A positive Thompson test indicates a likely complete rupture of the Achilles tendon. The test is performed by squeezing the calf muscles while the patient lies face down with their feet hanging off the edge of the exam table. Normally, squeezing the calf causes the foot to point downward; when the Achilles tendon is torn, the foot stays still. That absence of movement is the “positive” result, and it remains one of the fastest, most reliable bedside assessments for this injury.
How the Test Actually Works
The Achilles tendon connects the calf muscles to the heel bone. When you squeeze the fleshy part of someone’s calf, you’re mechanically shortening the gastrocnemius and soleus muscles, which pulls on the Achilles tendon and tips the foot downward into what clinicians call plantar flexion. If the tendon is intact, this happens reliably. If the tendon is ruptured, the mechanical chain is broken and squeezing the calf produces no foot movement at all.1Journal of Education and Teaching in Emergency Medicine. Thompson Test in Achilles Tendon Rupture – Section: Discussion
The test is typically done with the patient prone on a table, knees bent at roughly 90 degrees or with the feet hanging freely off the edge. Clinicians usually test both legs for comparison: the uninjured side produces obvious plantar flexion when squeezed, making the lack of motion on the injured side dramatically clear. It takes about ten seconds to perform and requires no equipment, which is why it’s a staple of emergency departments and sports sidelines alike.
Where the Name Comes From
The test carries two names depending on where you trained. In much of Europe it’s called the Simmonds test, after Franklin Simmonds, who described it in 1957. In North America it’s more commonly called the Thompson test, after T.C. Thompson, who observed the same findings independently after encountering a patient with an acute Achilles tear in 1955. Thompson went a step further: he tested cadavers to determine exactly how much tendon had to be disrupted before the foot stopped moving. He found that squeezing the calf still produced plantar flexion even when up to 90% of the soleus contribution was torn, which is why the test is best at catching complete or near-complete ruptures rather than partial ones.2Journal of Foot and Ankle Surgery. The Simmonds-Thompson Test: A Biography of the Surgeons Behind the Eponym – Section: The Simmonds-Thompson Test
Diagnostic Accuracy
In a prospective study of 174 patients presenting with suspected Achilles tendon tears, the calf squeeze test had a sensitivity of 0.96, meaning it correctly identified 96% of actual ruptures. Its specificity was 0.93, meaning it correctly cleared 93% of patients whose tendons were intact.3PubMed. The clinical diagnosis of subcutaneous tear of the Achilles tendon. A prospective study in 174 patients Those numbers make it the most sensitive of the commonly used bedside tests for Achilles rupture. It outperformed both palpating for a gap in the tendon and the Matles test, which checks whether the foot drifts into a neutral position when the knee is bent.
A separate study looking at a combination of clinical findings, including the Thompson test alongside a palpable gap and decreased plantar flexion strength, found that when all three signs were present, the combination had 100% sensitivity for complete ruptures confirmed during surgery.4PubMed Central. MRI is unnecessary for diagnosing acute Achilles tendon ruptures: clinical diagnostic criteria – Section: RESULTS The researchers concluded that MRI was unnecessary when the clinical picture was this clear, a point that matters both for speed of diagnosis and healthcare costs.
When the Thompson Test Can Mislead
No bedside test is perfect. The Thompson test has a few known blind spots that clinicians and patients should be aware of.
The most clinically significant limitation involves partial tears. Thompson’s own cadaver work showed that the foot could still plantar flex with substantial tendon damage, as long as some continuity remained.2Journal of Foot and Ankle Surgery. The Simmonds-Thompson Test: A Biography of the Surgeons Behind the Eponym – Section: The Simmonds-Thompson Test A patient with a high-grade partial tear might have a negative Thompson test (the foot still moves) and walk out of the emergency room with a missed diagnosis. This is why clinicians are taught to combine the squeeze test with other findings rather than rely on it alone.
Swelling can also complicate interpretation. In the hours after an injury, significant soft tissue swelling around the calf can transmit some of the squeeze force through tissues other than the torn tendon, producing a faint flicker of foot movement that a rushed examiner might read as normal. Testing the uninjured side first helps calibrate what a normal response looks like, making a diminished response on the injured side easier to catch.
