To assess radiological fusion rates in posterolateral fusions using SiS-CaP.

Retrospective, radiological follow-up study.

Single surgeon series of 76 consecutive patients were evaluated, in a regional spinal unit. All patients had clinical and radiological (MRI) spinal canal stenosis secondary to degenerative spondylosis or spondylolisthesis. Surgery consisted of instrumentation, decompression and meticulous preparation of the posterolateral graft bed by removal of all soft tissues posterior to the inter-transverse membrane and decortication of transverse processes (TPs). SiS-CaP putty was injected into this gutter and moulded around the instrumentation. Good quality, well prepared bone chips from the posterior decompression were seeded into the putty. Patient radiographs were reviewed at 3-6 months, 1 year and 2 years.

Radiographs were assessed using a protocol to examine granularity, bone formation and evidence of pseudarthrosis, based upon previously reported literature ¹ and our personal experience.

Of the 76 patients, 26 were excluded. M:F was 21:29. Mean age was 58yrs. Average number of motion segments fused per case was 2.2. There was one pseudarthrosis with metalwork fracture, and thus a total fusion rate of 98%. In addition, one patient had scanty bridging of TPs, and one patient had lucency around the S1 screws.

SiS-CaP, as a bone graft substitute in posterolateral instrumented fusions, gives comparable results to published fusion rates using autologous iliac crest grafting and/or Bone Morphogenic Protein ². Moreover, it avoids the associated morbidity of iliac bone harvest.

To evaluate and describe the plain radiographic changes observed with time in fusions using SiS-CaP. We describe, for the first time, 4 stages of bone substitute fusion mass (BSFM) radiographic appearance in relation to time post-op.

Retrospective, radiological evaluation.

Over 200 plain radiographs were evaluated. 70 consecutive fusions for degenerative spinal stenosis were included, in all cases performed by the same surgeon using the same operative technique. Follow-up was from 3 months to 2 years post-op.

Radiographs were evaluated for the presence or absence of SiS-CaP granules, bone formation and for evidence of pseudarthrosis.

Trends were seen within the BSFM with respect to time. At 6-12 weeks post-op a ‘homogenous granular stage’ indicates the presence of the unchanged SiS-CaP.

At 12 weeks, small pockets appear within the BSFM in the ‘vacuolation stage’, indicating bioresorption of the graft. Vacuoles become increasingly radio-opaque indicating bone proliferation during the ‘homogenous lamellar stage’. At variable time between 6 months and 2 years, the BSFM becomes encapsulated in the ‘cortication stage’ visible as a sclerotic rim around the BSFM.

We have seen a clear trend in the behaviour of the fusion mass in this case series. The radiological stages we have described above can be closely correlated with previously reported in-vitro and in-vivo studies looking at the micro-function of SiS-CaP. We hope that this description will help to judge the progress of graft incorporation and fusion. Further study of inter and intra-observer correlation will be required.

Clinical and radiological assessment of results of vertebral body stenting procedure. Introduction: Use of metallic stents along with cement have shown good restoration of the vertebral body in cadaveric spines. We have presented the early results of vertebral body stenting done at Royal Derby Hospitals. Patients and Methods: All patients had a transpedicular approach to the vertebral body. The vertebral body stent was expanded using a balloon as in balloon kyphoplasty. The balloon was removed leaving the stent in place. The resultant cavity was filled with partially cured polymethyl methacrylate in osteoporotic fractures and calcium phosphate cement in traumatic fractures. Radiological assessment included pre operative measurement of vertebral body angle, correction achieved and maintenance of correction at follow up. All patients were assessed using the visual analogue score and oswestry disability index. The procedure was done in 14 fractures (10 patients). 9 fractures were traumatic while 5 were osteoporotic fractures. The mean age of the traumatic fractures was 54.28 years while the mean age of osteoporotic fractures was 82.34 years. Mean follow up was 10 months. All traumatic fractures were type A 3.1. Mean vertebral body angle correction achieved was 8.3° (4° to 14.2°). None of the patients lost the reduction at follow up. The mean VAS for pain at 6 months was 3.8. The mean oswestry disability index was 22% for traumatic fractures, while it was 44% for osteoporotic fractures. Vertebral body stenting is a safe procedure. It was successful in restoring the anterior column with encouraging radiological and clinical results

In patients with osteoporosis there is always a strong possibility that pedicle screws will loosen. This makes it difficult to select the appropriate osteoporotic patient for a spinal fusion. The purpose of this study was to determine the correlation between bone mineral density (BMD) and the magnitude of torque required to insert a pedicle screw. To accomplish this, 181 patients with degenerative disease of the lumbar spine were studied prospectively. Each underwent dual-energy x-ray absorptiometry (DEXA) and intra-operative measurement of the torque required to insert each pedicle screw. The levels of torque generated in patients with osteoporosis and osteopenia were significantly lower than those achieved in normal patients. Positive correlations were observed between BMD and T-value at the instrumented lumbar vertebrae, mean BMD and mean T-value of the lumbar vertebrae, and mean BMD and mean T-value of the proximal femur. The predictive torque (Nm) generated during pedicle screw insertion was [-0.127 + 1.62 × (BMD at the corresponding lumbar vertebrae)], as measured by linear regression analysis. The positive correlation between BMD and the maximum torque required to insert a pedicle screw suggests that pre-operative assessment of BMD may be useful in determining the ultimate strength of fixation of a device, as well as the number of levels that need to be fixed with pedicle screws in patients who are suspected of having osteoporosis.