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Aseptic loosening is the failure of the bond between an implant and bone in the absence of infection. Loosening of shoulder arthroplasties is less common than in knee or hip arthroplasties. This is attributed to the non-weight-bearing status of the shoulder joint.
Glenoid component loosening occurs more commonly than humeral component, and is one of the most frequent complications requiring revision surgery.
Radiographic signs of loosening include:
- Progressive and extensive widening of interfaces between bone-cement, bone-prosthesis or cement-prosthesis.
- Fragmentation or fracture of cement
- Migration/subsidence of prosthetic components
- Bead shedding in porous-coated prosthesis
Ideally, there is no interface lucency. However, frequently thin interfaces up to 1.5 mm wide are identified, particularly about the glenoid component.9 These may develop about the bone-cement interfaces in cemented components or about the bone-component interface in non-cemented components. Sclerotic lines at the interface edge may be present.
Comparison with initial baseline and early radiographs must be made. if these interfaces are stable, and do not progress, they are usually considered normal. Progressively widened interfaces greater than 2 mm suggest loosening and/or infection.
Marked widening of the bone-cement interfaces and thinning of the lateral humeral cortex, resulting in loosening. Infection was also present.
Change of position of any component is diagnostic for loosening. Comparison with baseline radiographs may need to be made to diagnose subtle changes.
Loose and dislocated polyethylene glenoid component. The component and its cement fixation has migrated posteriorly (arrows).
Loose and dislocated polyethylene glenoid component in different patient. AP radiograph demonstrates abnormal curvilinear lucency in axillary pouch of the joint (arrow). Axillary radiographic obtained during arthrogram demonstrates contrast outlining the posteriorly dislocated component (arrows).