Gap Pattern in Valgus Knee: An Assessment with TKA Navigation

Background: Valgus knee is a challenge of ligament balance in total knee arthroplasty (TKA). A lateral release is often recommended to achieve symmetric extension gaps in valgus deformity, due to the traditional requirements of tight lateral gap. However, the gap pattern valgus osteoarthritis knee has not been studied. Materials and Methods: The present study was a retrospective study on navigated TKA with 89 valgus osteoarthritis knees. The gap measurement, bone cut, and component rotation values were collected from navigation and the data were analyzed. Results: Only 6.70% of valgus knees in the present series had a narrower lateral flexion gap than medial flexion gap and 7.90% had narrower lateral extension gap than medial extension gap. Conversely, most of valgus cases were seen in bigger lateral flexion gaps than medial flexion gaps at 76.4%. This was consistent with the extension gap patterns of 80.9%. The degree of valgus deformity positively correlated with all gaps, except for flexion lateral gap. The present study demonstrated a mean external rotation of 2.25±2.09° in the femoral component rotation and the degree of valgus deformity had no significant correlation with femoral rotation. Conclusion: The lateral distal femoral condyle hypoplasia might have more important role in the extension gap than the ligament tension. The lateral ligament might influence the lateral flexion gap more than the lateral femoral condyle deficiency. Lateral structural release for correction of valgus deformity during extension could lead to instability in flexion especially for gap patterns with a lateral flexion gap that is wider than the medial flexion gap. Keywords: Valgus knee; Navigated TKA; Gap pattern