A system of surgery . to laceration by the fall or blow, ren-dering the injury compound. Far more often they are caused by muscular action, bending and finally cracking the bone across the convex femoral condyles. When a person misses a step, or stumbles and makes a strong effort to pull himself up, the knee being already bent in the fall, the patella rests on the condyles by a comparatively narrow transverse surface; and the piece above this surface is a longer or shorter lever upon which the quadriceps acts. The resulting fracture is generally transverse, but may be markedly oblique. The fra
A system of surgery . to laceration by the fall or blow, ren-dering the injury compound. Far more often they are caused by muscular action, bending and finally cracking the bone across the convex femoral condyles. When a person misses a step, or stumbles and makes a strong effort to pull himself up, the knee being already bent in the fall, the patella rests on the condyles by a comparatively narrow transverse surface; and the piece above this surface is a longer or shorter lever upon which the quadriceps acts. The resulting fracture is generally transverse, but may be markedly oblique. The fragments vary much in size, being sometimes equal, again very unequal; now the upper, now the lower is the smaller. In cases from direct violence the surrounding fibrous tissue (periosteum, fascia, and aponeuroses of the vasti muscles) are not much torn, the fragments do not separate much, and union by bone, though not very strong, is usual (Fig. 305). But muscular action tears the fibrous coverings of the bone, and the. Fig. 307.—Union of theFragments of a trans-versely fractured Pa-tella by a thin fibroussheath 4 ins. long.(Charing Cross Mu-seum, No. 403.) 858 INJURIES OF BONES. rent may extend into the fascia lata and the aponeuroses of the vastiwhen the force is great and continues acting after the bone hasyielded, and whilst the knee is bending; the gap between thefragments varies accordingly from a narrow cleft to a gap of someinches, and union is almost always by a shorter or longer, thickeror thinner fibrous bond (Fig. 307). A patella may be broken twiceand even thrice : usually one of the fragments breaks, not the fibrousbond, though this does happen and the skin has torn with it. Symptoms.—A loud snap is often heard as the bone from the ground after the fall is a matter of difficulty. Agroove indicating the gap between the fragments is often seen. Butthe joint quickly swells, as a rule, and the outline of the synovialmembrane becomes clear ; bloody flui
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