Prevention of loosening in total hip replacements using guided bone regeneration.

The aim of this study was to prevent wear debris from reaching the interface of the acetabular cup and femoral component by using a partially occlusive expanded polytetrafluoroethylene membrane. This membrane initially acted as a physical seal, which became incorporated by bone and soft tissue, forming a secondary biologic seal, preventing loosening. An animal model was developed to test the hypothesis. The model replicated the mechanisms of loosening where the effects of wear debris were studied. Using femoral heads with the appropriate roughness, a goat model produced the radiologic and histologic presentation of loosening as observed in total hip replacements in humans. Loosening was assessed by measurement of the radiolucent lines, and was attributed to wear debris by histologic investigation. The expanded polytetrafluoroethylene membrane prevented acetabular implant loosening to a statistical significance of 0.02 in a blinded assessment when compared with the control groups. Loosening of the first 5 mm of the proximomedial aspect of the femur also was prevented. The authors of the current study prevented wear particle-induced osteolysis in the acetabular component by using an expanded polytetrafluoroethylene membrane to seal the bone-cement interface.

Joint resurfacing using allograft chondrocytes and synthetic biodegradable polymer scaffolds.

Cartilage implants which could potentially be used to resurface damaged joints were created using rabbit articular chondrocytes and synthetic, biodegradable polymer scaffolds. Cells were serially passaged and then cultured in vitro on fibrous polyglycolic acid (PGA) scaffolds. Cell-PGA constructs were implanted in vivo as allografts to repair 3-mm diameter, full thickness defects in the knee joints of adult rabbits, and cartilage repair was assessed histologically over 6 months. In vitro, chondrocytes proliferated on PGA and regenerated cartilaginous matrix. Collagen and glycosaminoglycan (GAG) represented 20 to 8% of the implant dry weight (dw), respectively, at the time of in vivo implantation; the remainder was PGA and unspecified components. Implants based on passaged chondrocytes had 1.7-times as much GAG and 2.6-times as much collagen as those based on primary chondrocytes. In vivo, cartilaginous repair tissue was observed after implantation of PGA both with and without cultured chondrocytes. Six month repair was qualitatively better for cell-PGA allografts than for PGA alone, with respect to: 1) surface smoothness, 2) columnar alignment of chondrocytes, 3) spatially uniform GAG distribution, 4) reconstitution of the subchondral plate, and 5) bonding of the repair tissue to the underlying bone. These pilot studies demonstrate that it is feasible to use cell-polymer allografts for joint resurfacing in vivo.

Bone remodeling and in vivo strain analysis of intact and implanted greyhound proximal femora.

Pre- and poststudy motion and gait analyses of eight size-matched male greyhounds confirmed uniform loading of their femora. Subminiature strain gages implanted on the intact inferior and anterior aspects of the femoral neck in six greyhounds indicated in vivo strain variations among test animals. Motion and gait analyses confirmed uniform loading of femora following unilateral hemiarthroplasty with cobalt-chromium hip implants. In vivo strain measurements adjacent to the implants indicated large variations among test animals. A consistent direction of strain change relative to the intact femur was noted, even though strain changes varied in magnitude. Image analysis of microradiographs indicated insignificant differences in the cortical areas of implanted and intact femora. Extensive new trabecular bone formation was noted along the implant in the endosteal cavity and correlated with a combination of implant placement and exercise level. Most of the bone was formed with centrally placed implants in exercised dogs, and the least with stems on the medial neck surface in rested dogs. Iliac crest biopsies indicated that bone formation rates slowed in rested animals and remained constant throughout the study in exercised animals. All implanted femora had a thin (< 1 mm thick) aligned fibrous tissue layer separating the implant from bone. It varied in thickness as a function of the aspect of the implant. Exercised dogs had a larger proportion of fibrous tissue on the anterior and posterior aspects, while rested dogs had a larger proportion of fibrous tissue on the medial and lateral aspects.

Composition of cell-polymer cartilage implants.

