Periprosthetic microvasculature in loosening of total hip replacement

Contributions of human tissue analysis to understanding the mechanisms of loosening and osteolysis in total hip replacement

Aseptic loosening and osteolysis are the most frequent late complications of total hip arthroplasty (THA) leading to revision of the prosthesis. This review aims to demonstrate how histopathological studies contribute to our understanding of the mechanisms of aseptic loosening/osteolysis development. Only studies analysing periprosthetic tissues retrieved from failed implants in humans were included. Data from 101 studies (5532 patients with failure of THA implants) published in English or German between 1974 and 2013 were included. "Control" samples were reported in 45 of the 101 studies. The most frequently examined tissues were the bone-implant interface membrane and pseudosynovial tissues. Histopathological studies contribute importantly to determination of key cell populations underlying the biological mechanisms of aseptic loosening and osteolysis. The studies demonstrated the key molecules of the host response at the protein level (chemokines, cytokines, nitric oxide metabolites, metalloproteinases). However, these studies also have important limitations. Tissues harvested at revision surgery reflect specifically end-stage failure and may not adequately reveal the evolution of pathophysiological events that lead to prosthetic loosening and osteolysis. One possible solution is to examine tissues harvested from stable total hip arthroplasties that have been revised at various time periods due to dislocation or periprosthetic fracture in multicenter studies.

Role and regulation of VEGF and its receptors 1 and 2 in the aseptic loosening of total hip implants

It was hypothesized that vascular endothelial growth factor (VEGF) in fibroblasts participates in aseptic loosening of total hip replacement (THR) implants. Therefore, osteoarthritic (OA) samples (n = 11) were compared with synovial membrane-like interface tissues from revision THR (n = 10). VEGF-A and its receptors were stained using streptavidin-immunoperoxidase method. Their regulation by hypoxia and cytokines were studied in cultured fibroblasts using quantitative real-time polymerase chain reaction (qRT-PCR). VEGFR1(+) lining cells (p < 0.01), stromal fibroblast-like cells (p = 0.001) and stromal macrophage-like cells (p < 0.05) were more numerous in rTHR than in OA. As to VEGFR2(+), only stromal fibroblast-like cells in rTHR outnumbered those found in OA (p < 0.05). VEGFRs in synovial fibroblasts were not affected by hypoxia, but VEGF increased 2.4-fold (p < 0.05). Interleukin-4 up-regulated VEGFR1 expression 23-fold. This is the first study to describe a difference between rTHR and OA in VEGF receptors, particularly VEGFR1. Hypoxia increased VEGF, but the VEGFR1 increase in the lining and stroma is probably IL-4 driven, in accordance with the M2-type macrophage dominance in interface tissues. VEGF/VEGFR system is also affected by hypoxia and may play a role in angiogenesis and bone pathology in aseptic loosening of total hip implants.

Osteoconductivity and growth factor production by MG63 osteoblastic cells on bioglass-coated orthopedic implants

We have produced Bioglass coatings for Orthopedic implants by using a novel coating technique, CoBlast. The two resultant surfaces, designated BG and hydroxyapatite (HA)/BG, were compared with their HA counterpart, OsteoZip in terms of osteoblastic cell attachment, adhesion, proliferation, differentiation, and growth factor production. BG and HA/BG were demonstrated by goniometry to be more hydrophilic than OsteoZip. This corresponded to enhanced protein adsorption, cell attachment, and cell adhesion documented by both quantitative and qualitative assessments. BG and HA/BG surfaces had a significant initial release of Si and Ca ions, and this was consistent with elevated cell proliferation and basic fibroblast growth factor levels. However, OsteoZip, being similar to HA/BG, exhibited better osteogenic differentiation than BG did, shown by augmented differentiation marker activity at both protein and mRNA levels. Sandwich ELISA was used to quantify angiopoietin and inducible nitric oxide synthase which are involved in peri-prosthetic angiogenesis and aseptic loosening of total hip replacement, respectively. Both Bioglass-derived coatings provide superior initial osteoconductivity to OsteoZip, and HA/Bioglass composite coating outruns in long-term osteogenic differentiation and prognostic bioprocesses. The novel coatings discovered in this study have significant potential in providing both orthopedic and therapeutic functions.

Circulating blood monocytes traffic to and participate in the periprosthetic tissue inflammation

OBJECTIVE

To examine the trafficking of human circulating blood monocytes and their influence on the inflammation of periprosthetic tissues using a novel mouse-human chimera model.

METHODS

Periprosthetic tissue and bone chips from patients with aseptic prosthetic loosening were implanted into the muscles of immune-deficient SCID mice depleted of host macrophages by periodic intraperitoneal injection of anti-asialo GM1 rabbit sera (ASGM1). Autologous patient peripheral blood monocytes (PBMCs) were labeled with PKH2 fluorescent dye and injected intraperitoneally into the implanted animals. Mice were sacrificed 14 days after PBMC transfusion for molecular and histological analyses.

