Tendons are strong, fibrous bands of connective tissue that transmit force from muscles to bones. When these tissues cause pain, the injury is often broadly termed a tendon injury. However, the specific medical terms—tendinitis or tendinosis—have fundamentally different meanings. Distinguishing between them is paramount because their underlying biological mechanisms differ, which determines the correct treatment approach and influences the recovery timeline.
The Underlying Pathology: Inflammation Versus Degeneration
The primary distinction between tendinitis and tendinosis lies in the suffix. The suffix “-itis” denotes acute inflammation, meaning tendinitis involves a short-term inflammatory response. This reaction is the body’s immediate attempt to heal a sudden injury or micro-trauma, often involving immune cells like macrophages and neutrophils. It typically occurs shortly after the onset of pain.
Conversely, the suffix “-osis” signifies chronic degeneration, the hallmark of tendinosis. This pathology involves a structural breakdown of the tendon’s collagen fibers and cellular death, with a noticeable lack of inflammatory cells. Instead, tendinosis tissue shows disorganized collagen bundles, increased ground substance, and often neovascularization (the formation of new, abnormal blood vessels). This degenerative process develops over an extended period, often months or years, due to chronic overuse and a failed healing response.
Recent clinical understanding suggests that many long-standing tendon pain conditions previously diagnosed as tendinitis are actually tendinosis, lacking classic inflammatory markers. The tissue also exhibits a shift in its collagen makeup, producing mechanically inferior Type III collagen instead of the strong Type I collagen found in healthy tendons. This structural disorganization makes the tissue weaker and less capable of handling normal loads over time.
How Symptoms and Onset Differ
The symptoms of tendinitis and tendinosis mirror their underlying biological processes in terms of timeline and presentation. Tendinitis presents with an acute, sudden onset of sharp, severe pain, often following a specific incident or trauma. Because it involves active inflammation, the affected area may display classic signs like localized swelling, redness, and warmth. Movement usually makes the discomfort immediately worse.
Tendinosis, a chronic degenerative condition, follows a gradual timeline, with symptoms persisting for months or years. The pain is frequently described as a nagging ache rather than sharp pain. It often improves as the tendon warms up with activity, but returns later or the next day, accompanied by significant stiffness, particularly in the morning. Unlike tendinitis, signs of surface inflammation like redness or heat are usually absent, though the tendon may feel thickened or nodular upon examination.
Navigating the Treatment Divide
The differing pathology necessitates a distinct approach to treatment, making a correct diagnosis crucial for recovery. Since tendinitis is an acute inflammatory condition, treatment focuses on reducing inflammation and resting the tendon to allow immediate healing. This typically involves short-term interventions like applying ice, resting from the aggravating activity, and using non-steroidal anti-inflammatory drugs (NSAIDs). This regimen is usually successful, with patients often recovering within several weeks.
Treatment for tendinosis must center on reversing chronic degeneration and stimulating the tendon to rebuild its damaged collagen structure. Crucially, the anti-inflammatory approach used for tendinitis is often ineffective or detrimental for tendinosis. NSAIDs can interfere with the cellular signaling pathways that promote the long-term remodeling and repair of the degenerated tissue. Therefore, the focus shifts away from rest and toward controlled mechanical loading.
The most supported treatment involves specific physical therapy protocols, especially those incorporating eccentric exercises. Eccentric contractions involve lengthening the muscle while under tension, applying a targeted load to the tendon. This mechanical stimulus encourages tenocytes (specialized tendon cells) to increase the production of healthy Type I collagen and reorganize the matrix. Other modalities that stimulate a healing response include dry needling or regenerative procedures like platelet-rich plasma (PRP) injections, which introduce growth factors directly into the damaged area.