Sprained Ankle Differential Diagnosis: A Comprehensive Guide for Clinicians

Introduction

Acute ankle sprains are a ubiquitous presentation in primary care, sports medicine clinics, and emergency departments. These injuries, while frequently perceived as minor, can lead to significant short-term discomfort, recurrent episodes, and persistent functional limitations if not properly evaluated and managed. A crucial aspect of effective ankle sprain management is accurate diagnosis, which necessitates a robust understanding of the Sprained Ankle Differential Diagnosis. This article provides an in-depth review of ankle sprains, emphasizing the importance of differential diagnosis to ensure appropriate treatment and minimize the risk of complications. Effective initial assessment and treatment are paramount in mitigating the potential for long-term issues such as chronic ankle instability, the development of arthritis, and prolonged disability.

Etiology of Ankle Sprains

Ankle sprains predominantly involve injuries to the ligaments of the lateral ankle complex, most commonly the anterior talofibular ligament (ATFL) and the calcaneofibular ligament (CFL). The specific ligaments injured and the severity of the sprain are dictated by the mechanism of injury, which can range from low-energy events to high-impact trauma. Factors such as the foot’s position at the time of injury and the rotational forces applied to the ankle joint play critical roles. Low-grade sprains (Grade I and II) typically result in stretching or microscopic tears within the ligaments. In contrast, high-grade sprains (Grade III) involve more substantial ligamentous damage and may include injury to the syndesmotic ligaments, which connect the tibia and fibula. In high-energy scenarios, the injury mechanism can also lead to tendon ruptures and fractures of the ankle and foot bones, further complicating the sprained ankle differential diagnosis.

Epidemiology of Ankle Sprains

Ankle sprains are an incredibly common injury, with over two million cases treated annually in emergency departments across the United States and the United Kingdom alone. They represent the most frequent injury encountered in sports activities, highlighting their prevalence across diverse populations. While the incidence rates may vary slightly between male and female athletes depending on the specific sport, studies comparing sports with comparable participation levels show similar rates of ankle sprains in both sexes. Notably, research indicates a high rate of recurrence and persistent instability following an initial ankle sprain. Up to 40% of individuals who experience a lateral ankle sprain report ongoing symptoms, repeated sprains, and chronic lateral ankle instability, underscoring the importance of effective initial management and accurate sprained ankle differential diagnosis to prevent these long-term sequelae.

Pathophysiology of Ankle Sprains

The ankle joint is a complex structure formed by the articulation of the tibia, fibula, and talus. Stability is provided by three primary ligamentous systems: the lateral ligament complex, the medial deltoid ligament, and the syndesmotic ligaments. The most common mechanism of ankle sprain is ankle inversion, which places stress on the lateral ligament complex. This complex comprises the ATFL, CFL, and posterior talofibular ligament (PTFL), which are typically injured in that order of frequency. The ATFL, being the weakest of the lateral ligaments, is involved in approximately 70% of lateral ankle sprains, usually resulting from plantar flexion and inversion forces. The CFL is more frequently injured with dorsiflexion and inversion mechanisms. The PTFL is the least commonly injured lateral ligament.

The medial deltoid ligament, the strongest ankle ligament, is injured less frequently, typically with eversion forces. Isolated deltoid ligament injuries are rare. The superficial deltoid limits abduction of the talus, while the deep deltoid restricts external rotation.

The syndesmotic ligaments stabilize the distal tibia and fibula. Syndesmotic injuries, often termed “high ankle sprains,” are less common than typical ankle sprains. These injuries usually result from significant force, most often external rotation and/or dorsiflexion of the ankle, and are more prevalent in athletes. Understanding the specific anatomical structures involved and the mechanisms of injury is critical for accurate diagnosis and for differentiating ankle sprains from other conditions in the sprained ankle differential diagnosis.

History and Physical Examination for Ankle Sprains

Evaluating an ankle injury begins with a thorough history, focusing on the mechanism of injury. Clinicians should determine if the injury involved inversion, eversion, rotational stress, or direct impact. A history of prior ankle injuries and the patient’s ability to bear weight immediately after the injury and at the time of evaluation are also important factors to consider.

