What are the indications of reverse shoulder arthroplasty (RSA) hardware loosening on a bone scan?

From the Guidelines

A three-phase bone scan with SPECT or SPECT/CT is the recommended initial imaging study for evaluating suspected loosening of reverse shoulder arthroplasty hardware, as it provides high sensitivity for detecting acute osteomyelitis and mechanical loosening with osteolysis. The procedure involves intravenous injection of technetium-99m methylene diphosphonate (Tc-99m MDP) followed by immediate blood flow images, blood pool images at 5-10 minutes, and delayed images at 2-4 hours 1. Increased uptake around the prosthesis components, particularly at the bone-implant interface, may indicate loosening.

Key Considerations

• The specificity of bone scans for periprosthetic complications increases in older prostheses once the postoperative remodeling has stabilized 1.
• SPECT/CT imaging provides additional anatomical correlation and improves diagnostic accuracy, and can also differentiate symptomatic from asymptomatic scapular notching associated with reverse shoulder prostheses 1.
• Normal uncomplicated postoperative change tends to decrease over time and up to 2 years or longer after surgery, whereas aseptic loosening generally tends to progress 1.
• Patients should be well-hydrated before the procedure and should empty their bladder frequently afterward to reduce radiation exposure.

Diagnostic Approach

• A three-phase bone scan can detect metabolic changes in bone that occur before structural changes become visible on X-rays, making it particularly useful when standard radiographs are inconclusive.
• For enhanced specificity, a labeled white blood cell scan (using In-111 or Tc-99m HMPAO) can be combined with the bone scan to differentiate between aseptic loosening and infection.
• The test involves minimal radiation exposure and generally has no side effects beyond potential minor discomfort from lying still during imaging 1.

From the Research

Bone Scan Reverse Shoulder Hardware Loosening

• The loosening of reverse shoulder arthroplasty (RSA) hardware is a significant concern, with glenoid component loosening being a primary cause of failure 2.
• A study of 127 consecutive shoulders that underwent revision to RSA for the treatment of loosening of a polyethylene cemented glenoid component found that 16 shoulders (13%) underwent revision surgery for the treatment of baseplate loosening, and radiographic baseplate loosening was present in 6 additional shoulders (overall rate of baseplate loosening, 17%) 2.
• Another study of 2,342 cases found that humeral loosening is a rare complication in RSA, representing approximately 1% of total complications, and that revisions of RSA for humeral loosening yield modest clinical improvements 3.
• Glenoid loosening and migration in RSA can be treated with different options, including conservative treatment, revision of the glenosphere, and conversion to hemiarthroplasty, with conservative treatment and glenoid revision achieving similar improvements in pain and function 4.
• The incidence of radiographic aseptic loosening of the humeral component in RSA is low, with a study of 292 patients finding an overall rate of loosening of 0.74%, and no loosening occurring in the press-fit group 5.
• Complications leading to reoperation after RSA are often multiple, and the most common causes of revision surgery are prosthetic instability, infection, humeral problems, and glenoid loosening, with functional results of revised RSA being inferior to those of primary prostheses 6.