Stem neck-shaft angle as a biomechanical prerequisite for aseptic loosening of the acetabular componen (experimental study)

Introduction Causes of aseptic loosening of THA components and improvement of the implants remain the subject of scientific discussions. The objective was to perform comparative analysis of the results of biomechanical modeling of cementless total hip arthroplasty using implants with different stem neck-shaft angles as a prerequisite of aseptic loosening of the acetabular component. Material and methods A biomechanical model of the pelvis and an implant with different stem neck-shaft angles was constructed based on computed tomography findings. Stresses and strains that the patient typically experienced under full weight-bearing on the operated lower limb were explored. Results The use of a stem neck-shaft angle of 125° provided the most favorable localization of the contact patch at the border of the acetabular component - the pelvic bone and lower values of equivalent stresses and contact pressure in comparison with more "valgus" femoral components (135° and 145°). Discussion The data obtained were fully consistent with the results of biomechanical studies by L. Quagliarella et al. (2006) who reported the substantial significance of the neck-shaft angle for on the parameters of contact pressure, since wear and debris-associated osteolysis decrease with a decreased neck-shaft angle. The use of stem neck-shaft angles equal to 125° can be indicated for young patients with good bone quality and equal lower limb length. Unstable femoral cup can be caused by eccentric position of the contact spot at the border of the bone and the acetabular component and distribution of contact pressure and equivalent stresses inside the spot that are typical for artificial joints with stem neck-shaft angle of 145°. Conclusion The findings suggested that the value of stem neck-shaft angle was likely be considered a prerequisite for aseptic loosening of the acetabular component.