Acetabular Region Research Articles

A semiautomated method to quantitatively assess osteolytic lesion volume and bone mineral density within acetabular regions of interest from CT.

The objectives of this study were to (1) develop a semiautomated method to obtain lesion volume and bone mineral density (BMD) in terms of Hounsfield units from pelvic computed tomography (CT) scans in three regions of interest, and (2) assess accuracy and reliability of the method based on cadaveric CT scans. Image artefacts due to metal implants reduce CT clarity and are more severe with more than one implant in situ. Therefore, accuracy and reliability tests were performed with varying numbers of total hip arthroplasties implanted. To test the accuracy of lesion size measurements, microcomputed tomography was used as a reference. Mean absolute error ranged from 36 to 284 mm3 after five measurements. Intra- and inter-operator reliability of the entire method was measured for a selection of parameters. All coefficient of variation values were good to excellent for CT scans of the native pelvic anatomy and a CT scans of the same pelvis with one and two implants in situ. Accuracy of quantifying lesion volume decreased with decreasing CT image clarity by 0.6%-3.6% mean absolute relative error. Reliability of lesion volume measurement decreased with decreasing CT clarity. This was also the case for reliability of BMD measurements in the region most disrupted by metal artefact. The presented method proposes an approach for quantifying bone loss which has been proven to be accurate, reliable, and clinically applicable.

New material of the frog Hungarobatrachus szukacsi Szentesi & Venczel, 2010, from the Santonian of Hungary, supports its neobatrachian affinities and reveals a Gondwanan influence on the European Late Cretaceous anuran fauna

The Late Cretaceous anuran Hungarobatrachus szukacsiSzentesi & Venczel, 2010 was erected for isolated ilia and tibio-fibulae from the Santonian-age Iharkút locality, in northwestern Hungary. On the strength of ilial features, H. szukacsi was interpreted as a neobatrachian and possible ranoid, making it the only pre-Cenozoic occurrence for both clades in Laurasia. New ilia and the first examples of skull bones (incomplete frontoparietals, squamosals, maxillae, and angulosplenials) from the type locality provide new insights into the taxonomic distinctiveness, osteology, and evolutionary history of H. szukacsi. In addition to its diagnostic ilia (e.g., dorsal crest tall and ornamented laterally with prominent ridges; extensive interiliac tubercle developed across entire medial surface of acetabular region), H. szukacsi is characterized further by having a moderately hyperossified skull exhibiting such traits as frontoparietals, squamosals, and maxillae externally covered with prominent pit-and-ridge and weakly developed tuberculate ornament (i.e., exostosis), frontoparietals solidly fused along midline, frontoparietals expanded posterolaterally to form a broad squamosal process, squamosals expanded anteroposteriorly to form a plate-like lamella alaris, and maxilla articulating posteriorly with the quadratojugal to form a solid bony ‘cheek'. The first cladistic analysis to include H. szukacsi corroborates its neobatrachian status, but consistently places it among hyloids, rather than ranoids as originally proposed. Indications of hyloids on the African continent and in Madagascar during the Late Cretaceous, suggest that the ancestor of H. szukacsi may have dispersed from Africa, across the proto-Mediterranean and into Europe, prior to the Santonian.

Allocation of Anchors During Labral Repair: A Multicenter Cohort Analysis of Labral Treatment in Hip Arthroscopy

