The purpose of this study is to elucidate the possibility of an ideal joint alignment after monofocal lengthening of tibia in achondroplastic patients. In 10 cases of the alignments of knee and ankle joints of tibias in which plane radiographs were examined.Unilateral fixators were applied to both tibias,after lengthening in the normal manner, deformity was corrected manually in a single procedure without anesthesia. In order to determine the amount of angle to be corrected, a line was first drawn on the radiograph from the center of the knee joint to the center of the ankle joint. (This line is named the Knee-ankle line: KAL).

Next we drew a line along the ankle joint and measured the angle between this line and KAL. We also drew a line across the tibial plateau and measured the medial angle between this line and KAL. We tried to align the ankle joint perpendicular to KAL and the medial angle between the tibial plateau and KAL at 87 degrees , instead of trying to align the axis of the tibial shaft perfectly straight. The medial angles between the line across the tibial plateau and KAL were corrected to 86 degrees in average, with a range from 84 to 90 degrees, and the medial angles between the line across the ankle joints were corrected to 87 degrees in average, ranging from 80 to 90 degrees in result.

In conclusion, joint alignments of tibias in achondro-plastic patients were able to be corrected successfully without any complications using our monofocal lengthening technique. And severe varus deformities of tibias can be corrected even with monofocal lengthening technique by trying to correct the alignments of knee and ankle joints rather than trying to straighten tibial shafts.