Biomedical subjects

Joan E Bechtold

Publications and source records attributed to Joan E Bechtold.

18 recordsLinked to original sources

PubMed2007

Local alendronate increases fixation of implants inserted with bone compaction: 12-week canine study.

Bone compaction has been shown to increase initial implant fixation. Furthermore, bone compaction creates a peri-implant zone of autograft that exerts osteoconductive properties. We have previously shown that locally applied bisphosphonate (alendronate) at 4-week observation can preserve the autograft generated by bone compaction. We now investigate whether the increased amount of autograft, seen at 4 weeks, can increase implant osseointegration and biomechanical fixation. Porous-coated titanium implants were bilaterally inserted with bone compaction into the proximal part of tibia of 10 dogs. On the right side, local bisphosphonate was injected into the bone cavity prior to bone compaction immediately prior to implant insertion. On the left side, saline was used as control. Observation period was 12 weeks. Locally applied bisphosphonate significantly increased biomechanical implant fixation (approximately twofold), bone-to-implant contact (1.2-fold), and peri-implant bone volume fraction (2.3-fold). This study indicates that local alendronate treatment can increase early implant osseointegration and biomechanical fixation of implants inserted by use of bone compaction. Long term effects remain unknown.

Alendronate↗

PubMed2006

Use of high-resolution MRI for investigation of fluid flow and global permeability in a material with interconnected porosity.

We present a multi-scale experimental approach designed to improve the investigation of both localized and global fluid flow in biomaterials with randomly interconnected porosity. Coralline hydroxyapatite (ProOsteon 500 from Interpore-Cross), having a relatively well-defined porosity, was used as an in vitro model of typical bone architecture. Axial fluid velocity profiles within the pores of a cylindrical hydroxyapatite sample were characterized using high-resolution MRI in conjunction with the measurement of global flow and associated permeability based on the Darcy-type relationship. Assuming Newtonian fluid behaviour, image analysis permitted computation of local porosity, intra-pore fluid shear, and visualization of flow heterogeneity within the sample. These results may benefit applications in biomaterials for the evaluation of factors influencing bony incorporation in porous scaffolds and on porous implant and bone surfaces. Normal and diseased biological tissues are also clinical relevant applications.

Bone Substitutes↗

PubMed2006

High-resolution magnetic resonance flow imaging in a model of porous bone-implant interface.

PURPOSE: To evaluate the application of high-resolution MRI methodology for characterizing the fluid velocity field and evaluate fluid shear field within a simplified in vitro model of a bone-implant interface. MATERIALS AND METHODS: The study used a specific micromotion canine bone implant that has been used for over a decade in the experimental evaluation of anatomical, biomaterial, mechanical and surgical factors influencing the quality of the implant interface. To allow its implementation in an MR coil, a nonmagnetic model of the micromotion implant was fabricated. The model consisted of a cylinder of polymethylmethacrylate (PMMA) representing the implant, located within an annular controlled gap into a block of coralline-derived bulk porous hydroxyapatite (HA; Interpore Cross International, Irvine, CA, USA). The assembly was potted in a polycarbonate shell and connected to a gravity-feed flow system consisting of a water fluid reservoir and peristaltic pump. Cross-sectional fluid velocity images through the principal axis of the implant were generated using a phase-encoding MR imaging technique; axial fluid flow was derived, and fluid shear was evaluated using a Newtonian fluid model. RESULTS: Due to the nonuniform gap of the actual experimental construct, a highly nonuniform flow through the annular gap and a secondary flow through the porous HA block were observed. Axial velocity magnitudes in the range 0.04 to 14 mm/s were measured, and the flow velocities within the annular gap and the surrounding bone differed by nearly two orders of magnitude. Image analysis showed that 95% of total flow passed through the annular gap and 5% was transported through the porous HA block. Fluid shear was computed within the porous structure and the annular gap, and they differed by one order of magnitude. CONCLUSION: We demonstrated that high-resolution MR flow imaging has the resolution to measure fluid transport processes noninvasively through a nonmagnetic model bone implant. Gap fluid flow and fluid flow into the permeable skeleton (HA block) were quantified, and these data allowed the noninvasive determination of fluid shear. These promising results are encouraging for applications in biological tissue, artificial bone substitutes, tissue engineering and clinically relevant studies concerning implant fixation.

