Introduction

Unicompartmental knee arthroplasty (UKA) is a successful procedure for medial compartment osteoarthritis (OA). Recent studies using the same implant report a revision rate of 2.9%. Other centers have reported revision rates as high as 10.3%. The purpose of this study was to retrospectively review the clinical results of Oxford Phase 3 UKA's performed in the setting of isolated medial compartment OA and to compare our results to the previous mid-term studies. Our secondary goal was to determine reasons for revision and evaluate selected independent predictors of failure.

Source of the study: University of Auckland, Auckland, New Zealand. Unicompartmental knee arthroplasty (UKA) is effective for patients with isolated compartment osteoarthritis, however the procedure has higher revision rates. Long-term survivorship and accurate characterisation of revision reasons are limited by a lack of long-term data and standardised revision definitions. We aimed to identify survivorship, risk factors and revision reasons in a large UKA cohort with up to 20 years follow-up. Patient, implant and revision details were recorded through clinical and radiological review for 2,137 consecutive patients undergoing primary medial UKA across Auckland, Canterbury, Counties Manukau and Waitematā DHB between 2000 and 2017. Revision reasons were determined from review of clinical, laboratory, and radiological records for each patient using a standardised protocol. To ensure complete follow-up data was cross-referenced with the New Zealand Joint Registry to identify patients undergoing subsequent revision outside the hospitals. Implant survival, revision risk and revision reasons were analysed using Cox proportional-hazards and competing risk analyses. Implant survivorship at 15 years was comparable for cemented fixed-bearing (cemFB; 91%) and uncemented mobile-bearing (uncemMB; 91%), but lower for cemented mobile-bearing (cemMB; 80%) implants. There was higher incidence of aseptic loosening with cemented implants (3–4% vs. 0.4% uncemented, p<0.01), osteoarthritis (OA) progression with cemMB implants (9% vs. 3% cemFB/uncemMB; p<0.05) and bearing dislocations with uncemMB implants (3% vs. 2% cemMB, p=0.02). Compared with the oldest patients (≥75 years), there was a nearly two-fold increase in risk for those aged 55–64 (hazard ratio 1.9; confidence interval 1.1-3.3, p=0.03). No association was found with gender, BMI or ASA. Cemented mobile-bearing implants and younger age were linked to lower implant survivorship. These were associated with disease progression and bearing dislocations. The use of cemented fixed-bearing and uncemented mobile-bearing designs have superior comparable long-term survivorship

Permanent patellar subluxation is treated with surgeries such as proximal realignment and distal realignment, however, it is difficult to cure this condition by using any methods. We performed mobile-bearing total knee arthroplasty (TKA) in a case of severe knee osteoarthritis complicated with permanent patellar subluxation since childhood, and obtained good results without performing any additional procedures. The patient was an 82-year-old woman with severe pain in the left knee. During the initial examination, the range of motion of the left knee joint was -10°of extension to 140°of flexion, and the Japanese Orthopaedic Association (JOA) score for knee osteoarthritis was 40 points (maximum score: 100). Preoperative radiographs showed a varus deformity in the left lower extremity with a femorotibial angle (FTA) of 188°, the axial view showed luxation of the patella. We performed TKA using a mobile-bearing implant. Intraoperative findings revealed that the central articular surface of the distal femur had disappeared, and that the patellar articular surface was concave and dome-shaped. The lateral patellofemoral ligament was released; this procedure was identical to that performed in conventional TKA. Postoperative radiographs showed good alignment, with an FTA of 173°. In the axial view, the patella was located in a reduced position at any angle of knee joint flexion. The postoperative range of motion of the left knee joint was 0°of extension to 130°of flexion. The patient was able to walk without the support of a T-shaped cane. There are many surgical treatments for permanent patellar subluxation. The appropriate treatment is selected according to the type and seriousness of the dislocation and the age of the patient. From the findings of the present case, we believe that in a case of knee osteoarthritis complicated with permanent patellar subluxation, surgery performed using a mobile-bearing implant would eliminate the necessity of performing additional proximal realignment and distal realignment

