Manual of Surgery Volume Second: Extremities—Head—Neck. Sixth Edition.

by Alexis Thomson; Alexander Miles

Fractures of the Vault

Mechanism.—When the skull is broken by direct violence, the fracture takes place at the seat of impact, and its extent varies with the nature of the impinging object and the degree of violence exerted. If, for example, a pointed instrument, such as a bayonet, a foil, or a spike, is forcibly driven against the skull, the weapon simply crashes through the bone, disintegrating it at the point of entrance, and cracking or splintering it for a variable, but limited, distance beyond. On the other hand, when the head is struck by a “blunt” object—for example, a batten falling from a height—the force is applied over a wider area and the elastic skull bends before it. If the limits of its elasticity are not exceeded, the bone recoils into its normal position when the force ceases to act; but if the bone is bent beyond the point from which it can recoil, a fracture takes place—“fracture by bending.” The bone gives way over a wide area, the affected portion may be comminuted, and one or more of the fragments may remain depressed below the level of the rest of the skull. Cracks and fissures spread widely in different directions—often (70 to 75 per cent.) extending into the base. In almost all fractures of the vault the inner table splinters over a wider area than the outer, partly because it is more brittle and is not supported from within, but also because the diffusion of the force as it passes inwards affects a wider area. If a bullet traverses the cranial cavity the inner table is more widely shattered at the aperture of entrance, and the outer table at the aperture of exit. Von Bergmann reported thirty cases in which the inner table alone was fractured by a blow on the head.

Fractures by indirect violence—that is, fractures in which the bone breaks at a point other than the seat of impact—are almost always due to violence inflicted with a blunt object, and acting over a wide area—such, for example, as when the head strikes the pavement. Much discussion has taken place as to the method of their production. It has been shown that when the skull is depressed at one point by a force impinging on it, it bulges at another, so that its whole contour is altered. But the elasticity of the bone varies at different parts of the skull, owing to differences in thickness and in structure. If, therefore, the part which is depressed—that is, the part directly struck—happens to be less elastic than the part which bulges, it gives way, and a fracture by “bending” results; but if the bulging part is the less elastic, it bursts outwards—fracture by “bursting.” The term “fracture by contre-coup” has been incorrectly applied to such fractures when the area of bulging happens to be opposite to the seat of impact. Contre-coup, properly so-called, is only possible in a perfectly spherical body, which, of course, the skull is not.

When a high-velocity bullet penetrates the head, it exerts on the incompressible, semi-fluid brain an explosive (hydro-dynamic) force, which is transmitted to all points on the inner surface of the skull and leads to shattering of the bone.

Repair.—The repair of fractures of the skull is usually attended with an exceedingly small amount of callus. Except in the presence of infection, separated fragments live and become reunited, but they may unite in such a manner as to project towards the brain and, by irritating the cortical centres, cause traumatic epilepsy. In comminuted fractures, the lines of fracture remain permanently visible on the bone, but fissured fractures may leave no trace. Gaps left in the skull by injury or operation are, after a time, filled in by a fibrous membrane, which may undergo ossification from the periphery towards the centre, but unless the aperture is a small one it is seldom completely closed by bone. The new bone which forms is derived from the old bone at the margins of the opening. Permanent defects in the skull are chiefly injurious if they are accompanied by lesions of the underlying dura, such as adhesions to the brain; large gaps may cause giddiness on stooping, or on forcible expiration, as in blowing the nose or playing a wind instrument.

Varieties.—For descriptive purposes, fractures of the vault are divided into the fissured, the punctured, the depressed, and the comminuted varieties. Clinically, however, these varieties are often combined. The practical importance of a given fracture depends upon whether it is simple or compound, rather than upon the exact nature of the damage done to the bone. Compound fractures which open the dura mater are the most serious. Simple fractures result, as a rule, from diffuse forms of violence, and are liable to spread far beyond the seat of impact. Compound fractures result from severe and localised violence—for example, the kick of a horse or the blow of a hammer—and tend to be limited more or less to the seat of impact. In gun-shot injuries, however, there are usually numerous fissures radiating from the point at which the missile enters the skull.

Fissured fractures generally result from blows by blunt objects or from falls, and they usually extend far beyond the area struck, in most cases passing into the base. The fissure may pass through the bone vertically or obliquely, and it may implicate one or both tables. So long as the fracture is simple, it can scarcely be diagnosed except by inference from the associated symptoms of meningeal or cerebral injury. When compound, the crack in the bone can be seen and felt. It is recognised by the eye as a split in the bone, filled with red blood, which, as often as it is sponged away, oozes again into the gap. In fractures by bursting a tuft of hair may be caught between the edges of the fracture, and this adds to the difficulty of purifying the wound.

Diagnosis.—A normal suture may be mistaken for a fissured fracture. A suture, however, may generally be recognised by its position, the irregularity of its margins, and the absence of blood between its edges. At the same time, it is not uncommon, especially in children, for a suture to be sprung by violence applied to the head, or for a fissured fracture to enter a suture and, after running in it for some distance, to leave it again. The edges of a clean cut in the periosteum may be mistaken for a fissure in the bone, especially if reliance is placed on the probe for diagnosis. This error can be avoided by raising the edge of the periosteum from the bone, with the gloved finger. On combined auscultation and percussion a peculiar “hollow-cask” sound may be detected in some cases of fissured fracture of the vault.

Fissured fractures as such call for no treatment. When compound, the wound must be disinfected; and intra-cranial complications, such as meningeal hæmorrhage, laceration of the brain, or infection, are to be treated on the lines already described.

Punctured fractures are of necessity compound, and on account of the risks of infection are to be looked upon as serious injuries. They result from the localised impact of a sharp, and usually infected object the point of which is not infrequently left either in the bone or inside the skull. Fragments of bone are often driven into the brain, and short fissures frequently pass in various directions from the central aperture.