The effectiveness of anular repair as illustrated in an in vitro laboratory simulation

Abstract

Surgeries to repair herniated discs are one of the most performed spinal surgeries worldwide. During a lumbar discectomy the herniated portion of the intervertebral disc (IVD) is removed; however, the defect in the anulus fibrosus (AF) remains and can provide a pathway for future herniation. Repairing the anulus is shown to diminish reherniation rates. There is a lack of data regarding the ability of anular repair methods to withstand intradiscal pressures, especially in an in vitro laboratory setting. This study has focused on creating an in vitro laboratory apparatus to simulate intradiscal pressure, allowing for controlled and repeatable results. By using a commercially-available anular repair device, and developing a protocol to test the efficacy of this device, the benefit of anular repair with discectomy compared to an unrepaired defect was demonstrated. An artificial AF was developed and used in conjunction with a pressurization chamber to simulate herniation of the IVD. Four configurations were evaluated: 1) circular or slit defect (control); 2) a single tension band; 3) two tension bands in a cruciate pattern; and 4) two tension bands in a parallel configuration. Anular defects were repaired with the XcloseTM Tissue Repair System. Input pressure was increased until failure (i.e. extrusion of the NP) occurred. The maximum failure pressure, representing the pressure at herniation, was recorded. Maximum failure pressure for the non-repaired conditions were significantly different compared to the repaired conditions for both defect types. For the circular defect, the failure pressure increased by approximately 76 and 131 percent with one or two tension bands, respectively, as compared to the control. In addition, the failure pressure for two tension bands (in either configuration) was approximately 32 percent higher than that for one tension band; this difference was significant. For the slit defect, with one or two tension bands the maximum failure pressure increased by approximately 21 and 37 percent, respectively, as compared to the control. No significant difference was found between two tension bands in the cruciate and parallel configurations for either defect. Current literature and the results of this laboratory simulation suggest anular repair reduces reherniation after a lumbar discectomy. First, the significant differences found in the maximum failure pressures for repaired versus non-repaired groups suggest a reduced risk for reherniation when anular repair is performed. Second, this study indicated that defect size and shape are relevant when choosing a repair configuration. Finally, two tension bands were seen to improve the ability to retain disc material, especially for the circular defect. The use of a laboratory experiment such as this enabled control of variables that would normally be difficult to test in a surgical setting, and laid the groundwork for the use of laboratory simulations in evaluating anular repair and its respective techniques.