A 43-year-old woman comes to the office due to acute back pain after dragging a heavy box. The pain is located in her lower back and radiates down the right posterior thigh to the foot. The patient describes the pain as "shooting" and grades it 8/10 in intensity. She has no bowel or bladder symptoms. The patient has tried over-the-counter analgesics with limited symptomatic relief. Vital signs are within normal limits. On physical examination, straight leg raise testing is positive on the right. Right hip extension is weaker when compared to the left. Patellar reflexes are 2+ and bilaterally symmetric, but the right Achilles reflex is absent. Which of the following nerve roots is most likely affected in this patient?
Features of lumbosacral radiculopathy | |||
Nerve Root | Reflex affected | Sensory loss* | Weakness |
L2-L4** |
|
|
|
L5 |
|
|
|
S1 |
|
|
|
S2-S4** |
|
|
|
*Radicular pain typically has a similar distribution to sensory loss. **Difficult to distinguish between individual nerve roots clinically. | |||
This patient's presentation is consistent with sciatica, a nonspecific term for low back pain that radiates down the leg. This condition occurs due to compression of the lumbosacral nerve roots and is most commonly caused by vertebral disc herniation or spinal foraminal stenosis (eg, due to degenerative arthritis of the spine). Irritation of the nerve roots results in characteristic dermatomal and myotomal deficits (radiculopathy) depending on the level of involvement. Patients may have worsening of their radicular pain when the symptomatic leg is extended at the knee and the hip is passively flexed by the examiner (straight leg raise test).
The sciatic nerve is derived from the L4-S3 nerve roots and compression most often occurs at the level of L5 or S1. S1 radiculopathy is characterized by pain and sensory loss down the posterior thigh and calf to the lateral aspect of the foot. Patients may also have weakness on thigh extension (eg, due to denervation of the gluteus maximus), knee flexion (hamstrings), and foot plantarflexion (gastrocnemius) with an absent Achilles reflex.
(Choices A and B) Patients with L2 or L3 radiculopathy typically have pain radiating down the anterior thigh with weakness on hip flexion (eg, due to denervation of the iliopsoas). Patellar and Achilles reflexes usually remain intact.
(Choice C) L4 radiculopathy typically presents with pain/paresthesia radiating down the anterior thigh to the medial lower leg and foot. Patients can also have weakness on knee extension (eg, due to denervation of the quadriceps) with a diminished patellar reflex.
(Choice D) Compression of the L5 root results in pain/paresthesia radiating down the lateral thigh and calf to the dorsal foot. Patients often have weakness on foot dorsiflexion and inversion (eg, due to denervation of the tibialis anterior), foot eversion (peroneus), and toe extension (extensor digitorum brevis).
Educational objective:
Sciatica is a nonspecific term for low back pain that radiates down the leg due to compression of the lumbosacral nerve roots (eg, from vertebral disc herniation). The S1 nerve root is commonly involved, resulting in pain/sensory loss down the posterior thigh and calf to the lateral aspect of the foot. Patients may also have weakness on thigh extension, knee flexion, and foot plantarflexion with an absent Achilles reflex.