Incidence, Etiology, and Risk Factors Associated with Foot Drop

The inability or diminished ability to lift the foot is primarily the result of neurological disorders. The origin of the neurological impairment can be central (motor cortex lesions [cerebral palsy and stroke]), intraspinal (nerve root L4, L5, S1, and S2 damage), or peripheral (lumbosacral plexus, mononeuropathies of the deep peroneal, common peroneal, or sciatic nerves).^1,2Carolus et al³recently reported that lumbar spinal nerve root damage (radiculopathy) and peroneal nerve compression were the most frequent causes of foot drop, followed by polyneuropathy and nerve trauma in 65 patients with foot drop. Radiculopathy is typically associated with back pain and numbness while patients with neuropathies do not report pain.² Ma et al⁴ also recently reported that 22.9% of their foot drop cases were due to lumbar disc degeneration. Amin et al⁵ found that 95% of this degeneration occurs at L4-L5 or L5-S1 as the dorsiflexor muscles of the ankle (ie, tibialis anterior, extensor digitorum peroneus tertius, and extensor hallucis longus) are primarily innervated by L5 nerve roots. Bakhsh⁶ reported that the long-term outcome of lumbar disc surgery was unsatisfactory, and new neurological deficits caused foot drop postoperatively in 8.8% of their patients. Failed back surgery syndrome (FBSS) is a leading cause of postoperative back and leg pain, injury, and foot drop.^6-8 Dellon ⁹found that 58.4% of 24 cases of palsy developing after hip or knee arthroplasty were due to sciatic or peroneal neuropathy. Falls, motor vehicle accidents, sports and recreational activities, knee replacement surgeries, tumors, cysts, gunshot wounds, and stab wounds are other known causes of foot drop.  

Presenting symptoms depend on the location, type, and severity of the injury. Ultrasonography and magnetic resonance imaging are more powerful tools to identify the lesion directly, and electromyography and nerve conduction study results are used to diagnose and grade nerve injuries. Here, the authors reported the frequent and rare causes of foot drop in 1022 patients who received consultations at their clinic over 18 years. 

The authors reviewed retrospective data collected from 1022 patients with foot drop to find the incidence, causes, and risk factors for the condition. All patients who received consultations from 2004 to 2022 were included. Excel 2013 (Microsoft Corp) was used to perform descriptive statistical data analysis and generate graphs. Median age and percentage of male and female patients were calculated to determine whether age and sex were among the risk factors for foot drop. In addition, the incidence of each cause of foot drop was determined and compared. 

The Table shows the etiology, patient sex (percentage of male and female), age (median and range), and incidence of foot drop in this population. Most patients had steppage gait with ankle dorsiflexion ranging from 0 to 2+/5 Medical Research Council grade. A few patients used crutches or were in a wheelchair because they could not lift their involved foot. A total of 21 causes of foot drop were found. Of 1022 patients, 142 patients (13.9%) developed foot drop after lumbosacral (LS) spine surgery, while 131 patients (12.8%) with LS spine complications who did not have surgery also reported foot drop. The LS spine complications and surgeries were influenced by age (median ages, 63 and 55 years, respectively) and were marginally higher in male patients (55%). 

A total of 79 patients (7.8%) had previously undergone hip replacement surgery. Both age (median, 60 years) and sex (85% female) were found to be risk factors for hip replacement surgery, the second most iatrogenic cause of foot drop. Another iatrogenic group of 52 patients (5.1%) with foot drop who had previously undergone a knee replacement, foot surgery, and other related surgeries had a median age of 50 years; 63% of patients in this group were female. Falls (11%), motor vehicle accidents (7.1%), sports and recreational activities (5.0%), tumors (4.4%), and stroke (3.2%) were the other most frequent causes of foot drop in the current study (Table, Figures 1 and 2). 

Gunshot and stab wounds and other violence-related injuries, injection drug use, drug or medication overdoses, and motor vehicle accidents mostly affected young (median age range, 24-32 years) male patients. The incidence of foot drop in these groups of male patients ranged from 71% to 83%. Stroke and general muscle weakness and pain as the causes of foot drop were also seen more frequently in male patients (67% and 64%, respectively). Patients with Guillain-Barré syndrome (GBS) and Charcot-Marie-Tooth (CMT) disease were mostly male (67%) with a median age of 11 years (Table, Figures 1 and 2).

