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A comparison of the holding strengths of bone screws in healthy and unhealthy cancellous bone
Abstrilcts
TITANIUM SURPACBS ON THE INTERFACE THE INPLUBNCB OP VARIOUS ST@NQTH BbT’WEEN IMPLANTS AND BONE L CIua, H.-J. WI&e, S. m Bloma&& uldvar&&t lnm AbmeiImlg * Unfauw porrchprate
461
SHEAR
Surface morphology affects the anchorage strength of implants in bone since structured and porous surfaces lead to a mechanical anchoring. This study investigated the mechanical effect of the bone healing response to various surface morphologies of titanium implants with respect to their implantation time. Titanium cortical screws (ASIF) with six different types of surface treatments were implanted in tibiae of sheep and tightened with a standardized insertion torque of I Nm. After periods of 2, 9, 13, 18, 24 and 52 the removal torque of the screws was recorded. The results demonstrate that it is possible to influence the holding power of implants by altering surface structure morphology. Thus, the optimum surface of implants for variable biomechanical situations, e.g. strong anchoring can be chosen. However, it can not be infered exclusively from the depth of the roughness of a surface as shown in this experiment. Obviously the shear strength is also dependant on the kind of roughness and local structure in the rough surface which can be modified by chemical treatment.
EVALUATION OF A NEW PROSTHESIS INTERFACE SURFACE GEOMETRY S.A. Goldstein, L.S. Matthews, K. Choi, K. Jespen, K. Sweet Biimecbanics, Trauma and Sports Medicine Laboratory, Ortbopaedic Surgery, University of Michigan, Ann Arbor, MI 48109-0486, U.S.A. The purpose of these studies was to evaluate a new concept in prosthesis interface surface design incorporating a
series of porous conical projections designed to provide immediate stability and a spectrum of contact stress distribution. Three phases of the investigation were Formed including 1. an evaluation of initial stability in 56 fnqh human cadaver tibias, 2. development and stability analysis of a canine tibia1 implant and 3. an evaluation of the in-vivo response of the prototype tibia1 component in large dogs at 1,3,5.7,9,12 months post-surgical implantation. The results of the studies demonstrate that the new surface provides excellent immediate stable fixation both in human and canine tibias. In particular, the shear and torsional stiffness of the implant was near that of cemented implants. The in-vivo study demonstrated exceknt functional results and by 5 months significant ingrowth particularly in the bottom half of the conical projections was documented. In conclusion, it was found that immediate experimentally determined secure fixation of tibial components utilizing a multiple porous coqed cone design can be achieved. In vivo studies demonstrate that the spectrum of cyclic contact stresses provided by the conical projections in concert with unrestricted activity significantly influence the extent and location of mkecular ingrowth and remodeling.
A COMPARISON OF THE HOLDING STRENGTHS OF BONE SCREWS IN HEALTHY AND UNHEALTHY CANCELLOUS BONE. LG. Turner and G.N. Rice School of Materials Science, University of Bath, Bath BA2 7AY, UK
In this study, the relationship betwien trabecular orientation, mineral density and the holdin strength of screws was investigated in both healthy arid diseased bone. Pullout tests were carried out on two Ant diameter, self-@ping, cancellous bone screws (4mm and 6.4mm) inserted in bovine cancellous bone sections taken perpendicular and at 45 degrees to the kmg axis of the bone, Comparison wss made with the same type of screws inserted into sections taken from osteoc~~tic and/or osteoaAritic human femoral heads. The mean holding saen ths of the lark and small diameter scltws in the hansverse b&ine bone sections were found to be 100.2 (+/-29 -J! and 90.6(+/-29.2) N/cm rcs tively. Those for the sections cut at 45 degrees to the long axis were found to be 59 (+/-25.9) and 54.3 (+/-26) Em respectively. The holding strengths mconledfor the small and lar diaqeter screws in the diseased femoral head sections Were found to be sifchificantlv diffcmnt at 40.8 (+/-a 8.9)iurd 63.2 (+/-29.2) N/cm resoectivelv. This difference in philout strengt% corrcl&s wiih the low m&r111 cokent mea&&l f& th&e secdons of &tween 40% 8nd 60%. com@red to 66% by weight, for the bovine bone. In conulusion, the results show that the screw diameter, trahecular orientation, mineral content and the health of the bone all need to be considered in order to optimise the holding strength of the screws in cancellous bone particularly where there is evidence of degenerative disease.
