Molecular mediators of tendon remodeling and repair: Histological and molecular analysis of the biceps tendon long head post-tenotomy

Date of Completion

January 2008


Health Sciences, Recreation




Introduction. Load induced tendon degeneration (tendinopathy) results from insufficient growth factor mediated matrix deposition and overexpression of matrix degrading metalloproteinases (MMPs). Morphologic alterations of tendinopathic matrix include disorganization of collagen, increased type III collagen and proteoglycan. While extensively studied in the rotator cuff, Achilles and patellar tendons, no study to date has examined the histological and molecular characteristics of the tendinopathic biceps long-head (LHB). The anatomy of the LHB is unique in that it comprises intra- and extra-articular portions, each exposed to differing loading patterns. ^ Purpose. The purpose of this study was to histologically and molecularly examine the intra- and extra-articular portions of the LHB. We hypothesized the intra-articular portion of the tendon would exhibit tendinopathic characteristics while the extra-articular portion would resemble healthy tendon. ^ Methods. Histological analyses: Eleven LHB post-tenotomy were sectioned, fixed in formalin, and stained (H&E; Alcian blue), and gross structural organization of collagen measured using polarized light microscopy. Protein Analyses: Protein expression of intra- and extra-articular portions of the tenotomized biceps for IGF-I, Collagen III and MMP-1,2,3 and 13 was determined with Western blot analyses. ^ Results. The intra-articular LHB exhibited significantly greater histological evidence of tendinopathy inclusive of increased proteoglycan (P < 0.05) and decreased organization as measured by polarized light microscopy (P < 0.01). The intra-articular LHB also had significantly increased expression of collagen type III (P < 0.01) and of MMP-1 and 3 (P < 0.01, P < 0.05 respectively). No significant differences were found for IGF-I or for MMP-2 and 13. ^ Discussion. The intra-articular LHB exhibits histological characteristics of tendinopathy. Protein expression of the intra-articular LHB did not universally display signs of tendinopathy in comparison to the extra-articular portion of the tendon. ^