Background:While previous studies have established several techniques for suture anchor repair of the acetabular labrum to bone during arthroscopic surgery, the current literature lacks evidence defining the appropriate number of suture anchors required to effectively restore the function of the labral tissue.Purpose/Hypothesis:To define the location and size of labral tears identified during hip arthroscopy for acetabular labral treatment in a large multicenter cohort. The secondary purpose was to differentiate the number of anchors used during arthroscopic labral repair. The hypothesis was that the location and size of the labral tear as well as the number of anchors identified would provide a range of fixation density per acetabular region and fixation method to be used as a guide in performing arthroscopic repair.Study Design:Cross-sectional study; Level of evidence, 3.Methods:We used a multicenter registry of prospectively collected hip arthroscopy cases to find patients who underwent arthroscopic labral repair by 1 of 7 orthopaedic surgeons between January 2015 and January 2017. The tear location and number of anchors used during repair were described using the clockface method, where 3 o’clock denoted the anterior extent of the tear and 9 o’clock the posterior extent, regardless of sidedness (left or right). Tear size was denoted as the number of “hours” spanned per clockface arc. Chi-square and univariate analyses of variance were performed to evaluate the data for both the entire group and among surgical centers.Results:A total of 1978 hips underwent arthroscopic treatment of the acetabular labrum; the most common tear size had a 3-hour span (n = 820; 41.5%). Of these hips, 1645 received labral repair, with most common repair location at the 12- to 3-o’clock position (n = 537; 32.6%). The surgeons varied in number of anchors per repair according to labral size (P < .001 for all), using 1 to 1.6 anchors for 1-hour tears, 1.7 to 2.4 anchors for 2-hour tears, 2.1 to 3.2 anchors for 3-hour tears, and 2.2 to 4.1 for 4-hour tears.Conclusion:Variation existed in the number of anchor implants per tear size. When labral repair involved a mean clockface arc >2 hours, at least 2 anchor points were fixated.

Primary Stability of Revision Acetabular Reconstructions Using an Innovative Bone Graft Substitute: A Comparative Biomechanical Study on Cadaveric Pelvises.

Hip implant failure is mainly due to aseptic loosening of the cotyle and is typically accompanied by defects in the acetabular region. Revision surgery aims to repair such defects before implantation by means of reconstruction materials, whose morselized bone graft represents the gold standard. Due to the limited availability of bone tissue, synthetic substitutes are also used. The aim of this study was to evaluate if a synthetic fully resorbable tri-calcium phosphate-based substitute can provide adequate mechanical stability when employed to restore severe, contained defects, in comparison with morselized bone graft. Five cadaveric pelvises were adopted, one side was reconstructed with morselized bone graft and the other with the synthetic substitute, consisting of dense calcium phosphate granules within a collagen matrix. During the biomechanical test, cyclic load packages of increasing magnitude were applied to each specimen until failure. Bone/implant motions were measured through Digital Image Correlation and were expressed in terms of permanent and inducible translations and rotations. The reconstruction types exhibited a similar behavior, consisting of an initial settling trend followed by failure as bone fracture (i.e., no failure of the reconstruction material). When 2.2 Body Weight was applied, the permanent translations were not significantly different between the two reconstructions (p = 0.06–1.0) and were below 1.0 mm. Similarly, the inducible translations did not differ significantly (p = 0.06–1.0) and were below 0.160 mm. Rotations presented the same order of magnitude but were qualitatively different. Overall, the synthetic substitute provided adequate mechanical stability in comparison with morselized bone graft, thus representing a reliable alternative to treat severe, contained acetabular defects.

Reply to comments on “A well-preserved pelvis from the Maastrichtian of Romania suggests that the enigmatic Gargantuavis is neither an ornithurine bird nor an insular endemic”

We appreciate the comments of Buffetaut and Angst on our recent study of a Gargantuavis-like pelvis from the Late Cretaceous of Romania. We consider some of their points to be valid, but maintain our conclusion on the likely absence of a glycogen body in Gargantuavis and the lack of fusion of the pelvic elements in the acetabular region. Both characters conflict with a classification of the taxon into Ornithurae. We also uphold our hypothesis that Gargantuavis is possibly related to the enigmatic theropod Balaur bondoc.

Morphometric analysis of the anterior column of the acetabulum and safety of intramedullary screw fixation for its fractures in Indian population: a preliminary report.

