A New Method to Attain a Balanced Total Knee Arthroplasty

INTRODUCTION & AIMS: The ANJRR has reported no improvement in early revision rates for patient matched versus conventional instrumentation and Nam et al demonstrated no improvement in PROMS or alignment data at 2 year follow-up patient matched TKA. Patient matched instrumentation may not provide clinically meaningful improvements. The purpose of this study was to assess whether a novel design process for patient matched cutting guides could both normalise soft tissue tension and produce a knee balanced mediolaterally and between 0 and 90°of flexion. METHOD: Patient specific guides of a novel and standard design were manufactured based on a novel design process and assessed via a prospective cohort study. The novel guides were applied to the intact knee in extension and/or flexion at the start of a TKA prior to soft tissue releases to mark bone resections. The guides contacted the femur and tibia simultaneously and acted to re-align the knee and tension the peri-articular soft tissues. 10 patients had novel guides applied in flexion and extension and 3 additional patients used guides in extension only. 9 patients had standard guides manufactured with the novel design process. We prospectively collected data on these 22 patients examining medial and lateral soft tissue laxity in maximum extension, 20 and 90° of flexion pre and post-operatively. RESULTS: Soft tissue tension within parameters described for normal subjects was attained medially and laterally in: maximum extension in all 22 cases. For the 19 cases where the guides were used to plan the flexion resections; normal medial soft tissue tension was attained in 18/19 (94.7%) cases and normal lateral soft tissue tension in 16/19 (84.2%) cases. The 4 cases where normal soft tissue tension was not attained were outside this range by 1°. Post-operatively the mean difference in medial versus lateral laxity was 0.75°at 0°, 1.36° at 20° and 1.20° at 90°of flexion with a range of 0 - 4.5° across all positions and all knees. Pre-operatively the difference between medial and lateral laxity across all knees and positions ranged from 0 – 9°. Preoperatively the mean difference in medial versus lateral laxity was 4.43°at 0°, 5.25° at 20° and 1.64°at 90°of flexion. In the 19 cases where guides planned both the extension and flexion gap, 0 versus 90 ° flexion laxity on the medial side displayed a mean difference of 1.18° (range 0 - 3) and on the lateral side a mean difference of 1.52° (range 0 - 4.5) was recorded. To attain these balance parameters 16/22 (72.7%) cases utilised a 9mm poly and 6/22 (27.3%) utilised an 11mm poly. CONCLUSIONS: Patient Matched Instrumentation is widely used without clear benefit. This novel patient matched instrumentation design process shows promise for attaining soft tissue tension that is both normal and balanced. This may help diminish revision due to instability which was recorded as the revision diagnosis in 18.7% of patients (Lombardi 2013).