_a_, Epiphysis of head. _b_, Epiphysis of great trochanter. _c_, Epiphysis of small trochanter. _d_, Capsular ligaments.
It has long been customary to divide fractures of the neck of the femur into two groups--"intra-" and "extra-capsular"; but as in a considerable proportion of cases the line of fracture falls partly within and partly without the capsule, this classification is wanting in accuracy. It is more correct to divide these fractures into (1) those occurring _through the narrow part of the neck_, which are nearly always purely intra-capsular; and (2) those occurring _through the base of the neck_ in which the line of fracture lies inside the capsule in front, but outside of it behind.
It is of considerable importance to distinguish between fractures in these two positions. The first group occurs almost exclusively in old persons as a result of slight forms of indirect violence, and it is liable, on account of the feeble vascular supply to the upper fragment, to be followed by absorption of the neck, which delays or may even entirely prevent union (Fig. 61). The second group usually occurs in robust adults, and results from severe forms of violence applied to the trochanter. In this group firm osseous union usually takes place.
[Illustration: FIG. 61.--Fracture through Narrow Part of Neck of Femur on section. The Neck of the bone has undergone absorption.]
#Fracture of the Narrow Part of the Neck# or #Intra-capsular Fracture#.--This fracture is most frequently met with in elderly persons, especially women, and is usually produced by comparatively slight forms of indirect violence--such, for example, as result from the foot catching on the edge of a carpet, a stumble in walking, or missing a step in going downstairs.
The line of fracture, which is usually transverse but may be oblique or irregular, lies for the most part within the capsule, and the posterior part of the neck is more comminuted than the anterior. The distal fragment, which includes the base of the neck, the trochanters, and the shaft, is usually displaced upward and rotated laterally. If the periosteum and the retinacular ligaments remain intact, displacement is prevented and union favoured.
Impaction is less common than in fracture through the base of the neck; it usually results from the patient falling on the trochanter, the distal fragment being driven as a wedge into the proximal (Fig. 62).