Ankle Sprain

01Pathophysiology

The ankle joint is stabilized by three primary ligament complexes: the lateral ligament complex, the medial (deltoid) ligament complex, and the syndesmotic ligaments (tibiofibular ligaments). Understanding which complex is injured dictates the entire clinical picture.

The lateral complex consists of three ligaments: the anterior talofibular ligament (ATFL), the calcaneofibular ligament (CFL), and the posterior talofibular ligament (PTFL). The ATFL is the weakest and most commonly injured because it is taut during plantarflexion and inversion, the position the ankle assumes during a typical "rolling" injury. This is why the classic mechanism is a plantarflexed, inverted foot, and the patient presents with pain and swelling anterior and inferior to the lateral malleolus.

When the force is greater, injury progresses sequentially: ATFL first, then CFL, then PTFL. This sequential failure explains why isolated ATFL tears (Grade I-II) are far more common than combined ligament tears (Grade III). The CFL provides stability in both dorsiflexion and neutral position, so its involvement produces broader lateral instability and a positive talar tilt test.

The deltoid ligament on the medial side is considerably stronger and broader, which is why isolated medial sprains are uncommon. When the deltoid is injured, the examiner must consider an associated fibula fracture (Maisonneuve fracture) or syndesmotic injury, because the force required to tear the deltoid is often enough to disrupt other structures. This is a classic exam trap: medial ankle tenderness after an eversion/external rotation injury should prompt palpation of the proximal fibula and full-length leg radiographs.

Syndesmotic (high ankle) sprains involve the anterior inferior tibiofibular ligament (AITFL), the interosseous membrane, and the posterior inferior tibiofibular ligament. These occur through external rotation and dorsiflexion, commonly seen in contact sports. The tibia and fibula are forced apart, disrupting the "mortise" that cradles the talus. This mechanism explains why patients have pain above the ankle joint line (not over the malleoli) and why weight-bearing is disproportionately painful compared to the amount of visible swelling. High ankle sprains heal more slowly because the interosseous membrane has poor blood supply and the forces of normal gait continuously stress the syndesmosis.

02Classification and Clinical Manifestation

Lateral Ankle Sprain Grading

Classification by Anatomic Location

03Diagnostic Workup

Summary Table

The Ottawa Ankle Rules are the most tested concept in ankle sprain workup. These rules state that radiographs are only needed if there is bone tenderness at the posterior edge or tip of either malleolus (within the distal 6 cm), bone tenderness at the base of the fifth metatarsal or navicular, or inability to bear weight for four steps both immediately after the injury and in the emergency department. The clinical value lies in their near-perfect sensitivity (~98%) for excluding fractures, meaning a negative Ottawa rule safely avoids unnecessary imaging. However, their low positive predictive value means that most patients who meet the criteria and get radiographs will not have a fracture. On exams, a vignette describing an ankle injury with tenderness only over ligamentous areas and the ability to walk four steps is testing whether you know imaging is not needed.

When radiographs are indicated, the standard series includes anteroposterior (AP), lateral, and mortise views. The mortise view (15-20 degrees of internal rotation) is critical because it allows assessment of the clear space between the medial malleolus and talus. A medial clear space >4 mm suggests deltoid ligament disruption or mortise widening, pointing toward an unstable injury that may require operative fixation. Additionally, the tibiofibular overlap on the AP view should be >6 mm; decreased overlap raises concern for syndesmotic injury.

For suspected high ankle sprains, if plain films are normal but clinical suspicion remains high (positive squeeze test, positive external rotation test, point tenderness over the AITFL), MRI is the confirmatory study. MRI directly visualizes the syndesmotic ligaments and can detect subtle interosseous membrane tears that plain films miss.

A subtle but important test-taking point: if a vignette describes medial ankle pain and swelling after a twisting injury, always think about the Maisonneuve fracture before selecting "deltoid sprain" as the answer. The correct next step is to palpate and image the proximal fibula. This tests whether you understand that medial ankle injury can be the visible component of a more dangerous proximal injury pattern.

