Effect of use of different landmark methods on determining stifle angle and on calculated tibial tuberosity advancement.

OBJECTIVES

Firstly, to investigate the effect that using different landmarks has on the measured stifle angle. Secondly, to determine whether any differences in measured stifle angle would lead to variations in the required extent of tibial tuberosity advancement (TTA).

METHODS

Three greyhound stifles were positioned in a total of 66 different angles. Radiographic exposures of each stifle angle were made. For each radiograph i) the stifle angle was measured using each of three sets of landmarks and ii) the extent of TTA required to obtain a patella tendon angle of 90° was measured. Each radiograph was plotted graphically according to the stifle angle and the extent of TTA required. Linear regression analysis was used to calculate the TTA required for a stifle angle of 135° measured using each of the three landmark sets.

RESULTS

On average, the stifle angle determined by the Long Axes method differed by 18° from the stifle angle determined with the Kinematic method. The stifle angle determined using the Eminence method differed from that determined using the Kinematic method by three degrees. The use of the Long Axes of the tibia and femur as landmarks to determine a stifle angle resulted in 5 mm and 4 mm over-advancement of the tibial tuberosity compared to the use of Kinematic or Eminence landmark methods respectively.

CLINICAL SIGNIFICANCE: The method used to measure the stifle joint angle can influence the value of the required TTA advancement. This is an additional variable that should be considered during TTA planning and when comparing in vivo and in vitro studies.