The physical examination should include careful inspection, palpation, and functional testing. Palpate each of the lateral ligaments (ATFL, CFL, PTFL) around the lateral malleolus and the medial ankle structures. Crucially, palpate the proximal fibula to assess for pain or crepitus, which may indicate a Maisonneuve fracture. This fracture pattern involves a high ankle injury with external rotation, potentially combined with inversion or eversion, leading to a proximal fibular fracture, syndesmotic disruption, and deltoid ligament injury.

Examine the foot for associated injuries, particularly by palpating the base of the fifth metatarsal, the navicular, and the midfoot to rule out Lisfranc injuries. Plantar ecchymosis may be a visual indicator of a Lisfranc injury.

Syndesmotic sprains can be assessed with the squeeze test and the external rotation stress test. A positive squeeze test, indicated by pain at the tibiofibular syndesmosis upon compression of the mid-calf, suggests syndesmotic involvement. The external rotation stress test involves externally rotating a slightly dorsiflexed foot; pain with this maneuver also suggests a syndesmotic sprain. These tests can be performed under fluoroscopy or compared with static radiographs taken in a mortise view position. Another specialized test is the gravity stress view, performed in lateral decubitus position to assess mortise widening.

The anterior drawer test assesses ATFL stability. Stabilize the distal leg and pull the calcaneus forward with the foot in 20 degrees of plantar flexion. Greater than 1 cm of anterior translation compared to the uninjured side suggests ATFL laxity.

The talar tilt test evaluates lateral ankle ligament laxity, particularly CFL integrity. Stabilize the distal leg in neutral position and invert the ankle, comparing the degree of inversion to the uninjured side. It’s important to note that both the talar tilt and anterior drawer tests may be falsely negative acutely due to pain and muscle spasm. A detailed history and physical examination are vital in narrowing down the sprained ankle differential diagnosis and guiding further evaluation.

Evaluation and Diagnostic Tools for Ankle Sprains

The Ottawa ankle rules are a valuable clinical decision tool to determine the necessity of radiographs in patients with ankle injuries, applicable to both adults and children over five years old.

According to the Ottawa ankle rules, ankle radiographs are indicated if there is pain in the malleolar region plus any of the following:

• Tenderness along the posterior edge or tip of the lateral malleolus (distal 6 cm)
• Tenderness along the posterior edge or tip of the medial malleolus (distal 6 cm)
• Inability to bear weight immediately after injury and take four steps at evaluation

Foot radiographs are indicated if there is midfoot pain and any of the following:

• Tenderness at the base of the fifth metatarsal
• Tenderness over the navicular bone
• Inability to bear weight immediately after injury and take four steps at evaluation

These rules are not applicable in cases with distracting injuries, intoxication, diminished lower extremity sensation, head injuries, or conditions hindering patient cooperation. While the Ottawa ankle rules have moderate specificity, they exhibit high sensitivity for detecting ankle fractures, with less than 2% of patients cleared by these rules found to have a fracture.

A standard ankle x-ray series includes anteroposterior, lateral, and mortise views. Foot series include anteroposterior, lateral, and oblique views. Advanced imaging, such as MRI, may be considered in cases of persistent symptoms, suspected ligamentous injuries not evident on radiographs, or to further evaluate conditions considered in the sprained ankle differential diagnosis, such as osteochondral lesions or tendon injuries.

Treatment and Management of Ankle Sprains

Initial management of ankle sprains centers on the PRICE protocol: Protection, Rest, Ice, Compression, and Elevation. Resting the injured ankle for the first 72 hours, followed by a gradual return to activity as tolerated, is generally recommended. Crutches can be used for initial comfort and non-weight-bearing. Early weight-bearing with support, using elastic compression wraps, walking boots, aircasts, or walking casts, has been shown to improve outcomes compared to immobilization, facilitating faster return to sports and work, reducing persistent swelling, improving range of motion, and increasing patient satisfaction.

Compression can be achieved with elastic bandages or various ankle supports. Elevating the ankle above heart level as much as possible for the first 24-48 hours helps to minimize swelling. Range of motion exercises should be initiated as pain and swelling subside. Pain management can be achieved with nonsteroidal anti-inflammatory drugs (NSAIDs) or acetaminophen.

