The commencement of an incomplete groove extending from the anterior margin is seen, resembling the groove of the humerus, fig. 58.
1. Stellate comminuted fractures.—a shows the primary nature of the lesion in all comminuted fractures of compact bone, consisting in the production of a number of radiating fissures, which assume a stellate form of which the point of impact corresponds to the centre. b shows an incomplete development of this form, the fragments being simply displaced laterally with slight loss of substance, so as to simulate a real punctured fracture. An illustration of this fracture produced by a bullet travelling at a low degree of velocity is seen in plate XXIII., which also shows the unaltered bullet lying in close proximity to the injured fibula.
The degree of comminution in these fractures depends first on the range of fire and consequent striking force retained by the bullet, a high degree of velocity producing extreme comminution of compact bone. The severity of the latter again may be influenced by the measure of resistance dependent on the density and brittleness of any individual bone, or on the possession of the same characters as a special property by the tissues of the man struck. Thus plate IV. shows a fracture of the humerus produced by a bullet shot from a short range, and the fragments are comparatively large and of even dimensions, while plate XIV. shows extreme comminution of the portion of the femur exposed to direct impact, with elongated large fragments at the sides of the track. Plate XIX. shows less extreme comminution and less separation of the fragments, and was probably produced by a bullet from a longer range of fire.
The separation of elongated lateral fragments is a special feature, and best marked when the portion of bone struck is considerably wider than the bullet, as in the case of the shaft of the femur. These fragments correspond in the method of their production to those seen in the wedge fractures described below, while their separation leaves a pointed extremity to either segment of the shaft. This fracture in its purest type is, I believe, spoken of as the 'butterfly fracture.'
With regard to the spread of the fissures in the long axis of the bone into neighbouring articulations I think fractures produced by bullets of small calibre differ considerably from those produced by larger projectiles, in that their general tendency is not to extend beyond the commencement of the cancellous bone forming the joint end. This is perhaps capable of explanation on several grounds: first, the smaller area of impact results in the assumption of a strongly marked stellate figure, the radiating fissures of which rapidly reach the lateral limits of the shaft, producing a solution of continuity in the bone which interrupts the continuance of the action of the wedge represented by the bullet. Secondly, the small size of the wedge itself is opposed to the wide separation of the parts directly implicated, which is necessary for the continued progress of the process of fissuring, and again the rapidity of passage minimises the period during which the force is exerted. It is in these points that I believe the chief differences between the modern and old gunshot fractures find their explanation, since with the larger bullets fractures extending from some distance into the joints were a somewhat special feature. In addition it is probable that the alteration in structure at the junction of the shafts with the cancellous ends also tends to check the regular extension of the fissures, as a similar limitation is illustrated even in some fractures by Snider bullets. Fig. 51 of the lower end of the femur illustrates a not uncommon lower limit to a comminuted injury in this region.
Fig. 51.—Lower end of Femur.
From Case needing amputation. It shows the usual tendency of the fissures to stop short of the articular ends of the long bones
The degree and nature of the comminution also vary with the directness of impact on the part of the bullet. The more nearly this approaches at a right angle, the more severe is the local comminution, but probably a lesser area of the shaft is implicated. Plate V. shows an example of this: all trace of continuity is lost, a wide gap separates the bone ends, while the fragments themselves have been for the most part driven altogether out of the wound. Oblique impact, on the other hand, may widen the comminuted area at the point of impact, while, if the bullet retains sufficient force and regularity of outline, it may then travel 'cutting its way' through the remainder of the bone in an oblique direction. It will be of course recognised that the exact impact of the bullet depends not alone on the direction of the projectile, but also on the nature of the slope offered by the surface of bone struck.
2. Wedge fractures.—This form (c and d, fig. 50) is equally characteristic of gunshot injury with pure perforation; it is met with in two varieties. c illustrates the more strongly marked type; in it the bullet makes passing lateral impact with the shaft, and from the point struck radiating fissures extend to the opposite margin, so that a wedge-shaped piece of bone often secondarily comminuted is separated from the remainder of the shaft; see plate X. of the radius.