Sony Michel: The Impact of His Recent Surgery & “Bone on Bone” Condition

Sony Michel has a history of left knee injuries that began with an ACL rupture during his sophomore year at American Heritage High School in 2011and then an unspecified ligament injury to his left knee during the SEC Championship game in 2017 (he was able to play in the National Semifinal a month later). In the lead up to the NFL draft, The Ringer’s Mike Lombardi reported that teams were concerned about a “bone on bone condition” in the same knee.

Even with those concerns withstanding and all medical information at their disposal, the Patriots were “comfortable” with the injury history of Sony Michel and opted to take him with the 31st pick in the 2018 draft, replacing Dion Lewis who they let go in free agency.

sony michel
Credit – PFF

However, on Wednesday August 1st Sony Michel suffered a reported left knee injury during practice. He underwent a nebulous procedure on the left knee that was initially reported as “draining fluid from the knee” with a recovery time of 10 days but was later described as a “clean-up” procedure that would address some pre-existing issues but keep him out of the pre-season and possibly into the start of the regular season.***

***Update: Sony Michel returned to practice on 8/27

There’s a lot of grey in those different reports. In this piece, I”ll try and connect the dots between his injury history, “bone on bone” condition, and recent surgery, ending with what it all means for his career prospects.

Lets begin with the ACL tear Sony Michel had during high school.

I. Sony Michel ACL Rupture 2011

ACL stands stands for “anterior cruciate ligament” and is a major stabilizer in your knee during any forwards, backwards, or rotational movement.  Think of it like a rubber band that connects your thigh bone (femur) to your shin bone (tibia) and keeps the knee joint from moving outside its intended normal range of motion.

Here’s what the ACL anatomy looks:

sony michel
Credit – Mayo Clinic

Sony Michel ruptured the ACL (meaning it was a complete tear of the ligament) as a sophomore in high school and had surgery to repair it.

Check out this work-safe video of an ACL reconstruction:

The overall outcomes on ACL repair in elite athletes is pretty dang good.  Recent high level evidence on return to sport after ACL surgery has shown that nearly 83% of elite athletes return to sport following an ACL surgery and most performed comparably to non-injured counterparts.

However, the research also shows some potentially serious long-term consequences after ACL surgery.  These include:

  • Higher degeneration rate of knee cartilage (think of this as cushioning in the knee, I go into more detail in section III)
  • Nearly a 3.6x increase in developing osteoarthritis (OA), compared to an uninjured knee.  However, not getting an ACL repair leads to a 4.98x increase in developing OA.
  • OA risk is even higher when the original ACL rupture also involves damage to the knee cartilage. Research shows anywhere from an 18% to 48% increase in osteoarthritis (OA) risk with this combined injury compared to only an ACL rupture.

This table does a good job of summarizing the risk differential for developing OA after an isolated ACL repair vs combined (ACL + cartilage) injury:

sony michel
Credit – World J Orthop. 2017

There are a couple theories as to why an ACL rupture, even after repair, leads to these higher rates of osteoarthritis (OA):

The first is that the traumatic impact to the knee during the initial ACL rupture initiates a chemical degeneration process of the knee cartilage (cushioning in the knee), eventually progressing to OA (click here, here, and here for more info).

The second theory is that an ACL injury, even after it’s been repaired and the ligament is providing optimal stability, can change the mechanics and loading patterns at the knee. This results in accelerated wear and tear and irreversible changes on the knee cartilage (click here, here, and here for more info).

I like to use the analogy of a shoe insole.  Normally, the force from taking a step is distributed evenly across the cushioned insole of your shoe. However, if you start to walk differently (lets say you start to favor the inside of your foot, for whatever reason), then the inner part of the insole is going to wear out much quicker.

sony michel
Credit – Bike Test Reviews

It’s the same concept for the knee cartilage.  Repetitive force on the same spot leads to increased wearing out of the cartilage on that spot.

In the case of Sony Michel, he was able to return from ACL repair at a high level, suffering no reported ill-effects during high school or his time at Georgia.  However, he was still at-risk for those long term consequences.

Risks that may have been increased by his second distinct left knee injury…

II. Undisclosed Grade 1 Ligament Injury

During the 2017 SEC championship game, Sony Michel left the game with an undisclosed knee injury. All I could find is that the injury was classified as a “grade 1 knee sprain“, which means some ligament was stretched out with minor tearing (often just micro-tears).

sony michel
Credit – KneePainExplained

In a vacuum, the grade 1 knee ligament tear isn’t a big deal. In fact, Sony Michel played a month later in Georgia’s College Playoff semifinals against Oklahoma (and played very well).

However, in conjunction with his previous ACL tear, it’s another insult to the same left knee and may have further damaged knee cartilage while exacerbating ongoing changes in his mechanics and loading at the left knee joint.

After Georgia’s loss in the national championship game to Alabama (sorry to bring that up Georgia fans), Sony Michel declared for the draft.  In April 2018, news came out that he had a…

III. Left Knee “Bone on Bone” Condition

To understand what this means, we have to first understand what the typical knee joint looks like.

The knee joint is comprised of the upper leg bone (femur), the shin bone (tibia), the patella (kneecap), and two types of cartilage (articular cartilage and the meniscus).

sony michel
Credit – 3CB Performance and Complete Anatomy

Told ya’ll I’d go into more detail!

Generally, cartilage serves to reduce friction and dampen force. The first type, articular cartilage, covers the ends of the femur (thigh bone) and tibia (shin bone) and the inside of the patella (kneecap). The second type of cartilage, the meniscus, is a dual-crescent shaped pad that sits between the femur and tibia:

sony michel
Credit – MMG 2011

When the articular cartilage and/or meniscus have deteriorated to the extent that the bones are actually rubbing against each other, it’s indicative of knee osteoarthritis aka “bone on bone”.

