Objectives: Advances in biomedical engineering have led to a thorough understanding of the body’s own capacity for ACL healing if provided the correct impetus—a long-term bioresorbable graft scaffold that anticipates the defect site’s biological and mechanical requirements. We hypothesize that by providing a structural scaffold which anticipates ACL repair mechanisms, “engineered” autologous ligament with excellent functional integrity can be developed by the body itself. This study evaluated the SeriACL™ graft, a non-mammalian derived long-term bioresorbable multi-bundled silk-based implant, for ACL replacement in a goat model at 3, 6 and 12 months post-operatively.
Methods: The ACL of 43 goats was replaced with the SeriACL graft in an arthroscopically assisted procedure. The ACL was excised, a guide pin driven into the femur and 6mm diameter antegrade drilling performed. The tibial tunnel was drilled under direct visualization. The SeriACL, designed to mimic hamstring grafts, was anchored around a post on the femur. The graft was tensioned to 50N and cycled 30x before tibial fixation with a staple and sutures around a post. Animals were clinically, mechanically and histomorphometrically evaluated at 3, 6 and 12 months.
Results: The SeriACL graft or surgical procedure did not induce early signs of acute inflammation, swelling or initial scar formation as indicated by rapidly declining scores for pain and knee size. All animals were weight bearing at 3, 6 and 12 months, with 95% returning to normal gait by 6 months. Lachmann showed the majority of knees were clinically stable at all points. Range of motion assessment indicated the knees maintained a normal range flexion and extension at all points. No gross cartilaginous damage, synovitis or particulate debris in lymph nodes was observed at any time point. Organized collagen and aligned fibroblasts in a crimp pattern were observed in the periphery of the ligament structure, adjacent to and attached to the remaining SeriACL device at all necropsy times. Collagen development throughout the graft and bone tunnels increased with time. Conversely, inflammation and device mass loss decreased with time. Fluoroscopy indicated no abnormal bone tunnel findings. Total plasma IgG levels did not increase from pre-surgery levels at any time. AP laxity indicated joint stability at all time points. Implant abrasion was observed to varying extents yet mechanical testing revealed tissue development supported increased load bearing over time.
Conclusions: Results clearly demonstrate the potential of a scaffold-first strategy in engineering viable autologous ACL tissue that may serve over the patient’s life time. The SeriACL graft supported autologous development of a mechanically robust, biologically viable ligament which stabilized the joint over a 12 mo period. Mechanical, clinical and histological results indicated the safety of the SeriACL with initial indications of efficacy. Thus, the implant may offer the potential of an ACL replacement graft without the deleterious side-effects associated with donor-site morbidity and allogenic and xenogenic grafts.
