Biomechanical effects of cement discoplasty on the lumbar spinal unit

BACKGROUND: Percutaneous cement discoplasty (PCD) is used to treat patients with low back and leg pain due to the intervertebral disc vacuum phenomena. Whether PCD can restore lumbar spinal stability remains unknown. OBJECTIVE: The purpose of our in vitro study was to evaluate the biomechanical changes brought about by PCD. METHODS: Eight fresh pig lumbar spines were tested in the following order: intact, after nucleotomy, and after discoplasty. Flexion/extension, lateral bending, and axial rotation were induced by pure moments. The range of motion and neutral zone were recorded. A CT scan was performed to assess the injection volume of the bone cement and to observe whether the bone cement was fractured. After removing the facet joint, a compression failure test was conducted to observe the fracture of bone cement. RESULTS: Compared with nucleotomy, range of motion (ROM) after discoplasty was reduced only in lateral flexion (P < 0.05). The results of the neutral zone showed that the neutral zones in flexion–extension and lateral bending were significantly reduced after discoplasty (P < 0.05). The neutral zone was more sensitive to changes in lumbar stability than ROM. Bone cement slides were observed during the biomechanical test. The CT scan and compression failure test showed that bone cement fracture was more likely to occur at the puncture channel in the annulus fibrosus region. CONCLUSION: In all, the biomechanical study indicates that discoplasty helps enhance the stability of the lumbar spine in flexion–extension and lateral bending, which explains how PCD works for low back pain. Fractures and sliding of bone cement were observed after discoplasty, and this was more likely to occur at the puncture channel in the annulus fibrosus region. This suggests that bone cement displacement after PCD may cause nerve compression.