MRI Findings of Peroneal Tendon Pathology


The peroneal longus and brevis are both found in the lateral compartment of the lower extremity (2). The peroneal brevis muscle originates from the distal fibula and will insert upon the base of the fifth metatarsal (1). The peroneal longus muscle originates more proximally on the fibula and will insert on both the base of the first metatarsal and the medial cuneiform (1). Both tendons aid in plantarflexion and eversion of the foot (1). The two tendons are found together at the level of the retromalleolar sulcus on the distal fibula under the superior peroneal retinaculum (1,2).

Image of the tendons at the level of the retromalleolar groove (7)

At the level of the sulcus, the peroneal brevis tendon is adjacent to the fibula and the peroneal longus sits superior (2). Once the tendons reach the distal fibula, they are enclosed in the same tendon sheath until the peroneal tubercle, where the tendons go separate ways (2).

Image showing the Superior Peroneal Retinaculum (5)

Also present in seven percent of the population is the peroneus quartus (2). This muscle will originate from the peroneal brevis muscle belly and insert on the peroneal tubercle (2). The presence of a peroneus quartus is attributed as a risk factor to developing stenosing tenosynovitis (2).

Patients with injury to their peroneal tendons will typically complain of posterolateral ankle pain (4). This pain can be secondary to tendinosis, tenosynovitis, tears, and dislocation of the tendons (4).

MRI Findings

Tears of the peroneal tendons can be traumatic or due to repetitive trauma. Tears of the peroneal brevis are more commonly seen than tears of the peroneal longus (3). One of the more common pathologies seen on an MRI is a peroneal brevis split tear. These tears are thought to occur from subluxation of the tendon from trauma causing damage due to contact with the distal fibula or from direct compression of the tendon between the fibula and peroneus longus (3). A low lying peroneus brevis muscle belly that extends into the retromalleolar groove can also lead to split tear formation (8).

The arrow shows a peroneus brevis muscle belly distal to the distal fibula (8)

The optimal images to view a split tear of the peroneal tendons are an axial or axial oblique view with the foot in slight plantarflexion (3). The sagittal views will help show the degree of tendon damage (6). A normal tendon will appear homogenous with low signal intensity (7). Providers are evaluating for longitudinal split tears, which can be seen as a separation of tendon fibers (3).  On a T2 image, pathology will be seen as tendon heterogeneity and an increase in fluid signal (6).

The yellow line indicates a split tear in the peroneal brevis tendon (2)

Another finding of a peroneal brevis split tear is the flattening appearance of the peroneal brevis that causes it to appear to wrap around the peroneal longus tendon (3). A criteria for defining a split tear of the peroneal tendon was created by Sobel (3). He proposed that a grade I tear has splaying of the tendon, grade II partial thickness tear <1cm, grade III full thickness 1-2cm, and grade IV split tear >2cm (3).

Surgical visualization of a peroneal brevis split tear (3)

Providers must be cautious of MRI findings mimicking tears at what is known as the magic angle. This occurs just distal to the fibula where the tendons change direction (3).

Other common findings on MRI are tenosynovitis of the peroneal tendons. As seen in the image below, the axial oblique image shows fluid surrounding the peroneal longus tendon (4). Fluid collection that is >3mm is typically seen with tenosynovitis (7). This will differ from tendinosis, which can show some fluid within the sheath and only intermediate signal within the tendons (7).

Tenosynovitis of the peroneal longus tendon (4).

The peroneal tendons can also sublux or dislocate from the retromalleolar groove (6). This can be seen on an MRI as a lateral translation of the tendons (6).

Peroneal tendon dislocation from the retromalleolar groove (6)


The peroneal tendons are subject to multiple stresses at the level of the ankle joint, which can lead to the development of tears, tenosynovitis, and tendinosis. MRI images in either the axial or axial oblique plane are best used to visualize the peroneal tendon.

By Gregory Rubin, DO

– More Peroneal Tendon Pathology @ Wiki Sports Medicine


1)      Roster, Brent, et al. “Peroneal Tendon Disorders.” Clinics in Sports Medicine, vol. 34, no. 4, Oct. 2015, pp. 625–41. PubMed,

2)      Kane, Justin M., et al. “Acute Peroneal Tendon Injuries in Sport.” Operative Techniques in Sports Medicine, vol. 25, no. 2, June 2017, pp. 113–19. ScienceDirect,

3)      Mostovoy, Amelia, and Thomas Chang. “Peroneal Pathology in the Athlete.” Clinics in Podiatric Medicine and Surgery, vol. 40, no. 1, Jan. 2023, pp. 139–55. PubMed,

4)      Gorelik, N., et al. “Impact of the T2-Weighted Axial Oblique MRI Sequence in the Assessment of Peroneal Tendons.” Clinical Radiology, vol. 75, no. 8, Aug. 2020, p. 642.e15-642.e23. PubMed,

5)      Sharpe, Jonathan, et al. “Comparison of Preoperative MRI With Intraoperative Findings for Peroneal Tendon Pathologies.” The Journal of Foot and Ankle Surgery: Official Publication of the American College of Foot and Ankle Surgeons, vol. 61, no. 4, 2022, pp. 680–85. PubMed,

6)      Lugo-Pico, Julian G., et al. “Peroneal Tendinosis and Subluxation.” Clinics in Sports Medicine, vol. 39, no. 4, Oct. 2020, pp. 845–58. PubMed,

7)      Philbin, Terrence M., et al. “Peroneal Tendon Injuries.” The Journal of the American Academy of Orthopaedic Surgeons, vol. 17, no. 5, May 2009, pp. 306–17. PubMed,

8)      Lee, Sun Joo, et al. “Ultrasound and MRI of the Peroneal Tendons and Associated Pathology.” Skeletal Radiology, vol. 42, no. 9, Sept. 2013, pp. 1191–200. PubMed,