Horrible Injury

If you watch college football, then you have probably seen or heard about the injury to South Carolina running back Marcus Lattimore.  During the play above, Lattimore dislocated his knee, and tore all four primary knee ligaments.  This type of injury will require extensive surgery and rehabilitation, but Willis Mcgahee was able to make a comeback from a similar injury.  I'm going to post some pictures of his knee after the injury at the bottom of this post, so if you have a weak stomach, you may not want to look at them.

As you can see in the picture above, Lattimore is being tackled from behind, and while his right foot is planted in the ground, he is hit just above the knee on the medial (inside) side of the femur.  These forces causes the femur and tibia to lose their normal articulation with each other, resulting in a knee dislocation.  Because of the large amount of force required to dislocate the knee, the ligaments of the knee are often damaged during a dislocation.  In Lattimore's case, the forces were so large that it tore all four ligaments of the knee: the medial (tibial) and lateral (fibular) collateral ligaments on the sides of the knee, and the anterior and posterior cruciate ligaments inside of the knee.  There have also been reports that he fractured his femur and patella as well, but I have not been able to confirm them.

If you look at the two pictures below, you can clearly see his lateral (outside part) femoral condyle, which you normally cannot see because it articulates (touches) with the top of the tibia.  You can also see that his femur and tibia are not aligned normally, it appears that the tibia (lower leg) is rotated internally.  Anytime someone has a knee dislocation, it is treated as a medical emergency because of the blood vessels and nerves that run behind the knee that could be injured.  I have not seen any reports of this occurring as a result of his injury.  Lattimore is looking at a very long road to recovery, but considering he is an elite athlete, the modern advances that have been made in sports medicine, and his desire to return to competition, I would not bet against him.

Pre-Programmed Reactions: Part II

One type of pre-programmed reaction is the corrective stumbling reaction.  Some times when we are walking, we encounter some type of obstacle or perturbation that affects our balance and may cause us to fall.  The corrective stumbling reaction is present to help prevent us from falling, that is, to maintain our balance until the nervous system has to prepare and initiate a voluntary response to help correct for the perturbation. 

If we are walking and our swing leg (the one that is off the ground) hits something (a curb, step, object, etc.), the correct stumbling reaction creates a flexor response in the leg muscles of the swing leg that will lift the leg up over the obstacle.  If the stance leg (the one that is on the ground) steps on something uneven, or hits something, it creates an extensor response in the muscles of that leg that will shorten the amount of time it is on the ground, allowing the person to place the other leg (the swing leg) on the ground quickly, which will increase the chances of maintaining balance and not falling down.  This pre-programmed reaction will take place approximately 50-100 ms after the person encounters the perturbation, and hopefully will prevent the person from falling.  In the picture above, this reaction helped prevent some of the runners from falling, but did not occur fast enough or cause a great enough response to prevent some of the other runners from falling.

Pre-programmed reactions: Part I

We have recently discussed reflexes and their role in movement.  We said reflexes are an involuntary response to a specific stimulus.  One example was the tendon tap reflex: the doctor taps your patellar tendon with a hammer, and you extend your knee.  Another example is the stretch reflex: when a muscle is stretched, it activates the muscle spindles that cause a reflexive contraction of the same muscle group.  What if we need a bigger, more sustained response to a certain stimulus?  That is where pre-programmed reactions come in.

Like reflexes, pre-programmed reactions are an involuntary response to a specific stimuli.  However, there are some differences between the two.  It takes about 35-40 ms (milliseconds) after a stimulus is presented for the reflexive contraction to take place.  A pre-programmed reaction takes place about 50-100 ms after the stimulus is presented, and it is followed by a voluntary muscle contraction.  Generally, the reflex is a quick burst of muscle activity that does not have many long lasting effects.  The pre-programmed reaction is a stronger muscle contraction and may involve several muscle groups that cross many different joints.  Pre-programmed reactions can also be modified by instructions.  If a person is told that a perturbation is upcoming, and to try not to resist the perturbation, the pre-programmed reaction will be smaller than if they have received no instructions.  Likewise, instructions can be given to increase the pre-programmed response after a perturbation.  This indicates some involvement of the brain with pre-programmed reactions, which is not the case with reflexes.

Later this week, we will discuss some examples of pre-programmed reactions.  The picture above is a hint (think about what happens when you stumble).

Update on Chris Carpenter

At the end of August, I wrote a post talking about thoracic outlet syndrome and the surgery Cardinals pitcher Chris Carpenter underwent to help with the syndrome.  They basically removed his first rib on his right side of the body and released some of the muscles in his neck to relieve the pressure on his brachial plexus (the group of nerves running from his neck to his arm).  Since there were only about 2-3 months left in the season, the plan was for Carpenter to start rehab and get ready to pitch again in 2013. 

Well, apparently Carpenter did not get the memo about this plan.  He was very aggressive with his rehab, and began throwing off a mound with about 4 weeks left in the regular season.  He was able to make 3 starts before the end of the regular season, and tonight will make his second start of the postseason.  All of this is very remarkable, for several reasons.  One, this is not a common procedure performed on baseball pitchers, so the actually recovery and rehabilitation time was a bit of an unknown.  However, for Carpenter to pitch less than 3 months after having a rib removed says a lot about him and the Cardinals medical staff.  Two, Carpenter is 37 years old, and he pitched over 270 innings last year.  We all know that the older we get, the longer it takes the body to heal.  Now everyone heals at different rates, but it is a big unknown after surgery.

