This section is from the book "Applied Anatomy: The Construction Of The Human Body", by Gwilym G. Davis. Also available from Amazon: Applied anatomy: The construction of the human body.
Fractures of the carpal bones are often only suspected or detected by-means of a skiagraph. They are quite rare and are almost impossible to distinguish clinically from ordinary sprains.
Fractures of the metacarpal bones are more common. The bones are subcutaneous on the dorsum of the hand and can be readily felt throughout their entire length. They are not infrequently broken by a blow on the end of the bone in fighting. Hamilton states that in every case in which the fracture has been produced by a blow on the knuckles the distal end of the distal fragment has been drawn toward the palm and its proximal end projected toward the dorsum. This is accounted for by the greater strength of the flexor muscles.
The first, third, and fourth metacarpophalangeal joints have one extensor tendon, the extensor communis digitorum. The second and fifth have in addition the extensor indicis and the extensor minimi digiti. There are two powerful flexors, the sublimis and profundus, and these are aided by the palmaris longus, interossei, and lumbri-cales muscles. In one case Hamilton saw a dorsal projection of the proximal fragment which he believed to be due to the action of the extensor carpi radialis muscle because the deformity became less marked when the hand was bent backward and the tendon relaxed.
On anatomical grounds one would expect this dorsal displacement to occur in fractures of the third metacarpal bone. It has only one carpal tendon inserting into it, the extensor carpi radialis brevior. The second has the flexor carpi radialis inserting on its palmar surface and the extensor carpi radialis longior on its dorsal surface.
The fifth metacarpal bone has the flexor carpi ulnaris on its palmar surface and the extensor carpi ulnaris on its dorsal surface. Hence it would be expected that the flexor and extensor muscles would neutralize each other.
In order to relax the parts as well as to allow for the concavity of the palmar surface of the metacarpal bones a rounded pad is to be placed in the palm and the hand placed on a splint; sometimes an additional flat pad and small dorsal splint is of service. Care should be taken not to displace the fragments laterally by constricting the hand with the bandage.
These are frequently compound, necessitating amputation. Fracture of the proximal phalanx necessitates a splint extending into the hand, but for the middle and distal phalanges a short splint is sufficient. The action of the interossei and lumbricales through their insertion into the extensor tendon is liable to draw the distal fragment toward the dorsum if the fracture is left untreated.
A knowledge of the exact position of the joints is essential to avoid mistaking fractures and dislocations for one another.