Analysis of Regional Strain Patterns Following Surgical Disruption of the Enthesis in a Murine Model of Patellar Tendon Injury

Tendon injuries are common yet often fail to heal naturally, especially in cases in which the native tendon-to-bone insertion site is disrupted. Surgical tendon repairs are often limited by the inability of the ruptured tendon to functionally attach back to the underlying bone. For patients with tendon injuries, poor tendon-to-bone integration prolongs recovery time and increases the risk of re-rupture. Improvements in tendon repair will require a more complete understanding of both the biological and mechanical phenomena that occur during natural tendon-to-bone healing. Mechanical studies of tendon repair often utilize larger animal models such as rabbits or canines, but these animals lack many of the genetic and biological tools that are available in the mouse. Thus, the objective of this study was to analyze the biomechanical outcomes of natural tendon-to-bone healing following surgical disruption of the enthesis in a murine model of patellar tendon injury. In particular, this study attempted to define the regional (insertion site versus midsubstance) strain patterns present in normal tendon and compare these patterns to those seen at various stages of healing following a central-third patellar tendon avulsion injury. We hypothesized that 1) murine patellar tendon avulsions would exhibit inferior structural properties compared to contralateral shams and normal controls and 2) insertional strains would greatly exceed midsubstance strains in the healing tendons, resulting in failure initiation at the tendon-bone junction.