RESULTS

Patient periprosthetic tissues were well tolerated in SCID mice and preserved a high level of viability. Cell trafficking studies revealed the accumulation of fluorescent PBMC within the xenografts, with total cell counts in the xenografts significantly increased following the systemic PBMC infusion. PBMC infusion also promoted the expression of IL-1, IL-6, TNFalpha, and RANK within the periprosthetic tissue.

CONCLUSION

Systemic PBMC migrated to the implanted periprosthetic tissues and contributed to the local inflammation. The data provide evidence that circulating blood monocytes may play a role in pathologic process during aseptic loosening of total joint replacement.

Increased angiogenesis and cellular proliferation as hallmarks of the synovium in chronic septic arthritis

OBJECTIVE

To characterize histologic alterations and inflammatory infiltrates in the synovium of patients with chronic septic arthritis (SeA).

METHODS

Synovial membranes from patients with SeA (9 specimens; disease duration >4 weeks) were compared with specimens from patients with septic joint prosthesis loosening (septic total arthroplasty [SeTA]; 9 specimens), rheumatoid arthritis (RA; 25 specimens), osteoarthritis (25 specimens), and normal histology (10 specimens). Sections were stained with hematoxylin and eosin, tissue gram stain, and immunostains for von Willebrand factor (vWF; blood vessels), Ki-67 (dividing cells), CD15 (neutrophils), CD3 (T cells), CD20 (B cells), CD38 (plasma cells), and CD68 (macrophages).

RESULTS

Gram stains were positive in all SeA and SeTA specimens. Mixed polymorphonuclear and mononuclear infiltrates predominated in SeA and SeTA. SeA could be differentiated from RA by higher densities of CD15+ cells (SeA:RA ratio 6.5:1; P < 0.001) or Ki-67+ cells (ratio 2.1:1; P = 0.012). The inflammatory infiltrate of SeTA was similar to SeA but contained fewer CD3+ cells (SeTA versus SeA 0.26:1; P = 0.009) and a tendency toward fewer CD20+ cells. Mean vascular density was strikingly increased in SeA (SeA:normal ratio 3.0:1; P < 0.001) and, to a lesser extent, in the vascularized areas of the SeTA specimens (SeTA:normal ratio 1.9:1). Ki-67/CD31 double immunostains demonstrated proliferating endothelial cells in small subintimal blood vessels, suggesting angiogenesis. Receiver operating characteristic curve analysis identified higher densities of CD15+ and Ki-67+ cells and vWF-positive vessels as histologic markers that differentiated SeA from RA.

CONCLUSION

This first analysis of the synovium in patients with chronic pyogenic arthritis identified dramatic neovascularization and cell proliferation, accompanied by persistent bacterial colonization and heterogeneous inflammatory infiltrates rich in CD15+ neutrophils, as histopathologic hallmarks.

What are the local and systemic biologic reactions and mediators to wear debris, and what host factors determine or modulate the biologic response to wear particles?

New clinical and basic science data on the cellular and molecular mechanisms by which wear particles stimulate the host inflammatory response have provided deeper insight into the pathophysiology of periprosthetic bone loss. Interactions among wear particles, macrophages, osteoblasts, bone marrow-derived mesenchymal stem cells, fibroblasts, endothelial cells, and T cells contribute to the production of pro-inflammatory and pro-osteoclastogenic cytokines such as TNF-alpha, RANKL, M-SCF, PGE2, IL-1, IL-6, and IL-8. These cytokines not only promote osteoclastogenesis but interfere with osteogenesis led by osteoprogenitor cells. Recent studies indicate that genetic variations in TNF-alpha, IL-1, and FRZB can result in subtle changes in gene function, giving rise to altered susceptibility or severity for periprosthetic inflammation and bone loss. Continuing research on the biologic effects and mechanisms of action of wear particles will provide a rational basis for the development of novel and effective ways of diagnosis, prevention, and treatment of periprosthetic inflammatory bone loss.

Effect of robotic milling on periprosthetic bone remodeling

The ROBODOC system has provided better fit and fill of the stem and less destruction of the bony architecture than with manual surgery. These benefits might affect femoral periprosthetic bone remodeling. We evaluated the effects of robotic milling in cementless total hip arthroplasty (THA) in a longitudinal 24-month follow-up study using dual energy X-ray absorptiometry (DEXA) and plain radiographs of 29 patients (31 hips) after ROBODOC THA and 24 patients (27 hips) after manual THA with the same stem design. To minimize the influence of other factors on bone remodeling, only female osteoarthritis patients, who had no drugs that might affect bone metabolism were enrolled. Significantly less bone loss occurred at the proximal periprosthetic areas in the ROBODOC group. In zone 1, the decrease was 15.5 versus 29.9% using conventional rasping; in zone 7, the loss was 17.0% with ROBODOC compared to 30.5% with conventional rasping (p < 0.05). On radiographs, endosteal spot welds in the proximal medial portion were more pronounced in the ROBODOC group (48 vs. 11% in the conventional group, p < 0.05). Our results suggest that robotic milling is effective in facilitating proximal load transfer around the femoral component and minimizing bone loss after cementless THA.

