Teitge et al. (A-48) describe a radiographic method to demonstrate patellar instability. The 90 subjects ranged in age from 13 to 52 years and were divided into the following four groups on the basis of clinical findings regarding the nature of instability of the knee: normal (no symptoms or signs related to the knee), lateral, medial, and multidirectional instability. Among the data collected were the following radiographic measurements of the congruence angle

(degrees):

Normal Lateral Medial Multidirectional 8 412 16 10 15 16 18 8 25 5 26 22 5 8 20 10 8 26 6 20 8 12 12 8 32 5 8 14 40 12 30 10 14 20 8 10 18 16 12 28 4 34 20 6 20 14 20 9 20 6 5 10 20 35 10 20 22 24 4 9 15 25 2 10 10 10 6 12 5 16 7 0 5 30 0 35 6 30 2 1 15 15 5 25 5 22 10 22 20 Source: Data provided courtesy of Dr. Robert A. Teitge.