Subtrochanteric Fractures- Current Management Options

摘要

Introduction The Subtrochanteric fractures account for 10-34% of all hip fractures (David G Lavelle 2003).These fractures have long been recognized as the most difficult of femoral fractures in terms of treatment (Delong William G. 2001). These are the fractures between lesser trochanter and 5cm distally. They may occur as singly but sometimes extension of intertrochanteric fractures. Prior to twentieth century these fractures were less common but more complicating to the patient. As the treatment options were few therefore, the situation used to be life threatening (Delong William G. 2001).The treatment of these fractures continues to present a challenge to an Orthopaedic surgeon. This challenge stems from a combination of anatomical and biomechanical features pertinent to this area. (Fielding. clinic orthop 192;86,1973.,Heiple. JBJS 61A; 730, 1979)Anatomical features The subtrochanteric region has been defined in various ways, but most commonly the area between the inferior border of the lesser trochanter and the isthmus of the femoral shaft or the inferior border of the lesser trochanter to the junction of proximal and middle one third of the femur is taken as subtrochanteric region (Stephen H. Sims 2002). The area is mainly cortical due to which the area of healing as well as the vascularity are less. This prolongs the healing time. Moreover the Proximal fragment is short and medullary canal wide leading to less than optimal fixation. The attachment of muscles across the fracture is such that the proximal fragment is flexed, abducted and externally rotated and the distal fragment adducted causing a shear at the fracture site so closed reduction and holding is not possible in these fractures. In the late teens and early adult life the proximal femoral metaphysis and the femoral neck are filled with dense cancellous bone. Because this cancellous bone becomes increasingly sparse with advancing age, contact and purchase for any intramedullary nail type of fixation are poor. The trabecular structure of the femoral head also thins, this result in a relative void of the trabeculae deep to the subchondral bone. Only the centre of the femoral head where the tension and compression trabecular systems cross contains a relatively dense trabecular network that can give adequate purchase for any fixation device.Biomechanical featuresBecause of its shape the femur is subjected to eccentric loading The proximal end of the femur has been likened to a cantilevered arch that transfers the force of weight bearing to the hip and pelvis. In vivo this bending force loads the medial cortex in compression and lateral cortex in tension, the forces are not in equilibrium. There are high stresses acting in Subtrochanteric area, up to 1200lb/sq inch. There is high compressive stress on the medial side and high tensile stress on the lateral side (Kock am J orthop. 21; 177-193, 1917). Although lateral muscles partly compensate for the high compressive medial forces, proximal femur is still eccentrically loaded as the compressive medial forces are considerably greater than the lateral tensile forces (Rybicki etal J. Biomech. 5; 2003,1972 ). Major compressive stresses in the femur are greatest in the medial cortex 1-3 inches below lesser trochanter. If the medial buttress is not intact or can not be re-established, the internal fixation devices are subjected mainly to bending stresses and the loads are concentrated in this high stress area resulting in implant failure or loss of fixation. This is the most highly stressed region in the body. This dissimilar loading pattern is of great importance in selecting internal fixation devices and in understanding the causes and prevention of failure of internal fixation devices. The loading pattern further emphasizes the importance of integrity of medial half of the column as well as the importance of prestressing of the implant in tension. This in turn increases axial compression, which increases the stability of