Making Sense of Neurapraxia and Denard Robinson’s Injury
Hello all. This is the first of what I hope to be many posts related to various sports injuries related to sports medicine and (in this case) the University of Michigan. I am a physical therapist currently working in Boise, ID , and have been a lifelong Wolverine fan after growing up in the Grand Rapids area.
First of all, it’s important to note that we do not have any definitive information regarding the severity of Denard Robinson’s injury. What we do know is that he appeared to suffer an injury (or “boo-boo”, as Brady Hoke would put it) in October 13th against Ilinois, then suffered what appears to be a more serious ulnar nerve injury on October 27th at Nebraska. Heiko touched on some of the following points HERE. Denard’s injury is particularly concerning due to his responsibilities as a dual-threat quarterback. We’ve all hit our “funny bone,” which is actually an example of minor ulnar nerve compression. This nerve is specifically exposed with the elbow bent (note the position of Denard’s elbow during his injury vs. Nebraska ), hence the risk of re-injury/aggrevation that Denard faces on every dropback and every carry. More importantly, as Heiko mentioned the Ulnar nerve’s motor function involves the use of the interosseous muscles in the hand, which with the lumbricals are responsible for gripping. The lumbricals are actually innervated by both the ulnar and median nerves, with the ring finger and pinky finger innervated by the ulnar nerve. Weakness to the interossei and the lumbricals means that Denard cannot strongly grip the football, hence his absence since the Nebraska injury.
The most likely diagnosis of Denard’s injury is neuropraxia. Essentially this is the least serious form of serious nerve injury, if that makes any sense. Weakness and altered sensation result due to a temporary cessation of conduction in the nerve. When compression is severe enough the axon, which acts as the conducting material of a neuron (see above), undergoes constriction resulting in Wallerian Degeneration, which results essentially in the breakdown of myelin, which is responsible for a nerve’s conduction. Nerves work at a microscopic level by sending electrical signals – disruption of conduction will result in poor function of the nerve. At a neuromuscular junction as shown above (on the right) , the nerve communicates with the muscle by sending neurotransmitters to the muscle. If the nerve is compressed, this process is altered, leading to weakness and altered sensation (1,2).
What does it mean? The bottom line is that it is very hard to prognosticate timetables for nerve injuries (ask Peyton Manning) , as it is so dependent upon the degree of damage to the region. Following Wallerian Degeneration, the body disposes of the injured myelin promptly and begins to regenerate. Regeneration happens at the pace of roughly 1 mm per day. Axons that were crushed and altered by the original injury actually grow back, guided by the help of a structure called the endoneurium. In regards to Denard’s injury, all we can do is wait and hope that his injury isn’t too severe. Electromyelogram’s can be useful in determining the speed of conduction, but their accuracy is questionable in the first 3 weeks following injury (3).
So is there a treatment for the injury? Yes and no – to an extent what Denard needs is time and rest. Rest will help reduce the inflammation that can also compress the nerve and disrupt the connection between nerve and muscle. In my opinion, the use of ice however is counter-productive as it should decrease the circulation to the region, slowing the healing response. I would be interested to see what some of you other health professionals believe in regards to icing Denard’s arm in this situation.
In the meantime treatment also includes exercises the muscles innervated by the ulnar nerve to maximize function following regeneration. Specifically, Neuromuscular Electrical Stimulation (NMES) has been shown to reduce atrophy in denervated muscles and improve strength (4,5,7). Other Physical Therapy techniques include lymphatic massage to reduce swelling, and other modalities to reduce inflammation including electrical stimulation or an Ionto patch with an anti-inflammatory such as Dexamethazone.
Once Denard can confidently grip and throw a football I would expect him to play wearing a protective sleeve that allows elbow flexion (bending) but does provide some cushion to the nerve.
Results following serious peripheral nerve injuries are difficult to prognosticate, and there are numerous variables at play in recovering from an injury such as this. It is my opinion that a team approach of sports medicine professionals is required to maximize function following injury. Thanks for your time, get healthy Denard, and GO BLUE.
1. Clark, R. Skeletal Muscle Response to Denervation. WASH U IN ST LOUIS PHYSICAL THERAPY LECTURE 9-10-08.
2. EARHART G. Neurotransmitters. WASH U IN ST LOUIS PHYSICAL THERAPY LECTURE 8-25-08.
3. Frykman GK, Wolf A, Coyle T. An algorithm for management of peripheral nerve injuries. Orthop Clin North Am. 1981;12(2):239-244.).
4. . Johnson ME, Foster L , DeLee JC. Neurologic and Vascular Injuries Associated with Knee Ligament Injuries. AJSM. 2008;12:2448-2462
5. . Lenman JAR: A clinical and experimental study of the effects of exercise on motor weakness in neurological disease. J Neurol Neurosurg Psychiatry. 22:182-194, 1959
6. . Netter F. Atlas of Human Anatomy. 2006.
7 . Nicolaidis SC, Williams HB. Muscle preservation using animplantable electrical system after nerve injury and repair.Microsurgery. 2001;21:241-247