Knee deformity. X-ray of the legs of a patient with a valgus instability of their left knee (right). The knee is facing inwards, causing the hips (top) to become mis-aligned. This condition will be treated by replacing the left knee with a prosthetic (artificial) joint. For a sequence showing the surgery see images M551/397-M551/406. For an X-ray of the prosthetic joint see M600/318.