ABSTRACT
Objective Bone cement joint prosthetic aseptic loosening always occurs in the bone cement-bone interface, while the mechanical strength of the interface mainly depends on the microstructure and adhesive strength.The aim of this study was to ex-plore the bone microstructure and the cement bone interfacial biomechanics of osteoarthritis(OA) and rheumatoid arthritis(RA), and also discuss the correlation. Methods Twenty trabecular bone specimens of tibial plateaus were taken from OA and RA patients who underwent total knee arthroplasty( TKA) .The microstructural parameters of the trabecular bone specimens were measured by Skyscan1176 microcomputed tomography.The bone specimens were made into cementbone models, which were tested by INSTRON strength tester.The association of bone microstructure and interfacial shear stress was analyzed subsequently. Results ①Bone volume fraction ( BV/TV) ( r=-0.313) , trabecular thickness ( Tb.Th) ( r=-0.340) ,trabecular spacing ( Tb.Sp) ( r=0.345) of OA had obvious correlation to shear strength (P<0.05).The cement-bone interfacial strength of medial tibial plateaus[(87.45±52.50)N] was lower than lateral tibial plat-eaus[(177.25±71.11)N] of OA (P<0.05).②Bone volume fraction (BV/TV)(r=0.343), trabecular number (Tb.N)(r=0.391) of RA had obvious correlation to shear strength (P<0.001).The cement-bone interfacial strength of lateral tibial plateaus[(62.23±46.22) N] was lower than medial tibial plateaus[(79.20±56.37N)] of RA (P<0.05).③The interfacial strength of OA[(132.35±76.64)N] was higher than RA[(71.05±51.55)N] (P<0.05). Conclusion There are differences of microstructure between OA and RA, which lead to the distinction of strength of cement -bone interface.And it has a certain guiding role of analyzing the biomechanics in TKA.
ABSTRACT
Debonding of cement-femoral stem interface has been suggested as a initial focus of loosening mechanism in many previous studies of cemented total hip replacement. The purpose of this study was to investigate the effect of debonding of cement-femoral stem interface to the cement-bone inter- face by using three-dimensional non-linear finite element analysis. Three cases of partial debonded, full debonded, and full bonded cement-bone interface were modelled with partial bonding of distal 70mm from the tip of femoral stem. Each situation was studied under loading simulating one-leg stanced gait of 68kg patient. The results showed that under partial and full debonded cement-stem interface conditions the peak von Mises stress (3.1 MPa) were observed at the cement of cement-bone interface just under the calcar of proximal medial of femur, and sudden high peak stresses (3.5 MPa) were developed at the distal tip of femoral stem at the lateral bone-cement interface in all 3 cases of bonding. The stresses were transfered very little to the cement of upper lateral bone-cement interface in partial and full debonded cases. Once partial or full debonded cement-femoral stem interface occured, 3 times higher stress concentration were developed on the cement of proximal medial cement-bone interface than full bonded interface, and these could cause loosening of cemented total hip replacement. Clinically, preservation of more rigid cement-femoral stem interface may be important factor to prevent loosening of femoral stem.