Cathepsin G and alpha 1-antichymotrypsin in the local host reaction to loosening of total hip prostheses

Cathepsin g Degrades Both Glycosylated and Unglycosylated Regions of Lubricin, a Synovial Mucin

Lubricin (PRG4) is a mucin type protein that plays an important role in maintaining normal joint function by providing lubrication and chondroprotection. Improper lubricin modification and degradation has been observed in idiopathic osteoarthritis (OA), while the detailed mechanism still remains unknown. We hypothesized that the protease cathepsin G (CG) may participate in degrading lubricin in synovial fluid (SF). The presence of endogenous CG in SF was confirmed in 16 patients with knee OA. Recombinant human lubricin (rhPRG4) and native lubricin purified from the SF of patients were incubated with exogenous CG and lubricin degradation was monitored using western blot, staining by Coomassie or Periodic Acid-Schiff base in gels, and with proteomics. Full length lubricin (∼300 kDa), was efficiently digested with CG generating a 25-kDa protein fragment, originating from the densely glycosylated mucin domain (∼250 kDa). The 25-kDa fragment was present in the SF from OA patients, and the amount was increased after incubation with CG. A CG digest of rhPRG4 revealed 135 peptides and 72 glycopeptides, and confirmed that the protease could cleave in all domains of lubricin, including the mucin domain. Our results suggest that synovial CG may take part in the degradation of lubricin, which could affect the pathological decrease of the lubrication in degenerative joint disease.

Enzymes and cytokines disease in total hip arthroplasty: promoters of immune loosening

Introducción. Una de las causas más importantes de falla de la prótesis de cadera lo constituye el fenómeno de aflojamiento, el cual se relaciona con la liberación de enzimas mediada por citocinas y produce la lisis del hueso que soporta el implante.Objetivo. Describir los mecanismos de interacción biológica de las moléculas promotoras del aflojamiento de la prótesis total de cadera que con mayor frecuencia están presentes en el proceso.Materiales y métodos. Se realizó una búsqueda de artículos originales y casos clínicos en las bases de datos PubMed y Scopus, sin límite de fecha de publicación, utilizando los términos MeSH “hip prosthesis loosening”, “aseptic loosening”, “cytokines” y “hip arthroplasty failure”. La extracción de datos se hizo mediante la lectura de 250 estudios, de los cuales se seleccionaron 66 para fines de redacción.Resultados. Los autores describen las moléculas más representativas implicadas en el aflojamiento de la prótesis de cadera, además se presentan las interacciones entre ellas.Conclusiones. Enzimas y citocinas han sido ampliamente estudiadas por cuatro décadas, aunque sus mecanismos de interacción son poco conocidos. Los autores proponen un mecanismo de interacción, proceso que podría denominarse “enfermedad de las enzimas y citocinas” o “aflojamiento inmunológico”.

Evaluation of the Role for Synovial Aspiration in the Diagnosis of Aseptic Loosening After Total Knee Arthroplasty

BACKGROUND

Aseptic prosthetic loosening is known to be an inflammatory, cellular process. We hypothesized that the synovial cell count would significantly differ among normal controls, patients with aseptic loosening, and patients with other etiologies of aseptic failure after total knee arthroplasty and thus that the cell count would be useful in the diagnosis of aseptic loosening.

METHODS

Over a six-year time period, all patients undergoing revision total knee arthroplasties at our institution underwent prospective intraoperative aspiration by the two senior authors. Each patient was assigned to a failure category on the basis of a priori criteria: aseptic loosening, periprosthetic infection, component wear, periprosthetic fracture, component malposition, instability, stiffness, and extensor mechanism failure. Simultaneously, patients with well-functioning total knee replacements underwent aspiration as normal controls. Aspirate characteristics were then compared between groups. Receiver-operating characteristic curves were created to determine optimal white blood-cell cutoffs when periprosthetic infection was compared with each individual failure category.

