A novel allograft combined with modified purse-string suture fixation for annulus fibrosus repair: biomechanical evaluation in a porcine lumbar disc model.

Background: Annulus fibrosus (AF) defects may permit recurrent nucleus pulposus extrusion and are difficult to repair because of limited vascularity and persistent mechanical loading. Commercial bone-anchored annular closure devices are intended to occlude large post-discectomy defects, whereas tissue-derived grafts may provide an alternative defect-filling strategy. However, the immediate sealing performance of allograft-based AF repair remains incompletely characterized. Purpose: This study developed an allograft designed to stably repair AF defects and evaluated its sealing performance in porcine lumbar discs. Methods: Thirty porcine lumbar motion segments were allocated to five experimental groups. Group A received a 26-gauge annular puncture injury without repair and served as a puncture-reference condition rather than a defect-matched control. In Groups B1, B2, C1, and C2, a standardized 3-mm annular defect was created to accommodate a 3-mm-diameter allograft. Group B1 received a standard cylindrical allograft, whereas Group B2 received an allograft that expanded asymmetrically after hydration to form a truncated-conical geometry. Groups C1 and C2 received the corresponding allografts secured using modified purse-string suture (MPSS) fixation. Acute sealing performance was evaluated by static leakage testing, and primary statistical comparisons were restricted to Groups B1-C2. Results: Group A, included descriptively as a puncture-reference condition, had a mean failure pressure of 0.395 ± 0.083 MPa and was excluded from the primary inferential analysis. Among groups with standardized 3-mm defects, mean failure pressures were 0.802 ± 0.334 MPa for the standard cylindrical allograft (Group B1), 1.539 ± 0.334 MPa for the hydration-expanded truncated-conical allograft (Group B2), 2.638 ± 0.386 MPa for the standard cylindrical allograft with MPSS fixation (Group C1), and 2.892 ± 0.685 MPa for the hydration-expanded truncated-conical allograft with MPSS fixation (Group C2). Failure pressure differed significantly among Groups B1-C2 (p < 0.001). MPSS fixation significantly increased failure pressure for both graft configurations, whereas the difference between Groups B1 and B2 did not reach statistical significance after adjustment for multiple comparisons (adjusted p = 0.052). Conclusion: Among porcine lumbar motion segments with standardized 3-mm AF defects, MPSS fixation significantly increased acute leakage resistance for both graft configurations. The hydration-expanded truncated-conical allograft showed a higher mean failure pressure than the standard cylindrical allograft when used without fixation, although this difference did not reach statistical significance after adjustment for multiple comparisons. These findings support the acute mechanical feasibility of the allograft-MPSS construct.