Restoring tibial obliquity for kinematic alignment in total knee arthroplasty: conventional versus patient-specific instrumentation.

INTRODUCTION: In total knee arthroplasty (TKA), tibial obliquity-restoration using kinematic alignment (KA) poses a major difference to conventional mechanical alignment. This study aimed at analysing the accuracy of conventional instrumentation (CI) versus patient-specific instrumentation (PSI) to restore anatomic tibial obliquity measured by the medial proximal tibial angle (MPTA) on conventional X-rays. MATERIALS AND METHODS: One-hundred patients were randomized to receive CI (n = 50) or PSI (n = 50) for TKA. Further 100 patients received CI without randomisation, resulting in 200 patients in total (127 women, mean age: 70.7 (range: 48-90 years). Pre- and postoperative X-rays were measured twice by two observers with a 2-week break in-between. Inter- and intraclass correlations were calculated and postoperative tibial obliquity compared to preoperative anatomy. RESULTS: In 150 patients with CI, no case with tibial obliquity-deviation greater than 2° was found, whilst 21.3% (n = 32) and 0.7% (n = 1) of cases and had a deviation of 0°-1°, and 1°-2°, respectively. In the remaining 78.0% (n = 117), tibial obliquity was restored. In 50 patients with PSI, no single case with a deviation greater than 1° was found. Sixty percent (n = 30) had a deviation of 0°-1°. In the remaining 40.0% (n = 20), no deviation from preoperative measurements was found. Consequently, CI resulted in a significantly smaller change in tibial obliquity from preoperative to postoperative than PSI (p < 0.001). Inter- and intra-class correlations showed a substantial agreement (any ICC > 0.90). CONCLUSION: Both conventional and patient-specific instrumentation revealed adequate results with respect to restoring tibial obliquity in kinematically aligned TKA, with conventional instrumentation achieving superior results.