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Biomedical subjects

D R Sumner

Publications and source records attributed to D R Sumner.

At least 55 records · Page 3Linked to original sources
PubMed1997

Finite Element analyses to study periprosthetic bone adaptation.

Periprosthetic bone adaptation around orthopaedic implants can be studied with Finite Element models. It requires a comparison between the mechanical status of the bone in the operated (unnatural) situation and the natural situation. The difference between these two situations is the alteration in mechanical condition of the bone, which is assumed to be the driving force of the adaptation process. The time dependent bone adaptation process can be simulated with a computer algorithm by an iterative (time stepping) procedure. This study reviews some clinical and experimental issues, it addresses the value of computer models of periprosthetic bone adaptation and discusses a new development of voxel based models directly converted from CT scans.

Algorithms↗
PubMed1997

Use of bone morphogenetic protein 2 on ectopic porous coated implants in the rat.

The ability of recombinant human bone morphogenetic protein 2 to remain osteoinductive and stimulate appositional bone formation on a porous coated implant was tested in a rat quadriceps muscle pouch. Implants with or without hydroxyapatite were used to compare the effects on bone formation of two different does (23 micrograms or 46 micrograms) of recombinant human bone morphogenetic protein 2 against controls as evidenced by contact radiography, histologic examination, and backscatter scanning electron microscopic analysis. Cylindrical plasma sprayed porous titanium implants were placed bilaterally within a muscle pouch surgically created in 48 Lewis rats. Implants treated with recombinant human bone morphogenetic protein 2 formed significantly more bone than did control implants independent of the dose or presence of hydroxyapatite. In all implants with bone formation, osteoinduction via endochondral ossification began within 7 days. By 21 days, cartilage largely was replaced by bone and marrow. The results of this ectopic, nonweightbearing in vivo assay suggest that recombinant human bone morphogenetic protein 2 remains biologically active after application to a titanium implant and may be used to enhance appositional bone formation by direct application to the implant surface.

Analysis of Variance↗
PubMed1996

Unilateral hip replacement causes bilateral changes in tibial bone mineral content in a canine model.

The presence of asymmetry in tibial bone mineral content (BMC) of the operated and control limbs at the end of the experimental period following unilateral hip replacement surgery is used as a marker of limb function. The goal of the present study was to determine the contribution of ipsilateral and contralateral bone gain and loss to control-treated side differences in BMC of the tibia in dogs following unilateral hip replacement surgery. Seven animals were followed longitudinally with single beam photon absorptiometry for 6 months after unilateral hip hemiarthroplasty. Bone loss, compared with preoperative baseline values, was observed in both limbs, with recovery in bone mass beginning 1 month after surgery in the contralateral tibia and 3 months after surgery in the ipsilateral tibia. Thus, the asymmetry in tibial BMC frequently seen after unilateral experimental hip replacement in the canine appears to be caused by differential timing of recovery of bone mass following a transient loss in both limbs. The mechanism defined in this study is in contrast to an alternative mechanism involving bone loss in the treated limb coupled with bone gain in the control limb.

Animals↗
PubMed1996

Altered load history affects periprosthetic bone loss following cementless total hip arthroplasty.

Dual energy x-ray absorptiometry was used to measure periprosthetic, distal femoral, and proximal tibial bone mass in the affected and contralateral limbs of eight patients 10 years after unilateral total hip arthroplasty with a cementless, porous-coated titanium alloy femoral stem. Gait analyses to assess the presence of asymmetries in loading of the lower extremities were also performed 10 years postoperatively. The patients had excellent clinical results and no other significant lower extremity pathology. On the basis of comparison of the affected and unaffected proximal femora, bone loss adjacent to the proximal medial aspect of the femoral stem was determined to be 34% (p < 0.001). However, the patients also had 16% less bone in the ipsilateral proximal tibia (p = 0.003) and 15% less bone in the ipsilateral femur 3 cm distal to the prosthesis (p = 0.007) compared with the contralateral limb. When normalized to the asymmetry in tibial bone mineral content, the estimated proximal medial periprosthetic bone loss was still statistically significant, but the magnitude was reduced from 34 to 17% (p = 0.009). The gait analyses indicated that several measures that influence the loads at the hip and knee joints were reduced in the involved limb compared with the contralateral limb. Furthermore, the bilateral difference in the vertical component of the external force acting on the proximal tibia was correlated with the bilateral difference in tibial bone mineral content (r = 0.80, p = 0.02). These data suggest that two mechanical factors, the local stress-shielding effect of the prosthesis and the global effect of decreased loading of the limb, can both make significant contributions to periprosthetic bone loss. It is apparent that the magnitude of the periprosthetic bone loss related to stress-shielding has been overestimated by as much as 50% in retrospective studies.

