Humeral head in rotator cuff tear arthropathy shows reduced cartilage damage and uniform subchondral bone osteoporosis: a histomorphometric analysis.

Background: This study histologically assessed alterations in the articular cartilage, subchondral bone, and trabecular bone in patients with rotator cuff tear arthropathy (CTA) versus those with osteoarthritis (OA) of the humeral head. Methods: This retrospective study evaluated 59 humeral heads (37 CTA and 22 OA cases) resected during shoulder arthroplasty and 7 shoulder specimens from cadaveric controls. Bone density was evaluated by computed tomography. Histological evaluations were analyzed semiquantitatively for Osteoarthritis Research Society International scores, articular cartilage thickness, subchondral bone plate thickness, and trabecular bone mass and distribution, using standard staining techniques. Results: CTA cases showed significantly lower Hounsfield units in the trabecular and metaphyseal bones on the affected side than on the healthy side. In contrast, no significant difference in Hounsfield units was observed in OA cases. A histological analysis showed lower Osteoarthritis Research Society International scores in CTA than in OA, which indicated moderate cartilage degeneration. Subchondral trabecular bone in CTA cases was uniformly thinned, whereas OA cases showed variable trabecular morphology, with areas of both thickening and thinning. Consequently, the humeral head bone volume was smaller in CTA than in OA. Conclusion: CTA is characterized by moderate cartilage degeneration and uniform subchondral trabecular bone loss, which may underlie complications associated with reverse shoulder arthroplasty. These findings may serve as a foundation for further studies of appropriate surgical strategies and preoperative interventions for osteoporosis.