A 21 years old male patient visited the outpatient clinic for lateral ankle pain of his left ankle. There was pain over the peroneal tendons on palpation with loss of strength in eversion.

Picture 2: According to the radiologist, the MRI suggested peroneal tendinopathy.  Because of the flattened shape of the tendons (red contour) a longitudinal rupture could not be ruled out. 

However, during peroneal tendoscopy, a third tendon was identified: a Peroneus Quartus tendon. (Picture 1)

Picture 3: In retrospect, the third tendon was also identified on MRI. More proximal axial slides clearly show three seperate tendons.

Picture 3:  Peroneus Longus (1), Peroneus Quartus (2), Peroneus Brevis (3).

Picture 4: The sagittal image shows the Peroneus Quartus to leave the course of the Longus and Brevis and run to its insertion at the lateral aspect of the calcaneus.

On the axial MRI slides the course of the peroneal tendons can be identified. From proximal to distal, first three tendons can be distinguished, at the middle part they appear as one flattened tendon and more distal the Peroneus Quartus tendon runs to its insertion at the calcaneus. (Picture 2 & 3)

Picture 5: After the tendoscopic inspection an open resection of the accessory tendon was performed. The patient had an uneventfull recovery.

The peroneal quartus tendon is the most common accessory muscle around the ankle. Several studies reported on prevalence, ranging from 1.1-21.9%. Usually this accessory muscle remains asymptomatic.

For the complete Peroneal Tendoscopy Technique: CLICK HERE