Mediolateral and Craniocaudal Distribution of Anterior Longitudinal Ligament Pullout Strength: Determining the Optimal Location for Sacrocolpopexy Graft Fixation

INTRODUCTION: Determining the optimal location for sacrocolpopexy graft fixation is subject to multifactorial anatomic considerations. Principles include avoidance of key neurovascular structures, minimization of rare orthopedic complications, as well as selection of a strong and durable attachment site within the anterior longitudinal ligament (ALL). Although some published studies have described a midline craniocaudal variation in ALL thickness and tensile strength within the presacral space, there is a dearth of data regarding its relative strength in the lateral aspects and variation along the mediolateral axis. OBJECTIVE: To evaluate the variation in anterior longitudinal ligament pullout strength along the craniocaudal and mediolateral dimensions within the presacral space to inform the optimal location for sacrocolpopexy graft fixation. METHODS: ALL pullout strength was examined in 10 unembalmed female cadavers. The presacral space was dissected to expose the ALL. A two-dimensional grid with 1-cm increments centered upon the midsacral promontory (SP) was superimposed atop the ALL surface, extending 2 cm superiorly (+), 3 cm inferiorly ( −), and 2 cm bilaterally. A high tensile strength, 2-0 multifilament suture with long chain ultra-high weight polyethylene (UHMWPE) core and braided polyester and UHMWPE jacket was selected to avoid suture failure when subjected to the high tensile forces. A 5-mm-wide, full-thickness purchase of the ALL was obtained at each craniocaudal and mediolateral location within the grid. With use of a force gauge, the tensile force required to achieve ligament fracture and resultant suture pullout was determined at each site. Statistical analysis was performed using two-way repeated measures analysis of variance. Within and between-group pairwise comparisons were performed with Bonferroni adjustment for multiple comparisons. RESULTS: Average±SD donor age was 77±5.9 years with body mass index 20.9±3.9 kg/m2. Pullout strength differed significantly in the craniocaudal dimension with a mean force of 55.9±28.1 N at SP +2 cm, 76.0±30.8 N at SP +1 cm, 62.3±36.2 N at SP 0 cm, 41.3±20.9 N at SP −1 cm, 31.9±20.7 N at SP −2 cm, and 33.0±20.8 N at SP −3 cm when including all mediolateral segments (p<0.001, Figure 1A). Relative to the sacral promontory, mean pullout strengths at the SP −2 cm (p=0.003) and SP −3 cm levels (p=0.002) were significantly lower on pairwise comparison. Pullout strength similarly differed across mediolateral segments with a mean force of 61.5±31.6 N in the midline, 51.0±31.6 N and 53.6±30.6 N at 1 cm right and left laterally, respectively, and 41.6±27.5 N and 42.6±30.9 N at 2 cm right and left laterally when including all craniocaudal levels (p<0.001, Figure 1B). Relative to midline, the pullout strengths were significantly lower in the most lateral segments, right +2 cm (p<0.001) and left +2 cm (p=0.002). There was no interaction between craniocaudal level and mediolateral segment on pullout strength (p=0.110, Figure 2). CONCLUSIONS: The tensile strength of the presacral-space anterior longitudinal ligament decreases with progressive caudal and lateral deviation from the midsacral promontory. Knowledge of the biomechanics of the ALL in both the craniocaudal and mediolateral dimensions facilitates efficacious sacrocolpopexy graft attachment and aids in navigating highly variable presacral space anatomy.