Effect of anular repair on the healing strength of the intervertebral disc- A sheep model

Study Design. The intervertebral disc, in a sheep model, was used to assess the effect of directly repairing three different anular incisions on the s ubsequent healing strength of the intervertebral disc, Objectives. To assess whether directly repairing an anular defect, made at the time of lumbar discectomy, could influence the healing rate and strengt h of the anulus fibrosus. Methods. Twenty-four sheep underwent a retroperitoneal approach to five lum bar disc levels. An anular incision , followed by partial discectomy was do ne at each exposed level. Anular incisions used in this study consisted of 1) a straight transverse slit, 2) a cruciate incision, and 3) a window or b ox excision. Healing strength was measured at three time intervals: 2 weeks , 4 weeks, and 6 weeks. Each anular incision type was performed on 30 lumba r discs, 10 discs in each time interval. Five discs in each time interval u nderwent direct repair, and five discs were left unrepaired to heal as cont rols. The sheep were killed at 2, 4, and 6 weeks after surgery. The lumbar Spines were removed en bloc, and the intervertebral discs were subjected to pressure-volume testing to assess the anular strength of repaired versus u nrepaired disc injuries at each time interval. Results. Statistical analysis was performed to evaluate the effects of heal ing time, incision technique, and repair on the pressure-volume characteris tics of the involved discs. Pressure-volume testing showed trends of strong er healing for repaired discs, but at no time interval was any significant difference round between repaired and nonrepaired anular strength. Of the n onrepaired discs, the box incision was only 40 to 50% as strong as the slit or cruciate incised discs during early healing. Conclusion. Direct repair of anular incisions in the lumbar spine does not significantly alter the healing strength of the intervertebral disc after l umbar discectomy.