When the quadriceps is overcome by a _contraction of the hamstrings_, as in spastic paraplegia, the knee is fixed in the flexed position and the child is unable to walk. The flexion may be corrected by lengthening the hamstring tendons, bringing the divided biceps tendon through an opening in the vastus lateralis, and attaching it to the rectus and to the patella. If there is a combination of flexion and genu valgum, the knee-joint should be resected and ankylosed in the straight position. #Contracture and Ankylosis at the Knee.#--In addition to the different paralytic forms above described, contracture may result from ulceration and suppuration in the popliteal space, and from disease (osteomyelitis) in one of the adjacent bones. The greater number of contractures and ankyloses are the result of disease in the joint, and have already been described. GENU VALGUM AND GENU VARUM In the normal limb, a line drawn from the centre of the head of the femur to a point midway between the malleoli passes through the centre of the knee-joint. If the line passes outside the centre of the knee-joint, the condition is one of genu valgum; if inside, it is one of genu varum (Fig. 135). [Illustration: FIG. 135.] #Genu Valgum--Knock-knee.#--In this deformity the leg joins the thigh at an angle which is open outwards, and when the affection is bilateral, the projecting knees tend to knock against each other in walking; the term X-legs is sometimes applied to it. _Etiology._--The observations of Macewen and of Mikulicz, and information afforded by the Röntgen rays, have shown that the primary cause of the deformity is an inequality of growth at the ossifying junction of the femur or tibia or of both. This inequality of growth is nearly always due to rickets, and its direction is determined by a faulty attitude of the limbs in standing and walking. The legs being abducted, the weight of the body falls unequally on the medial and lateral parts of the ossifying junctions, and inequality of growth results. _Pathological Anatomy._--Examination of the femur usually shows that the lower third of the diaphysis is lengthened on its medial side and shortened on its lateral side, and that the epiphysis, itself unaltered, is fitted on to the diaphysis obliquely, so that the medial condyle appears to be increased in length and to occupy a level distinctly below that of the lateral condyle. In many cases the tibia shows corresponding alterations. On section of the bones, the epiphysial cartilage and the zone of ossification are found to be unduly broad and irregular. [Illustration: FIG. 136.--Female child with right-sided Genu Valgum, the result of Rickets. The pelvis is tilted, and the spine is curved.]