It started with a simple video tweeted by The Athletic's David Lombardi. You can see the video above. It is just a run-of-mill, 28-second video of some San Francisco 49ers players stretching. What was notable about the video was that one of the players was defensive star, Nick Bosa. Bosa, as you will painfully recall, tore his left ACL last September, forcing him to miss the remainder of the 2020 season.


It was just a normal video that showed Bosa on the field warming up. But the video caught the eye of a medical professional who liked what he saw. Dr. Nirav Pandya, Associate Professor of UCSF Orthopedic Surgery, and Director of Sports Medicine at Benioff Children's Hospitals, tweeted, "Great double leg squat form for Nick Bosa. This (along with single leg squat) is one of the tests we use after ACL surgery to track recovery and predict future injury risk." I saw his tweet and was curious. Since I tend to worry about players returning from serious injuries, I wanted to know what he was looking for, and how this predicted future injury risk.

I reached out to ask what he meant, and he graciously replied. Dr. Pandya told me they look for "symmetry between the legs, balance, and fluid motion. The knees dropping inward during a squat is predictive of both weakness & future re-injury." He encouraged me to Google "RG3 NFL Combine Valgus" for images that would serve as a great example. And so I did.

One website I found showed images of Robert Griffin III at the 2012 Combine. In the images, you can see how his knees cave in as he takes off and lands his vertical and broad jump attempts. The angle between his hips and knees, known as the Q angle, are not normal. This abnormality is known as valgus knee collapse. It is where the knees cave in, rather than out, like during a squat, a jump and landing, or any other quick move, like cutting. And while there can be multiple factors that develop this, one likely cause appears to be years of poor knee mechanics. Knee valgus collapse, or medial knee, can be a predictor of future problems, and even ACL problems.

But when Dr. Pandya saw the video of Bosa, he did not see the collapsing, or caving of the knees. Said Dr. Pandya, "Signs that someone is still not fully recovered usually shows up physically, such as swelling or a limp. More subtle things that can indicate that recovery is going well include symmetry between the two legs during more functional activities such as squatting, running, or jumping. The reason why symmetry is so important is that equal strength between the two legs is one of the last criteria we use to 'clear' a player." Bosa does not appear to have swelling or limping. And 49ers medical staff has cleared him, so he appears to be fully healed.

But I wanted to know how this looked, as far as Bosa's future with his knees. This is his second ACL tear. He tore his right ACL in 2015, while in high school. Is there anything we can learn, even from a short video clip, that can inform us about possibilities of knee problems moving forward? Obviously this is football, and injuries can happen at any point. But Dr. Pandya did give me some comfort, saying, "...the combination of the fact that 49ers medical staff has cleared him, plus how well he looked in his videos from yesterday, are good signs. The lack of his knee dropping in when he does a squat is a good sign, both for current recovery and future injury risk. Overall, greater than 75 percent of NFL players return to play after an ACL tear, so the numbers are in his favor. The largest risk factor for him moving forward is the fact that he has had an ACL surgery in both legs. That all being said, it's a short 15-second clip, but a good sign, nonetheless!"


This was good news to me. I was concerned. Now I'm not as much. I'll pass this on to the future defensive player of the year...just in case he's worried, too.

Special thanks to Dr. Nirav Pandya for his time and insight. Follow him on Twitter @DrNiravPandya. He also has a sports medicine podcast. Go check it out.

Written By:

Marc Adams


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