Prevention of displacement or angulation
As a general rule, the broken fragments will not become displaced more
severely than they were at the time of the original injury. Therefore, if the
original position is acceptable, immobilisation to prevent further displacement
is often unnecessary. In fractures of the shafts of the major long bones, however,
immobilisation is usually necessary in order to maintain correct alignment.
Prevention of movement
As has been mentioned already, absolute immobility is not always essential to
union of a fracture. It is only when movement might shear the delicate capillaries
bridging the fracture that it is undesirable, and, theoretically, rotation
movements are worst in this respect. There are three fractures that constantly
demand immobilisation to ensure their union—namely, those of the scaphoid
bone, of the shaft of the ulna, and of the neck of the femur.
Examples of fractures that heal well without immobilisation are those of
the ribs, clavicle and scapula, and stable fractures of the pelvic ring.
Immobilisation is also unnecessary for certain fractures of the humerus and
femur, and many fractures of the metacarpals, metatarsals and phalanges. In
some fractures, excessive immobilisation may do more harm than good. The
injured hand, in particular, tolerates prolonged immobilisation badly. Whereas
the wrist may be immobilised for many weeks or even months with impunity,
to immobilise injured fingers for a long time is to court disaster in the form of
permanent joint stiffness.