New implant acetabular cup

Abstract

The management of large acetabular defects remains one of the most challenging aspects of revision total hip arthroplasties. Failure of frequently used acetabular reconstruction components are, among others, caused by the lack of biological fixation, a non-physiological stress distribution and stress-shielding. Attempting to diminish these drawbacks of current implants a new acetabular cup has been explored. The double layer of this new acetabular cup better fills the acetabular defect. According to Wolff’s law this should reduce stress shielding and stimulate bone ingrowth. Part one of this study explores the relationship between unit cell size of the titanium and mechanical properties for the body centred cubic unit cell. Three graded lattices using different unit cell sizes were designed and 3D-printed out of commercially pure titanium (Grade 1) using selective laser melting. An unconfined compression test with cylindrical samples as well as a confined compression test with hemispherical samples were performed to obtain mechanical properties. An additional finite element study was used to validate the confined compression test. Acetabular defects were made in five Sawbones hemipelves which served as the basis for the design of the ‘patient specific’ acetabular cups. Three triflange and two unflanged acetabular cups were designed and 3D-printed out of commercially pure titanium (Grade 1) using selective laser melting. Mechanical properties were obtained from the unconfined compression tests. All acetabular cups were inserted by two orthopaedic surgeons at the UMC Utrecht. Cyclic testing was performed up to 1000 cycles to assess femoral head penetration under load after insertion. Additional penetration of the femoral head was found to be between 0.1781 and 0.3793 mm. Future work is needed to prevent strut breakage upon insertion and more research is needed in the fatigue behaviour of these new cups and their biological effect on living bone tissue.