Femoral stem sagittal balance - Do we need a new entry point?

Abstract

Total hip replacement (THR) is one of the most common orthopaedic procedures. In the USA, the prevalence of THR was about 0,83% in 2010 corresponding to approximately 2,5 million patients. Complication rates tend to increase as primary THA procedures increase as well, resulting in a high clinical and economic burden Component malposition is a common factor for further complications, regarding joint stability and function. Impingement and dislocation constitute a post-operative complication directly affected by improper component implantation like stem anteversion discrepancy. Femoral stem loosening has been also recognised as an additional complication even in modern stem designs. Data from studies by Hoenders et al and Greenfield et al, regard initial stem micro movement and early stage migration, as an independent negative predictive factor of implant loosening, acting as osteoclast differentiation stimuli. Camine et al have also announced similar results about the negative effects of stem micro motion and migration, using a parametric model. Finally, femoral stem positioning is regarded as a predisposing factor of periprosthetic fractures acting as a “stress riser”. Taking into account the importance of proper stem positioning, sagittal stem balance might play a critical role in these complications, especially on initial implant micro movement. While coronal stem centering has been traditionally controlled in order to avoid a varus or valgus positioning, sagittal centering is less studied in the literature, while its importance remains unknown. Husmann et al examined four femoral canal flare indexes and described the difference between the anteroposterior (AP) and the mediolateral (ML) distances of the proximal femur, indicating Abstract Objectives: Femoral stem positioning is of great importance in hip arthroplasty. Straight stem sagittal balance gains recently more attention in the literature. Methods: We performed a both clinical and cadaveric study in order to identify a possible ideal stem entry point at the level of the proximal femur, that ensures an optimal sagittal stem centering. We compared the sagittal tilt of 52 patients with femoral stem implantation in post-operative x-rays, dividing them in two groups depending on posterior neck cortex perforation. Subsequently, femoral neck osteotomy was performed in 40 cadaveric femurs. After placing an average straight stem, measurements of stem axis and femoral neck were made, in order to identify a possible area that could be used as a landmark, through which an optimal sagittal centering could be achieved. Results: Based on our results, stem sagittal tilt differed significantly when posterior neck was spared. In cadaveric evaluation, when posterior neck cortex was not perforated, the tip of stem was in contact with the posterior diaphysis cortex, thus malpositioned in the sagittal plane. We additionally found a statistically significant difference between neck centre and a) stem posterior boarder and b) neck posterior cortex distance. Conclusions: We conclude that placing the femoral stem just posteriorly to the posterior neck cortex, seems to be a good technique in order to achieve optimal sagittal balance of the femoral component.