The role of hairs in the adhesion of octopus suckers: a hierarchical peeling approach.

Organisms like the octopus or the clingfish are a precious source of inspiration for the design of innovative adhesive systems based on suction cups, but a complete mechanical description of their attachment process is still lacking. In this paper, we exploit the recent discovery of the presence of hairs in the acetabulum roof of octopus suction cups to revise the current model for its adhesion to the acetabulum wall. We show how this additional feature, which can be considered an example of a hierarchical structure, can lead to an increase of adhesive strength, based on the analysis of the cases of a simple tape and an axisymmetrical membrane adhering to a substrate. Using peeling theory, we discuss in both cases the influence of hierarchical structure and the resulting variation of geometry on the adhesive energy, highlighting how an increase in number of hierarchical levels contributes to its increment, with a corresponding improvement in functionality for the octopus suckers.

An in vitro model of impaction during hip arthroplasty.

Impaction is required to properly seat press-fit implants and ensure initial implant stability and long term bone ingrowth, however excessive impaction or press-fit presents a high fracture risk in the acetabulum and femur. Current in-vitro impaction testing methods do not replicate the compliance of the soft tissues surrounding the hip, a factor that may be important in fracture and force prediction. This study presents the measurement of compliance of the soft tissues supporting the hip during impaction in operative conditions, and replicates these in vitro. Hip replacements were carried out on 4 full body cadavers while impact force traces and acetabular/femoral displacement were measured. Compliance was then simulated computationally using a Voigt model. These data were subsequently used to inform the design of a representative in-vitro drop rig. Effective masses of 19.7 kg and 12.7 kg, spring stiffnesses of 8.0 kN/m and 4.1 kN/m and dashpot coefficients of 595 N s/m and 322 N s/m were calculated for the acetabular and femoral soft tissues respectively. A good agreement between cadaveric and in-vitro peak displacement and rise time during impact is found. Such an in-vitro setup is of use during laboratory testing, simulation or even surgical training.

What is the tolerated width of periacetabular osteophytes to avoid impingement in cementless THA?: a three-dimensional simulation study.

BACKGROUNDS: Impingement is a risk factor for instability and prosthetic failure following total hip arthroplasty (THA). If the periacetabular osteophytes are not removed at surgery, impingement could occur between the osteophytes and the femoral stem following THA. However, excessive removal of the osteophytes could lead to bleeding from the bone. The aim of our study, therefore, was to locate the site of the impingement and to determine the width of tolerable osteophytes, which does not induce impingement during activities of daily living (ADL), using a three-dimensional simulation. METHODS: On 35 hip models, virtual THA was performed. The acetabular cups were positioned at 45° abduction and 20° anteversion, and the anteversion of femoral stems was 15°. Circular osteophytes with a 30-mm rim were built around the acetabular cup. Fourteen ADL motions were simulated, and the osteophytes were removed until there was no impingement. A clock face was used to map the location and the width of tolerable osteophytes. RESULTS: The impingement mainly occurred in antero-superior and posterior portions around the acetabular cup. Only 4.2-6.2-mm osteophytes were tolerable at the antero-superior portion (12-3 o'clock) and 6.3-7.2-mm osteophytes at the posterior portion (8-10 o'clock) following a total hip arthroplasty. In antero-inferior and postero-superior portions, over-20-mm osteophytes did not induce any impingement. CONCLUSION: Osteophytes in the antero-superior and posterior portion of the acetabulum should be excised during a THA to avoid impingement of the femur-stem construct on the acetabular osteophytes during ADLs.

Hip chondrolabral mechanics during activities of daily living: Role of the labrum and interstitial fluid pressurization.

Osteoarthritis of the hip can result from mechanical factors, which can be studied using finite element (FE) analysis. FE studies of the hip often assume there is no significant loss of fluid pressurization in the articular cartilage during simulated activities and approximate the material as incompressible and elastic. This study examined the conditions under which interstitial fluid load support remains sustained during physiological motions, as well as the role of the labrum in maintaining fluid load support and the effect of its presence on the solid phase of the surrounding cartilage. We found that dynamic motions of gait and squatting maintained consistent fluid load support between cycles, while static single-leg stance experienced slight fluid depressurization with significant reduction of solid phase stress and strain. Presence of the labrum did not significantly influence fluid load support within the articular cartilage, but prevented deformation at the cartilage edge, leading to lower stress and strain conditions in the cartilage. A morphologically accurate representation of collagen fibril orientation through the thickness of the articular cartilage was not necessary to predict fluid load support. However, comparison with simplified fibril reinforcement underscored the physiological importance. The results of this study demonstrate that an elastic incompressible material approximation is reasonable for modeling a limited number of cyclic motions of gait and squatting without significant loss of accuracy, but is not appropriate for static motions or numerous repeated motions. Additionally, effects seen from removal of the labrum motivate evaluation of labral reattachment strategies in the context of labral repair.

