Orthopedists need several methods to gauge stability of distal tibiofibular joint

Issue: February 2013

Syndesmosis associated with ankle fracture can be overlooked or fixed inadequately. In this month’s 4 Questions interview, Randall C. Marx, MD, shares his experience with distal tibiofibular joint stability with ankle fractures.

Douglas W. Jackson, MD,
Chief Medical Editor

Douglas W. Jackson, MD: How should surgeons assess syndesmosis with an associated ankle fracture?

Randall C. Marx, MD: There are no proven reliable clinical or radiographic exams to accurately assess the stability of the syndesmosis. As a result, the orthopedist must be facile with several methods to adequately gauge the stability of the distal tibiofibular joint and the behavior of an ankle fracture.

4 Questions with Dr. Jackson

On preoperative imaging, syndesmotic disruption should be suspected in fibular fractures that extend 4.5 cm above the ankle joint, proximal fibular (Maisonneuve) fractures, as well as Lauge Hansen pronation external rotation fracture patterns. However, syndesmosis injury can occur in nearly all fracture types or as an isolated ligamental disruption.

Radiographic indices used to assess the syndesmosis are relatively inaccurate but helpful as part of the overall assessment. Diastasis of the posterior tibiofibular clear space greater than 6 mm on a true AP or mortise view and tibiofibular overlap less than 6 mm on a true AP or less than 1 mm on a mortise view may indicate syndesmosis instability. Medial clear space widening indicates deltoid incompetence, but should be assessed concomitantly.

Avulsion fractures involving the syndesmotic ligaments occur from the anterolateral tibia (Chaput’s tubercle), the anterior fibula (Wagstaffe) or the posterolateral tibia (Volkmann) and should be considered equivalent to a ligament disruption. Avulsion fractures can be detected via X-ray, preoperative CT scan or during surgery. The operating surgeon also can determine the integrity of the syndesmosis by direct observation of the fibula in the incisura and the integrity of the syndesmotic ligaments through the lateral incision or during arthroscopy if performed.

Jackson: What are the considerations for accurately assessing intraoperative syndesmotic reductions?

Randall C. Marx

Marx: Intraoperative assessment of the syndesmosis reduction is based on the Cotton test (or Hook test) or an external rotation stress test after malleolar stabilization. The Cotton test places a bone hook or key elevator in the incisura to attempt to separate the fibula from the tibia. The external rotation stress test can be performed manually or with a standardized force (usually 7.5 Nm) using an F-tool. The shaft of a screw driver with a known diameter can be held under the fluoroscope for use as a reference. The medial clear space should also be carefully assessed for widening.

Intraoperative assessment of the syndesmosis reduction is based on the Cotton test (or Hook test) or an external rotation stress test after malleolar stabilization. The Cotton test places a bone hook or key elevator in the incisura to attempt to separate the fibula from the tibia. The external rotation stress test can be performed manually or with a standardized force (usually 7.5 Nm) using an F-tool. The shaft of a screw driver with a known diameter can be held under the fluoroscope for use as a reference. The medial clear space should also be carefully assessed for widening.

Clinically, the fibula should rest concentrically in the incisura fibularis. The anterior cortex of the distal fibula should align with the lateral edge of Chaput’s tubercle. Syndesmotic instability produces posterior subluxation of the fibula and may be detected by observing posterior translation of the anterior fibular cortex in relation to Chaput’s tubercle. The lateral fluoroscopic images should be critiqued for posterior fibular subluxation. Finally, the fibular length and rotation must be restored in cases of fibular comminution and can be evaluated with the talocrural angle, congruity of the fibula against the lateral aspect of the talus or a version of Shenton’s line between the fibula and tibial plafond. X-rays of the contralateral ankle can be used for comparison if any uncertainty exists about accuracy of reduction.

Jackson: What should we tell patients about outcomes from an internally fixed reduction?

Marx: Syndesmosis malreduction or chronic instability can alter joint mechanics and increase the likelihood of early post-traumatic arthritis. Several clinical studies have demonstrated that anatomic reduction and fixation of the syndesmosis is the most important predictor of functional outcome after ankle fracture regardless of the technique used for stabilization.

Jackson: What have been the outcomes for treatments of chronic syndesmotic disruptions?

Marx: Salvage of the chronically unstable distal tibiofibular syndesmosis is a clinical and surgical challenge. Depending on the chronicity and severity of the condition, syndesmotic instability can manifest as subtle tibiofibular incongruity or as lateral talar shift, lateral tibial plafond erosion and advanced ankle arthrosis.

Subtle diastasis of the syndesmosis can be treated with arthroscopic debridement and screw or endobutton stabilization and has been associated with good results. Syndesmosis ligament reconstructions with bone block advancement of the elongated ligaments or with ligamentoplasty using a portion of the peroneal tendons have reported encouraging results in small retrospective studies. Alternatively, distal tibiofibular arthrodesis has been used to stabilize the ankle mortise with reported good clinical and radiographic results, which may delay the need for ankle arthrodesis or arthroplasty.

For more information:

Randall C. Marx, MD, is from UTSA Orthopedics, San Antonio Orthopedic Group. He can be reached at marxrandy@aol.com.
Disclosure: Marx has no relevant financial disclosures.