Evolution of the Koch model of the biomechanics of the hip: clinical perspective.

Over the past several decades numerous researchers have revisited the model of the biomechanics of the hip first predicated by John Koch in 1917. The contributions of Blount (1956), Frankel (1960), Pauwels (1976), Toridis (1969), Rybicki (1972), Fetto (1994, 1995), Ling (1996), and Lu (1997, 1998) among others created a more complete picture. The present article briefly reviews the previous biomechanical concept and its clinical inconsistencies and offers a model that includes the dynamic and static input of the soft tissues. The action of the iliotibial band (ITB) and the vastus lateralis-gluteus medius complex (as static and dynamic tension bands lateral to the femur) counterbalance the varus bending torque of the loads acting on the hip, transforming the tensile stresses in the lateral femur (as hypothesized by Koch) into compressive stresses. The inclusion of the soft tissues, extending the previous model, widens our understanding of the forces acting on the hip. Thus, a variety of clinical observations can be better explained in a comprehensive theoretical framework.