Wallis interspinous implantation to treat degenerative spinal disease: description of the method and case series.

The Wallis interspinous implant is most commonly used in the treatment of intervertebral disc herniation and for tears in the outer layer of the disc. The dynamic vertebral fixation concept was first initiated in 1984 with the goal of imitating the physiologic spinal kinetic. A total of 15 years later, a second generation of implant has been developed, termed the 'Wallis interspinous Implant', which aims to preserve the mobility of the operated spinal segment. To underline our own experience, a retrospective review of 15 patients that were treated with 'Wallis implantation' at our institution between January 2006 and March 2008. Our main inclusion criterion for Wallis implantation was low back pain because of degenerative lumbar spinal stenosis associated with segmental instability along with Modic changes 0-1 and with UCLA arthritic grade <II, while the main exclusion criteria were previous lumbar surgery, severe osteoporosis or degeneration UCLA grade >II in the adjacent two segments cephalad to implantation. The outcome was analyzed according to clinical and radiological parameters. One (n = 9), two (n = 4) and three levels (n = 2) were operated on using Wallis implantation, ranging from L2-L3 to L5-S1. We used implants of 8-14 mm in size. There was a reduction in low back pain (73 vs 43%) and gait disturbances (73 vs 14%) at the 3-month follow-up compared with preoperative values. In line with these results, the modified Japan Orthopedic Association Score (mJAOS) was increased from 12 preoperatively to 18 at 3 months and 20 at 12 months postoperatively. A reduction in low back pain could only be demonstrated for implants that were 10 mm in size or greater at 3 months and 12-15 months postoperatively. An improvement was seen in Modic grades after the operations as compared with those observed at preoperative MRI. The outcome in our patients was rated as good or excellent according to Odom's criteria in all cases, independent of the levels that were used. Wallis implantation is therefore a safe procedure with a good to excellent outcome in the short- and mid-term follow-up and can lead to disc rehydration, as confirmed by postoperative MRI. Principal postoperative (clinical) success is based on the correct implant size.