So often when describing motion and forces we simplify our descriptions, but it is vital that we have a more advanced understanding of engineering terms that are applied in lower extremity motion. Our understanding of terminology will help us both understand normal function and allow us to formulate treatment plans to avoid malfunction.
Torque is a measure of how much a force acting on an object causes that object to rotate.
Torque, also called moment or moment of force, is the tendency of a force to rotate an object about an axis, fulcrum or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist.
Lower Extremity Scenarios and Treatment Applications
1) Lateral Ankle Instability
Problem: The torque that causes inversion around the STJ axis and AJ is too large.
Answer: Combat abnormal inversion torque by increasing the eversion torque via a reverse morton's extension, adding a valgus rearfoot wedge to the rearfoot post or adding a forefoot valgus wedge.
2) Anterior ankle impingement
Problem: The torque around the ankle joint axis is too large, leading to increased forces at the tibial/talar interface.
Answer: Add a heel lift to decrease the forces at end of dorsiflexion range of motion.
For many years, a mutlitude of disciplines have applied wedges, skives and lifts when treating lower extremity pathology. To balance out strong torques, either decrease the abnormal torque or increase the torque of the opposite force. Recognizing the imbalance of power that leads of joint pathology will help when formulating conservative and surgical intervention. In either instance, the torques affecting a joint should be determined and addressed accordingly.
A interesting paper that discusses the effect of wedges on medial knee arthritis can be read in today's eJournal: Valgus Wedging.