Ankle Sprain Workup

Updated: Jul 24, 2017
  • Author: Craig C Young, MD; Chief Editor: Sherwin SW Ho, MD  more...
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Workup

Approach Considerations

Plain radiographs may be clinically indicated to diagnose a fracture of the ankle or foot. Ankle stress radiographs contribute little to the management of acute ankle sprains because surgical treatment of the acute sprain is rarely indicated. Abnormal swelling or clinical ankle instability in an acute sprain may be documented with bilateral stress radiographs of the ankle.

MRI is not indicated unless unusual features are present, such as extensive swelling, ecchymosis, or pain, that suggest an osteochondral lesion not observed on plain radiographs. Even if MRI scans demonstrate bone bruising or actual articular cartilage damage, conservative ankle sprain treatment is indicated initially.

The National Athletic Trainers’ Association (NATA) noted the following regarding imaging studies [40, 41] :

  • The Ottawa Ankle Rules remain valid for determining the need for x-rays
  • Stress radiography is unreliable for detecting acute injuries to the ankle and midfoot
  • Magnetic resonance imaging (MRI) and computed tomography (CT) scanning accurately detect talar osteochondral lesions; both techniques are also more accurate than arthrography and tenography for detecting lateral ligamentous injury, especially when arthrography and tenography are performed 48 hours post injury
  • MRI is reliable for detecting acute tears of the anterior talofibular ligament and calcaneofibular ligament; diagnostic ultrasonography is useful but less accurate and sensitive than MRI
  • MRI is highly sensitive, specific, and accurate after acute trauma for determining the level of injury to the ankle syndesmotic ligaments
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Plain Radiographic Imaging

The use of radiographs in patients with ankle injuries is guided by the Ottawa Ankle Rules. These rules state that an ankle radiographic series is required only if the patient has pain in the malleolar zone and any of the following 3 findings [42, 43, 44] :

  • Bone tenderness at the posterior edge or tip of the lateral malleolus (ie, the lower 6 cm of the fibula)
  • Bone tenderness at the posterior edge or tip of the medial malleolus (ie, the lower 6 cm of the tibia)
  • Inability to bear weight immediately after the injury and in the emergency department

The Ottawa Ankle Rules state that a foot radiographic series is required only if the patient has any pain in the midfoot zone and any of the following 3 findings:

  • Bone tenderness at the base of the fifth metatarsal
  • Bone tenderness at the navicular bone
  • Inability to bear weight immediately after the injury and in the emergency department

The Ottawa Ankle Rules are contingent upon the patient presenting within 10 days of the injury. Although they were not originally intended for patients younger than age 18 years, a meta-analysis of 12 studies showed that the Ottawa foot and ankle rules can be reliably used to exclude fractures in children older than age 5 years. The studies included a total of 3,130 patients and identified 671 fractures, resulting in a prevalence of 21.4%. Demonstrating a pooled sensitivity of 98.5% and a missed fracture rate of 1.2%, the report indicated that the Ottawa foot and ankle rules are useful (level 2 evidence) for excluding fractures in children. [8] Another study suggests they may be useful for children as young as 2 years. [9]

Radiographic studies of the ankle should include the following views:

  • An anteroposterior (AP) film with the ankle in 5-15° of adduction
  • A true lateral film
  • A 45° oblique film with the ankle in dorsiflexion (ie, Mortise view)
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Stress-View Radiographic Imaging

Stress radiographic films may provide further assessment for ankle stability; however, patient cooperation may be limited, depending on the severity of the injury. Stress-view exams include the talar tilt and anterior drawer tests. Because of muscular guarding due to patient pain, the accuracy of these tests is dramatically increased with the use of local anesthesia. Compare the stress views with those of the uninvolved ankle in both tests. Other variables in determining the reliability of these tests include the degree of patient relaxation and cooperation, the amount of force used, the angle of ankle flexion, and the amount of laxity in the uninvolved side. (See Clinical Presentation.)

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Computed Tomography Scanning

Computed tomography (CT) scanning may be indicated if imaging of soft tissues is warranted or if bone imaging beyond radiography is indicated. CT scanning is useful for evaluating osteochondritis dissecans and stress fractures. In complex injuries, 3-dimensional CT scanning may be useful.

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MRI

MRI may be a useful evaluation when a syndesmotic or high ankle sprain is suspected or if osteochondrosis or meniscoid injury is suspected in patients with a history of recurrent ankle sprains and chronic pain. [6, 5] However, caution must be used when evaluating the findings on MRI since a study of asymptomatic patients revealed that approximately 30% had findings consistent with abnormal anterior talofibular ligaments and peroneal muscles. [45]

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Arthrographic Imaging

Ankle arthrograms may be useful for determining capsular damage and the number of ankle ligaments damaged; however, arthrography is indicated only if surgery is needed, and the criteria for surgery to repair double lateral ligament complete tears are still under debate. Staples found that arthrograms provide the most preoperative information. [46, 47]

Ankle arthrograms are not indicated in every patient considered for surgical treatment. Marked clinical instability in a young individual with great physical demands being considered for surgery requires an ankle arthrogram.

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Bone Scanning

A bone scan can detect subtle bone abnormalities (e.g., stress fracture, osteochondral defects). A bone scan can also detect syndesmotic disruption.

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