Morphological Characteristics of Lateral Ankle Ligament Injuries Associated With Recurrent Instability After Arthroscopic Repair for Chronic Ankle Instability: 3D Volume Rendering MRI Model Analysis.

Background: Arthroscopic lateral ligament repair is widely performed to treat chronic lateral ankle instability (CLAI), with good clinical outcomes. However, some patients show residual or recurrent instability after surgery. Although some risk factors of recurrent instability have been reported, the morphological characteristics of lateral ankle ligament injuries with residual or recurrent instability remain unclear. Hypothesis: Characteristic patterns of anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) injuries may be observed in patients with CLAI who have residual instability after isolated ATFL repair or recurrent instability after arthroscopic lateral ligament repair. Study Design: Cohort study; Level of evidence, 3. Methods: We retrospectively reviewed 27 patients with CLAI and 10 controls without CLAI who underwent arthroscopic surgery. Three-dimensional volume-rendering models were reconstructed from preoperative magnetic resonance imaging scans of the ankle joints. For the primary outcome, the distance between the tip of the fibula and the proximal end of the CFL (dCFL), 3 vectors of the dCFL, and the horizontal angle of the ATFL (ATFL angle) were measured. For the secondary outcome, the clinical scores of patients with CLAI were evaluated pre- and postoperatively. Differences in parameters were compared among patients with no residual ankle instability, those with residual ankle instability immediately after arthroscopic ATFL repair, and the control patients. In addition, these parameters were compared between patients with non-recurrent and recurrent ankle instability at 1 year postoperatively. Results: As the primary outcome, the dCFL was greater, and its mediolateral vector, defined as the lateral direction as positive, was lower, indicating a medially shifted dCFL, in patients with residual ankle instability compared with patients without residual ankle instability and control patients. As a secondary outcome, there were no significant differences in clinical scores between the non-recurrence and recurrence groups. However, the ATFL angles in patients in the recurrent group were significantly smaller, indicating the talar side drooping of the ATFL, than in the nonrecurrence group. Conclusion: The CFL was injured and shifted medially in patients with residual ankle instability. Moreover, the ATFL in patients with recurrent instability showed talar side drooping. These findings suggest that additional CFL repair or ATFL augmentation may be beneficial in preventing recurrent instability after arthroscopic repair.