When the fracture is caused by _direct violence_, such as a fall on the knee or the kick of a horse, it may be transverse, oblique, or vertical, but in many cases it is stellate, the bone being broken into several irregular pieces. These comminuted fractures are frequently compound. In transverse and oblique fractures, the displacement depends upon the same causes as in fracture by muscular action. In vertical and stellate fractures, unless the knee has been forcibly flexed after the bone has been broken, there is little or no displacement. The treatment is governed by the same considerations as in fractures by muscular action. _Old-standing Fracture._--As fibrous union, even with an interval of several inches between the fragments, is not incompatible with a useful limb, it is not often necessary to operate for this condition, but when the usefulness of the limb is seriously impaired, operative treatment is indicated. The operation is carried out on the same lines as for recent fracture, the ends of the bones being rawed and adhesions divided. When the proximal fragment has become attached to the femur, it should be separated and a layer of fascia interposed; it is sometimes necessary to lengthen the quadriceps muscle by making a number of V-shaped incisions through its substance; or a flap may be turned down from the rectus and stitched to the patella and the ligamentum patellæ. When operative treatment is contra-indicated, the patient should be fitted with a firm apparatus which will limit flexion of the knee and support the fragments. #Dislocation of the patella# is rare. It results from exaggerated muscular movements when the limb is in the fully extended position, or from a blow on one or other edge of the bone. Laxity of the ligaments and knock-knee are predisposing factors. It is sometimes associated with fracture of the edge of the trochlear surface, which renders retention in position difficult. The _lateral_ is the most common variety--the _medial_ being rare. Either may be complete or incomplete. Sometimes the bone is rotated so that its edge rests on the front of the femur--_vertical_ dislocation; and in a few cases it has been completely turned round, so that the articular surface is directed forwards. _Clinical Features._--The joint is fixed, usually in a position of slight flexion, and the displaced patella can readily be palpated. The deformity is a striking one, and at first sight suggests a much more serious injury. Although easily reduced, the dislocation is liable to recur.