Session IV - Foot & Ankle

Correlation of Interosseous Membrane Tears to the Level of Fibular Fracture

Jason H. Nielson, MD; Julian G. Sallis, MD; Hollis Potter, MD; David L. Helfet, MD; Dean G. Lorich, MD, Albert Einstein College of Medicine, Bronx, NY; The Hospital for Special Surgery, New York, NY

Purpose: The interosseous membrane (IOM) is a well-described part of the ankle syndesmosis. The physiologic role is not agreed upon, but it has been shown to be an important stabilizer of the ankle syndesmosis, especially in the absence of the deltoid ligament. Many authors have described the IOM tear to extend to the level of the fibular fracture. Some authors base syndesmotic instability on the level of the fibular fracture to be 3.0 to 4.5 cm proximal to the ankle joint and thus indicate the requirement for syndesmotic stabilization. The assumption in these studies is that the IOM is disrupted to the level of the fibular fracture. We used MRI to evaluate the integrity of the IOM in all ankle fractures to determine whether the height of the fibular fracture is predictive of the level of the IOM tear. The literature is not clear concerning the level of fibular fracture that requires trans-syndesmotic fixation. Even with low fibular fractures, if the interosseous membrane is disrupted proximally, the syndesmosis could be unstable.

Methods: We prospectively studied 67 ankle fractures with preoperative AP, mortise, and lateral plain radiographs and MRI. The surgeons classified these ankle fractures and then predicted their corresponding ligamentous injuries, both according to the Lauge-Hansen and Danis-Weber classifications. The soft tissue predictions were then compared to the MRI findings read by an experienced radiologist.

Results: Twenty-eight of the 67 ankle fractures had IOM tears identifiable on MRI. Of the 43 ankle fractures with adequate MRI evaluation above the level of the fibular fracture, 4 had IOM tears proximal to the fibular fracture as detected by MRI. Surprisingly, two of these cases were SER 4-Weber-B-type fractures and two were PER 4-Weber C type ankle fractures. Conversely, two cases of Danis-Weber C-type fractures did not have IOM tears to the level of the fibular fracture.

Discussion and Conclusions: The results raise many questions including that of the accepted idea that the height of the fibular fracture is predictive of a stable rather than an unstable syndesmosis and that the interosseous membrane tears to the level of the fibular fracture. Tears above the level of the fibular fracture have been briefly reported; however, an accurate method of assessment of these tears has not been truly described prior to the use of MRI. If the IOM is torn above the level of the fibular fracture, is the syndesmosis rendered unstable, thereby requiring syndesmotic fixation? To explain the mechanism of ligamentous tears proximal to the fractured fibula might suggest more complex forces involved in ankle injuries. One cannot reliably estimate the integrity of the IOM and subsequent need for trans-syndesmotic fixation solely on the level of the fibular fracture. This conclusion supports the need for intraoperative testing (Cotton test, etc.) of the ankle syndesmosis in all operative ankle fractures.