SLR - February 2010 - Ernesto Hernandez
Reference:
Stoffel, K., Wysocki, D., Baddour, E., Nicholls, R., Yates, P. (2009). Comparison of two intraoperative assessment methods for injuries to the ankle syndesmosis. A cadaveric study. Journal of Bone & Joint Surgery (American), 91, 2646-2652.
Scientific Literature Reviews
Reviewed by: Ernesto Hernandez, DPM
Residency Program: Kaiser Foundation, Hayward/Fremont
Podiatric Relevance:
Intraoperative stress testing is required for detection of syndesmotic injury when instability is suspected. This study compares two stress test techniques for the detection of ankle syndesmotic injury.
Methods:
This is a cadaveric study with 14 fresh frozen human donor specimens. Fluoroscopic images confirmed the intact ankle mortise and the absence of pathology in all specimens. True mortise radiographs of the ankle where made for the fourteen cadaver joints. Initial measurements where taken from intact specimens and were defined as Weber B (i). Specimens were then randomized into two dissection groups. The dissection performed was designed to simulate ligament instability and syndesmotic injury according to the Danis-Weber classification system. In the first group, the anterior inferior tibiofibular ligament was divided first (Weber B(r)), followed sequentially by division of the interosseous membrane (Weber C), and then the deltoid ligament (Weber C (dl)). In the second group, the deltoid ligament was divided first, followed by the anterior inferior tibiofibular ligament (Weber B(r + dl)). Radiographs were made at each stage with use of two methods of stressing the ankle mortise: (1) external rotation of the foot with an external moment of 7.5 Nm, and (2) application of a lateral force of 100 N with a bone hook. A nonparametric-paired test (the Mann-Whitney U test) was used to compare the tibiofibular overlap, tibiofibular clear space, and medial clear space. Each measurement was compared to the baseline values of the fresh frozen specimens, along with comparison to normative values obtained from the literature.
Results:
A trend in increase in the medial clear space and tibiofibular clear space was observed with increasing ligamentous instability in both stress tests. The external rotation stress test produced a significant increase in the medial clear space in the presence of isolated anterior inferior tibiofibular ligament and deltoid ligament injuries (p < 0.05). All of the sectioned deltoid ligaments had a medial clear space value greater than 4 mm. For the Weber C group, the lateral stress test produced a significant increase in medial clear space. Lateral stress produced a significantly greater increase in the tibiofibular clear space than did the external rotation test for Weber C injuries and Weber C plus deltoid ligament injuries. Both stress tests produced significant increase in the tibiofibular clear space in the Weber Br plus deltoid ligament group (p < 0.05 for both tests). Both stress tests showed a significant decrease in tibiofibular overlap for the Weber Br plus deltoid ligament group and both the Weber C groups. Half of the specimens showed a tibiofibular overlap of less than 1 mm.
Conclusions:
For the detection of syndesmotic instability after acute ankle fractures on stress radiographs, this cadaver study supports the use of the lateral stress test over the external rotation stress test.