Silicate-substituted Calcium Phosphate as a Bone Void Filler After Kyphoplasty in a Young Patient With Multiple Compression Fractures due to Osteogenesis Imperfecta Variant

Mitchell A. Hardenbrook, M.D., L.C.D.R., M.C., U.S.N.; Sergio R. Lombardo, D.O., L.T., M.C., U.S.N.

Disclosures

Neurosurg Focus. 2006;21(6) 

In This Article

Case Report

History and Examination

This 25-year-old man presented with a 13-month history of low-back pain radiating to the right lower extremity, accompanied by numbness and paresthesias. He rated his back pain as a 5 on a scale of 0 to 10 in intensity, worsening to an 8 with minimal activities. On physical examination, the patient had tenderness to palpation of the lower lumbar spine and asymmetrical weakness of the right quadriceps. Initial AP and lateral radiographs of the lumbar spine (Fig. 1) showed compression fractures of nearly all VBs, with a radiographic ap pearance of osteoporosis. Magnetic resonance imaging of the lumbar spine (Fig. 2) revealed multiple compression fractures and foraminal stenosis in the right L3–4 and L4–5. Dual-energy x-ray absorptiometry of the lumbar spine showed a bone mineral density of 0.62 and a T-score of –4.28, which is consistent with severe osteoporosis. After an extensive metabolic evaluation, a rare variant of osteogenesis imperfecta was diagnosed. The patient's pain failed to improve despite bracing, medication, and activity modification that continued for 9 months. He therefore underwent kyphoplasty of L-3, L-4, and L-5 in which silicate-substituted calcium phosphate was used as a bone void filler, and foraminotomy of the right L3–4 and L4–5 was also performed.

Operation

A void was created in each vertebra by using a balloon tamp (Kyphon), and silicate-substituted calcium phosphate crystals were inserted through a 4-mm cannula into the L-3, L-4, and L-5 VBs. The amount of bone filler inserted was determined by the volume of the void created by the balloon tamp. Kyphoplasty at L-3 and L-4 was performed via a unipedicular approach, whereas the L-5 kyphoplasty was performed via a bipedicular approach. The bone void filler was easily visualized using fluoroscopic imaging intraoperatively (Fig. 3). The right L-3 and L-4 nerve roots were decompressed without incident. The patient tolerated the procedure well without complications.

Postoperative Course

On postoperative Day 1, before the patient was discharged, standing AP and lateral radiographs of the lumbar spine were obtained (Fig. 4), which showed the bone void filler within the VBs. At his initial follow-up appointment 4 weeks postoperatively, the patient described improvement of his back pain and mild improvement of his right leg symptoms. Follow-up radiographs of the lumbar spine (Fig. 5) were obtained at 3 and 5 months postoperatively, and these showed bone incorporation. Axial (Fig. 6A and B) and sagittal (Fig. 6C) CT scans of the lumbar spine obtained 9 months postoperatively demonstrated trabecular bone forming into the bone filler and no lucency around the bone filler, confirming bone incorporation of the silicate-substituted calcium phosphate crystals within the VBs. Clinically, the patient had minimal back pain at the most recent follow-up visit 9 months postoperatively.

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