The medial and lateral dislocations are generally incomplete, and are liable to be mistaken for separation of the lower epiphysis of the femur. When the tibia passes medially, the lateral condyle of the femur forms a prominence, and there is a depression below it. The head of the tibia projects on the medial side, and the medial condyle is in a depression.
When the tibia is displaced laterally, the relative position of the prominences and depressions is reversed.
Treatment.—In dislocations of the knee no special manipulations are necessary to restore the displaced bone to its place, and reduction is not accompanied by a distinct snap.
If, while the patient is fully anæsthetised, traction is made on the leg and counter-traction on the thigh with the knee in the flexed position, the bones can usually be replaced by manipulation.
After reduction has been effected, in antero-posterior dislocations, the limb should be flexed and placed on a pillow, massage and movement being employed from the first. The patient is usually able to walk within a month.
In medial and lateral dislocations there is at first considerable tendency to re-displacement, and it is therefore necessary to secure the joint in a box splint, specially padded, for about fourteen days, massage being employed from the first, and movement commenced when the splint is removed. It is usually about six weeks before the patient can use the limb with freedom.
In compound dislocations, and in those complicated by injury to the popliteal vessels, the question of amputation may have to be considered.
Dislocation of the Superior Tibio-Fibular Articulation.—This joint may be dislocated by twisting forms of violence applied to the foot or leg, or by forcible contraction of the biceps muscle. The displacement may be forward or backward, and the head of the fibula can be felt in its new position with the prominent tendon of the biceps attached to it. The movements of the knee are quite free, but the patient is unable to walk on account of pain. Reduction and retention are, as a rule, easy, and the ultimate result satisfactory. We have frequently met with this injury accompanying compound fractures of both bones of the leg resulting from railway and similar accidents.
By applying direct pressure over the displaced bone with the knee flexed, the dislocation is easily reduced. It is kept in position by a firm bandage or a light rigid splint.
Total Dislocation of Fibula.—Very rarely the fibula is separated from the tibia at both ends and displaced upwards. Bennett of Dublin has pointed out that in some persons the upper end of the fibula does not reach the facet on the tibia—a condition which might be mistaken for a dislocation.