Animals↗

PubMed2006

Tobacco extract but not nicotine impairs the mechanical strength of fracture healing in rats.

The influence of nicotine and tobacco extract (without nicotine) alone and in combination on and mechanical strength of closed femoral fractures in rats was investigated. One hundred four male Sprague-Dawley rats were divided into four groups receiving: nicotine, tobacco extract, tobacco extract plus nicotine, and saline. One week prior to fracture, osmotic pumps were implanted subcutaneously in all animals to administer nicotine equivalent to the serum level of nicotine observed in a smoker consuming one to two packs of cigarettes daily. An equivalent volume of saline was administered to the control animals. Tobacco extract was administered orally. A closed transverse femoral diaphysial fracture was performed, and stabilized with an intramedullary pin. The fractures were mechanically tested after 21 days of healing. Tobacco extract alone decreased the mechanical strength. Ultimate torque and torque at yield point of the tobacco extract group were decreased by 21% (p=0.010) and 23% (p=0.056), respectively, compared with the vehicle (saline) group, and by 20% (p=0.023) and 26% (p=0.004), respectively, compared with the nicotine group. No difference was found between the tobacco extract and tobacco extract plus nicotine groups. An 18% (p=0.013) reduction in torque at yield point was observed in the tobacco extract plus nicotine group compared with the nicotine group. No differences in ultimate stiffness, energy absorption, and callus bone mineral content at the fracture line were found between any of the groups. Serum levels of nicotine were between 40-50 ng/mL in the group given nicotine alone and the group given tobacco extract plus nicotine (equivalent to serum levels observed in persons smoking one to two packs of cigarettes per day).

Animals↗

PubMed2006

Precooling an acetabular liner makes its insertion into a metal shell easier.

Temporary shrinkage of an acetabular polyethylene liner due to precooling could reduce the force required to snap the liner into its metal shell. This study documented cooling and heating rates of liners with a particular locking mechanism design, determined forces required to seat liners in their shells as a function of temperature, and quantified the force surgeons can exert with their thumbs when seating a liner. It took up to 8 minutes to cool 58- and 70-mm liners in an ice-water bath from room temperature to near 0 degrees C, and up to 24 minutes to subsequently warm these liners to near body temperature. Forces required to seat liners were greater at room and body temperatures than at 0 degrees C. Liners precooled to 0 degrees C required insertion forces that could be generated manually by surgeons.

Acetabulum↗

PubMed2006

Effect of topical alendronate treatment on fixation of implants inserted with bone compaction.

Bone compaction has been shown to enhance the critical initial implant stability that is important for secure long-term fixation. We investigated whether topical bisphosphonate treatment improves fixation of implants inserted with bone compaction. Porous-coated titanium implants were inserted with bone compaction into the knees of eight dogs. In the right knee, topical bisphosphonate treatment was applied before bone compaction. Saline was used as a control in the left knee. The knees were observed for 4 weeks. We found an increase in total bone-to-implant contact and total bone density around the implants in the bisphosphonate-treated group. These were results of increased nonvital bone-to-implant contact and increased nonvital periimplant bone density. No change in biomechanical fixation was found. Studies with a longer followup are needed to investigate whether the preservative effect of alendronate on nonvital bone might enhance implant fixation by osteoconduction.

Administration, Topical↗

PubMed2005

In vivo effects of RGD-coated titanium implants inserted in two bone-gap models.

RGD (Arg-Gly-Asp) coating has been suggested to enhance implant fixation by facilitating the adhesion of osteogenic cells to implant surfaces. Orthopedic implants are unavoidably surrounded partly by gaps, and these regions represent a challenging environment for osseointegration. We examined the effects of cyclic RGD-coated implants on tissue integration and implant fixation in two cancellous bone-gap models. In canines, we inserted loaded RGD-coated implants with 0.75-mm gap (n = 8) and unloaded RGD-coated implants with 1.5-mm gap (n = 8) into the distal femur and proximal tibia, respectively. Control gap implants without RGD were inserted contralaterally. The titanium alloy (Ti-6Al-4V) implants were plasma sprayed and cylindrical. The observation period was 4 weeks and the fixation was evaluated by push-out test and histomorphometry. Mechanical implant fixation was improved for RGD-coated implants. Unloaded RGD-coated implants showed a significant increase in bone whereas both loaded and unloaded implants showed a significant reduction in fibrous tissue anchorage. The results are encouraging, because RGD had an overall positive effect on the fixation of titanium implants in regions where gaps exist with the surrounding bone. RGD peptide coatings can potentially be used to enhance tissue integration in these challenging environments.

