SANTA CLARA — Dr. James Andrews isn’t astonished the 49ers have nine players — two shy of a full huddle — who are battling back from torn anterior cruciate ligaments.

As arguably the most renowned doctor in American sports, he has seen it all, even a team coping with 13 ACL tears.

No matter the number of patients, a common thread exists.

“Everyone wants to be ready for next season and get back in the line of fire,” Andrews said in a recent phone interview.

This week, the 49ers’ ACL apocalypse reaches a new level with organized team activities. Full-squad workouts will ensue for a month. Quick bursts, sudden stops and turn-on-a-dime cuts will test those surgically repaired knees.

“The success rate depends a lot more than on just the ACL itself,” Andrews said, referring to rehabilitation and recovery, both physically and mentally.

No other NFL team has more than four players coming off ACL tears. The average is about two players per team, and only six rosters have no such comebacks in the works.

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To get back into Super Bowl contention, no team needs triumphant comebacks as much as the 49ers, with linebacker NaVorro Bowman’s chief among them.

“I’d say we’re more treating Bow like a vet than we are treating Bow like a post-injury guy,” coach Jim Tomsula said Friday. ” … We go straight off what the trainers and sports medicine guys recommend, and obviously converse with the guys to see how they’re feeling.”

No-contact drills in OTAs don’t come without risk. Since 2011, nearly one in four ACL tears occurred in practice (61 of 224), according to NFL research.

“You have ACL (tears) because there are high-speed practices with big guys putting torque on their knee,” said Dr. David Chao, the San Diego Chargers physician from 1997-2013. “A walk-through becomes a run-through, and that high intensity is how you get a foot caught (in grass) and tear an ACL.”

The 49ers will continue to exercise caution. Sharing that prescription is former 49ers cornerback Chris Culliver, who missed the 2013 season with an ACL tear and parlayed his 2014 comeback into a free-agent payday with Washington.

“It’s a building block. You’re not going to get back and think you’re Superman,” Culliver said of OTAs. “You have to keep building so the knee gets better through practice. You can’t go 1,000 mph.”

Stark reminders of practice-field pitfalls came last week when two teams saw rookies rip their ACLs: the Jacksonville Jaguars’ Dante Fowler, the No. 3 overall pick, and the Denver Broncos’ Jeff Heuerman, a third-rounder.

“We looked at it closely to see if there’s anything going on there that we shouldn’t do,” Tomsula said. “No. We’ll be doing the same things Jacksonville was doing.”

Among those wishing Fowler a speedy recovery was 49ers defensive lineman Darnell Dockett, whose tweet to Fowler also read: “This will test you to the fullest.”

Dockett tore the ACL in his right knee last August, in his 11th and final training camp with the Arizona Cardinals. In March, he came to a division rival via free agency offering plenty of company in its ACL ward.

Running back Kendall Hunter, wide receiver Chuck Jacobs, guard Brandon Thomas, cornerback Keith Reaser and fullback Trey Millard also missed last season because of ACL reconstruction. Outside linebacker Chase Thomas tore his right ACL before the offseason program began in April, and he’s rehabbing on the reserve/non-football-injury list.

“A lot of us have worked together and motivated each other to get back on the field,” Hunter said.

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For the sixth time in three years, general manager Trent Baalke has drafted a player coming off a torn ACL: Georgia Tech wide receiver DeAndre Smelter (fourth round). He’s expected to “medically redshirt” as a rookie. That was the tactic for 2013 draft picks Tank Carradine and Marcus Lattimore, as well as last year’s trio of Brandon Thomas, Reaser and Millard.

Of course, not all ACL comebacks succeed, and Lattimore retired from his gutsy try in November. He toiled for two years after a multiple-ligament tear ended his sensational career as a running back at South Carolina.

It has been 16 months since Bowman’s left knee reached Andrews’ operating table in Pensacola, Florida. Bowman suffered a torn ACL and medial collateral ligament in the 49ers’ NFC Championship game loss at Seattle in January 2014.

Andrews confirmed that Bowman’s injury was different from an isolated ACL tear, which is most common and occurs in noncontact action.

“Multiple ligament tears are more complex and take longer to come back from,” said Andrews, who was not at liberty to discuss Bowman’s progress nor any other of his 49ers patients, including Dockett and Reaser. (The 49ers’ lead orthopedist, Dr. Tim McAdams, and their head trainer, Jeff Ferguson, declined interview requests for this story.)

