Tendinopathy as opposed to  tendinitis or tendinosis is the best term for clinical conditions arising from tendons. Here is an article about what a tendinopathy actually is and how to treat it!

What is a tendon made of:

A tendon attaches a muscle to a bone and transmits force from muscle to bone allowing movement. Tendons are composed of 30% Type I collagen, glycosaminoglycans, elastin, and 68% water. Glycosaminoglycans and water are the primary components of ground substance.

The role of collagen in a tendon is to provide tensile strength to the tendon. The ground substance on the other hand  provides structural support and helps to maintain interfibre distance and prevent adhesions. The tendon is covered by a epitendon, a fine connective tissue sheath that provides the tendon with vascular lymphatic and nerve supply.

Within the extracellular matrix network,  tenocytes and tenoblasts make up 90-95% of the cellular elements of tendon. Tenoblasts are immature tendon cells that when mature turn into tenocytes. Tenocysts synthesis collagen and parts of the extracellular matrix.

In a healthy tendon- the collagen fibres are dense, clearly defined and wavy. This wave-like appearance at rest makes them available to stretch when needed.

Why tendons get injured:

Tendon injuries can be acute or chronic and are caused by intrinsic or extrinsic factors.

Intrinsic  factors such as alignment or biomechanical faults can cause tendon disorders. An example of this is that excessive pronation is believed to increase the prevalence of Achilles tendinopathy. Extrinsic factors like excessive overloading during training may also lead to tendon problems especially in the presence of intrinsic factors (Sharma and Maffuli 2005). Oxygen consumption is seven and a half times lower in tendons compared to muscle. This and a low metabolic rate (which is needed in tendons) may result in slow healing after injury.

Histological examination of tendinopathy shows disordered, haphazard healing with an absence of inflammatory cells, a poor healing response, noninflammatory intratendinous collagen degeneration, fiber disorientation and thinning, hypercellularity, scattered vascular ingrowth, and increased interfibrillar glycosaminoglycans.

In summary, tendinopathy shows features of disordered healing, and inflammation is not typically seen. Therefore NSAIDs and Corticosteriod injections are not appropriate treatments for tendinopathies.  So considering there is no actual inflammatory process in tendinopathy, what is causing the pain?

One theory suggested by Khan et al 2000 is that biochemical irritants released from the injured tendon may aggravate surrounding nocioceptors in tissue other than the tendon leading to pain. Therefore treatment should focus on reducing the specific irritant (perhaps with medication) and not inflammation! Work is still being done to figure out which specific irritant is responsible.

How does Eccentric Exercise help with tendinopathy:

In an eccentric contraction, the muscle tendon unit lengthens as load is applied to it.

Tendons responds to mechanical forces by adapting their metabolism ,structural and mechanical properties. The tenocytes in the tendons are responsible for their adaptive response, and respond to mechanical forces by altering their gene expression patterns, protein synthesis and cell phenotype which can be used to aid the healing process.

The mechanism for the efficacy of eccentric loading is unknown. Stanish and colleagues  proposed that during eccentric loading the tendon is subjected to greater forces than in concentric loading and hence to a greater re-modelling stimulus.

The optimum exercise ‘dose’ for eccentric exercise is also unknown, both in terms of numbers of repetitions and also the speed of movement; neither is the optimum duration of treatment known. The exercises frequently cause discomfort.

In a study by Rees et al, increased force fluctuations, rather than force magnitude, provide a mechanism to explain the therapeutic benefit of eccentric loading in Achilles tendinopathy

Kahn KM et al (2000).Where is the pain coming from in tendinopathy? It may be biochemical, not only structural, in origin. Br J Sports Med. 34:79–85

Kahn KM et al (1998). Patella tendinopathy : some basics of science and clinical management. Br J Sports Med.32:346–355

Lorenz et al (2011). Shoulder Tendinopathy. Physical Therapy Reviews. 16(5): 365-373

 

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