Murine model of prosthesis failure for the long-term study of aseptic loosening

We examined a novel mouse model of wear debris-induced prosthesis instability and osteolysis, and its application for the evaluation of therapy. A stainless steel or titanium-alloy pin was implanted into the proximal tibia to form a contiguous surface with the articular cartilage. In some mice, titanium particles were injected into the tibial canal during the surgery, followed by monthly intraarticular injection. MicroCT scans revealed that the implants without particle challenge were stable without bone mineral density changes for 6 months. Histological analysis showed new bone formation around the implant at 6 weeks postsurgery. Periprosthetic soft tissue with inflammatory cells was a ubiquitous finding at the interface between the implant and surrounding bone in samples exposed to titanium particles, and expression of IL-1beta, TNFalpha, and CD68 was common in these joints. Pullout tests indicated that an average 5N load was required to pull out stable implants from surrounding bone. However, particle stimulation dramatically reduced the pullout force to less than 0.4 N. The feasibility of in vivo gene transfer on this model was confirmed by X-gal staining of synovial membrane and periprosthetic tissue after injection of AAV-LacZ in the prosthetic joint. This murine model of weight-bearing knee prosthesis provides an economical, reproducible, and easily obtained means to study joint arthroplasty failure. The ability to evaluate the biomechanical properties of the prosthetic joint, in addition to histological and biochemical examination, results in a useful model to investigate many of the properties of prosthetic joint components during the response to debris-associated osteolysis.

Femoral head blood flow during hip resurfacing

Preserving femoral head vascularity during hip resurfacing may avoid femoral neck fractures and late femoral loosening. The posterior approach and notching of the femoral neck influence femoral head perfusion. However, it is not known if standard preparation of the femoral head during hip resurfacing can disrupt blood flow. Ten patients (10 hips) with advanced osteoarthritis having metal-on-metal hip resurfacing by means of a vascular-preserving surgical approach had femoral head blood flow measurements using laser Doppler flowmetry. Nine hips had a mean decrease of 70% in femoral head blood flow after standard reaming and preparation. The data suggest femoral head reaming during hip resurfacing substantially impacts blood flow to the femoral head and infers the extra osseous blood supply is still important in the arthritic femoral head. To avoid damaging the retinacular vessels, surgeons should direct the cylindrical reamer superolaterally staying as close as possible to the inferomedial neck.

Acid attack and cathepsin K in bone resorption around total hip replacement prosthesis

Normal bone remodeling and pathological bone destruction have been considered to be osteoclast-driven. Osteoclasts are able to attach to bare bone surface and produce an acidic subcellular space. This leads to acid dissolution of hydroxyapatite, allowing cathepsin K to degrade the organic type I collagen-rich osteoid matrix under the acidic condition prevailing in Howship lacunae. Using a sting pH electrode, the interface membrane around a loosened total hip replacement prosthesis was found to be acidic. Confocal laser scanning disclosed irregular demineralization of the bone surface in contact with the acidic interface. Cathepsin K, an acidic collagenolytic enzyme, was found in interface tissue macrophages/giant cells and pseudosynovial fluid. Tissue extracts contained high levels of cathepsin K messenger RNA (mRNA) and protein. These observations suggest the presence of an acid- and cathepsin K-driven pathological mechanism of bone resorption, mediated not by osteoclasts in subosteoclastic space, but rather by the uncontrolled activity of macrophages in extracellular space.

Interleukin-11 (IL-11) in aseptic loosening of total hip replacement (THR)

The chronic inflammatory response to abrasion particles from total hip replacement (THR) is believed to cause osteolysis and to contribute to prosthetic loosening. The expression of interleukin-11(IL-11) and its major cellular sources in the interface and pseudocapsular tissues obtained from total hip revisions performed for aseptic loosening were investigated. The avidin-biotin-peroxidase complex (ABC) and alkaline phosphatase-anti-alkaline phosphatase (APAAP) methods were used for staining and VIDAS image analysis for quantification. IL-11 was found in the interface and pseudocapsular tissues in the aseptic loosening of THR. IL-11 containing cells were more numerous in the interface (760 +/- 171 cells) and pseudocapsular tissues (684 +/- 171 cells) than in the control synovial tissue (235 +/- 68 cells). Because IL-11 is an important component of cytokine network mediating osteoblast-osteoclast communication in normal and pathological bone remodeling, the current findings suggest that IL-11 may contribute to periprosthetic osteolysis and to the loosening of THR.