Abstract
We noted, in the immature ankle, a discrepancy between the alignment of the distal tibial physis, the distal tibial articular surface and the talar dome in the coronal plane. This led to variability in the orientation of wires and half pins used for limb reconstruction depending on which landmark was used. We aimed to investigate the variability in normal ankle joints to determine which is the most reliable landmark to use for correct wire or pin insertion.
Radiographs of the ankle of 98 children were analysed. A variety of angular measurements were made with respect to the axis of the tibia and classified according to methods described by Shapiro & Mulhotra.
We investigated the inter- and intra-observer variation in these measurements and classifications. Using the Bland-Altman method we found that the talar plafond angle (TPA) showed less variation than the lateral distal tibial angle (LDTA) with narrower limits of agreement and coefficients of repeatability. This was the same across the age and gender groups studied.
The Shapiro classification of distal tibial epiphyseal shape did not appear to correlate with age or gender, but showed more inter- and intra-rater variation using weighted Kappa analysis.
This study suggests that when measuring the orientation of the ankle joint from plain radiographs that the TPA is a more reliable measurement than the LDTA and this should be taken into consideration during decision making and pre-operative planning of lower limb deformity correction.
