Peroneus quartus tendon and complete rupture of peroneus brevis tendon

Clinical History

The patient complained about a lateral retromalleolar pain after inversion sprain of the left ankle. Perimalleolar oedema, tenderness of the lateral aspect of the ankle and difficulty walking were evident on physical examination. A fluoroquinolone antibiotic was prescribed for five days to treat a urogenital infection three weeks before.

Imaging Findings

Radiography of the left ankle evidenced swelling of the lateral soft tissue but ruled out fractures (Fig. 1). On axial MRI the peroneus brevis tendon (PBT) was inhomogeneous and not recognizable just below the peroneal malleolus; the PBT was proximally retracted and enveloped the peroneus longus tendon (PLT) in a spiroid fashion (Fig. 2, 3a). The distal insertion of the PBT into the cuboid was normal (Fig. 3b). MRI reveal also split of the PLT and (Fig. 2d) and a peroneus quartus tendon inserting into a prominent peroneal turbercle (Fig. 2, 3b, 4a). The peroneal groove was flat (Fig. 2b); a small amount of fluid into the tendons' sheath was also demonstrated (Fig. 4b). MRI ruled out injuries of ankle ligaments or osteochondral lesions.

Discussion

Peroneal tendons injury (PTI) usually affects young athletes or elder subjects because of degenerative changes and are frequently underdiagnosed due to a non-specific lateral ankle pain. Oedema and tenderness at the level of the peroneal groove are typical physical findings; manual muscle strength test can be negative or ambiguous in case of a split tear [1, 2].
PT tears are precipitated by an inversion ankle sprain in 61% of cases and chronic ankle ligamentous laxity or peroneal subluxation are recognized as main causes; convex or flat fibular groove, low-lying muscle belly, anomalous tendon, peroneal tenosynovitis, superior peroneal retinaculum incompetence, posterior lateral fibular spurring, and cavovarus foot are anatomical conditions predisposing to tendon tear [1-4]. A peroneal tubercle larger than 5 mm is often associated to inframalleolar pathology of the PLT [4]. It is thought that PTI are not independent of each other and always related to predisposing conditions [2].
Biomechanism of PTI is not wholly explained; tendons’ attrition for “crowding”, dislocation or direct injury from spurs are considered determinant pathophysiological factors [1, 5]. Moreover risk of tendon rupture is increased by quinolone antibiotics, a well-known extrinsic cause of tendinopathy [6].
Approximately 40% of patients did not refer history of trauma [2]. Split tear of PBT is likely to be very frequent and often clinically overlooked as it is observed in up to 37% of cases of anatomic investigations [1].
MRI findings of PTI include synovial fluid accumulation, swelling, high signal intensity on T1- and T2-weighted sequences, clefts and defects; in case of a complete rupture with gap the tendon is not visible along all its course and the proximal stump retracted. A PBT with a split tear exhibits a C-shape and envelops the PLT [4, 5].
PBT tear is very rarely isolated but usually associated to other lesions, a fact which makes a complete clinical and MRI evaluation of the entire lateral ankle complex mandatory [3, 7].
MRI is highly sensitive but poorly specific for diagnosing peroneal tendon tear, with a positive predictive value of 48% in patients with positive clinical findings [3, 5, 7, 8]. MRI sensitivity in detecting PBT lesions is higher for orthopaedic surgeons than for radiologists (71% versus 56% ) [9]: poor familiarity with ankle pathology of radiologists not specialized in musculoskeletal MRI, and lack of knowledge of history and clinical data account for a higher accuracy rate of orthopaedic surgeons scrutinizing MRI findings [8, 9].

Differential Diagnosis List

Final Diagnosis

Complete rupture of peroneal brevis tendon; peroneus quartus tendon

URL:	https://www.eurorad.org/case/11588
DOI:	10.1594/EURORAD/CASE.11588
ISSN:	1563-4086