Manual of Surgery Volume Second: Extremities—Head—Neck. Sixth Edition.

by Alexis Thomson; Alexander Miles

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.

Fig. 136.—Female child with right-sided Genu Valgum, the result of Rickets. The pelvis is tilted, and the spine is curved.

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.