Animals↗

PubMed2005

Biomechanical analysis of the shear behaviour adjacent to an axially loaded implant.

Good mechanical fixation of an implant to the surrounding bone is important for its longevity, and is influenced by both biological and mechanical factors. This study parametrically evaluates the mechanics of the interface with a computationally efficient analytic structural model of the shear stress field and global shear stiffness of an axially loaded implant. The utility of the analytic model was first established by validating its assumptions with a case-specific finite element model. We then used the analytic model for a sensitivity analysis of the relationship between the pattern of tissue growth and shear properties of the interface for our previously reported loaded in vivo experimental micromotion device. The bone located directly at the implant surface was found to be the most effective site for increasing interface stiffness. This suggests that the implant surface is the most desirable site for bone growth, yet is also the most mechanically challenging environment due to its maximal shear stresses. Thus, these findings support the further investigation of osteo-conductive coatings and other biological stimuli to overcome the challenging mechanics, and to promote bone growth directly at the implant surface. The model also demonstrated that the mechanical contribution to the global implant shear stiffness of a commonly observed isolated sclerotic bone rim is very limited. The results of this sensitivity analysis agree with experimental studies with the micromotion device, and with clinical studies reporting good results with osteo-conductive coatings.

Animals↗

PubMed2005

Bone compaction enhances fixation of hydroxyapatite-coated implants in a canine gap model.

Primary cementless joint replacement depends partly on the ability of bone to heal into those areas of an inserted implant where a gap to surrounding bone initially exists. A new bone preparation technique, compaction, has enhanced gap-healing around grit-blasted implants without osteo-conductive properties. However, hydroxyapatite (HA) porous-coated implants with osteo-conductive properties are often inserted clinically to enhance gap healing and implant fixation. It is unknown whether the osteo-conductive properties of HA porous-coated implants might overwhelm the beneficial effects of compaction on gap healing. Therefore, we compared the compaction technique with the conventional bone-removing technique, drilling, using HA porous-coated implants in a canine gap model. HA porous-coated titanium implants were bilaterally inserted into oversized cavities of the proximal humeri of seven dogs. Each dog served as its own control. Thus, one humerus had the implant cavity prepared with compaction, the other with drilling. Two weeks after surgery push-out test and histomorphometry was performed. Compaction significantly increased ultimate shear strength, energy absorption, apparent shear stiffness, bone implant contact, and peri-implant bone density. The results of this study suggest that compaction may enhance gap healing when osteo-conductive HA porous coated implants are inserted in joint replacements.

Absorbable Implants↗

PubMed2005

In vivo study of the effect of RGD treatment on bone ongrowth on press-fit titanium alloy implants.

Early bone ongrowth is known to increase primary implant fixation and reduce the risk of early implant failure. Arg-Gly-Asp (RGD) peptide has been identified as playing a key role in osteoblast adhesion and proliferation on various surfaces. The aim for this study is to evaluate the effect of RGD peptide coating on the bony fixation of orthopaedic implants, to justify its further evaluation in clinical applications. Sixteen unloaded cylindrical plasma sprayed Ti6Al4V implants coated with cyclic RGD peptide were inserted as press-fit in the proximal tibia of 8 mongrel dogs for 4 weeks. Uncoated control implants were inserted in the contralateral tibia. Results were evaluated by histomorphometry and mechanical push-out test. A significant two-fold increase was observed in bone ongrowth for RGD-coated implants. Also, fibrous tissue ongrowth was significantly reduced for RGD-coated implants. Bone volume was significantly increased in a 0-100 microm zone around the implant. The increased bony anchorage resulted in moderate increases in mechanical fixation as apparent shear stiffness was significantly higher for RGD-coated implants. Increases in median ultimate shear strength and energy to failure were also observed. This study demonstrates that cyclic RGD coating increases early bony fixation of unloaded press-fit titanium implants.