RESULTS

Thirty normal control patients and 433 patients who underwent revision total knee arthroplasties were included in this study. The synovial white blood-cell count in the normal control group was 558 ± 522 cells/μL, which did not significantly differ (p = 0.091) from that taken from patients with aseptic loosening (947 ± 1027 cells/μL). However, normal controls had significantly higher white blood-cell counts than subjects with stiffness (367 ± 392 cells/μL; p = 0.002) and significantly lower white blood-cell counts than subjects with periprosthetic fractures (1687 ± 1613 cells/μL; p = 0.002). Subjects with aseptic loosening had significantly higher white blood-cell counts than subjects with component malpositioning (p = 0.002) or stiffness (p = 0.001). When individual aseptic failure categories were compared with periprosthetic infection, the optimal white blood-cell cutoff varied widely, including 2104 cells/μL for component malposition and 4697 cells/μL for periprosthetic fracture, and the optimal differential segmented cell count percentages varied from 47% to 83%.

CONCLUSIONS

Although synovial fluid aspirates in patients with aseptic loosening and those with normal total knee arthroplasties did not differ, synovial fluid aspirate characteristics differed among categories of aseptic failure. As a result, the optimal diagnosis of periprosthetic infection on the basis of synovial aspiration results may need to utilize different cutoff values depending on the alternative mode of failure being considered. Large prospective studies will be necessary to validate these threshold values.

Titanium particles up-regulate the activity of matrix metalloproteinase-2 in human synovial cells

PURPOSE

Wear debris particle-induced osteolysis and subsequent aseptic loosening is one of the major causes of failure of total joint replacement. The purpose of this study was to investigate the effect of titanium implant material and inflammatory cytokines on human synovial cells and the development to osteolysis and aseptic loosening.

METHODS

This study investigated the effect of titanium implant material on the ECM-degraded MMP-2 in human synovial cells and analyzed the contribution of synovial cells in osteolysis and aseptic loosening.

RESULTS

When human synovial cells are exposed to titanium materials, MMP-2 activity is induced by 1.72 ± 0.14-fold with Ti disc and 3.95 ± 0.10-fold with Ti particles, compared with that of the controls, respectively. Inflammatory cytokines TNFα and IL-1β are also shown to induce MMP-2 activity by 3.65 ± 0.28-fold and 6.76 ± 0.28-fold, respectively. A combination of Ti particles and cytokines induces MMP-2 activities to a higher level (10.54 ± 0.45-fold). Inhibitors of various signal pathways involved in MMP-2 reverse Ti particle-induced MMP-2 activities.

CONCLUSIONS

Synovial cells surrounding the bone-prosthesis interface may contribute to production of MMP-2, and NFκB inhibitors may be explored as potential therapeutics to alleviate wear debris-induced osteolysis and aseptic loosening.

Correlation of aspiration results with aseptic loosening in total hip arthroplasty

In the evaluation of patients with a persistently painful total hip arthroplasty establishing an accurate diagnosis is paramount in the selection of a successful treatment regimen. It is unknown whether synovial analysis might differentiate aseptic loosening from other causes of failure. A physiological basis exists to suggest that aseptic loosening might be a process of non-segmented leukocytes. The objective of this study was to determine if the synovial fluid differential cell count might aid in the diagnosis of aseptic loosening. A retrospective chart review of all patients who had undergone revision hip arthroplasty with pre-operative or intra-operative aspiration results was performed. Aseptic loosening was defined as gross intraoperative movement in the absence of infection. From these results Relative-Operating Characteristic (ROC) curves were created, and sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) were calculated. A diagnosis of aseptic loosening was established in 76 of the 253 hips. The ROC curves indicated that lymphocyte count does have utility in the diagnosis of aseptic loosening. If an aspirate has a combination of fewer than 2500 WBCs (sensitivity 93%, specificity 42%, NPV 94%, accuracy 57%) or more than 10% lymphocytes (sensitivity 86%, specificity 42%, NPV 87%, accuracy 55%) then the sensitivity for aseptic loosening is 96%, the specificity is 33%, the NPV is 95% and the accuracy is 52%. In patients with painful total hip arthroplasties in whom infection has been excluded, aspiration data can be a useful adjunct in the diagnosis of aseptic loosening. In aspirates with neither a WBC cell count of less than 2500 nor a lymphocyte cell count of greater than 10% aseptic loosening can be effectively "ruled out" as fewer than 5% of these patients will have aseptic loosening. While non-specific, aspirate differential can be useful to "rule-out" aseptic loosening with a sensitivity and negative predictive value well exceeding that of standard radiographs.

