Tennis elbow, the biomechanics

Tennis elbow (lateral epicondylitis) is a condition caused by damage to the tendons of the forearm due to repetitive strain and mechanical overload over time.

A particular tendon, the extensor carpi radialis brevis (ECRB), is implicated in the condition due to its function in stabilising the wrist during the motions of lifting and gripping.¹ When this tendon is overused, it can lead to microtrauma, which affects the matrix of collagen in the tendon.² In other parts of the body, this usually triggers the usual inflammatory response; however, in Tennis Elbow, a gradual degradation of the structure of the tendon is observed. Therefore, without appropriate recovery time, degenerative changes are accelerated, leading to chronic pain and dysfunction.

Individuals who are predisposed to the condition appear to have improper biomechanics in wrist angle during motions that are repeated, such as playing racquet sports.² Manual labour and other activities that require repetitive eccentric loading on the wrist and forearm play a critical role in triggering tendinopathic changes.³ Additionally, excessive stress applied to the grip and wrist extension causes an uneven load distribution along the forearm muscles, which aggravates tissues.

While a traumatic event on the wrist and arm can trigger the onset of symptoms, repetitive microtrauma from overuse remains the primary cause of the condition.⁴ It is important, therefore, that in order to mitigate the risks of developing tennis elbow, strengthening exercises as well as ergonomic adjustments to the movement patterns of the wrist and forearm should be implemented.

Risk factors: occupation and recreation

The repetitive gripping, wrist and forearm load means that tennis elbow is not a condition that affects only tennis players; it is also prevalent among individuals who have occupations that involve continuous strain on the tendons involved.

Any profession that demands continuous forearm and wrist exertion, such as plumbing, carpentry and painting, can lead to progressive tendon degradation. A systematic review of workplace-related muscular conditions found that tennis elbow is a leading cause of work disability, with a higher incidence among people performing heavy and repetitive manual jobs.⁵ Furthermore, microtears in the tendons are exacerbated when using vibrating tools, such as drills, which transmit mechanical energy into the tissues, causing damage.⁶

It is not only work related to movements, but also recreational activities that involve a repetition in eccentric loading of the wrist that can trigger the condition, such as:

• Weightlifting
• Rock climbing
• Gardening

In tennis players, the improper racquet grip size and tension on the strings change the biomechanical forces on the forearm, causing an increasing strain on the ECRB tendon, which is heightened by prolonged and intense training.⁷ Other factors, such as improper stroke technique, contribute to the strain on the muscles in question.⁸

Therefore, strategies to prevent the occurrence of the condition in both occupational and recreational settings should focus on proper grip techniques, as well as incorporating sufficient rest periods between significantly straining activities. But in order to understand how to prevent the development of the condition, it's important to understand the role cellular changes play in the degradation of the tendon.

Tendon degeneration and cellular changes

Unlike acute inflammatory conditions, tennis elbow is a degeneration of collagen and tendon matrix. This is known as tendinosis, primarily involving the formation of new blood vessels (neovascularisation) and cell death within the tissues of the tendon. A chronic and repetitively loaded tendon that fails to heal has an abnormal build-up of dysfunctional connective tissues.

In classic inflammation, affected tissues retain fluid due to increased vascular permeability, which aids in recovery. In tennis elbow, however, there are no external signs of inflammation. Rather, the affected tendons exhibit degeneration of structural proteins (collagen fibrils), leading to a weakening in anatomical integrity.⁹

This process is known as angiofibroblastic hyperplasia, where there is an accumulation of disorganised scar tissue with abnormal vascular infiltration that eventually leads to a failure to maintain a normally functional tendon. And as such, MRI studies have identified that over time and without intervention, affected individuals will experience a degeneration of the tendon.¹⁰

Certain enzymes known as matrix metalloproteinases (MMPs)  are responsible for maintaining tissue health and seem to be implicated. An imbalance of the activity of these enzymes contributes to the excessive breakdown of collagen and the inability to repair the affected tendon.

In order to effectively manage the condition and prevent further progression, it is also important to understand the role of age, genetics and other systemic conditions on the likelihood of developing the condition. 

The role of age, genetics, and systemic factors

While repetitive load is the main cause of tennis elbow, other factors such as age, genetic predisposition, and systemic conditions also contribute to the development of the condition.

Ageing is associated with diminished tendon elasticity, a reduction in collagen, and a general reduction in the tissue’s ability to regenerate itself after injury. This makes older individuals more susceptible to injuries that arise from overuse of joints and tendons.

Epidemiological studies have shown that tennis elbow is most prevalent among individuals aged 35-55, which is a time when tendon resilience begins to diminish, and an individual is more susceptible to injury.¹¹

Genetic links have been found to contribute to an individual's likelihood of developing the condition. Genes that are responsible for the synthesis of collagen, such as the COL5A1 gene, have been found to increase the risk of tendon dysfunction, which suggests that a predisposition to tendon injury can be inherited.¹¹

Furthermore, systemic conditions such as obesity, diabetes and dyslipidemia (an abnormally high level of lipids in the blood), have been linked to a failure to heal injured tendons in affected individuals, which renders them more susceptible to overuse injuries.

Similarly, smoking impacts vascularisation of tendons and the synthesis of collagen, causing an increased risk of developing the condition.¹²

These lifestyle and genetic risk factors should be addressed, with appropriate alterations and medical management offered in order to rehabilitate affected individuals to reduce the incidence of the condition. 

Summary

Tennis elbow (lateral epicondylitis) is a condition caused by repetitive overload and strain on the ECRB tendon. Overuse causes microtrauma, which affects the structure of the tendon and leads to degeneration of the tendon over time.

Improper wrist and forearm placement during eccentric loading, such as during racquet sports and manual labour, increases the likelihood of the condition manifesting. Jobs that require repetitive wrist exertion, such as painting and carpentry, as well as recreational activities such as weightlifting and gardening, can elevate the risk. Additionally, improper grip and prolonged loading without rest can further strain the tendon.

Unlike classic inflammation, tennis elbow is not characterised by any visible external symptoms, such as swelling. In fact, it is the collagen breakdown, neovascularisation, as well as excessive enzyme activity that impedes healing. Other factors such as ageing, genetics and systemic conditions such as diabetes and smoking can reduce the ability of the tendon to regenerate itself.

Prevention of the condition should focus on ergonomic adjustments, plenty of rest and exercises that strengthen the muscles involved.