First insights into human acetabular labrum cell metabolism.

OBJECTIVE: Hip labrum pathology has only begun to emerge as a significant source of groin pain in the last decade since the development of hip arthroscopy. Few data are available on the anatomy, histology and function of this structure. Moreover, no metabolic data exist at cellular level. The aim of this study was to characterize extracellular matrix (ECM) genes and pro-inflammatory mediators expressed by these cells. METHODS: Isolated human acetabular labrum cells were cultured in alginate beads for 10 days and additionally stimulated with interleukin (IL)-1 for 24 h. Gene expression levels and secretion of different ECM genes, enzymes and cytokines were examined by quantitative polymerase chain reaction (qPCR) and enzyme-linked immunosorbent assay (ELISA) to assess the metabolic characteristics of labrum cells. Articular chondrocytes and meniscus cells served as controls. RESULTS: Labrum cells expressed high levels of COL1A1 and low levels of COL2A1, aggrecan and SOX-9 compared to chondrocytes. However, COL2A1 was more expressed by labrum cells than by meniscus cells. The expression of matrix metalloproteinase (MMP)-1/-2/-9, ADAMTS-4 and IL-6 was significantly higher in labrum cells than in chondrocytes. IL-1 suppressed the ECM gene expression levels of labrum cells, but increased the expression levels and release of MMP-1/-3/-9/-13 and ADAMTS-4 and IL-6 by these cells. Remarkably, MMP-9 was only significantly upregulated in acetabular labrum cells. CONCLUSIONS: The findings in this study demonstrated that the acetabular labrum is populated with unique highly active fibrochondrocyte-like cells. These cells are capable of expressing and releasing pro-inflammatory enzymes and cytokines and react to a pro-inflammatory stimulus. In this way, they contribute obviously to disturbed tissue function in hip labrum pathology.

Changes in the acetabular fossa of the hip: MR arthrographic findings correlated with anatomic and histologic analysis using cadaveric specimens.

OBJECTIVE: The objective of our study was to determine the morphologic and histologic pattern of tissue changes in the acetabular fossa and evaluate its association with osteoarthritis of the hip joint. MATERIALS AND METHODS: Eleven cadaveric hip joints derived from elderly persons were examined using MR arthrography. All 11 joints were then sectioned. The pattern of acetabular fossa changes determined during inspection of the anatomic and histologic sections in all cadaveric specimens was correlated with MR arthrographic findings. We classified acetabular fossa changes into three stages. Imaging findings of osteoarthritis were reviewed to assess for an association between acetabular cartilage changes and acetabular fossa changes. RESULTS: MR arthrographic findings of changes in the acetabular fossae included low signal intensity related to multiple thin or thick fibrous strands in the acetabular fat and a decrease in the amount of peripheral fatty tissue. Histologic findings revealed fat necrosis, fibrous strands, a decrease in the amount of fat, fibrocartilaginous metaplasia of fat, and chondroid metaplasia at the bony surface of the acetabular fossa. There was a statistically significant correlation between the advanced stage (stage IV) of acetabular cartilage degeneration and the advanced stage (stage 3) of acetabular fossa change (p < 0.001). CONCLUSION: In a small number of specimens, MR arthrographic findings and histologic analyses showed fibrofatty tissue changes and chondroid metaplasia in the acetabular fossae of cadavers derived from an elderly population. The advanced stage of acetabular fossa change was correlated statistically with the advanced stage of acetabular cartilage degeneration.

Donor variation and loss of multipotency during in vitro expansion of human mesenchymal stem cells for bone tissue engineering.

