Clinical History
A 30 year old female dancer and a 44 year old male taxi-driver were referred to our department due to long-lasting ankle pain and tenderness on palpation along the course of the peroneal tendons at the level of lateral malleolus.
Imaging Findings
A 30 year old female dancer and a 44 year old male taxi-driver were referred to our department for an MRI examination due to 6- and 12-month lasting retromalleolar pain and swelling respectively. Both had unremarkable medical history and complained for almost everyday ankle pain worsening after activities (the female patient as a dancer was practicing for at least 3-4 hours per day and the male patient was driving for at least 9-10 hours per day). Clinical examination revealed tenderness on palpation along the course of the peroneal tendons posterior to the distal fibula.
MRI examination in male patient showed the peroneus brevis tendon to present the characteristic pathologic C-shape configuration (boomerang sign), enveloping the anterior aspect of peroneus longus tendon, associated with fluid accumulation in the peroneal tendon sheath (Fig 1). Irregular configuration of fibular groove was also detected.
At the female patient longitudinal tear of the PB tendon distal to fibular groove with formation of two subtendons, small amount of fluid in the peroneal tendon sheath and a low-lying PB muscle belly was detected (Fig 2).
Discussion
Peroneus brevis split syndrome (PBSS) refers to the longitudinal tear of the peroneus brevis (PB) tendon at the retrofibular groove near the distal tip of lateral malleolus with frequent proximal and distal extension.
PBSS is commonly found in young adults after spontaneous tear or sports related trauma (soccer players and ballet dancers), but it may also be found in older adults due to tendon degeneration, in whom it may be clinically silent.
PBSS appears with chronic ankle pain and mild swelling worsening with activities, though clinical examination may reveal oedema at the anatomic position of peroneal tendons, popping and clicking with active foot eversion, crepitus and pain with peroneal compression test.
The position of the PB tendon in the fibular groove predisposes to tendon injury, as it is compressed between fibula, superior peroneal retinaculum and the peroneus long tendon (as it bends and slides around the hard cortical surface of the fibula). Other predisposing MRI-apparent factors for PBSS are an abnormally shaped peroneal groove (convex or flat instead of concave) or a ruptured/incompetent superior retinaculum, both allowing the peroneal tendons to subluxate out of the peroneal groove. The mechanical attrition worsens when osseous ridges are present at the lateral margin of the peroneal groove. The already narrow retromalleolar groove gets overcrowded when either low-lying muscle belly of the peroneus brevis tendon or accessory peroneus quartus muscle are present (anatomic variations). The possibility for PBSS increases also when peroneal tubercle or retrotrocheal eminence are hypertrophied (leading to tenosynovitis and tear)
The torn PB tendon on MRI appears as a C-shaped structure on multiple axial levels (boomerang sign) partially enveloping the peroneus long tendon. As the tendon totally splits longitudinaly, medial and lateral “limbs” are formed whereas peroneus longus tendon may interpose between the two subtendons. On T2-weighted images the peroneus brevis tendon appears initially hyperintense, and finally longitudinal tear and clefts in tendon’s substance as well as fluid in the peroneal tendon sheath become evident. Associated MR findings may be peroneal subluxation or dislocation, abnormally shaped retromalleolar groove and marrow-containing spur at the edge of the groove.
The PBSS should be differentiated mainly from peroneal tenosynovitis and normal anatomic variants, such as: 1.) the presence of a peroneus quartus tendon, particularly when it inserts into the peroneus brevis tendon (thus simulating a PB tendon tear), 2.) the occasional normal flattening of the PB tendon at the level of the distal fibula (without extending distally), 3.) the mildly normal crescenting shape of the peroneus brevis tendon at the retromalleolar groove, and finally 4.) the normally bifurcated peroneus brevis tendon at the distal leg.
Treatment of PBSS, except for anti-inflammatory agents, rest and orthotics, includes primary anastomosis, debridement and tenodesis as well as surgical correction of MRI-proven associated predisposing factors.
Differential Diagnosis List
Peroneus Brevis Split Syndrome
Final Diagnosis
Peroneus Brevis Split Syndrome
