Anatomical landmark to locate the ankle center for determination of the mechanical axis of the lower extremity in Thai subjects.

OBJECTIVE: The present study was carried out to determine the relationship of true ankle center, the extreme-midpoint of the ankle and tibial axis for identification of lower limb alignment in Thai subjects.

MATERIAL AND METHOD: There were 26 volunteers in our study, 13 male and 13 female with their ages ranged between 20 and 40 years. All underwent plain true antero-posterior radiograph of their both ankle joint including distal one-third of their tibias, which were controlled by a special splint. Three variables were made on the radiograph including one line and two points. The line was the axis of the distal tibia, which was performed by the use of connecting of center points of tibial diaphysis and metaphysis. The first point was the center of talar dome at the subchondral bone or the true ankle center and the second point, the anatomical ankle center or the extreme-midpoint of the ankle, which was the mid-point between the lateral most rim of lateral malleolus and the medial most rim of medial malleolus. Then the distances between the tibial axial line and these two points were measured by the use of perpendicular lines between the tibial axial line and those points.

RESULTS: The center of the talar dome was in the distal tibial axis in all radiographs. The anatomical ankle center or the extreme-midpoint of the ankle located lateral to the axis with an average distance of 2.1 +/- 1.1 mm. This finding did not depend on our volunteers' biodata.

CONCLUSION: To identify the lower endpoint of mechanical axis of the lower extremity in Thai subjects, the true ankle center located approximately 2 mm medial to the extreme-midpoint, which commonly used as anatomic landmark of the ankle center.