Most patients benefit from nonsurgical care of foot drop. Your task is to identify the optimal bracing options and work closely with the patient to understand their personal treatment expectations and goals.
By Jason Wright, DPM, PGY-2, And Marshall G. Solomon, DPM, FACPM, FACAS
Foot drop refers to loss of strength of the pedal dorsiflexors, leading to a decrease in ankle dorsiflexion during gait. Patients with foot drop are at an increased risk of falls because of their toes “catching” the ground while ambulating. Foot drop can be a challenging condition to manage: there are numerous causes, and each patient can have different needs and expectations about treatment. Understanding the possible causes of foot drop, recent advances in treatment, and specific patient goals allow healthcare professionals to provide the best possible care.
The etiology of foot drop includes disorders of the peripheral nervous system and central nervous system.
Peripheral trauma and disorders. Injury to the common peroneal nerve (CPN) is a common cause. Ankle dorsiflexors, including the anterior tibialis, are innervated by the deep peroneal nerve, which branches from the CPN. As this nerve passes into the leg, it wraps around the fibular head. At that location, the nerve is vulnerable to injury because soft-tissue coverage is sparse; patients who sustain a knee injury, high fibular fracture, laceration, or other trauma can experience injury to the CPN.
Prolonged increased pressure on the lateral leg can also lead to nerve damage. Examples include prolonged lateral sleeping position, driving while resting the left leg against the car door, and prolonged working while kneeling.1,2
Nerve injury can also be iatrogenic: The CPN can be injured during arthroscopic knee surgery, and the sciatic nerve can be injured during hip or knee arthroplasty. Also, poor patient positioning on the operating table can lead to increased pressure on the CPN. Last, a below-knee cast that extends too far proximally can lead to nerve damage.1,2
Other causes of foot drop do not involve direct nerve injury. Soft-tissue masses, including lipomas and ganglion cysts, can put pressure on the nerve, leading to a mass effect that contributes to foot drop. In such cases, surgical removal of the mass is usually indicated.2
Proximal disorders. It is also important to consider proximal causes when evaluating foot drop. Radiculopathy at L4 and L5 is a common cause.1,2 Last, many patients experience loss of muscle strength following a cerebrovascular accident or other cerebral injury.1,2,3
Take These Steps to the Diagnosis
Diagnosis of foot drop starts by obtaining a thorough history and physical examination. Patients often complain of falls caused by the toes dragging on the ground while walking. Physical examination reveals loss of muscle strength of the pedal dorsiflexors and, sometimes, loss of sensation to the dorsal foot. Shoewear examination is also highly important. Wear patterns on the outsoles can provide clues to biomechanical imbalances resulting from foot drop or worsening its effect. Electromyography and nerve-conduction velocity studies can be used to confirm the diagnosis. These studies can also determine the location and severity of the nerve lesion.1
Treatment With Ankle Foot Orthoses
The mainstay of nonsurgical treatment of foot drop is an ankle–foot orthosis (AFO), which functions by decreasing ankle–joint plantarflexion during gait. These orthoses are constructed of various designs and materials; it is important to consider patient factors when prescribing and fitting an AFO. Lifestyle, comorbidities, and goals of treatment determine which AFO is best suited to the individual patient.
Double-upright AFO. An earlier AFO design was the double-upright AFO, comprising a pair of metal bars rigidly attached to the shoe and a leather band wrapped around the calf. Bulkiness and inability to transfer between different shoes are major drawbacks of this AFO. A key benefit, however, is that the double-upright AFO can accommodate changes in the size of the leg. This is especially helpful in patients with lymphedema and venous insufficiency.4
Solid AFOs are typically made from a plastic polymer, such as polypropylene. Their design includes a foot plate and a posterior shell, with a strap at the level of the calf. Patients are able to move these AFOs between shoes. Because solid AFOs tend to be less bulky than metal AFOs, they increase patient satisfaction and adherence. Solid AFOs can be modified to meet the needs of an individual patient and can be either purchased prefabricated or custom-molded to the patient’s foot, using plaster casting.4,5
The mechanical properties of solid AFOs can be changed by adjusting the width of the posterior shell along trim lines. Lehmann et al6 showed that solid plastic AFOs with a wider and stronger posterior shell have increased stiffness leading to more plantarflexion resistance, thus reducing the possibility of toe drag during swing phase. Stiffer AFOs are also recommended in patients with ankle instability.7 Narrower posterior shells are more flexible and allow for some plantarflexion during gait. Many experts have proposed that some AFO flexibility creates a spring-like function that allows for a more natural gait.4,8,9 It is important to find the ideal balance of strength and flexibility for each patient.
In 2019, Totah and co-workers7 performed a literature review to identify the effect of ankle stiffness in AFOs on gait and patient satisfaction. The researchers compiled the results of 25 articles and reached the following conclusions:
- Increased AFO stiffness led, as expected, to a decrease in peak ankle plantarflexion, peak ankle dorsiflexion, and ankle–joint range of motion (ROM).
- Increased AFO stiffness also led to an increase in knee flexion during the early stance phase of gait.
- There is no statistical correlation between AFO ankle stiffness and hip-joint biomechanics, energy use, or gait speed.
The review by Totah was unable to ascertain an association between patient satisfaction and stiffness of the AFO.7 This further emphasizes the need to understand the individual patient’s conditions and goals of treatment.
