Time-course changes in bone mineral density after anatomical and reverse total shoulder arthroplasty : a dual-energy X-ray absorptiometry-based study.

AIMS: Bone resorption around cementless short humeral stems is increasingly recognized after shoulder arthroplasty, but quantitative longitudinal data are lacking. We measured bone mineral density (BMD) around the humeral component after anatomical total shoulder arthroplasty (aTSA) and reverse total shoulder arthroplasty (RSA) using dual-energy X-ray absorptiometry (DEXA) and evaluated the time-course changes over two postoperative years. Additionally, we investigated the association between osteoporosis and clinical outcomes.

METHODS: The subjects were patients who underwent aTSA or RSA, and for whom DEXA evaluation was available at three weeks, six months, one year, and two years postoperatively. The area around the humeral component was divided into five zones, and the BMD of each zone was measured. To evaluate clinical outcomes, we investigated their association with osteoporosis and measured the postoperative American Shoulder and Elbow Surgeons (ASES) score using the minimal clinically important difference (MCID) as the reference. Overall, 94 RSAs and 43 aTSAs were observed.

RESULTS: In RSA, BMD decreased significantly over time in zones 3 and 5 (both p < 0.05). In aTSA, BMD decreased in zones 2, 3, and 4 from three weeks to six months, with little sustained decrease thereafter. Additionally, in RSA, a decrease in zone 3 BMD was significantly associated with osteoporosis (both p < 0.05). Failure to achieve the MCID for the ASES score was also significantly associated with both zone 3 BMD loss and osteoporosis (both p < 0.05).

CONCLUSION: Time-course changes in BMD around cementless short humeral components differed between aTSA and RSA. In RSA, BMD decreased over time in zones 3 and 5. Zone 3 BMD loss was significantly associated with osteoporosis, and both zone 3 BMD loss and osteoporosis were linked to failure to achieve the MCID for the ASES score. These findings suggest that patients undergoing RSA with osteoporosis may benefit from careful postoperative follow-up, including monitoring of periprosthetic bone loss and optimization of osteoporosis management.