As with all diagnoses, a thorough history is paramount. Syndesmosis injuries are easily missed and may have been missed previously or incorrectly diagnosed. Discerning the mechanism of injury may provide greater suspicion for syndesmosis injury. Pain is usually diffuse about the ankle and can have pain anterolaterally proximal to lateral ankle ligaments. Pain is commonly reported while walking up hills, pivoting, or doing a single leg heel raise.
The physical examination is conducted in a systematic sequence starting with the least painful maneuver and progressing to more painful to help with patient compliance. A comprehensive ankle examination should be done as to not miss concomitant injury to other ankle structures. The following maneuvers are specific to the syndesmosis and should be done in concert with your typical ankle evaluation. To do the crossed-leg test have the patient cross their painful leg across the contralateral side with the distal third of the fibula resting on the opposite knee, and then, the examiner applies downward pressure over the medial knee of the painful side. (Figure 2A) Pain reproduced with gentle force on the medial knee indicates a positive test. Palpation is helpful as a syndesmosis injury is typically tender at the anterolateral joint line and proximal compared with a typical sprain which is over the distal fibula. Tenderness to palpation at the level of the joint and the distance the pain extending proximally has been termed the "tenderness length" (Figure 2B). The tenderness length has been correlated with MRI findings and time to return to sport in NFL athletes. Perform the squeeze test with the patient seated on the examination table with the leg hanging off the bed in 90 degrees of flexion. The examiner squeezes the fibula and tibia together using the palms to distribute the force broadly avoiding point tenderness, pain at the syndesmosis indicates a positive examination (Figure 2D). Perform the fibula translation test by having the patient in a seated or supine position; the examiner stabilizes the tibia with one hand then grasps the fibula and attempts to translate it anterior and posterior (Figure 2C). The amount of translation and pain should be carefully compared with the contralateral side; a painful soft end point with greater than 2 to 3 mm of translation is a positive examination. Once again, perform the external rotation stress examination by having the patient in the seated position; the examiner stabilizes the tibia with one hand then dorsiflexes the foot while applying an external rotational force, pain indicates a positive examination (Figure 2E). Following the aforementioned examination maneuvers, the patient may be in pain increasing the sensitivity of the subsequent dynamic examinations.
Photograph showing the physical examination maneuvers: A, Crossed-leg Test; B, Tenderness Length; C, Fibular translation test; D, Tibiofibular squeeze test; E, Dorsiflexion external rotation stress test; and F, Stabilization Tape test—Prewrap is applied to protect skin and hair, and then, a 4-inch silk tape is circumferentially wrapped around the ankle tightly with the foot and ankle in a neutral position.
The patient is asked to ambulate approximately 10 ft; on the return, they are asked to walk on heels then tiptoes, followed by standing-double and single leg heel raises. The standing pivot test is then done by keeping the symptomatic foot planted on the ground and externally pivoting the ipsilateral leg and trunk; pain indicates a positive test. The ankle is then tightly taped, in a circumferential fashion (4-inch silk tape), just above the ankle joint to ensure that the foot is in a nonweight-bearing neutral position to stabilize the syndesmosis. Then, the gait and pivot examination mentioned above is repeated; reduction of pain with increased function indicates a positive stabilization examination (Figure 2F).
Although these provocative maneuvers are classically described, studies show that clinicians should not rely on a single test in isolation. The sensitivities and specificities of the physical examination maneuvers vary widely among the literature. Sman et al performed a cross-sectional diagnostic accuracy study and found the squeeze test to have the highest specificity of 88%, whereas syndesmosis ligament tenderness and external rotation stress test had the highest sensitivities of 92% and 71%, respectively. They concluded that no single test is sufficiently accurate for diagnosis and recommend combination of tests. Previous systematic review performed by the same authors showed poor diagnostic accuracy of these tests with varying sensitivities and specificities.
Standard lower extremity weight-bearing radiographs should be done including the ankle and proximal tibia to rule out fracture about the ankle in addition to Maisonneuve fracture, and plain radiographs also aid to evaluate joint symmetry. Stress radiographs can also be beneficial; the lead author (K.D.M.) prefers a gravity stress examination which minimizes pain and can also be done reliably by the radiographic technician.[19,20] Radiographic findings that have been identified as syndesmosis injury indicators are increased tibiofibular clear space, decreased tibiofibular overlap, and increased medial clear space. (Table 1) (Figure 3A–B). The tibiofibular clear space is defined as the distance between the medial border of the fibula and the lateral border of the posterior tibia at the incisura approximately 1 cm proximal to the joint line. This distance should be less than 6 mm on AP and mortise views of the ankle. Tibiofibular overlap is defined as the overlap of the lateral malleolus and anterior tibial tubercle. This distance should be greater than 6 mm on A/P and greater than 1 mm on mortise views. Medial clear space is the distance from the lateral aspect of the medial malleolus to the medial aspect of the talus. This distance should be equal to the superior clear space, but not greater than 4 mm (Figure 4). Although plain radiograph is the most common method to evaluate the syndesmosis, the usefulness of this to diagnose syndesmosis injury is limited. MRI has been shown to have sensitivity, specificity, and accuracy of 100%, 93%, and 96%, respectively. Fluid making a contiguous signal from the mortise up through the syndesmosis is termed the "Lambda sign", which has been shown to yield high sensitivity (75%) and specific (85%) for syndesmosis complex injury. The fluid extravasation also indicates a potential insufficient IOL which helps direct surgical management (Figure 5).
A, AP radiograph demonstrating A, Tibiofibular clear space; B, Tibiofibular overlap; and C, Medial clear space. B, Mortise radiograph demonstrating A, Tibiofibular clear space.
Radiograph demonstrating the lambda sign as described by Ryan et al showing extravasation of fluid to the syndesmosis on coronal T2-weighted fat-suppressed image.
Examination Under Anesthesia
Examination under anesthesia (EUA) should be done in patients when a high index of suspicion exists for syndesmosis injury in the absence of plain radiograph or MRI findings. In addition, EUA should be done before operative fixation to validate the fixation. EUA is done to include dorsiflexion, dorsiflexion external rotation stress, fibular translation test, medial/lateral talar tilt, and an anterior drawer, noting the radiographic parameters described above. Next, a complete diagnostic arthroscopic examination is done to include evaluating for distal tibiofibular stability, osteochondral defects, and deep deltoid continuity. Arthroscopic stability testing includes repeating all the previous listed maneuvers while directly visualizing and noting incompetent anatomic structures. Gross instability is easily noted, but a more detailed syndesmosis examination is needed. The fibular translation test is done by applying anterior to posterior force in the sagittal plane with a blunt instrument on the distal fibula, greater than 2 to 3 mm is a positive examination. The coronal plan can be evaluated with a cotton test, but we prefer placing an instrument into the syndesmosis on known size (4.0 mm shaver) to estimate instability (Figure 6). Ryan et al have demonstrated promising results in treating patients with >4 mm of diastasis, showing improvements in subjective outcome scores, and high rates of return to running sports. The deltoid must also be evaluated because it may block talar reduction or have notable injury requiring repair.
J Am Acad Orthop Surg. 2020;28(13):517-527. © 2020 American Academy of Orthopaedic Surgeons