Bone density loss following ankle fusion persists at long-term follow-up

Abstract

Introduction: The aim of ankle fusion is to create a stable and pain-free hind foot. A decrease in bone density secondary to postoperative immobilization is well established. It is commonly accepted that bone density is restored toward normal values when normal weight bearing is permitted. To the current authors' knowledge, this restoration of bone density has not been definitively established via clinical studies. Subjects and Methods: Patients who underwent an isolated ankle fusion between January 1998 and March 2015, to address advanced degenerative or posttraumatic osteoarthrosis or rheumatoid arthritis were included. Clinical and radiological examination, Foot Function Index (FFI), and American Orthopedic Foot and Ankle Society-Score (AOFAS) scoring systems were utilized. Pain intensity was calculated using the Visual analogue scale (VAS). We use semiquantitative ultrasound osteodensitometry to measure bone density. Results: Bone density was determined in 60 patients, at an average follow-up of 9 years following ankle fusion. The mean T-score for bone density of the calcaneus was significantly lower in the treated foot compared to the contralateral side (−1.4 vs.−0.4; P = 0.001). With the numbers available, a reduction in bone density was found without a significant difference in the AOFAS score (P = 0.875), FFI (P = 0.655), VAS (P = 0.804), and body mass index (P = 0.272). Seven (12%) developed a nonunion. Conclusions: These results demonstrate that a reduction in bone density as a consequence of immobilization while bone union was achieved did not completely return to baseline values even at 10 years postoperative. This persistent reduction in bone density does not correlate in a statistically significant way with higher pain scores, inferior AOFAS scores or nonunion rates. Postoperative partial weight bearing should be instigated as soon as possible to minimize bone loss.