The Effect of Mechanical Load on Tendon-to-Bone Healing in a Rat Model

Background:Joint motion is commonly prescribed after tendon repair surgeries such as rotator cuff repairs; however, the ideal rehabilitation program to optimize tendon-to-bone healing is unknown.Hypotheses:(1) Delayed loading would result in a mechanically stronger and better organized tendon-to-bone interface compared with prolonged immobilization or immediate loading. (2) Low-magnitude load would lead to superior healing compared with high-magnitude load.Study Design:Controlled laboratory study.Methods:A total of 192 rats underwent unilateral patellar tendon detachment and repair followed by placement of a custom external fixator. Rats were assigned to immobilization, immediate postoperative loading, or delayed-onset loading (4- or 10-day delay). Loading was controlled using a specially designed motorized device to apply constant strain until 3 N (low load) or 6 N (high load) of axial tensile force was reached through the healing bone-tendon complex for 50 cycles per day. Rats were sacrificed at 4, 10, ...