Arthroscopic accessibility of the talus quantified by computed tomography simulation

Background: Anterior ankle arthroscopy is the preferred surgical approach for the treatment of osteochondral defects of the talus (OCDs). However, the ankle is a congruent joint with limited surgical access. Purpose: The dual purpose of this study was (1) to quantify the anterior arthroscopic reach (defined as the proportion of the talar dome articular surface located anterior to the anterior distal tibial rim) with the ankle in full plantar flexion and (2) to identify predictive factors of the arthroscopic reach. Study Design: Descriptive laboratory study. Methods: Computed tomography scans were obtained of 59 ankles (57 patients aged 33 ± 11 years) in full plantar flexion in a nonmetallic 3-dimensional footplate. The arthroscopic reach of both the medial and lateral talar domes was assessed on sagittal reconstructions using a custom-made software routine. Intraobserver and interobserver reliability were calculated by intraclass correlation coefficients (ICCs). Various predictive factors of the arthroscopic reach were analyzed by multivariate linear regression analysis. Results: The arthroscopic reach was 48.2% ± 6.7% (range, 26.7%-60.7%) of the medial talar dome and 47.8% ± 6.5% (range, 31.2%-65.1%) of the lateral talar dome (P = .62). The intraobserver and interobserver reliability of both measurements were excellent (ICC, .99). The clinical plantarflexion angle was a statistically significant predictive factor of both the medial and lateral arthroscopic reaches (ie, increased plantar flexion corresponded to increased area of access), while joint laxity, gender, and age were not predictive. Conclusion: Almost half of the talar dome is accessible anterior to the anterior distal tibial rim. The plantarflexion angle is an independent predictive factor of the arthroscopic reach both medially and laterally. Clinical Relevance: These results may facilitate preoperative planning of the surgical approach for OCDs.