The mid-term longevity of femoral components varies considerably, with some showing failure due to early aseptic loosening. Since the hip joint is subject to heavy mechanical loads, it can be assumed that the mechanical interaction of the implant, bone cement and femur will play a key role in the resultant reliability of an arthroplasty. This study was designed to examine this mechanical interaction in four femoral components different in construction (Poldi-Cech, CF-30, MS-30 and PFC) using mathematical simulation. MATERIAL AND METHODS Four stem/cement/femur 3-D mathematical models, comparable in quality, infolving the Poldi-Cech, CF-30, MS-30 and PFC stems, respectively, were constructed. A 3-D model for each stem was created according to its real, middle-size femoral component. Each 3-D model of the cement mantle corresponded in shape to the mantle of the appropriate real stem, with its thickness based on the recommended values of 4-7 mm in the proximal and 1-3 mm in the distal part, and with the cement mantle reaching as far as 10 mm distal to the femoral stem tip. For simplicitys sake the outer surface of the cement mantle was simulated as smooth. A 3-D model involving the proximal epiphysis and the metaphysis of a femur was reconstructed, based on a series of CT cross-sections obtained periodically at 10.5-mm and 2.5-mm distances. The sten/cement/femur model with the MS-30 stem also included a centraliser. The mechanical interaction of the stem, bone cement and bone tissue was examined by means of mathematical stimulation using ANSYS 5.7 software based on finite element analysis. RESULTS For the sake of simplicity, only two key parameters are presented, namely, contact stress at the stem-cement interface and equivalent deformation in the stem/cement/femur system. The least satisfactory stress loading was in the CF-30 stem whose sharp edges showed the values of contact stress about six-times higher than on the mid-medial portion of the stem, with the sharp edges behaving as stress concentrators. A satisfactory stress loading was found in Poldi-Cech, MS-30 and PFC stems, in which contact stress was evenly distributed along the whole lenght of the stem and the values at the edges and on the midmedial portion did not differ much. DISCUSSION The distribution of contact stress is one of the most important factors for the long-term longevity of implants. It was found least satisfactory in the CF-30 stem whose sharp edges act as stress condenser adversely affecting not only the stemcement interface, but also the resultant stress distribution within the femur. The most satisfactory results of stress distribution were recorded in the Poldi-Cech and MS-30 stems. The PFC stem also responded satisfactorily to the simulated stress loading. However, on loading whose substantial part would be torsion, the stems circular or oval cross-section could interfere with rotation stability of the implant; but this was impossible to detect by the mathematical simulation used in this study. CONCLUSIONS The results presented here show that, in the Poldi-Cech, CF-30, MS-30 and PFC femoral stems, a good agreement was achieved between the results of their clinical application and those of mathematical modelling of their mechanical properties. It can be concluded that mechanical interaction among the femoral stem, cement mantle and bone tissue plays the key role in the long-term longevity of such an implant. Key words: Poldi-Cech, CF-30, MS-30, PFC, mechanical interaction, contact stress.
- MeSH
- femur MeSH
- kostní cementy MeSH
- kyčelní protézy MeSH
- lidé MeSH
- mechanický stres MeSH
- počítačová simulace MeSH
- Check Tag
- lidé MeSH
Cílem studie bylo měření periprotetické hustoty kosti BMD (bone mineral density – hustota kostního minerálu), kterou jsme měřili metodou DEXA (duálně energetické rentgenové měření absorpce). BMD je objektivní parametr, kterým lze posoudit změny mechanických vlastností femuru. Hustotu kosti jsme měřili pomocí přístroje Hologic 2000 v sedmi Gruenových zónách. Jedná se o zóny velkého trochanteru, kalkaru, laterální a mediální oblasti střední části dříku, laterální a mediální oblasti dolní části dříku a oblast pod hrotem dříku. Denzitometrické vyšetření bylo provedeno desátý den po operaci, rok po ní a za dva roky po operaci. Srovnávali jsme BMD v jednotlivých časových údobích u dříků PFC, Exeter a CLS. Z denzitometrických vyšetření jako nejlepší vychází cementový dřík Exeter, u něhož došlo ke statisticky významnému zvýšení středních hodnot BMD celkem ve čtyřech zónách (R1, R3, R4, R5). U necementovaného dříku CLS došlo ke statisticky významnému zvýšení BMD ve třech zónách (R1, R4, R5). Z pohledu denzitometrie se jako nejhorší jeví cementovaný dřík PFC, u něhož se nepodařilo zjistit statisticky významné změny středních hodnot v žádné zóně. Denzitometrie může být přínosem pro zhodnocení a sledování kvality kosti kolem dříku totálních endoprotéz kyčelního kloubu.
The aim of this study was to measure periprosthetic bone mineral density (= BMD). We measured BMD by DEXA (= dual energetic X-ray absorption). BMD is an objective parameter by which changes of mechanical properties of the femur can be assessed. BMD was measured by Hologic 2000 in seven Gruen´s areas. It means: greater trochanter area, calcar area, area of lateral and medial zone of middle part of the femoral stem, area of lateral and medial zone of lower part of the femoral stem and area under the tip of the femoral stem. Densitometric measurement was made 10 days after the implantation of total hip arthroplasty (= THA), one year and two years after the operation. In such time intervals after implantation the PFC stem, Exeter stem and CLS stem BMD were compared. Exeter stem shows the best densitometric data. There is a statistic significant increase of medial values of BMD in four areas (R1, R3, R4, R5). Non-cement stem CLS has a statistic significant increase in three areas (R1,R4, R5). Cemented PFC stem has the worst densitometric measurement. There is no statistic significant increase of BMD in any areas. The densitometric measurement can contribute to evaluating and monitoring the quality of periprosthetic bone around the femoral stem of the THA.
1.vyd. 48 s.
- Klíčová slova
- texty učební vysokoškolské,
- MeSH
- fraktury kostí MeSH
- traumatologie MeSH
48 s. ; 22 cm
- Konspekt
- Patologie. Klinická medicína
- NLK Obory
- traumatologie
- NLK Publikační typ
- učebnice vysokých škol
