On the Anatomy, Biomechanics, and Dumb Luck Behind Zach LaVine’s Torn ACL

It was announced Saturday afternoon that Zach LaVine tore his ACL during the third quarter of the Wolves’ recent loss to the Detroit Pistons meaning that his season is done. “Torn ACL” is a common injury across all sports and has worked its way into nearly every fan’s lexicon, but what exactly is the ACL? How does it tear? What does rehab look like and how long does it take to return to play? I thought it would be a good idea to answer these questions. (Full disclosure: I am currently in my second year of graduate school and am studying to become a physical therapist.) 

What is the ACL?

Let’s start with the basics. ACL stands for anterior cruciate ligament and it is one of the four main ligaments of the knee alongside the posterior cruciate ligament (PCL), medial collateral ligament (MCL), and lateral collateral ligament (LCL). While the MCL and LCL lie outside of the joint capsule of the knee (read: they aren’t actually inside the knee joint), the ACL and PCL are housed within the knee joint and connect to the tibia, or shin bone, and the femur, or thigh bone. The ACL and PCL are so named because they run past each other, which make them look like a cross (cruciate means cross).

The ACL runs from the bottom, back, and outside border of the femur to the top, front, and inside border of the tibia; essentially, it runs diagonally. Because of its orientation within the knee, the ACL’s main functions are to resist extension, or straightening, and rotation of the knee as well as preventing the tibia from excessively moving forward when the femur is fixed (the biomechanical term for this is anterior translation or anterior drawer). Basically, it is the ACL’s job to prevent hyperextension and excessive rotation of the knee and to keep the tibia in close proximity to the femur.

credit: http://www.bionebio.com/

credit: http://www.aclsolutions.com/theacl_1.php

What are the mechanisms behind ACL injuries?

There are three main mechanisms that cause rupture of the ACL. The first two are the ones that are probably instantly thought of when you think of ACL injuries: getting hit with a strong force on the outside of the knee when the foot is planted (think of a running back getting hit by a linebacker from the side) and rotation of the knee when the foot is planted (think typical non-contact injury when the player goes down holding their knee). The third mechanism, and the one I originally thought was the mechanism behind LaVine’s injury, is hyperextension of the knee. However, after looking at the video, I believe LaVine most likely ruptures his ACL when he lands.

When I saw it happen live and when the news was announced that LaVine tore his ACL, I thought his injury occurred when he collided with Pistons big man Andre Drummond in the air; I thought his knee hyperextended. However, this still image of the moment when LaVine and Drummond collided clearly shows that LaVine’s knee is actually bent to roughly 90-degrees; this is important because the ACL is most slacked when the knee is bent and is most taught when the knee is in full extension (totally straight).

It’s a little tough to see on video due to it happening so quickly, so here’s the still of the moment I believe LaVine’s injury occurs.

Even though his knee is bent when he lands (so theoretically the ACL should be slacked), the sudden impact of LaVine landing thrusts his tibia forward while his femur remains relatively still. Remember, this movement (anterior translation) is one of the movements that the ACL resists. The force of the tibia moving away from the femur is too great to be controlled and overcome by the ACL and it gives way.

If you recall the three mechanisms that cause ACL rupture from before, this sudden anterior translation with a bent knee was not one of them, at least not directly. You see, in at least two of the three mechanisms (getting hit from the side and hyperextension), excessive anterior translation of the tibia relative to the femur is a component.

But what makes LaVine’s injury such a freak accident is that even though the tibia excessively anterior translates relative to the femur, you don’t really ever see it happening due to a player landing on their butt/back with their knee bent in such a fashion that the force of said landing drives their tibia forward relative to the femur instead of upward and into their femur (that’s a common mechanism for a meniscus injury, but that’s an article for a later day). There’s nothing that could have prevented this injury; it is pretty much the definition of bad luck.

The only other possible moment that LaVine could have torn his ACL is when he first takes off to jump. However, there was no contact to the outside of his, his leg didn’t rotate as he jumped, and his knee was still in a bent position when he takes off (so it didn’t hyperextend). When you also consider that LaVine didn’t react until right after his hard landing, all of the evidence strongly suggests that the impact was the culprit.

What does rehabilitation look like?

Most post-ACL surgery rehabilitation programs follow a similar progression and guideline.  Rehab typically consists of two focuses: strengthening the muscles of the major muscle groups of the leg and progressing from basic cardiovascular exercise to more functional (in the case of LaVine more basketbally) activities. The strength progression begins at simply contracting the muscles via electrical stimulation and/or self-contraction to eventually lifting weights and the cardiovascular progression begins at biking and moves towards jogging and eventually cutting drills and basketball activities. Rehab usually begins as soon as possible after surgery and most of the time it begins the same day.

What is the timeline for return to play?

Generally, players return to game action 6-9 months after surgical reconstruction of their ACL, though, with many players, they don’t return to their “old self” until at least a year after surgery. The main reason why recovery takes so long is because of the poor blood flow to the ACL, meaning it takes a while for the graft, the new ACL, to receive the key nutrients and building blocks it needs to heal. Despite the new graft being fully healed (in the sense that all of the new ACL tissue has been laid down by the body) after approximately 32-weeks post-surgery, its strength is typically only 50-60% of that of a normal, healthy ACL one year later. In addition, the musculature of the thigh (the quadriceps, hamstrings, and groin) are typically fairly atrophied from being underutilized and need time to return to their previous strength.

