The influence of tendon length and fit on the strength of a tendon-bone tunnel complex - A biomechanical and histologic study in the dog

Using a dog model, we examined the influence of tendon length and fit withi n a bone tunnel on the pullout strength of a tendon-bone tunnel complex at 6 weeks after fixation. Fourteen adult mongrel dogs (weight, 25 to 30 kg) u nderwent bilateral hindlimb surgery in which the extensor digitorum longus tendon was transplanted into an extraarticular metaphyseal bone tunnel. Our findings demonstrated that pull-out strength at 6 weeks was enhanced by in creasing the length of tendon within the tunnel. The average load to failur e with 1 cm of tendon within the tunnel was 153.7 +/- 78.6 N, compared with 265.5 +/- 93.3 N for the specimens with 2 cm of tendon in the tunnel. Tend on fit within the tunnel was also found to be important. The average load t o failure when a tendon was placed in a 4.2-mm diameter tunnel was 301 +/- 61 N at 6 weeks. The average load to failure when the tendon was placed wit hin a 6-mm diameter tunnel was 228 +/- 65 N. These differences were statist ically different. Histologically, the interface between the tendon and bone appeared to be most mature when there was intimate bone-to-tendon contact. These data suggest that maximizing tendon length within a bone tunnel and minimizing tendon-tunnel diameter mismatch will maximize the strength of a tendon-bone tunnel complex at 6 weeks.