Cath Lab Digest

Given the complexity of drop foot and its impact on gait biomechanics, these authors offer a primer on the diagnostic workup, and share their thoughts on the potential merits of tendon transfer procedures.

   Drop foot and foot drop are interchangeable terms that illustrate an abnormal neuromuscular disorder, which affects the patient’s capacity to lift up the foot at the ankle. Drop foot is further characterized by failure to dorsiflex the foot or move the foot inward or outward at the ankle. Pain, weakness and numbness may be associated with a loss of function.

   Typically, walking becomes a challenge due to the patient’s inability to control the foot at the ankle. These patients subsequently compensate with an exaggerated or high stepping walk referred to as steppage or foot drop gait.

   Notably, the patient may use a characteristic tiptoe walk on the opposite leg (raising the thigh excessively as if he or she were walking upstairs) while letting the opposite toe drop. This serves to raise the foot high enough to prevent the toe from dragging and prevents the slapping of the foot to the ground. Without compensation, however, the afflicted foot may appear floppy and typically drags or slaps down onto the floor.

   Other gaits such as a wide outward leg swing (to avoid lifting the thigh excessively or to turn corners in the opposite direction of the affected limb) may also be indicative of foot drop.

   Drop foot is not a disease but an indication of an underlying problem. Depending on the etiology, drop foot may be temporary or permanent. Often drop foot is caused by injury to the peroneal nerve stemming from the lumbar and sacral spine. Although other causes exist, lumbar disc herniation is a common cause. The peroneal nerve, a division of the sciatic nerve, innervates the muscle groups responsible for ankle, foot, toe movement and sensation.

   The peroneal nerve is susceptible to different types of injury. Some types of injury include nerve compression from lumbar disc herniation (e.g. L4, L5, S1), trauma to the sciatic nerve, spondylolisthesis, spinal stenosis, spinal cord injury, bone fractures (leg, vertebrae), stroke, tumor, diabetes, lacerations, gunshot wounds or crush-type injuries. Sometimes the peroneal nerve becomes injured when it is stretched during hip or knee replacement surgery, etc.

   Other causes of drop foot stem from a variety of etiologies such as: traumatic induced tumor; lower motor neuron lesions such as poliomyelitis and Charcot-Marie-Tooth disease; or diseases of the muscle fiber such as muscular dystrophy and polymyositis.

   With the classic drop foot, the common peroneal nerve is affected and leads to anterior and lateral muscle group weakness. Since the posterior group is unopposed, equinovarus deformity ensues from the pull of the posterior tibial muscle and triceps surae.

A Quick Overview Of Possible Treatment Options

   Drop foot is a complex problem. Determining the underlying cause of drop foot is one of the physician’s first endeavors and ultimately determines the course of treatment. Treatments include the use of an ankle foot orthosis (AFO), gait training, physical therapy and possible surgical reconstruction.

   For example, if drop foot is caused by nerve compression from a lumbar herniated disc, then a spinal procedure would possibly be indicated. If the drop foot has not progressed and is limited to a local level (the lower extremity), then surgical reconstruction associated with a tendon transfer is possible.