DO ABNORMAL HEMIPELVIC BONE STRESSES CONTRIBUTE TO LOOSENING AND MIGRATION OF SCREW-THREADED CUPS

Excellent long-term results have been reported with the Charnley low-f riction arthroplasty. Failure of the cemented acetabular component has been identified as a problem in the longer term, while cemented hip r eplacements in active young patients have exhibited a disconcerting in cidence of early clinical or radiological failure. This resulted in th e development of the cementless arthroplasty. Bone responds favourably to an optimal stress window and reacts dynamically to metal implants that have a greatly differing modulus of elasticity. This study repres ents a comparative qualitative analysis of the peri-acetabular hemipel vic stresses after loading two cementless (press-fit and screw-threade d) acetabular components inserted into identical bone models. A simpli fied model of the artificial hip joint was constructed and the very se nsitive stress analysis technique of holographic interferometry was us ed for the investigation. Peri-acetabular stress concentrations were n oted with the screw-threaded cup. This may predispose to bone resorpti on and it is suggested that these could be implicated in the migration of these cups described in published reports.