It has been calculated that 45 million children between 6 and 18 participate in organized athletics1 with 4.5 million pediatric sports-related injuries annually in the United States.2 Pediatric ankle injuries result in >2 million emergency department visits in Canada and the United States each year.3 Furthermore, ankle fractures in children are the third most common fracture involving the growth plate after finger and distal radial physeal fractures.4,5
The syndesmosis is a complex of ligaments that joins the distal fibula to the distal tibia at the level of the ankle joint. The fibula sits in a groove created by the anterior and posterior tibial processes, which provide bony stability to the syndesmosis.6 The ligaments of the distal tibiofibular (TF) syndesmosis include the anterior-inferior tibiofibular ligament (AITFL), the posterior-inferior tibiofibular ligament (PITFL), the inferior transverse ligament (or distal portion of the PITFL), and the interosseous ligament (IOL).6,7 The deep fibers of the deltoid ligament provide additional stability to the complex.8 The AITFL is trapezoidal in shape and runs in an oblique direction from the anterolateral distal tibia to the anteromedial distal fibula.9 The PITFL runs horizontally from the posterolateral distal tibia to the posteromedial distal fibula.10 Stability of the syndesmosis is provided by primarily by the AITFL (35% strength) and the PIFTFL (42% strength).11 Cadaveric biomechanical studies have shown that sectioning the AITFL produces 2.3 mm of syndesmotic diastasis, sectioning the PITFL leads to 2.8 mm of diastasis and that 0.5 mm of diastasis occurs for every 2 cm of the IOL that is violated.12
Injuries to the ankle syndesmosis, commonly referred to as “high ankle sprains,” can affect both high-level and recreational athletes and have been related to delayed return to play, persistent pain, and significant long-term disability; however, little has been written about this injury in the pediatric population.9 The most common mechanism of injury involves external rotation and excessive dorsiflexion of the foot, with injury to at least one of the AITFL, PITFL, or IOL.9,13 Children most at risk for syndesmotic injuries are those who participate in football, soccer, and other sports that involve cutting and pivoting or those involved in sports with rigid immobilization of the ankle (skiing, hockey).9,14 The reported incidence of syndesmotic ankle sprains is anywhere from 1% to 11% in adult populations15,16; recently Kramer et al17 reported an incidence of pediatric syndesmotic injuries to be approximately 1% of all pediatric ankle injuries.
PRINCIPLES OF MANAGEMENT
External rotation of the foot is the most common injury mechanism associated with ankle syndesmosis injuries. Typical symptoms include: pain localized to the syndesmosis above the ankle joint, pain with active or passive external rotation of the foot, and pain with forced dorsiflexion. Special tests for the evaluation of syndesmosis injuries include the squeeze test, the external rotation test, the fibula-translation test, the Cotton test, and the crossed-leg test.18 Although a positive test should arouse suspicion to this injury, there are no studies demonstrating single test superiority at predicting syndesmosis injury or severity.9,19–21 In addition, up to 20% of syndesmotic injuries may go undetected on clinical examination alone.22
The presence of any ankle fracture should prompt careful evaluation of the syndesmosis. Kramer et al17 in reviewing 220 syndesmotic injuries in children and adolescents found that children with a syndesmosis injury seen in conjunction with an ankle fracture had a 44 times greater odds of requiring surgical fixation of the syndesmosis. The authors also found that an open physis may be protective as patients with closed physes and syndesmosis injuries were more likely to require operative fixation of their syndesmosis.17 It is believed that when the distal tibial physis is open, these injuries generally result in Salter-Harris type I or II injuries of the distal tibia and/or fibula, but as the physis closes from central medial to anterolateral at puberty, transitional fractures and ligamentous injuries become more likely.23
Imaging of syndesmosis injuries should begin with plain radiographs to rule out fracture and to look for the presence of static diastasis of the syndesmosis. Specifically, the TF overlap [on anteroposterior (AP) and mortise radiographs], TF clear space (on AP and mortise), and medial clear space (MCS) (on mortise only) are commonly measured parameters for syndesmotic injury (Fig. 1A, B). Static diastasis generally refers to lateral translation of the fibula and has been defined with radiographic parameters in adults such as MCS widening (>4 mm), decreased TF overlap or increased TF clear space (>6 mm).9,24,25 Similar parameters have not yet been established in children and adolescents and in fact Bozic et al26 showed that loss of TF overlap or increased TF clear space may not be applicable in the skeletally immature patient due to delayed ossification of the incisura fibularis. Other authors have noted that the lack of TF overlap on the mortise view may be a normal variant, especially in skeletally immature patients.27 In Kramer et al’s17 cohort, significant differences were noted between operative and nonoperative groups with regard to all 3 radiographic parameters; however, patients with an MCS >5 mm had an 8 times greater odds for requiring surgical intervention demonstrating this could be the most reliable indicator in the younger age group. Comparison with other parts of the ankle or to the contralateral ankle may be necessary in the pediatric population if suspicion exists.