Here’s an anatomical representation:

sony michel
Credit – ReachMD

And what it looks like on x-ray (notice the decreased space and side to side asymmetry):

sony michel
Credit – Mathew Driscoll

To that point, some reports have referred to Sony Michel’s left knee “bone on bone” condition as “mild arthritis”. This makes sense when you consider all the risk factors of his left knee:

  • ACL rupture in 2011
  • Grade 1 ligament tear in 2017
  • Repetitive and constant loading at the knee (running, jumping, cutting, blocking, etc etc)
  • Constantly geting hit on or around the knee or lower body
  • His body mass index (BMI) of 29.6, placing him in the “overweight” category*.  This has been associated with increased odds for developing arthritis.

*Most NFL players would be in this overweight category due to their high muscle mass

Considering Sony Michel developed “mild arthritis” only seven years removed from his ACL reconstruction, I’d wager his ACL rupture also involved articular cartilage and meniscal damage. As we talked about in section I, that means his left knee was at significantly higher risk for developing osteoarthritis.

All that being said, the Patriots still viewed the risk/reward calculus as tilting toward reward so they drafted him in the first round.  However, that left knee gave him some trouble during practice and Sony Michel was slated for a procedure…

IV. Sony Michel Recent Left Knee Surgery

Originally, Sony Michel was scheduled to have fluid drained from his left knee (medically known as a “joint aspiration” or arthrocentesis).

sony michel
Credit – Epainassist

That fluid refers to excess swelling (“effusion”) in the knee which can cause pain and interfere with function.

The cause of the swelling can be from an immediate (acute) cause like a hit which irritated something in the knee (tends to happen in football) or it can be from an underlying factor like a change in knee mechanics, loading patterns, and decreased cushioning that is gradually exacerbated by thousands and thousands of steps and eventually leads to irritation within the knee.  It could also be both.

Based on follow-up reports about Sony Michel’s knee procedure that termed it a “clean-up to address underlying issues”, my educated guess is that the Patriots medical staff decided the time was right to address the underlying insults rather than just the symptom (the swelling).

This line of thinking was confirmed when it was reported that the original injury was stemming from a meniscus issue.

Thus, they opted to do a more involved procedure (very likely a arthroscopic knee surgery) to remove or clear out (“clean-up”) any cartilage that was irritated or loose and causing his excessive pain and swelling.  This all lines up with his previous ACL injury and degeneration of knee cartilage.

A knee arthroscopy is usually a straight forward surgery that is relatively non-invasive compared to other surgery types.  The surgeon makes tiny holes (portals) into the knee joint, threads in a camera to view the joint, and then uses tiny instruments to complete the task.

sony michel
Credit – Dr. Kunal

The change in course from joint aspiration to arthroscopic knee surgery vibes with the change in Sony Michel’s timeline for return.  It went from 10 days to nearly 4 weeks (from the date of his injury on 8/1 to when he returned to practice on 8/27)

So with this recent procedure, injury history, and alleged “bone on bone” condition in mind, what does mean for him in a Patriots uniform, in the short and long-term?

V. Short and Long-Term Ramifications


We’ve already seen the short-term ramifications in action.  As he ramped up activity and intensity, his knee started to swell, be painful, and limit his ability, resulting in the likely arthroscopic “clean-up” procedure.

If the procedure is able to effectively address the underlying immediate concerns in the knee joint then it’s quite possible that Sony Michel has a  great rookie season without missing more time.

However, regardless of how effective the procedure is, one thing is crystal clear: Sony Michel will have to be extremely proactive and disciplined in taking care of his left knee and body.

The keys for preventing knee pain and symptoms will be muscle strength and proprioceptive/vestibular (sensory system) training.

  1. Muscles are the body’s shock absorbers so the stronger and more endurance they have, the less force goes into the knee joint.
  2. Proprioception and vestibular systems are unconscious feedback systems that inform the brain of where the body is in space (joint positioning for example) and help activate the appropriate muscles.  The more they’re trained and finely tuned, the more stable and safe the knee joint becomes.

    sony michel
    Credit – University of Utah

However, building muscle strength and training the proprioceptive and vestibular systems around the knee after an ACL rupture can be an uphill battle.  Research shows that an ACL rupture causes long-term weakness in key knee muscles, specifically the quads, and decreased proprioception around the knee joint due to something called “arthrogenic muscle inhibiton” in which pain and swelling in the knee joint actually impair muscle activation.


The long-term prognosis is difficult to make.  We don’t have much evidence on how NFL players get on with early onset arthritis but we do know that football itself doesn’t preclude players to developing early onset osteoarthritis.

Therefore, if Sony Michel is able to avoid additional serious injuries to his left knee and works extremely diligently on his left knee muscle strength, sensory systems, and overall fitness, it’s definitely possible that he has an extended career in the NFL (the average career length for an NFL running back is only 2.57 years, might want to have your kid pick a different position).

A good comparison and example for Sony Michel is the similar case of Philadelphia Eagles’ running back Jay Ajayi.

sony michel
Credit –

He dropped to the 5th round in the 2015 NFL draft after reports of a “bone on bone” medical report but still went on to make the Pro Bowl in Miami and had an excellent year in 2017-18′.

Ajayi’s knee has had to be carefully managed (he’s been on the injury report multiple times) and he’s best in a running back by committee role (Sony Michel will have a similar shared role for New England) but overall he’s been an impactful player with a high level of success, bone on bone and all.

I hope the same for Sony Michel.

Thanks for reading and until next time.


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Disclaimer: This is not medical advice and shouldn’t be taken as such. If you’re having medical issues, reach out to a medical professional.

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