11.5.3\ Hardware Loosening

and Pseudarthrosis

11.5.3.1\ Discussion

Spine hardware loosening is a fairly frequent finding on imaging, occurring in nearly 20% of patients and 5% of pedicle screws. Iliac screws followed by sacral screws are most commonly affected, perhaps related to torque. Loosening appears as a gap between the hardware and the bone greater than 2 mm (Fig. 11.94). Although loosening can be related to the presence of particulate debris activates phagocytes that release enzymes that result in ­osteolysis, it can be also a sign of underlying hardware infection. Furthermore, there can be associ-

ated pseudarthrosis (Fig. 11.95), which can be suggested by the following imaging findings:

Fig. 11.94  Loosening. Axial CT image shows lucency surrounding the bilateral screws

Fig. 11.95  Transsacral interbody fusion loosening and pseudarthrosis. Sagittal CT cisternogram image shows lucency surrounding the device and across the previously fused disc space (arrow)

11.5.4\ Hardware and Periprosthetic

Fractures

11.5.4.1\ Discussion

Pedicle screw fracture has an incidence of 0.5– 2.5%. CT can readily demonstrate hardware fracture, particularly if there is displacement

a

(Fig. 11.96). The presence of a broken screw is strongly associated with loosening and pseudarthrosis, which should be sought on imaging. In addition, hardware can alter the stresses on the surrounding bone and predispose to fractures. The pedicle is a common location for hardware-­ related fracture (Fig. 11.97).

b

Fig. 11.96  Screw fracture. The patient has a history of three prior lumbar spine surgeries and presents with mechanical back pain. Axial (a) and coronal (b) CT

myelogram images show a displaced fracture (encircled) of the left L5 pedicle screw