How Is Tendonitis Diagnosed? A Physical Therapy Perspective

Tendon pain is one of the most common complaints we see in an outpatient orthopedic physical therapy clinic. Whether it’s an achy elbow after too much pickleball, a painful Achilles following marathon training, or nagging shoulder pain with overhead lifting, tendon-related issues can limit both everyday function and athletic performance.

One of the most frequent questions patients ask us is: “How do I know if this is tendonitis?”

Diagnosing tendonitis is more complex than many realize. Unlike a fracture that shows up clearly on an X-ray, tendon injuries involve a combination of clinical examination, movement assessment, and an understanding of tendon physiology. As physical therapists, we rely on a combination of patient history, objective testing, and evidence-based reasoning to determine whether tendon pain is truly tendonitis—or if another musculoskeletal issue is at play.

In this article, we’ll walk through:

• What tendonitis actually is (and why the term can be misleading)

• The physiological and anatomical background of tendons

• The key steps in a physical therapist’s diagnostic process

• How tendonitis differs from tendinopathy and tendinosis

• What tests, imaging, and assessments are most useful

• Why accurate diagnosis matters for effective treatment

By the end, you’ll have a deeper understanding of how tendonitis is identified and why a skilled PT evaluation is so valuable when tendon pain strikes.

What Is Tendonitis?

The term tendonitis (sometimes spelled tendinitis) literally means inflammation of the tendon. A tendon is a dense, fibrous connective tissue that connects muscle to bone. When excessive or repetitive loading stresses the tendon beyond its capacity, microscopic tears, chemical irritation, and in some cases, true inflammatory processes can occur.

However, research in the last two decades has shown that most persistent tendon pain is not driven by classic inflammation. Instead, histological studies of painful tendons often reveal:

• Disorganized collagen fibers (loss of the normal parallel alignment)

• Increased ground substance and proteoglycan content, making the tendon thicker

• Neovascularization (new blood vessel ingrowth) that can irritate nerve fibers

• Cellular changes within tenocytes (specialized tendon cells)

Because of these findings, many clinicians now prefer the term tendinopathy, which describes a broader spectrum of tendon pathology, including acute inflammation (tendonitis), chronic degeneration (tendinosis), and mixed presentations.

Still, patients (and many providers) often use “tendonitis” as shorthand for any painful tendon condition—which is why clarifying the diagnosis is essential.

Tendon Anatomy and Physiology 101

To understand how tendonitis is diagnosed, it’s helpful to review tendon structure and function.

Tendon Structure

• Collagen fibers: Tendons are primarily composed of Type I collagen fibers arranged in a hierarchical structure—fibrils, fibers, fascicles, and bundles—that allows for both tensile strength and elasticity.

• Tenocytes: The primary tendon cells that maintain extracellular matrix and respond to mechanical loading.

• Endotenon and epitenon: Sheath-like connective tissue layers that provide blood supply and house nerves.

• Vascularity: Tendons have relatively poor blood supply compared to muscle, which is why healing can be slow.

Tendon Function

Tendons are designed to:

1. Transmit force from muscle to bone, enabling movement.

2. Store and release energy during dynamic tasks like running or jumping.

3. Absorb shock to protect muscle and joint structures.

   
   

When tendons are loaded appropriately, they adapt and become stronger. But when the balance tips toward overload without adequate recovery, the tendon matrix can begin to break down—leading to pain and dysfunction.

How Physical Therapists Diagnose Tendonitis

In physical therapy, diagnosis is not about a single test or image. It’s a process of clinical reasoning, combining patient history, observation, movement analysis, and targeted physical examination. Here’s how we approach it step by step:

1. Detailed Patient History

The story patients tell us often provides the biggest clues. We listen for:

• Onset of pain: Gradual buildup with repetitive activity vs. sudden traumatic event.

• Location: Tendon pain is typically well-localized to the tendon or its insertion point.

• Aggravating activities: Pain that increases with loading tasks—jumping, gripping, throwing, or running—points toward tendon involvement.

• Morning stiffness: Many tendon conditions cause increased stiffness after periods of rest.

• Training or activity changes: Sudden spikes in volume, intensity, or frequency often precede tendon irritation.

• Medical history: Systemic factors such as diabetes, high cholesterol, or certain medications (e.g., fluoroquinolone antibiotics, corticosteroids) can predispose tendons to injury.

This narrative helps us form hypotheses: Is this truly tendon-related? Or could it be referred pain from a joint, nerve, or muscle?

2. Observation and Movement Analysis

Next, we watch how the patient moves. For example:

• Achilles tendon pain: Does heel rise cause discomfort? Is there asymmetry in calf muscle activation?

• Patellar tendon pain: Does jumping, squatting, or lunging reproduce symptoms?

• Lateral elbow pain (“tennis elbow”): Does gripping, wrist extension, or lifting a coffee cup trigger pain?

Movement analysis also includes identifying contributing factors, such as hip weakness in runners with Achilles pain, or shoulder instability in athletes with biceps tendon pain.

3. Palpation and Localized Tenderness

One hallmark of tendon pathology is point tenderness. A PT palpates along the tendon’s length and at its bony insertion. Localized pain that matches the patient’s symptoms strongly supports a tendon diagnosis.