Absorptiometry, Photon↗
PubMed1996

Adaptation to differential loading: comparison of growth-related changes in cross-sectional properties of the human femur and humerus.

Changes in long bone cross-sectional geometry during growth can be influenced by biological and mechanical factors. Here, we assess relationships between cross-sectional geometric properties and length of the human humerus and femur during postnatal growth to test the hypothesis that loading history plays an important role in the development of adult bone morphology. A skeletal sample including 83 paired humeri and femora from individuals between birth and age 30 was examined. Midshaft cross-sectional geometric properties were determined based on computed tomographic scans and the two bones were compared by examining growth trajectories and scaling relationships between the cross-sectional properties and bone length. The growth trajectories for both bones were similar in many respects and showed that increase in length ceased by age 20, whereas increase in cross-sectional properties continued into the third decade of life. When compared to bone length, the cross-sectional geometric properties of the femur and humerus were similar early in postnatal life, but increased at a greater rate in the femur particularly during the first decade of life, leading to divergent adult morphologies. A beam model was developed to predict maximum midshaft strains in each bone as a function of age. The moment acting on the femur was estimated from an analysis of gait in children and the moment acting on the humerus was chosen so that the magnitude of the maximum midshaft strains in the two bones was equivalent in adulthood. With this model, the maximum midshaft strains for the femur were predicted to be higher than for the humerus during the first decade of life. These data support the concept that load history plays an important role in accretion of bone mass during postnatal growth.

Adaptation, Physiological↗
PubMed1996

Impacted particulate allograft for femoral revision total hip arthroplasty. In vitro mechanical stability and effects of cement pressurization.

The initial migration and micromotion of the revision femoral stem stabilized with morselized impacted cancellous allograft and bone-cement and the influence of cement pressurization on fixation of the cement/allograft composite to the host were examined with human cadaver femurs. The stability of the allograft/cemented reconstruction was found to be intermediate between those of conventional cemented and cementless stems. In most cases, the stability of the reconstruction was closer to that of cemented than to that of cementless stems. This may account for histologic findings of graft incorporation in experimental and retrieved specimens reported by other authors. Although increased cement pressurization led to greater penetration of cement into the graft bed, greater cement penetration did not increase fixation strength of the cement/allograft composite to the host.

Adult↗
PubMed1996

The bone-implant interface of femoral stems with non-circumferential porous coating.

UNLABELLED: A histological study was performed of the bone-implant interface of fifteen titanium-alloy femoral stems with porous coating limited to three proximal areas that did not cover the full circumference of the device. The specimens were obtained at autopsy from ten cadavera at a mean of forty-six months (range, one to eighty-nine months) after the implant had been inserted without acrylic cement. The volume fraction of bone within the porous spaces (the percentage of the porous space that was filled with bone) and the extent of bone ingrowth (the percentage of the porous-coated surface covered with in-grown bone that was more than one-half fiber-diameter deep, as measured from the outer surface of the porous coating), were determined with histomorphometric methods. Eleven of the fifteen stems had bone within the porous coating that was in continuity with the surrounding medullary bone. The mean volume fraction of bone ingrowth in these specimens was 26.9 per cent (range, 12.2 to 61.0 per cent), and the mean extent of bone ingrowth was 64.3 per cent (range, 28.6 to 95.2 per cent). Both of these parameters increased with time. In the other four stems, the bone lacked continuity with the surrounding trabecular bed. Two of these stems had a limited amount of bone within the porous coating, and two stems (from one patient) had no bone ingrowth. Periprosthetic membranes surrounded by a shell of trabecular bone covered the uncoated surfaces of the stems. The membranes of implants that had been in situ for eight months or more demonstrated polyethylene wear debris, and other particles generated at the level of the joint, within histiocytes throughout the length of the femoral stem. CLINICAL RELEVANCE: The findings in this study are relevant to the utilization and mechanisms of failure of femoral stems inserted without cement. Bone ingrowth and the resulting stability of the implant can be achieved with porous-coated stems. However, the extent of the surface that is porous-coated must be sufficient to prevent trabecular fracture as a secondary mechanism of loosening. Interruptions in the circumferential extent of the porous surface are associated with the formation of periprosthetic membranes, which provide a pathway for migration of particulate wear and corrosion products to the distal part of the stem. A circumferential coating may retard the access of particles and thus decrease the possibility of diaphyseal osteolysis.