Chronic or “neglected” ruptures present another challenge. If a patient doesn’t seek care for weeks after the initial injury, scar tissue can form in the gap between the torn tendon ends. That scar tissue may transmit enough force to produce a weakly positive plantar flexion response during the squeeze, masking an old complete tear. Patients with chronic ruptures often present with weakness and difficulty pushing off the ground rather than the dramatic immobility of an acute injury.
Other Tests Used Alongside the Thompson Squeeze
Clinicians rarely base a diagnosis on a single test. For suspected Achilles rupture, several other bedside maneuvers round out the picture:
- Palpable gap: Running a finger along the tendon often reveals a noticeable depression or soft spot at the rupture site, usually a few centimeters above the heel. This test had a specificity of about 0.89 in the same study that evaluated the Thompson test.
- Matles test: With the patient face down and the knee bent to 90 degrees, the injured foot tends to fall into a more neutral or slightly dorsiflexed position compared to the uninjured side. Its sensitivity was 0.88, lower than the calf squeeze but still useful as a confirmatory sign.
- Decreased plantar flexion strength: Simply asking the patient to push their foot down against resistance. With a complete rupture, they’ll have almost no power, though they can sometimes weakly flex the foot using accessory muscles, which can mislead an unwary examiner.
The combination of these findings together is more powerful than any single test. When a patient has a positive Thompson test, a palpable tendon gap, and noticeably decreased plantar flexion strength, the clinical diagnosis is essentially certain.4PubMed Central. MRI is unnecessary for diagnosing acute Achilles tendon ruptures: clinical diagnostic criteria – Section: RESULTS
Does a Positive Thompson Test Mean You Need an MRI?
Not always, and there’s a genuine argument that in clear-cut cases you don’t. When the clinical picture is unambiguous, with all three bedside signs pointing to a complete rupture, some orthopedic groups consider advanced imaging unnecessary before proceeding with treatment planning. The study that found 100% sensitivity for the clinical triad explicitly argued that MRI added cost and delay without changing the diagnosis.4PubMed Central. MRI is unnecessary for diagnosing acute Achilles tendon ruptures: clinical diagnostic criteria – Section: RESULTS
Ultrasound is another option and has the advantage of being fast, inexpensive, and available at the bedside. One approach, called the Realtime Achilles Ultrasound Thompson (RAUT) test, combines the physical squeeze maneuver with live ultrasound imaging so the examiner can watch the tendon in real time. Among experienced clinicians, this combined technique achieved sensitivity around 86% and specificity around 92%, higher than static ultrasound alone.5PubMed Central. Realtime Achilles Ultrasound Thompson (RAUT) Test for the Evaluation and Diagnosis of Acute Achilles Tendon Ruptures – Section: METHODS
In practice, imaging tends to be ordered when the clinical picture is muddled: a partial tear is suspected, the injury is days or weeks old, or the patient’s anatomy or body habitus makes the bedside exam unreliable. MRI remains the gold standard for characterizing the exact location and extent of a tear when that detail matters for surgical planning.
What Else Could Cause Similar Symptoms
Not every sudden calf pain with difficulty walking is an Achilles rupture. Injuries to other muscles in the posterior calf can mimic some of the same symptoms, including the gastrocnemius, plantaris, soleus, and flexor hallucis longus.6Foot and Ankle Clinics. Disorders of the Calf Muscles and Flexor Hallucis Longus A classic example is the “tennis leg” injury, a tear at the junction of the gastrocnemius muscle and its tendon. It produces sudden calf pain and difficulty pushing off, and patients often report a popping sensation. The Thompson test helps distinguish these injuries because it specifically tests the mechanical integrity of the Achilles tendon. With a gastrocnemius tear, the Achilles tendon is intact, so squeezing the calf still produces plantar flexion.
Deep vein thrombosis can also cause calf pain and swelling that occasionally enters the differential. The clinical presentation is usually different, with more diffuse swelling and less of the classic sudden “snap” that patients with Achilles ruptures describe. Still, in a swollen, painful lower leg where the history is unclear, ruling out a clot is important before focusing on the tendon.
