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Taking the Proper Steps

Identifying the causes of foot drop syndrome and its effects on gait

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Vol. 18 • Issue 20 • Page 25

Foot Drop Syndrome

Foot drop is a generic term used to describe difficulty or inability to lift the front of the foot during swing phase. It is characterized by dragging the foot or toe as a result of inadequate toe elevation during single-limb advancement. It can also be identified by foot slap with initial contact when the forefoot slaps to the ground due to unopposed or poorly opposed plantar flexion. There are several causes either relating to weakness or paralysis of the pretibial muscles or hypertonicity of the plantar flexors. Depending on the mechanism, it can be temporary or permanent.

Damage to the peroneal nerve can arise from lumbar spine pathologies, following orthopedic surgery, ankle or calf trauma and compartment syndrome. Foot drop due to one of these reasons will resolve as the damaged peripheral or peroneal nerves regenerate.

Foot drop is probably more commonly associated with neuromuscular insults such as cerebral vascular accidents or post-tumor resection and degenerative processes such as amyotrophic lateral sclerosis (ALS), Guillain-Barre syndrome and multiple sclerosis. Cerebral palsy is a common cause of spastic foot drop.

Sometimes foot drop is a deliberate mechanism employed to compensate for another deficit. Contracture of the plantar flexors can cause foot drop as the foot will remain plantar flexed. Maintaining the ankle in plantar flexion will decrease demand on the quadriceps to compensate for weakness. Use of an extensor pattern for limb advancement will cause the ankle to go into plantar flexion.

Judging Movement

The presence of foot drop will not cause much impairment during stance phase because the foot is in contact with the floor. Stance begins with initial contact of the heel to the floor and continues as the tibia progresses forward across the forefoot with weight acceptance. Three rockers are present to aid with forward tibial movement. The pre-tibial muscles work to control tibial movement and counteract plantar flexion as the metatarsals and phalanges move into extension for toe off. Absent or weak pretibial muscles will slow forward tibial procession, decrease stride and velocity.

Archive ImageA

Author Toni Patt, DPT, works on gait with this patient who is experiencing a foot drop condition..

During swing phase, the pretibial muscles play a key role. For adequate foot clearance the hip, knee and ankle must flex. Thirty-five to 40 degrees are required at the hip. The knee must flex at least 20 degrees and the ankle must dorsiflex to neutral. This provides approximately 1 centimeter for foot clearance. Dorsiflexion of the ankle begins during initial swing. It remains at neutral from mid- through terminal swing. Neutral ankle position sets the foot in place for initial heel contact.

When the pretibial muscles are weak or paralyzed, the ankle doesn't dorsiflex into neutral. The swing limb increases in length and is unable to move forward without contact with the floor. It is most obviously during mid-swing when the greatest amount of clearance is needed. When only the ankle is involved, foot drop will be characterized by toe drag.

Pretibial weakness often results from hemiparesis or hemiplegia of a limb, making the impact on gait more significant. In isolation, other muscle groups can compensate for the loss of foot clearance and minimize or avoid significant gait deviation.

When caused by hemiparesis, the hip and knee are unable to compensate for foot drop. Instead, the limb length may be further increased by lack of knee flexion or ipsilateral pelvic drop. When motor activation is absent in the foot and ankle, toe drag becomes foot drag. The forefoot may move into inversion, which increases the drag and energy requirement to bring the limb forward. If muscle function is lacking, initial floor contact may be made by the lateral border of the foot or the lower, lateral ankle. In either instance, the risk of ankle and soft-tissue injury is substantial.

Compensatory Ambulation is Common

Ambulating with foot drop increases the energy cost of walking. This energy demand becomes even greater as the gait deviations and substitutions develop. Premature heel off, knee hyperextension and forward trunk lean can all be seen as the body attempts to compensate. Forward trunk lean occurs to assist with bringing the tibia forward. Knee hyperextension and premature toe off are compensations for increased limb length.

