Lower Limb Alignment in Patients with Primary Valgus Ankle Arthritis: A Comparative Analysis with Patients with Varus Ankle Arthritis and Controls

Abstract

Category: Ankle Arthritis; Ankle Introduction/Purpose: A comprehensive analysis of lower limb alignment may be a critical component of successful ankle joint preservation surgery. Although it is widely recognized that the combined effect of lower limb orientation and ankle and hindfoot alignment plays a fundamental role in ankle arthritis, supramalleolar/lower limb alignment has received less attention in valgus ankle arthritis. This study aims to analyze the lower limb alignment of patients with valgus ankle arthritis with primary origin, compared to those with varus ankle arthritis and normal controls. We hypothesize that patients with valgus ankle arthritis will exhibit the opposite pattern of lower limb alignment to those with varus ankle arthritis: valgus mechanical axis, valgus distal tibial plafond, and valgus hindfoot alignment. Methods: A retrospective radiographic analysis was conducted on 61 patients (62 ankles, mean age: 59.2 years) with valgus ankle arthritis with primary origin was performed. Preoperative weightbearing radiographs were used to measure seven radiographic parameters: Talar tilt angle, medial distal tibial angle (MDTA), talar center migration (TCM), anterior distal tibial angle (ADTA), talo-first metatarsal (Meary’s) angle, hindfoot moment arm (HMA), and mechanical axis deviation (MAD). For comparative radiographic analysis, a varus arthritis group with primary origin (n=55, mean age: 59.7 years) and a control group (n=58, mean age: 29.3 years) were included. Subgroup analyses of lower limb alignment were performed in the valgus arthritis group based on the MDTA (greater or less than 90 degrees, subgroup analysis 1) and Meary's angle (greater or less than -20 degrees, subgroup analysis 2). Results: The valgus group had a significantly lower mean MDTA than the control group (p < 0.0001, Figure 1), indicating a varus distal tibial plafond in comparison to the control group. Meary's angle and HMA were significantly lower in the valgus group compared to the varus group (p < 0.05 and p< 0.0001, respectively). On whole limb radiographs, the valgus group showed a greater MAD than the control group (p < 0.05), indicating a varus lower limb alignment. However, there was no significant difference in MAD between the valgus and varus groups (p=0.7031). Subgroup analysis 1 revealed that the MAD was varus- angulated regardless of the MDTA. Subgroup analysis 2 showed that both groups had comparable MDTA (p=0.8504); however, patients with a lower Meary’s angle had a significantly greater MAD. Conclusion: Our findings indicate that a significant proportion of ankles with primary valgus arthritis have a varus tibial plafond and a varus lower limb mechanical axis, which contradicts our current understanding. The similar lower limb and distal tibia orientation and different foot and hindfoot alignment between the valgus and varus group suggest that foot and hindfoot alignment may play an important role in the development of both types of arthritis. This study adds to our understanding of primary valgus ankle arthritis and suggests that lower limb alignment should be analyzed and considered throughout valgus ankle arthritis realignment procedures.