Musculoskeletal ImagingLoosening
lessening of tightness, such as occurs in the components of joint replacement. The loosening may result from inadequate component fixation or from infection. Although in hip replacement, improvements in cement technique have reduced loosening rates on the femoral side, loosening has been found to increase with time on the acetabular side. Table 1 lists the
radiographic findings that suggest loosening of a cemented total hip prosthesis.
Loosening, Table 1. Radiographic features suggesting prosthetic loosening.
| Cement bone lucent zone of 2 mm or more |
| Widening of the cement bone lucent zone |
| Migration of prosthetic components |
| Devleopment or widening of metal cement lucent zone |
| Cement fracture |
| Periosteal reaction |
| Motion of components demonstrable on stress view or fluoroscopy |
On arthrography the amount of contrast material that collects at the bone cement and cement prosthesis interfaces may provide an indication of loosening. Subtraction techniques allow the contrast medium to be differentiated from the opaque cement, making the distribution of injected contrast material easier to define. In addition, injection of isotope into the joint at the time of contrast arthrography (termed arthroscintigraphy) has been advocated to improve the accuracy of detecting femoral component loosening. Focal uptake at the proximal and distal ends of the femoral prosthesis is thought to be highly suggestive of loosening, whereas diffuse uptake is reported to indicate infection.
DR