Functionally, this is quite important in such things as shaking hands, taking change from a cashier, paying for and receiving food at a drive-through, combing the hair, holding a plate of food, playing sports, keyboard use, and many others. Lack of supination results in an abnormal posture of the hand which is easily noticeable.

The major muscle that causes supination, surprisingly, is the biceps. Therefore, weakness of the biceps will result in supination weakness. Injury to the C6 nerve root in brachial plexus injuries will weaken or paralyze the biceps and therefore affect supination as well as elbow flexion. There is a separate supinator muscle in the forearm that is supplied by the C7 nerve root, and this can also contribute to weakness of supination if injured.

Normal supination relies on an intact and neutral shoulder joint position. The most common cause of supination loss in our experience with several thousand obstetric brachial plexus patients is actually an abnormal shoulder posture. This is an important concept and must be understood to know how to manage the problem.

                    Pronation                           Neutral                              Supination

The most common injury to the brachial plexus in infants is to the upper roots, C5 and C6. This results in paralysis of the shoulder and biceps, and leads to contractures (shortening and scarring) of the large muscles under the arm and chest. This in turn leads to internal twisting of the arm (internal rotation) and the "waiter’s tip" posture. Even in the space of a few months, a posterior shoulder dislocation can occur due to faulty formation of the shoulder joint. Typically the shoulder dislocates backward (posteriorly) but sometimes downward (inferiorly) as well.

The posture of a patient with posterior dislocation is severe internal rotation at the shoulder. This prevents supination, and the treatment is at the shoulder level, not at the forearm or wrist. The surgery (capsulodesis) replaces the arm into the proper location in the shoulder joint and then holds it there with stitches. This usually allows neutral position of the arm and shoulder and supination is then possible. If the supinator muscle is also weak, then a tendon transfer in the forearm (pronator tendon transfer) can be done to help at that level as well. It is important to note that the shoulder dislocation is often accompanied by a contracture of the biceps tendon, which can be surgically released at the same time as the capsulodesis is performed.

Supination loss affects most children who have had a brachial plexus injury. Appropriate diagnosis and treatment will reduce functional consequences. The team at Texas Children’s Hospital has the world’s largest experience with this problem and recently developed techniques have increased the functional improvements that are possible.

Rahul Nath, M.D., is a full-time academic surgeon at Baylor College of Medicine in Houston, Texas, specializing entirely in surgery of peripheral nerve injuries. He also holds the title of Reconstructive Microsurgeon in the Texas Children's Hospital Brachial Plexus Clinic. His practice is 75% surgery of obstetric brachial plexus injuries, and 25% adult nerve injuries. Dr. Nath has performed brachial plexus and nerve surgery on over 2,500 separate patients in the past 6 years and has developed many newsurgical procedures for brachial plexus and nerve reconstruction. He was named as one of "America's Top Doctors" in 2001 and 2002 by Castle-Connelly Group, a peer-nominated listing of outstanding physicians in the United States; less than 1% of American physicians are on this list. Dr. Nath was the only specialist named in the field of Pediatric Brachial Plexus Injury.