A 28-year-old man presents to the health-care provider with…
A 28-year-old man presents to the health-care provider with lower back pain that began 3 days ago. The pain is worse when he stands or bends, and it is somewhat relieved when he sits. The clinician performs the straight-leg raise test and it is negative. Plain film x-ray is positive for straightening of the vertebral curve. Which diagnosis is most likely?