The interosseous membrane is a strong osseofascial ligament that holds the tibia and fibula in close anatomic alignment to each other along their entire length, which is of utmost importance to the function of the ankle mortise (Fig. 51.1). There is a convex shape of the distal fibula that articulates with a convex matching shape of the distal lateral tibia. At the level of the ankle mortise, the syndesmosis is composed of the anterior and posterior tibiofibular ligaments and the distal aspect of the interosseous membrane.

Intra-articular causes of ankle pain include damage to the articular surfaces, loose bodies, soft tissue proliferation, and arthropathies. Extra-articular problems can be diagnosed by anatomical site. Pain on palpation to the distal anterior syndesmosis is almost always present during examination.

A patient’s history and chief complaint are a great source in the diagnosis of syndesmosis injuries. Patients usually complain of pain during any high-impact activity or ambulation on rough surfaces. Syndesmosis injuries usually occur as a result of external rotation of the talus. Reproducing this external rotator force during physical examination is helpful in confirming diagnosis (3) (Fig. 51.2). This type of force causes the energy of the rotation to migrate from anterior to posterior through the mortise. The manual squeeze test can also be useful in assisting with clinical diagnosis. This is performed by compressing the fibula and tibia toward each other at a level in the middle one-third of the leg, which produces pain in the syndesmotic region. This results in a splaying of the distal fibula away from the distal tibia in a ruptured distal syndesmosis.

Undiagnosed or untreated syndesmosis injuries can mimic chronic ankle instability. Feelings of tightness, stiffness, chronic swelling, and instability on uneven ground are symptoms to be aware of when evaluating these patients (4,5). Chronic pain in the syndesmosis can be due to the instability of the syndesmosis and lack of anatomical alignment and also due to the presence of scar tissue.

Diastasis of the ankle mortise without fibular fracture is categorized as latent or frank diastasis. Latent diastasis occurs when on normal radiographs there is no widening or distortion of normal anatomy; however, with a stress gravity or external stress radiograph, the mortise widens (Fig. 51.3). Frank diastasis is easily visualized on normal routine radiographs (6,7).

There are many published studies as to the usefulness in diagnosing diastasis and tibiofibular syndesmosis injuries, and there are conflicting opinions (8,9 and 10). With normal nonstressed radiographs, the injury can be easily missed and can lead to chronic pain and functional limitations (Fig. 51.4). Stress gravity films can be of great diagnostic value in those injuries resulting in a latent diastasis (11,12). Computed tomography (CT) and magnetic resonance imaging (MRI) have been proven as very useful tools in evaluating the position of the syndesmosis articulation and the MRI for ligamentous disruption (3,10,13) (Fig. 51.5). A torn or stretched ligament can appear noncontiguous, thickened, absent, and retracted and will often have a different signal intensity compared with adjacent tissue when an MRI is performed. A CT scan can detect 1 mm of syndesmosis displacement, whereas plain radiographs miss 3 mm of displacement 50% of the time (14). In a study by Gardner (15) in 2006, CT scanning detected a 52% postoperative incongruity of the fibula within the incisura, and only 24% demonstrated diastasis by traditional radiographic measurements. There are multiple procedures for treating chronic syndesmosis injuries from arthroscopic débridement with fixation, screw fixation, screw and plate fixation, osteotomies, ligamentoplasty, tenodesis, and fusion (3,4 and 5,10,13,16,17). Chronic syndesmosis disruption can lead to osteoarthritis and calcifications in the syndesmosis area (Fig. 51.6).