Fibril Morphology And Tendon Mechanical Properties In Patellar Tendinopathy - Effects Of Heavy Slow Resistance Training.

Abstract

Patellar tendinopathy (PT) is a prevalent and disabling overload injury that is associated with cellular and extracellular matrix changes. However, how the specific structural and functional properties of the tensile bearing components of tendons are affected by tendinopathy remain elusive. We recently showed that heavy slow resistance training (HSR) is effective in the management of PT, but the underlying mechanisms remain to be established. PURPOSE: To investigate the effect of HSR on patellar tendon fibril morphology and whole tendon mechanical properties in persons with PT. METHODS: Eight male PT patients completed 12 wks of HSR. Healthy patellar tendons from nine matched subjects served as controls. Subjects were examined at 0 and 12 wks. PT patients assessed symptoms and function (VISA-p questionnaire) and indicated maximal tendon pain during activity (VAS). Patellar tendon biopsies were obtained and subsequently analyzed for fibril density, volume-fraction and fibril mean-area using stereological techniques of digitized electron microscopy biopsy cross-sections. Patellar tendon mechanical properties were assessed using simultaneous force and ultrasonography samplings. RESULTS: PT patients improved both in VISA-p (wk 0: 57+3, wk 12: 72+7), and VAS (wk 0: 59+6, wk 12: 23+5), p<0.05. There were no differences in tendon mechanical properties between control and tendinopathy tendons at baseline. Tendon mechanical properties (stiffness and modulus) remained unaffected in control tendons, but declined in tendinopathy tendons with HRS (-9+6 & and -13+8%, p<0.05). At baseline, fibril volume fraction was equal, the fibril density smaller (p<0.05) and the fibril mean-area tended to be higher (p=0.07) in tendinopathy compared to control tendons. Fibril morphology parameters remained unchanged in control tendons but fibril density increased (70+18%, p<0.01) and fibril mean-area decreased (-26+21%, p<0.05) in tendinopathy tendons following HSR. CONCLUSION: Whole tendon mechanical properties are unaffected by tendinopathy but fibril morphology differ in healthy vs. tendinopathy tendons. Clinical improvements in PT following HSR were associated with changes in fibril morphology possibly related to increased turnover of the collagen matrix.