Tendon pain, often referred to clinically as tendinopathy when persistent, occurs when a tendon or its surrounding tissues become painful in response to mechanical loading, injury or other biological processes. Tendons connect muscles to bones and transmit force so that muscle contraction produces joint movement. Common painful tendon conditions include Achilles tendinopathy, patellar tendinopathy, rotator-cuff-related tendinopathy, lateral elbow tendinopathy and gluteal tendinopathy. Tendon pain is often associated with a mismatch between the loads placed on the tendon and its capacity to tolerate and adapt to those loads, although the biology is more complex than simple "overuse". Acute tears can also produce tendon pain, ranging from microscopic disruption to complete rupture.
Tendons adapt to mechanical loading by altering their structure and cellular activity. Normal loading stimulates tendon cells, particularly tenocytes, to maintain and remodel collagen and extracellular matrix. Problems can develop when loading is suddenly increased, repeated without sufficient recovery, or combined with biological factors that reduce tendon capacity. Running, jumping, throwing and repetitive manual work can all expose tendons to substantial forces. However, tendinopathy is not restricted to athletes and can occur in sedentary people who abruptly increase activity. Age, metabolic disease, previous tendon problems, obesity, certain medications and genetic or anatomical factors can influence susceptibility. The relationship between activity and pain is therefore not simply that repetitive movement "wears out" a tendon.
Tendinopathy is generally understood as a disorder involving altered tendon structure, mechanical properties, cellular activity and pain rather than purely acute inflammation. Degenerative changes can include disruption of normal collagen organisation, increased ground substance, changes in tendon-cell behaviour, altered vascularity and changes in the tendon matrix. These changes can reduce mechanical efficiency and may be associated with pain, although structural abnormalities can exist without symptoms. Conversely, severe pain can occur with relatively modest structural abnormalities. The modern term tendinopathy is therefore broader and more accurate than assuming that all chronic tendon pain is tendinitis.
Acute tendon injury can cause pain through partial or complete tearing. A tendon rupture can occur when a tendon is exposed to a sudden high force, especially when it has pre-existing degenerative changes. Achilles tendon rupture, for example, can occur during jumping or sprinting and may produce a sudden sensation of being struck in the back of the ankle, followed by difficulty pushing off. Rotator-cuff tears can occur traumatically or develop gradually as part of age-related tendon degeneration. The distinction between tendinopathy and rupture is important because a rupture can produce substantial weakness and may require different management, including surgical consideration in selected cases.
Tendon pain is often strongly related to loading. A tendon may hurt when first subjected to activity, sometimes improve during the activity and become painful afterwards, or become progressively more painful as the load continues. Morning stiffness is common in some tendinopathies. Symptoms often respond to carefully graduated loading because tendons require mechanical stimulus to maintain capacity, while excessive loading can aggravate symptoms. Complete rest is not generally a universal solution and can reduce muscle and tendon capacity if prolonged. Rehabilitation therefore commonly aims to find a tolerable level of loading and progressively increase it as capacity improves.
Several systemic and medication-related factors can increase tendon vulnerability. Diabetes and other metabolic conditions are associated with altered tendon structure and increased risk of tendinopathy. Some antibiotics in the fluoroquinolone class have been associated with an increased risk of tendon injury, particularly Achilles tendon problems, and systemic corticosteroid exposure can also influence tendon integrity. The risk is affected by age, concurrent conditions and other medications. These associations do not mean that every person exposed to a particular risk factor will develop tendon disease, but they are relevant when a new tendon problem appears in an appropriate clinical context.
The location of pain helps identify the tendon involved but can also reveal alternative diagnoses. Pain at the back of the heel may originate from the Achilles tendon or nearby structures, while pain below the kneecap may involve the patellar tendon. Lateral elbow pain can involve the common extensor tendon, and lateral hip pain can involve the gluteal tendons. Nerve, joint, bone and bursal disorders can mimic tendon pain. Imaging such as ultrasound or MRI can demonstrate tendon structure, but abnormalities must be correlated with symptoms because asymptomatic tendon changes are common. Clinical examination, including assessment of strength and response to tendon loading, remains central to diagnosis.
Treatment generally involves load management and progressive rehabilitation, with the precise programme depending on the tendon and severity. Exercise can improve tendon and muscle capacity, while temporary modification of aggravating activities can reduce excessive mechanical stress. Analgesic strategies may help symptoms, and selected cases may be considered for other interventions or surgery.
Persistent pain does not necessarily mean that the tendon is continuing to deteriorate; pain can remain influenced by changes in the nervous system and by expectations, sleep and other factors after tissue capacity has begun to improve. Sudden severe pain with a popping sensation, immediate weakness, visible deformity or inability to perform the relevant movement raises concern for rupture and requires prompt assessment.
