Stress changes of femoral head in developmental dislocation of the hip

Abstract

Objective To explore the changes of surface stress and angle of inclination of femoral head in developmental dislocation of the hip. Methods Left hip dislocation model was established surgically in 7 Tibetan pigs while right sides served as control group. Pelvic radiological examination was performed. And bilateral values of Sharp angle and acetabular head index were measured at different timepoints of postoperative immediately, postoperative Month 1 and Month 3 respectively. Computed tomography examinations of pelvis and lower extremities were performed. Then, a three-dimensional finite element model was established for analyzing the characteristics of stress distribution of femoral head and control side. Results Postoperative immediately, Sharp angle showed no significant difference between experimental and control sides. At postoperative Month 1 & 3, Sharp angle increased at experimental side versus control side and the difference was insignificant. At postoperative immediately, Month 1 and Month 3, head acetabular index at experimental side decreased versus control side and the difference was significant; ipsilateral comparison showed that, with elapsing time of dislocation, Sharp angle increased at experimental side and the difference was insignificant; acetabular head index decreased with elapsing time of dislocation, the difference was significant. Finite element analysis of surface stress of femoral head: stress distribution of the same site was compared with that of control side femoral head at Month 1 and 3. Stress distribution significantly increased at experimental side and the difference was statistically significant (P<0.05); With elapsing time, stress value of medial femoral head at experimental side and lateral stress of femoral head increased and stress distribution of the same site was statistically significant (P<0.05). Conclusions Increase of anterior tilt angle and deformation of femoral head and acetabulum occur gradually and it is correlated with surface stress distribution of femoral head. Thus early detection, timely operation and correcting anterior tilt angle are essential. Key words: Hip dislocation, developmental; Finite element analysis; Models, animal