Comparison of two metaphyseal-fitting (short) femoral stems in primary total hip arthroplasty: study protocol for a prospective randomized clinical trial with additional biomechanical testing and finite element analysis

Abstract

Background Total hip replacement has recently followed a progressive evolution towards principles of bone- and soft-tissue-sparing surgery. Regarding femoral implants, different stem designs have been developed as an alternative to conventional stems, and there is a renewed interest towards short versions of uncemented femoral implants. Based on both experimental testing and finite element modeling, the proposed study has been designed to compare the biomechanical properties and clinical performance of the newly introduced short-stem Minima S, for which clinical data are lacking with an older generation stem, the Trilock Bone Preservation Stem with an established performance record in short to midterm follow-up. Methods/design In the experimental study, the transmission of forces as measured by cortical surface-strain distribution in the proximal femur will be evaluated using digital image correlation (DIC), first on the non-implanted femur and then on the implanted stems. Finite element parametric models of the bone, the stem and their interface will be also developed. Finite element predictions of surface strains in implanted composite femurs, after being validated against biomechanical testing measurements, will be used to assist the comparison of the stems by deriving important data on the developed stress and strain fields, which cannot be measured through biomechanical testing. Finally, a prospective randomized comparative clinical study between these two stems will be also conducted to determine (1) their clinical performance up to 2 years’ follow-up using clinical scores and gait analysis (2) stem fixation and remodeling using a detailed radiographic analysis and (3) incidence and types of complications. Discussion Our study would be the first that compares not only the clinical and radiological outcome but also the biomechanical properties of two differently designed femoral implants that are theoretically classified in the same main category of cervico-metaphyseal-diaphyseal short stems. We can hypothesize that even these subtle variations in geometric design between these two stems may create different loading characteristics and thus dissimilar biomechanical behaviors, which in turn could have an influence to their clinical performance. Trial registration International Standard Randomized Controlled Trial Number, ID: ISRCTN10096716 . Retrospectively registered on May 8 2018. Electronic supplementary material The online version of this article (10.1186/s13063-019-3445-x) contains supplementary material, which is available to authorized users.

Comparative analysis of the biomechanical behavior of two different design metaphyseal-fitting short stems using digital image correlation

“…We are also aware that cortical strain measurement cannot directly reflect the in vivo performance because composite models represent a nonviable bone without the capacity to be remodeled. For this purpose, a simultaneous clinical study is already running, aiming to assess the remodeling process around these specific implants in vivo, by means of a detailed radiological analysis [76]. Nevertheless, this testing setup provides useful data for the biomechanical behavior of these implants, which in turn may indicate their clinical performance in the first postoperative period.…”

Comparative Analysis of the Biomechanical Behavior of two different design metaphyseal-fitting short stems using digital image correlation

“…We are also aware that cortical strain measurement cannot directly re ect the in vivo performance because composite models represent a nonviable bone without the capacity to be remodelled. For this purpose, a simultaneous clinical study is already running, aiming to assess the remodelling process around these speci c implants in vivo, by means of a detailed radiological analysis (76). Nevertheless, this testing set-up provides useful data for the biomechanical behavior of these implants, which in turn may indicate their clinical performance in the rst postoperative period.…”

Promising medium-term results of anterior approach with an anatomical short stem in primary hip arthroplasty

“…In general, short stems have a significantly smaller bone contact area than standard stems and, as a result, may have less torsional and axial resistance. A solution proposed in the literature to overcome the problem is to spare the femoral neck, by means of a high osteotomy [3,4,[29][30][31]. The short neck-sparing stems provide additional axial and torsional stability and reduce stress at the bone interface of the implant.…”