Circumduction, using hip abduction, pelvic drop and rotation, to advance the limb is a common deviation. Sometimes contralateral lean is present to assist with moving the limb forward. The result is more room for foot clearance as the foot is swung around and forward and the leg lifted higher. Hip hike is another common response. It is similar to circumduction in that the goal is to lift the foot further from the floor. With hip hike, the hip is hiked up to increase foot clearance without the accompanying ipsilateral pelvic drop or abduction. Contralateral lean may still be present.

Steppage gait is unique to foot drop. It resembles the gait of high stepping horses. Exaggerated hip and sometimes knee flexion are created to lift the foot off the floor. The person appears to be prancing with the involved limb as it advances. Steppage gait is not as common as circumduction and hip hike because it requires normal muscle activation of the hip flexors.

The treatment of foot drop is to maintain neutral ankle position during swing phase. Treatment is the same whether the weakness is permanent or likely to resolve. An ankle-foot orthotic (AFO) is used to hold the ankle at neutral. Although AFO designs vary, the ankle is generally held at neutral through all phases of the gait cycle. This eliminates the additional limb length as well as keeping the foot properly positioned for heel strike.

Using Orthotics

There are two forms of AFO available. A solid AFO is a well-shaped piece of plastic that holds the ankle at a predetermined ankle. This is inexpensive and relatively easy to don and doff. A solid AFO is the first choice for a peroneal nerve injury.

The principal drawback of a solid AFO is lack of ankle motion for transfers and positioning. Because the angle is preset, the patient must position the foot forward when transitioning between sitting and standing.

A hinged AFO eliminates that problem. The hinge allows some ankle flexion so the foot can be properly placed beneath the patient when transferring. The amount of movement at the ankle is limited by the design. Dorsiflexion and plantar flexion stops can be used to control range of motion. Elastic can be used for the hinge to increase dorsiflexion assist for patients who are beginning to develop motor return of their dorsiflexors.

Functional electrical stimulation (FES) can be used to assist with facilitation and strengthening of the pretibial muscles. Unlike traditional electrical stimulation applied to muscles at rest, FES is applied during gait training.

A heel trigger is used to activate the muscles as the limb moves into swing phase and turn off the stimulation when the heel contacts. Manual activation can also be applied. FES is used as an adjunct with body-weight-supported treadmill training and overland gait training.

FES use can be limited to the pretibial muscles or in combination with the calf muscles. Alternating pretibial and calf-muscle activation more closely mimics normal gait. When done together, knee flexion is increased. There is more plantar flexion at toe off and forward propulsion is greater.

Neuroprostheses are available that combine FES into the design. The electrodes are located on the pretibial muscles. A heel trigger can be used. The electrical stimulation fires the muscles whenever a step is taken. There are some drawbacks to this. Initial application can be time-consuming and require several sessions. The cost is substantial compared to an AFO, FES or in combination.

In some cases, tendon-transfer surgery may be the treatment of choice. A tendon is transferred from the posterior tibialis to the tibialis anterior. Nerves can also be transferred from less important muscles to the tibialis anterior. These surgeries are usually done within a few months because peroneal nerve injuries tend to have poorer outcomes if treatment is delayed. 

Resources

Hanna, D., & Harvey, R. (2001). Review of preorthotical biomechanical considerations. Top Stroke Rehabilitation, 7(4), 29-37.

Kesar, T., Perumal, R., et al. Functional electrical stimulation of ankle plantar flexors and dorsiflexors: Effect on post-stroke gait. Stroke, 40, 3821-3827.

Malas, B., & Kacen, M. (2001). Orthotic management of patients with stroke. Top Stroke Rehabilitation, 7(4), 38-45.

The Pathokinesiology Service and The Physical Therapy Department. (2001). Gait; Observational Gait Analysis. Rancho Los Amigos National Rehabilitation Center, Downey, CA.

Perry, J., & Bumfield, J. (2010). Gait Analysis: Normal and pathological function, 2nd ed. SLACK Inc.: Thorofare, NJ.

Toni Patt has been practicing physical therapy for more than 25 years and currently works at a hospital in the Houston area. She writes a weekly blog on the ADVANCE website titled "Toni Talks about PT Today." Patt has spoken for the Texas Physical Therapy Association and the southeast district of that association on hemiparetic gait rehabilitation.




     

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