Polyethylene wear particles do not induce inflammation or gelatinase (MMP-2 and MMP-9) activity in fibrous tissue interfaces of loosening total hip arthroplasties

In vitro and in vivo studies have suggested that polyethylene wear particles are the main cause for osteolysis in prosthetic loosening. Elevated amounts of proteases including gelatinases (or matrix metalloproteinases MMP-2 and MMP-9) have been found in fibrous tissue interfaces of loosened total hip arthroplasties suggesting that proteolysis plays a role in osteolysis. The presence of proteases does not mean that they are active, because activity of proteases is highly regulated at the post-translational level. We investigated whether the activity of two major proteases that are active extracellularly and have been associated with loosening, MMP-2 and MMP-9, is involved in loosening of non-cemented hip implants with polyethylene acetabular components. Eight interface tissues retrieved during revision were studied with light and electron microscopy and by in situ zymography to localize MMP-2 and MMP-9 activity in combination with immunohistochemistry to localize MMP-2 and MMP-9 proteins. All interface tissues contained large amounts of polyethylene wear particles, either in large accumulations or dispersed in the extracellular matrix or intracellularly in fibroblasts. Particles were not encountered in association with MMP-2 or MMP-9 activity or leukocytes. Inflammation was never found. MMP-9 activity was restricted to macrophages and MMP-2 activity was restricted to microvascular endothelial cells mainly outside areas where particles were present. Our data indicate that wear particles do not induce activation of leukocytes or MMP-2 or MMP-9 activity. Therefore, aseptic loosening may not be particle induced but initiated by other mechanisms such as mechanical stress.

Alpha1-antichymotrypsin activity correlates with and may modulate matrix metalloproteinase-9 in human acute wounds

Matrix metalloproteinase-9 (MMP-9) plays a central role in many physiologic processes including acute and the chronic wounds. MMP-9 is not routinely expressed in healthy tissues but is promptly expressed as a proenzyme and converted into active enzyme after tissue injury. The mechanisms involved, including the activators and inhibitors for this enzyme in human tissue remain largely obscure. We recently identified alpha1-antichymotrypsin (alpha1-ACT), an acute phase factor, as a potent inhibitor controlling activation of pro-MMP-9 by human skin. The aim of this study is to establish the clinical relevance of the inhibitor in cutaneous wound healing. Fluids from acute burn blisters and conditioned media from skin explants of burn patients were analyzed. We observed that the presence pro-MMP-9 and its activation correlated with the proximity to and degree of injury. Early after trauma, massive levels of wound alpha1-ACT were associated with an absence of pro-MMP-9 activation. Conversely, the active MMP-9 occurs simultaneously with inactivation of alpha1-ACT. Our results suggest a role for alpha1-ACT as a physiologic inhibitor of MMP-9 activation in human wound healing.

Small ubiquitin-like modifier 1 [corrected] mediates the resistance of prosthesis-loosening fibroblast-like synoviocytes against Fas-induced apoptosis

OBJECTIVE

To study the expression of small ubiquitin-like modifier 1 (SUMO-1) in aseptic loosening of prosthesis implants and to investigate its role in regulating the susceptibility of prosthesis-loosening fibroblast-like synoviocytes (FLS) to Fas-induced apoptosis.

METHODS

Specimens of aseptically loosened tissue were obtained at revision surgery, and the expression of SUMO-1 was analyzed by in situ hybridization. SUMO-1 levels in FLS were determined by quantitative polymerase chain reaction and Western blot analysis. Immunohistochemistry and confocal microscopy were used to study the subcellular localization of SUMO-1. The functional role of SUMO-1 in Fas-induced apoptosis of prosthesis-loosening FLS was investigated by small interfering RNA-mediated knockdown of SUMO-1 and by gene transfer of the nuclear SUMO-specific protease SENP1.

RESULTS

SUMO-1 was expressed strongly in aseptically loosened tissue and was found prominently at sites adjacent to bone. Prosthesis-loosening FLS expressed levels of SUMO-1 similar to the levels expressed by rheumatoid arthritis (RA) FLS, with SUMO-1 being found mainly in promyelocytic leukemia protein nuclear bodies. Knockdown of SUMO-1 had no effect on spontaneous apoptosis but significantly increased the susceptibility of prosthesis-loosening FLS to Fas-induced apoptosis. Gene transfer of the nuclear SUMO-specific protease SENP1 reverted the apoptosis-inhibiting effects of SUMO-1.

