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.
Purulent collections in the palm of the hand are located either beneath the palmar fascia or are connected with the sheaths of the flexor tendons. When the fingers are affected the pus may be either in the sheaths of the tendons or in the cellular tissue beneath the skin.
As a result of infected wounds pus may accumulate beneath the palmar fascia. The construction of this fascia (see page 357) limits the spread of the pus in some directions and favors it in others. Pus originating beneath the thick middle triangular portion will tend to point to either side, and it may show on the inner side at the hypothenar eminence, or work toward the outer side and point in the web of the thumb (Fig. 379).
If it tends downward it escapes through the openings for the exit of the digital arteries and nerves, and shows in the webs of the fingers.
Sometimes the pus works directly toward the surface through small gaps in the fascia. In such cases a small amount of pus may accumulate above the palmar fascia and between it and the skin; so that there is a collection of pus both above and below the fascia, communicating through a hole in the fascia. This is called an hour glass abscess, or the abces en bissac of the French.
In incising palmar abscesses the only safe way is to limit the incision to the skin and open the deep parts by inserting a closed pair of forceps and then separating its blades. Incisions should not be made nearer to the wrist than on a level with the web of the thumb, or the superficial palmar arch may be cut. The spaces between the metacarpal bones are occupied by the digital arteries and nerves; hence any longitudinal incisions should be made over the tendinous sheaths and metacarpal bones. Usually it is not necessary to carry the incision so deep as to open the sheaths. Incisions over the second, third, and fourth metacarpal bones are tolerably certain to avoid the digital arteries, but an incision over the fifth is liable to wound the artery going to the ulnar side of the little finger as it crosses over from the superficial palmar arch. These arteries of the palm are also liable to be more or less irregular in their location, hence it is better to avoid using the knife in the deeper structures.
If the sheath of the tendons of the hand or fingers become infected, either by being penetrated by a foreign body or by extension from the surrounding tissues, the pus travels along the tendon as far as the sheath extends.
The sheaths of the tendons vary in their extent. The flexor profundus and sublimis tendons lie together in single sheaths, which commence at the base of the distal phalanx. That of the thumb follows the long flexor tendon up the thumb, beneath the annular ligament, to 3 or 4 cm. (1 1/2 in.) above the wrist; that of the little finger passes up to almost opposite the level of the web of the thumb and then spreads over toward the radial side and envelops the remaining tendons of the other three fingers, forming the great carpal bursa which extends up under the annular ligament to 3 or 4 cm. above the wrist (Fig. 380).
The sheaths of the remaining three fingers extend only to the heads of the metacarpal bones, about 2 cm. ( 3/4 in.) above the webs of the fingers. This would leave a space of about 2 cm. ( 3/4 in.) intervening between the proximal ending of the tendon sheaths of the middle three fingers and the great carpal bursa. This is the usual arrangement, but not infrequently the sheath for the little finger ends, as do the other three, opposite the head of the metacarpal bone, or it may go up the entire way to the wrist as a separate sheath, in which case the great carpal bursa envelops only the tendons of the index, middle, and ring fingers.
Fig. 379. - Cadaveric preparation with wax injected beneath the palmar fascia to illustrate where palmar abscesses tend to find an exit.
When suppuration occurs in the sheath of the thumb or little finger it is much more serious than in the other three, because the pus tends to travel directly upward and involve the palm, and go even above the wrist. When suppuration involves the index, middle, or ring fingers it stops when it reaches the vicinity of the metacarpophalangeal joints and involves the palm and carpal bursa only by breaking through its own sheath and breaking into the carpal sheath. This it is not likely to do unless the infection is virulent and the suppuration abundant.