BIOMECHANICS OF THE HIP-JOINT CAPSULE - A MATHEMATICAL-MODEL AND CLINICAL IMPLICATIONS

Objective. Our aim was to develop a mathematical model to calculate fo rces, tension and stretching in the hip joint capsule, under condition s caused by the joint effusion usually accompanying hip disease. Desig n. A mathematical model was developed, based on experimental data from cadaver studies. Background. Intracapsular pressure is important with respect to the degree of painless movement in the hip. Previously, we established the relations between the rotation around the axis of the neck of the femur, joint effusion, intracapsular pressure and joint s tability. Methods. in six cadaver adult hips the joint distraction, th e traction force along and the rotation around the axis of the neck of the femur and the intracapsular pressure, were simultaneously monitor ed as the volume of intracapsularly infused saline was increased. The elasticity-constants included in the extracted formula for the fluid p ressure were calculated in a designed computer software based on these experimental data. Results. Presented in Figures 3-12. Conclusions. I n the normal joint there is no increase in intracapsular pressure, nor any tension in the hyperboloid shape capsule within the normal range of rotation around the axis of the neck of the femur. This shape is di storted in a hip with effusion, rotation then resulting in an increase d intracapsular pressure and tension in the capsule, with potential ri sk of ruptures. Relevance Our findings explain the clinical symptomato logy as well as sequele following hip joint tamponade in hip condition s such as transient synovitis, septic arthritis, juvenile chronic arth ritis, hemophilia, congenital dislocation of the dip, fractures of the neck of the femur and in hip joint dislocations, either traumatic or following arthroplasty. (C) 1997 Elsevier Science Ltd.