Alloys↗

PubMed2005

Importance of pre-clinical testing exemplified by femoral fractures in vitro with new bone preparation technique.

BACKGROUND: A new bone preparation technique, using smooth tamps for bone compaction, has increased crucial initial implant stability. However, preparing the femur with bulky smooth tamps, which from size to size increases the same amount in anterior to posterior as in lateral to medial dimensions, has increased the risk of a femoral fracture. This study examined whether compaction also involved an increased femoral fracture risk when using newly developed smooth tamps with a slim anterior to posterior dimension. METHODS: One femur in each pair of 10 cadaver femurs was prepared by the compaction technique using cylindrical reamers and smooth tamps. The contralateral femur was conventionally prepared with conical reamers and toothed rasps. The tamps and rasps differed in design as a proximal lateral tip was only present on the smooth tamps. Using a standardized test protocol, the instruments were driven into the femoral canal in controlled manner by a drop tower. FINDINGS: At maximum test conditions, five of 10 femurs in the compaction group had fractured, as compared with no fractures in the rasping group. All fractures were longitudinal fissures in the greater trochanter, and these fissures were associated with the extended proximal lateral tip of the tamps. INTERPRETATION: Since the lateral fractures in the compaction group were associated with the extended proximal lateral tip of the tamps, it seems that fracture rates are influenced by instrumentation design. Therefore adequate pre-clinical evaluation is warranted prior to the introduction of new implantation techniques.

Aged↗

PubMed2005

Fixation of revision implants is improved by a surgical technique to crack the sclerotic bone rim.

Revision joint replacement has poorer outcomes compared with primary joint replacement, and these poor outcomes have been associated with poorer fixation. We investigated a surgical technique done during the revision operation to improve access from the marrow space to the implant interface by locally cracking the sclerotic bone rim that forms during aseptic loosening. Sixteen implants were inserted bilaterally by distal femur articulation of the knee joint of eight dogs, using our controlled experimental model that replicates the revision setting (sclerotic bone rim, dense fibrous tissue, macrophages, elevated cytokines) by pistoning a loaded 6.0-mm implant 500 microm into the distal femur with particulate PE. At 8 weeks, one of two revision procedures was done. Both revision procedures included complete removal of the membrane, scraping, lavaging, and inserting a revision plasma-spray Ti implant. The crack revision procedure also used a splined tool to circumferentially locally perforate the sclerotic bone rim before insertion of an identical revision implant. Superior fixation was achieved with the cracking procedure in this experimental model. Revision implants inserted with the rim cracking procedure had a significantly higher pushout strength (fivefold median increase) and energy to failure (sixfold median increase), compared with the control revision procedure. Additional evaluation is needed of local perforation of sclerotic bone rim as a simple bone-sparing means to improve revision implant fixation and thereby increase revision implant longevity.

Animals↗

PubMed2005

Use of tissue ultrafiltration for treatment of compartment syndrome: a pilot study using porcine hindlimbs.