Morphometric variations of the anterior column of the acetabulum have been described in the literature for its complex structure, which can influence the safe containment of intramedullary screw for fixation of its fractures. The purpose of this CT-based study is to present a preliminary report on the morphometric variations and safety of intramedullary screw fixation of the anterior column of the acetabulum in the Indian population. CT-based data from 102 uninjured pelves were retrospectively analyzed in iPlanⓇ BrainLab AG, Feldkirchen, Germany. Narrowest zones around acetabulum and superior pubic ramus were measured. We calculated the axis of the anterior column of the acetabulum by joining the centres of these narrowest zones. Standard screws trajectories were directed along this axis. Screw length up to the first cortical perforation, the distance of the exit point from the pubic symphysis, and the length of the anterior column up to the pubic tubercle were measured. The osseous corridor of the anterior column of acetabulum had variable cross-section along its length with two constriction zones, first in the acetabular region and second in the superior pubic ramus. Only 54% of our cases allowed safe applicability of 6.5-mm-diameter screw trajectories with safety margin of 2 mm on either side of the screw. Significant morphometric and screw applicability-related differences were observed among male and female cases with males having a wider osseous corridor in general. Elimination of safety margin results in a significant increase in the screw applicability. The osseous corridor of the anterior column varies in its dimensions from individual to individual. Standard screws of 6.5-mm and 7.3-mm diameters may not be safe for intramedullary screw fixation in every patient and carry a risk of cortical violation when a 2 mm of width around the screw is considered as a safety margin. However, with a precise screw placement within the extents of the cortices of the anterior column, 6.5-mm screws can be applied in most of the female cases and 7.3-mm screws can be applied in most of the male cases for anterior column fixation.

The earliest equatorial record of frogs from the Late Triassic of Arizona.

Crown-group frogs (Anura) originated over 200 Ma according to molecular phylogenetic analyses, though only a few fossils from high latitudes chronicle the first approximately 60 Myr of frog evolution and distribution. We report fossils that represent both the first Late Triassic and the earliest equatorial record of Salientia, the group that includes stem and crown-frogs. These small fossils consist of complete and partial ilia with anteriorly directed, elongate and distally hollow iliac blades. These features of these ilia, including the lack of a prominent dorsal protuberance and a shaft that is much longer than the acetabular region, suggest a closer affinity to crown-group Anura than to Early Triassic stem anurans Triadobatrachus from Madagascar and Czatkobatrachus from Poland, both high-latitude records. The new fossils demonstrate that crown anurans may have been present in the Late Triassic equatorial region of Pangea. Furthermore, the presence of Early Jurassic anurans in the same stratigraphic sequence ( Prosalirus bitis from the Kayenta Formation) suggests that anurans survived the climatic aridification of this region in the early Mesozoic. These fossils highlight the importance of the targeted collection of microfossils and provide further evidence for the presence of crown-group representatives of terrestrial vertebrates prior to the end-Triassic extinction.

Morphogenetic mechanism of the acquisition of the dinosaur-type acetabulum.

Understanding morphological evolution in dinosaurs from a mechanistic viewpoint requires the elucidation of the morphogenesis that gave rise to derived dinosaurian traits, such as the perforated acetabulum. In the current study, we used embryos of extant animals with ancestral- and dinosaur-type acetabula, namely, geckos and turtles (with unperforated acetabulum), and birds (with perforated acetabulum). We performed comparative and experimental analyses, focusing on inter-tissue interaction during embryogenesis, and found that the avian perforated acetabulum develops via a secondary loss of cartilaginous tissue in the acetabular region. This cartilage loss might be mediated by inter-tissue interaction with the hip interzone, a mesenchymal tissue that exists in the embryonic joint structure. Furthermore, the data indicate that avian pelvic anlagen is more susceptible to paracrine molecules, e.g. Wnt ligand, secreted by the hip interzone than ‘reptilian’ anlagen. We hypothesize that during the emergence of dinosaurs, the pelvic anlagen became susceptible to the Wnt ligand, which led to the loss of the cartilaginous tissue and to the perforation in the acetabular region. Thus, the current evolutionary-developmental biology study deepens our understanding of morphological evolution in dinosaurs and provides it with a novel perspective.

The effect of cement mantle thickness on strain energy density distribution and prediction of bone density changes around cemented acetabular component.

Cement mantle thickness is known to be one of the important parameters to reduce the failure of the cemented acetabular component. The thickness of the cement mantle is also often influenced by the positioning of the acetabular cup. The aim of this study is to determine the effect of uniform and non-uniform cement mantle thickness on strain energy density distribution and prediction of the possibility of bone remodelling around the acetabular region. Furthermore, tensile stress distribution in the cement mantle due to non-uniform cement mantle thickness was also investigated. Three-dimensional finite element models of intact and 17 implanted pelvic bone were developed based on computed tomography data sets. Results indicate that implantation with non-uniform cement thickness variation in the anterior-posterior direction has a significant influence on strain energy density distribution around the acetabulum as compared to thickness variation in the superior-inferior direction. Increase in density is predicted at the anterior part of the acetabulum, whereas density decrease is predicted at the posterior, inferior and superior part of the acetabulum. The non-uniform cement mantle thickness affected the tensile stress distribution in the cement mantle, in particularly superiorly placed acetabular cup. This study concludes that uniform cement thickness is desired for the longer success of the cemented acetabular component.

