The second variety, d, is an incomplete development of the stellate fracture in which the fissures pass to one margin of the bone only. The explanation of this variation is probably to be sought in the direction of impact on the part of the bullet, since the main fissure is often accompanied by secondary lines which run a somewhat parallel course to the main one, and suggest the dispersion of the force in the form of concentric waves. Such fractures were most strongly marked in the tibia, the breadth of the surfaces of this bone presenting especially favourable conditions for their production.
3. Notched fractures.—These may be a slight degree of the form of wedge fracture last described; such a one is depicted in plate XXII. where a portion of the spine of the tibia has been carried away by a passing bullet. Other notched fractures approximate themselves more nearly to perforations, the notch being a groove secondary to the opening up of such a track as is shown in the illustration of a perforation of the lower third of the shaft of the tibia (fig. 57 on p. 219). Notching or grooving is naturally much more common in the cancellous portions of bones.
4. Oblique fractures.—These also occur in two varieties: the first has been already alluded to; in it the bullet actually cuts an oblique track in the bone; the main line of fracture is often considerably comminuted, usually at the proximal end of the track (see plates XV. and XIX.).
The second variety (e, fig. 50) is less common; in it two of the main limbs of the simple stellate figure are suppressed, while the remaining two form a continuous line from one margin of the shaft to the other, the point of impact lying approximately in the centre of the line of fracture. Such a fracture is illustrated by the skiagram of a femur in plate XVI. in which the bullet traversed the soft parts transversely at the level of the centre of the fracture, which was 9 inches in length. In another case the line of fracture occupied the lower third of the femur, passing from the inner border of the shaft, the lower end of the upper fragment was formed by the compact tissue forming the outer wall of the external condyle. This latter perforated the vastus externus and lay beneath the skin; as it could not be disentangled, an incision was made over it, and the fragments when reduced were screwed together by Mr. S. W. F. Richardson. In neither fracture was there any comminution. Such fractures most nearly resemble the oblique or spiral ones met with in civil practice as the results of falls. In all the instances I observed the patients were supported on the lower extremities at the time of the accident, and one can only assume that a twist of the trunk consequent on the fall of the body diverts the most forcible vibrations resulting from the impact of the bullet into one line, and thus produces a solution of continuity of a simple oblique nature. In both the cases mentioned above the bullet was probably travelling at a low degree of velocity; in the first it was a ricochet and was retained. I never saw one of these fractures in the upper extremity.
Plate XXI. affords an excellent example of this mechanism. The patient was standing when struck, and then fell backwards. An incomplete fissure 7 inches in length is seen to extend from an otherwise pure perforation of the shaft of the tibia.
5. Transverse fractures.—Throughout these were of very rare occurrence. Plate XX. illustrates a pure transverse fracture produced by passing contact of a bullet probably fired at a distance not exceeding 400 yards, and which subsequently struck the fibula plumb and produced considerable comminution. No fissure extended into the ankle-joint. Comminutions such as that illustrated by plate V. more or less simulated transverse fractures, but I saw no examples of transverse tracks comparable to the oblique ones described above 'cut through' the shaft of a bone.
6. Perforations.—Although these were common in cancellous bone, they were comparatively rare in the compact shafts. I saw, however, complete pure perforations of the shafts of the tibia, femur, clavicle, and other bones. These perforations were, I believe, always the result of low degrees of velocity, and they took the place of simple transverse fractures of the 'cut' variety. The apertures of entry and exit in the bones resembled in character those seen in the soft parts, or in the bones of the skull in low-velocity injuries (see figs. 71 and 72, p. 261). The entry was more or less cleanly cut, while at the exit a plate of bone was raised, and either separated or turned back on a hinge by the bullet (fig. 52), (plate XVII.) Such a projecting hinged fragment was sometimes a source of some trouble; thus in a case of postero-anterior perforation of the lower third of the shaft of the femur, the long exit fragment projected into the substance of the quadriceps extensor muscle, and interfered with flexion of the knee-joint. Fig. 57 of a superficial tunnel of the lower third of the tibia is especially interesting as bringing such injuries of the long bones into line with fractures of the flat bones of the skull, such as are illustrated in fig. 68, p. 259.
Plate XXI. affords an excellent example of perforation of the shaft of the tibia, although complicated by the secondary fissure.
Plates XXIII., VIII., and III., of the fibula, humerus, and clavicle, exhibit examples of what may be called spurious perforations of the shafts of bones, since comminution or loss of continuity accompanies all three.
Subsequently to writing the above paragraphs, I took the opportunity of re-examining the magnificent series of gunshot fractures collected during the Franco-German campaign by Sir William MacCormac, and afterwards presented by him to the museum of St. Thomas's Hospital.