Classic radiographic measurements may be inadequate to accurately assess the syndesmosis.28 Advanced imaging may better show the 3 dimensional distal TF relationship. Nault et al29 validated the use of computed tomographic (CT) scans to define 6 measurements and 2 angles that describe the distal TF anatomy in uninjured ankles with regard to rotation, lateral translation, and AP position of the fibula at the syndesmosis. In addition, the use of magnetic resonance imaging (MRI) has increased in pediatric syndesmosis injuries; however, MRI findings have yet to be correlated with clear surgical indications.30 In adults, MRI has been found to be 93% to 100% sensitive and specific for both AITFL and PITFL tears.30 In Kramer et al’s cohort, MRI was more often utilized in the nonoperative group, to confirm an absence of syndesmotic injury and guide nonoperative management.17
Syndesmosis anatomy may vary with growth, which is especially important in the pediatric population. Nault et al31 attempted to define the normal anatomy of the immature and growing syndesmosis through a retrospective imaging study utilizing MRI criteria similar to the CT criteria referreed above. The authors found that with growth lateral fibular translation increases, fibular external rotation decreases and the AP ratio at the level of the physis remains the same.31
The primary goal in the management of syndesmotic injuries is to achieve stable, anatomic alignment of the ankle joint, regardless of patient age, or method of management.32 Most agree that ligamentous syndesmotic injuries, which retain the normal bony relationship of the distal TF joint, can be managed without surgery. Nonoperative treatment of syndesmosis injuries often begins with some form of ankle immobilization for 3 to 6 weeks to allow the ligaments to heal. Subsequent rehabilitation then focuses on the initial return to normal gait with restoration of ankle mobility, strength and function followed by more advanced training, neuromuscular control, and return to sport specific activities.19
Most authors agree that syndesmotic injuries with clear disruption and displacement of the TF joint on static radiographs require formal syndesmotic reduction and stabilization. The management of patients with borderline radiographic diastasis, or with MRI proven multiple syndesmotic ligament injury without clear radiographic diastasis is controversial. Some authors recommend conservative management while others support operative intervention.9,25,33 Factors such as a combined medial ligamentous injury, talar shift with widened MCS, or a high fibula fracture (Maisonneuve fracture) may imply syndesmotic instability and support operative intervention.34 In some cases, formal examination under anesthesia may be necessary to assess the stability of the syndesmosis under fluoroscopy, yet the method or degree of syndesmotic instability has not been established.25 Few of these reports with recommendations have focused on the pediatric patient with a syndesmotic injury.
There are several described techniques for syndesmotic reduction in both adults and children. Indirect reduction involves the use of a reduction clamp between the distal fibula and tibia without direct visualization of the syndesmosis.35 The alternative direct approach involves open visualization and palpation of the anterior aspect of the syndesmosis to gauge reduction.36 Once reduced, the syndesmosis is stabilized to allow for ligamentous healing with preservation of the bony alignment of the syndesmosis and ankle mortise. The most common fixation technique involves placement of a screw or screws across the distal syndesmosis. One or 2 screws are used to position and hold but not compress the syndesmosis. Because the fibula is posterior to the tibia anatomically, the syndesmotic screw should be angled from posterolateral to anteromedial to engage the tibia (angled 30 anteriorly) and be placed parallel to the ankle joint approximately 2 to 4 cm proximal to the tibial plafond.37 There is no evidence to suggest that 1 versus 2 screws or 3 versus 4 cortices per screw result in any significant long-term functional difference.38 Finally, the choice of the implant size (3.5 vs. 4.5 mm) is probably best directed by the size of the fibula. To assess reduction in skeletally immature patients, comparison with the other ankle can be invaluable. Gardner et al39 concluded that based on postoperative CT scans, up to 42% of syndesmosis are malreduced after formal open reduction and internal fixation of associated ankle fractures.
Screw removal is at the discretion of the operating surgeon. Screw breakage has been reported in 7% to 29% of patients, with smaller screws (3.5 mm) more likely to break than larger screws (4.0 or 4.5 mm).22 Timing for screw removal is also controversial with most recommending removal between 6 and 12 weeks postoperatively. Screw removal at 6 weeks after surgery reduces rate of implant failure but increases the rate of recurrent diastasis.22
Alternative methods of fixation that do not require future hardware removal such as a suture-button fixation have been reported. Suture-button fixation has been studied in the adult literature with potential advantages of greater anatomic mobility of the syndesmosis, quicker return to weight bearing (without fear of screw breakage), and lack of need for hardware removal.33 However, long-term outcomes following suture-button fixation are lacking.
Pediatric syndesmosis ankle injuries are rare events, which require physician vigilance for accurate diagnosis. They most often occur in patients with a closed distal tibial physis and concomitant fibular fracture. Although there are few published studies on this injury in the pediatric population, in the adult literature, the only consistently significant predictive factor associated with improved functional outcome has been anatomic reduction of the syndesmosis.22,25,40,41 This should remain the goal for care of these injuries in the pediatric patient.
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