Restoring Glenoid Concavity: Angled Bone Blocks Provide Biomechanically Superior Function and Restore Glenohumeral Forces Over Flat Constructs in Glenoid Augmentation

Abstract

Background:

Surgical treatment of shoulder instability with glenoid bone loss using a distal tibial allograft has achieved success, with the bone graft placed parallel, flush, or recessed to the articular surface, but questions remain about optimal graft positioning.

Hypothesis:

Given evidence that glenoid concavity and congruence influence stability, we hypothesized that angled bone blocks better restore native concavity and biomechanics compared to flat graft placement.

Study Design:

Controlled laboratory study.

Methods:

A total of 9 cadaveric shoulders were dissected, separating rotator cuff muscles from the capsule. Native glenoid dimensions were measured with a digitizer. A 20% anterior bone defect was created and then reconstructed with a distal tibial allograft (bone graft). There were 4 conditions tested: intact, defect, flat bone block, and angled bone block (30°). Using a testing machine, the humeral head was translated anteriorly 10 mm, and distraction and contact forces were recorded.

Results:

Mean peak distraction forces were as follows: 48.28 ± 8.06 N (intact), 33.99 ± 10.54 N (defect; 70.4% of intact), 41.83 ± 9.07 N (flat; 89.6% of intact), and 45.64 ± 9.03 N (angled; 98.5% of intact). Humeral head contact with the graft occurred in 100.0% of angled trials versus 70.0% of flat trials. Mean glenohumeral contact forces were as follows: 71.81 ± 16.42 N (intact), 31.39 ± 16.60 N (defect), 46.91 ± 4.12 N (flat), and 62.17 ± 9.26 N (angled). One-way analysis of variance showed a significant effect of construct type on both contact and distraction forces (P < .001). Pairwise comparisons showed significant differences in distraction forces between intact and defect conditions and between defect and angled bone block conditions. Comparisons also demonstrated significant differences in contact forces between intact and defect, intact and flat bone block, defect and flat bone block, defect and angled bone block, and flat bone block and angled bone block conditions. No significant difference was observed between the intact shoulder and angled bone block repair.

Conclusion:

Angled bone blocks more closely restored native glenoid concavity and were biomechanically superior to flat bone blocks in re-establishing stability and centering the humeral head after glenoid bone loss.

Clinical Relevance:

This study provides a quantitative comparison between different bony glenoid augmentation methods.