Tendon injuries are frequent complaints involving the musculoskeletal system, often causing confusion because the terms “tendonitis” and “tendinosis” are frequently used interchangeably. These terms refer to two fundamentally different biological processes. Understanding the distinction is important because one is an acute inflammatory response, while the other is a chronic degenerative condition. Each condition requires a completely different treatment strategy for successful recovery, based on its microscopic pathology and timeline.
Tendonitis: The Inflammatory Phase
Tendonitis is defined as an acute inflammatory condition of the tendon, typically resulting from a sudden overload or trauma. It is characterized by the rapid infiltration of inflammatory cells, such as neutrophils and macrophages, responding to micro-tears within the tissue. This defense mechanism cleans up damaged tissue and initiates the repair process.
The pathology of tendonitis is short-lived, usually lasting from a few days up to roughly two weeks. This acute response involves fluid and cellular changes that result in the classic signs of inflammation. If the source of acute overload is removed, the tendon has a strong chance of fully recovering.
Tendinosis: The Degenerative Shift
Tendinosis represents a chronic condition defined by the degeneration and disorganization of the tendon’s internal structure. This pathology occurs when a tendon fails to heal after repetitive microtrauma, often due to continued loading without sufficient recovery time. Crucially, microscopic examination reveals a distinct lack of the inflammatory cells seen in tendonitis.
The core issue is a structural breakdown, marked by a reduction in strong, organized Type I collagen fibers. The tissue instead shows an increase in disorganized, weaker Type III collagen, along with a proliferation of fibroblasts. This structural disarray may also be accompanied by neovascularization—the growth of new, fragile blood vessels and nerves—which contributes to chronic pain and tissue weakness.
Distinct Symptoms and Diagnostic Clues
The difference in underlying pathology leads to clear distinctions in how each condition presents. Tendonitis typically manifests with acute, sharp pain, often accompanied by visible signs of inflammation, including localized swelling, heat, and redness. The pain is usually constant and severe at the onset of the injury.
Tendinosis presents as a chronic, nagging ache that has persisted for months, often without visible swelling or heat. A characteristic pattern is pain that feels stiff and worse in the morning or after rest. The pain often slightly improves during activity, only to stiffen again afterward, and is highly localized to a specific point on the tendon.
While clinical presentation provides strong clues, definitive diagnosis often relies on medical imaging. Tendonitis may show fluid accumulation or an increased signal on an MRI, indicative of the acute inflammatory process. Tendinosis is diagnosed by imaging revealing structural changes, such as tendon thickening, disorganization of the collagen fibers, and signs of neovascularization, often visible on a Doppler ultrasound scan.
Tailored Treatment Approaches
The distinct nature of these two conditions dictates entirely different treatment philosophies. Treatment for tendonitis aims at resolving the acute inflammatory episode and protecting the tendon from further irritation. This management often involves the use of rest, ice, compression, and elevation (RICE) to reduce swelling and pain.
Anti-inflammatory medications, such as non-steroidal anti-inflammatory drugs (NSAIDs), are effective for tendonitis because they target the specific inflammatory chemicals present in the acute phase. The goal is short-term relief and allowing the tendon’s natural healing process to conclude. Recovery for tendonitis is often measured in weeks.
Conversely, the treatment for tendinosis must focus on stimulating long-term cellular activity and remodeling the damaged tendon structure. Since inflammation is not the problem, NSAIDs are often ineffective and may even be detrimental by inhibiting the cellular activity required for collagen repair. The primary intervention involves load management and physical therapy.
Specific physical therapy techniques, such as heavy-slow resistance training and eccentric exercises, are employed to mechanically stimulate the tendon to produce stronger, more organized collagen fibers. Other modalities like dry needling, shockwave therapy, or platelet-rich plasma (PRP) injections may be used to encourage tissue repair. The recovery period for tendinosis is significantly longer, often requiring three to six months of consistent rehabilitation.