LATERAL ANKLE LIGAMENT INJURY

Lateral ligament injuries are divided into • High ankle sprain and • Low ankle sprains Low ankle sprain is considerably more common and

is the injury typically referred to as a 'twisted ankle'.

Three ligaments are considered in relation to low ankles sprain In practical terms however the posterior talofibular ligament is rarely torn and usually only where there is tibiotalar dislocation The other two are the anterior talofibular ligament and calcaneofibular ligament Of these, the calcaneofibular ligament is the more important as isolated tears of the anterior talofibular ligament do not usually rendered the ankle unstable

Many of these ligaments around the ankle are made of multiple strands and frequently separate bundles can be identified

Acute injuries to the anterior talofibular ligament results in loss of definition of the ligament which appears swollen and oedematous.

The normal ligament is approximately 3mm in thickness and 2cm in length.

Like other normal ligaments it should have low signal on both T1 and T2 weighted imaging.

Any significant inversion injury where the patient has difficulty in weight bearing afterwards is likely to indicate a tear of this ligament.

Clinically, tenderness is below and anterior to the lateral malleolus.

Classification systems have been proposed but correlation with clinical findings and outcome is not clear cut.

Fluid extravasation into the extra-articular soft tissues is suggestive of complete rupture particularly if coupled with obvious discontinuity.

Chronic changes include a diffusely thickened or thinned ligament most heal but some result in synovial debris in the area of the ankle joint below it, called the anterolateral gutter Chronic synovitis here is referred to as anterolateral impingement Assessment of the calcaneofibular ligament is difficult as it runs in both the sagittal and, more proximally, the axial plane

It is easiest to visualise on coronal T1 images deep to the peroneal tendons

Similar to the anterior talofibular ligament, acute injury results in swelling and increased signal.

It is often difficult to differentiate partial from complete injuries.

Complete rupture of the ligament is associated with extravasation of fluid into the peroneal sheath which may assist with diagnosis.

In the chronic phase, an injured ligament can become thickened or thinned.

Under these circumstances, ultrasound can be helpful in differentiating and normal thin ligament from a previously torn thin ligament As it provides better depiction of the internal structure of the ligament

Loss of this pattern is indicative of injury. Ultrasound has the advantages of allowing the ligament to be stressed which may demonstrate a more occult injury.

Injuries to the calcaneofibular ligament are most frequent at the fibular insertion An important indirect US signs of tear are: absence of tightening of the calcaneo-ligament during a dynamic examination with dorsal flexion of the ankle The posterior component of the lateral ligament complex is rarely torn It contains multiple laminations

When seen in sagittal section, it can be misconstrued as a loose body in the posterior joint space