Spinal stenosis is the most likely cause of this patient's symptoms. Spinal stenosis results from narrowing of the spinal canal, usually due to degenerative arthritis of the spine that causes mechanical compression and ischemia of the lumbosacral spine nerve roots. Clinical manifestations of spinal stenosis are progressively worsening low back discomfort and severe leg pain that tends to be minimized when the low back is flexed (leading patients to lean forward) and worsened with spinal extension (such as when standing and walking up steps). Plain radiographs may reveal degenerative changes or alterations in the mechanical structure of the lumbosacral spine; however, CT may be more helpful in defining bony changes, and MRI is the study of choice for evaluating the neural structures in the low back. It is important to note that spinal stenosis may be incidentally detected in a substantial number of asymptomatic patients who have imaging for other reasons, and the degree of stenosis does not predict development of symptoms. Therefore, this finding alone does not require further evaluation in the absence of symptoms or possibly associated clinical findings.

Compression fractures may cause low back pain and, if severe, may cause nerve compression and radiculopathy. However, this patient does not have clear risk factors for compression fracture (such as trauma, glucocorticoid use, or osteoporosis), and the symptoms associated with compression fracture tend to be of acute onset (and not progressive, as in this patient) with significant point tenderness over the spine at the level of the fracture. Additionally, the symptoms associated with compression fracture tend to be less positional than those seen in spinal stenosis.

Hip osteoarthritis may be worsened with walking, and pain may radiate posteriorly toward the low back and groin region. However, it would not explain this patient's lower extremity symptoms and other positional findings.

Symptoms associated with spinal stenosis are sometimes termed pseudoclaudication because they worsen with ambulation and improve with rest, similar to claudication due to peripheral arterial disease. However, these conditions are usually distinguished by the fact that vascular claudication symptoms do not tend to worsen with standing or spinal extension. Additionally, this patient has no clear risk factors for peripheral arterial disease.