A review of tip apex distance in dynamic hip screw fixation of osteoporotic hip fractures

Fractured neck of femur is a common problem seen in elderly osteoporotic females, mostly in Western countries, among which are the extra-capsular fractures such as intertrochanteric and pertrochanteric fractures also known as peritrochanteric fractures, and commonly treated with dynamic hip screw (DHS) or compression hip screw (CHS). The DHS is based on tension band principle and allows the screw to slide within the barrel to enable compression of the fracture when the patient begins to bear weight. This principle only works in the presence of intact medial wall and so cannot be successful in a reverse oblique fracture of the proximal femur. However, it is important that the technique of screw placement is precise and should ideally be central in the femoral neck, on both AP and lateral radiographs. This is why the concept of tip apex distance (TAD) is critical to the outcome of fixation and can accurately predict failure or survival of the screw. A systematic review of articles published in PubMed/Medline, from 1991 to 2011 (twenty years), was carried out to critically analyse common practice with regards to DHS fixation of extra-capsular femoral neck fractures, and review the recommendations of previous authors, with regard to the effect of TAD in DHS fixation. Search words used include TAD, DHS, sliding hip screw, femoral neck fractures, peritrochanteric fractures, tension band principle, fracture collapse, screw cut-out, DHS failure, and failure of fixation. At the end of the review, recommendations and suggestions regarding the ideal techniques of placement of DHS screw into the femoral neck will be made in line with current published literature, in order to establish an evidence base for best practice. A total of forty eight (48) published articles were found relevant to the review topic. Most papers suggested that Tip Apex Distance (TAD) is the most important predictive factor for DHS failure, followed by lag screw position, fracture pattern and reduction, patient's age and presence of osteoporosis. Therefore, we recommend proper training of surgeons, as well as attention to detail while performing DHS for intertrochanteric neck of femur fractures.