However, where things get a little murkier is when there is other structural damage in addition to the ACL. Other structures that may be involved in ACL ruptures are the meniscus, the cartilage of the femur and tibia, and one of the other three main ligaments of the knee. Many times, this “extra damage” is caught on the MRI, though sometimes, rather unfortunately, it isn’t discovered until the surgery begins; any extra damage would throw off the timeline for return to play.

Luckily for Zach LaVine and the Minnesota Timberwolves, ACL reconstruction and rehabilitation has become a fairly exact science over the last couple of decades plus; that is to say, it is no longer the career-ender that it used to be. It’s difficult, and would be irresponsible of me, to speculate how this injury will affect LaVine and his career moving forward; many times players return to full strength, but sometimes they do not. I wouldn’t feel comfortable speculating until we know when the surgery is taking place, whether or not the surgery was successful, and to what extent, if at all, his other knee structures were damaged. And even then, it could be a year before we start seeing the real impact. Right now and for the foreseeable future, all we can do right now is wait and see.

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3 Responsesso far.

  1. gjk says:

    Detail like this is why I like reading this site. For a time, I assumed it was possibly connected to overcompensating for other injuries, since he hasn’t looked healthy for a month. Long-term, the main concern should surround whether his acceleration comes back; he doesn’t use his leaping ability in a way that really strengthens his effectiveness, but his acceleration is the elite physical skill that helps his play the most. Either way, recovering from surgery is an arduous process for anyone, and it’s too bad he has to go through this in the midst of a good season.

    At this point, it’s probably time to use that roster spot they opened when cutting John Lucas. They can’t go into games with 3 healthy wings, especially since Muhammad has missed games here and there and Rush is in his 30s. It might also be time to officially say goodbye to Pek and use his roster spot as well. Even if I don’t expect this team to make the playoffs, it doesn’t make much sense to play Rush 30+ minutes regularly unless they’re winning, nor does it make sense to go into games shorthanded at any position when they’re still in the mix.

  2. pyrrol says:

    I think of ACL tears as the prototype ‘freak injury’ and this case is no different. All the same, I hope this is a wake up call to the organization. When LaVine was injured he was allowed back in the game. This when he was already banged up, and then had some sort of knee issue going on after the tear play. Now, obviously in this case the damage was done and it eventually became clear that LaVine would have to at least leave the game. Still, that’s just not being careful with the talent.

    Though it may not have been a factor at all in this case, I think we need to think twice about playing players as hurt as LaVine seemed to be with his hip issue. He did not seem to recover enough when he came back. I also think we need to take a hard look at the minutes we asked LaVine to play, along with other starters. Simply put, playing with injuries that cause ‘favoring’ and or excessive fatigue can raise the chances of injury. This even includes ligament tears which often happen in one quick, awkward movement encouraged by gassed legs and compensating for injuries (or more often, happen for no reason at all). I’m not saying this was the case with LaVine, but it is a moment to pause as an organization to look at how we approach health and see if we could do more to protect the players.

    I hope LaVine gets back soon and isn’t too upset. He’s a very hard worker, and he has Rubio and Rush to speak to about the process. It’s tough to see–and as Thibs says, he’s not a guy who can be replaced as a player or a personality in the locker room. One thing I like about our guys is that they work really hard. I question only Wiggins’ effort out of our team, but I will say that this is an in game thing. I know he’s a hard working professional guy in general and has busted his butt in the off season to get better. It’s nice to have hard workers on our team. LaVine will be back fast—the challenge will be slowing him down enough to make sure he’s medically ready to return because he’s going to be raring to go.

  3. Tom says:

    I feel for Zack. He has constantly tried to improve his game, and he seems to be a team favorite. That is the type of leader that gets the Wolves deep into the playoffs, He isn’t going to sit and pout, but probably work pretty hard to get back. Hopefully, he will come back with those marvelous hops and change of speed that made him so appealing, but I also hope that he comes back bigger and stronger. If he is going to be a part of Thib’s plans, he needs to be able to handle the extended minutes and rugged play that is Thibs-ball. I also hope that he doesn’t feel rushed to return. The Bulls can tell you have that worked for D Rose.

    This leads me to the extended minutes quandary for our stars. It is important for the big three to be on one page and to play as if they are of one mind by playing together. However, Jack Nicklaus said that Practice doesn’t make perfect, Perfect practice makes perfect. When I see KAT and Wiggins jogging up the court (either on defense or offense), I see guys that know that they are in for a long night and are pacing themselves. Those are minutes that reinforce bad play and Thibs should make changes to make sure that when KAT and Wiggins (possibly Rubio and Zack too) are playing, they are playing full speed by taking shorter, more frequent breaks and building their stamina. Kind of like short shifts in hockey. No one gets overly tired, so everyone can play at maximum effort. Same minutes, but in shorter bursts. As these young guys fill out and get smarter, they can deliver more punishment, remove wasted effort from their game and play at a higher level longer . By playing them extended minutes, night after night, they start cutting corners, like not running in lanes on fast breaks, or not blocking out, but running out in the hopes that they can get a long outlet for a quick score. They get tired and stop moving the ball and moving away from the ball and that’s how leads like the griz game get lost. You saw how they manhandled KAT, and he tends to get pushed away from the low block. When he is fresh, he pushes back harder and gets better shots. As the night goes on, they just keep banging him out further and further away. Rubio gets tired and his shot goes flat and haywire. Wiggins dribbles more and settles for turn around fade-aways. These are symptoms of fatigue and shouldn’t be allowed. Give these guys more and shorter breaks and see if those first quarter spurts are more sustainable. They might stay healthy too.

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