knee Society Score (function score) was 55 and rose to 77 postoperatively (standard deviations 15 and 28, respectively).

CONCLUSION

This was the first large-scale, 10-year, multi-site follow-up of the Oxford mobile-bearing medial UKA undertaken in the United States, displaying good survivorship and excellent patient outcomes.

Long-term results and comparison of the three different high tibial osteotomy and fixation techniques in medial compartment arthrosis

BACKGROUND

The purpose of this study is to report and analyze the long-term outcomes of the patients who underwent high tibial osteotomy (HTO) with three different techniques for the treatment of medial compartment arthrosis.

METHODS

A total of 187 patients (195 knees) who underwent HTO between 1990 and 2010 were retrospectively evaluated. Eighty-eight knees, opening-wedge osteotomy with Puddu plate (group A); 51 knees, transverse osteotomy below the tubercle with external fixator (group B); and 29 knees, closing-wedge osteotomy with staple fixation (group C) were included in the study. The patients (mean age 44.9 ± 10.6 years, mean follow-up of 12.4 ± 3.2 years) were called for final controls and survival rates of the knees, and functional evaluations of the patients were performed using Knee Society Score (KSS) and Hospital for Special Surgery (HSS) knee score assessments.

RESULTS

In the comparison of the three groups, there were no differences regarding the mean age, preoperative arthrosis levels, or preoperative deformity analyses (n.s.). The main finding of these comparisons showed that the closing-wedge osteotomy has the greatest lateralization effect on mechanical axis deviation (MAD) (p = 0.024), the greatest valgization effect on medial proximal tibial angles (MPTA) (p = 0.026), and the lowest posterior tibial slope (PTS) angles (p = 0.032) in comparison to the other groups. There were no functional differences between the three groups in the long-term assessment of patients with KSS and HSS knee scores. According to the Kaplan-Meier survival analysis, the probability of the survival of the native knee joint after HTO was 93.4% in 5 years and 71.2% in 10 years in our study group. During the follow-up of the 168 knees, revision surgery with total knee replacement was needed in 27 knees (16%). The mean time from HTO to total knee replacement was 8.9 years in these patients.

CONCLUSIONS

HTO has acceptable long-term clinical and functional results that should not be underestimated by orthopedic surgeons under pressure to perform arthroplasty operations.