OBJECTIVES: To demonstrate the efficacy of compartment syndrome ultrafiltration for the treatment of acute compartment syndrome in an animal model. Our hypothesis is the removal of interstitial fluid will result in a reduction of intramuscular pressure compared with untreated controls in a model of bilateral induced compartment syndrome. DESIGN: Controlled experimental model. SETTING: Animal research facility. PATIENTS/PARTICIPANTS: Three pairs of porcine hindlimbs. INTERVENTION: Acute compartment syndrome was created in the pig hindlimb by infusion of saline to maintain the intramuscular pressure 30 mm Hg greater than the animal's mean arterial pressure for 8 hours. After a 2-hour reperfusion interval, ultrafiltration (removal of fluid through 1 mm diameter porous catheters, connected to -500 mm Hg suction) was commenced in 1 limb only and continued for 9.5 hours. MAIN OUTCOME MEASURES: Intramuscular pressure, ultrafiltrate volume, ultrafiltrate and serum levels of creatine kinase and lactate dehydrogenase, histologic measurement of extracellular and intracellular edema, as well as the degree of cellular necrosis. RESULTS: Intramuscular pressure tended to be lower on the treated side at the end of the treatment period [treated leg: 9.3 +/- 4.0 mm Hg (+/- SE), control leg: 19.3 +/- 1.4 mm Hg, P = 0.03]. Analysis of ultrafiltrate fluid showed that levels of creatine kinase and lactate dehydrogenase were elevated compared with serum levels. Creatine kinase levels in serum were measured at 4150 +/- 780 U/L, whereas ultrafiltrate levels of creatine kinase were 28,700 +/- 17,700 U/L (+/- SE) (P = 0.1). Lactate dehydrogenase was measured at 1950 +/- 180 U/L in serum, but markedly elevated in ultrafiltrate [160,000 +/- 88,900 U/L (+/- SE), P = 0.05]. Quantification of cellular and interstitial dimensions showed no difference in control and experimental limbs. Quantification of the degree of muscle necrosis revealed 6.1 +/- 2.7% necrosis in the treated limb compared to 11.3 +/- 1.6% necrosis in the control group (P = 0.02, df = 2, 1-tailed paired t test). CONCLUSION: This pilot study demonstrates the feasibility of tissue ultrafiltration for reduction of intramuscular pressure in this porcine model. Further studies are underway. Compartment syndrome ultrafiltration may be useful prophylactically in patients at risk for acute compartment syndrome. Sampling of interstitial fluid and frequent measurement of intramuscular pressure may allow earlier diagnosis and treatment of acute compartment syndrome, whereas the reduction of tissue pressure by compartment syndrome ultrafiltration may prevent acute compartment syndrome from occurring. Additionally, compartment syndrome ultrafiltration will not hinder the ability of clinicians to use the clinical examination and pressure monitoring as the gold standard.

Animals↗

PubMed2004

Differential effect of a bone morphogenetic protein-7 (OP-1) on primary and revision loaded, stable implants with allograft.

Morselized impacted bone allograft is often used to reconstruct the bone bed in the revision of failed total joint arthroplasties. We hypothesized that addition of the bone morphogenetic protein OP-1 (BMP-7) to bone allograft would improve early implant fixation. We inserted one loaded 6-mm-diameter titanium implant (surrounded by 0.75-mm gap) in each medial condyle of 24 canines. On one side, the implant was inserted in a controlled experimental revision setting resembling the clinical revision situation. A primary implant was inserted on the contralateral side in a previously unoperated site. Three groups were studied: 1) allograft alone, 2) allograft + 0.4 mg OP-1, and 3) allograft + 0.8 mg OP-1. Implant fixation was evaluated at 4 weeks. Grafted implants inserted in the primary setting without OP-1 had better fixation than the grafted revision setting with or without OP-1 (significantly more bone coverage, more mineralized tissue in the gap, and better mechanical interface strength). However, grafted primary implants with OP-1 had impaired fixation compared with grafted primary implants without OP-1 (less bone coverage of the implant and less bone formation in the gap). In contrast, grafted revision implants with OP-1 significantly increased implant fixation compared with grafted revision implants without OP-1 (increased mechanical interface strength and fraction of mineralized tissue in the gap). We found no differences between the two doses in any of the settings. Addition of OP-1 to bone allografted implants may show benefit at sites with impaired bone healing capacities, such as the revision setting.

Animals↗

PubMed2004

Mechanical interface conditions affect morphology and cellular activity of sclerotic bone rims forming around experimental loaded implants.

A characteristic bony structure found at revision surgery for failed joint replacement, and implicated as being associated with poorer subsequent implant fixation, is a sclerotic bone rim (SB rim). This study is a histomorphometric analysis of the SB rim formed around an experimental canine micro-motion implant system under stable or unstable conditions with polyethylene (PE) particles, after 8 weeks. A point count histomorphometric analysis was performed to determine the cellular activity at the surface of the SB rim, and the morphology of the structure was determined by image analysis. A SB rim was found to form under both stable and unstable conditions, but with unstable conditions the rim was more distinct, thick, continuous, and was located near the drill hole, and had high and ongoing formative activity at both surfaces with little resorption. Under stable conditions, thinner second or third SB rims were observed. The difference in width and distance between implant and the SB rim is significant (p<0.05), as was the difference in fraction of resorption surfaces at the SB surface facing the implant. This study observed an in vivo primary bone response to controlled stable and unstable loaded implants. Sclerosis of trabeculae in a semi-continuous SB rim can serve to isolate the implant from the marrow space. The increases in SB rim width and continuity is consistent with the previously demonstrated knowledge that increase of total bone mass and low risk for trabeculae perforation is the consequence of low resorptive and high formative activity.