Early functional rehabilitation programs are crucial, focusing initially on restoring range of motion, followed by proprioceptive and neuromuscular training, and strengthening exercises, particularly of the peroneal muscles, to prevent recurrent injuries. Strengthening should begin once swelling and pain have decreased and full range of motion (active and passive) is achieved. Functional bracing should be used during the strengthening phase and upon return to activity.

Mild to moderate ankle sprains typically resolve within 7 to 15 days. Persistent symptoms beyond this timeframe warrant reevaluation. Complete symptom resolution is necessary before returning to sports. For competitive athletes, specialist review by a sports medicine physician is advisable for all but the mildest sprains before returning to play to ensure full recovery and minimize the risk of reinjury and chronic ankle instability.

Patients with ligamentous laxity should be immobilized, provided with crutches for non-weight-bearing ambulation, and referred to a sports medicine specialist or orthopedic surgeon. Referral is essential as higher-energy injuries can be associated with osteochondral defects, peroneal tendon injuries, intra-articular loose bodies, and fractures, all of which must be considered in the sprained ankle differential diagnosis.

Suspected syndesmotic injuries also require specialist referral due to their prolonged recovery and potential need for surgical intervention. Acute syndesmotic injuries with diastasis and instability on examination and stress radiographs may require surgical fixation using screws or tightrope techniques. Chronic ankle instability should be referred for ligamentous reconstruction.

Sprained Ankle Differential Diagnosis

The sprained ankle differential diagnosis is broad and includes several conditions that can mimic the symptoms of an ankle sprain. Accurate differentiation is crucial for appropriate management and to avoid missing more serious injuries. Key conditions to consider include:

• High Ankle Sprain (Syndesmotic Injury): While technically a type of ankle sprain, syndesmotic injuries involve the ligaments connecting the tibia and fibula, are often more severe, and have a longer recovery. Differentiating features include mechanism of injury (external rotation/dorsiflexion), location of pain (above the ankle joint), and positive squeeze and external rotation tests.

• Ankle Fractures: Fractures of the malleoli, distal tibia, or talus must be ruled out, especially in higher-energy injuries or when Ottawa ankle rules suggest radiography. Point tenderness over bony prominences, inability to bear weight, and radiographic findings are key differentiators.

• Maisonneuve Fracture: This complex injury involves a proximal fibular fracture in conjunction with a distal ankle injury (syndesmotic and deltoid ligament disruption). Proximal fibular pain, even with normal ankle radiographs, should raise suspicion. Palpation of the proximal fibula is critical in the physical exam to rule this out.

• Subtalar Dislocation: Dislocation of the subtalar joint can occur with high-energy trauma and present with significant deformity and pain. Radiographs are essential for diagnosis.

• Lisfranc Injuries: These injuries involve the ligaments and bones of the midfoot and can be subtle. Midfoot pain, plantar ecchymosis, and tenderness, particularly with inability to bear weight, should prompt consideration. Weight-bearing radiographs are often necessary to diagnose Lisfranc injuries.

• Peroneal Tendon Injuries: Peroneal tendonitis, subluxation, or tears can occur with ankle inversion injuries and cause lateral ankle pain. Pain posterior to the lateral malleolus, pain with resisted eversion, and potential for snapping or instability differentiate these.

• Osteochondral Lesions of the Talus (OLTs): These cartilage and bone injuries within the ankle joint can result from ankle sprains and cause persistent pain, clicking, or catching. MRI is the diagnostic modality of choice for OLTs.

• Achilles Tendon Rupture: While typically presenting with posterior heel pain, Achilles tendon ruptures can sometimes be confused with ankle injuries. The Thompson test is crucial to assess Achilles tendon integrity.

• Nerve Entrapment Syndromes: Conditions such as tarsal tunnel syndrome can cause pain radiating into the ankle and foot, mimicking some symptoms of ankle sprains. Neurological examination and specific nerve compression tests are important in differentiation.

A systematic approach to history, physical examination, and appropriate use of diagnostic tools is essential to effectively navigate the sprained ankle differential diagnosis and ensure patients receive the correct treatment.

Prognosis of Ankle Sprains

The prognosis for most ankle sprains is generally good with nonoperative management. However, recurrent instability and associated complications can occur in a significant proportion of patients, ranging from 25% to 40%. Early recognition of potential concomitant injuries and timely referral to orthopedic or sports medicine specialists are crucial to minimize the risk of long-term detrimental outcomes and chronic ankle problems.

