Equine tendon injuries: cellular structure and healing with LIPUS

01 July 2014, at 1:00am

Dr Helen Floyd managing director of Curar Ltd, discusses equine tendon injuries with comments by Ricky Farr of Wendover Heights Equine Veterinary Practice on a gelding treated using low intensity pulsed ultrasound.

TENDON injuries need little introduction and are a common feature of the busy equine vet’s diary.

Tendons begin to form in the embryo from stem cells. As they develop, they produce extracellular matrix proteins, giving the tendon both elasticity and the tensile strength required to connect muscle to bone and provide both the storing of energy required to operate limbs and resistance to strain.

Histologically, a healthy tendon is composed of parallel arrays of Type I collagen, with small amounts of other collagens, elastin, proteoglycans and glycosaminoglycans contributing to the overall structure.

The collagen molecules aggregate to produce collagen fibrils bundles which then form fibres, with tendiocytes packed between them. The proteoglycans are interwoven with the collagen fibrils and interact with the surface of the collagen fibrils via glycosaminoglycan side chains, e.g. dermatan sulphate and chondroitin sulphate demonstrating that proteoglycans play an important structural role.

Injury triggers a number of events that recruit cells and stimulate the tenocyte population to synthesise collagen and proteoglycans. Appropriate stimuli such as mechanical stress and strain encourage synthesis and remodelling of the collagen fibres.

Injury to tendons sees both elasticity and strength impaired after healing because the collagen fibres are re- formed haphazardly and often do not regain the “ideal” architecture. 

Poor vascular supply to tendons is a significant factor in the speed of healing and the tendency for scar tissue to form.

Before reviewing treatment options it is worth brie y covering the classic symptoms, noting that problems often lie in gradual tendonitis going unnoticed, when early action could prevent further deterioration: 

  • Heat and swelling
  • Lameness – although some horses will remain sound 
  • Pain under palpation
  • Swollen tendon sheath Ultrasound scanning after initial diagnosis will reveal the extent of tendon damage and fibre disruption.

Depending on the extent of the injury, initial treatment options (largely irrespective of which tendon is injured) will address reduction of inflammation by means of cold treatment, combined with NSAIDs. 

Rehabilitation regime 

Once the inflammation is stabilised, a rehabilitation regime needs to be decided upon, beginning with box rest and hand walking which increases by a few minutes each week. Again a balance is required between the owner’s desire for progress and risk of re-injury. A schedule of ultrasound scans is essential. 

Beyond a controlled schedule of rest and exercise, there are numerous other treatments that are used with varying degrees of success. A recent development which takes advantage of the natural response to mechanical stress in promoting the remodelling of the collagen fibres is low intensity pulsed ultrasound (LIPUS). 

LIPUS is non-invasive and the horse feels no sensation during the 20-minute daily treatments. LIPUS signals travel through skin into soft tissue to stimulate a clear biological response at the cellular level. It shortens the inflammatory period, enhances vascularisation, promotes collagen synthesis and remodelling and overall promotes quality repair. 

LIPUS signals cause cell surface molecules called integrins to change protein conformation and cluster at the cell membrane, which initiates intracellular signal transduction. This in turn up-regulates protein expression, releasing factors that play a key role in tendon repair including IGF-1, PGE2, COX-2, VEGF, PDGF, bFGF, TGFβ and BMP-12.