(last updated July 25, 2006)
PERONEALS:
Important stabilizers of the ankle joint.
Uniform low signal
Peroneus brevis is anteromedial to peroneus longus
On ultrasound, P longus is superficial and P brevis is deep
On sagittal MR, P longus is posterior and P brevis is anterior
On axial MR, P brevis is cresectic and P longus is more rounded
Susceptible to the magic angle effect; Imaging with foot in mild plantar flexion of 20° decreases magic angle effect.
Peroneus longus:
Origin: lateral tibial condyle, head and proximal two-thirds of lateral fibula, intermuscular septa Course: passes inferior to cuboid in a tunnel (cuboid tunnel) Insertion: plantar surface of the medial cuneiform bone laterally and proximal first metatarsal bone Action: plantar flexion of first ray of foot and eversion of foot at ankle.
Peroneus brevis:
Origin: distal two-thirds of the lateral fibula and adjacent intermuscular septa
Insertion: tuberosity on the lateral aspect of proximal fifth metatarsal bone
Action: plantar flexion and eversion of foot at ankle
Sometimes, the muscle belly lies distal to the fibular groove, which can cause crowding and tear
In dorsiflexion, the belly can be seen normally below fibular groove
Accessory peroneal muscles:
Peroneus quartus (12-22%), peroneus-calcaneus externum, peroneus accessories, peroneus digiti minimi, and peroneus digiti quinti
Best seen on axial MR
Posteromedial to peroneus brevis, usually inserts into retrotrochlear eminence
Occasionally these can cause crowding in retromalleolar groove, predisposing to peroneus brevis tendon dislocation and tear
Can mimic preoneus brevis tear
Common peroneal synovial sheath:
Passes through fibro-osseous tunnel, posterior to lateral malleolus (retromalleolar groove)
Peroneus brevis is anteromedial to peroneus longus
Superior peroneal retinaculum:
Fibrous band
Forms posterolateral border of retromalleolar groove
Origin: posterior ridge of distal fibula
Courses posteroinferiorly
Insertion: lateral wall of the calcaneus
Variant: conjoined insertion onto aponeurosis of Achilles tendon
Inferior peroneal retinaculum.
(To be written)
Other important anatomical considerations:
Retromalleolar groove: On axial MR, it is normally concave posteriorly. If flat or convex or irregular(18%), can predispose to lateral disclocation and longitudinal tears in peroneals.
Pseudosubluxation of peroneus brevis: occasionally partially medial to medial edge of fibular groove rather than anteromedial to peroneus longus. Best seen on axial MR. Supination can increase this finding.
Lateral calcaneal protruberances:
1. Peroneal tubercle seperates the peroneal tendons in the lateral calcaneal margin and is seen n 40%. Hypertrophy (hypertrophic peroneal tubercle) may lead to peroneal tenosynovitis or tear. A bursa may also develop. Best seen on axial and coronal MR
2. Retrotrochlear eminence is seen in nearly all, located posterior to the peroneal tubercle. Hypertrophy is associated with peroneus quartus muscle. Best seen on axial MR.
Os peroneum: sesemoid within peroneus longus. Adjacent to cuboid bone. In 20% foot x-rays. Can mimic peroneus longus intrasubstance tear. Proximal migration indicates peroneus longus tear. Os peroneal fracture, diastasis of multipartite os peroneum or peroneus longus tenosynovitis or rupture can lead to os peroneum syndrome
Links:
Peroneal injuries
Reference:
Wong XT et al. Normal variants and diseases of the peroneal tendons and superior peroneal retinaculum: MR imaging features. Radiographics 2005 May-Jun;25(3):587-602
