Clanton TO, Williams BT, Backus JD, et al. Biomechanical Analysis of the Individual Ligament Contributions to Syndesmotic Stability. Foot & Ankle International, 2016, 38: 66-75.
The purpose of this study was to describe the specific contribution of individual ligaments to the stability of the distal tibia-fibula syndesmosis joint at the ankle. Since this was a study used 8 cadaveric lower leg specimens, readers need to exercise some caution when transferring the results to function when the muscles are intact. With this caution, the data provides insight into the mechanisms of injury to these structures during what is referred to as a “high ankle sprain.” The “high” refers to the joint just above the ankle between the tibia and fibula. The integrity of this joint is important to ankle (talo-crual) stability. Injuries to the syndesmotic ligaments require a different approach than the more common injuries to the lateral ankle ligaments.
This blog will focus on the results when the specimens were loading vertically and then an external rotation force was applied to the foot. Specifically, the results when the anterior-inferior talofibular ligament (AITFL) was cut will be described. The most common mechanism of injury occurs when the foot is fixed on the surface and the body and leg are forcibly rotated in the direction of internal rotation of the leg. With the leg rotating internally, the talus creates substantial forces on the fibula that can cause ligament disruption. In the study, the external rotation of the foot recreates relative motion between the tibia and fibula, and the stress on the AITFL.
The external rotation force was applied to the foot until 15 degrees of rotation had occurred. In the intact specimens, 10.5 Newton-meters of torque was required to create the 15 decrees of rotation. During this torque application the distal fibula rotated an average of 4.3 degrees and translated posteriorly an average of 3.3 millimeters. After sectioning the AITFL, the torque needed to rotate the foot was reduced by 24% indicating a loss of joint stability. The movement of the fibula relative to the tibia increased, even with the reduced torque. The fibula rotation increased 1.7 degrees. The posterior translation increased slightly, but the lateral translation of the fibula relative to the tibia also increased substantially but was described by the authors as being very variable.
When this data is combined with the Chain Reaction Biomechanics of functional movements, it provides a cautionary note to early weight-bearing exercises, but at the same time informs a rehabilitation strategy for program progression. Movement practitioners know from this and other studies that there is movement at this distal syndesmosis during function. The anterior aspect of the ligaments is stressed not only with external rotation, but also dorsiflexion. Understanding how “real” bone motion creates “relative” joint motion is essential to appreciating which functional movements will stress the healing syndemosis. These movements should be avoided / controlled during the early healing phase, but then gradually introduced to the rehab program to help the ligaments mature.
If the entire syndesmosis has not been disrupted, after a period of controlling the inflammatory process, exercises can begin. To allow healing, end-range dorsiflexion and relative external rotation of the foot should be avoided. These positions will tension the AITFL. But weight-bearing motion can be used to activate muscles enhance edema reduction, and promote proprioceptive control. Movements that cause external rotation of the lower leg will create relative internal rotation at the ankle (opposite the injury mechanism). Lunges with the uninjured leg, as well as reaches with either hand can be used to create appropriate motion as long as the practitioner selects the proper angle, distance, and height of the movement target.
At Gray Institute®, these 3 variables form the basis of the movement triangulation in 3D space. They are part of the 10 Observational essentials that define any functional movement. They provide the “power of tweakology” that Applied Functional Science® practitioners use to create movement success for their patients / clients without interfering with the healing process.