How does an Achilles tendon injury present clinically?

Clinical Presentation of Achilles Tendon Injury

Achilles tendon injury presents with sudden posterior ankle pain (often described as feeling like being "kicked" or hearing a "pop"), immediate weakness in plantar flexion, and a palpable gap in the tendon approximately 2-5 cm proximal to its calcaneal insertion. 1, 2

Key Clinical Features

Subjective Symptoms

• Acute onset pain: Sudden, sharp pain in the posterior ankle during activity (jumping, running, or pushing off) 2, 3
• Audible "pop" or snap: Patients frequently report hearing or feeling a popping sensation at the moment of injury 2, 4
• Immediate weakness: Inability to push off or stand on tiptoes on the affected side 1
• Morning stiffness: Worsened by prolonged rest, particularly in chronic tendinopathy 5, 6
• Activity-related pain: Pain that increases with physical activity and tendon loading 5, 3

Objective Physical Examination Findings

The AAOS guidelines recommend performing at least two of the following four clinical tests to establish diagnosis 1:

1. Positive Thompson test (Simonds squeeze test): The most reliable clinical test - squeezing the calf fails to produce plantar flexion of the foot when the tendon is ruptured 1, 4

2. Palpable gap or defect: A depression can be felt in the tendon, typically 2-5 cm above the calcaneal insertion 1, 4

3. Decreased ankle plantar flexion strength: Marked weakness when attempting to stand on toes or push off 1

4. Increased passive ankle dorsiflexion (Matles test): The affected ankle can be dorsiflexed more than the uninjured side when the patient lies prone with knees flexed 1

Additional Clinical Signs

• Visible swelling: Localized edema around the tendon 5, 6
• Tendon thickening: Palpable enlargement of the tendon in chronic tendinopathy 3
• Pain on palpation: Tenderness along the tendon, particularly 2-5 cm from insertion 3
• Pain with loading activities: Discomfort during single-leg heel raises or hopping 3

Anatomical Location Patterns

Injuries typically occur in two distinct locations:

• Noninsertional (midportion): Most common site, 2-5 cm proximal to calcaneal insertion, representing the watershed zone with poorest blood supply 4, 6
• Insertional: At or near the tendon's attachment to the calcaneus 5, 6

Common Clinical Pitfall

The most critical error is missing the diagnosis entirely. The Thompson test has high sensitivity (89.8% of cases show positive findings) 4, yet ruptures are frequently missed in emergency departments when clinicians rely solely on the patient's ability to weakly plantar flex using accessory muscles (tibialis posterior, flexor hallucis longus, flexor digitorum longus). Always perform the Thompson test - if it's positive, the tendon is ruptured regardless of residual plantar flexion ability.

Imaging Considerations

While diagnosis is primarily clinical, the AAOS guidelines state they are unable to recommend for or against routine use of MRI, ultrasonography, or radiography for confirmation due to insufficient evidence 1. However, in clinical practice:

• Ultrasonography: Can demonstrate tendon thickening, heterogeneous echogenicity, and gaps; used in 42.9% of cases 7, 4
• MRI: Highly sensitive (95%) and specific (95%) for detecting ruptures and degenerative changes, often obtained for surgical planning 7, 2
• Plain radiography: May show calcific tendinosis or soft tissue swelling but cannot visualize tendon integrity 7

Distinguishing Acute Rupture from Chronic Tendinopathy

Acute rupture (75.5% of presentations) 4:

• Sudden onset during specific activity
• Immediate severe pain and weakness
• Clear traumatic mechanism
• Positive Thompson test

Chronic tendinopathy 5, 6:

• Gradual onset over weeks to months
• Pain worse with activity, better with rest
• Morning stiffness
• Maintained (though painful) plantar flexion strength
• Negative Thompson test