Neutralizing excess stem anteversion during femoral preparation improves initial stability of a triple-tapered stem: a cadaveric biomechanical analysis

Single-tapered (ST) total hip arthroplasty (THA) stems achieve fixation namely through coronal metaphyseal fit. Dual (DT) and Triple-taper (TT) stems have an added sagittal taper to achieve fixation in the anteroposterior plane as well. A single-taper preparation (STP) technique is commonly used for TT stems often resulting in stem hyper-anteversion, under-sizing and loosening. A new technique was developed to decrease the hyper-anteverting effect of and permit stem preparation collinear to the mid-sagittal femoral axis. Eighteen cadaveric femurs (9 pairs) were divided into 2 groups: the conventional STP and the experimental Triple-taper preparation (TTP). Dynamic loading was performed with the hip at 30° flexion to simulate stairdescent. Samples were sprayed with a stochastic pattern for digital image correlation. Each sample ran 10,000 cycles with an increment in compressive load until reaching last load step (LS) or failure (≥ 10 mm of displacement and/or fracture). A total of 80% TTP samples survived to the last load step compared to the 20% STP samples. The overall stiffness of TTP was superior to STP ( p < .001). The TTP had significantly less displacement than the STP ( p = .003). The TTP resulted in less micromotion when compared to STP ( p = .018). On the lateral view, the STP group had 7.6 ± 1.4° of stem anteversion, which significantly decreased to 2.7 ± 2.1° of antervsion after TTP ( p = .002). The TTP technique for a TT stem decreases the excess anteversion permitting an increase in stem size, metaphyseal fit and mechanical stability (subsidence and micromotion) and resistance to fracture compared to using a STP.