The risk factors of subsidence of the talar component in the 3 rd generation TNK ankle

Abstract

Category: Ankle Arthritis Introduction/Purpose: One of the major reasons for revision surgeries after total ankle arthroplasty (TAA) was subsidence of the talar component. The purpose of this study was to evaluate mid-term outcomes after total ankle arthroplasty(TAA) using the 3 rd generation TNK ankle and investigate risk factors leading to subsidence of the talar component. Methods: Fifty consecutive patients who received the 3 rd generation TNK prosthesis between October 2007 and December 2014 were investigated in this study. Weight-bearing foot and ankle radiographies were taken and evaluated before and after surgery. At least 1 mm sinking of the talar component was defined as the subsidence. BMI, age at the surgery, complications were investigated as patient specific parameter and talar tilting angle(TTA) and inclination of the articular surface of the distal end of tibia were investigated as preoperative radiographic parameters. Position and angle of replaced implant were also investigated using postoperative radiography. Results: Preoperative TTA had positive correlation (p=0.049, Cox model), and the angle between the talar and the 1st metatarsal axis (Meary angle) had negative correlation with subsidence (p=0.042, Cox model). Conclusion: The larger TTA shows varus deformity of the ankle and indicates the potential instability of the ankle, that leads to frequent incidence of ankle sprain postoperatively. Repeated micro trauma causes the loosening and subsidence of the talar component. The smaller Meary angle shows the cavus deformity, that prevents the favorable load distribution to the navicular and calcaneus, and leads to higher pressure concentration to the implant. The larger TTA and smaller Meary angle were risk factors of subsidence of the talar component in the TAA.