04Management and Treatment

Summary Table

The cornerstone of ankle sprain management across all grades is functional rehabilitation with early mobilization, not prolonged immobilization. This is a frequently tested principle. Multiple trials have shown that functional treatment (bracing + early motion + physical therapy) produces superior outcomes compared to rigid casting for Grade I-III lateral ankle sprains. Casting leads to muscle atrophy, joint stiffness, and delayed return to activity without improving long-term stability.

For Grade I and II sprains, the acute phase focuses on PRICE for the first 48-72 hours. Ice application of 15-20 minutes every 2-3 hours reduces edema and provides analgesia. A semi-rigid ankle brace or lace-up support is applied as soon as tolerated. Weight-bearing is encouraged as pain allows. NSAIDs (ibuprofen 400-600 mg three times daily or naproxen 500 mg twice daily) are first-line analgesics for 5-7 days. In patients with contraindications to NSAIDs (renal disease, peptic ulcer disease, pregnancy in the third trimester), acetaminophen is used.

The rehabilitation phase is the most important determinant of outcome and recurrence risk. It progresses through three stages: first, range of motion (ankle alphabet exercises, towel stretches); second, peroneal and ankle evertor strengthening (resistance band exercises), because the peroneal muscles are the primary dynamic stabilizers against inversion; and third, proprioceptive and neuromuscular training (single-leg stance, wobble board, sport-related agility drills). Proprioceptive deficit is the primary reason ankle sprains recur, and this is a commonly tested concept.

For Grade III injuries, a brief period of immobilization in a walking boot (1-3 weeks) is reasonable, followed by the same functional rehabilitation protocol. Immediate surgical repair of acute lateral ankle sprains has not been shown to improve outcomes compared to structured conservative treatment in the general population.

High ankle (syndesmotic) sprains require longer recovery. If there is no widening of the mortise on stress or weight-bearing views, treatment involves a walking boot for 2-4 weeks with gradual progression. If imaging demonstrates mortise widening (medial clear space >4 mm) or diastasis of the tibiofibular joint, the injury is classified as unstable and requires surgical fixation with a syndesmotic screw or suture button. This distinction between stable and unstable syndesmotic injuries is the key management decision point.

Chronic mechanical instability (recurrent giving way, persistent instability after 3-6 months of rehabilitation) is the indication for surgical reconstruction, most commonly the modified Brostrom procedure (anatomic repair and tightening of the ATFL and CFL with reinforcement from the inferior extensor retinaculum).

05Differential Diagnosis and Distractors

06Traps and High-Yield Pearls

The most common way students lose points on ankle sprain questions is ordering unnecessary imaging. A vignette will describe a classic inversion injury with swelling and tenderness isolated to the ATFL region, and the patient can bear weight. The question asks for the next step, and the incorrect answer is "X-ray of the ankle." The correct answer is clinical diagnosis and functional treatment. The Ottawa Ankle Rules exist to reduce unnecessary imaging, and demonstrating that you can apply them correctly is a core competency being tested.

The second major trap involves missing a Maisonneuve fracture. A patient presents with what appears to be a medial ankle sprain, and the student selects "deltoid ligament sprain, treat conservatively." The vignette will contain a subtle clue: tenderness at the proximal fibula, or a mortise view showing widened medial clear space. The correct answer involves obtaining full-length tibia/fibula films and recognizing that this is an unstable injury pattern requiring surgical consultation, not a simple sprain.

Third, students frequently confuse lateral ankle sprains with high ankle sprains and apply the same expected recovery timeline. A vignette describing an athlete who is not improving after 2-3 weeks despite "typical sprain management" should prompt you to reconsider a syndesmotic injury. The squeeze test and external rotation test are the distinguishing exam maneuvers, and MRI is the confirmatory study. Recognizing that high ankle sprains have a substantially longer recovery (6-12 weeks vs. 1-4 weeks for lateral sprains) is a tested concept.

Finally, for chronic ankle instability questions, the tested principle is that proprioceptive rehabilitation is the first-line intervention, not surgery. Surgery (Brostrom procedure) is reserved for patients who fail a structured rehabilitation program of at least 3-6 months. The question tests whether you understand the role of neuromuscular retraining as the primary treatment for recurrent sprains before escalating to operative management.