Muscle ‘tendon’ pain is a common issue in sports as well as in the general population. Tendon disorders are even seen in physically inactive individuals. Thus, physical activity is not always directly associated with histopathology but may provoke the symptoms than being the only cause of the tendon injury or tendinopathy. However, repetitive overuse of the muscle has been described as the major cause of tendon injury or tendinopathy resulting in pain, decreased functional abilities and exercise tolerance.
Until, recently, the term ‘tendinitis’ was widely used for chronic pain in the tendon. However, recent histologic studies have shown that there are no signs of prostaglandin inflammation and, as a result the term “tendinopathy” is now used to describe a painful tendon. With the new terminology, it is also supported by the new studies that tendinopathy is more related to loading and overuse, and that the affected tendon has a disorganized collagen structure, abnormal tenocytes, and an increased in ground substance.
In the past tendon pathology has been described as inflammatory, degenerative and failed healing or angiofibroblastic hyperplasia condition. Recently, to reflect the heterogenic nature of history, mechanism of injury, the timeline of symptoms, and nature of signs and symptoms of tendon pain; a “continuum model of tendinopathy” has been proposed. While this model has not been scientifically validated, it has been widely accepted as it can help the clinicians decide how to treat an athlete/individual presenting different nature of tendon pain.
A continuum model of tendinopathy
- Reactive tendinopathy
- It is a non-inflammatory proliferative response in the cell and matrix, occurs with acute tensile or compression overload. This results in a short term adaptive and relatively homogenous thickening of a portion of the tendon and causing pain in the tendon. This differs from normal tendon adaptation to tensile load, which generally occurs through tendon stiffening with little changes in thickness. Imaging studies at this stage show mild fusiform swelling. A period of relative rest and analgesia is the treatment recommendation for this stage.
- Tendon dysrepair
- At this stage, tendon continues to try to healing but with greater matrix breakdown. There is a marked increase in proteoglycan and collagen production resulting in the separation of the collagen and disorganization of the matrix. Ultrasound may show some hypoechoic areas or neovascularity within the tendon. The symptoms are now likely to have been present for longer.
- Degenerative tendinopathy
- This stage generally develops after the signs and symptoms have been present for a prolonged period. Areas of acellularity, larger areas of disorganized matrix and collagen have been described at this stage. There is little capacity for the reversibility of pathological changes at this stage. It is more common in older and recreational athletes. Tendon changes, including neovascularity and hypoechoic regions, are common during this stage. These patients are likely best treated with aggressive eccentric strengthening exercises.
The mechanism of tendon injuries is mostly related to the type of force that is exerted on the tendon. The repetitive force of compression, friction, traction or other repetitive stimuli of low intensity is the major cause of tendon injury or tendinopathy. The classic complaint includes an insidious onset of well-localized pain and mild swelling. The pain typically starts with activities or exercises, which feels okay during activity, then aches again following activity. As time goes on pain persists during and after exercises or activities. Morning pain and stiffness which warms up over a few minutes is one of the common patient complaints. Intrinsic factors like biomechanical disorders (eg. Hyper pronation of foot, lateral tibial torsion, pes cavus, etc), overweight and extrinsic factors like poor training, rapid progression of exercises/activities are an important factor to consider during history taking. Moreover, the possibility of tendon rupture must be considered if sudden acute popping/snapping sensation followed by a major bruising, swelling or disability is reported during the history taking.
Common findings during examination are but not limited to;
- Tenderness on palpation of the tendon
- More localized area of pain in tendon during load-bearing activity
- Loss of muscle volume and strength caused by reflex inhibition
- Biomechanical disorders like hyper pronation of foot, lateral tibial torsion, pes cavus, tibial varus, poor posture, etc.
Physical therapy can help
At the early stage of tendon pain (reactive tendinopathy/early tendon disrepair), reduced load or proper load management is likely to help reduce pain. Thus, relative rest with proper use of analgesia may be the major clinical intervention. Identifying the proper intensity, duration, frequency, and type of activities or exercising load is the major challenge for maintaining muscle strength while controlling the pain and enhancing the tendon healing. Similarly, identifying and implementing the corrective exercises to correct potential biomechanical issues is the key clinical intervention at this stage. Regular isometric exercises have been shown to help reducing pain by some studies and may be helpful to maintain muscle strength particularly in those with severe pain. Heavyweight strength training or eccentric loading with little recovery time may have an adverse effect on tendons at this stage.
At the later stage of tendon pain (late tendon disrepair/degenerative tendinopathy), strength training, particularly eccentric exercise (https://www.youtube.com/watch?time_continue=86&v=PAMjaEyxWMk&feature=emb_logo) has shown to affect both tendon structure and pain. Many studies have advocated the use of eccentric exercise to alleviate pain, improve functional abilities and return to sports/activity. However, clinicians may need to explain to the patients that eccentric exercises may be painful to begin with, which is normal, and that they must be compliant with the exercise protocol for lengthy period of time. The patient may need to do large numbers of exercises/repetitions every day which may be different in every patient’s condition.
Other treatments that are widely used in tendinopathy are cryotherapy, heat therapy, manual therapy (deep transverse massage, soft tissue mobilizations, etc), extracorporeal shock waves, hydrokinesiotherapy, laser treatments, etc.