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 Roentgen 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.]

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 e