The use of multipotent human mesenchymal stem cells (hMSCs) for tissue engineering has been a subject of extensive research. The donor variation in growth, differentiation and in vivo bone forming ability of hMSCs is a bottleneck for standardization of therapeutic protocols. In this study, we isolated and characterized hMSCs from 19 independent donors, aged between 27 and 85 years, and investigated the extent of heterogeneity of the cells and the extent to which hMSCs can be expanded without loosing multipotency. Dexamethasone-induced ALP expression varied between 1.2- and 3.7-fold, but no correlation was found with age, gender, or source of isolation. The cells from donors with a higher percentage of ALP-positive cells in control and dexamethasone-induced groups showed more calcium deposition than cells with lower percentage of ALP positive cells. Despite the variability in osteogenic gene expression among the donors tested, ALP, Collagen type 1, osteocalcin, and S100A4 showed similar trends during the course of osteogenic differentiation. In vitro expansion studies showed that hMSCs can be effectively expanded up to four passages (approximately 10-12 population doublings from a P0 culture) while retaining their multipotency. Our in vivo studies suggest a correlation between in vitro ALP expression and in vivo bone formation. In conclusion, irrespective of age, gender, and source of isolation, cells from all donors showed osteogenic potential. The variability in ALP expression appears to be a result of sampling method and cellular heterogeneity among the donor population.

Two distinct cellular mechanisms of osteoclast formation and bone resorption in periprosthetic osteolysis.

PURPOSE: TNFalpha and IL-1alpha are proinflammatory cytokines that are abundant in periprosthetic tissues. These cytokines stimulate bone resorption and have recently been shown to directly induce osteoclast formation in mouse marrow cultures. We examined whether TNFalpha and IL-1alpha can directly induce osteoclast formation from human arthroplasty-derived (CD14(+)) macrophages by a mechanism independent of RANKL-induced osteoclastogenesis. METHODS: TNFalpha and M-CSF (+/-IL-1alpha) were added to cultures of magnetically sorted (CD14(+)) and unsorted (CD14(+)/CD14(-)) cells isolated from the pseudomembrane of loosened hip arthroplasties. Osteoprotegerin (OPG), RANK:Fc and antibodies to TNF receptors (p55 and p75) were added to these cultures to distinguish the pathway of osteoclastogenesis. Osteoclast differentiation was assessed by expression of tartrate-resistant acid phosphatase (TRAP), vitronectin receptor (VNR) and lacunar resorption. RESULTS: The addition of TNFalpha (+/-IL-1alpha) resulted in differentiation of CD14(+) macrophages into TRAP(+) and VNR(+) multinucleated cells capable of extensive lacunar resorption. Both OPG and RANK:Fc (which inhibit RANKL-induced osteoclastogenesis) did not block osteoclastogenesis. The addition of antibodies directed against the p55 receptor subunit of TNF resulted in significant inhibition of osteoclast formation and lacunar resorption. CONCLUSIONS: Our results indicate that, in the presence of M-CSF, TNFalpha is sufficient for inducing human osteoclast differentiation from arthroplasty macrophages and that TNFalpha acts synergistically with IL-1alpha to stimulate lacunar resorption. This process is distinct from the RANK/RANKL signalling pathway and is likely to operate in periprosthetic tissues when there is heavy wear particle deposition and cytokine production.

The material properties of the bovine acetabular labrum.

The compressive and tensile material properties of the bovine acetabular labrum were measured. Confined compression testing was used to determine the aggregate compressive modulus and the permeability of the labrum. The compressive modulus of the labrum (0.157 +/- 0.057 MPa) is comparable to that of the morphologically similar meniscus, and approximately one-quarter to one-half that of the adjoining acetabular cartilage. The permeability of the labrum (4.98 +/- 3.43 x 10(-16) m4/N s) was lower than that of the meniscus and cartilage. With a significantly higher resistance to interstitial fluid flow across the acetabular rim than along the rim. Specimens from the posterior and superior regions of the labrum were tested to failure in uniaxial tension. The maximum stress at failure (11.9 +/- 6.1 MPa), maximum strain at failure (26.5 +/- 7.6%) and tangent modulus (74.7 +/- 44.3 MPa) were similar to those reported for the bovine meniscus, and to other tissues composed of highly oriented collagen fiber bundles. In tension, the labrum is much stiffer (10-15 x) than the adjoining articular cartilage, and the posterior region of the labrum is significantly stiffer (45%) than the superior region. The labrum's low permeability may contribute to sealing of the hip joint. The high circumferential tensile stiffness of the labrum, together with its ring structure, reinforce the acetabular rim and may contribute to joint stability.

Macrophage colony-stimulating factor and interleukin-6 release by periprosthetic cells stimulates osteoclast formation and bone resorption.

