Torsional Stability of a Polished, Collarless, Tapered Total Replacement Hip Joint Stem under Vertical Load: An In Vitro Investigation

The torsional stability of a polished, collarless, tapered total replacement hip joint stem has been investigated. It was believed that such a stem would show increasing torsional stability as the vertical component of load on the stem increased. The aim of the study was to examine this hypothesis by testing a number of specimens (including Exeter stems) with either a matt or polished finish, under increasing vertical load, measuring the torsional resistance of a specimen-cement construct within an outer constrained cement shell. It was concluded that stems with a polished, collarless, tapered shape showed increased torsional stability with increasing vertical load, while stems with a matt finish or a collar did not.