The Memory Metal Spinal System in a Posterior Lumbar Interbody Fusion (PLIF) Procedure: A Prospective, Non-Comparative Study to Evaluate the Safety and Performance

A prospective, non-comparative study of 27 patients to evaluate the safety and performance of the Memory Metal Spinal System used in a PLIF procedure in the treatment of spondylolisthesis, symptomatic spinal stenosis or degenerative disc disease (DDD).

To evaluate the clinical performance, radiological outcome and safety of the Memory Metal Spinal System, used in a PLIF procedure, in the treatment of spondylolisthesis, symptomatic spinal stenosis or degenerative disc disease in human subjects.

Spinal systems that are currently available for correction of spinal deformities or degeneration such as lumbar spondylosis or degenerative disc disease, use components manufactured from stainless steel or titanium and typically comprise two spinal rods with associated connection devices. The Memory Metal Spinal System consists of a single square spinal rod made from a nickel titanium alloy (Nitinol) used in conjunction with connection devices. Nitinol is characterized by its shape memory effect and is a more flexible material than either stainless steel or titanium. With current systems there is loss of achieved reposition due to the elastic properties of the spine. By using a memory metal in this new system the expectation was that this loss of reposition would be overcome due to the metal’s inherent shape memory properties. Furthermore, we expect a higher fusion rate because of the elastic properties of the memory metal.

Twenty-seven subjects with primary diagnosis of spondylolisthesis, symptomatic spinal stenosis or degenerative disc disease (DDD) were treated with the Memory Metal Spinal System in conjunction with the Brantigan IF® Cage in two consecutive years. Clinical performance of the device was evaluated over 2 years using the Oswestry Disability Index (ODI), Short Form 36 questionnaire (SF-36) and pain visual analogue scale (VAS) scores. Safety was studied by collection of adverse events intra-operative and during the followup. Interbody fusion status was assessed using radiographs and a CT scan.

The mean pre-operative ODI score of 40.9 (±14.52) significantly improved to 17.7 (±16.76) at 24 months postoperative. Significant improvement in the physical component from the SF36 questionnaire was observed with increases from the baseline result of 42.4 to 72.7 at 24 months (p<.0001); The emotional component in the SF36 questionnaires mean scores highlighted a borderline significant increase from 56.5 to 81.7 at 24 months (p=0.0441). The average level of leg pain was reduced by more than 50% postoperation (VAS values reduced from 5.7 (±2.45) to 2.2 (±2.76) at 24 month post-operation with similar results observed for back pain. CT indicated interbody fusion rate was not significantly faster compared to other devices in literature. No device related adverse events were recorded in this study.

The Memory Metal Spinal System, different from other devices on the market with regard to material and the one rod configuration, is safe and performed very well by improving clinically important outcomes in the treatment of spondylolisthesis, symptomatic spinal stenosis or degenerative disc disease. In addition the data compares favorably to that previously reported for other devices in the literature.