DALY CITY, Calif. — Trigg McClellan’s next patient is just moments away, arriving in a heap of dust and dirt, adrenaline and pain.

An orthopedic trauma surgeon in San Francisco and San Jose, he usually treats the casualties of urban life: shootings and car rollovers, falls and motorcycle wrecks, attempted suicides.

But his passion is helping riders at rodeos, fixing the men who straddle angry bulls and broncs, rocket into the air and then land with a thud.

“I want to help them to be able to do their job, and do as well as they can,” says McClellan, who volunteered at this year’s Grand National Rodeo, staged this month at the Cow Palace.

“They’re athletes,” says McClellan, a Nashville, Tennessee, native who grew up on horseback. “It’s not a matter of if they’re going to get hurt — but when, and how bad.”

He leans against the arena fence, watching and waiting, his trained eyes squinting below the low brim of a cowboy hat. If there is an injury, he wants to witness it.

Then the gate swings open and a one-ton bull thunders out, a raging barrel of beef — free and riderless. That means bad news for somebody back in the chute.

McClellan rushes to the rodeo’s medical room, where he meets Wyoming rider Clayton Savage, 32, barely able to stand, carried in by a friend.

Part of a proud tribe of vagabond men who circle the West in search of eight-second rides and quick payouts, Savage moans as the doctor pulls off one of the cowboy’s boots and rolls up his jeans.

His leg, fractured in July, is held together with a rod and screws.

But it healed nicely and felt fine — until just now, when his bull, named Gin and Sin, bucked in the chute and hit Savage in the face, then bucked again and smashed him against a fence.

“Does that hurt?” asks McClellan, prodding a spot on Savage’s tibial plateau, critical to knee alignment and stability.

“Yes, sir,” says Savage, throwing back his head with a low roar of pain.

Bull riding — dubbed “the most dangerous eight seconds in sport” — has long been mythologized for its challenge, and its risk.

Every ride is different. Some bulls lunge, legs stretched. Others leap, popping high in the air. Those who know say the toughest rides are the “spinners,” bulls who drop a shoulder and pivot.

The cowboy clings tight and often is tossed off, like a rag doll. Yet even in the dirt, there is peril. The bull might trample the downed (now-defenseless) rider, or use its horns to gouge and toss him.

The more thrilling the ride, the happier the crowd.

If cowboys hang on for eight seconds, that one ride might pay $1,000 to $4,000, even more. Anything less and they are disqualified, earning nothing but aches and pain. Unlike team sports, they are not paid to sit on the bench.

Bulls are selectively bred for bucking prowess, and today they are so fierce that the odds are stacked against the cowboys before they even straddle the 2,000-pound beast. A diminishing number of riders stay on long enough to score. The horses, called broncs, are also getting better, and bolder.

Deaths are rare in rodeo, but they happen. Earlier this year, Missouri bull rider Mason Lowe, 25, died after a bull stomped on his chest, causing massive heart, heart valve and aorta damage, even though he was wearing a protective vest. Last year, Colorado’s Jason Blasdel died after landing, when the bull turned and tossed him into the fence.

More common are injuries. The list is long and grievous, dominated by concussions, with an occasional dislocated shoulder, facial laceration, elbow dislocation, wrist fracture and ligament tear.

Last year, McClellan fixed a face laceration on Clayton Biglow, ranked first in the world in bareback riding with Professional Cowboys Rodeo Association career earnings of $619,130 — at only age 24.

He also taped up Dalton Shepard, 19, from Southern California, who arrived at the Grand National already banged up: a broken left hand from a car crash. Then while riding, his right hand got caught on a rope and fractured.

“So I came with one broken hand and left with two,” Shepard quips. “But now they feel brand new.”

Riders lead hardscrabble, itinerant lives, crisscrossing tens of thousands of miles to compete in 40 or 50 events a year across the West.

Many have chronic nagging injuries through the season and must prep before every ride, said McClellan. Rodeo medics borrow the shin splits and knee guards from other sports, adapting them for rodeo.

“A lot of these riders will spend an hour taping their own elbow for an eight-second ride,” says McClellan. “They’ve had at least one concussion, if not multiple. They might go through the whole season with something that hurts. They keep going.”

Professional bull riding has surged in popularity since the early 1990s, fueled by the popularity of televised events and escalating prize money.

McClellan, a 65-year-old physician and clinical professor of orthopedic surgery at UC-San Francisco, lives south of San Francisco and splits his time between San Francisco General Hospital and San Jose’s Regional Medical Center. His specialties are trauma and spinal injuries, directing SFGH’s Spine Service.

On weekends, he is up at his ranch in San Joaquin County, east of Lodi, competing in the discipline of reining, executing equestrian patterns of tight circles, spins and sliding stops.

Rodeo work is a volunteer gig. He is team physician for the Justin Sports Medical Team, which provides medical support services and a “crisis fund” to professional rodeo athletes at events nationwide, including the PRCA and Professional Bull Riders, Inc.

Back near the Grand National’s medical room, cowboys prep, fidget and stretch, slender and supple as ballerinas. Bull riding is always the last event — after the Star Spangled Banner, clown stunts, roping and barrel racing.

Cameron Messier, 22, tapes up his wrist before climbing aboard a small chestnut saddle bronc named Yeti.

“The doctors are really a blessing, honestly,” says Messier, a Sacramento Valley native who rode last year with a torn knee meniscus. “We have to compete to get paid.”

He adds: “I’ve had knee injuries and shoulder injuries and there’s been times towards the end of the year when I’m banged up and hurt and I really need to keep going. They tape me up and take care of me so I can feel my best. When I’m done, they put me on ice.”

The riders and doctor swap jokes, laughing. “If a cowboy doesn’t have a girlfriend, he’s homeless,” Dalton says.

“If a cowboy doesn’t have pain,” McClelland adds, “he’s lonesome.”

Then the announcer calls, and it’s time to ride.

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