Introduction Dynamic stabilisation is a new technology with origins in France. Interspinous spacers are placed in the lumbar spine to offload the facet joints and posterior disc annulus. Three devices are presently available in Australia. Finite element analysis suggests that such devices can restore or ‘normalise’ the biomechanics of a degenerate motion segment without effecting adjacent motion segments. This study reports an evaluation of the safety of these devices, their potential applications, the technique for implantation and complications experienced by a single surgeon over two years.

Methods 120 patients were selected and had either Wallis or DIAM dynamic stabilisation implants placed in the lumbar spine during surgery for disc prolapse, degenerative stenosis or ‘discogenic’ back pain.

Results 55% of patients had implants placed after discectomy, 30% of patients after stenotic decompression, 10% for ‘discogenic’ pain and 5% above an instrumented fusion. 58% of patients had a single level procedure, 38% had a two level procedure and 4% a three level procedure. No device related or other significant complications were encountered. Three patients required removal of devices, two to remove an L45 Wallis implant and place L45 and L5S1 DIAM implants and one to remove DIAM implants for recurrent disc prolapse before performing a fusion procedure. Patient bed stay has averaged less than 4 days.

Discussion Dynamic stabilisation is a safe and simple procedure for several common lumbar spinal conditions. The DIAM implant is a simpler device to insert compared to the Wallis implant and can almost always be fitted to the L5S1 level. The Wallis implant appears to be better suited to degenerative spondylolithesis as it is of more robust design and may better limit flexion instability. Patient outcomes and satisfaction are satisfactory to date. Surgical technique must be modified to preserve the spinous process and lamina.

Introduction: Recently frameless stereotaxy has been introduced to assist with the spinal instrumentation. The mobility of individual vertebra however limits its accuracy and ease of use. The authors have developed a novel method of spinal stereotaxy using exact plastic copies of the spine manufactured using biomodelling technology.

Methods: Fifteen patients with complex spinal disorders requiring instrumentation were recruited. A 3D CT scan of their spine was performed and the data were transferred via DICOM network to a computer workstation. ANATOMICS BIOBUILD software was used to generate the code required to manufacture exact acrylate biomodels of each spine using rapid prototyping. The biomodels were used to obtain informed consent from patients and simulate surgery. Simulation was performed using a standard power drill to place trajectory pins in the appropriate pedicles. Acrylate drill guides were manufactured using the biomodels as templates. The biomodels and templates were sterilised and used intra-operatively to assist with the placement of the instrumentation.

Results: The biomodels were found to be highly accurate and of great assistance in the planning and execution of the surgery. The ability to drill optimum screw trajectories in the biomodel and then accurately replicate the trajectory was judged especially helpful. Accurate screw placement was confirmed with post-operative CT scanning. The design of the first two templates was suboptimal as the contact surface area was too great and complex. Approximately 20 minutes was spent pre-operatively preparing each biomodel and template. Operating time was reduced, as less reliance on intra-operative X-ray was necessary. Minimal invasive surgery was greatly facilitated in planning and execution. Patients stated that the biomodels improved informed consent.

Conclusion: Biomodel spinal stereotaxy is a simple and accurate technique which may have advantages over frameless stereotaxy.