Congruent-Arc Posterior Distal Tibial Allograft Shows Greater Radiographic Glenoid Concavity Compared With Traditional Lateral Tibial Allograft in Glenoid Bone Loss.

PURPOSE: To compare radiographically the concavity depth and slope angle of the congruent-arc distal tibial allograft (CA-DTA), harvested from the posterior distal tibia, with the traditional lateral distal tibial allograft (traditional DTA) used for glenoid reconstruction in anterior shoulder instability with bone loss.

METHODS: A convenience sample of 32 ankle computed tomography scans from patients ≤35 years old without prior trauma, arthritis, or ankle pathology were retrospectively reviewed. Using standardized coronal (traditional DTA) and sagittal (CA-DTA) reconstructions, 2 independent reviewers measured allograft concavity depth (mm) and slope angle. Paired t tests compared traditional versus CA-DTA measurements. Intraclass correlation coefficients assessed reliability. Significance was set at P < .05.

RESULTS: The mean age of patients was 25.2 years, with 50% (n = 18) of patients being male. Compared with the traditional DTA, the CA-DTA showed significantly greater glenoid concavity change (2.9 ± 0.65 mm vs -2.3 ± 0.71 mm; P < .001) and slope angle (22.9°± 4.02 vs -9.78°± 4.07; P < .001). All CA-DTAs showed positive concavity and slope, whereas all traditional DTAs produced negative values.

CONCLUSIONS: The CA-DTA consistently increased both concavity and slope, whereas the traditional DTA decreased these measures. By leveraging the posterior tibial surface, the CA-DTA more reliably recreates the anatomic "half-pipe" glenoid contour that contributes to bony concavity-compression-based stability.

CLINICAL RELEVANCE: The CA-DTA offers a graft alternative that more reliably restores glenoid concavity in anterior shoulder instability with glenoid bone loss. This has potential implications for improved glenohumeral stability and clinical outcomes.