Imaging evaluation of extraarticular posterior loose bodies in varus ankle osteoarthritis

Purpose: Multiple loose bodies (LBs) are often found in patients with varus ankle osteoarthritis (OA). This study aimed to investigate the characteristics of extra-articular posterior ankle LBs in patients with varus ankle OA. We also sought to determine whether there were variations in the characteristics of LBs according to the degree of ankle OA. Methods: We retrospectively reviewed 50 patients who had appeared posterior extraarticular LBs on preoperative ankle imaging among the patients who underwent operative treatment for varus ankle OA from March 2011 to February 2023. We categorized the entire patient cohort into four groups according to the degree of ankle arthritis (Takakura stage II, IIIA, IIIB, and IV). Size, number, and location of LBs were evaluated using preoperative computed tomography and magnetic resonance imaging. Results: 142 LBs were identified (mean size: 11.5 mm); 76.8% were located within the flexor hallucis longus (FHL) tendon sheath, 20.4% in the posterior recess, and 2.8% in the flexor digitorum longus tendon sheath. Average LB size was significantly larger in Takakura stage IIIB and IV patients ( p < .05), and the LB number was significantly lower in stage II patients ( p = .013). Conclusion: Extra-articular posterior LBs in varus ankle OA are predominantly located within the FHL tendon sheath and were larger in Takakura stages IIIB and IV patients. Level of Evidence: Level III. Retrospective comparative study.