Animals↗

PubMed2003

The effects of hydroxyapatite coating and bone allograft on fixation of loaded experimental primary and revision implants.

We used our established experimental model of revision joint replacement to examine the roles of hydroxyapatite coating and bone graft in improving the fixation of revision implants. The revision protocol uses the Søballe micromotion device in a preliminary 8-week period of implant instability for the presence of particulate polyethylene. During this procedure, a sclerotic endosteal bone rim forms, and a dense fibrous membrane is engendered, having macrophages with ingested polyethylene and high levels of inflammatory cytokines. At the time of revision after 8 weeks, the cavity is revised with either a titanium alloy (Ti) or a hydroxyapatite (HA) 6.0 mm plasma-sprayed implant, in the presence or absence of allograft packed into the initial 0.75 mm peri-implant gap. The contralateral limb is subjected to primary surgery with the same implant configuration, and serves as control. 8 implants were included in each of the 8 treatment groups (total 64 implants in 32 dogs). The observation period was 4 weeks after revision. Outcome measures are based on histomorphometry and mechanical pushout properties. The revision setting was always inferior to its primary counterpart. Bone graft improved the revision fixation in all treatment groups, as also did the HA coating. The sole exception was revision-grafted HA implants, which reached the same fixation as primary Ti and HA grafted implants. The revision, which was less active in general, seems to need the dual stimulation of bone graft and HA implant surface, to obtain the same level of fixation associated with primary implants. Our findings suggest that the combination of HA implant and bone graft may be of benefit in the clinical revision implant setting.

Animals↗

PubMed2003

Compacted cancellous bone has a spring-back effect.

A new surgical technique, compaction, has been shown to improve implant fixation. It has been speculated that the enhanced implant fixation with compaction could be due to a spring-back effect of compacted bone. However, such an effect has yet to be shown. Therefore we investigated in a canine model whether implant cavities prepared with compaction had spring back. Before killing the animals, we used one of two surgical techniques to make implant cavities of identical dimensions in both lateral femoral condyles of 7 dogs. One side had the implant cavity prepared with compaction, the other side with drilling. The cavities were left empty in vivo for 10 minutes before the dogs were killed. Postoperative micro-CT scanning showed that the diameters of the compacted cavities were significantly smaller than those of the drilled cavities, although they had had identical dimensions initially. Thus we found a spring-back effect of compacted bone, which may be important for increasing implant fixation by reducing initial gaps between the implant and bone.

Animals↗

PubMed2003

Femoral fracture risk in hip arthroplasty: smooth versus toothed instruments.

Compaction of cancellous bone with smooth tamps in total hip arthroplasty has been shown to improve initial implant fixation. It is not known, however, whether this improved fixation occurs at the expense of an increased risk of intraoperative femoral fracture. The current authors explore this issue by comparing the risk of fracture in 10 pairs of femurs prepared with either smooth tamps or conventional toothed broaches. Using one pass for each size, smooth tamps were advanced incrementally into one femur of each pair and toothed broaches were advanced incrementally into the contralateral femur. A controlled impulse, representative of a typical impact during surgery, was applied to the instruments by a drop tower (mean starting force, 3017 N). When the instruments no longer advanced distally, the applied force was increased incrementally. Instrument sizes were increased until a femoral fracture was observed or the impact exceeded 8000 N without causing a femoral fracture. At preoperative templated size, significantly more femurs that had tamps had fractured (eight of 10), compared with femurs that had broaches (two of 10). Smooth tamps therefore increased the risk of intraoperative femoral fracture in vitro in this particular implant design developed for cemented fixation of the femoral component.

Absorptiometry, Photon↗