After sitting out last season, Bowman rejoiced last month at returning to the practice field, well aware he faces many more tests. “I continue to work through the little aches I have,” Bowman said, “but that’s going to be there for at least another year, and I’ve got to figure out a way to deal with it.”

He’s not the only one in his locker room, and he’s not the first, nor the most famous (see: Jerry Rice, 1997).

“So many things challenge you mentally,” Culliver recalled of his ACL rehab. “You have to be patient. It’s not going to be a weekly or monthly deal.”

Baalke, after using three draft picks last year on ACL-recovering prospects, hedged that gamble on his staff’s analysis of those players’ mindsets.

“You try to look at the intangibles, look at the wiring, look at their work ethic, look at their mental toughness,” Baalke said, “and you bet on where you think those guys are going to take themselves post-injury.”

Andrews wholeheartedly agreed: “There’s a certain amount of depression that comes with any injury. That’s why we need to be upbeat when we get in rehab and become cheerleaders to them.”

Inspiration also comes from success stories. Frank Gore tore the ACL in both of his knees in college but became the 49ers’ all-time leading rusher. Adrian Peterson rushed back from his December 2011 knee injury to total 2,097 rushing yards en route to the NFL MVP award in 2012.

The NFL says ACL injuries have decreased, albeit slightly, in recent years: 63 in 2012, 57 in 2013 and 49 in 2014. Only 27 of last year’s ACL tears came in regular-season action. But 22 occurred in the preseason, including 12 in practices.

Rule changes have helped, somewhat. Blockers were banned last year from rolling up on the side of a defender’s leg. Such a play led to 49ers nose tackle Ian Williams’ 2013 ankle fracture at Seattle. Also, defenders are prevented from striking a passer in the knee area or below.

Jeff Miller, the NFL’s senior vice president of health and safety policy, said the league has a committee dedicated to “lower-extremity issues.” Current initiatives are underway with shoe and turf manufactures. Said Miller: “We’re analyzing cleat patterns, shoe flexibility and softness and hardness of turf, in terms of artificial vs. natural, to optimize player safety.”

For its part, the NFL Players Association is funding research at Harvard University, where Dr. Martha Murray has developed a bridge to connect torn ends of a ligament for self-repair. Another study there intends to develop more flexible knee braces.

“The medical advances, not only in the surgical techniques but also with the rehab and recovery, it’s night and day what these guys get to do,” Baalke said last year.

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When John Madden tore his ACL and MCL as a Philadelphia Eagles rookie in 1958, it’s not as if he could choose from today’s methods of knee reconstruction, with grafts taken from a patellar or hamstring tendon or from a cadaver. “No, they just stitched it,” Madden recalled last week.

When Reaser reported to the NFL scouting combine before last year’s draft, medical exams revealed his body was rejecting his ACL’s cadaver graft, prompting a visit to Andrews for a second surgery using a patellar tendon.

“For an ACL recovery, you need three things,” Chao said. “You need a good injury that’s amendable to recover. If you have a multiple ligament injury, it’s very tough. Second, you have to have a good surgeon. And then, you need good rehab. You have to be 3 for 3.”

Culliver’s ACL took so well to his patellar graft (performed by McAdams at Stanford) that he started 14 games last year. His free-agent stock soared, and he scored a four-year, $32 million deal from Washington.

Culliver still vividly recalls his 2013 postsurgery struggles, with his leg “feeling like Jell-O” and needing to build back muscle. That’s common in ACL patients, Andrews said, noting athletes especially have a lot of muscle to lose and thus reclaim.

The degree of difficulty also varies among a player’s position, just as does it among different sports, with playing soccer known as more difficult from which to recover than baseball, for example.

“A defensive back and wide receiver need everything perfect to make it at their position,” Andrews said. “Power is extremely important for a lineman coming out of a stance. A running back has got to cut and change direction. Everyone is a little different.”

Every ACL is different, too. Every recovery is unique. The 49ers have cornered the market in learning that.

“These trainers are on top of it,” Andrews said, “particularly with the 49ers.”

For more on the 49ers, see Cam Inman’s Hot Read blog at blogs.mercurynews.com/49ers. Follow him on Twitter at twitter.com/CamInman.