Medial Ankle Sprains

Medial ankle sprains, injuries of the deltoid ligament, are significantly less common than lateral sprains because of the deltoid's strength and the biomechanics of ankle injury. They matter out of proportion to their frequency: they travel with other injuries, and the deep deltoid is critical to the stability of the ankle.

Why the isolated injury is rare. The deltoid is the strongest ankle ligament, and it takes significant force to injure it. Most mechanisms that stress the deltoid fracture the lateral malleolus or injure the syndesmosis first. A truly isolated deltoid injury typically follows forced eversion or external rotation on a planted foot.

Who gets it. The high-risk activities:

• Contact sports (football, rugby)
• Landing on an inverted ankle
• External rotation injuries
• Motor vehicle accidents
• Falls from height

The risk factors are a previous ankle injury, hindfoot valgus alignment, ligamentous laxity, inadequate proprioception and poor neuromuscular control.

Two layers. The deltoid ligament is a fan-shaped complex arising from the medial malleolus in two distinct layers. The superficial layer has four bands, the tibionavicular, tibiocalcaneal, tibiospring and superficial posterior tibiotalar, the tibionavicular most anterior, the tibiocalcaneal in the middle and the superficial posterior tibiotalar most posterior. The deep layer is the anterior tibiotalar ligament (ATTL) and the posterior tibiotalar ligament (PTTL), and it attaches directly to the talus. Boss and Hintermann's dissections found the tibionavicular band to be a thickened fold of capsule rather than a discrete ligament.

The medial malleolus. Its three landmarks are the origins, and they matter for surgical planning:

• Anterior colliculus - the superficial deltoid origin, although the superficial posterior tibiotalar band arises from the posterior colliculus (see the table)
• Intercollicular groove - the ATTL origin
• Posterior colliculus - the PTTL origin

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What each layer does. The superficial layer resists eversion and valgus tilt. The deep layer resists lateral talar translation, and the ATTL is the primary restraint against lateral talar shift: it is what keeps the talus centred in the mortise. Together the layers contribute 20-50% of mortise stability, working with the lateral ligament complex to balance the ankle.

Three frameworks describe the injury: the general sprain grade, the layers involved, and the fracture pattern it belongs to.

History. The mechanism is eversion, external rotation or an awkward landing. Establish whether this is an acute injury or chronic instability, and localise the swelling and tenderness to the medial ankle. Ask whether the patient heard or felt a pop and whether they could weight-bear.

Examination. Look for medial swelling and ecchymosis, and palpate the deltoid ligament, the medial malleolus and the proximal fibula. Range of motion is often limited by pain and swelling. Then stress the ankle in eversion and in external rotation.

The Ottawa rules are not enough. They exist to exclude fracture. Even when they give no indication for a radiograph, persistent medial tenderness with the right mechanism warrants stress imaging to assess deltoid competence and mortise stability.

Weight-bearing radiographs first. AP, lateral and mortise views, taken weight-bearing, because non-weight-bearing films miss instability. Measure the medial clear space (MCS) on the mortise view. Normal is under 4mm and equal to the superior clear space; an MCS over 4mm, or one that exceeds the superior clear space by more than 1mm, means deltoid incompetence. The films also show:

• Talar tilt on stress views
• An associated fibular fracture or syndesmotic injury
• An avulsion from the medial malleolus

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Stress views. A gravity stress view (lateral decubitus, affected side down) or a manual eversion stress view is essential when clinical suspicion is high but the standard films are normal, and it confirms mortise instability. The two are not interchangeable; the section below compares them.

MRI. The gold standard for soft-tissue assessment. It distinguishes superficial from deep layer involvement, showing oedema or a partial or complete tear of the superficial layer and the integrity of the ATTL and PTTL, and grades the tear. It also identifies associated injuries, including an osteochondral lesion of the talus (OLT), syndesmotic injury, tibialis posterior pathology and bone marrow oedema from stress at the medial malleolus.

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The most accurate single test. Ultrasound is the most accurate single test for confirming deltoid rupture in the acute setting, yet it is routinely overlooked in favour of radiographs and MRI. In the pooled meta-analysis by de Krom and colleagues it carried the highest diagnostic accuracy of any modality (sensitivity 1.00, specificity 0.89-1.00, the largest area under the curve), outperforming plain mortise radiography, stress views and even MRI for detecting deltoid incompetence in supination-external-rotation ankle fractures.

Why it works. It is dynamic: valgus or external-rotation load can be applied to the ankle while the medial gutter is imaged in real time, directly revealing fibre discontinuity, haematoma, effusion and pathological gapping. It gives a direct soft-tissue view of the superficial deltoid fibres and the medial clear space, carries no radiation, and is a low-cost, point-of-care test that can be repeated at the bedside.

Its limits.

• Highly operator-dependent - accuracy reflects sonographer experience
• The deep deltoid (ATTL) is harder to insonate than the superficial layer
• It does not replace weight-bearing films for whole-mortise assessment
• It is less useful once marked swelling obscures the medial structures

Two ways to stress the ankle. Knowing which to trust, and when to abandon stress views for MRI, is a frequent exam discriminator. Gravity stress uses the weight of the limb (patient in lateral decubitus, injured side down) to apply a consistent, passive valgus and external-rotation load, so the patient cannot guard. Manual stress relies on examiner-applied force, which is painful and prone to protective guarding.

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The decision. Most isolated deltoid injuries heal well with conservative treatment, and surgery is reserved for specific indications. A widened medial clear space means mortise instability, but what it demands depends on the setting: with a fracture it points to fixation, and an MCS that stays wide after fibular or syndesmotic fixation is the point to consider deltoid repair; an isolated tear with a widened MCS is protected in a boot first, with surgery if instability persists despite conservative treatment.

Chronic medial instability. An underdiagnosed entity. Patients present with vague medial pain, giving way and difficulty on uneven ground, and the key examination finding is a positive eversion stress test. It may require reconstruction if it remains symptomatic despite rehabilitation.

Rehabilitation after reconstruction is similar to that after primary repair but may be slightly more conservative initially. The first two weeks are non-weight-bearing to let the wound heal, and return to sport comes at 4-6 months, on the same criteria as after conservative treatment.

Who goes on to chronic instability. The risk factors are deep layer involvement, missed associated injuries, inadequate rehabilitation and a premature return to sport. Chronic medial instability may require reconstruction for definitive management.