Normal Achilles Tendon Width Size on Radiography, Ultrasound, CT & MRI
The Achilles tendon is the largest and strongest tendon in the human body, connecting the gastrocnemius and soleus muscles to the calcaneal tuberosity. Accurate measurement of its width is essential for detecting early tendinopathy, grading tears, and guiding surgical or conservative management decisions.
Normal Reference Values
| Orientation | Measurement |
|---|---|
| Lateral | 4-9 mm |
Clinical Significance
A normal Achilles tendon width ranges from 4 to 9 mm in the lateral plane. Widths exceeding 9 mm are associated with tendinopathy, characterized by mucoid degeneration, neovascularization, and loss of the normal fibrillar architecture. Diffuse fusiform thickening is the hallmark of non-insertional tendinopathy, while focal enlargement near the calcaneal insertion suggests insertional tendinopathy or Haglund deformity-related changes.
Conversely, apparent thinning or discontinuity of the tendon on imaging raises concern for partial or complete rupture, particularly when combined with clinical findings such as a positive Thompson test or a palpable gap. It is important to note that patient age, body habitus, and athletic history can influence baseline tendon dimensions, and side-to-side comparison is recommended when asymmetry is suspected.
- Achilles tendinopathy — fusiform thickening >9 mm, hypoechoic foci on ultrasound
- Partial tear — focal intrasubstance defect with regional widening
- Complete rupture — discontinuity, retraction, and wavy tendon ends
- Peritendinitis — preserved tendon width with surrounding hypoechoic fluid
- Xanthoma — nodular tendon enlargement in hypercholesterolemia
Reference: Mantke R, Peitz U. Surgical Ultrasound, An Interdisciplinary Approach for Surgeons, Internists, and Ultrasound Technicians. TIS. (2007).
Imaging Notes
On lateral radiography, the Achilles tendon is visible as a soft-tissue density anterior to the pre-Achilles fat pad (Kager's triangle); width is measured perpendicular to the long axis of the tendon. Ultrasound is the preferred first-line modality, allowing dynamic assessment in longitudinal and transverse planes; measurements should be taken at the point of maximum thickening with the transducer perpendicular to the tendon to avoid anisotropy artifact, which can falsely simulate hypoechogenicity.
MRI provides superior soft-tissue contrast for characterizing intrasubstance signal changes, extent of tear, and peritendinous edema, with width measured on axial sequences using T1 or proton-density fat-saturated sequences. CT is less commonly used for tendon evaluation but can demonstrate calcific tendinopathy or osseous insertional changes; width measurement follows the same axial-plane principles as MRI.