Tendons are the fibrous tissues connecting muscle to bone, required for all forms of movement. An injury to a tendon disrupts this connection, leading to pain and functional loss. The healing process for a tendon is distinct from other tissues due to its structure and limited blood supply, which is why recovery requires significant time and care.
The Biological Process of Healing
The initial response to a tendon injury is the inflammatory phase. A hematoma, or localized blood clot, forms at the injury site and releases chemical signals that attract inflammatory cells like neutrophils and macrophages. These cells clear away damaged tissue, preparing the site for repair.
Following inflammation, the proliferative phase begins and can last for several weeks. During this period, cells called fibroblasts and tenocytes migrate to the injury site and produce new collagen. This initial collagen is predominantly Type III, which is structurally weak and disorganized, leaving the tendon fragile and susceptible to re-injury.
The final and longest stage is the remodeling phase, which can extend for more than a year. This phase involves a gradual transformation of the weak Type III collagen into the much stronger Type I collagen. The new collagen fibers slowly align themselves along the lines of mechanical stress, which restores the tendon’s tensile strength, though it may never fully regain the properties of the original tissue.
Factors Influencing Healing Speed and Quality
A tendon’s blood supply determines its healing speed. Tendons are poorly vascularized compared to muscle tissue, receiving less blood flow. This limited circulation slows the delivery of oxygen, nutrients, and cells needed for repair, which is why these injuries are slow to heal.
The body’s healing capabilities also change with age. As individuals get older, cellular activity and metabolic rates decrease, and circulation can become less efficient. These age-related changes may slow the healing phases and affect the quality of the repaired tissue.
Nutrition provides the building blocks for tissue repair. Protein is needed for synthesizing new collagen fibers, the primary component of tendons. Vitamin C also plays a direct role in collagen formation, and deficiencies in key nutrients can impair the mending process.
The nature of the injury affects the healing process. An acute tear has a different healing trajectory than chronic degeneration from overuse, known as tendinosis. Systemic health conditions like diabetes or habits such as smoking can also impair blood flow and cellular function, creating additional hurdles for repair.
The Role of Loading and Movement
Following a tendon injury, an initial period of rest is necessary for the inflammatory process to begin without disruption. However, extended immobilization is detrimental. Without mechanical forces, new collagen fibers do not receive the signals needed to align properly, resulting in weaker, disorganized scar tissue.
Mechanotransduction, the process by which cells respond to mechanical stimuli, is a key concept in tendon rehabilitation. Controlled, progressive loading of the healing tendon sends signals to the tenocytes, guiding them to organize new Type I collagen fibers parallel to the direction of force. This alignment rebuilds the tendon’s strength and functional capacity.
Achieving the right balance of load is important. The goal is to apply enough stress to stimulate remodeling without overwhelming the fragile tissue, as too little load leads to a weak repair and too much can cause further damage. This is why therapeutic exercise must be carefully managed and progressed.
Medical and Therapeutic Interventions
Physical therapy applies controlled loading principles to manage tendon injuries. Therapists design specific, progressive exercise programs tailored to the individual’s stage of healing. These programs increase the load on the tendon to stimulate collagen remodeling and restore strength, flexibility, and function.
For pain management, non-steroidal anti-inflammatory drugs (NSAIDs) are sometimes used in the early stages of an acute injury. However, there is debate about their use. Since inflammation is a necessary part of the initial healing cascade, suppressing it may interfere with the overall repair process.
Physicians may recommend injections to treat persistent symptoms. Corticosteroid injections are used for their anti-inflammatory effects but are often used with caution due to potential impacts on tendon integrity. Other options, like platelet-rich plasma (PRP), involve injecting a patient’s own platelets to introduce growth factors to the injury site.
Surgical intervention is reserved for severe injuries, such as a complete rupture where the tendon ends are no longer in contact. The goal of surgery is to physically reattach the severed ends of the tendon. Following surgery, a lengthy period of rehabilitation is still required to regain strength and function.