Measurement of the medial distal tibial angle

The aim of this study was to describe the difference between the medial distal tibial angle (MDTA) when measured on whole lower limb radiographs and mortise radiographs of the ankle.

A total of 48 legs were included of 24 healthy volunteers. Standard radiographs were obtained of the whole lower leg. Mortise radiographs were obtained of the ankle. The MDTA was measured on the digitized radiographs by three orthopaedic residents, one orthopaedic surgeon and one biomechanical movement scientist. For each leg, the angles measured from the two images were compared. The inter-observer reliability of each method was calculated.

The MDTA as measured on whole lower leg images (94.6 ± 2.6 degrees) was significantly different compared with the angle measured on mortise ankle images (92.1 ± 2.2 degrees) (p < 0.01). The mean measurement difference between observers was less than 1 degree. Reliability of the measurements was good with a high association (κ = 0.85) between observers for the angles measured on the whole lower leg images and also a high association (κ = 0.83) between the observers for the mortise ankle image measurements.

The MDTA is not the same on whole lower leg images and mortise views of the ankle. There was an excellent interobserver reliability for the angles measured.

Foot and ankle surgeons should take this into account when planning coronal deformity correction of the distal tibia. We believe whole lower leg images should be used to assess the medial distal tibial angle.