Cartilage implants for potential in vivo use for joint repair or reconstructive surgery can be created in vitro by growing chondrocytes on biodegradable polymer scaffolds. Implants 1 cm in diameter by 0.176 cm thick were made using isolated calf chondrocytes and polyglucolic acid (PGA). By 6 weeks, the total amount of glycosaminoglycan (GAG) and collagen (types I and II) increased to 46% of the implant dry weight; there was a corresponding decrease in the mass of PGA. Implant biochemical and histological compositions depended on initial cell density, scaffold thickness, and the methods of cell seeding and implant culture. Implants seeded at higher initial cell densities reached higher GAG contents (total and per cell), presumably due to cooperative cell-to-cell interactions. Thicker implants had lower GAG and collagen contents due to diffusional limitations.Implants that were seeded and cultured under mixed conditions grew to be thicker and more spatially uniform with respect to the distribution of cells, matrix, and remaining polymer than those seeded and/or cultured statically. Implants from mixed cultures had a 20-40-mum thick superficial zone of flat cells and collagen oriented parallel to the surface and a deep zone with perpendicular columns of cells surrounded by GAG Mixing during cell seeding and culture resulted in a more even cell distribution ad enhanced nutrient diffusion which could be related to a more favorable biomechanical environment for chondrogenesis. Cartilage with appropriate for and function for in vivo implantation ca thus be created by selectively stimulating the growth and differentiated function of chondrocytes (i.e., GAG and collagen synthesis) through optimization of the in vitro culture environment. (c) 1994 John Wiley & Sons, Inc.

Cement particles inhibit bone growth into titanium chambers implanted in the rabbit.

Particles of bone cement have been shown previously to stimulate the resorption of bone. The purpose of this study was to determine whether particles of bone cement (BC) have an adverse effect on bone ingrowth. The bone harvest chamber was implanted bilaterally in the proximal tibial metaphysis of 6 mature rabbits. Both the fixed outer cylinder and the inner removable core of the chamber have a transverse 1 mm wide pore providing a continuous canal for tissue ingrowth. After an initial 6-week period for osseointegration of the outer cylinder, the contents of the inner core were harvested repeatedly at 3 weekly intervals. In the first series of rabbits, the carrier solution, 1% sodium hyaluronate (Healon) was implanted first. In subsequent implantations, Healon was mixed with small fabricated particles of BC (averaging 3.54 mm in diameter) to fill the channel of the core. The contralateral chamber was left empty and served as a control. In the second series of rabbits, implantation was carried out sequentially using the same material bilaterally. The sections from the control harvests, and those with Healon alone contained extensive trabecular bone arranged longitudinally in the canal, in a fibrovascular stroma. The sections containing BC particles were infiltrated by foamy, mononuclear and multinuclear histiocytic cells. Less trabecular bone was seen in the sections containing BC particles compared to the control sections or those containing Healon alone. Previous studies have shown that particles of bone cement stimulate bone resorption. In this study, BC particles have also been shown to diminish the formation of new bone.

Hydroxyapatite-coated strain gauges for long-term in vivo bone strain measurements.

