Stress shielding and bone resorption in shoulder arthroplasty

Area of Science:

• Orthopedic Surgery
• Radiology
• Biomedical Engineering

Background:

• Shoulder arthroplasty is a common procedure for shoulder joint replacement.
• Stress shielding, characterized by reduced bone density around an implant, is a potential complication.
• Understanding factors contributing to stress shielding is crucial for improving implant design and patient outcomes.

Purpose of the Study:

• To investigate the incidence and radiographic signs of stress shielding after humeral head replacement.
• To identify potential risk factors, such as relative stem size and patient comorbidities, associated with stress shielding.
• To evaluate the long-term radiographic changes in bone density around shoulder arthroplasty implants.

Main Methods:

• Retrospective review of 70 humeral head replacements in 64 patients (49 rheumatoid arthritis, 21 osteoarthritis).
• Radiographic assessment of cortical thickness changes in four regions around the implant stem over an average follow-up of 5.3 years.
• Calculation of relative stem size (implant stem diameter to humeral diameter ratio).

Main Results:

• Stress shielding was observed in 9% of patients (6/70), predominantly in the proximal-lateral region.
• Patients exhibiting stress shielding had a significantly higher relative stem size (0.58) compared to those without (0.48).
• Rheumatoid arthritis patients, often with osteoporosis, showed a higher incidence of stress shielding.

Conclusions:

• Stress shielding is a significant long-term complication following shoulder arthroplasty.
• Relative stem size is a critical factor in the development of stress shielding.
• Osteoporosis, particularly in rheumatoid arthritis patients, may increase the risk of stress shielding.