Tendons fail for internal and external reasons. Intrinsically the tendon is a strong fibrillar rope of collagen joining muscle to bone. Tendons fail when the rate of damage outstrips the rate of repair. This can develop slowly due to repetitive microtrauma cumulative or due to a catastrophic event.

Points of weakness occur where the tissues morphs from one type to another i.e. at the tendon/bone interface with failure manifesting as avulsion injuries, origin/insertional tears and enthesopathy. They are also vulnerable where the tendon muscle/interface manifesting as musculotendinous junction (MTJ) tears.

Intrinsically tendons are very strong but with ageing they become weaker and catastrophic injuries which in the younger age group usually result in avulsion of the tendon from the bone now result in mid tendon rupture.

The commonest external factor is chronic tendon overuse. In the Australian population this occurs in recreational sportsmen whose tendons are ageing faster than their desire to compete. But it also occurs due to workplace demands and activities of daily living. for example "tennis elbow" results from excess loads to the common extensor tendon from activities such as a carpenter hammering or a cook chopping.

Internal factors contributing to tendon damage occur when they;
1. Pivot around a bony fulcrum e.g. the lateral malleolus.
2. Go around a bend e.g. the insertion of the long head of biceps femoris
2. Pass under another structure e.g. Compartment one passing beneath the retinaculum at the level of the radial styloid process ( De Querverains)
3. Cross over another tendon e.g. EPL over wrist extensors leading to mini intersection syndrome
4. The usual mechanical restraints have failed allowing abnormal movement of the tendon e.g. peroneal tendon dislocation secondary to rupture of the extensor retinaculum.
5. Have to pass through passageways narrowed by bone spurs.

Therefore the discovery of "tendinopathy" should trigger the search for internal triggers which will allow a specific therapeutic approach or alternatively indicate when lifestyle changes to reduce external cumulative microtrauma are needed .