Bone morphotypes of the varus and valgus knee

Coronal deformity correction with total knee arthroplasty (TKA) is an important feature in the treatment of osteoarthritis (OA). The hypothesis of this study was that bone morphology would be different in varus and valgus deformity, both before osteoarthritis development as well as during and after the disease process of OA. Retrospective study with measurements on preoperative and postoperative full leg standing radiographs of 96 patients who underwent TKA. The included patients were selected for this study because they had an OA knee on one side and a non-arthritic knee on the contralateral side presenting the same type of alignment as the to-be-operated knee (varus or valgus alignment on both sides). The control group of 46 subjects was a group of patients with neutral mechanical alignment who presented for ligamentous problems. A single observer measured mechanical alignment, anatomical alignment, anatomical-mechanical femoral angle and intra-articular bone morphology parameters with an accuracy of 1A degrees. Varus OA group has less distal femoral valgus (mLDFA 89A degrees) than control group (87A degrees) and valgus OA group (mLDFA 85A degrees). Varus OA group has same varus obliquity as control group (MPTA 87A degrees) but more than valgus OA group (MPTA 90A degrees). Joint Line Congruency Angle (JLCA) is 3A degrees open on lateral side in varus and medially open in valgus OA group (2A degrees). The non-arthritic valgus group presents a constitutional mechanical valgus of 184A degrees Hip-Knee-Ankle (HKA) angle. Varus deformity in OA as measured with an HKA angle (HKA) < 177A degrees is a combination of distal femoral wear, tibial varus obliquity and lateral joint line opening. Valgus deformity in OA with an HKA > 183A degrees is a combination of femoral distal joint line obliquity and wear combined with medial opening due to medial collateral ligament stretching. The clinical importance of bone morphotype analysis is that it shows the intra-articular potential of alignment correction when mechanical axis cuts are performed. Bone morphology in varus and valgus deformity is different before and after osteoarthritis. Perpendicular cuts to mechanical axes do not necessarily lead to neutral mechanical axis. Constitutional mechanical valgus was observed as 184A degrees HKA angle before the development of OA. Level IV study.