Medial UKA for patients with isolated medial osteoarthritis preoperative varus no > 12° deformity can improve functional outcomes with up to 17-year follow up. We believe that intraoperative alignment correction of 2°-3° not correction to neutral yields optimal outcomes.
Isolated medial compartment knee osteoarthritis is a common cause of knee pain and a primary indication for medial unicondylar knee arthroplasty (UKA). Traditionally, varus alignment >10° was a contraindication for medial UKA with intraoperative goal to correct varus deformity to neutral. We believe that correcting to neutral could be detrimental to outcomes in varus-malaligned knees. Intraoperative alignment correction and postoperative alignment were investigated in patients with medial UKA to determine the impact and clinical significance on long-term functional outcomes.
Using modern, previously published surgical indications for medial UKA, a consecutive series of 180 knees in 157 patients (80 males, 77 females; mean age=65±10 years; mean body mass index=28.7±5) underwent medial UKA by the senior author between 1999-2017. All patients completed a physical examination and radiographic evaluation including anteroposterior and 3-foot standing alignment films. Exclusion criteria was malalignment >15º. Postoperative function was assessed using the Lysholm, Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC), and Knee Injury and Osteoarthritis Outcome (KOOS) questionnaires. A minimum of 2-year follow-up was required for inclusion. Alignment was defined as the mechanical axis measured on 3-foot standing or anteroposterior films by an independent observer. Valgus alignment was represented by a negative number. Means ± standard deviations were computed for all variables. Regression analysis was used to determine the influence of pre- and postoperative alignment on postoperative functional outcomes. Significance was defined as p<0.05.
Preoperative alignment was 7.7°± 4°(varus) and postoperative alignment was 5.6°± 4.3°(varus). Average intraoperative alignment correction was -2.5° (less varus) (range:0°-10°). Preoperative extension was 3°± 4.1° and flexion 121°±12°. Postoperatively, extension was 1°±2° and flexion was 128°±8°. At maximum 17-year follow-up (7±3 years, range 2-17), patients exhibited significant improvement in function as demonstrated by 85.7±19 on the Lysholm Score, 14±11 on WOMAC, and 73±10 on KOOS Symptoms, 84±16 on KOOS Pain, 88±13 KOOS Life, 68±27 KOOS Sport, and 73±22 KOOS Quality of Life. Regression analysis revealed that preoperative and postoperative alignment did not significantly impact functional outcomes (all R2<0.10, all p-values>0.05). There were 2 failures in this cohort (1.4%) that occurred early in the surgeon’s series. The first patient had 12° varus alignment and was corrected to 2° varus. This patient had continued pain in the lateral compartment and was revised to a total knee arthroplasty (TKA) at 19 months. The second patient was in 2° varus preoperatively and was corrected to neutral. This patient was eventually revised to TKA at 21 months.
Medial UKA is an excellent option for patients with isolated medial compartment osteoarthritis even in patients with up to 12° preoperative varus deformity. While early procedures suggested correction to neutral alignment, we believe that an average 2°-3° change will yield optimal outcomes. Surgeons can proceed with a medial UKA in properly selected patients with a flexible, passively correctable, varus deformity of up to 12° on physical examination or stress view radiographs.