A new study from Osaka Metropolitan University is drawing attention to an overlooked consequence of shoulder replacement surgery: the gradual loss of bone surrounding the implant. Using dual-energy X-ray absorptiometry, or DEXA, researchers tracked changes in bone mineral density around shoulder implants for two years and found that the pattern of bone loss differed sharply between two major procedures. The findings suggest that patients undergoing reverse shoulder arthroplasty, particularly those with osteoporosis, may require closer monitoring of bone health after surgery.
Shoulder arthroplasty has become increasingly common as surgeons seek to relieve pain and restore movement in people with severe arthritis, fractures, and other disorders of the shoulder joint. In recent years, cementless short-stem implants have gained popularity because they may preserve more of the patient’s existing bone and potentially make future revision surgery easier. These implants depend on bone growing directly onto or around the implant for long-term fixation, making the condition of the surrounding bone especially important.
Despite the importance of bone quality, postoperative changes around shoulder implants have traditionally been assessed mainly through conventional X-rays. Radiographs can show obvious structural changes, implant position, and signs of loosening, but they are relatively insensitive to modest changes in bone density. Unlike a visual assessment on a plain X-ray, DEXA provides a quantitative measurement of bone mineral density by using two low-dose X-ray beams to distinguish bone from soft tissue. The technique is widely used to diagnose osteoporosis and to study bone loss around hip and knee replacements, but it has been used far less often in shoulder arthroplasty.
To obtain a clearer picture of what happens after surgery, a research team led by Dr. Katsumasa Nakazawa and Professor Hidetomi Terai at Osaka Metropolitan University’s Graduate School of Medicine conducted a retrospective observational study. The researchers examined 137 patients who had received shoulder replacement surgery, including 94 patients who underwent reverse total shoulder arthroplasty and 43 who underwent anatomical total shoulder arthroplasty. The investigators divided the upper humerus—the upper portion of the arm bone—into five zones and used DEXA measurements to follow bone mineral density at multiple time points during the first two years after implantation.
The two procedures alter shoulder mechanics in fundamentally different ways. In anatomical total shoulder arthroplasty, the normal arrangement of the joint is reproduced: an artificial ball replaces the humeral head, while a socket component is placed on the shoulder blade. This approach generally depends on functioning rotator-cuff tendons to stabilize and move the joint. Reverse shoulder arthroplasty switches the geometry, placing a ball on the shoulder blade and a socket on the upper arm. The reversed design allows the deltoid muscle to power shoulder elevation when the rotator cuff is severely damaged, but it also changes how forces travel through the arm and implant.
The DEXA results revealed that bone density declined in distinct regions after reverse shoulder arthroplasty. Significant decreases were observed over time in areas surrounding the implant stem, indicating that the bone may be adapting to altered mechanical loading. This process, known as stress shielding, occurs when an implant carries a greater share of the forces that would normally pass through the surrounding bone. Reduced mechanical stimulation can encourage bone remodeling and gradual loss of mineral content, potentially weakening the bone around the implant even when the implant itself remains stable.
Patients who underwent anatomical shoulder replacement showed a different trajectory. Their bone mineral density fell during the interval between approximately three weeks and six months after surgery in regions below the humeral head, but the decline largely stabilized afterward. The early reduction may reflect the immediate effects of surgery, temporary changes in loading, reduced activity during rehabilitation, or the body’s normal response to the implantation of a prosthesis. The relative stabilization after six months suggests that the remodeling process may be more limited or may reach a new equilibrium sooner in anatomical replacements than in reverse replacements.
The most concerning association appeared in the reverse arthroplasty group. Bone loss in the middle region of the humeral shaft was significantly linked to osteoporosis, a systemic disease in which bone becomes less dense and more fragile. The study also found that both osteoporosis and bone loss were associated with a lower likelihood of achieving a clinically meaningful improvement in shoulder function. Although the observational design cannot prove that bone loss directly causes poorer recovery, the relationship highlights the possibility that skeletal weakness may influence implant support, rehabilitation, muscle performance, or the patient’s ability to regain useful shoulder movement.
“Our study showed that bone density around the implant after RSA declines over time, particularly in patients with osteoporosis,” Dr. Nakazawa said. The researchers suggest that evaluating osteoporosis before surgery, measuring bone density after surgery, and optimizing treatment for low bone mass could become important elements of long-term care. Such measures might help physicians identify patients at increased risk of periprosthetic fractures or implant-related complications, although future prospective studies will be needed to determine whether treating osteoporosis changes DEXA results or functional outcomes. Published in The Bone & Joint Journal, the study points toward a more precise approach to shoulder replacement follow-up—one that treats bone around the implant as a dynamic biological tissue rather than a passive structure visible only on an X-ray.
Subject of Research: People
Article Title: Time-course changes in bone mineral density after anatomical and reverse total shoulder arthroplasty: a dual-energy X-ray absorptiometry-based study
Web References: https://www.omu.ac.jp/en/ ; https://doi.org/10.1302/0301-620X.108B7.BJJ-2025-1462.R1
References: The Bone & Joint Journal. DOI: 10.1302/0301-620X.108B7.BJJ-2025-1462.R1
Image Credits: Osaka Metropolitan University
Keywords: shoulder arthroplasty, reverse shoulder arthroplasty, anatomical total shoulder arthroplasty, bone mineral density, DEXA, osteoporosis, implant-related bone loss, orthopedic surgery, shoulder replacement, bone remodeling
Tags: bone mineral density changesbone preservation techniques in shoulder arthroplastycementless short-stem shoulder implantscomplications related to bone loss after shoulder surgerydual-energy X-ray absorptiometry (DEXA) for implant monitoringimpact of bone quality on shoulder implant stabilitylong-term effects of shoulder joint replacementmonitoring strategies for shoulder implant patientsosteoporosis and shoulder surgerypostoperative bone remodeling in shoulder replacementsreverse shoulder arthroplastyshoulder bone loss
