Brachial Plexus (Shoulder Nerves) Compression vs. Cervical Nerve Root Compression (or How Thoracic Outlet Syndrome Presents)
The brachial plexus is the tangle of nerves that occurs in the shoulder when the cervical nerve roots exit from the spine. They form a “tango” (called a plexus) where these nerves join together and then separate into the final nerves that travel down the arm (the ulnar, median and radial nerves). The brachial plexus nerves can be compressed at the shoulder through three distinct tunnels, the scalene muscles, the tunnel between the collar bone and the first rib and finally between the shoulder blade and the tendon of the pectoralis minor muscle. This is similar to carpel tunnel syndrome at the wrist or cubital tunnel syndrome (“funny bone” nerve) at the elbow but thoracic outlet syndrome as noted, occurs in the shoulder.
If thoracic outlet syndrome is present, symptoms in the arm will occur with arm position and symptoms should be unaffected by neck position. That is, if you raise your arm overhead but do not let your neck go backwards (you prevent extension) and then develop arm symptoms, this might be thoracic outlet syndrome. Typically, thoracic outlet syndrome will cause numbness and paresthesias (pins and needles) to radiate into the pinky side of the hand but there are instances of thumb side of hand numbness too.
Local Neck Pain
Local pain can occur in the neck but typically not from spinal cord or nerve root compression. Neck pain generally derives from the degenerative changes of the disc or facet that causes the bone spur formation in the first place. Degenerative disc changes in the neck can produce neck pain just like arthritis of the knee can cause knee pain. The pain is normally worse with activity or a prolonged stationary positioning (sitting at a computer). Some patients develop increased pain when exposed to vibration forces (driving, running, airplane travel). Instability develops when the two vertebra have lost the restraining couplers that normally stabilize the vertebra (discs, ligaments, facets). Sharp pain develops with quick motions and the neurological structures are possibly at risk for injury with falls and impacts. See the section on cervical degenerative facet and disc disease for further information.
Specific Nerve Injuries
C1-C4 Nerve Injury
There nerves are somewhat different in the neck compared to the lower nerves at C5-T1. Compression of these nerve roots can cause neck pain but generally do not connect to any muscles. Injury to these nerves will therefore not cause arm weakness. Even within this group, the first two nerves (C1 and C2) are different as these two nerves (AKA the greater and lesser occipital nerves) supply sensation to the back of the skull and irritation can generate headaches. The C3 and C4 nerves supply sensation to the neck and very top of the shoulders. Numbness, paresthesias (pins and needles) and pain will follow the distribution of these nerves. Interestingly, the C4 nerve also supplies the anterior chest wall to the nipple line. Compression of this nerve can sometimes mimic chest pain from a heart attack (called cervical angina).
C5 Nerve Injury
The C5 nerve innervates the deltoid muscle and some of the muscles of the rotator cuff. Weakness of any of these muscles can create a problem with shoulder function. Deltoid weakness will make raising the arm at the shoulder difficult and weakness of the rotator cuff muscles can produce problems with internal rotation and external rotation (pulling in or out- the forehand and backhand in tennis for example). There is some evidence that rotator cuff disorders could result from an imbalance of some of the four muscles of the rotator cuff due to either C5 or the C6 nerve malfunctioning.
Compression of the C5 nerve will produce numbness, paresthesias (pins and needles) and pain into the top of the shoulder and the top of the arm but these symptoms will not radiate down below the elbow. Commonly, pain can also radiate into the shoulder blade region (scapula).
C6 Nerve Injury
Involvement of the C6 nerve can produce weakness of the biceps muscle and the wrist extensors (muscles that pull the wrist back opposite the palm side). With biceps weakness, the patient would notice difficulty with lifting objects or holding an object up at eye level. Wrist extension is important for a strong grip. Patients might notice that with weakness of this muscle, their grip feels somewhat weak.
Pain and numbness would radiate down the shoulder into the thumb side of the hand. Pain may not radiate down the entire arm but may stop at the elbow.
C7 Nerve Injury
The C7 nerve innervates three main arm muscles, the triceps, the wrist flexors and the MCP extensors. The triceps is the muscle that is involved with pushing objects away from the body or with pushing your body away from an object like the floor (pushups). The motion of throwing is governed by the triceps and a weak triceps muscle will reduce the throwing ability of one who has the C7 nerve involved.
Weakness of the wrist flexors can be noticed when you pull object towards you with your wrist.
MCP extensors are the muscles that straighten out your fingers. These muscles are important for putting your hand in your pocket. Curled fingers do not fit in pockets well (but It should be noted that it is rare that this muscle is so weak that the fingers cannot be straightened out a little to enter a pocket).
Pain and paresthesias will radiate into the hand in the middle three fingers focusing mainly on the middle finger.
C8 and T1 Nerve Injury
The C8 with the T1 nerve covers the hand muscles. Loss of grip strength is more noticeable with C8 weakness. T1 innervates more of the intrinsic hand muscles important for fine motor skills but C8 also contributes to those. Pain, numbness and paresthesias (pins and needles) from injury of these nerves would radiate to the pinky side of the hand and the inside forearm.
For more resources on symptoms of cervical nerve injuries, please contact the Vail, Aspen, Denver and Grand Junction, Colorado area office of back doctor and spine specialist Dr. Donald Corenman.