Biomechanical Evaluation and Surface Analysis of Glenoid Reconstruction Using a Subtalar Joint Allograft for Significant Glenoid Bone Loss in Recurrent Shoulder Instability: A Novel Alternative Graft Option

Background: Glenoid and humeral head bone defects are common in chronic shoulder instability. The talus, and more specifically, the subtalar joint, has been proposed as a unique allograft from which bipolar bone loss can be addressed. However, there are few biomechanical data or joint reconstruction analyses of the glenoid using the posterior facet of a subtalar joint allograft (STA). Purpose: To compare the contact mechanics of an STA versus a coracoid graft (Latarjet procedure) versus a distal tibial allograft (DTA) for anatomic glenoid reconstruction. Study Design: Controlled laboratory study. Methods: A total of 8 fresh-frozen, unpaired cadaveric specimens underwent repeated-measures biomechanical testing in 5 stages: native (intact) state, bone loss (30% glenoid bone defect), Latarjet procedure, glenoid reconstruction using a DTA, and glenoid reconstruction using an STA. A compressive load of 440 N was applied to the glenohumeral joint when the humerus was mounted to a dynamic tensile testing machine in 3 shoulder positions: 30 degrees of abduction, 60 degrees of abduction, and 60 degrees of abduction with 90 degrees of external rotation (ER). Average contact pressure, contact area, and peak contact pressure were determined from the sensors. Surface area and surface congruency were calculated using a custom script. Data were analyzed using analysis of variance. Results: There was a significantly higher surface area with glenoid reconstruction using the DTA (859 +/- 78 mm2; P = .005) than with glenoid reconstruction using the STA (806 +/- 88 mm2; P < .001) and the Latarjet procedure (692 +/- 91 mm2). Surface congruency was significantly better with reconstruction using the DTA (2.0 +/- 0.3 mm; P = .003) or the STA (1.9 +/- 0.3 mm; P = .004) than with the Latarjet procedure (2.6 +/- 0.4 mm). In all shoulder positions, the average contact pressure in the bone loss state was significantly higher than that in the native state (P < .05). All repair states restored average contact pressure to the native state at 60 degrees of abduction and 60 degrees of abduction with 90 degrees of ER. There was less contact area after the Latarjet procedure than in the native state at 30 degrees and 60 degrees of abduction (P = .009 and P = .040, respectively). There was no significant difference in contact area and peak contact pressure after reconstruction with the DTA or STA compared with the native state. Conclusion: Anatomic glenoid reconstruction using a DTA or STA restored average contact pressure, peak contact pressure, and contact area at 60 degrees of abduction and 60 degrees of abduction with 90 degrees of ER in a cadaveric model. In addition, surface congruency and surface area improved over the traditional Latarjet procedure. Clinical Relevance: The STA showed comparable contact mechanics and surface geometry to the DTA. Further research is needed to determine the in vivo clinical outcomes of this new alternative graft.