Fibularis longus tendon tear

Fibularis longus tendon tears can be partial or complete, longitudinal or transverse, acute or chronic, and might be associated with tendon instability.

Epidemiology

Fibularis longus tendon tears are a frequent cause of lateral foot and ankle pain ^1-3. However, they are less common than fibularis brevis tendon tears ^1,4.

Risk factors

Conditions that account as predisposing factors for fibularis longus tears include ^1-3:

• convex or flat retromalleolar groove

• cavovarus deformity

• prominent retrotrochlear eminence and/or peroneal tubercle

• fibularis quartus muscle

• low-lying fibularis brevis muscle belly

• os peroneum

Associations

Fibularis longus tendon tear can occur in isolation or can be associated with the following conditions ^1-4:

• fibularis longus tendon dislocation or intrasheath subluxation

• fibularis brevis tendon tear

• tendinosis and/or tenosynovitis

• lateral ankle sprain

• chronic ankle instability

Diagnosis

Several disorders of the lateral ankle and hindfoot have overlapping clinical presentations. Only about 60% of fibular tendon injuries are detected on initial clinical examination ^1,4. Therefore imaging plays a crucial role in the diagnosis ¹.

Clinical presentation

A common presentation of fibularis longus tendon tears is chronic lateral ankle pain aggravated by movement or activity and sometimes associated with a clicking or popping sensation ^2,3.

Complications

If untreated fibular tendon tears can lead to chronic ankle pain and chronic instability ⁵.

Pathology

A fibularis longus tendon tear is a discontinuity (longitudinal or transverse) in the tendon morphology. They can be longitudinal or transverse, partial or complete and can be associated with tendon instability ^1-5.

Etiology

Causes of fibularis longus tendon tears include the following ^1,2:

• acute injury (typically inversion injury)

• overuse causing increased friction and shear stress

Location

Common sites for the occurrence of fibularis longus tears include the following ^1-3,5:

• retromalleolar groove (often associated with fibularis brevis tear)

• retrotrochlear eminence (most common site for split tears and partial tears)

• cuboid tunnel (most common site for complete tears)

Subtypes

Fibularis longus tendon tear can be subdivided with respect to their location to the os peroneum ⁶:

• proximal to the os peroneum

• os peroneum

• distal to the os peroneum

Radiographic features

Plain radiograph

Standard anteroposterior (AP), lateral and mortise views are usually acquired in the setting of an acute injury of the ankle. It might show a retracted os peroneum in the case of a complete distal tendon rupture, but in most cases, the examination is unremarkable ².

However, they might help in the exclusion of differential diagnoses.

Ultrasound

Ultrasound can aid in the detection of fibularis longus tendon tears and can show peroneus tendon dislocation.

The proximal and lateral part up of the fibularis longus tendon up to the peroneal tubercle can be examined with the patient supine, knee partially flexed and ankle rotated internally together with the fibularis brevis tendon, whereas the distal plantar part is evaluated separately best with the patient in prone position ^2,6.

Partial tears might show up as hypoechoic thickening or thinning of the fibularis longus tendon with a fluid-filled defect or cleft, whereas complete or full-thickness tears might show a longitudinal split or a discontinuity of the normal echogenic fibrillar tendon structure with retraction of the tendon stumps ^1,2,5,6.

MRI

MRI can detect and localize longitudinal and transverse tears as hyperintense or fluid-like signal defects within the otherwise hypointense tendon structure, tendon discontinuity or empty fluid-filled tendon sheath ^1-3. Other signs are tendon contour irregularities or a shredded appearance ⁵.

It is important to note that peroneal tendons are susceptible to magic angle artefacts that might occur when the tendon fibers are oriented at an angle of approximately 55° to the magnetic field on sequences with lower echo times ≤ 35 ms ^1,2. Besides increasing the echo time, options of artefact reduction include conducting the MRI examination in plantar flexion and or prone position ^1-4.

Secondary signs of fibularis longus tendon tears might include subcortical bone marrow edema of the lateral calcaneus, peroneal tubercle or cuboid bone.

Signal characteristics

• T1: intermediate signal intensity

• T2: intermediate to high signal intensity

• PDFS/STIR: hyperintense

Radiology report

The radiological include a description of the following:

• type and degree of the tear

• location and extent

• associated injuries

  • fibularis brevis tendon

  • peroneal retinaculum

  • os peroneum

Treatment and prognosis

Management will depend on the extent and associated injuries and includes non-operative, conservative therapy as orthotics physical therapy and functional rehabilitation as well as surgical treatment options ^1-3.

Surgical treatment can be considered in case of conservative treatment failure and/or symptomatic tendon ruptures ⁷. This might comprise excision, debridement and tubularization in partial tears where >50% of the tendon is intact or direct repair in the setting of an acute tendon rupture. If direct repair is not possible tenodesis between fibularis longus and fibularis brevis tendons is an option, if one of the tendons is torn and the other is still functional, tendon transfer or tendon grafts can be done in settings where both tendons are torn and no longer functional ^1-4,7.

Differential diagnosis

Conditions that might mimic the imaging appearance of a fibularis longus tendon tear include ^1-5:

• fibularis longus tendinosis/tendinopathy

• fibularis longus tenosynovitis

• fibularis longus tendon instability

• magic angle artefact

• painful os peroneum syndrome