Comparison of Cartilage Thickness and Curvature Analysis Between Glenoid, Distal Tibial Allograft, and Subtalar Allograft for Anatomic Glenoid Reconstruction: The Magnetic Resonance Imaging–Based Mapping Study

Background: Bipolar bone loss is critical to consider in the surgical management of shoulder instability. Subtalar joint allograft (STA) is proposed as a new alternative graft option that could accommodate both glenoid and humeral head reconstruction, with limited literature comparing its anatomic morphology with the native glenoid and other graft options. Purpose: To compare the cartilage thickness and radius of curvature (ROC) analysis of the STA versus distal tibial allograft (DTA) and native glenoid for anatomic glenoid reconstruction. Study Design: Controlled laboratory study. Methods: Ten fresh-frozen, unpaired shoulders and 12 specimens of STA and DTA were scanned on a magnetic resonance imaging (MRI) scanner. The bone and cartilage were segmented from the MRI scans and divided into the regions of interest (ROIs) for localized analysis. The ROC was determined as a best-fit sphere along the short and long axes of the area of interest. Results: The entire articular surface and ROI (anteroinferior quadrant) of the native glenoid had significantly higher cartilage thickness than both the STA and DTA ( P < .001). There was no significant difference in cartilage thickness between the STA and DTA. There was a significantly higher ROC of the native glenoid (median, 24.45 mm; range, 12.07-32.89 mm) compared with the DTA (median, 13.55 mm; range, 8.76-30.43 mm) ( P = .008) in the short axes. However, there was no difference between the ROC of the STA in the short axis (median, 19.88 mm; range, 10.30-40.96 mm) compared with that of the glenoid ( P = .418). In addition, there was no significant difference between the ROCs of the glenoid, DTA, and STA in the long axis ( P > .05) Conclusion: STA and DTA contained similar thicknesses of cartilage; however, both demonstrated significantly less cartilage thicknesses than the native glenoid. There was no significant difference between STA and the native glenoid in terms of ROC in both the short and long axes. There was a difference in morphology between the DTA and the native glenoid in the short axis. Clinical Relevance: STA showed comparable cartilage thickness and ROC analysis to DTA. Further studies are indicated to further investigate the anatomic morphology, indications, and outcomes of STA for anterior shoulder instability.