TITANIUM SURPACBS ON THE INTERFACE THE INPLUBNCB OP VARIOUS ST@NQTH BbT’WEEN IMPLANTS AND BONE L CIua, H.-J. WI&e, S. m Bloma&& uldvar&&t lnm AbmeiImlg * Unfauw porrchprate
461
SHEAR
Surface morphology affects the anchorage strength of implants in bone since structured and porous surfaces lead to a mechanical anchoring. This study investigated the mechanical effect of the bone healing response to various surface morphologies of titanium implants with respect to their implantation time. Titanium cortical screws (ASIF) with six different types of surface treatments were implanted in tibiae of sheep and tightened with a standardized insertion torque of I Nm. After periods of 2, 9, 13, 18, 24 and 52 the removal torque of the screws was recorded. The results demonstrate that it is possible to influence the holding power of implants by altering surface structure morphology. Thus, the optimum surface of implants for variable biomechanical situations, e.g. strong anchoring can be chosen. However, it can not be infered exclusively from the depth of the roughness of a surface as shown in this experiment. Obviously the shear strength is also dependant on the kind of roughness and local structure in the rough surface which can be modified by chemical treatment.
EVALUATION OF A NEW PROSTHESIS INTERFACE SURFACE GEOMETRY S.A. Goldstein, L.S. Matthews, K. Choi, K. Jespen, K. Sweet Biimecbanics, Trauma and Sports Medicine Laboratory, Ortbopaedic Surgery, University of Michigan, Ann Arbor, MI 48109-0486, U.S.A. The purpose of these studies was to evaluate a new concept in prosthesis interface surface design incorporating a
series of porous conical projections designed to provide immediate stability and a spectrum of contact stress distribution. Three phases of the investigation were Formed including 1. an evaluation of initial stability in 56 fnqh human cadaver tibias, 2. development and stability analysis of a canine tibia1 implant and 3. an evaluation of the in-vivo response of the prototype tibia1 component in large dogs at 1,3,5.7,9,12 months post-surgical implantation. The results of the studies demonstrate that the new surface provides excellent immediate stable fixation both in human and canine tibias. In particular, the shear and torsional stiffness of the implant was near that of cemented implants. The in-vivo study demonstrated exceknt functional results and by 5 months significant ingrowth particularly in the bottom half of the conical projections was documented. In conclusion, it was found that immediate experimentally determined secure fixation of tibial components utilizing a multiple porous coqed cone design can be achieved. In vivo studies demonstrate that the spectrum of cyclic contact stresses provided by the conical projections in concert with unrestricted activity significantly influence the extent and location of mkecular ingrowth and remodeling.
A COMPARISON OF THE HOLDING STRENGTHS OF BONE SCREWS IN HEALTHY AND UNHEALTHY CANCELLOUS BONE. LG. Turner and G.N. Rice School of Materials Science, University of Bath, Bath BA2 7AY, UK
In this study, the relationship betwien trabecular orientation, mineral density and the holdin strength of screws was investigated in both healthy arid diseased bone. Pullout tests were carried out on two Ant diameter, self-@ping, cancellous bone screws (4mm and 6.4mm) inserted in bovine cancellous bone sections taken perpendicular and at 45 degrees to the kmg axis of the bone, Comparison wss made with the same type of screws inserted into sections taken from osteoc~~tic and/or osteoaAritic human femoral heads. The mean holding saen ths of the lark and small diameter scltws in the hansverse b&ine bone sections were found to be 100.2 (+/-29 -J! and 90.6(+/-29.2) N/cm rcs tively. Those for the sections cut at 45 degrees to the long axis were found to be 59 (+/-25.9) and 54.3 (+/-26) Em respectively. The holding strengths mconledfor the small and lar diaqeter screws in the diseased femoral head sections Were found to be sifchificantlv diffcmnt at 40.8 (+/-a 8.9)iurd 63.2 (+/-29.2) N/cm resoectivelv. This difference in philout strengt% corrcl&s wiih the low m&r111 cokent mea&&l f& th&e secdons of &tween 40% 8nd 60%. com@red to 66% by weight, for the bovine bone. In conulusion, the results show that the screw diameter, trahecular orientation, mineral content and the health of the bone all need to be considered in order to optimise the holding strength of the screws in cancellous bone particularly where there is evidence of degenerative disease.