Adult↗
PubMed1995

Biologic factors affecting spinal fusion and bone regeneration.

STUDY DESIGN: Literature review. OBJECTIVES: This article reviews the existing data on the multiplicity of local and systemic factors affecting lumbar spinal fusion and the general biology of bone regeneration. SUMMARY OF BACKGROUND DATA: Arthrodesis is one of the most commonly performed, yet incompletely understood, procedures in spinal surgery. There exists a paucity of knowledge about the basic biology involved in achieving a successful fusion. METHODS: Medline and manual search of all relevant articles were performed and summarized. RESULTS: The success or failure of spinal fusion may be influenced by a host of local and systemic factors. CONCLUSIONS: Future research should focus on expanding our existing knowledge pertaining to the basic biology of bone regeneration specific to spinal fusion.

Bone Regeneration↗
PubMed1995

Bone ingrowth and wear debris in well-fixed cementless porous-coated tibial components removed from patients.

Bone ingrowth and the distribution of wear debris within the porous coating of 13 primary cementless porous-coated tibial components removed for reasons unrelated to fixation or infection were quantitatively described. The average length of implantation was 15.3 months (range, 3-30 months). The implants were all of the same design, made for Ti6A14V with a commercially pure titanium fiber-metal porous coating, which covered the undersurface of the tray and the four fixation pegs. In all but one component, supplemental screw fixation was used. The average extent of bone ingrowth within the tray was 27.1 +/- 16.1%, and the average volume fraction was 9.5 +/- 7.5%. There was significantly more bone ingrowth within the fixation pegs than within the tray and also more bone ingrowth in the anterior half of the tray than posteriorly. There was no correlation between the amount of bone ingrowth and the length of implantation, age, or sex of the patient; however, the depth and orientation of the resection plane were found to correlate with the topographic distribution of bone ingrowth. Particulate debris appeared to gain access to the interface via soft tissue pathways both at the periphery and through the holes for adjuvant screw fixation.

Alloys↗
PubMed1995

Enhancement of bone ingrowth by transforming growth factor-beta.

Enhancement of bone ingrowth with transforming growth factor-beta was evaluated in a canine model. Ten dogs had bilateral implantation of a titanium-fiber-metal-coated rod in the proximal part of the humerus. A three-millimeter gap between the outer surface of the porous coating and the surrounding cancellous bone was created to impair bone ingrowth. All of the implants were plasma-flame-sprayed with hydroxyapatite and tricalcium phosphate. In each animal, one implant was also treated with recombinant transforming growth factor-beta 1 while the other implant, which was not so treated, served as a paired control. Two doses of transforming growth factor-beta 1 were used: 335 micrograms in five animals and 120 micrograms in the other five. At four weeks, the amount of bone ingrowth in the implants that had been treated with 120 micrograms of transforming growth factor-beta 1 was threefold higher than that in the paired controls (p = 0.009), but with the numbers available there was no significant increase in bone ingrowth with the higher dose. The amount of new-bone formation in the three-millimeter gaps adjacent to the treated implants was twice that in the gaps of the paired controls, regardless of the dose. The differences between the treated and control implants with regard to the architecture of the new bone in the gap indicate that the mechanism of action of transforming growth factor-beta 1 may include both proliferation of osteoprogenitor cells and production of matrix by committed osteoblasts. Compared with the findings in a previous study in which this canine model was used, the data from the present investigation indicate that enhancement of bone ingrowth in implants that have been treated with a combination of a hydroxyapatite-tricalcium phosphate coating and transforming growth factor-beta 1 may exceed that obtainable with grafting of the gap with autogenous cancellous bone.

