The Hand: Anatomy and Medical Issues

Basic Anatomy
The hand has a very complex anatomy. There is a fine balance between the flexor tendon system, principally from muscles in the forearm that bend the fingers into a grasp, the extensor muscle tendon system from the extensor muscle side of the forearm, and the intrinsic muscles in the palm and proximal portion of the hand.

The tendons that originate from the muscles in the forearm all pass through tunnels. On the extensor side of the wrist, the extensor retinaculum is a thick sheath of fibrous tissue which keeps the tendons from bowstringing, and allows the tendons to function effectively in extending the hand. The forearm muscles that generate the flexor tendons pass through the carpal tunnel, and then in the hand pass through multiple tunnels, which are easily described best as located at every place in the palm where there is a skin crease, in the middle palm and at the base of each phalangeal joint.

Every finger including the thumb, has nerves, arteries, and veins on each side of the digit. This supports the circulation and the sensation to those fingers. Knowing where the neurovascular is would allow at the time of laceration or injury the physician to know the risk to the nerve or the circulation that any particular injury has caused.

A finger can usually get by with one artery and one vein, because the circulation from the opposite side of the finger will usually be sufficient and cross over and fill the need. But if the nerve is lacerated one must expect loss of sensation distal to that laceration. The most important sensation of the fingers to preserve or attempt to restore by surgical repair would be both sides of the thumb, the radial side of the index and long finger, which is necessary for effective sensory pinch, and the ulnar side of the ring and little finger, which commonly are in contact with the surface. It is not that the other areas of sensation are not useful, just not as important.

Laceration / Amputation
Lacerations of flexor tendons can be serious injuries and may need special skills of a surgeon and then special physical therapy for the hand, usually also with a hand therapy specialist. Extensor tendon lacerations and repairs are more "forgiving', and are commonly repaired, even in the emergency room, followed by appropriate splinting and then appropriate therapy.

Amputation of fingertips or phalanges beyond the mid of the middle finger are seldom "reimplanted". They are usually treated with a primary wound closure, or treated "expectantly" with continued wound care of the amputation site (which is left initially open), but does require continued wound care for 4-6 weeks. This is a technique that has the advantage of preserving the maximum length possible of the digit that has been partially amputated. This technique is time consuming and does require a very cooperative patient, but will usually offer a benefit.

Reimplantation means re-attaching the amputated part, finger, or other part of an extremity to the remainder of that extremity or hand. It is usually done by a very specialized surgical team at a referral center. Everything must be ideal. The surgery takes many hours and the recovery takes many months. The results are seldom perfect and almost always a compromise after significant trauma and investment of a great amount of time, cost, and effort. This effort is usually considered primarily for a dominant hand, a thumb, an index finger particularly in a younger injured patient where activity function and job function makes the effort and the commitment reasonable. Reconstruction must be considered an exceptional and not a common procedure, and the choice for reconstructing the amputation site, as opposed to reimplantation, is generally most preferable in a working person and early return to function is highly desirable.

Fractures of the Hand
Fractures of the hand usually require an attempt to achieve close to anatomic or anatomic realignment. The type of reduction can be closed, or non-surgical, just by manipulating the fracture externally. It can surgically open. There can be multiple types of fixation devices used internally surgically, screws, and plates; externally there can be pins applied through the skin and casts and external fixators. It remains important to allow the hand, wrist, and forearm to regain function and use as early as possible, but safely.

Fractures do need to be assessed, however, in 3 planes: the front plane, the side plane, and also the rotational plane. If a fracture heals with a rotational deformity of the metacarpal or finger, it will underlap or overlap the adjacent fingers. It is an issue like this that will commonly force one toward a more aggressive and even surgical approach in treating a hand fracture.

An exception to the above is known as treating the "boxer's fracture." This is a fracture of the distal end of the fifth metacarpal commonly angulated 20-45 degrees usually occurring either in a fight or hitting a hard surface, such as a wall with one's hand. A study done over 30 years ago demonstrated that reducing a boxer's fracture surgically does not give as good a result as just splinting the fracture, as long as it does not exceed an acceptable degree of flexion deformity, with that splint maintained for approximately 3 weeks. Then early function is attempted, and early movement encouraged. This noninvasive technique and treatment has given very good results with very few complaints, very little stiffness issues whereas the surgical approach had far less desirable results, though surgery may be considered for an exceptional case.

The phalanges are notorious for having hyperextension and twisting injuries, and it is common to see minor chip fractures about the joints of the fingers. Though these fractures seem minor, they are always accompanied by damage and injury to the ligaments, the capsules of the joint, or the tendon attachments to the joint. These injuries should be evaluated and a treatment plan established by a skilled practitioner. They should not be ignored or just treated with extension splinting or buddy taping. Dislocations of the joints of the digits are common in sports, and they, too, need to be assessed clinically and radiologically to be certain that there is no more serious injury that needs to be addressed.

Fractures of the distal joint are commonly caused by having a ball hit awkwardly off the extended finger. This may cause either a fracture of the tuft of the phalanx, or can cause a hyperflexion of the distal joint tearing the extensor tendon, usually with a flake of bone off its insertion site. This is known as a mallet finger, and can usually be treated simply after an x-ray to demonstrate that there is no deformity of the joint by a hyperextension splint that needs to be worn until there is evidence of healing. Occasionally surgery is necessary to repair the tendon and the bony fragment into its normal site. Epiphyseal fractures through the growth plate in children need special attention to minimize deformity, which sometimes cannot be avoided, depending on the damage to the epiphysis (growth plate) and should not be ignored by the parents.

Diagnostic Tools
The mainstay of diagnosis is the physical clinical exam by a physician skilled and knowledgeable in hand anatomy and function. X-rays are the primary line of diagnostic study. As most x-rays are now principally digital, they can be reviewed by a consulting physician on an almost-immediate basis. By accessing the films online, there is little excuse for having potential complex injuries not identified as the injured party passes through the emergency room. Computerized x-ray scanning such as CT scan is generally used in the hand solely to identify complex fractures of the carpal bones and/or the wrist in anticipation of surgical reconstruction.

MRI, magnetic resonance imaging is helpful in several ways: one is identifying soft tissue injury, as the MRI is more specific for soft tissue injury than a CT scan or x-ray; another is evaluating the rare risk of tumor or deep infection; also MRI is useful for identifying the subtle circulatory changes and the response of the bone that has been injured; and, it can be a useful diagnostic tool for the complicated wrist or hand problem, acute or chronic, when diagnosis seems very elusive.

Medical-Legal Considerations
Clearly, the hand functions with its tendons, its nerves, its vascular circulation, its multiple carpal bones, metacarpals, and phalanges as a very complex part of our body, needing particular care. That care should include proper diagnosis in an early and timely way and skilled treatment for an ideal result.

Dr. John Toton is an Orthopedic Expert for American Medical Forensic Specialists. Visit AMFS to get more information on Medical Expert Witness articles and opinions.

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