The Actual Tendon-Bone Interface Strength in a Rabbit Model

PurposeThe purpose of this study was to evaluate the strength of the interface throughout the entire integration process by use of tendon graft reinforced with a suture material compared with nonreinforced tendon graft.MethodsUsing 60 skeletally mature female Japanese white rabbits, we performed biomechanical testing and histologic evaluation to compare tendon grafts reinforced with a suture material (suture group) and nonreinforced grafts (control group). The tendon graft was drawn through a bone tunnel measuring 2.5 mm in diameter and was tightly fixed. For biomechanical testing, the tendon graft was tested in tensile loading along the axis of the bone tunnel at a crosshead speed of 100 mm/min.ResultsOn biomechanical testing, at 4, 6, 8, and 12 weeks, tendon grafts had pulled out of the bone tunnel in the suture group. In the control group all tendon grafts had pulled out at 4 and 6 weeks, and rupture at the midsubstance was seen at 8 and 12 weeks. The failure load–to–tunnel length ratio was significantly larger in the suture group compared with the control group at 8 and 12 weeks. On histologic evaluation, both groups had similar findings with direct attachments to bone by 12 weeks.ConclusionsIn this study of the healing characteristics of augmented and nonaugmented tendon grafts placed in a bone tunnel, we found that the suture-augmented tendons had superior failure load–to–tunnel length ratios at 8, 12, and 16 weeks compared with nonaugmented tendons. The failure mode in the augmented grafts was tendon pullout at all time points except 16 weeks, whereas the nonaugmented grafts failed by midsubstance rupture after 8 weeks. Histologically, both groups had similar findings with direct attachments to bone by 12 weeks.Clinical RelevanceThe tendon graft has the potential to be pulled out of the bone tunnel after complete integration.