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.

Abstract

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° of abduction, 60° of abduction, and 60° of abduction with 90° 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° of abduction and 60° of abduction with 90° of ER. There was less contact area after the Latarjet procedure than in the native state at 30° and 60° 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° of abduction and 60° of abduction with 90° 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.