There are several varieties. In the congenital form, which is apparently due to a faulty attitude of the lower extremities in utero, the patella may be imperfectly developed or absent; the knee is convex backwards, and attempts to flex the joint cause pain. Other deformities frequently coexist. The treatment consists in flexing the joint to a right angle under an anæsthetic, and maintaining this attitude by means of plaster-of-Paris or splints until the growth of parts overcomes any tendency to relapse.
Acquired Forms.—The most common acquired form is the result of anterior poliomyelitis, and is described in the next section.
The deformity may also be due to rickets which has caused a backward bend of the tibia immediately below its upper epiphysis—sometimes combined with an exaggerated forward curve of the femur. If there is no prospect of spontaneous rectification, the upper end of the tibia should be divided with the osteotome, and the limb straightened.
It may result also from fracture or from separation of one of the epiphyses in the region of the knee, or from cicatricial contraction of the quadriceps. As a result of bone and joint disease, it is met with chiefly in neuro-arthropathies when the knee has become disorganised and flail-like.
Deformities of the Knee resulting from Anterior Poliomyelitis and from Spastic Paralysis.—When there is paralysis of all the muscles acting on the knee, the joint may be so flail-like that the patient is unable to stand without the aid of a crutch, or when weight is put on the limb, it assumes the attitude of genu recurvatum. The usefulness of the limb may be improved by the application of a rigid apparatus with a lock at the joint so that it can be used in the extended position for walking or in the flexed position for sitting. The rigid knee produced by arthrodesis affords good support but is inconvenient in sitting.
When the quadriceps alone is paralysed, the patient is obliged to maintain the joint in the position of extreme extension, because the least degree of flexion results in the limb giving way under him. In course of time the posterior ligament is stretched, and the joint becomes hyper-extended, acquiring the attitude of genu recurvatum. When it is bilateral the gait is seriously impaired. The treatment consists in applying an apparatus which prevents hyper-extension, in improving the condition of the thigh muscles, and in wearing a splint at night which secures the flexed position. Recourse may be had to operative measures, such as transplanting one of the hamstrings into the patella, so as to compensate for the loss of power in the quadriceps, arthrodesis, or supra-condylar osteotomy of the femur.
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]).