Can implant removal restore mobility after fracture of the thoracolumbar segment? A radiostereometric study

Background and purpose - Randomized trials have found that treating spinal burst fractures with reduction and posterior fixation is adequate without the use of bone grafting for definitive fusion. Restitution of intervertebral mobility of such an unfused segment after fracture healing may unload the adjacent parts of the spine and reduce the risk of degeneration of these segments. We used radiostereometry (RSA) to study whether late implant removal would restore the intervertebral mobility of a thoracolumbar segment treated with posterior instrumentation but no bone grafting for unstable spinal fracture. Patients and methods - We identified 7 patients with implant related back pain at least 1.5 years after a thoracolumbar fracture (Th12 or L1) treated with reduction and posterior instrumentation. The implants were removed and tantalum indicators for RSA were inserted. 3 months later, each patient was examined with RSA. The intervertebral translations and rotations of the thoracolumbar segment, induced by change in position from flexion to extension, were measured. Progressive deformity was registered by conventional radiography and the overall clinical outcome was assessed by the patients. Results - According to RSA, all 7 patients regained some mobility of the fractured thoracolumbar segment. In 1 patient who was primarily treated for a flexion-distraction type of injury, conventional radiography revealed a progressive kyphotic deformity 3 months after implant removal and the clinical outcome was poor. According to the patients, 1 had a fair clinical outcome and 5 had good outcome. Interpretation - Late implant removal may restore segmental mobility after posterior fracture fixation of the thoracolumbar segment if bone grafting has not been used. The clinical consequences, positive or negative, of the residual mobility demonstrated in our small number of patients should be evaluated in studies based on extended patient series and with different fracture types.