This biomechanical study tested whether the acromion acts as a bony restraint to posterior humeral head translation. Using 3D-printed statistical shape models of normal and Walch B1 scapulae, the authors compared translation before and after simulated surgical corrections. The goal was to explain why glenoid version correction alone often fails in posterior instability.
When you see a young patient with static posterior subluxation, a Walch B glenoid, and eccentric osteoarthritis, remember the deformity is not just the glenoid. This model shows the acromion works as a bony buttress. A high, flat B1 acromion lets the humeral head translate posteriorly until nothing stops it.
That mechanism explains a clinical pattern boards love to test: isolated glenoid opening-wedge osteotomy and J-graft procedures often fail to durably recenter the head. Only combined correction of glenoid version, glenoid inclination, and acromial orientation restored near-normal stability here.
Keep the limits in mind. This is Level V evidence, osseous-only, with soft tissue and muscle contributions blocked, so it is proof-of-concept rather than a surgical mandate. The practical lesson is to evaluate acromial morphology on 3D CT before assuming glenoid version correction alone will solve posterior instability.
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This biomechanical study tested whether the acromion acts as a bony restraint to posterior humeral head translation. Using 3D-printed statistical shape models of normal and Walch B1 scapulae, the authors compared translation before and after simulated surgical corrections. The goal was to explain why glenoid version correction alone often fails in posterior instability.
When you see a young patient with static posterior subluxation, a Walch B glenoid, and eccentric osteoarthritis, remember the deformity is not just the glenoid. This model shows the acromion works as a bony buttress. A high, flat B1 acromion lets the humeral head translate posteriorly until nothing stops it.
That mechanism explains a clinical pattern boards love to test: isolated glenoid opening-wedge osteotomy and J-graft procedures often fail to durably recenter the head. Only combined correction of glenoid version, glenoid inclination, and acromial orientation restored near-normal stability here.
Keep the limits in mind. This is Level V evidence, osseous-only, with soft tissue and muscle contributions blocked, so it is proof-of-concept rather than a surgical mandate. The practical lesson is to evaluate acromial morphology on 3D CT before assuming glenoid version correction alone will solve posterior instability.