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Updated: Mar 23 2024

High Ankle Sprain & Syndesmosis Injury

Images syndesmosis.jpg c and syndesmosis injury.jpg b plus syndesmosis.jpg fibula fracture.jpg overlap.jpg clear space.jpg space.jpg
  • summary
    • High Ankle Sprain & Syndesmosis Injuries are traumatic injuries that affect the distal tibiofibular ligaments and most commonly occur due to sudden external rotation of the ankle.
    • Diagnosis is suspected clinically with tenderness over the syndesmosis which worsens with squeezing of the tibia and fibula together at the midcalf. Plain stress radiographs of the ankle are required to diagnosis complete syndesmosis injuries with tibiofibular diastasis.
    • Treatment is nonoperative for syndesmotic sprains without diastasis or ankle instability. Operative management is indicated for patients with diastasis of the tibiofibular joint or injuries with associated fractures. 
  • Epidemiology
    • Incidence
      • 0.5% of all ankle sprains without fracture
      • 13% of all ankle fractures
  • Etiology
    • Pathophysiology
      • mechanism of injury
        • most commonly associated with external rotation injuries
      • pathoanatomy
        • external rotation forces the talus to rotate laterally and push the fibula away from tibia
        • may lead to
          • increased compressive stresses seen by the tibia
          • increased likelihood of lateral subluxation of the distal fibula
          • incongruence of the ankle joint articulation
    • Associated injuries
      • osteochondral defects (15% to 25%)
      • peroneal tendon injuries (up to 25%)
      • fractures
        • ankle
          • Weber C
          • Weber B
        • other
          • 5th metatarsal base
          • anterior process of calcaneus
          • lateral or posterior process of talus
      • deltoid ligament injury
      • loose bodies
  • Anatomy
    • See complete ligament of ankle
    • Ligaments
      • distal tibiofibular syndesmosis includes
        • anterior-inferior tibiofibular ligaments (AITFL)
          • originates from anterolateral tubercle of tibia (Chaput's)
          • inserts on anterior tubercle of fibula (Wagstaffe's)
        • posterior-inferior tibiofibular ligament (PITFL)
          • originates from posterior tubercle of tibia (Volkmann's)
          • inserts on posterior part of lateral malleolus
          • strongest component of syndesmosis
        • interosseous membrane
        • interosseous ligament (IOL)
          • distal continuation of the interosseous membrane
          • main restraint to proximal migration of the talus
        • inferior transverse ligament (ITL)
    • Syndesmosis Biomechanics
      • function
        • maintains integrity between tibia and fibula
        • resists axial, rotational, and translational forces
      • motion
        • during dorsiflexion, wider anterior talus engages the ankle mortise
          • distal fibula externally rotates and translates proximally and posterolaterally
        • during plantarflexion, the narrow posterior talus engages the ankle mortise
          • Distal fibula internally rotates and translates distally and anteromedially
      • normal gait
        • syndesmosis widens 1mm during gait
      • deltoid ligament
        • indirectly stabilizes the medial ankle mortise
  • Presentation
    • Symptoms
      • anterolateral ankle pain proximal to AITFL
      • may have medial sided ankle tenderness/swelling
      • difficulty bearing weight
        • lateral ankle sprains are often able to bear weight
    • Physical exam
      • palpation
        • syndesmosis tenderness
          • single best predictor for return to play
      • provocative tests
        • squeeze test (Hopkin's)
          • compression of tibia and fibula at midcalf level causes pain at syndesmosis
        • external rotation stress test
          • pain over syndesmosis is elicited with external rotation/dorsiflexion of the foot with knee and hip flexed to 90 degrees
        • Cotton
          • widening of the syndesmosis with lateral pull on the fibula
        • fibular translation
          • anterior and posterior drawer force to the fibula with the tibia stabilized causes increased translation of the fibula and pain
  • Imaging
    • Radiographs
      • recommended views
        • AP, lateral, mortise view of ankle
        • AP, lateral of entire tibia
          • may show fracture of proximal fibula
          • abnormal lateral tibiofibular ratio is reliable way of diagnosing injury
      • optional views
        • external rotation stress radiograph
        • gravity stress view
          • will help determine competence of deltoid ligament
        • contralateral ankle radiographs
          • may help clarify syndesmosis widening versus normal anatomic variant
      • findings
        • decreased tibiofibular overlap
          • normal >6 mm on AP view
          • normal >1 mm on mortise view
        • increased medial clear space
          • normal less than or equal to 4 mm
        • increased tibiofibular clear space
          • normal <6 mm on both AP and mortise views
    • CT
      • indications
        • clinical suspicion of syndesmotic injury with normal radiographs
        • useful post-operatively to assess reduction of syndesmosis after fixation
      • sensitivity and specificity
        • more sensitive than radiographs for detecting minor degrees of syndesmotic injury
    • MRI
      • indications
        • clinical suspicion of syndesmotic injury with normal radiographs
      • sensitivity and specificity
        • lambda sign described as being highly sensitive and specific for detecting syndesmotic injury
  • Treatment
    • Nonoperative
      • non-weight-bearing CAM boot or cast for 2 to 3 weeks
        • indications
          • syndesmotic sprain without diastasis or ankle instability
        • technique
          • delayed weight-bearing until pain free
          • physical therapy program using a brace that limits external rotation
        • outcomes
          • typically display a notoriously prolonged and highly variable recovery period
          • recovery may extend to twice that of standard ankle sprain
    • Operative
      • syndesmosis screw fixation
        • indications
          • syndesmotic sprain (without fracture) with instability on stress radiographs
          • syndesmotic sprain refractory to conservative treatment
          • syndesmotic injury with associated fracture that remains unstable after fixation of fracture
        • outcomes
          • excellent functional outcomes if syndesmosis is accurately reduced
          • often requires removal
      • syndesmosis fixation with suture button
        • indications
          • same as for screw fixation
        • technique
          • fiberwire suture with two buttons tensioned around the syndesmosis
          • may be performed in addition to a screw
        • outcomes
          • early results promising with some showing earlier return to activity when compared to screw fixation
          • does not require removal
  • Techniques
    • Syndesmotic screw fixation
      • technique
        • two 3.5 or 4.5 mm syndesmotic screws through 3 or 4 cortices placed 2-5 cm above the plafond
          • screw material
            • no difference between stainless-steel and titanium screws
            • bioabsorbable screws with similar outcomes
          • number of cortices
            • no difference between 3 or 4 cortices
          • number of screws
            • fixation with two screws is preferable
          • position of foot during fixation
            • a recent study challenges the principle of holding the ankle in maximal dorsiflexion to avoid overtightening
      • postoperative
        • typically non-weight-bearing for 6-12 weeks
          • may prolong if screw breakage is a concern
  • Complications
    • Posttraumatic tibiofibular synostosis
      • incidence
        • ~10% after Weber C ankle fractures
      • treatment
        • surgical excision
          • reserved for persistent pain that fails to respond to nonsurgical management
          • ossification must be "cold" on bone scintigraphy prior to removal
  • Prognosis
    • Missed injuries may result in end-stage ankle arthritis
    • Excellent functional outcomes if syndesmosis is anatomically reduced
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