Alterations in articular cartilage T2 star relaxation time following mechanical disorders: in vivo canine supraspinatus tendon resection models

Abstract

<jats:title>Abstract</jats:title> <jats:p><jats:bold> </jats:bold><jats:bold>Background: </jats:bold>The role of altered joint mechanics on cartilage degeneration in <jats:italic>in vivo</jats:italic> models has not been studied successfully due to a lack of pre-injury information. We aimed 1) to develop an accurate <jats:italic>in vivo</jats:italic> canine model to measure the changes in joint loading and T2 star (T2*) relaxation time before and after unilateral supraspinatus tendon resections, and 2) to find the relationship between regional variations in articular cartilage loading patterns and T2* relaxation time distributions.<jats:bold>Methods: </jats:bold>Rigid markers were implanted in the scapula and humerus of tested dogs. The movement of the shoulder bones were measured by a motion tracking system during normal gaits. <jats:italic>In vivo</jats:italic> cartilage contact strain was measured by aligning 3D shoulder models with the motion tracking data. Articular cartilage T2* relaxation times were measured by quantitative MRI scans. Articular cartilage contact strain and T2* relaxation time were compared in the shoulders before and three months after the supraspinatus tendon resections.<jats:bold>Results: </jats:bold>Excellent accuracy and reproducibility were found in our <jats:italic>in vivo</jats:italic> contact strain measurements with less than 1% errors. Changes in articular cartilage contact strain exhibited similar patterns with the changes in the T2* relaxation time after resection surgeries. Regional changes in the articular cartilage T2* relaxation time exhibited positive correlations with regional contact strain variations three months after the supraspinatus resection surgeries.<jats:bold>Conclusion: </jats:bold>This is the first study to measure <jats:italic>in vivo</jats:italic> articular cartilage contact strains with high accuracy and reproducibility. Positive correlations between contact strain and T2* relaxation time suggest that the articular cartilage extracellular matrix may responds to mechanical changes in local areas.</jats:p>