We all know what happened to Marcus Lattimore. The star running back was blocking for Bruce Ellington in the fourth quarter of the Gamecocks’ battle with Mississippi State when a Bulldogs defender rolled into Lattimore’s knee.

Every USC fan — and just about every college football fan — anxiously anticipated the devastating nature of the injury. Lattimore had torn his ACL. After several weeks of working to decrease swelling and increase motion and strength, Lattimore underwent knee surgery to reconstruct his ACL.

Sports fans read about football players returning from ACL surgery all the time. Lattimore’s injury should be fairly straightforward, right?

Maybe. It depends on what his injury and surgery really involved.

Days after the fateful game, head coach Steve Spurrier admitted, “Our worst fears were realized.” According to ESPN, Spurrier told reporters that Lattimore had a torn ligament in his left knee and also suffered “some cartilage damage.”

Since that statement, and especially after his surgery on Nov. 17, there has been little mention of any other damage found in Lattimore’s knee. Specifically, as an orthopaedic surgeon, what I would like to know is whether he suffered a meniscus tear that was treated during that procedure.

An attempt to interview Marcus through the USC media relations office was unsuccessful.

I’ve searched for more information but cannot find a definitive answer. Even the New York Times, in an article published Sunday, observed that “South Carolina has not released specific information about Lattimore’s injury, other than to say it was to his knee.”

As the Heisman Trophy candidate prepares for his return against Vanderbilt today, I am curious for medical reasons. The presence of a meniscus tear could have a profound impact on his football future.

Traditional thinking among sports medicine surgeons has maintained that athletes have terrific success returning to sports at the same or higher level after ACL injuries. Those beliefs have been questioned in recent years. In a column I wrote earlier this year, I even cited a study that showed only 70 percent of college football players returned to play.

Running backs have been shown to have particularly tough recoveries. A 2006 study in the American Journal of Sports Medicine looked at return to play for NFL running backs and wide receivers. More than 20 percent of those skill players never returned to play after ACL surgery. A power rating analysis of those players showed that performance dropped by one third if they did return.

A meniscus tear could have an even more detrimental effect. The meniscus is a C-shaped piece of cartilage that serves as a shock absorber in the knee. It has been estimated that meniscus tears are found in 40 to 80 percent of ACL reconstructions.

The problem for athletes with meniscus tears lies in the loss of some of their shock- absorbing properties. If the player has part of the meniscus trimmed out (a partial meniscectomy), then the repetitive stress of running, cutting and pivoting places more stress on the bones and cartilage lining of the knee. That stress could cause degenerative changes over time.

The combination of an ACL and meniscus tear could have an adverse effect on a running back’s career. Last year, Robert Brophy, M.D., and other researchers showed that NFL players who had undergone ACL reconstruction and partial meniscectomy had shorter careers in terms of future games and years played than those who underwent either meniscectomy or ACL reconstruction alone.

I certainly understand if USC wants to protect Lattimore’s privacy and medical information. As the Ray Glier article in the New York Times pointed out, NFL teams will eventually learn the extent of his injury. The team doctors of all the teams potentially interested in drafting him will examine his knee thoroughly at the NFL Scouting Combine. They will test his ACL and meniscus, review the latest MRIs and inspect operative records. NFL teams understand the effects of these injuries and calculate risks accordingly.

As the former Byrnes High star returns to the practice field in preparation for USC’s season opener, Lattimore sounds like he’s ready to go.

“I’m not thinking about (the knee) anymore, that’s the main thing. I’m just going out there trying to be myself. I just block it out and remember how I worked for those nine months and knowing that I’m strong enough to be able to take a hit or make that cut. I’m just relying on my faith in God and all the hard work I put into my leg to get it back to full strength.”

Clearly it doesn’t sound like a fear of reinjury will keep them off the field. I just hope structural damage in his knee doesn’t hinder him — this year or for many years to come.

Dr. David Geier is an orthopaedic surgeon and Director of MUSC Sports Medicine. For information about football injuries and other sports medicine topics, go to Dr. Geier’s blog at drdavidgeier.com.