Periprosthetic bone loss is an important contributory factor for aseptic loosening of total joint replacements. It has recently been shown that osteoclast precursor cells are present in the wear particle-associated macrophage infiltrate found in the membrane surrounding loose implants and that these cells are capable of differentiating into osteoclastic bone-resorbing cells. Long-term co-culture of arthroplasty-derived macrophages and the rat osteoblast-like cell line, UMR-106, in the presence of 1,25(OH)2D3 results in the formation of numerous multinucleated cells that are positive for tartrate-resistant acid phosphatase and vitronectin receptor and capable of extensive lacunar bone resorption. The aim of this study was to determine the effect of cytokines/growth factors, known to be present in the arthroplasty membrane, on this process of osteoclast differentiation. During osteoclast formation, increased levels of macrophage colony-stimulating factor, interleukin-6, and to a lesser extent, interleukin-1beta, but not tumour necrosis factor alpha, were detected in the co-culture supernatants. Addition of neutralising antibodies to human interleukin-1beta or tumour necrosis factor alpha to the co-culture system did not inhibit osteoclast formation. In contrast, co-cultures to which neutralising antibodies to human macrophage colony-stimulating factor or interleukin-6 were added contained fewer cells positive for tartrate-resistant acid phosphatase and vitronectin receptor and formed significantly fewer resorption pits. Time-course studies showed that macrophage colony-stimulating factor and interleukin-6 increase osteoclast formation mainly in the early stages of osteoclast differentiation. These results indicate that the release of macrophage colony-stimulating factor and interleukin-6 by activated cells in the arthroplasty membrane is likely to contribute to pathological bone resorption associated with aseptic loosening by stimulating differentiation of mononuclear phagocyte osteoclast precursors into mature bone-resorbing cells.

Rotational acetabular osteotomies: a rabbit model.

We investigated the morphological changes in the articular cartilage after rotational acetabular osteotomy in 16 adolescent rabbits. Radiological and histological studies were conducted at 12 and 24 weeks postoperatively. The radiological evaluations at 12 and 24 weeks showed significantly increased femoral head coverage. No cases of osteonecrosis of the acetabulum or femoral head nor narrowing of the joint space was observed. The histology of the articular cartilage at 12 weeks postoperatively showed cloning and hypercellularity of the chondrocytes in the medial portion of the acetabular roof, indicating remodelling due to the increased weight-bearing stress caused by the osteotomy. The histology at 24 weeks postoperatively showed less cloning of the chondrocytes, indicating that the remodelling process in the articular cartilage induced by this procedure was almost complete at 24 weeks. Degeneration of the articular cartilage was not observed within 24 weeks of the operation.

Comparative development of the antitrochanter in three strains of domestic fowl.

Lameness and musculoskeletal disease were more frequent in two strains of broilers (selected [S] and relaxed [R]) than in an unselected layer (J). Defective fibrocartilage accounted for 0.15 of the total area of antitrochanteric cartilage at 29 weeks of age in the S-strain birds. There was more retained hyaline cartilage in the R- and S-strain birds at 15 weeks, and at 22 and 29 weeks there was delayed ossification. Occluded blood vessels, death of chondrocytes and degenerate areas of fibrocartilage occurred only in the broiler strains; they were worse in the S-strain and degenerate fibrocartilage occurred more frequently and in larger amounts. The area, length and depth of cartilage were larger in the heavier strains but the differences were considerably smaller than the difference in their relative bodyweights. The degeneration of the antitrochanter appeared to be associated with a reduction in the blood supply to the underlying hyaline cartilage and with the death of chondrocytes and the degeneration of matrix within the fibrocartilage of the antirochanter.

Tissue reactions to cemented hip sockets. Histologic and morphometric autopsy study of 25 acetabula.

To gain an insight into the tissue reactions leading to noninfectious loosening, 25 autopsy specimens of acetabula with well-fixed cemented sockets were analyzed histomorphologically and morphometrically. The mean duration of the implant was 7 (0.2-16) years. With the exception of some focal direct bone-cement contacts, bone and cement were separated by a soft tissue membrane which increased in thickness with increasing duration of the implant. Necroses in the membrane were also commoner with advancing implant time. The soft tissue membranes developed increasingly dense infiltrates of histiocytes, mainly containing wear particles of the bone cement and--though less abundant--polyethylene. The cancellous bone adjacent to the soft tissue membrane showed an increasing histiocytic infiltration with an increasing duration of the implant. The trabecular bone showed remodeling with formation of a neocortical layer parallel to the border of the cement mantle.

