This cross-sectional study characterizes the anatomy of constitutional static posterior shoulder instability (type C1 of the ABC classification), a pre-osteoarthritic deformity in young adults. It compares osseous shoulder morphology, scapulothoracic orientation, and shoulder girdle muscle volume in 17 C1 shoulders versus matched healthy controls. The goal is to identify the full set of anatomic differences that may drive posterior decentering.
When you see a young man with atraumatic posterior shoulder pain, weakness, and clicking but no true instability episodes, think constitutional static posterior decentering (type C1).
The central teaching point is that C1 is not a single glenoid problem. Increased glenoid retroversion, increased anterior glenoid offset, and reduced humeral retrotorsion co-vary and appear to compensate one another, so the head stays centered on the glenoid despite the deformity.
This is why isolated glenoid osteotomy has failed to recenter the joint. The authors suggest that adding a humeral rotational osteotomy to increase retrotorsion may be needed to address both sides of the imbalance.
A high-riding, flat acromion with reduced posterior coverage is a second contributor, removing a posterior bony buttress. Recognize C1 early, because it is a pre-osteoarthritic deformity that drives posterior decentering osteoarthritis in young adults.
This cross-sectional study characterizes the anatomy of constitutional static posterior shoulder instability (type C1 of the ABC classification), a pre-osteoarthritic deformity in young adults. It compares osseous shoulder morphology, scapulothoracic orientation, and shoulder girdle muscle volume in 17 C1 shoulders versus matched healthy controls. The goal is to identify the full set of anatomic differences that may drive posterior decentering.
When you see a young man with atraumatic posterior shoulder pain, weakness, and clicking but no true instability episodes, think constitutional static posterior decentering (type C1).
The central teaching point is that C1 is not a single glenoid problem. Increased glenoid retroversion, increased anterior glenoid offset, and reduced humeral retrotorsion co-vary and appear to compensate one another, so the head stays centered on the glenoid despite the deformity.
This is why isolated glenoid osteotomy has failed to recenter the joint. The authors suggest that adding a humeral rotational osteotomy to increase retrotorsion may be needed to address both sides of the imbalance.
A high-riding, flat acromion with reduced posterior coverage is a second contributor, removing a posterior bony buttress. Recognize C1 early, because it is a pre-osteoarthritic deformity that drives posterior decentering osteoarthritis in young adults.