Drop foot mechanics outweigh etiology

When prescribing an ankle foot orthosis or neuroprosthesis for a patient with acute drop foot following stroke, lower extremity practitioners should consider the device’s potential effects on neural plasticity and motor relearning in addition to its potential effects on gait.

by Cary Groner Lower Extremity Review December 2009

Conditions associated with drop foot are as varied as post-stroke hemiplegia, brain or spinal cord injury, and neuromuscular disorders including multiple sclerosis (MS). Patients with drop foot are unable to use the dorsiflexor muscles to lift the foot clear of the ground during the gait’s swing phase, nor can they control plantar flexion during heel strike. The result is an awkward, unstable gait and a tendency to trip when the toes brush the ground.

Although clinicians have long used AFOs to control drop foot, better designs and more recent innovations such as functional electrical stimulation (FES) have improved prospects for a more normal gait. Such approaches—particularly FES—have raised questions about whether they may be more appropriate for patients with a progressive underlying problem (e.g., MS) or those with a nonprogressive condition such as stroke.

Practitioners, however, are increasingly arriving at a basic consensus about the best ways to approach the problem. With some exceptions, they usually prefer to address biomechanical issues directly rather than dwell on etiology.

“An orthotist’s approach is usually to look at the patient’s functional abilities and match the solution to them,” said Ian Engelman, MS, CPO, owner of Insightful Products in Scarborough, ME. “An example of a decision I would make based on a diagnosis of the underlying condition would be with an early stroke patient, or with someone who was obviously going to either improve or deteriorate. Generally, though, I just want to identify the biomechanical pathology and design the brace according to that.”

Engleman emphasized the importance of addressing both swing- and stance-phase issues in post-stroke patients with drop foot and significant clonus.

“Nearly all braces handle swing phase, but a patient with high spasticity will need something with a plantar flexion stop and probably a trim line that goes to the sulcus level,” he said.

Stefania Fatone, PhD, BPO(Hons), is a research assistant professor in the department of physical medicine and rehabilitation at Northwestern University’s Feinberg School of Medicine. Her research into the biomechanical effects of AFO designs also looks at improved swing- and stance-phase control, via a plantar flexion stop and a full-length foot plate.

In her research, published in the Archives of Physical Medicine & Rehabilitation in May, Fatone and her colleagues found that in stroke patients, the stop minimized the knee moment that leads to hyperextension deformity. Like Engelman, she made a distinction between drop foot due to stroke versus neurodegenerative disease.

“Stroke patients have spasticity—high tone in the extensors—so it’s not that the dorsiflexors don’t activate, but that they’re weaker than the plantar flexors,” she explained. “In a patient with a flaccid joint, you only have to overcome the effect of weight and gravity, but in a stroke patient you have to apply more force with a stiffer, stronger AFO.”

Patients with drop foot due to brain or spinal cord injury may have spasticity as well, she noted.

In the same vein, Fatone said that FES tends to work fairly well on more flaccid patients because they primarily need to contract the tibialis muscles.

“But if you’re talking about a patient with a fairly compromised stance phase, you’re not going to see a lot of benefit from something that only has a swing-phase effect,” she said. “Then you need something more substantial.”

Overall, she concurs with Engelman about the relative value of etiology.

“There’s too much heterogeneity in each diagnostic population to say that everyone in that group would benefit from a certain type of device,” she said. “It’s really about seeing what problems that individual presents with, then making a decision about what device might be most appropriate.”

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Source Lower Extremity Review

Also see
Orthotic considerations for foot drop after stroke Lower Extremity Review
Patients feel both electrical stimulation and AFOs have a place in stroke rehab Lower Extremity Review