Why Missed Achilles Ruptures Are a Real Problem
Achilles tendon ruptures are one of the more commonly missed diagnoses in emergency medicine. This matters because a delay in treatment can lead to chronic problems including abnormal gait, ongoing pain, and reduced function that may affect a person’s ability to work or stay active.7Advanced Emergency Nursing Journal. Assessment and Management of Patients With Achilles Tendon Rupture – Section: Surgical Intervention A fresh rupture is far easier to repair than one that has been sitting for weeks, where the tendon ends retract and scar tissue fills the gap.
The most common scenario for a missed diagnosis is a patient who visits the emergency room with ankle or calf pain and is told they have a sprain. They can still weakly point their foot downward using accessory muscles, which leads the examiner to assume the Achilles is intact. If the Thompson test isn’t performed, or is performed hastily on a swollen leg, the rupture slips through. The test exists specifically to avoid this trap: it bypasses voluntary muscle contraction and mechanically tests the tendon’s integrity directly.
What Happens After a Confirmed Rupture
Once a positive Thompson test and supporting findings confirm a complete Achilles rupture, the treatment decision comes down to surgery versus structured nonoperative care. Both approaches involve an initial period of immobilization, typically a week in a cast or boot, followed by a gradual transition into a functional brace that allows controlled movement.
A randomized trial comparing the two approaches found that functional scores at 18 months were not significantly different between the surgical and nonsurgical groups. However, surgery did produce faster and greater recovery of calf muscle strength: at six months, the surgically treated group had 16% to 24% greater strength, and at 18 months, they maintained a 10% to 18% advantage across different ankle positions.8PubMed. A Prospective Randomized Trial Comparing Surgical and Nonsurgical Treatments of Acute Achilles Tendon Ruptures – Section: METHODS The primary concern with nonoperative treatment has traditionally been a higher rerupture rate, though modern functional rehabilitation protocols have narrowed that gap considerably compared to older approaches that relied on prolonged casting.
The Thompson test also plays a role in follow-up. In studies tracking outcomes after both surgical and nonsurgical treatment, a positive Thompson squeeze test during recovery was used as one of the criteria for diagnosing a rerupture.9Journal of Bone and Joint Surgery. Operative versus Nonoperative Treatment of Acute Achilles Tendon Ruptures – Section: Methods If the test turns positive again after initially normalizing, it signals that the repaired or healing tendon has failed.
Achilles Ruptures in Children and Adolescents
Achilles tendon ruptures are overwhelmingly an adult injury. In children and adolescents, the growth plate at the heel bone is typically the weakest link in the chain, so a forceful push-off is more likely to injure the growth plate than snap the tendon. Acute Achilles ruptures in the pediatric population are uncommon enough that they mainly appear in case reports rather than large studies.10PubMed Central. Case Report: Traumatic Distal Achilles Tendon Rupture in a Pediatric Patient – Section: Introduction The Thompson test works the same way mechanically in younger patients, but the rarity of the diagnosis means it may not be the first thing a clinician thinks to check in a child with heel pain. Awareness that the injury can happen, even if rarely, helps prevent the kind of diagnostic delay that causes problems in adults.
Risk Factors Worth Knowing About
Understanding who tends to rupture their Achilles tendon provides useful context for interpreting a positive Thompson test. The typical patient is a man between 30 and 50 years old, often a recreational athlete who plays sports involving sudden acceleration and jumping. Weekend warriors who are relatively sedentary during the week and then go hard on a basketball court or tennis court are the classic demographic.
Certain medications increase tendon fragility. Fluoroquinolone antibiotics have a well-documented association with Achilles tendon rupture, and the risk is compounded when these drugs are taken alongside corticosteroids. Systemic corticosteroid use on its own also weakens tendons over time. Local corticosteroid injections around the Achilles tendon carry risk as well. Chronic conditions like diabetes and rheumatoid arthritis can affect tendon health, as can chronic kidney disease. If a patient presents with a positive Thompson test and a history of fluoroquinolone use, the clinical picture fits together quickly.
One practical implication: if you’re on a fluoroquinolone antibiotic and develop sudden calf pain, don’t assume it’s a muscle cramp. The Thompson test is something even a non-physician can attempt as a rough screen, though any suspicion of a tendon rupture warrants prompt medical evaluation.