The aim of this study was to examine the bonding process between hydroxyapatite-coated strain gauges and bone in order to continue development of a long term in vivo strain measurement device. Two types of commercially available hydroxyapatite (HA) particles were applied to the sensing surface of uniaxial strain gauges using a polysulfone solution as an adhesive. Characterization by scanning electron microscopy and x-ray diffraction (XRD) was used to determine materials property differences between the two powders. Interfacial strengths between the HA coatings and the strain gauges were tested and found comparable to interfacial strength obtained by a plasma sprayed HA coating on the surface of a titanium implant. Gauges were surgically placed on the periosteal surface of greyhound femora. Three groups of dogs were implanted with gauges for periods of 3, 6, and 12 weeks using cyanoacrylate, resorbable sutures, and cable ties to initially hold the gauge against the surface of the bone. Following euthanasia, the femora of the dogs were explanted and subjected to cantilever loading. Response of the implanted HA-coated gauges were compared to a control set that had been freshly glued onto the contralateral femur. Full response, that is, 100% of the strain measurement with respect to the control, was obtained after 12 weeks in vivo. Attachment of HA-coated gauges with circumferential suture showed bonding, while HA-coated gauges attached with cyanoacrylate did not bond to bone. After mechanical testing, femora were embedded in polymethylmethacrylate, cut, ground, and polished. Sections were stained using mineralized bone stain (MIBS) and optical microscopy was performed using transmitted and fluorescent light to allow analysis of remodeling occurring in the region of the strain gauges. Bone formation occurred at the HA surface of sutured gauges, and a fibrous tissue layer developed between the bone and HA coating when the tissue adhesive was used to initially bond the gauge. Fluorescence microscopy indicated an increase in the number of areas of bone remodeling adjacent to the gauge but a normal rate of remodeling of 0.93 +/- 0.07 mum/day was observed. No gross bone remodeling due to strain gauge placement was observed. Backscattered electron imaging (BSE) indicated new bone apposition at all time periods.

Neocartilage formation in vitro and in vivo using cells cultured on synthetic biodegradable polymers.

Cartilaginous implants for potential use in reconstructive or orthopedic surgery were created using chondrocytes grown on synthetic, biodegradable polymer scaffolds. Chondrocytes isolated from bovine or human articular or costal cartilage were cultured on fibrous polyglycolic acid (PGA) and porous poly(L)lactic acid (PLLA) and used in parallel in vitro and in vivo studies. Samples were taken at timed intervals for assessment of cell number and cartilage matrix (sulfated glycosaminoglycan [S-GAG], collagen). The chondrocytes secreted cartilage matrix to fill the void spaces in the polymer scaffolds that were simultaneously biodegrading. In vitro, chondrocytes grown on PGA for 6 weeks reached a cell density of 5.2 x 10(7) cells/g, which was 8.3-fold higher than at day 1, and equalled the cellularity of normal bovine articular cartilage. In vitro, the cell growth rate was approximately twice as high on PGA as it was on PLLA; cells grown on PGA produced S-GAG at a high steady rate, while cells grown on PLLA produced only minimal amounts of S-GAG. These differences could be attributed to polymer geometry and biodegradation rate. In vivo, chondrocytes grown on both PGA and PLLA for 1-6 months maintained the three-dimensional (3-D) shapes of the original polymer scaffolds, appeared glistening white macroscopically, contained S-GAG and type II collagen, and closely resembled cartilage histologically. These studies demonstrate the feasibility of culturing isolated chondrocytes on biodegradable polymer scaffolds to regenerate 3-D neocartilage.

Performance of a hydrogel composite pericardial substitute after long-term implant studies.

A novel composite patch has been tested as a pericardial substitute to reduce adhesion formation after cardiac surgery. The patch consists of poly 2-hydroxyethyl methacrylate (pHEMA) hydrogel reinforced with a polyethylene terephthalate (PET) mesh. The hydrogel-PET composite pericardial patches were implanted in canines for 6, 9, and 12 months. Upon termination, adhesion formation and epicardial reaction to the implant were rated. No adhesions formed between the patch and the native pericardium or epicardium. A thin fibrous layer on the epicardium progressively developed where the patch contacted the heart. The coronary anatomy remained visible. Histologically, the response to the implant was fibrous in nature. No significant signs of cellular inflammation were found. The gross appearance of the retrieved patches was nearly identical to that of preimplant patches. Mechanical tests showed no significant changes (alpha = 0.05) in patch strength or stiffness. Hydrogel water content initially increased during implantation. The thickness of the patch did not change significantly (alpha = 0.05) throughout the study. Scanning electron microscopy (SEM) revealed unequal layers of hydrogel on either side of the PET mesh and cracks in the hydrogel surfaces of retrieved patches. Both SEM and light microscopic observation of the patches showed traces of calcification in patches in the 9 and 12 month studies.

Iron overload in Africa. Interaction between a gene and dietary iron content.

