Estudo numérico e experimental da biomecânica da prótese do joelho

• Author(s): Completo, António Manuel Godinho
• Date: 2006
• Persistent ID: http://hdl.handle.net/10773/2550
• Origin: RIA - Repositório Institucional da Universidade de Aveiro
• Subject(s): Biomecânica; Próteses; Ortopedia
• Document Type: Doctoral Thesis
• Language: Portuguese
• Advisor(s): Simões, José António de Oliveira; Fonseca, Fernando Manuel Pereira da

Description

Nesta tese foi objectivo estudar os aspectos biomecânicos da prótese do joelho e a problemática da artroplastia do joelho, nomeadamente a sua revisão. Para o efeito, diversos estudos biomecânicos sobre hastes da artroplastia total do joelho foram realizados através de modelos numéricos e experimentais. Foi seleccionada a prótese do joelho P.F.C. Sigma Knee System como elemento para a realização do estudo comparativo das hastes. Foram validados modelos numéricos de elementos finitos através da comparação das defromações-extensões de modelos da tíbia e do fémur sintéticos instrumentados com extensómetros. O estudo referente às hastes usadas na revisão incluiu as cimentadas e press-fit, tendo-se determinando a repartição de carga, deformações nas diferentes interfaces, tensões no manto de cimento e os micromovimentos relativos. Estes parâmetros mecânicos foram determinados de forma individual para a tíbia e para o fémur e foram correlacionados com efeitos clínicos como reabsorção óssea, descolamento e a dor. Os mesmos foram também analisados em conjunto, determinando-se a influência biomecânica que a haste exerce sobre o osso contrário. O estudo foi finalizado com uma avaliação préclínica dum novo conceito de implante de fixação combinada aplicado à haste tibial. Os resultados obtidos evidenciaram que a capacidade de transferência de carga dos componentes condilianos da prótese do joelho é somente efectiva com as hastes cimentadas. No entanto, a estabilidade proporcionada pelas hastes press-fit é superior à proporcionada pelas hastes cimentadas. A haste press-fit induz deformações mais elevadas no osso cortical, na zona da extremidade, podendo estas estarem na origem da dor sentida pelos pacientes. A haste cimentada evidencia um efeito de stress-shielding mais pronunciado na zona vizinha dos componentes condilianos; no entanto, as hastes press-fit originam uma maior extensão deste efeito no osso. Este facto pode ser correlacionado clinicamente com o efeito de reabsorção óssea associada às zonas vizinhas dos componentes condilares. Os resultados permitiram igualmente concluir que a utilização de hastes na tíbia pouco alteram a estabilidade do componente femoral. Já a utilização de hastes no fémur aumentam a instabilidade dos componentes tibiais, levando a aconselhar os cirurgiões à utilização de hastes tibiais sempre que se utilizam hastes no fémur. O novo conceito de haste adaptado à tíbia evidenciou uma estabilidade que se situa entre os dois conceitos convencionais, com uma capacidade efectiva de transferência de carga, minimiza os efeitos de necrose térmica originados pelo cimento e permite um contacto directo entre a haste e o osso, facilitando a osteointegração, e evita a destruição massiva de osso em caso da sua retirada (revisão), quando comparada com as hastes cimentadas. vii keywords Biomechanics, knee prosthesis, cemented stem, press-fit stem, finite element method, stress shielding, experimental strain measurement, end-of-stem pain, pre-clinical validation, primary stability, bone resorption, aseptic loosening. abstract The main objective of this thesis was to study different biomechanical aspects of the knee prosthesis and revision arthroplasty. Finite element and experimental studies were performed concerning the use of stems in revision knee arthroplasty. The P. F. C. Sigma Knee System prosthesis was used within the study. Numerical finite element models were validated by the measurement of principal strains on synthetic tibia and femur models. Press-fit and cemented stems were analyzed and load share, interface strains, cement mantle stresses and relative micromotions were assessed. These mechanical parameters were determined solely for the tibia and for the femur and correlated with clinical effects such as bone resorption, loosening and pain. Same parameters were also assessed considering the tibia and the femur stems as a set and the influence of the stem was analyzed over the other bone structure. Finally, a pre-clinical evaluation of a new combined fixation concept applied to the tibial stem was made. For this, the results evidence that load transfer capacity of the condylar components of the knee prosthesis is only effective for cemented stems. However, press-fit stems provide higher stability. These types of stems induce higher cortical strains in the distal-tip region of cemented stems, and can be responsible for pain referred by patients at this region of the stem. Cemented stem provoke higher stress shielding in the region close to the condylar components. However, this effect is more extensive in bone and can be clinically correlated with the effect of bone resorption in the condylar region. The results also allowed drawing the conclusion that the use of tibial stems does not change the stability of the femoral component. On the contrary, femoral stems raise instability of the tibial components, and therefore it is advisable to use tibial stems if femoral stems are used. The new tibial stem concept evidenced a degree of stability in between the two conventional stems analyzed. The novel stem provokes effective load transfer, minimizes bad effects of thermal necrosis due to cement polymerization and allows direct bone contact, facilitating potential osteointegration. It also minimizes bone destruction in revision, when the stem needs to be taken out. ABSTRACT: The main objective of this thesis was to study different biomechanical aspects of the knee prosthesis and revision arthroplasty. Finite element and experimental studies were performed concerning the use of stems in revision knee arthroplasty. The P. F. C. Sigma Knee System prosthesis was used within the study. Numerical finite element models were validated by the measurement of principal strains on synthetic tibia and femur models. Press-fit and cemented stems were analyzed and load share, interface strains, cement mantle stresses and relative micromotions were assessed. These mechanical parameters were determined solely for the tibia and for the femur and correlated with clinical effects such as bone resorption, loosening and pain. Same parameters were also assessed considering the tibia and the femur stems as a set and the influence of the stem was analyzed over the other bone structure. Finally, a pre-clinical evaluation of a new combined fixation concept applied to the tibial stem was made. For this, the results evidence that load transfer capacity of the condylar components of the knee prosthesis is only effective for cemented stems. However, press-fit stems provide higher stability. These types of stems induce higher cortical strains in the distal-tip region of cemented stems, and can be responsible for pain referred by patients at this region of the stem. Cemented stem provoke higher stress shielding in the region close to the condylar components. However, this effect is more extensive in bone and can be clinically correlated with the effect of bone resorption in the condylar region. The results also allowed drawing the conclusion that the use of tibial stems does not change the stability of the femoral component. On the contrary, femoral stems raise instability of the tibial components, and therefore it is advisable to use tibial stems if femoral stems are used. The new tibial stem concept evidenced a degree of stability in between the two conventional stems analyzed. The novel stem provokes effective load transfer, minimizes bad effects of thermal necrosis due to cement polymerization and allows direct bone contact, facilitating potential osteointegration. It also minimizes bone destruction in revision, when the stem needs to be taken out. Doutoramento em Engenharia Mecânica