The snapping knee of infancy.

Three infants with generalized joint laxity and a negative family history had painful episodes of snapping of one or both knees caused by involuntary, momentary lateral subluxation of the tibia. These episodes of subluxation appeared to be due to involuntary contraction of the biceps femoris muscle. Older children learned to produce the phenomenon voluntarily. Treatment should be symptomatic, since the two children who were followed gradually stopped having involuntary subluxations.