Thompson Calf Squeeze Test for Achilles Tendon Rupture
The Thompson test (calf squeeze test) is a critical clinical maneuver to diagnose complete Achilles tendon rupture by assessing whether squeezing the calf produces passive plantar flexion of the foot—absence of this movement indicates complete tendon disruption. 1
How to Perform the Test
The patient lies prone with the foot hanging over the edge of the examination table. The examiner squeezes the calf muscle belly firmly. 2
Test Interpretation:
- Positive test (rupture present): No plantar flexion occurs when the calf is squeezed 2, 3
- Negative test (tendon intact): Normal plantar flexion of the foot occurs 4
- Intermediate response: Reduced or slight reactive plantar flexion, which may indicate partial healing or elongated tendon repair 4
Clinical Utility and Accuracy
The American Academy of Orthopaedic Surgeons recommends performing at least two specific tests for Achilles tendon rupture diagnosis, including the Thompson test, assessment of decreased ankle plantar flexion strength, palpation for a gap or defect in the tendon, and evaluation of increased passive ankle dorsiflexion. 1
The Thompson test should be performed in any evaluation of ankle pain to avoid misdiagnosis. 2 It directly determines the integrity of the distal ten centimeters of the Achilles tendon. 5
Important Clinical Pitfalls
Excessive swelling and pain can limit examination accuracy, potentially masking the diagnosis in acute cases. 1 A palpable gap and the Thompson test are sometimes difficult to evaluate when a large hematoma is present. 3
The definitive benchmark for complete rupture is the inability to perform a single leg heel raise. 3
Post-Operative Considerations
In the follow-up after Achilles tendon repair, negativization of the Thompson test is not always homogeneous or absolute. 4
Intermediate Thompson test results (reduced plantar flexion response) correlate with:
Approximately 75% of post-operative patients demonstrate normal negative Thompson tests, while 25% show intermediate responses with reduced or slight reactive plantar flexion. 4
Complementary Diagnostic Approaches
When clinical examination is equivocal, ultrasound can determine the localization of rupture and enable dynamic examination to detect possible adaptation of tendon ends. 3 Complete adaptation of tendon ends on ultrasound provides the possibility of conservative treatment. 3
Ultrasound can differentiate full-thickness from partial-thickness Achilles tendon tears with 92% accuracy. 6