Changes in Cross-Sectional Area of Hamstring Anterior Cruciate Ligament Grafts as a Function of Time Following Transplantation

Purpose: To measure the cross-sectional area (CSA) of hamstring anterior cruciate ligament (ACL) grafts in humans up to 2 years postoperatively and to estimate the appropriate graft-notch distance (the distance between ACL graft and roof or wall of the notch) at surgery. Type of Study: Case series. Methods: Fifty-nine patients, who had consented to have a magnetic resonance imaging (MRI) evaluation postoperatively, underwent endoscopic ACL reconstruction using 3- to 5-strand autogenous hamstring tendons. Intraoperatively, the CSA of the graft was measured using a custom-made area micrometer. Postoperatively, 115 axial MRIs of the grafts (48 at 3 months, 44 at 12 months, and 23 at 24 months) were obtained. They were transmitted to a personal computer and the CSAs of the grafts' midsubstance were calculated. To evaluate the accuracy of the MRI measurement, another 15 patients who consented to have MRI 2 days after surgery were selected and intraoperative graft CSA measurements and graft axial MRI were performed 2 days after surgery. Results: The CSAs of the grafts measured by MRI 2 days after surgery were well correlated with those directly measured intraoperatively (γ = 0.905). The CSA of the grafts measured intraoperatively was 43 ± 5 mm2, and those estimated by MRI at 3, 12, and 24 months were 50 ± 9 mm2, 54 ± 9 mm2, and 48 ± 12 mm2, respectively. The increase in graft diameter at 3, 12, and 24 months was 9% ± 8%, 13% ± 10%, and 7% ± 12%, respectively. Conclusions: In humans, the increase in CSA of the ACL graft was smaller compared with previous animal studies. The graft CSA increased up to 29% (13% in diameter) 12 months after surgery. When a 95% confidence interval was used, the percent increase in diameter of the reconstructed graft was estimated to be less than 32% in 95% of the cases. When the graft diameter was 7, 8, or 9 mm, a 1.1-, 1.3-, or 1.4-mm graft-notch distance, respectively, was suitable for impingement-free graft during postoperative periods with 95% of probability. Level of Evidence: Level IIII.