If you follow the Cardinals, baseball, and/or Chris Carpenter, then you know he is one of the toughest players in baseball, and also has a remarkable postseason resume.  There aren't many players that would have been able to make this comeback.  Hopefully he can continue to pitch well for a few more starts and the Cardinals can win another World Series.

Neural Control of Movement Part VI: Reflexes

What is a reflex?  If you ask 10 different people, there is a good chance you will get 10 different answers.  Many different and imperfect definitions of reflexes exist.  For example, if the car in front of you suddenly stops, and you quickly step on the brake, is that a reflex?  Well, if we go by the textbook definition of a reflex, which is an involuntary muscle contraction or coordinated patterns of muscle contraction and relaxation elicited by a specific stimuli, it is not a reflex.  You have a choice of whether or not to press the brake pedal (sometimes people don't and rear end the car in front of them).  Reflexes are involuntary movements that are very difficult or almost impossible to override.

There are many different types of reflexes.  One of the simplest and most familiar is the Tendon (T) tap reflex.  Everyone has had this reflex tested at one time or another.  You sit on the end of the exam table with your knee flexed (bent) at about 90 degrees, and the doctor taps your patellar tendon with a mallet.  What should is happen is that after the tap, the knee should extend (straighten).  Why does this happen?  When the doctor taps the tendon, it activates the muscle spindles, which send signals to the CNS that the muscle (the quadriceps) is lengthening.  In order to counteract this lengthening, the CNS will activate the alpha motoneurons of the quadriceps, causing the muscle to shorten in order to counteract the lengthening.  The entire process should take around 35 milliseconds (thousandths of a second).

What is the purpose of this reflex?  Its functional significance is very small.  We aren't walking and moving around often where we get "hit" on a tendon and need a reflexive response.  However, this is a fairly easy reflex to elicit, meaning that it is a useful diagnostic tool for a doctor.  He or she is making sure the reflex is present, and that there is a normal response, and not an exaggerated or diminished response.  This would indicate some type of neurological disorder.  We will talk about more complicated reflexes and their significance in the future.

Hey Roger Goodell, want to really get serious about player safety?

Roger Goodell and the NFL have supposedly started to "crack" down on player safety.  This includes larger fines for hitting defenseless players, especially quarterbacks, especially in the head, and cracking down on bounty programs.  Why is a player penalized and fined for hitting a quarterback in the head?  Because of the potential injury the quarterback may suffer.  So, why isn't the NFL doing more to protect all players from injury head/neck injuries?

I blogged a few weeks back about what seems to be an increase in head and neck injuries this year in the NFL and college football.  I watch many games, and the biggest thing I have seen that puts these players at risk for injury is 1) lowering their head (flexing the neck) when making a tackle (see picture above), and 2) a defender projecting himself head first into an offensive player (it just happened in the Rams/Cardinals game. Very scary but fortunately the players was able to walk off the field).  The second holds the greater risk for a potential head and/or neck injury.  Once the defender leaves the ground, they cannot change their motion until they a) hit the ground or b) hit another player.  Too many times a player dives headfirst to make a tackle and the top of his head makes contact with an opposing player or a teammate.  So, if this type of tackle can lead to the worst possible type of injury, why are players still allowed to do it?  I realize it is something they have probably been doing since they first started playing football, but they risk/reward just isn't worth it.  Is it worth making a tackle this way when the possible consequence could be a concussion or neck injury?  Isn't the NFL concerned about the quality of life for it's players after football?  I am not saying that this would eliminate all head or neck injuries in football, but it would sure cut down on a lot of them.  If you watch any videos of recent injuries like these, in almost all of them the player either puts his head down or projects himself headfirst into a defender or teammate.  I am in no way saying that these players deserve to be injured.  It just seems that more should be done to eliminate this potentially hazardous technique.  We don't teach pitchers to throw at other players heads because of the risk of injury. Youth baseball players are not allowed to slide headfirst because of the injury risk. Why are we letting football players put themselves in danger when the outcome could be disastrous?

I still do not have a simple solution for this.  I think it has to start with the youth leagues and work its way up.  But, if NFL players were penalized and fined for diving headfirst into another player, I imagine some of them would stop doing it, and if even just one head/neck injury is prevented, the it is worth it. 

Neural Control of Movement Part V: Recurrent Inhibition

Last week we talked about reciprocal inhibition, in which the CNS would inhibit the muscles of the one muscle group because their shortening would cause the opposite muscle group to lengthen.  This week, we are going to talk about recurrent inhibition, in which the CNS actually inhibits muscle fibers of the same muscle that is contracting.  This is known as recurrent inhibition, and the inhibitory neuron found in the spinal cord is called a Renshaw cell.

So, how does recurrent inhibition work?  The Renshaw cells are located near the cell bodies of the alpha motoneurons in the spinal cord.  When the alpha motoneurons are excited and send signals to the muscle fibers to contract, the Renshaw cells are also excited.  These Renshaw cells make inhibitory connections on these same alpha motoneurons, thus preventing them from sending more signals down to the muscle fibers.

Now, why would the CNS want to inhibit the same neurons that are causing a muscle to contract?  Well, it gives the CNS more control over the movement.  One way to increase force/decrease force/maintain force is to control the number of muscle fibers that are activated.  Renshaw cells can serve this function by inhibiting alpha motoneurons and limiting the number of muscle fibers involved in the movement.  However, this may not always be the most effective strategy.  The Renshaw cells can be inhibited (turned off) by descending inputs in the spinal cord, so that they cannot inhibit the alpha motoneurons, which would allow for the activation of more motor units and muscle fibers.