A Review of Tip Apex Distance (TAD) in Dynamic Hip Screw (DHS) Fixation of Femoral Fractures

Abstract

Femoral neck fractures commonly occur in elderly osteoporotic females, and include extra-capsular fractures (intertrochanteric and pertrochanteric), and usually treated with the Dynamic Hip Screw (DHS). This is based on tension band principle which allows the screw to slide within the barrel to enable compression of the fracture when the patient bears weight. However, the surgical technique must be precise, as the Tip Apex Distance (TAD) is critical to the outcome of fixation and accurately predicts failure of fixation.
Methodology: A systematic review of articles published in PubMed/Medline, from 1991 to 2011, was carried out to critically analyse common practice with regards to TAD in DHS fixation of extra-capsular fractures, and review previous recommendations.
Search Strategy: Search words include Tip Apex Distance, Dynamic Hip Screw, Sliding Hip Screw, Femoral neck fractures, Peritrochanteric fractures, Tension band principle, Fracture collapse, Screw cut-out, DHS failure, Failure of fixation and similar variations.
Results: At the time writing, Injury has the highest number of relevant publications (9), followed by International Orthoapedics (6), and JBJS (Br) (4), while JBJS (Am) and Orthoapaedics have 3 relevant publications each. Also, during the twenty year review period (1991-2011), 2009 had the highest number of relevant publications (10), with a total of 48 articles related to the review topic.
Conclusions and Recommendations: TAD is the most important predictive factor for lag screw cut-out, followed by lag screw position, fracture pattern, adequacy of fracture reduction and patient age. Although some new devices and techniques have theoretical and biomechanical advantages over DHS, overall, they are not superior in terms of failure rate and functional outcomes. Therefore, there is good evidence to show that DHS still remains the gold standard for the treatment of stable intertrochanteric fractures. However, intra-medullary devices are better for sub-trochanteric or very osteoporotic fractures, being biomechanically more stable than DHS.

Keywords: Tip Apex Distance (TAD), Dynamic Hip Screw (DHS), femoral fractures, intertrochanteric fractures, Screw cut-out, DHS failure.