Getting to the root cause of foot drop STUDY TITLE: Assessment of hip abductor power in patients with foot drop: A simple and useful test to differentiate lumbar radiculopathy and peroneal neuropathy AUTHORS: Jeon C, Chung N, Lee Y et al. PUBLICATION INFORMATION: Spine 2013; 38(3): 257–263. Foot drop, or dorsiflexion weakness, is one area of clinical practice that can sometimes be misleading. This clinical sign can stem from various problems, including a lumbar disc herniation, pressure on the lumbosacral plexus and compression of the fibular (peroneal) nerve. Weakness of the hip abductors can also stem from several sources, including muscular weakness and neurological compromise. The superior gluteal nerve, which is derived from the lumbosacral trunk and the L5 root, supplies the hip abductor muscles (gluteus medius, gluteus minimus and tensor fasciae latae). The L5 nerve root also supplies the ankle dorsiflexors. Weakness of these muscles can be produced by the lesions proximal to the division of superior gluteal nerve. This study aimed to determine the diagnostic validity and reliability of assessing hip abductor power for differentiating between lumbar radiculopathy and peroneal neuropathy as a root cause of foot drop. The authors hypothesized concomitant weakness of hip abductor power and foot drop would be associated with lumbar radiculopathy. Pertinent result Unilateral foot drop involvement was found in 85.2 per cent of the patients (the remaining patients had bilateral involvement). The most common etiology of foot drop was peroneal neuropathy (45. 9 per cent), followed by lumbar Radiculopathy (34.4 per cent), lumbosacral plexopathy (14.8 per cent) and sciatic nerve disorder (4.9 per cent). When considering all the manual muscle tests and sensory outcome measures evaluated, statistically, hip abduction power was the only significantly different measure between the lumbar radiculopathy and peroneal neuropathy groups (P < 0.001). Among the 21 foot drop patients associated with lumbar radiculopathy, hip abductor weakness (MRC grade of < 3) was found in 18 patients with three patients showing false-negative results. Meanwhile, among the 28 foot drop patients with peroneal neuropathy, hip abductor weakness (MRC grade of < 3) was found in one patient, while 27 patients showed true negative results. Therefore, the sensitivity and specificity of hip abductor power in the differential diagnosis of foot drop due to lumbar radiculopathy and peroneal neuropathy were found to be 85.7 per cent and 96.4 per cent, respectively. The positive and negative predictive values were found to be 94.7 per cent and 90 per cent, respectively. The interobserver reliability of the hip abductor power assessment by the three orthopedic surgeons had kappa values of 0. 85 to 0.91, indicating excellent agreement. Conclusions and practical applications The foot drop patient can present with Vague and atypical signs. Clinically, it can be difficult to identify the exact location of the problem or the pathological structure involved. In this study, the majority of spontaneous foot drops that were difficult to diagnose were caused by fibular (peroneal) neuropathy and lumbar radiculopathy. Concomitant hip abductor weakness was usually present in foot drop cases that were due to lumbar radiculopathy, and rarely in those from peroneal neuropathy – this is the take-home message from this study. The electrodiagnostic test is useful and commonly used in the diagnosis of both peroneal neuropathy and lumbar radiculopathy. Unfortunately, the crucial findings in these tests do not appear until two to three weeks after the initial injury. The results from this study suggest that assessment of hip abductor power is a fast, simple and valid test in determining the etiology of the foot drop when discriminating between peroneal neuropathy and lumbar radiculopathy as differential diagnoses. Peroneal neuropathy at the fibular head is fairly common due to the proximity of the nerve to the skin with limited protection. Direct trauma, sustained pressure and a mass around the knee joint are common mechanisms of peroneal nerve injury. Lumbar degenerative disease, including herniated nucleus pulposus and spinal stenosis, are very common lumbar related causes of foot drop. Since peroneal neuropathy and lumbar radiculopathy are two of the most common causes of foot drop that present in clinical practice, this simple hip abductor muscle test can help speed up the diagnostic and treatment process. dr. ShAwn thiStLe is the founder and president of Research Review Service, an online, subscriptionbased service to help busy practitioners integrate current, relevant, scientific evidence into their practice (www.researchreviewservice.com). This article was submitted by Dr. Daniel Avrahami for Research Review.