Summary

We found no significant difference in functional or radiographic outcomes between TKAs implanted with Mechanical or Kinematic Alignment at 5 years.

Abstract

Introduction

Kinematic Alignment (KA) technique in total knee arthroplasty (TKA) attempts to match implant position to the pre-arthritic anatomy of an individual patient, with the goal of improving functional outcomes. This contrasts with a traditional neutral mechanical alignment (MA) goal, and the effect of these changes on implant survivorship remains unknown. This study compares the mid-term survivorship and functional outcomes between these two techniques, including radiographic assessment for signs of implant loosening/failure.

Methods

Following a pilot study and power analysis, ninety-nine patients undergoing primary TKA for osteoarthritis were randomized to either MA (n=50) or KA (n=49) groups. All patients underwent pre-operative alignment assessment using full-length MRI scans. Computer Navigation was used for all patients in the MA group, and in the KA group patient specific cutting-blocks were manufactured using the individual pre-op MRI data. Alignment was assessed with post-operative CT scans in all patients, and radiographs obtained post operatively, and at 1,2, and 5 years. Functional outcome scores were assessed pre-operatively and at 6 weeks, 6 months, 1, 2 and 5 years post-operatively. Standard short-leg radiographs were assessed using the Modern Knee Society Radiographic Evaluation System.

Results

There was no significant difference in patient reported outcome measures (PROMs) at five years. The difference between the means (MA vs KA) were – Oxford Knee Score 0.42 ± 9.74 (p=0.77), Western Ontario and McMaster Universities (WOMAC) score 3.57± 3.12(p=0.32), Forgotten Joint score 6.08± 5.39 (p=0.26), EQ-5D 0.05±0.28 (p=0.25), and Knee Society Pain/Motion 1.44±2.43 (p=0.55) or Function scores 5.13± 3.65 (p=0.16), Range of Motion -1.80±1.7 (p=0.29), Visual Analogue Score (VAS) Rest -0.30±1.99 (p=0.32) and VAS Mobilisation -0.11±2.40 (p=0.76). There were no significant differences in the presence of static or progressive radiolucent lines between MA and KA groups. There were no differences in the number of re-operations. The MA group had two revisions for infection and one secondary patella resurfacing with medial retinacular reconstruction following a fall. The KA group had one liner exchange for stiffness and one liner change plus secondary patellar resurfacing for on-going pain and swelling.

Conclusions

We found no significant difference in functional or radiographic outcomes between TKAs implanted with MA or KA. The revision and re-operation rates were similar and at five years there were no significant differences in radiographic signs of loosening. These mid-term results support the two-year findings of no difference in MA vs KA, however the impact on long term survivorship is still unknown.