Aim: Concerning the biomechanical properties of the iliotibial tract different opinions can be found in the literature. Due to this fact it was the aim of this study to take measurements about the hip centralising forces of the iliotibial tract in a neutral position as well as in abduction, adduction and flexion of the hip joint at different femoral neck angles by using a custom-made hip prosthesis.
Method: By using a custom-made measuring endoprothesis with the capability for adjusting different femoral neck angles and lengths and, furthermore, by measuring the intra- and subligamentous forces at the height of the greater trochanter, we measured the forces for validating the influence of the iliotibial tract for hip joint centralisation.
Results: By increasing the CCD angle (coxa valga) a higher load on the hip joint results. By decreasing the CCD angle (coxa vara) a lowering of the coxalfemoral load results. Flexion of the knee joint leads to a decrease of the iliotibial tract tension. By extension of the knee joint and resulting tightening of the iliotibial tract, a triplication of the forces at the femoral neck was measured. Flexion of the hip joint exerted a ventralising of the iliotibial tract with an initial decrease of the centralising hip forces. Subligamentous measurement of the iliotibial tract showed increasing forces upon adduction as well as decreasing forces upon abduction of the hip joint. In the investigations about the forces with various femoral neck lengths, we saw a considerable increase by lengthening the femoral neck and resulting higher forces in the acetabulum.
Conclusion: The clinical relevance of these results concerns the predictability of the in- or decreasing tension band wiring effect of the iliotibial tract in correlation to the CCD angle and the direction of motion of the hip joint. The measurements give the clinical users a benchmark for the expected subligamentous forces of the iliotibial tract and the resulting hip centralising forces. The influence of the lengthening of the femoral neck for the hip centralising forces clarifies the importance of the iliotibial tract when planning displacement osteotomies or hip joint replacement.