SLR - August 2018 - Calvin J. Rushing
Reference: LaMothe JM, Baxter JR, Karnovsky SC, Murphy CI, Gilbert S, Drakos MC. Syndesmotic Injury Assessment with Lateral Imaging During Stress Testing in a Cadaveric Model. Foot Ankle Int. 2018 Apr; 39(4): 479-484.Scientific Literature Review
Reviewed By: Calvin J. Rushing, DPM
Residency Program: Westside Regional Medical Center – Plantation FL
Podiatric Relevance: Foot and Ankle Surgeons (FASs) have long relied upon 2-dimensional coronal plane parameters (tibiofibular clearspace, tibiofibular overlap, medial clear space) for assessing the syndesmosis during intraoperative stress testing. The lateral stress test (Cotton Hook), and mortise image have historically been perpetuated as the ideal method for determining diastasis indicative of syndesmotic instability (>2mm); although recent studies have demonstrated surprisingly poor accuracy and reliability. Despite the limitations of the lateral stress test and mortise image, no consensus currently exists amongst FASs regarding the stress test, and the image most suited for assessment.
Methods: A level V cadaveric study was performed on 9 specimens to characterize the fibular motion and applied stresses throughout the syndesmotic injury spectrum using external rotation, lateral, and sagittal stress tests. Three injury states were simulated by sequential sectioning of the anterior inferior tibiofibular ligament (AITF), interosseous membrane (IOM), posteroinferior tibiofibular (PITFL), and deltoid ligament (superficial/deep). For each condition (partial syndesmotic injury, complete syndesmotic injury, complete syndesmotic injury w/deltoid ligament injury), stress tests were performed in random order by a single fellowship trained foot and ankle surgeon; and the fibular motion and applied loads synchronously measured using a 4-camera motion capture system and a force transducer. The sensitivity and specificity of the lateral and external rotation stress tests under mortise imaging, and the sagittal and external rotation stress tests under lateral imaging were then assessed to determine their ability to correctly detect syndesmotic instability.
Results: Lateral imaging with applied external rotation, and sagittal stress tests (anterior-posterior cotton hook) were twice as sensitive as mortise imaging with applied external rotation, and lateral stress tests (cotton hook) for detecting syndesmotic instability. Specifically, fibular displacement increased linearly for both of the sagittal stress tests (external rotation, anterior-posterior cotton hook) but not the lateral stress test; which required more than twice the force (34N versus 16N) to produce at least 2mm of detectable syndesmotic motion. The sensitivity among the imaging planes and stress tests was variable (0.23-0.67), although the specificity of the stress tests was high (≥ 0.89).
Conclusions: Based on the results of this study, lateral imaging with an applied external rotation stress appears to be the most accurate method to diagnose syndesmotic instability intraoperatively. The method reduces the risk of a false negative, requires less force to produce a positive test (fibular shadowing of <50% of the tibial plafond on a true lateral radiograph), and possess the least iatrogenic risk to the patient. Alternatively, lateral imaging and an applied sagittal stress (Anterior- Posterior Cotton Hook test) is also acceptable, and provides a similar sensitivity, and risk.