Aseptic loosening is the failure of the bond between an implant and bone in the absence of infection. It is the most frequent cause of long-term implant failure [14, 15]. Its incidence is higher in patients who continue to use their elbow in strenuous activities and heavy lifting and in the more constrained, linked prosthesis types. Patients present with insidious onset of activity related pain in a previously well functioning prosthesis.
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 prostheses
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. Infection and loosening share overlapping radiographic findings. An infected prosthesis may become loose as the interfaces widen. A loose prosthesis may become infected.
|Lateral view of a radial head replacement in an elbow showing marked widening of the bone-cement interface and thinning of the radial cortex related to aseptic loosening. The prosthesis has moved in position, a finding diagnostic for loosening. Note track (red arrow) from prior external fixator pin placement has filled in on the follow up study.|
Change of position of any component is diagnostic for loosening. Comparison with baseline radiographs need to be made to diagnosis subtle changes.
|Posterolateral backout of radial head prosthesis (blue arrow) resulting in mechanical erosion of the capitulum (red arrow)|
|Marked loosening of humeral stem with migration anterolaterally beyond the humeral cortex. Proximal migration or subsidence (red arrow) has also occurred with the medial and lateral condyles more distal than the ulna.|
|Long stem total elbow replacement, revised secondary to loosening. Note metallic and cement particulate debris (red arrow) arising from initial loose prosthesis.|