Influence of the functional status of the anterior cruciate ligament on the posterior medial femoral condyle among varus osteoarthritic knees

Background

Morphologic changes in the posterior medial femoral condyle (PMFC) among varus osteoarthritic knees have not been described in the past. The aims of this study were to compare anterior cruciate ligament (ACL) competent and deficient varus osteoarthritic knees during computer-navigation assisted (CAS) total knee arthroplasty (TKA) in terms of their pre-operative deformity, rotation of the posterior condylar axis (PCA) with respect to Whiteside's axis, and prevalence of PMFC hyperplasia or attrition.

Methods

Data pertaining to pre-operative varus deformity, rotation of the PCA with respect to Whiteside's axis, and presence of PMFC hyperplasia or attrition were analyzed for 250 consecutive patients each, with ACL-competent and deficient knees, who underwent CAS TKA for varus osteoarthritis of the knee.

Results

ACL-deficient knees, compared to ACL-competent knees, were associated with greater pre-operative stressed (9.94° ± 6.14° versus 7.29° ± 4.48°, P < 0.001) and corrected (3.62° ± 4.36° versus 2.41° ± 3.08°, P < 0.001) varus deformities, internal rotation of the PCA with respect to Whiteside's axis (4.06° ± 2.32° versus 3.08° ± 2.03°, P < 0.001), and prevalence of PMFC attrition (8.4 % versus 0 %, P < 0.001) and hyperplasia (27.2 % versus 9.6 %, P < 0.001).

Conclusion

Chronic ACL deficiency in varus osteoarthritic knees may result in progression of the coronal deformity, PMFC attrition, increased internal rotation of the PCA with respect to Whiteside's axis, and eventually PMFC hyperplasia. This needs to be borne in mind during TKA to prevent inadvertent placement of the femoral component in inappropriate rotation.