BACKGROUND AND METHODS: In contrast to hemochromatosis, which in white populations is inherited through a gene linked to the HLA locus, iron overload in sub-Saharan Africa is believed to result solely from increased dietary iron derived from traditional home-brewed beer. To examine the hypothesis that African iron overload also involves a genetic factor, we used likelihood analysis to test for an interaction between a gene (the hypothesized iron-loading locus) and an environmental factor (increased dietary iron) that determines transferrin saturation and unsaturated iron-binding capacity. We studied 236 members of 36 African families chosen because they contained index subjects with iron overload. Linkage to the HLA region was tested with use of lod scores. RESULTS: In the index subjects, increased iron was present in both hepatocytes and cells of the mononuclear-phagocyte system. Among family members with increased dietary iron due to the consumption of traditional beer, transferrin saturation in serum was distributed bimodally, with 56 normal values (less than 60 percent saturation) and 44 elevated values; the mean serum ferritin concentration was five times higher in the subjects with elevated transferrin saturation (P less than 0.005). The pedigree analysis provided evidence of both a genetic effect (P less than 0.005) and an effect of increased dietary iron (P less than 0.005) on transferrin saturation and unsaturated iron-binding capacity. In the most likely model, increased dietary iron raised the mean transferrin saturation from 30 to 81 percent and lowered the mean unsaturated iron-binding capacity from 38 to 13 mumol per liter in subjects heterozygous for the iron-loading locus. The hypothesis of tight linkage to HLA was rejected. CONCLUSIONS: Iron overload in Africa may be caused by an interaction between the amount of dietary iron and a gene distinct from any HLA-linked gene.

Triple fluorochrome labeling of cochlear bone growth.

A new technique is described which measures the extent and time course of intracochlear bone formation after cochlear implantation in an experimental animal model. A series of fluorescent histochemical markers is used to delineate the amount of intracochlear bone deposition during specified time periods.

Histologic, biochemical, and ion analysis of tissue and fluids retrieved during total hip arthroplasty.

Large amounts of metal and polyethylene debris and high ion readings are found in capsule and fibrous membranes of both loose titanium and cobalt-chromium stems. Prostaglandin E2, interleukin-1, and collagenase levels are elevated when compared to control values with collagenase having the highest and most consistent elevations. Synovial fluid and blood ion readings were elevated in loose cemented and cementless stems made from both materials. Blood ion readings were not elevated in fixed stems. Fixed stems had much less particulate debris in soft tissues. The data showed that failure of most metal hip stems was initially due to a mechanical cause, with high debris and ion counts occurring secondarily in capsule and fibrous membranes. Particulate debris and high ion readings are primarily a focal problem contained by the periprosthetic fibrous connective-tissue encapsulation within the femoral canal and joint capsules. No systemic problems were manifest in any of the patients examined and followed in this study.

Preliminary development of a hydroxyapatite-backed strain gauge.

Long-term in vivo strain sensing would provide information about deformation changes adjacent to implants during bone remodeling. Biodegradation of the cyanoacrylate adhesive commonly used to attach strain gauges to bone has generally limited in vivo strain sensing to time periods less than one month. Hydroxyapatite (HA) which has been used to attach implants to bone in vivo, was attached to strain gauges using a solvent-thinned polysulfone solution. Three HA-polysulfone surface morphologies were tested in a preliminary bench-top test. The single layer pressed surface morphology, which responded most accurately during bench-top testing, was modified slightly and applied to two gauges which were implanted on the femur of a greyhound. Strain measurements from the HA-backed gauges in place for four months in vivo were compared to strains measured from the contralateral femur. Comparison of the results indicated these gauges were well-bonded and that they were sensing strain accurately. After embedding in PMMA, the femur having the HA-backed gauge and the control femur were sectioned at the level of one of the HA-backed gauges. Microradiographs of these sections indicated no adverse tissue response to the HA-backed gauge on the endosteal or periosteal surface.

Alteration of retrieved implants in vitro by processing and infiltrating fluids.

