Tendon pathology and biomechanical properties in an equine model — The Association Specialists
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Tendon pathology and biomechanical properties in an equine model (305)

Rachel Choi 1 2 , Joshua Martin 1 2 , Else Jacobsen 3 , Margaret Smith 1 2 , Jill Clarke 4 , Andrew J Dart 3 , Christopher B Little 1 2 , Elizabeth Clarke 1 2
  1. Bone & Joint Research Group, Kolling Institute, RNS Hospital, St Leonards
  2. Sydney Medical School, University of Sydney, Camperdown
  3. Camden Vet Hospital, University of Sydney, Camden
  4. Faculty of Health Sciences, University of Sydney, Lidcombe

Objectives:  Tendon injury can lead to progressive degeneration, which in turn can compromise repair and reduce functionality. Six weeks after a superficial digital flexor tendon (SDFT) mid-body hemi-transection in horses, we previously found widespread histopathology and proteoglycan deposition. These changes were seen on the underloaded (cut) and overloaded sides of the tendon and up to 15cm proximal and distal to the injury. The present study aimed to show how these pathological changes relate to the tissue’s regional biomechanical properties.

Methods:   Transected and control (n=6) SDFT were divided into 12 regions (medial/lateral halves; 3 x proximal and distal).  Samples were dissected longitudinally (~1-3 mm2) and cross-sectional area measured using high frequency ultrasound. Specimens were loaded in tension (1%/s using an Instron 8874 machine) and failure force measured using a 250N load cell. Force data was normalised by cross-sectional area (stress) and tendon elongation normalised by initial length (strain). The modulus (stiffness) was calculated as the slope of the normalised force-elongation curve at 4% strain. The effect of surgery and proximity to transection on failure stress and modulus were analysed in mixed models with and without proteoglycan score or histopathology score as predictors.

Results: Transected SDFT had lower modulus (p<0.05) and failure stress (p<0.01) than the controls. However, the reduction in modulus was driven by the intact/overstressed half of the transected tendon (p<0.02), rather than the unloaded side  (p=0.53). Other locational variables (proximal/distal; distance from lesion) did not significantly affect properties. Although not significantly correlated, proteoglycan score, but not histopathology score, could substitute for surgery in the mixed model for modulus changes (p = 0.04).

Conclusions:  This data suggests that changes in the material properties of equine tendon “weakened” by altered loading through injury, may be primarily associated with increased proteoglycan content of the tissue.