Calculation of Magnitude of Pre-operative Planning of Tibial Tuberosity Advancement Using the Common Tangent and the Conventional Method: A study of Intra and Inter Observer Variation

Introduction
Two methods to determine pre-operative planning of Tibial tuberosity Advancement (TTA) to achieve a PTA of 90° have been described. The Conventional Method, defines the PTA with the stifle at 135° of flexion and uses the anatomical landmarks of the tibial plateau slope. The Common Tangent Method uses the line tangent to a circle overlying the medial tibial condyle and a circle overlying the medial femoral condyle. The aim of this study was to compare the magnitude of pre-operatively calculated TTA assessed by three observers using the Conventional Method (CM1) and the Common Tangent method (CTM2) and to determine intra-observer and inter-observer variability.

Materials and Methods
Mediolateral digital radiographs were taken of the stifle joint positioned at 135° of flexion in 20 normal dogs, of various breeds and ages. Radiographs were anonymised and coded by an independent co-worker, facilitating blinded investigator’s measurement. Three investigators performed the measurements. TTA was calculated for each radiograph using each method on three separate occasions for a total of 60 measures. A 20 day interval was used between each measurement session.  [...]