Undecalcified histology has proved of immense value in the examination of the interface membrane between the prosthesis and bone. However, to provide such histological sections, dehydrating and clearing fluids as well as plastic infiltrating fluids must be used. This study investigates the possibility that some of these commonly used fluids may alter the biomaterial after removal from the body and be misinterpreted as an in vivo product. Ten different routinely used fluids were tested on 11 different biomaterials that are commonly used in prosthetic devices. The nonmetal biomaterials were placed in glass tubes containing the different fluids at room temperature for 5 days. The biomaterials were assessed for changes each day. After 5 days the biomaterial was examined and discarded and the glass tube was centrifuged. The pellet was examined using polarized light microscopy. Polysulfone and bone cement was found to be considerably altered in vitro by most of these fluids. While the components (plasticizer and catalyst) of the plastic fluids caused some changes to the biomaterial. Spurr's and GMA did not cause any alterations to any of the biomaterials that were examined.

Histological analysis of a central tarsal implant in a racing greyhound.

The hock of a greyhound containing a titanium alloy central tarsal replacement was examined histologically. The animal had raced competitively 43 times before retirement. The examination showed that the adaptation and encapsulation of the implant by the surrounding bones, together with the excellent purchase of the screw into the fourth tarsal bone, had maintained the implant in excellent position during vigorous load-bearing. There was no histopathological evidence to suggest that the fixation of the implant was failing. The results provide evidence for the value of titanium alloy implants as a central tarsal replacement in greyhounds with type V fractures, and as a feasible alternative to euthanasia.

Life stress and lymphocyte alterations among patients with rheumatoid arthritis.

The relation between life stress and immune parameters was investigated for 33 female rheumatoid arthritis (RA) patients interviewed during three routine monthly clinic checkups. Life stress from major and minor events, coping efficacy, and self-reported psychological distress were assessed, and immunofluorescence of T-cells and B-cells was performed on the blood drawn during each visit. Small stressful events were positively related to the proportion of circulating B-cells, psychological distress was inversely related to proportion of circulating T-cells, and major life events were associated with lower T-helper/T-suppressor cell ratios.

Kaposi's sarcoma in Zimbabwe. II. Peripheral lymphocytes, immunoglobulin G levels and HIV antibody positivity.

Patients with Kaposi's Sarcoma (KS) were grouped according to their clinical symptoms into "indolent", "locally aggressive", "endemic generalised aggressive" and "epidemic generalised aggressive" disease. Only the patients in the epidemic generalised aggressive disease group had serum antibodies to HIV. Complete peripheral blood counts, including lymphocyte subsets, and serum IgG assays were performed on all patients before treatment was initiated. In all the aggressive disease groups there was evidence of immune deficiency in that T helper/inducer (T4) cells were reduced leading to reduced T4,T8 (suppresser/cytotoxic) ratio. All patient groups had increased levels of serum IgG. Although immune deficiency and aggressive KS can be explained in the HIV infected patients no underlying cause has been found in the HIV negative patients with aggressive KS.

A polymethyl methacrylate method for large specimens of mineralized bone with implants.

A simple modified polymethyl methacrylate method is described for large mineralized bone specimens with implants and bioactive materials which produces consistently good histological preservation of the interface between bone and implant. Human femoral heads, whole rabbit condyles and canine tibias and femurs containing implants consisting of hydroxyapatite, smooth polyethylene, porous polyethylene and carbon were dehydrated in ascending grades of ethanol and cleared with xylene on an automated tissue processor which alternated vacuum and pressure for 22 hr. Infiltration was done with washed polymethyl methacrylate at 4 C under vacuum for 13 days. Polymerization was carried out in wide-mouth glass jars at 38 C for 36 hr so that the total processing time was less than 20 days. The only important modification was in the polymethyl methacrylate, which had less plasticizer than usual in order to give a harder block. This enabled production of 4 micron sections with good preservation of mineralized and cellular areas for the study of metabolic bone diseases, morphometry, fluorochrome labelling and interface analysis with the implant in situ.