The situation is infrequent, but happens several times a year: someone goes surfing for the first time, develops low back pain, comes out of the water, feels that their legs are weak, and can’t urinate. It’s known as surfer’s myelopathy each year, and most first-time surfers — and even most surfing instructors — have never heard of this rare complication and have no idea what the warning signs are.

Unlike most sports injuries, surfer’s myelopathy is not the result of an obvious accident or trauma. Instead, it seems to be a mechanical problem that starts in the blood vessels surrounding the spine.

When the spinal cord is hyperextended — as when a surfer arches his back on the board — it can interrupt the blood flow to the spine, he explained. One theory holds that frequent repetition of this motion causes a kink in the blood vessel. The spinal cord is starved of oxygen.

For now, there is no medication or surgery to treat surfer’s myelopathy. Many patients do recover, however, often through intense physical therapy.