The degree of displacement of the fragments depends upon the extent to which the expansion of the quadriceps tendon is lacerated. As a rule, it is but slightly torn, so that the separation of the fragments does not exceed an inch. In other cases it is widely torn, and the contraction of the quadriceps muscle is then able to separate the fragments by three or four inches, and sometimes causes tilting of the upper fragment. The blood effused into the joint tends still further to increase the separation. As the periosteum is usually torn at a level lower than the fracture, its free margin hangs as a fringe from the proximal fragment, and by getting between the broken ends may form a barrier to osseous union (Macewen). _Clinical Features._--Immediately the bone breaks, the patient falls, and he is unable to rise again, as the limb is at once rendered useless, and in attempting to do so we have known him to fracture the patella of the other limb. The power of extending the limb is lost, and the patient is unable to lift his foot off the ground. The knee-joint is filled with blood and synovia, which usually extend into the bursa under the quadriceps. The two fragments can be detected, separated by an interval which admits of the finger being placed between them, and which is increased on flexing the knee. On relaxing the quadriceps, the fragments may be approximated more or less completely. _Prognosis._--In cases with little displacement, if the fragments have been kept in perfect apposition, osseous union may take place, but in the great majority of cases the union is fibrous. The shortening of the quadriceps and the gradual stretching and thinning of the connecting fibrous band may allow of further separation of the fragments (Fig. 88), which to a variable extent interferes with the stability and functions of the limb. The proximal fragment sometimes becomes attached to the front of the femur, and moves with it, and the fibrous band between the two fragments gradually becomes stretched. After bony union has occurred, it is not uncommon for the patella to be fractured again by a fall within a month or two of the original accident. [Illustration: FIG. 88.--Fracture of Patella, showing wide separation of fragments, which are united by a fibrous band. (Anatomical Museum of the University of Edinburgh.)]