Expression of the differentiated phenotype of chondrocytes in newly synthesized acetabulum.

Human cartilaginous cells produce two types of proteoglycan monomers (PGI and PGII) distinguishable by their molecular size in density gradient centrifugation under dissociative conditions. In order to determine whether connective tissues on the sliding surface of the acetabulum on an endoprosthesis are able to differentiate into cartilaginous tissue, we made histological and biochemical analysis of the incorporation of 35S and the distribution of the molecular size of proteoglycans produced. Histologically, dense collagen fibers were observed both on weight-bearing and non-weight-bearing surfaces, but there was little evidence of cartilaginous metaplasia. Biochemical analysis, however, demonstrated that incorporation of 35S in newly synthesized glycosaminoglycan (GAG) was higher than that in non-cartilaginous tissues, suggesting that cartilaginous differentiation of mesenchymal tissues had occurred.

[The temporal behavior of the anchorage of a cement-free implanted acetabular cup in animal experiments]. / Das zeitliche Verhalten der Verankerung einer zementfrei implantierten Hüftpfanne im Tierversuch.

The mechanical qualities of the cementless press-fit cup of a hip prosthesis were examined in sheep. Primary anchorage of the cup is achieved by relative oversize of the cup in relation to the acetabulum, causing a press-fit effect. The surface of the cup consists of Sulmesh, a titanium net, which allows bony ingrowth. The quality of the mechanical anchorage in the acetabular bone was tested by measurements of the torque and cranio-caudal tilting moment needed to pull out the cup. It was shown that the secondary biological anchorage of the press-fit cup exceeds the primary mechanical anchorage (measured in previous in vitro experiments) by a factor of three. This improvement of the mechanical fixation of the press-fit cup in the acetabular bone can be explained by bony ingrowth into the Sulmesh and can be confirmed by histological findings.

Measuring the volume fraction of bone ingrowth: a comparison of three techniques.

The need for quick, accurate, and reproducible methods to measure the amount of bone within porous metals has increased as the use of these materials has become more common within orthopedics. The purpose of this paper is to compare measurements of bone ingrowth using microradiography, stained histology, and backscattered electron imaging-scanning electron microscopy (BEI-SEM) in cementless, porous-coated acetabular components retrieved from human patients. BEI-SEM of bone ingrowth into porous metal provided excellent images for quantitative analysis. The stained sections and BEI-SEM images provided very comparable results, while microradiography consistently underestimated the porosity of the porous coating and overestimated the amount of bone ingrowth.

[Effects of Chiari osteotomy on acetabular development in the growing subject. Experimental study in puppies]. / Effets sur le développement cotyloïdien de l'ostéotomie de Chiari chez le sujet en croissance. Etude expérimentale chez le chiot.

A Chiari osteotomy was performed on 10 dogs aged 2 months in order to assess the risks of mechanical or ischaemic loss of growth potential in the peri-acetabular cartilage. The development of the acetabular roof was studied by radiographs, microradiographs and histological assessment between 2 and 12 months. Apart from a few mechanical complications, the principal findings were the absence of any signs of necrosis, persistence of a strongly osteoblastic roof and readaptation of the trabecular pattern with articular remodelling, provided the mechanical conditions were satisfactory. The osteotomy must be sufficiently low, while remaining extra-articular, and adequate medial shift must be obtained. The interposed capsular tissue can then become dense and fibrous, providing a sliding surface.

[Results of experimental testing of a screw-in in polyethylene acetabulum in sheep]. / Ergebnisse der experimentellen Prüfung einer einschraubbaren Hüftgelenkspfanne aus Polyäthylen beim Schaf.

In 12 sheep 21 total hip endoprosthesis were implanted, using a polyethylene acetabulum, which was provided with a continuous conique thread for implantation without cement. Out of 14 non luxated hips only 2 acetabula were loosened. After an implantation between 1 week and 18 months the remaining 12 sockets were macroscopically stable and were examined radiologically and histologically. After 3 months of increased osteogenesis a layer of collagenous tissue developed between implant and bone. In the loadbearing area this layer is from 50-80 microns thick and often the ridges of the thread are stabilised by a thin layer of fiber-cartilage, expanding around the implant with longer implantation. Bore-holes in the thread are filled with partially lamellous bone after 6 months. Though sometimes a considerable amount of polyethylene wear particles caused by the disadvantageous and small shape of the sheeparthroplasty was observed, none of the examined acetabula showed any signs of loosening.