Musculoskeletal · Sports Medicine
The facts most likely to be tested
The anterior talofibular ligament (ATFL) is the most commonly injured ligament in a lateral ankle sprain due to inversion and plantarflexion of the foot.
The Ottawa Ankle Rules dictate that an ankle X-ray is required only if there is bone tenderness at the posterior edge or tip of the lateral or medial malleolus.
A foot X-ray is indicated if there is bone tenderness at the base of the fifth metatarsal or the navicular bone.
The calcaneofibular ligament (CFL) is the second most commonly injured ligament and is typically involved in more severe, higher-grade sprains.
Grade I sprains involve microscopic tearing of the ligament with no mechanical instability, while Grade III sprains involve complete ligamentous rupture with significant instability.
The anterior drawer test of the ankle is used to assess the integrity of the ATFL by evaluating for increased anterior translation of the talus.
Initial management for acute lateral ankle sprains consists of RICE (Rest, Ice, Compression, Elevation) and early functional rehabilitation rather than prolonged immobilization.
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A 22-year-old male presents to the urgent care clinic after twisting his right ankle while playing basketball. He reports immediate pain and swelling over the lateral aspect of the ankle. On physical examination, there is tenderness at the tip of the lateral malleolus and mild edema. He is able to bear weight for four steps in the office. The anterior drawer test is negative for significant laxity.
Based on the Ottawa Ankle Rules, what is the most appropriate next step in management?
Obtain an ankle X-ray
The Ottawa Ankle Rules require an ankle X-ray if there is bone tenderness at the posterior edge or tip of the lateral malleolus, which this patient exhibits.
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High yield triage
Etiology / Epidemiology
Most common musculoskeletal injury; inversion and plantarflexion is the classic mechanism.
Clinical Manifestations
Localized edema and ecchymosis over the lateral malleolus; anterior drawer test for ligamentous laxity.
Diagnosis
Ottawa Ankle Rules determine the need for imaging; MRI is the gold standard for chronic instability.
Treatment
RICE (Rest, Ice, Compression, Elevation) and early functional rehabilitation; avoid non-weight bearing.
Prognosis
Most recover in 4-6 weeks; chronic instability occurs in 20% of patients.
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Epidemiology & Etiology
Lateral ankle sprains account for 85% of all ankle injuries, frequently occurring during athletic activity. The primary risk factor is a prior history of ankle sprain. The mechanism involves forced inversion of a plantarflexed foot.
Pertinent Anatomy
The lateral ligament complex consists of the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and posterior talofibular ligament (PTFL). The ATFL is the most commonly injured ligament due to its relative weakness.
Pathophysiology
Inversion stress causes a sequential failure of the lateral ligaments. The ATFL is injured first, followed by the CFL if the force continues. This disruption leads to synovial inflammation, localized hematoma, and subsequent mechanical instability.
Clinical Manifestations
Patients present with acute lateral pain, swelling, and difficulty bearing weight. The anterior drawer test assesses ATFL integrity, while the talar tilt test evaluates the CFL. Red flags include inability to bear weight for 4 steps or bony tenderness, which mandate imaging to rule out malleolar fracture.
Diagnosis
The Ottawa Ankle Rules are the clinical standard to exclude fractures; radiographs are required only if there is bone tenderness at the posterior edge of the malleoli or inability to bear weight. MRI is reserved for suspected syndesmotic injury or persistent pain beyond 6 weeks.
Treatment
Initial management is RICE therapy combined with NSAIDs for pain control. Early functional rehabilitation (proprioceptive training) is superior to immobilization. Avoid prolonged casting as it leads to muscle atrophy and stiffness. Surgical intervention is rarely indicated for acute injuries.
Prognosis
Most patients return to full activity within 4-6 weeks. Chronic ankle instability is the most common complication, requiring physical therapy and potentially bracing. Recurrence rates are high, emphasizing the need for neuromuscular training.
Differential Diagnosis
Distal fibular fracture: bony tenderness at the posterior malleolus
Syndesmotic sprain: positive squeeze test
Peroneal tendon tear: pain with resisted eversion
Fifth metatarsal fracture: tenderness at the base of the 5th metatarsal
Osteochondral lesion: persistent deep joint pain