SLR - October 2017 - Hassan M. Usmani, DPM

Gravity Stress Radiographs and the Effect of Ankle Position on Deltoid Ligament Integrity and Medial Clear Space Measurements

Reference: Ashraf A., Murphree J., Wait E., Winston., Wooldridge A., Meriwether M., Wilson J., Grimes J., Gravity Stress Radiographs and the Effect of Ankle Position on Deltoid Ligament Integrity and Medial Clear Space Measurements. JOT. 2017 May; 31(5): 270–274.

Scientific Literature Review

Reviewed By: Hassan M. Usmani, DPM
Residency Program: New York Presbyterian/Queens

Podiatric Relevance: Rotational ankle injuries are a common pathology encountered by the podiatric physician. Gravity stress radiographs or external rotation manipulation under fluoroscopy is required to distinguish between stable supination-external rotaion-II (SER-II) and unstable SER-IV. Both strategies are useful in distinguishing the two fracture patterns. Gravity stress radiographs, unlike external rotation stress views, have not been researched extensively with regards to position of foot to ankle when attempting to distinguish the two fracture patterns.

Methods: Eight freshly frozen cadaveric ankles were used for this case study. All cadavers met the requirement of being free from prior injury, surgery or anatomical abnormality. Each cadaver was dissected in sequential order according to the supination external rotation mechanism of Lauge-Hansen. Dissection of ankles occurred in five stages and included the following: transection of anterior talofibular ligament, fibular osteotomy at level of ankle joint, midsubstance incision of posterior inferior tibial fibular ligament, transection of superficial deltoids, transection of deep deltoids. Between each stage, radiographs were taken of the ankle with the ankle in neutral position and that of plantarflexion. Medial and dorsal clear space was measured at each stage in both positions by a single senior observer. Mean values, sensitivities, specificities, positive and negative predictive values were calculated for both medial and dorsal clear space at 5 mm and 6 mm.

Results: Positive predictive value with medial clear space cutoff of 5 mm was 80 percent in plantarflexion and 72.72 percent in neutral with a negative predictive value of 100 percent in both positions. Interestingly, using a 6 mm cutoff, the positive predictive value improved to 100 percent, and negative predictive value remained the same at 100 percent for both positions. There was no statistically significant difference when comparing medial clear space widening with rupture of the deep deltoid ligament comparing neutral position and plantarflexed position.  

Conclusions: Unlike external rotation stress radiographs, the position of the ankle in gravity stress radiographs has no bearing on clinical effectiveness of the images. Increasing the cutoff to 6 mm may increase the positive predictive value in a clinical setting.

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