CONCLUSION

These data suggest that SUMO-1 is involved in the activation of both RA FLS and prosthesis-loosening FLS by preventing these cells from undergoing apoptosis. Modification of nuclear proteins by SUMO-1 contributes to the antiapoptotic effects of SUMO-1 in prosthesis-loosening FLS, providing evidence for the specific activation of sumoylation during their differentiation. Therefore, SUMO-1 may be an interesting target for novel strategies to prevent aseptic prosthesis loosening.

Disease-specific expression patterns of proteases in synovial tissues

To assess whether protease expression patterns can be discriminated according to matrix degradation mechanisms in aseptic prosthesis loosening (APL), rheumatoid arthritis (RA), and osteoarthritis (OA), we immunohistochemically examined the expressions of matrix metalloproteinase-1 and cathepsins B, D, and L in periprosthetic synovial-like interface tissues from 32 patients with failed prosthetic hips, from 29 RA-patients with hip synovial membranes, and from 35 patients with primary OA. Numerical values, calculated for the positivity of each protease, were used to rank the staining patterns, and a multivariate analysis was carried out to examine the discriminant probabilities. As a result of stepwise linear discriminant analyses, the three groups were successfully discriminated with probabilities of 100%, 62.1%, and 77.1%, respectively. Cathepsin L was significantly related to the discrimination of APL from RA and primary OA. Disease-specific protease activation pathways might exist, and cathepsin L can be a key enzyme for APL pathogenesis.

LEVEL OF EVIDENCE

Prognostic study, level III (retrospective study).

Reproducible genetic associations between candidate genes and clinical knee osteoarthritis in men and women

OBJECTIVE

Osteoarthritis (OA) is recognized to have a genetic component, and in this study, we aimed to replicate in a case-control study of men and women with clinical knee OA genetic associations in 12 candidate genes previously reported to be associated with OA.

METHODS

Twenty-five single-nucleotide polymorphisms were genotyped in 298 men and 305 women ages 50-86 who were diagnosed as having knee OA, as assessed both clinically and radiographically, and in 297 men and 299 women matched for age and ethnicity (controls). Standardized anteroposterior radiographs of the knee in extension were performed on each of the cases, and all cases met the American College of Rheumatology criteria for OA of the knee. Genotype and haplotype frequencies in cases and controls were compared separately in men and women. The 12 genes tested were AACT, ADAM12, BMP2, CD36, CILP, COX2, ESR1, NCOR2, OPG, TNA, TNFAIP6, and VDR.

RESULTS

Eight of the candidate genes were associated in women and 5 in men, and only 3 genes (TNFAIP6, NCOR2, and CD36) were not significantly associated in either sex. The strongest associations in terms of odds ratios (ORs) were a haplotype in ADAM12 (OR 7.1 [95% confidence interval (95% CI) 3.3-33.8]) and a haplotype in ESR1 (OR 3.6 [95% CI 1.18-10.98]) in women. The same ADAM12 haplotype (OR 2.54 [95% CI 1.2-5.4]) and a haplotype in the CILP gene (OR 0.38 [95% CI 0.23-0.62]) were the strongest associations in men.

CONCLUSION

We found that genes previously identified by their association with subclinical features of knee OA or progression were also associated with clinical knee OA. These genetic associations may identify individuals at a particularly high risk of developing knee OA.

Wear particulate and osteolysis

Total joint replacements of the hip and knee are generally highly successful, with satisfactory longevity and clinical results. Using modern biocompatible materials, optimal component design, and meticulous surgical technique, survivorship of cemented or cementless joint replacements is approximately 15 years with more than a 90% probability. The host's biologic response is critical to implant longevity. Particulate disease refers to the host's adverse biologic response to wear debris and byproducts generated from the prosthesis. Initially, emphasis was placed on particulate polymethylmethacrylate (cement disease), but more recently polyethylene wear debris has been underscored. Debris from several materials in sufficient quantities and physicochemical forms, however, can generate an inflammatory cascade resulting in periprosthetic bone destruction (osteolysis), jeopardizing long-term success of the implant.

