A 68-year-old man comes to the office because of a 9-month history of bilateral leg pain and sensation of heaviness that occurs when he walks to his mailbox or stands for long periods. He notes that the pain is primarily in his calves and thighs and is relieved when he sits down or leans forward on his shopping cart. He denies any recent trauma, fever, or changes in bowel or bladder function. His medical history is significant for osteoarthritis and a 30-pack-year smoking history. On physical examination, distal pulses in the feet are 2+ and symmetric. Neurological examination shows normal muscle strength and symmetric deep tendon reflexes. A straight-leg raise test is negative. The pain is not reproduced by passive hip rotation.
Which of the following is the most likely finding on imaging of this patient's spine?
The correct answer is:
C) Hypertrophy of the ligamentum flavum.
This patient's presentation is classic for lumbar spinal stenosis, which leads to neurogenic claudication. This is characterized by posture-dependent leg pain (pseudoclaudication) that is exacerbated by spinal extension during standing or walking and relieved by spinal flexion such as sitting or leaning forward (the "shopping cart sign"). Extension decreases the cross-sectional area of the spinal canal, further compressing the nerve roots. The most common cause of acquired spinal stenosis is degenerative changes, which include hypertrophy of the ligamentum flavum, bulging of the intervertebral discs, and osteophyte formation at the facet joints.
Answer choice A: Bulging of the nucleus pulposus through the annulus fibrosus, is incorrect. This describes a herniated disc. While disc herniation can contribute to spinal stenosis, it typically presents acutely with radiculopathy, positive straight-leg raise, and pain that is often worsened by flexion, which is the opposite of this patient's presentation.
Answer choice B: Displacement of one vertebral body over another, is incorrect. This describes spondylolisthesis. While spondylolisthesis can cause spinal stenosis, the most common underlying mechanism for the shopping cart sign in an elderly patient is the triad of facet joint arthritis, ligamentum flavum hypertrophy, and degenerative disc disease.
Answer choice D: Narrowing of the joint space with subchondral sclerosis, is incorrect. These are the hallmark radiographic findings of osteoarthritis. While this patient likely has osteoarthritis of the spine (spondylosis), the specific cause of his neurogenic claudication is the resulting narrowing of the central canal, often driven by ligamentous hypertrophy and facet enlargement.
Answer choice E: Ossification of the posterior longitudinal ligament, is incorrect. Ossification of the posterior longitudinal ligament (OPLL) is a condition that more commonly affects the cervical spine and is a frequent cause of myelopathy in East Asian populations. While it can cause stenosis, it is not the most common cause of lumbar neurogenic claudication in the general population.
Key Learning Point
Lumbar spinal stenosis presents with neurogenic claudication, with(leg pain relieved by flexion or leaning forward. The most common pathophysiology involves degenerative changes, specifically hypertrophy of the ligamentum flavum, facet joint osteophytes, and degenerative disc disease, leading to narrowing of the spinal canal.
