The influence of anulotomy selection on disc competence: A radiographic, biomechanical, and histologic analysis

Study Design. This study analyzed the radiographic, biomechanical, and histologic attributes of three commonly used anulotomy techniques. Objectives. This study defined the propensity of the anulus fibrosus to heal after discectomy and correlated biomechanical differences between subgroups of the motion segments studied. Summary of Background Data. No previous report that compares the influence of anulotomy selection on disc competence exists. Methods. Anulotomies were performed on the anterolateral aspects of the lumbar discs of 54 adult goats. The goats were randomly assigned to one of three subgroups containing 18 animals. In subgroup A, a full-thickness anular window was excised. In subgroup B, a full-thickness cruciate anulotomy was accomplished. In subgroup C, a full-thickness anulotomy was developed by inserting a trocar, 2.5 mm in diameter, into the disc. Results. Histologic analysis revealed that primary anular healing did not occur in any specimen. The anulotomy tracts in subgroup C (trocar) were consistently narrower than those of subgroups A and B. Discography demonstrated the presence of severe and early disc degeneration with subgroup A (anular window), a finding not observed within the trocar anulotomy group. Biomechanical testing demonstrated increased resistance to pull out by the trocar anulotomy group at 4 weeks, as well as increased torsional stiffness of the motion segment when compared to both window and cruciate anulotomy. Conclusions. The authors conclude that attempts should be made to minimize injury to the anulus fibrosus during the performance of discectomy.