Bone Mineral Density and Fracture Risk Assessment to Optimize Prosthesis Selection in Total Hip Replacement.

The variability in patient outcome and propensity for surgical complications in total hip replacement (THR) necessitates the development of a comprehensive, quantitative methodology for prescribing the optimal type of prosthetic stem: cemented or cementless. The objective of the research presented herein was to describe a novel approach to this problem as a first step towards creating a patient-specific, presurgical application for determining the optimal prosthesis procedure. Finite element analysis (FEA) and bone mineral density (BMD) calculations were performed with ten voluntary primary THR patients to estimate the status of their operative femurs before surgery. A compilation model of the press-fitting procedure was generated to define a fracture risk index (FRI) from incurred forces on the periprosthetic femoral head. Comparing these values to patient age, sex, and gender elicited a high degree of variability between patients grouped by implant procedure, reinforcing the notion that age and gender alone are poor indicators for prescribing prosthesis type. Additionally, correlating FRI and BMD measurements indicated that at least two of the ten patients may have received nonideal implants. This investigation highlights the utility of our model as a foundation for presurgical software applications to assist orthopedic surgeons with selecting THR prostheses.

Improving Planning and Post-Operative Assessment for Total Hip Arthroplasty.

UNLABELLED: Total Hip Arthroplasty (THA) remains the gold standard of treatment for patients who suffer with a variety of hip-related pathological degeneration or trauma. These patients often exhibit significantly less post-operative pain and an increase in the range of motion of the joint, but there are still relatively common instances of debilitating periprosthetic complications that call into question the method for pre-surgical implant choice. Currently, there are two principal options for THA prostheses: cemented or non cemented. Utilizing the cemented procedure ensures a faster acquisition of adequate implant stability than with the non cemented procedure, but can eventually lead to an increased periprosthetic fracture risk. Non cemented prosthetic stems are more frequently revised within the first few years following THA due to periprosthetic fracture, but non cemented revision surgeries generally result in fewer complications than those of cemented implants. Surgeons typically rely on experience or simple patient metrics such as age and sex to prescribe which implant procedure is optimal, and while this may work for most patients, there is a clear need to analyze more rigoriously patient conditions that correlate to optimal post-THA outcomes. The results from the investigation reported herein indicate that an understanding of how the percent composition and quality of a patient's quadriceps muscle in both healthy and operated legs may be a better indicator for prosthetic choice. Additionally, these data emphasize that the traditional metrics of age and sex inadequately predict changes in quadriceps composition and quality and thereby have comparatively minor utility in determining the patient-appropriate prosthetic type. KEY WORDS: Total Hip Arthroplasty, Prosthetic selection, Muscle size and quality, Anatomical modeling, Surgical planning.

Assessment of total hip arthroplasty by means of computed tomography 3D models and fracture risk evaluation.

Total hip arthroplasty (THA) can be achieved by using a cemented or noncemented prosthesis. Besides patient's age, weight, and other clinical signs, the evaluation of the quality of the bones is a crucial parameter on which orthopedic surgeons base the choice between cemented and noncemented THA. Although bone density generally decreases with age and a cemented THA is preferred for older subjects, the bone quality of a particular patient should be quantitatively evaluated. This study proposes a new method to quantitatively measure bone density and fracture risk by using 3D models extracted by a preoperative computed tomography (CT) scan of the patient. Also, the anatomical structure and compactness of the quadriceps muscle is computed to provide a more complete view. A spatial reconstruction of the tissues is obtained by means of CT image processing, then a detailed 3D model of bone mineral density of the femur is provided by including quantitative CT density information (CT must be precalibrated). A finite element analysis will provide a map of the strains around the proximal femur socket when solicited by typical stresses caused by an implant. The risk for structural failure due to press-fitting and compressive stress during noncemented THA surgery was estimated by calculating a bone fracture risk index (ratio between actual compressive stress and estimated failure stress of the bone). A clinical trial was carried out including 36 volunteer patients (ages 22-77) who underwent unilateral THA surgery for the first time: 18 received a cemented implant and 18 received a noncemented implant. CT scans were acquired before surgery, immediately after, and after 12 months. Bone and quadriceps density results were higher in the healthy leg in about 80% of the cases. Bone and quadriceps density generally decrease with age but mineral density may vary significantly between patients. Preliminary results indicate the highest fracture risk at the calcar and the lowest at the intertrocanteric line, with some difference between patients. An analysis of the results suggest that this methodology can be a valid noninvasive decision support tool for THA planning; however, further analyses are needed to tune the technique and to allow clinical applications. Combination with gait analysis data is planned.