The neck of the femur is shortened and its angle diminished. The bones of the leg are sometimes bent inwards in their lower thirds, and this compensates partly for the valgus deformity at the knee. The articular cartilage of the lateral condyle and the lateral meniscus are usually thickened. In pronounced cases the quadriceps tendon and the patella are displaced laterally, and this may be so pronounced that on flexion of the joint the patella is dislocated on to the lateral condyle of the femur. The biceps tendon and ilio-tibial band are shortened and more prominent as a result of the approximation of their attachments, and they are also displaced laterally. The sartorius and gracilis are displaced backwards, so that they descend behind instead of on the medial side of the knee. The popliteal artery lies on the back of the lateral condyle instead of in the hollow between the condyles, and the tibial (internal popliteal) nerve is displaced even farther outwards. The capsular and other ligaments are slack, so that the joint is unstable and easily hyper-extended. There is often some effusion into the joint. [Illustration: FIG. 137.--Female child with Rickety deformities of upper and lower extremities. (Mr. D. M. Greig's case.)] _Radiograms_ reveal the changes in the bones (Fig. 138); the shaft of the femur or tibia, or both, which may also be curved, is set obliquely on its epiphysis; and the clear zone, corresponding to the epiphysial cartilage, is uneven and broader than normal. There are also less obvious changes in the density of the shadow and in the arrangement of the trabecular structure of the bones. [Illustration: FIG. 138.--Radiogram of case of Double Genu Valgum in a child æt. 4.] _Clinical Features._--In the infantile form (Fig. 139) the knock-knee is commonly associated with rickets in other parts of the skeleton, and especially with bending of the tibia and femur, and in extreme cases the child may be unable to walk. [Illustration: FIG. 139.--Genu Valgum in a child æt. 4. Patient standing.] The deformity is about as frequently bilateral as unilateral. There may be knock-knee on the one side and bow-knee on the other. If, as is usually the case, the deformity is due to obliquity of the femur, it disappears on flexing the joint (Fig. 140), because in flexion the tibia glides behind the projecting median condyle; if the deformity affects the tibia only, the influence of flexion in disguising it is not so marked. It is usually possible to hyper-extend the joint, and, in the extended position, to rotate the leg outwards to a greater extent than is normal. In unilateral knock-knee, the affected limb is a little shorter than its fellow, but the patient compensates for this by depressing the pelvis on the affected side. [Illustration: FIG. 140.--Genu Valgum. Same patient as Fig. 139. Sitting, to show disappearance of deformity on flexion of knee.]