Goals of the study. (1) to investigate the relationships between the bony contours of the knee and the Popliteus Tendon (PT) in the healthy knee and after implantation of a TKA and (2) to analyze the influence of implant sizing. Hypothesis. With an apparently well-sized TKA, the position of the PT during knee flexion is modified compared with the preoperative situation. Method. In 4 fresh frozen cadavers we injected the PT with Barium-Sulfate and a CT-scan was performed from 0° to 140°. We implanted copies of TKAs’ obtained from the manufacturer, made with a non radio-opaque polymer (Acrylonitrile butadiene styrene) with additive manufacturing technology. Each cadaver received either a normosized (cortical fit), oversized (3mm overhang), undersized (3mm under-coverage) or mobile bearing (normosized) prosthesis. The limb was CT-scanned again. 3D-reconstructions were created using Mimics software (Fig 1). The pre-post operative position of the PT was analyzed with Matlab software. We quantified the postoperative posterior deviation of the tendon (PDT). Results. In the normal knee the PT overlaps the posterolateral corner of the tibial plateau, between 0° and 100° of flexion with a maximum overlapping distance of 5.5mm (Fig2). After implantation of a normosized TKA, the PT was displaced posteriorly from full extension to 100° of flexion (Fig 3). Mean PDT was 6.2mm (range 0 to 13; SD=1.2) in extension and 4.8mm (range −1 to 9.8; SD=1.1) at 20° of knee flexion. After implantation of an oversized TKA, PDT was significantly greater than with a normosized TKA, at each angle of flexion: mean PDT was 16.7mm (range 4.4 to 23; SD=0.6) knee in extension (p<0.0001) and 10mm (range 4.4 to 15.7; SD=1.1) at 20° (p<0.0001). The deviation of the PT decreased during knee flexion but remained significant up to full flexion. When an undersized plateau was implanted, the PDT was significantly decreased compared with a normosized implant and the deviation was non significant compared with the preoperative knee. Mean DPT in extension was −0.8mm (range; −3.1 to 1.8; SD=0.3) (p<0.001). This absence of deviation of the PT with an undersized implant was confirmed during the full range of flexion. With a mobile-bearing implant, the deviation of the PT was also decreased compared with the normosized TKA. The mean PDT in extension was −0.6mm (range; −4.6 to 5.9; SD=2.6) (p<0.001). Conclusions. This work demonstrates that the optimal sizing in TKA is very challenging due to the non-anatomic design of current implants. The main finding is that surgeons must analyze sizing in term of volume rather than in term of surface. In other words, most apparently «normosized» TKA, in term of surface coverage are in fact oversized in term of prosthetic volume. It may be advantageous to aim atundersizing tibial implants and to preserve an uncovered area in the posterolateral corner of the resected tibia

Introduction / Purpose. Many factors can influence postoperative knee flexion angle after total knee arthroplasty (TKA), and range of flexion is one of the most important clinical outcomes. Although many studies have reported that postoperative knee flexion is influenced by preoperative clinical conditions, the factors which affect postoperative knee flexion angle have not been fully elucidated. As appropriate soft-tissue balancing as well as accurate bony cuts and implantation has traditionally been the focus of TKA success, in this study, we tried to investigate the influence of intraoperative soft-tissue balance on postoperative knee flexion angle after cruciate-retaining (CR) TKA using a navigation system and offset-type tensor. Methods. We retrospectively analyzed 55 patients (43 women, 12 men) with osteoarthritis who underwent TKA using the same mobile-bearing CR-type implant (e.motion; B. Braun Aesculap, Germany). The mean age at the time of surgery was 74.2 (SD 7.3) years. The exclusion criteria for this study included valgus deformity, severe bony defect requiring bone graft or augmentation, revision TKA, active knee joint infection, and bilateral TKA. Intraoperative soft-tissue balance parameters such as varus ligament balance and joint component gap were measured in the navigation system (Orthopilot 4.2; B. Braun Aesculap) while applying 40-lb joint distraction force at 0°, 10°, 30°, 60°, 90°, and 120° of knee flexion using an offset-type tensor with the patella reduced. Varus ligament balance was defined as the angle (degree, positive value in varus imbalance) between the seesaw and platform plates of the tensor that was obtained from the values displayed by the navigation system. To determine clinical outcome, we measured knee flexion angle using a goniometer with the patient in the supine position before and 2 years after surgery. Correlations between the soft-tissue parameters and postoperative knee flexion angle were analyzed using simple linear regression models. Pre- and postoperative knee flexion angle were also analyzed in the same manner. Results. Mean pre- and postoperative flexion angle were 120.5 ± 1.9° and 121.9 ± 1.3°, which did not show significant improvement after surgery. Varus ligament balance at 90° of flexion was positively correlated with postoperative knee flexion angle (R = 0.56, P < 0.001) and calculated joint gap of the lateral compartment at 90° of flexion showed positive correlation with postoperative knee flexion angle (R = 0.51, P < 0.001), while no correlation was found between joint gap of the medial compartment at 90° of flexion and postoperative knee flexion angle. Also, as with some past studies, joint component gap at 90° of flexion was slightly correlated with postoperative knee flexion angle (R = 0.30, P < 0.05) and pre- and postoperative knee flexion angle showed a significant positive correlation (R = 0.63, P < 0.001). Conclusions. Varus ligament balance at mid to deep flexion was a factor that predicted postoperative knee flexion angle after CR-TKA. In addition to preoperative knee flexion angle and joint component gap at 90° of flexion, lateral laxity at 90° of flexion is one of the most important factors affecting postoperative knee flexion angle