Tendinosis is a chronic, painful condition resulting from the breakdown of a tendon’s structure. This condition involves the non-inflammatory degeneration of the collagen fibers that make up the tendon tissue. Tendinosis is a common musculoskeletal issue, frequently affecting individuals who engage in repetitive physical activities or sports. Common areas include the Achilles tendon, the rotator cuff tendons in the shoulder, and the tendons around the elbow and knee, often referred to as “tennis elbow” or “jumper’s knee.”
How Tendinosis Differs From Tendinitis
The distinction between tendinosis and tendinitis reflects a fundamental difference in underlying pathology. Tendinitis is an acute, short-term injury involving inflammation, where the tissue contains inflammatory cells and exhibits typical signs like swelling and heat. Tendinosis, conversely, is a long-term, degenerative process characterized by the breakdown of the tendon’s collagen matrix without a significant inflammatory response. Chronic tendon pain lasting more than a few months is usually tendinosis. Recognizing this difference is important because the treatments for each condition are nearly opposite, and anti-inflammatory drugs are often unhelpful or detrimental in tendinosis.
The Underlying Causes and Tissue Changes
Tendinosis develops primarily from a cycle of repeated microtrauma without sufficient time for the tendon to heal properly. The tendon tissue attempts to repair itself, but constant stress prevents successful healing, leading to a “failed healing response” and structural deterioration. At a microscopic level, healthy collagen fibers, which are normally straight and parallel, become disorganized, fragmented, and lose their uniform structure. This breakdown is accompanied by an increase in ground substance, a mucoid material that contributes to the tendon’s abnormal appearance and stiffness.
A hallmark feature of this degenerative process is neovascularization, or the growth of new, fragile blood vessels within the damaged tendon. These new vessels often grow alongside sensory nerve fibers, which is thought to be a major source of chronic pain. Furthermore, the cells within the tendon, called tenocytes, proliferate haphazardly, leading to hypercellularity and the production of lower-quality, haphazardly arranged collagen. Factors such as poor blood supply, age, and systemic conditions can contribute to the failure of the healing cascade and increase the risk of developing tendinosis.
Symptoms and Identifying the Condition
The symptoms of tendinosis generally develop gradually, beginning as a mild ache that progresses to chronic, localized pain lasting longer than three months. This discomfort often worsens noticeably during or after activity, particularly with movements that load the affected tendon. Unlike acute tendinitis, tendinosis typically does not present with outward signs of swelling, redness, or heat, as inflammation is absent.
A physical examination will often reveal localized tenderness directly over the affected tendon. In some cases, the tendon may feel thickened, firm, or have a palpable nodule due to the structural changes. To confirm the diagnosis and distinguish it from other conditions, medical imaging is frequently used.
Ultrasound or Magnetic Resonance Imaging (MRI) is often used to visualize the internal structure of the tendon. These scans can confirm tendinosis by showing a thickened tendon with disorganized or fragmented collagen fibers and signs of neovascularization, which correlates with the degenerative changes seen microscopically.
Pathways to Recovery and Management
Since tendinosis is a structural issue, the primary goal of management is to stimulate the tendon to rebuild a healthier collagen matrix. This begins with activity modification, reducing the load on the tendon without resorting to complete immobilization. Complete rest can be detrimental, as it does nothing to improve the tendon’s tolerance for future stress.
Physical therapy is the most important component of recovery, focusing on specific strengthening exercises that promote collagen remodeling. Eccentric strengthening, where the muscle lengthens under tension, is a highly effective exercise for tendinosis, applying controlled load to encourage better fiber alignment. A physical therapy program is a long-term commitment, often requiring eight to twelve weeks or more to see significant structural improvement.
Other non-surgical interventions are sometimes used to stimulate the healing response in the degenerative tissue. Platelet-Rich Plasma (PRP) injections involve injecting a concentration of the patient’s own growth factors into the tendon to encourage cellular regeneration and new collagen synthesis. Extracorporeal Shockwave Therapy (ESWT) delivers acoustic waves to the damaged area, which can help trigger a regenerative process and relieve pain. Traditional treatments for inflammation, such as corticosteroid injections and nonsteroidal anti-inflammatory drugs (NSAIDs), are generally avoided because they can inhibit necessary collagen synthesis and potentially weaken the tendon over time.