Animals↗
PubMed1995

The susceptibility of smooth implant surfaces to periimplant fibrosis and migration of polyethylene wear debris.

The purpose of this investigation was to establish whether the tissue response and migration of polyethylene debris differed at noncemented smooth and porous implant surfaces. This was accomplished through 3 separate but closely related studies: (1) a canine cylindrical implant model with smooth and porous surfaces exposed to polyethylene debris; (2) a canine total hip arthroplasty model analyzing the interface between bone and femoral implants with various porous-coating configurations; and (3) a histologic analysis of autopsy-retrieved, human, noncemented hip prostheses with noncircumferential porous coating. The cylindrical implant model involved the placement of split cylinders, 1/2 porous and 1/2 smooth, into the distal femur and proximal tibia of 4 dogs. Four control implants and 10 test implants (chronically exposed to simulated polyethylene debris with a mean size of 4.7 microns) were examined histologically as long as 30 weeks after surgery. The canine hip study involved the study of 54 noncemented hip prostheses at periods of 1, 6, and 24 months. The prostheses possessed 4 different porous surface configurations: 1 with circumferential porous coating, 2 with noncircumferential coating, and 1 without porous coating. The human retrieval analysis involved the study of 7 cadaveric femora (age, 6 months-5 years) implanted with a straight titanium-alloy prosthesis possessing proximal pads of titanium fiber metal on the anterior, posterior, and medial aspects. With all implants in all 3 studies, there was the common finding of bone ingrowth at the porous implant surface and a fibrous interface or periprosthetic cavity around the portion of the implant that was smooth surfaced. The periprosthetic cavity typically was encapsulated by a thin continuous shell of trabecular bone. In addition, polyethylene debris was found to have preferentially migrated along the smooth implant surfaces. In the longer-term canine and human hip retrievals, polyethylene particles in the micron size range were present within histiocytes, whereas larger particles as much as 100 microns were found within foreign-body giant cells. Of importance for the implants from all 3 studies, with the exception of some pronounced cavities on the lateral aspect of the human hip prostheses, the periimplant cavities around the smooth surfaces were not detectable radiographically. This study clearly established a fundamental principle of relative barriers to particulate debris migration. Smooth implant surfaces are more susceptible than porous surfaces to the development of a fibrous tissue filled periimplant cavity and the subsequent migration of polyethylene wear debris.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Effects of fixation technique on displacement incompatibilities at the bone-implant interface in cementless total knee replacement in a canine model.

Bone-implant displacements can be caused by rigid body motion and by differences in material properties of the implant and bone. In the present study of the tibial component in total knee replacement, we tested a series of tibial component fixation designs to determine how certain design features influenced the magnitude of the tangential displacement between the component and supporting bone in a canine model. The transverse expansion of the proximal tibia under static axial loading was measured in the intact tibia and then in the same bone following implantation of tibial components with different interface characteristics: cementless flat smooth, cementless flat porous-coated, cementless flat porous-coated with screws, cementless pegged porous-coated, cementless pegged porous-coated with screws, cemented pegged, and cemented pegged with screws. In all cases, the magnitude of the transverse expansion increased with higher applied loads. When the statistical analysis was restricted to the cementless interfaces, the presence/absence of the porous coating, the presence/absence of pegs, and the use of screws had no significant influence on tibial expansion. However, in an analysis including the cemented and cementless pegged components, tibial expansion was reduced with the use of screws. The magnitude of the interface motion due to these displacement incompatibilities was approximately fivefold lower than the amount of interface motion related to rigid body motion found in a separate study with the canine model. The measured expansion was similar in the intact tibiae and the implanted tibiae, suggesting that the transverse constraint in the canine proximal tibia must be provided by the surrounding cortical ring rather than the subchondral bone.

Animals↗
PubMed1994

Distribution of Young's modulus in the cancellous bone of the proximal canine tibia.