Complications of Ankle Sprains

Potential complications of ankle sprains, particularly if not properly managed or if more severe injuries are missed in the sprained ankle differential diagnosis, include:

• Chronic Pain and Disability: Persistent pain and functional limitations can significantly impact quality of life.
• Recurrent Ankle Instability: Repeated sprains and a feeling of “giving way” in the ankle.
• Osteochondral Defects of the Talus (OLTs): Damage to the cartilage and underlying bone in the ankle joint, leading to pain and potential arthritis.
• Peroneal Tendon Injuries: Ongoing issues with the peroneal tendons, including pain, weakness, and instability.
• Neurovascular Injury: Rare, but possible, damage to nerves or blood vessels.
• Tibiotalar Arthritis: Degenerative joint disease of the ankle joint.
• Pantalar Arthritis: Arthritis affecting multiple joints in the hindfoot and ankle.

Early and appropriate management, guided by accurate diagnosis and a thorough sprained ankle differential diagnosis, is key to minimizing the risk of these complications.

Pearls and Other Important Considerations

A critical injury to consider in the sprained ankle differential diagnosis, often mistaken for a simple ankle sprain, is the Maisonneuve fracture. This injury typically occurs with an eversion mechanism, resulting in deltoid ligament or medial malleolar fracture, syndesmotic disruption, and a fracture of the proximal fibula. Due to the complete ligamentous disruption, surgical fixation is usually required. Importantly, ankle radiographs may appear normal in the absence of a medial malleolar fracture, and the ankle mortise widening may not be evident. Weight-bearing radiographs can demonstrate the widened mortise but are often not obtained unless this injury is suspected. Proximal calf tenderness should raise suspicion for a Maisonneuve fracture, prompting radiographs of the tibia and fibula. Maintaining a high index of suspicion for less obvious but serious injuries is crucial in the evaluation of ankle trauma.

Enhancing Healthcare Team Outcomes in Ankle Sprain Management

Ankle sprains are a common musculoskeletal injury frequently seen in emergency departments and sports medicine settings. Optimal management requires a collaborative, interprofessional team approach. Prevention is paramount, emphasizing patient education on stretching and conditioning to minimize the severity of ankle sprains. Healthcare professionals, including nurses, should educate patients on the importance of warm-up exercises, proper footwear, and the use of ankle braces or taping for protection, especially during sports activities. For patients with ankle sprains, referral to physical therapy is essential before returning to sports to ensure proper rehabilitation and reduce the risk of recurrence. Effective communication and collaboration among physicians, nurses, physical therapists, and athletic trainers are vital to optimize patient outcomes in ankle sprain management and to ensure accurate sprained ankle differential diagnosis and treatment.

Review Questions

Figure 1: Grade 3 Ankle Sprain Talar Tilt Test

Grade 3 ankle sprain visualized via talar tilt stress radiograph, demonstrating varus talar positioning relative to the tibia.

Figure 2: Deltoid and Syndesmotic Insufficiency

Medial gutter widening indicating deltoid and syndesmotic insufficiency in an acute ankle sprain.

Figure 3: Grade 3 Ankle Sprain Anterior Drawer Test

Grade 3 ankle sprain shown on anterior drawer test stress radiograph, highlighting anterior talar translation on the tibia.

References

1.Koutras C, Antoniou SA, Jäger M, Heep H. Acute Injuries Sustained By Racing Drivers: A Cross-Sectional Study. Acta Orthop Belg. 2017 Dec;83(4):512-520. [PubMed: 30423656]

2.Swords M, Brilhault J, Sands A. Acute and Chronic Syndesmotic Injury: The Authors’ Approach to Treatment. Foot Ankle Clin. 2018 Dec;23(4):625-637. [PubMed: 30414657]

3.Slater K. Acute Lateral Ankle Instability. Foot Ankle Clin. 2018 Dec;23(4):523-537. [PubMed: 30414650]

4.Carto C, Lezak B, Varacallo M. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 8, 2023. Anatomy, Bony Pelvis and Lower Limb: Distal Tibiofibular Joint (Tibiofibular Syndesmosis) [PMC free article: PMC547655] [PubMed: 31613435]

