Use of a new model allowing controlled uniaxial loading to evaluate tendon healing in a bone tunnel.

The optimal mechanical loading regimen for the healing of a tendon graft in a bone tunnel is unknown. We developed a rat model that directly tensions a healing tendon graft, without the use of confounding joint motion. Fifty cycles of either 0, 3, or 6N of tension were applied to groups daily for 3 or 6 weeks. At 3 weeks the low load (3N) group had the highest failure load (p=0.009), but by 6 weeks there were no differences in failure load among groups. At 3 weeks the high load (6N) group had greater osteoclast activity compared to the immobilized (0N) group (p<0.05), and by 6 weeks there were significantly more osteoclasts in the high load group compared to the low load group (p=0.01). Bone volume fraction was higher in the immobilized group compared to the 3N load group at 3 weeks (p=0.014) and 6 weeks (p=0.007). At 6 weeks, the immobilized group had greater trabecular number compared to both loading groups (p<0.05). In conclusion, low magnitude loading had a beneficial early effect but continued loading led to poorer new bone formation over time and no beneficial effect at 6 weeks, perhaps due to delayed maturation from cumulative loads. (c) 2015 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 34:852-859, 2016.