Canine cancellous bone is used as a model for human bone in experimental orthopedic research, including models of total knee arthroplasty. Depth-force measurements produced by small-diameter indentation testing were used to derive the variation of Young's modulus over the transverse cross-sectional surface at three levels within the proximal canine tibia. At the most proximal section the presence of lateral and medial peaks of equal modulus (approximately 1100 MPa) was found. Modulus averages for the three resection levels revealed a trend of distally decreasing values, from 692 MPa proximally to 417 MPa distally. Average regional modulus values for the canine tibia were 50-75% higher than previously reported for the tibia of healthy young adult humans, although the local maxima were only 5-20% greater in canines.

Adult↗
PubMed1994

Initial in vitro stability of the tibial component in a canine model of cementless total knee replacement.

The tibial component of a canine cementless total knee replacement model was used to determine the degree to which pegs and screws contributed to the initial in vitro stability of the device. Three implant designs were investigated: (1) a four-peg implant in which cortical bone screws passed through the pegs, (2) the four-peg implant without adjuvant screw fixation, and (3) a flat implant with screws placed in the same positions as in the first design. For measuring the interface motion, the tibial component and proximal tibia were modeled as rigid bodies and an experimental method was developed which permitted all six degrees of freedom of the motion between these two objects to be determined. In tests performed to validate this methodological approach, the potential confounding influences of tibial deformation and differential amounts of tibial deformation with the use of screws or pegs were shown to be minimal, supporting the use of the rigid-body method. In general, the areas of greatest motion were at the periphery of the bone-implant interface, regardless of whether or not screws or pegs were used. The components secured with screws had up to five-fold reductions in interface motion compared to components which had pegs but lacked screw fixation. Components with pegs and screws and components with screws only had the same amount of interface motion. Thus, in the presence of screw fixation, the addition of pegs did not increase the stability of the tibial component.

Alloys↗
PubMed1994

Effect of pegs and screws on bone ingrowth in cementless total knee arthroplasty.

The purpose of the present study was to assess the effects of pegs and screws on bone ingrowth into the tibial component in cementless total knee replacement. Left total knee replacements were performed in 21 mature male dogs with 3 cementless porous-coated tibial tray configurations (7 animals per group): (1) 4-peg design implanted with cortical screws passing through the pegs; (2) 4-peg design implanted without screws; and (3) pegless design secured by 4 cortical screws. The animals were allowed unrestricted activity and were euthanized 6 months postoperatively. The pegless components (Group 3) had the highest extent of bone ingrowth into the tray (90.3% +/- 9.4%), followed by the components with 4 pegs only (Group 2, 82.8% +/- 9.2%), and the components with 4 pegs and 4 screws (Group 1, 75.9% +/- 11.8%). The difference between Groups 1 and 3 was statistically significant (p < 0.05). The volume fraction of bone ingrowth in the tray did not differ among the 3 groups, with an overall mean of 22.5% (+/- 4.6%). At the posterolateral quadrant, Group 1 had significantly less bone ingrowth than Group 3 within the tray whether measured as the extent (63.6% +/- 20.5% versus 91.0% +/- 10.6%, p < 0.05) or volume fraction (19.1% +/- 8.8% versus 32.9% +/- 10.5%, p < 0.05). There were no between-group differences at the other quadrants. This study indicated that pegs provided no added benefit in a circumstance where sufficient initial fixation was obtained with screws.

Animals↗
PubMed1993

Adaptive bone remodeling around bonded noncemented total hip arthroplasty: a comparison between animal experiments and computer simulation.

Severe loss of bone related to stress-shielding is one problem threatening the long-term integrity of noncemented total hip arthroplasty. It is widely accepted that this phenomenon is caused by adaptive bone remodeling according to Wolff's law. Recently, quantitative bone-remodeling theories have been proposed, suitable for use in computer-simulation models in combination with finite-element codes, which can be applied to simulate the long-term effect of the remodeling process. In the present paper, the results of such a computer simulation are compared with those in an animal experiment. A three-dimensional finite-element model was constructed from an animal experimental configuration concerning the implantation of a fully coated femoral hip prosthesis in dogs. The simulation results of the adaptive bone-remodeling process (geometric adaptations at the periosteal surface and density adaptations within the cancellous bone) were compared with cross-sectional measurements of the canine femurs after 2 years of follow-up. The detailed comparison showed that long-term changes in the morphology of bone around femoral components of total hip replacements can be fully explained with the present quantitative adaptive bone-remodeling theory.

Adaptation, Physiological↗