COMPARISON OF INTRA-OPERATIVE VARIATION IN MECHANICAL AXES DURING NAVIGATED TOTAL KNEE REPLACEMENT

Abstract

To analyse the intra-operative variation in mechanical axes of the lower limb at various stages during navigated total knee replacement. A prospective study was performed to analyse the intra-operative variation in the mechanical axes of the lower limb during navigated total knee replacement. All consecutive patients who underwent navigated total knee replacement were included and patients with inadequate data were excluded from the study. The intra-operative initial, trial and the final mechanical hip-knee-ankle axes were recorded from the navigation system. The differences between these axes were calculated and analysed. There were forty patients, of which 24 were females and 16 males with the age ranging from 37–89 (average 68.4) years. The right knee was replaced in 27 and the left knee in 13 patients. The average initial mechanical axes alignment was 0.03° valgus (3° varus to 3° valgus), trial alignment 0.64° varus (3° varus to 1.5° valgus) and final alignment 0.25° varus (4° varus to 4° valgus). Average deviation from initial to trial axes was 0.97°, trial to final axes was 0.74° and initial to final axes was 1.08°. The cor-relation co-efficient between the initial and the trial axes was 0.25, trial and final axes was 0.43 & initial and final axes was 0.09.

This study highlights a significant variation in mechanical axes between the different stages of navigated total knee replacement. The potential sources of intra-operative errors causing these changes could be soft tissue imbalance, variations in implant placement and possible tracker micro motion. Execution of bony cuts in near normal neutral alignment does not guarantee achievement of near normal final alignment. We advocate surgeons to be vigilant to avoid potential malalignment during navigated total knee replacement.