For instance:

• Medial epicondylitis: Pain at the common flexor tendon origin on the medial elbow.

• Rotator cuff tendinopathy: Tenderness over the supraspinatus tendon just below the acromion.

• Achilles tendonitis: Pain along the mid-portion of the tendon or at the calcaneal insertion.

4. Load and Provocation Tests

Tendons hurt most when they are loaded. Physical therapists use specific resistance tests to reproduce symptoms:

• Resisted wrist extension (Cozen’s test) for lateral epicondylitis.

• Resisted knee extension for patellar tendinopathy.

• Single-leg heel raises for Achilles tendon involvement.

• Empty can or resisted external rotation for rotator cuff tendinopathy.

The presence of pain during these tests—especially if it is localized to the tendon and not diffuse—adds diagnostic confidence.

5. Differentiating From Other Conditions

A skilled PT must also rule out other possible sources of pain, such as:

• Joint pathology (e.g., meniscus tear vs. patellar tendonitis)

• Nerve entrapment (e.g., cervical radiculopathy mimicking shoulder pain)

• Ligament injuries (e.g., ankle sprain vs. peroneal tendonitis)

• Bursitis (which often causes more diffuse swelling and pain compared to tendonitis)

This is where clinical reasoning and anatomical knowledge are critical—two conditions may present similarly, but treatment pathways differ dramatically.

6. Imaging (When Needed)

Most tendonitis diagnoses can be made clinically without imaging. However, in cases of uncertainty, persistent symptoms, or suspicion of more serious injury, imaging may be warranted:

• Ultrasound: Allows dynamic visualization of tendon thickening, tears, and neovascularization.

• MRI: Provides detailed structural information, particularly helpful for partial tendon tears or intra-articular tendons (like the hip or shoulder).

• X-ray: Not useful for soft tissue but may rule out bony pathology (e.g., calcific deposits at tendon insertion).

Physical therapists often collaborate with physicians to determine when imaging is necessary.

Tendonitis vs. Tendinosis vs. Tendinopathy

One of the most important parts of diagnosis is terminology:

• Tendonitis: Acute inflammatory response, usually short-term. Swelling, warmth, and redness may be present (though rare).

• Tendinosis: Chronic degenerative changes without classic inflammation. Characterized by collagen disorganization and thickening.

• Tendinopathy: The umbrella term encompassing all tendon-related pathology.

From a PT perspective, accurate labeling matters because treatment strategies differ. True acute tendonitis may benefit from short-term anti-inflammatory measures, while chronic tendinosis requires progressive loading programs to stimulate remodeling.

Why Accurate Diagnosis Matters

Misdiagnosis of tendon pain can lead to ineffective or even harmful treatments. For example:

• Treating tendinosis with excessive rest may actually worsen tendon health.

• Injecting corticosteroids repeatedly into degenerative tendons can weaken tissue further.

• Ignoring biomechanical contributors (like hip weakness in a runner with Achilles pain) leads to recurrent flare-ups.

A PT’s role is to provide a holistic, movement-based diagnosis that considers not just the tendon itself, but the entire kinetic chain.

A Case Example: Achilles Tendon Pain

Let’s walk through how this looks in practice.

Patient presentation: A 38-year-old recreational runner reports increasing pain in the back of the ankle after ramping up mileage for an upcoming marathon. Pain is worse in the morning and after long runs.

History clues: Recent increase in training volume; pain localized to the tendon; stiffness after rest.

Observation: Antalgic gait with reduced push-off on affected side.

Palpation: Tenderness 3 cm above calcaneal insertion.

Load tests: Single-leg heel raise reproduces pain.

Differential diagnosis ruled out: No ankle instability (ligament intact), no nerve symptoms, no diffuse swelling suggestive of bursitis.

Conclusion: Clinical diagnosis consistent with mid-portion Achilles tendinopathy (chronic degenerative overload rather than acute tendonitis).

Treatment plan: Progressive loading program with eccentric calf raises, movement retraining, and activity modification.

This illustrates how PT diagnosis informs not just a label, but a clear path forward.

The PT Edge in Diagnosing Tendonitis

What makes physical therapists uniquely positioned in diagnosing tendon issues?

• Movement expertise: We don’t just identify the injured tissue—we identify why it became overloaded.

• Hands-on assessment: Palpation, strength testing, and functional analysis reveal details imaging can’t.

• Holistic perspective: We integrate lifestyle, training, biomechanics, and systemic health into diagnosis and care.

• Evidence-based protocols: Our diagnostic process aligns with current research on tendon health and rehabilitation.

Final Thoughts

Diagnosing tendonitis is not about finding a “spot on an X-ray.” It’s about listening to the patient’s story, applying anatomical knowledge, reproducing symptoms through clinical tests, and ruling out other possible sources of pain.

From a physical therapy perspective, the diagnosis of tendonitis (or more broadly, tendinopathy) guides not only immediate symptom relief, but also long-term solutions that restore tendon resilience and prevent recurrence.

So, if you’re dealing with tendon pain that just won’t go away, don’t rely on guesswork—or generic internet advice. A thorough PT evaluation is one of the most effective ways to get to the root cause and start moving pain-free again.

Need help with tendon pain? Call us at (720) 248-4386 to schedule your free discovery call and get back in the saddle pain free!