Infections (poliomyelitis, chickenpox, transverse myelitis, acute flaccid myelitis, rhabdomyolysis with sepsis), diseases (Wegener’s granulomatosis, sickle cell, piriformis syndrome, kidney failure, systemic lupus erythematosus, GBS, and CMT), genetics (both parents are first cousins, anti–neurofascin-155 antibody presence, chronic inflammatory demyelinating polyradiculoneuropathy), and birth-related injuries (premature birth, birth palsy, congenital disorders, brain injury; cesarean delivery and epidural use during delivery) were some of the rarer causes of foot drop (range, 0.4%-1.7%) in patients in the present study (Table, Figures 1 and 2). 

A total of 48 patients (4.7%) reported they were unsure about the cause of their foot drop, and another 34 patients (3.3%) reported that they had general muscle weakness and pain in addition to foot drop.

To the authors’ knowledge, the strength of this report is that it is the most extensive sample study to find the underlying causes of foot drop. FBSS was the most common cause of foot drop, which aligns with reports that the relative risk of palsy is 6.5 times greater in patients who have undergone prior lumbar laminectomy.⁸ Crotti et al¹⁰ also reported that FBSS occurred in 30% of their operated patients. Other investigators have found that the patients who developed foot drop after primary hip arthroplasty also had spinal stenosis.¹¹ Patients with pre-existing spinal stenosis are at increased risk for foot drop after hip arthroplasty because of this proximal compromise, which is the double-crush. In another study, more than half of the patients with post arthroplasty palsy (total hip/knee replacement) showed evidence of sciatic or peroneal nerve injury in the EMG evaluation.⁹ The authors found the majority of 79 patients who had prior hip or hip replacement surgeries were female (85%) and older (median age, 60 years). In addition, more female patients in the current study had previously undergone a knee replacement, foot surgery, and other related surgeries; age was not necessarily a correlating factor.

The authors found that the second most common cause of foot drop was a pre-existing health condition that affected the lumbosacral spine region (e.g., lumbar disc bulge, herniated disc, chronic degeneration, compression/entrapment, tethered spinal cord syndrome, scoliosis, levoscoliosis, lumbar spondylosis, stenosis, and compartment syndrome). Such conditions affect older patients of both sexes, as neurodegenerative diseases are associated with old age. Many pathological changes might have already occurred when the clinical symptoms manifest.¹²

The other causes of foot drop in patients in this study, such as motor vehicle accidents, gunshot and stab wounds, interpersonal violence, injection drug use, and drug or medication overdoses, impacted predominantly younger (median age, 24-32 years) male patients. Other investigators have also reported sex-related disparities in this patient population. Williams and Shabanova¹³ reported that young men were more likely than young women to be responsible for fatal crashes. Turner and McClure¹⁴ studied 689 Australian drivers (a random sample of adults aged 17–88 years) who filled out a questionnaire about their attitudes toward driving behavior, general risk-taking behavior, and self-reported history of road crashes as drivers. Univariate analysis of their study results showed that young male drivers (17–29 years) scored higher means than females in driver aggression and thrill-seeking, as well as in their general risk acceptance.¹⁴  In the present study, of the 73 patients who had foot drop due to motor vehicle accidents, 83% were men (mean age of 27 years; Table 1 and Figures 1 and 2).

 Swedler et al ¹⁵ also reported that male teen drivers involved in fatal crashes were often engaged in risky driving activities, such as speeding and drunk driving. A recent study on the age and sex distribution of patients hospitalized following nonfatal road traffic accidents found that 88% of male patients had a median age of 25 years (range, 21-35 years).^16. 

Drug and alcohol use has been linked to the frequency of injury events, recurrent hospital admission for injury, and interpersonal violence in younger adults. According to toxicology screening, substance use is strongly associated with gunshot wounds (P = .003); 72% of teen patients (age <18 years) who were victims of gunshot wounds had evidence of substance use.^17,18 In the present study, younger male adults were also significantly affected by these causes (ie, motor vehicle accidents, drug use, and violence), as presented in the Results section and in the Table and Figures 1 and 2.

This is a retrospective study.

FBSS is the leading cause of foot drop after LS spine and hip replacement surgeries in both male and female older (median age, 60 years) patients. However, most (85%) of the foot drop patients in the present study who underwent hip replacement surgery were female patients. Sports and recreational activities, motor vehicle accidents, drug use, and violence are common causes of foot drop in younger male adults.

The authors extend their thanks to the patients and their families who participated in this study

Affiliations: ¹Texas Nerve and Paralysis Institute, Houston, TX.

Correspondence: Rahul K Nath, MD; drnath@drnathmedical.com

Disclosures: The authors declare no conflicts of interest.