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.