Abstract
Category:
Ankle Arthritis; Ankle; Hindfoot
Introduction/Purpose:
The role of implant positioning in total ankle arthroplasty (TAA) has garnered increasing attention, particularly in defining coronal and sagittal plane alignment. With the ongoing developments in patient specific instrumentation, advanced imaging is becoming a more common tool in preoperative planning. Despite this, there is limited information available on axial rotation of the ankle or variations in anatomy of the talus and foot. We aim to evaluate the rotational profile of the distal tibia and its relationship to morphology of the talus, as well as assess tibiotalar tilt, in a cohort of end-stage arthritic ankles.
Methods:
Computed tomography (CT) scans and plain radiographs were reviewed in 59 patients with end-stage ankle arthritis. Patients with previous tibial or ankle trauma were excluded. Scans were obtained prior to total ankle arthroplasty surgery as part of standard preoperative planning protocol. Demographic data was recorded. Measurements were obtained at the posterior condyles of the tibial plateau and transmalleolar axis to calculate tibial torsion, as well as along the talar neck and body to evaluate talar angle. Tibiotalar tilt angle was measured on weightbearing mortise view radiographs. Linear regression was performed to evaluate statistical associations between tibial torsion and other measured parameters.
Results:
The mean tibial torsion was 29.5±9.2 degrees external (range 13.6-50.8 degrees), no internal torsion was found. Mean talar neck-body angle was 38.2±8.8 degrees medial (range 24.1-59.5 degrees). Tibiotalar angle ranged from 26.5 degrees varus to 23.5 degree valgus. There was a statistically significant relationship between increasing tibial torsion and decreasing talar neck-body angle (r=-0.49, p<0.001), demonstrating more angulation of the talar neck corresponding to the least tibial torsion as seen in Figure 1. No relationship was found between tibial rotation and tibiotalar angle when assessing varus/valgus tilt on a spectrum (p=.89) or when evaluating absolute angulation from neutral (p=.43). Our cohort had a mean age of 63.1±8.2 years, and 54% were male.
Conclusion:
Our cohort displayed wide variation in axial anatomy of the ankle. Our analysis identifies a statistically significant correlation between tibial torsion and morphology of the talus. This is a previously unreported association that could help understand development of foot and ankle deformity and pathology. While there was no clear correlation to degree of tibiotalar angulation, these axial deformities surely play a role in altered foot and ankle mechanics and the development of end-stage ankle arthrosis. In patients undergoing ankle arthroplasty, these are important parameters for the surgeon to consider in conjunction with other aspects of the hindfoot deformity.
