Peroneus brevis tear

Peroneus brevis tendon tears can present with lateral ankle pain with or without a history of trauma, worsening with activity. They are usually diagnosed with ultrasound or MRI and management is typically conservative.

Epidemiology

Little epidemiological information available but patients typically are younger and active.

Clinical presentation

Symptoms can include pain, swelling, and erythema at the lateral ankle which worsens with activity or may be asymptomatic. Some tears occur following trauma, although there is a degenerative process which does not require an isolated episode. There is a suspected high rate of peroneal tendon injury in those with chronic ankle instability. There is also an association with systemic conditions e.g. rheumatoid arthritis, diabetes, or local steroid injection ¹.

Pathology

As the peroneus brevis tendon sits between the peroneus longus tendon and the bony retromalleolar groove of the fibula it is at risk of a degenerative tear, particularly in dorsiflexion.

Traumatic episodes and tendon dislocation can lead to degeneration. Other anatomical variants can predispose to injury:

• insufficiency of the overlying superior peroneal retinaculum
• low-lying peroneus brevis muscle belly or variant peroneus quartus muscle

As the brevis tear develops, the longus tendon moves forward into the space which further antagonises the injury and prevents healing.

One surgical review stated 40% of those undergoing brevis repair had longus tears at surgery ² which are likely secondary to degenerative change following migration.

Radiographic features

Ultrasound

Ultrasound has a high sensitivity (100%) and specificity (85%) for identifying tendon tears ³:

• partial tear: discontinuity and partial retraction of affected tendon fibres with fluid in the sheath, normal appearance proximal and distal to the tear
• longitudinal fissures: two "hemi-tendon" appearance at the apex of the malleolus affecting the deep fibres first
• full thickness: typical appearance of a rupture

MRI

Torn peroneus brevis tendons have a characteristic C-shape or "boomerang" appearance, with the tendon enveloping the peroneus longus tendon. Other signs include distortion of the tendon, increased T1w and T2w signal, with the anterior migration of the peroneus longus tendon.

Treatment and prognosis

Typically managed conservatively with anti-inflammatories and rest/immobilisation. Surgical fixation can be considered in persisting cases or for those with ankle instability with debridement or if required tenodesis to the adjacent peroneus longus tendon.

Differential diagnosis

• normal variant bifurcated peroneus brevis tendon: differentiate by identifying muscle fibres attaching to the tendon slips
• peroneus quartus tendon insertion simulating a tear on imaging

See also

• peroneus brevis muscle
• boomerang sign (ankle)