Morphological study of the newly designed cementless femoral stem.

A morphology study was essential to the development of the cementless femoral stem because accurate dimensions for both the periosteal and endosteal canal ensure primary fixation stability for the stem, bone interface, and prevent stress shielding at the calcar region. This paper focused on a three-dimensional femoral model for Asian patients that applied preoperative planning and femoral stem design. We measured various femoral parameters such as the femoral head offset, collodiaphyseal angle, bowing angle, anteversion, and medullary canal diameters from the osteotomy level to 150 mm below the osteotomy level to determine the position of the isthmus. Other indices and ratios for the endosteal canal, metaphyseal, and flares were computed and examined. The results showed that Asian femurs are smaller than Western femurs, except in the metaphyseal region. The canal flare index (CFI) was poorly correlated (r < 0.50) to the metaphyseal canal flare index (MCFI), but correlated well (r = 0.66) with the corticomedullary index (CMI). The diversity of the femoral size, particularly in the metaphyseal region, allows for proper femoral stem design for Asian patients, improves osseointegration, and prolongs the life of the implant.

Primary stability recognition of the newly designed cementless femoral stem using digital signal processing.

Stress shielding and micromotion are two major issues which determine the success of newly designed cementless femoral stems. The correlation of experimental validation with finite element analysis (FEA) is commonly used to evaluate the stress distribution and fixation stability of the stem within the femoral canal. This paper focused on the applications of feature extraction and pattern recognition using support vector machine (SVM) to determine the primary stability of the implant. We measured strain with triaxial rosette at the metaphyseal region and micromotion with linear variable direct transducer proximally and distally using composite femora. The root mean squares technique is used to feed the classifier which provides maximum likelihood estimation of amplitude, and radial basis function is used as the kernel parameter which mapped the datasets into separable hyperplanes. The results showed 100% pattern recognition accuracy using SVM for both strain and micromotion. This indicates that DSP could be applied in determining the femoral stem primary stability with high pattern recognition accuracy in biomechanical testing.

Design process of cementless femoral stem using a nonlinear three dimensional finite element analysis.

BACKGROUND: Minimal available information concerning hip morphology is the motivation for several researchers to study the difference between Asian and Western populations. Current use of a universal hip stem of variable size is not the best option for all femur types. This present study proposed a new design process of the cementless femoral stem using a three dimensional model which provided more information and accurate analysis compared to conventional methods. METHODS: This complete design cycle began with morphological analysis, followed by femoral stem design, fit and fill analysis, and nonlinear finite element analysis (FEA). Various femur parameters for periosteal and endosteal canal diameters are measured from the osteotomy level to 150 mm below to determine the isthmus position. RESULTS: The results showed better total fit (53.7%) and fill (76.7%) canal, with more load distributed proximally to prevent stress shielding at calcar region. The stem demonstrated lower displacement and micromotion (less than 40 µm) promoting osseointegration between the stem-bone and providing primary fixation stability. CONCLUSION: This new design process could be used as a preclinical assessment tool and will shorten the design cycle by identifying the major steps which must be taken while designing the femoral stem.

Fabrication of low-cost, cementless femoral stem 316L stainless steel using investment casting technique.

Total hip arthroplasty is a flourishing orthopedic surgery, generating billions of dollars of revenue. The cost associated with the fabrication of implants has been increasing year by year, and this phenomenon has burdened the patient with extra charges. Consequently, this study will focus on designing an accurate implant via implementing the reverse engineering of three-dimensional morphological study based on a particular population. By using finite element analysis, this study will assist to predict the outcome and could become a useful tool for preclinical testing of newly designed implants. A prototype is then fabricated using 316L stainless steel by applying investment casting techniques that reduce manufacturing cost without jeopardizing implant quality. The finite element analysis showed that the maximum von Mises stress was 66.88 MPa proximally with a safety factor of 2.39 against endosteal fracture, and micromotion was 4.73 µm, which promotes osseointegration. This method offers a fabrication process of cementless femoral stems with lower cost, subsequently helping patients, particularly those from nondeveloped countries.

Morphology study of the proximal femur in Malay population / Estudio de la morfología del fémur proximal en la población malaya

Clinical practice in our country showed a lack of suitable implants that perfectly match the anthropometry of the local population. However, there have been no reports or comprehensive studies conducted to substantiate this argument. We therefore prospectively studied 120 hips from sixty subjects with an average age of 25+/-5.18 years old. The average weight and height were 61.48+/-13.84 kg and 1.65+/-9.63 m respectively. The exclusion criteria were pregnant woman, those who had injury to the hip joint, and those with implant or prosthesis. Four parameters were measured ­ the femoral head diameter (FHD), femoral neck length (FNL), femoral neck width (FNW) and collo-diaphyseal angle (CDA). Statistical analysis showed no significant differences between left and right femora but significant differences were found between male and female subjects. The results for the male and female femurs are as follows ­ FHD: 43.6+/-3.1 mm and 38.9+/-2.2 mm; FNL: 91.1+/-5.7 mm and 81.8+/-4.3 mm; FNW: 28.9+/-3.4 mm and 26.0+/-4.3 mm; CDA: 132.3°+/-3.4° and 129.9°+/-4.0°. This data could be used as a guideline to design a more suitable implant for the Malay population which covers most of the South East Asian countries.

Problemas con respecto al tamaño de los implantes en relación a cada población se han convertido en una cuestión esencial para la sociedad ortopédica. Varios factores han sido identificados en la literatura, los que pueden afectar la estabilidad del implante, especialmente en el fémur proximal. Se estudió prospectivamente 120 caderas mediante imágenes de tomografía computarizada. Sesenta sujetos fueron reclutados, edad media 25+/-5,18 años, peso de 61,48+/-13,84 kg y altura de 1,65+/-9,63m. Los criterios de exclusión para este estudio incluyeron a mujeres embarazadas, quienes hubiesen experimentado lesiones cadera, uso de implantes o prótesis. Nuestros datos se compararon usando las pruebas de Anderson-Darling y t-test. Los parámetros medidos fueron diámetro de la cabeza femoral (FHD), longitud del cuello femoral (FNL), ancho del cuello femoral (FNW) y el ángulo cuello-diafisial (CDA). Los resultados de los fémures masculinos y femeninos fueron los siguientes: FHD 43,6 +/- 3,1 mm y 38,9 +/- 2,2 mm, FNL 91,1 +/- 5,7 mm y 81,8 +/- 4,3 mm, FNW 28,9 +/- 3,4 mm y 26,0 +/- 4,3 mm; CDA 132.3 +/- 3.4 y 129.9 +/- 4,. Este estudio prospectivo y transversal centrado en la población malaya, proporcionó información esencial sobre el valor normal de la porción proximal del fémur, datos que mejorarán el conocimiento de los aspectos anatómicos y, finalmente, ayuden al diseño del vástago femoral en la artroplastía total de cadera (ATC). Los resultados proporcionarán una nueva comprensión por parte del cirujano ortopédico.