Postoperative Limb Alignment and Its Determinants After Minimally Invasive Oxford Medial Unicompartmental Knee Arthroplasty

One hundred twenty-two consecutive minimally invasive Oxford phase 3 medial unicompartmental knee arthroplasties in 109 patients were evaluated for postoperative limb alignment and the influence of factors such as preoperative limb alignment, age, body mass index, sex, insert thickness, and surgeon's experience. The mean mechanical preoperative hip-knee-ankle (HKA) angle of 172.2° ± 3.1° improved to 177.1° ± 2.9° postoperatively. In 75% of the limbs, the HKA angle was restored to within an acceptable alignment of 177° ± 3°, 14% of the limbs were in excessive varus (<174°), and 11% were in valgus (>180°). Only preoperative HKA angle was predictive of postoperative HKA angle. Although most of the limbs had acceptable limb alignment after unicompartmental knee arthroplasty, limbs with more severe preoperative varus deformity had a tendency to remain in excessive varus, and limbs with lesser preoperative varus deformity had a greater tendency to go into valgus postoperatively.