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.
Fig. 140.—Genu Valgum. Same patient as [Fig. 139.] Sitting, to show disappearance of deformity on flexion of knee.
Prognosis.—In children below the age of six, the bones naturally tend to straighten if the child is kept off its feet. After this age, there is no such prospect.
The treatment of knock-knee in children is directed towards curing the rickets and preventing the child from putting its feet to the ground. If it cannot have the services of a nurse and the use of a perambulator, a light padded splint is applied on the lateral side of the limb, extending from the iliac crest to 3 inches beyond the foot. The splint is fixed above and below by bandages, and the projecting knee is drawn towards it by a few turns of elastic webbing. A method specially applicable to hospital out-patients, is to straighten the limbs as far as possible under anæsthesia, and apply a plaster bandage; the bandage is renewed at intervals of three weeks until the deformity is corrected. Whatever plan is adopted, it must be persevered with for at least six months, until the rickety changes in the bones have been entirely recovered from.
If the child is approaching the age of five or six before it comes under treatment, or if the deformity does not yield to treatment by splints, it is better to straighten the limb by osteotomy.
In adolescent knock-knee the patient seeks advice because of the deformity or of pain after exertion, especially at the medial side of the epiphysial junctions, of being easily tired, and of incapacity for any occupation involving standing. The bones are coarse and badly formed, and there is frequently a spinous process projecting downwards from the medial side of the tibia about three finger-breadths below the joint.
When the deformity is bilateral, the patient abducts the thigh and rotates the limb outwards at the hip to disguise the deformity, and to allow the projecting knees to pass each other. He usually supinates or inverts the foot, with the object of bringing the whole length of the lateral border of the sole into contact with the ground. Flat-foot is exceptional. The boots are usually more worn along the lateral than along the medial border of the sole and heel.