Protease expression in interface tissues around loose arthroplasties

To determine whether cathepsins and matrix metalloproteinase-1 are involved in accelerating tissue destruction, we examined, immunohistochemically, the expression of matrix metalloproteinase-1 and cathepsins B, D, L, and X in periprosthetic synovial-like interface tissues from 14 patients with failed prosthetic hips and in the synovial membranes of hips from 18 patients with rheumatoid arthritis and 25 patients with primary osteoarthritis. The expression levels of all these proteases in the interface tissue were higher than in the synovial membrane of osteoarthritis. The expression levels of cathepsins B and X in the interface tissue were higher than in the rheumatoid synovium. The results show similarities in the expression patterns of cathepsins D and L and matrix metalloproteinase-1 between aseptic prosthetic loosening and rheumatoid arthritis. In addition, these data suggest that the impact of cathepsins B and X on tissue degradation is more pronounced in aseptic prosthetic loosening than in rheumatoid arthritis.

Human serum opsonization of orthopedic biomaterial particles: protein-binding and monocyte/macrophage activation in vitro

Wear particles generated after total joint arthroplasty activate monocyte/macrophages and incite formation of a granulomatous periprosthetic tissue associated with bone loss and implant loosening. This study tested the hypothesis that selective opsonization of orthopedic implant biomaterial wear particles by human serum proteins influences monocyte/macrophage activation. Serum protein binding to metallic, polymeric, and ceramic particles was determined by one-dimensional sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). Individual proteins bound to particles were subsequently identified using two-dimensional SDS-PAGE, microsequencing techniques, and SWISS-PROT analysis. Effects of selective protein opsonization on particle-induced monocyte/macrophage activation were assessed by quantification of interleukin-1beta, interleukin-6, and tumor necrosis factor-alpha release. Results from one-dimensional gel analyses revealed distinct serum protein-binding patterns specific for each material tested. Two-dimensional gel analysis together with amino acid sequencing of the prominent protein species confirmed the presence of albumin and alpha-1-antitrypsin bound to all particles tested. In contrast to the metallic particles, apolipoprotein was a major species associated with polymeric particles. Opsonization of PMMA particles with purified preparations of each of the identified proteins showed that albumin significantly enhanced particle-induced monocyte/macrophage activation. These data confirm orthopedic biomaterial specific binding of human serum proteins and demonstrate that albumin exacerbates particle-induced monocyte/macrophage activation. Alterations in the chemical and surface properties of orthopedic biomaterials to modulate protein interactions may improve implant longevity.

Mid-term results in total hip arthroplasty with the basic noncemented hip prosthesis

The Basic (IQL-Biomet, Valencia, Spain) hip prosthesis was used in 430 implant procedures, of which 417 had mean follow-up of 6 years. Radiographic follow-up was performed at 1, 3, 6, and 12 months postoperatively, and annually thereafter. The average Harris hip score improved from 35.7 preoperatively to 90.9 postoperatively. Clinical results after 2 years of follow-up showed 6% thigh pain, which decreased to 2% at 6 years. Radiographic evaluation demonstrated 22 cases of calcar resorption, 14% of which had distal pedestal formation. Heterotopic ossification was noted radiographically in 36%. These mid-term results obtained with the Basic prosthesis are similar to the findings of other series and warrant its use.

Nationwide study of cancer risk among hip replacement patients in Sweden

BACKGROUND

Orthopedic implants and their fixatives contain materials with carcinogenic potential. Whether these implants are linked to subsequent cancer development remains unknown, mainly because large-scale, long-term follow-up data are scarce.

METHODS

We conducted a nationwide cohort study in Sweden to examine cancer incidence among 116,727 patients who underwent hip replacement surgery during the period from 1965 through 1994. Through record linkage to the Swedish Cancer Register, we identified all incident cancers through 1995 in this population (693,954 person-years of observation). For each cancer type, the observed number of cases was divided by that expected in the general Swedish population to produce standardized incidence ratios (SIRs).

RESULTS

Relative to the general population, the cohort had no overall cancer excess (SIR = 1.01; 95% confidence interval [CI] = 0.99 to 1.03). However, we observed elevated SIRs for prostate cancer (SIR = 1.16; 95% CI = 1.11 to 1.22) and melanoma (SIR = 1.15; 95% CI = 1.01 to 1.30) and a reduction in stomach cancer risk (SIR = 0.83; 95% CI = 0.75 to 0.92). Long-term follow-up (>or=15 years) revealed an excess of multiple myeloma (SIR = 1.86; 95% CI = 1.01 to 3.11) and a statistically nonsignificant increase in bladder cancer (SIR = 1.42; 95% CI = 0.98 to 1.99). There was no material increase in risk for bone or connective tissue cancer for either men or women in any follow-up period.

