Tip Apex Distance: a useful method to assess extra-capsular neck of femur fixation?

The Tip Apex Distance (TAD) is a simple measurement that predicts screw cut-out in the femoral head from trochanteric fractures treated with a fixed angle sliding hip screw device [1]. It uses a numerical value to show placement of the screw in the head: higher values indicating higher likelihood of fixation failure by extrusion of the screw. Currently the cost of hip fracture care in the UK is great, at an estimated £1.4 billion per annum [2]. In order to examine the care delivered to these 70,000 patients affected by a neck of femur fracture, The National Hip Fracture Database (NHFD) collects information about case-mix, care and patient outcomes. However, actual data pertaining to the adequacy of fixation for fracture treatment is not routinely audited. Analysis of NHFD data according to fracture subtypes has shown that for the UK population: 41% were displaced intracapsular, 13% undisplaced intracapsular, 35% intertrochanteric and 6% subtrochanteric fractures [2]. Intertrochanteric fractures therefore comprise a significant proportion of the fractures sustained in the population. Nationally, the majority (81%) were treated by a sliding hip screw device [2].