Razi Journal of Medical Sciences

    Background & Aim: Many factors influence the tensile strength of the tendon in a tendon-bone tunnel complex. The purpose of this study is to determine the influence of tendon length & time of implantation of the tendon in the bone tunnel on the tensile strength of the tendon in a rabbit model. Material and Methods: In this prospective study fourteen adult(age 6 months) White New Zealand rabbits(weight: 2.5-3 kg) underwent bilateral hindlimb(n=24) surgery in which the Extensor digitorum longus tendon was implanted into the tibial metaphyseal extra-articular bone tunnel. Based on the length of bone tunnel(1 or 2 cm) and duration of implantation(6 or 12 wks), the rabbits were divided into 4 groups. Seven rabbits were sacrificed after 6 weeks(groups 1 and 2) and 7 others were sacrificed after 12 weeks(groups 3 and 4) for tendon tensile loading test to determine ulitimate pull-out strenght. Results: In group one(1 cm, 6wks) one tendon was ruptured and four were pulled out, in group two(2 cm, 6 wks) one tendon ruptured and six pulled-out, in group three(1cm, 12wks) one tendon was pulled out and five ruptured and in group four(2 cm, 12 wks) five tendons ruptured and one was pulled-out. The mean failure force after 6 wks. was 4.98N for group one and 9.37N for group two. After 12 wks. it was 6.36N for group three and 10.81N for group four. Failure force difference was significant between 1 and 2 cm tendon lengths after 12 wks. Tendon rupture site was significantly different after 6 & 12 wks. Conclusion: This study demonstrated that the tendon length within a bone tunnel influences tendon tensile strength after 12 weeks. In other words, increase in tendon length within the bone tunnel, increases its' resistance against tensile strenght with the passage of time. Time of implantation has an additive effect to tendon length on the tendon tensile strength of the tendon-bone tunnel complex.