5.Bridgman SA, Clement D, Downing A, Walley G, Phair I, Maffulli N. Population based epidemiology of ankle sprains attending accident and emergency units in the West Midlands of England, and a survey of UK practice for severe ankle sprains. Emerg Med J. 2003 Nov;20(6):508-10. [PMC free article: PMC1726220] [PubMed: 14623833]

6.Doherty C, Bleakley C, Delahunt E, Holden S. Treatment and prevention of acute and recurrent ankle sprain: an overview of systematic reviews with meta-analysis. Br J Sports Med. 2017 Jan;51(2):113-125. [PubMed: 28053200]

7.Wang DY, Jiao C, Ao YF, Yu JK, Guo QW, Xie X, Chen LX, Zhao F, Pi YB, Li N, Hu YL, Jiang D. Risk Factors for Osteochondral Lesions and Osteophytes in Chronic Lateral Ankle Instability: A Case Series of 1169 Patients. Orthop J Sports Med. 2020 May;8(5):2325967120922821. [PMC free article: PMC7252382] [PubMed: 32518802]

8.Mauntel TC, Wikstrom EA, Roos KG, Djoko A, Dompier TP, Kerr ZY. The Epidemiology of High Ankle Sprains in National Collegiate Athletic Association Sports. Am J Sports Med. 2017 Jul;45(9):2156-2163. [PubMed: 28423285]

9.Ponkilainen VT, Laine HJ, Mäenpää HM, Mattila VM, Haapasalo HH. Incidence and Characteristics of Midfoot Injuries. Foot Ankle Int. 2019 Jan;40(1):105-112. [PubMed: 30269512]

10.Khan IA, Varacallo M. StatPearls [Internet]. StatPearls Publishing; Treasure Island (FL): Aug 8, 2023. Anatomy, Bony Pelvis and Lower Limb, Foot Talus. [PubMed: 31082130]

11.Ehrlichman LK, Gonzalez TA, Macaulay AA, Ghorbanhoseini M, Kwon JY. Gravity Reduction View: A Radiographic Technique for the Evaluation and Management of Weber B Fibula Fractures. Arch Bone Jt Surg. 2017 Mar;5(2):89-95. [PMC free article: PMC5410750] [PubMed: 28497098]

12.Kerkhoffs GM, Rowe BH, Assendelft WJ, Kelly K, Struijs PA, van Dijk CN. Immobilisation and functional treatment for acute lateral ankle ligament injuries in adults. Cochrane Database Syst Rev. 2002;(3):CD003762. [PubMed: 12137710]

13.Vuurberg G, Hoorntje A, Wink LM, van der Doelen BFW, van den Bekerom MP, Dekker R, van Dijk CN, Krips R, Loogman MCM, Ridderikhof ML, Smithuis FF, Stufkens SAS, Verhagen EALM, de Bie RA, Kerkhoffs GMMJ. Diagnosis, treatment and prevention of ankle sprains: update of an evidence-based clinical guideline. Br J Sports Med. 2018 Aug;52(15):956. [PubMed: 29514819]

14.Strudwick K, McPhee M, Bell A, Martin-Khan M, Russell T. Review article: Best practice management of common ankle and foot injuries in the emergency department (part 2 of the musculoskeletal injuries rapid review series). Emerg Med Australas. 2018 Apr;30(2):152-180. [PubMed: 29235235]

15.Wight L, Owen D, Goldbloom D, Knupp M. Pure Ankle Dislocation: A systematic review of the literature and estimation of incidence. Injury. 2017 Oct;48(10):2027-2034. [PubMed: 28826653]

16.Sprouse RA, McLaughlin AM, Harris GD. Braces and Splints for Common Musculoskeletal Conditions. Am Fam Physician. 2018 Nov 15;98(10):570-576. [PubMed: 30365284]

17.Barelds I, van den Broek AG, Huisstede BMA. Ankle Bracing is Effective for Primary and Secondary Prevention of Acute Ankle Injuries in Athletes: A Systematic Review and Meta-Analyses. Sports Med. 2018 Dec;48(12):2775-2784. [PubMed: 30298478]

Disclosures: Scott Melanson declares no relevant financial relationships with ineligible companies. Victoria Shuman declares no relevant financial relationships with ineligible companies.