Quantitative characterization of rat tendinitis to evaluate the efficacy of therapeutic interventions

Tendinitis is a painful soft tissue pathology that accounts for almost half of all occupational injuries in the United States. It is often caused by repeated movements and may result in loss of work and income. Current treatments for tendinitis are aimed at reducing inflammation, the major cause of the pain. Although anti-inflammatory drugs and various alternative therapies are capable of improving tendinitis, there are no quantitative scientific data available regarding their impact on inflammation. The objective of this study is to determine the time course for healing of rat tendinitis without intervention to be able to assess the efficacy of tendinitis treatments. We are interested in evaluating the therapeutic use of pulsed electromagnetic fields (PEMFs), a therapeutic modality that has been found to be beneficial for healing soft tissue injuries. Tendinitis was induced in Harlan Sprague Dawley rats by collagenase injections into the Achilles tendon, and tendons were collected for four weeks post-injury. To determine the amount of edema, we used caliper measurements of the rat ankles and quantified the tendon water content. To determine the extent of inflammation, we estimated the number of inflammatory cells on histological sections applying stereological methods. The data reveal that edema is maximal 24 hours after injury accompanied by a massive infiltration of inflammatory cells. Inflammatory cells are then gradually replaced by fibroblasts, which are responsible for correcting damage to the extracellular matrix. This natural time course of tendon healing will be used to evaluate the use of PEMFs as a possible therapeutic modality.