Comparing Mersilene* tape and stainless steel wire as sublaminar spinal fixation in the Chagma baboon (Papio ursinus).

The development of segmental instrumentation has been a major advancement in the treatment of spinal problems, but the use of sublaminar stainless steel wire (SSW) has not been without untoward effects. This study reports a comparison of Mersilene* tape (MT) and stainless steel wire (SSW) used for sublaminar fixation in the Chagma baboon (Papio Ursinus). A similar comparative study has not been reported, although the local effects of sublaminar SSW in the spinal canal have previously been described. The adult Chagma baboon was selected as the experimental animal due to its partial upright posture and spinal anatomy, similar to that of the human. Six levels of the thoracolumbar spine were instrumented with custom designed Harrington hooks and regular one-quarter inch threaded rods used as a distraction system. The four intervening laminae were fixed to the rods using doubled-over, eighteen gauge sublaminar SSW in six cases and five millimeter MT in six cases. Computed axial tomography used to measure the AP diameter of the bony spinal canal revealed the AP space occupied by the SSW and MT to be 32 percent and 14.8 percent respectively. In the MT group, the overlying dura mater was found to be totally intact and revealed no signs of abnormal tissue response. A well-formed connective tissue membrane consisting of dense connective tissue surrounded the MT and was found to consist of more mature fibers than that found in the SSW group. The dura-implant interface was examined histologically and a distinct membrane was identified between the dura and the superficial aspect of the MT's, as well as intervening between the two MT's. Following removal of the MT, in contrast to the SSW, it was apparent that the underlying dura was not injured, most probably due to the soft consistency of the Mersilene* tape and the well-formed overlying membrane. On clinical grounds the fixation in both groups was adequate but the MT group formed a well-circumscribed membrane that made removal of the MT easier and potentially safer. The AP space occupied by the spinal implant was also found to be less with MT as opposed to SSW.