Novel Measurement Technique for Talar Height Assessment in Total Ankle Arthroplasty

CATEGORY: Ankle Arthritis; Other INTRODUCTION/PURPOSE: Talar and calcaneal height have been identified as important not only to the biomechanics of ankle joint function but of the adjacent joints of the hindfoot as well. Many proposed measurement systems have been introduced to the literature to assess talar height in ankle arthroplasty, but have significant shortcomings. The malleoli frequently develop osteophytes after total ankle arthroplasty. If the subtalar joint is fused or arthritic, methods relying on landmarks such as the angle of Gissane are similarly unreliable. Lastly, subsidence is often asymmetrical. Measuring from the highest point of the talar component may not be reflective of functional talar height. We propose using adjusted talocalcaneal height to assess the functional restoration of talar height. METHODS: Pre and post-operative radiographs and weight bearing computed tomography (WBCT) were reviewed for 40 cases of failed total ankle arthroplasty undergoing revision. Bony landmarks were assessed for consistency over a time course of two to four years post operatively. Talocalcaneal height was measured along from the center of the tibial component of ankle arthroplasty on weight bearing lateral radiographs and on sagittal and coronal reconstructions on WBCT (fig 1). Measurements on radiographs and WBCT were compared for agreement. For implants where lateral radiographs could not be used (Agility(TM), Depuy), sagittal and coronal WBCT was used. RESULTS: Average adjusted talocalcaneal height as measured on lateral radiographs, sagittal WBCT, coronal WBCT, and averaged values from sagittal and coronal WBCT was 68mm, 67.4mm, 68.5mm, and 68mm respectively. There was not a significant difference between the lateral radiographs and WBCT measurement methods (p= 0.30, 0.37, 0.46), and correlation was 0.99 for all methods. Measurements did not vary in cases of angular subsidence or subtalar fusion. CONCLUSION: Adjusted talocalcaneal height is a reproducible and reliable measurement to assess talar height. It accommodates procedures frequently performed in tandem with total ankle arthroplasty such as calcaneal osteotomy and subtalar fusion. It relies on a single, static bony landmark, and remains valid in cases of asymmetric subsidence. Lastly, it incorporates calcaneal height, which affects not only ankle joint mechanics but adjacent joint mechanics as well.