Kobayashi and colleagues10 found that, in an AFO with high-ankle stiffness at initial contact, the tibia will be abruptly rotated forward, leading to knee flexion and instability. However, an AFO with too little stiffness will lead to increased knee flexion, similar to the genu recurvatum often seen in patients with foot drop.
Dynamic AFOs are designed from flexible material to allow spring-like function. This design absorbs energy during initial contact and then releases it during toe-off. Dynamic AFOs can be made from plastic or carbon fiber9,11; the latter material has the added benefit of being both lightweight and strong.9
One type of dynamic AFO, the posterior leaf spring AFO (PLS-AFO), is constructed similar to a solid AFO. However, the posterior shell portion is shaped in a way that allows it to function like a spring. Other dynamic AFO designs include flexible struts along the sides, which also act like springs. Bregman et al11 showed that use of PLS-AFOs can reduce the energy cost of walking by 9.8% and reduce net ankle work by almost 30%, compared to walking without an AFO.
Zollo et al9 compared dynamic AFOs and solid AFOs in patients with stroke-induced foot drop. They showed that both PLS-AFOs and dynamic AFOs improved cadence and decreased ankle ROM; in fact, there was no statistical difference between the 2 designs in regard to cadence and ankle movement. The researchers recorded subjects’ muscle activity in the calf and anterior ankle muscles while wearing the 2 types of AFO: While using the dynamic AFO, patients had less co-contraction of these muscles. Zollo concluded that use of the dynamic AFO will provide patients with a gait that is more similar to unimpaired gait.
Choi et al12 compared the effect of the stiffness of dynamic AFOs at different walking speeds. By analyzing gastrocnemius muscle and anterior tibialis muscle length during the gait cycle, they determined that, at slower walking speeds, patients received less energy return, compared with faster walking speeds. The researchers recommended taking the patient’s lifestyle demands into consideration when considering a dynamic AFO.
Articulating AFOs are constructed in 2 pieces, with a joint at the ankle. Hinges with adjustable resistance are used to control the patient’s plantarflexion and dorsiflexion. Stops can also be incorporated into the AFO to place an absolute limit on the plantarflexion and dorsiflexion ROM. Kobayashi13 confirmed that incremental increases in hinge resistance lead to decreased ankle ROM during stance and swing phases.
3-dimensional (3D) printed AFOS. Recent advancements in 3D printing technology have led to greater interest in developing a technique to manufacture custom AFOs using this technology.
Cha et al14 developed and tested a 3D printing technique in which the patient’s foot is scanned using a 3D scanner; the image is then adjusted using computer software and then “printed” using thermoplastic polyurethane. The 3D printed AFO was compared to a custom AFO manufactured using the traditional casting technique. Patients alternated use of the 2 AFOs for 2 months and reported that they were happier with the ease of use and comfort of the 3D printed AFO.
Wojciechowski et al5 performed a literature review (N = < 50 patients) of 3D-printed AFOs, which revealed little difference in biomechanical properties, including ankle movement and speed of gait, between 3D-printed and plaster-cast AFOs. The review did demonstrate increased patient comfort and satisfaction with 3D-printed AFOs. The authors concluded that 3D printing is a feasible option for future AFO manufacture that could lead to improved customization and patient satisfaction.
General problem of patient acceptance. Nonadherence has a significant effect on the success of treatment with an AFO. Holtkamp et al15 surveyed more than 200 patients for whom an AFO was prescribed and found that 1 of every 15 patients never used it. They also found that nearly 25% of AFO users were dissatisfied with their orthosis. Common causes of dissatisfaction included skin reaction, poor fit, and difficulty of use. Survey respondents also commented on lack of follow-up and attention to their needs in the design of the AFO. Other studies have shown that AFO complications include contracture at the ankle joint, trouble standing from a sitting position, and undesirable appearance.16
Treatment With Foot Drop Stimulators
Another treatment option for foot drop is a foot drop stimulator (FDS), wearable devices that electronically stimulate the common peroneal nerve to activate the pedal dorsiflexors. Stimulators are useful for treating foot drop resulting from central nervous system pathology. They require an intact common peroneal nerve to stimulate the dorsiflexors of the foot, which means that they are not indicated for treatment of common peroneal nerve injury. Other contraindications include ankle and knee instability.4,16
In a randomized controlled trial of 179 patients by Kluding et al16 that compared AFOs and FDSs, both treatment groups were found to have significant improvement in comfortable walking gait speed and fast walking gait speed. There was no statistical difference in improvement across several biomechanical markers. Participants in the FDS treatment group were more satisfied with treatment, however.
Reported adverse events with FDSs included skin irritation and falls. The rate of falls was equal in both treatment groups.
Foot drop encompasses a range of conditions of various causes; the common factor is loss of muscle strength of the pedal dorsiflexors. Most patients benefit from nonsurgical care of foot drop, regardless of the cause.
Because the cause of foot drop varies from patient to patient, and because individual patients therefore have different needs and expectations from treatment, it is the task of providers to identify the best bracing options for the individual by working closely with the patient to obtain and understand their goals for treatment of this condition.
Jason Wright, DPM, is a PGY-2 resident physician and Marshall G. Solomon, DPM, FACPM, FACFAS, is Residency Director, both at Beaumont Hospital, Farmington Hills, in Farmington Hills, MI.
LER is proud to partner with the American College of Foot & Ankle Orthopedics & Medicine to present clinically relevant peer-reviewed content, curated by Jarrod Shapiro, DPM, FACFAOM, FACFAS.