A Geometric Model to Determine Patient-Specific Cup Anteversion Based on Pelvic Motion in Total Hip Arthroplasty

Abstract

Introduction. Cup position is critical to stability in total hip arthroplasty and is affected by pelvis motion during positions of daily life. The purpose of this study was to explicitly define the relationship between sagittal pelvic motion and resultant cup functional anteversion and create a tool to guide the surgeon to a patient-specific intra-operative anteversion. Materials and Methods. 10,560 combinations of inclination, anteversion, and pelvic tilt were generated using a geometric model. Resultant functional anteversion was calculated for each iteration and variables were correlated. An electronic mobile tool was created that compares inputted patient-specific values to population-based averages to determine pelvic positions and dynamics that may lead to instability. Results. A third-degree polynomial equation was used to describe the relationship between variables. The freely downloadable mobile tool uses input from pre-operative plain radiographic measurements to provide the surgeon a quantitative correction to intra-operative cup anteversion based on differences in functional anteversion compared to population-based averages. Conclusion. This study provides a geometric relationship between planned cup position, pelvic position and motion, and the resultant functional anteversion. This mathematical model was applied to an electronic tool that seeks to determine an individualized intra-operative cup anteversion based on measured patient-specific pelvic dynamics.

Small Random Angular Variations in Pelvic Tilt and Lower Extremity Can Cause Error in Static Image-based Preoperative Hip Arthroplasty Planning: A Computer Modeling Study

“…Many of the previously published models concentrated on the sagittal pelvic tilt and ignored coronal and axial pelvic tilt [13, 14, 23, 33, 35-37, 41, 43-45, 48, 54, 55]. The effect of different spine conditions, especially scoliosis, on the pelvis is 3D and thus will affect not only the sagittal pelvic tilt but also coronal and axial pelvic orientation [15, 25, 38, 42].…”

The Hip-Spine Challenge

“…The increased risk of dislocation in abnormal spinopelvic mobility or following LSF has been well described, but current literature could benefit from investigations into the effect of a THA approach on dislocation in this patient population. Several groups have recently employed different models for designing patient-specific safe zones for acetabular implants, with hopes of decreasing dislocation risk 76,77 . No large study, to our knowledge, has demonstrated that , grade A indicates good evidence (Level-I studies with consistent findings) for or against recommending intervention; grade B, fair evidence (Level-II or III studies with consistent findings) for or against recommending intervention; grade C, poor-quality evidence (Level-IV or V studies with consistent findings) for or against recommending intervention; and grade I, insufficient or conflicting evidence not allowing a recommendation for or against intervention.…”

“…The increased risk of dislocation in abnormal spinopelvic mobility or following LSF has been well described, but current literature could benefit from investigations into the effect of a THA approach on dislocation in this patient population. Several groups have recently employed different models for designing patient-specific safe zones for acetabular implants, with hopes of decreasing dislocation risk 76,77 . No large study, to our knowledge, has demonstrated that these models reduce dislocation, but it is an area for future investigation.…”

Liner malseating is rare with two modular dual-mobility designs

“…7,8 Attempts to identify patient-specific safe zones for the positioning of components have been investigated, based on characteristics of spinopelvic mobility. 9,10 Dual-mobility (DM) components have become an attractive option for some patients undergoing primary THA, as they increase the effective size of the femoral head and jump distance to dislocation. 11 Several authors have evaluated the risk of dislocation in primary THA using modular DM components, and systematic reviews have confirmed their effectiveness.…”