The Achilles tendon, also called the calcaneal tendon, is the thickest and strongest tendon in the human body, connecting the calf muscles to the heel bone (calcaneus). This structure transfers force from the gastrocnemius and soleus muscles to the foot. An intact Achilles tendon makes plantarflexion—the ability to push off the ground—possible for walking, running, and jumping. When the tendon tears, function is disrupted and professional diagnosis is required. Diagnosis involves initial self-assessment, physical examination, and objective diagnostic imaging.
Identifying the Initial Symptoms and Self-Assessment
The immediate experience of an Achilles tendon rupture is often distinct from other injuries. Many individuals report hearing or feeling a sudden, loud “pop” or “snap” at the back of the ankle at the moment of injury. This sensation is accompanied by acute, sharp pain, often described as feeling like being kicked or shot in the back of the calf.
Following the initial trauma, significant swelling and bruising may develop rapidly in the posterior ankle area. The primary functional sign of a tear is a sudden loss of strength and movement, particularly the inability to point the foot downward (plantarflexion). The injured person finds it impossible to stand on the toes or push off the ground while walking, resulting in a distinct limp.
A simple observation involves visually and manually checking the area just above the heel. In the case of a complete rupture, a noticeable gap or depression can often be felt or seen in the tendon, typically 2 to 6 centimeters above the heel bone insertion. Comparing the injured ankle to the uninjured one may also reveal that the injured foot rests in a position of increased passive dorsiflexion. While these visual signs are highly suggestive of a tear, a definitive diagnosis requires a medical professional to perform specific physical maneuvers.
Clinical Physical Examination Techniques
A medical professional relies on a series of hands-on tests to confirm the clinical diagnosis of an Achilles tendon tear. The most widely recognized is the Thompson Test, also called the calf squeeze test. This test is performed with the patient lying face down on an examination table, with their feet relaxed and hanging freely over the edge.
The examiner gently squeezes the calf muscle of the injured leg and observes the movement of the foot. If the tendon is intact, this compression transmits force through the Achilles, causing the foot to spontaneously point downward (plantarflexion), which is a negative result. A positive Thompson test occurs when squeezing the calf fails to produce any plantarflexion movement. The sensitivity of the Thompson test for a complete rupture is reported to be very high, often between 96% and 100%.
Other physical methods contribute to the examination, including palpation and the Matles Test. Palpation involves the clinician gently feeling the course of the tendon for a defect or gap, which is a strong indicator of a complete tear. The Matles Test is performed with the patient lying prone and the knees bent to a 90-degree angle.
In a healthy ankle, the tension maintained by the intact Achilles tendon keeps the foot in a slightly pointed position. If the tendon is torn, this tension is lost, causing the foot to fall into a neutral position or even slight dorsiflexion, which is a positive Matles Test. When the Thompson Test, Matles Test, and palpation for a gap are all positive, the combined sensitivity for diagnosing an Achilles tear is 100%.
Objective Diagnostic Imaging
While the clinical examination provides a strong indication of a tear, objective diagnostic imaging is frequently used to confirm the diagnosis, determine the injury’s extent, and assist in treatment planning. The two most common modalities employed are ultrasound and Magnetic Resonance Imaging (MRI).
Ultrasound is an accessible and rapid method that uses high-frequency sound waves to create real-time images of the tendon. It allows the clinician to dynamically assess the tear, observing how the tendon responds when the ankle is moved. Ultrasound is effective for differentiating between partial and complete tears and for measuring the exact gap distance between the torn tendon ends.
Magnetic Resonance Imaging (MRI) provides a more detailed view of the soft tissues than ultrasound, though it is more expensive and less readily available. While ultrasound is recommended for initial diagnosis, MRI is used when the diagnosis is uncertain or when greater detail is needed, such as in cases of chronic rupture or pre-surgical planning. MRI excels at visualizing the precise location of the tear and its relationship to surrounding structures, which guides injury management decisions.