Incorporating BMP-2 and skeletal muscle to a semitendinosus autograft in an oversized tunnel yields robust bone tunnel ossification in rabbits: Toward single-step revision of failed anterior cruciate ligament reconstruction

Abstract

BackgroundBone tunnel widening after anterior cruciate ligament (ACL) reconstruction is a known complication that can lead to graft failure. Subsequent revision surgery typically involves a two-stage procedure. The aim of this study was to test a novel autologous tendon graft retaining muscle tissue combined with Human Recombinant Bone Morphogenetic Protein-2 (rh-BMP-2) leading to rapid ossification of the muscle tissue, simultaneously replenishing bone stock and producing a mechanically stable bone–tendon insertion. MethodsIn 12 skeletally mature New Zealand rabbits, the ACL was resected and oversized bone tunnels were drilled to model tunnel widening. The ipsilateral semitendinosus muscle–tendon graft was harvested and folded twice. Muscle tissue was removed in the middle third but retained at both distal ends. One side was wrapped in a collagen sponge loaded with rh-BMP-2 while the other end was used as its own control. ResultsAll animals were euthanized after six weeks. Micro-computed tomography (micro-CT) was used to analyze bone formation in 12 animals, with additional biomechanical testing to failure and histology performed for six animals each. Micro-CT showed that bone densities were higher by a factor of 2.4 in treated graft ends compared with their controls. Biomechanical testing showed a mean overall failure load of 37.5 N. Histology showed that the trabecular bone surrounding the implant was significantly (P = 0.0087) thicker on the treated (85.5 μm) compared with the control side (68.2 μm). ConclusionsWe conclude that a semitendinosus graft retaining the muscle tissue stimulated by recombinant Bone Morphogenetic Protein-2 (BMP-2) allows robust osseointegration of the graft within an oversized bone tunnel in an animal model.