Abstract
Introduction
Instability is a common reason for revision after total knee arthroplasty. A balanced flexion gap is likely to enhance stability throughout the arc of motion. This is achieved differently by the gap balancing and measured resection techniques. Given similar clinical results with the two techniques, one would expect similar rotation of the femoral component in the axial plane. We assessed posterior-stabilized femoral component axial rotation placed with computer navigation and a modified gap balancing technique. We hypothesized that there would be little variation in rotation.
Methods
90 surgeons from 8 countries used a modified gap-balancing technique and the same posterior-stabilized implant for this retrospective study. Axial rotation of the femoral component was collected from a navigation system and reported relative to the posterior condylar line. Patients were stratified by their preoperative coronal mechanical alignment (≥ 3° varus, < 3° varus to < 3° valgus, and ≥ 3° valgus).
Results
2442 consecutive patients were included in the analysis; 835 with ≥ 3° varus, 1343 with < 3° varus to < 3° valgus, and 264 with ≥ 3° valgus. Mean rotation was external 2.40 +/− 3.40 (range, 100 internal − 210 external). In 16.4% of the cohort, axial rotation was set in a position of internal rotation. In 15.6% of the cohort, axial rotation was set at > 50 of external rotation. Compared to both the neutral and varus groups, valgus knees required a different mean rotation to achieve a balanced flexion gap (p < .0001).
Conclusion
These data show a wide range of femoral rotation was needed to achieve a rectangular flexion gap. This suggests that choosing a pre-determined femoral implant axial rotation (measured resection) may lead to flexion gap asymmetry more frequently compared to adjusting the axial rotation intraoperatively (gap-balancing). Correlation to clinical outcome scores is needed.