CONCLUSIONS

In this, the largest study to date, hip implant patients had similar rates of most types of cancer to those in the general population. Although the excesses of melanoma, multiple myeloma, and prostate and bladder cancers may be due to chance, confounding, or detection bias and should be interpreted cautiously, they warrant further investigation because of the ever-increasing use of hip implants at younger ages.

Association between alpha-1-antichymotrypsin polymorphism and susceptibility to chronic obstructive pulmonary disease

BACKGROUND

The antiproteases, including alpha-1-antitrypsin, are supposed to prevent lungs from becoming emphysematous. Genetic susceptibility to smoking injury may confer a risk for the development of chronic obstructive pulmonary disease (COPD).

METHODS

We have investigated the association between the polymorphism of alpha-1-antichymotrypsin (AACT), one of the antiproteases, and susceptibility to the development of COPD among heavy smokers. Blood samples obtained from both patients with COPD (n = 53) and control subjects (n = 65) at the Tokyo University Hospital, the Juntendo University Hospital and the Tokyo Kenbikyoin Clinic were used for this genotyping assay. Polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) were performed to genotype the AACT biallelic polymorphism in the signal peptide (-15 alanine to threonine), and the two polymorphisms of the exon (Pro229Ala and Leu55Pro).

RESULTS

The proportion of AACT/Ala-15 homozygotes was significantly higher in the COPD patients than in the control subjects (COPD 37.7% vs. control 18.5%). The odds ratio for AACT/Ala-15 homozygotes vs. all other genotypes was 2.7 (95% CI 1.2-6.2) for the COPD group. We could not find any association between the other two polymorphisms and COPD.

CONCLUSIONS

Genetic polymorphism in the signal peptide of AACT may be associated with individual susceptibility to the development of COPD, because the AACT/Ala-15 genotype is predominantly found in patients with COPD. It is suggested that AACT/Ala-15 genotype may be less protective against smoking injury.

Histologic and biochemical differences between osteolytic and nonosteolytic membranes around femoral components of an uncemented total hip arthroplasty

The unique design characteristics of an uncemented femoral component were used to study differences in the periprosthetic membranes in the presence and absence of osteolysis. A component (Omniflex, Osteonics, Allendale, NJ) that has a large midportion of the stem that does not contact bone was studied. A membrane forms, even in the absence of bone resorption, in Gruen zones 3 and 5 of this component. Analysis of this membrane showed noninflammatory fibrous tissue, no or minimal particulate debris, and few macrophages. In contrast, analysis of membranes from osteolytic regions around the same prosthesis demonstrated typical inflammatory characteristics. Collagenase, gelatinase, and stromelysin expression was high in osteolytic membranes but was low in tissues from noninflammatory regions without osteolysis. The data suggest a sequence of events in periprosthetic membrane formation. A noninflammatory membrane initially forms between the bone and the prosthesis. This membrane is transformed into an inflammatory membrane by the influx of particulate debris. Matrix metalloproteinases are selectively expressed in regions of osteolysis, implicating these enzymes in periprosthetic bone loss and suggesting a possible level for pharmaceutical intervention to prevent or treat osteolysis. Formation of the noninflammatory membrane around the distal part of the prosthesis of this or similar designs in the absence of bone resorption implies that these tissue samples could serve as useful negative control tissues to identify factors present in osteolytic periprosthetic membranes.

Benign response to particles of diamond and SiC: bone chamber studies of new joint replacement coating materials in rabbits

Wear particles from total joint replacements are thought to accelerate prosthetic loosening. Diamond coating may improve the smoothness and wear characteristics of the femoral head component of total hip replacements, and thus increase their longevity. The brittleness of a thin diamond coat may be overcome by using an SiC-whisker diamond composite. This study describes the reactions of regenerating bone tissue to phagocytosable particles of diamond and SiC, using implanted bone harvest chambers in rabbits. The particles were dispersed in hyaluronan and introduced into a canal transversing the implant. The tissue that entered the canal during the following 3 weeks was then harvested. In previous studies using this model, particles of high density polyethylene, bone cement and chromium-cobalt all caused an inflammatory reaction and a marked decrease in the amount of ingrown bone. In the present study, neither the diamond nor the SiC particles caused any decrease in bone formation. It appears that particles of diamond and SiC are comparatively harmless.