Dendrorchis pampae sp. n. (Digenea: Gorgoderidae) from Cynopoecilus melanotaenia (Cyprinodontiformes: Cynolebiidae) a killifish from southern Brazil, with an emended diagnosis of Dendrorchis.

A new species of Dendrorchis is described and compared with others in the genus. The parasites were found in the swim bladder of the annual killifish Cynopoecilus melanotaenia. Hosts were collected from a seasonal wetland in southern Brazil. The main characteristics of D. pampae are: genital pore in the intestinal bifurcation region elongate and lobed vitellaria uterine loops limited to the acetabular region and to the rear end of the body; and wide intestinal caeca. An emended diagnosis of the genus Dendrorchis includes the characteristics of the new species. This is the first record of an adult digenean in an annual killifish from South America.

Editorial on “Bone remodeling in acetabular reconstruction using a Kerboull-Type reinforcement device and structural bone-grafting in total hip arthroplasty”

The article entitled “ Bone Remodeling in Acetabular Reconstruction Using a Kerboull-Type Reinforcement Device and Structural Bone-Grafting in Total Hip Arthroplasty” (1) was reviewed in detail. In primary or revision total hip arthroplasty, acetabular bone loss is one of the challenging conditions to place the acetabular component at the original acetabular region. Although recent advance of ultra-porous coated metal acetabular shell or augment implants may influence the surgeons’ decision making at the time of pre-operative planning for such technically demanding conditions, we have to recognize that the most important concept of total hip arthroplasty is to place the hip rotation center at around the anatomical position with preserving the bone stock of the hip joint.

Arthroscopic Focal Subspinal Decompression and Management of Pincer-Type Femoroacetabular Impingement

Femoroacetabular impingement syndrome is a common hip pathology significantly affecting not only the intra- and extra-articular structures but also the biomechanical function of the joint. Cam and pincer bony lesions have been extensively studied. However, during recent years, other types of extra-articular impingement between the pelvic and femoral bone have been investigated. When a prominent or morphologically abnormal anterior-inferior iliac spine (AIIS) impinges repetitively on the femoral side during motion, the subspinal acetabular region becomes prominent and extends toward the intra-articular part of the joint. This results in restriction of the range of motion of the hip and pain, especially with flexion. Therefore, during hip arthroscopy, it is necessary to evaluate the subspinal region (triangular area located at 1:30 to 2:30 o'clock using the acetabular clock face system). For the correction of the acetabular bone pathology to be complete, the surgeon should focus both on the pincer and subspinal impingement lesions. This article describes our preferred technique to successfully address subspinal and pincer acetabular impingement during hip arthroscopy. The pearls and pitfalls of this technique are discussed.

Evaluation of patients with painful total hip arthroplasty using combined single photon emission tomography and conventional computerized tomography (SPECT/CT) \u2013 a comparison of semi-quantitative versus 3D volumetric quantitative measurements

BackgroundIt was the primary purpose of our study to evaluate the inter- and intra-observer reliability of a standardized SPECT/CT algorithm for evaluating patients with painful primary total hip arthroplasty (THA). The secondary purpose was a comparison of semi-quantitative and 3D volumetric quantification method for assessment of bone tracer uptake (BTU) in those patients.MethodsA novel SPECT/CT localization scheme consisting of 14 femoral and 4 acetabular regions on standardized axial and coronal slices was introduced and evaluated in terms of inter- and intra-observer reliability in 37 consecutive patients with hip pain after THA. BTU for each anatomical region was assessed semi-quantitatively using a color-coded Likert type scale (0-10) and volumetrically quantified using a validated software. Two observers interpreted the SPECT/CT findings in all patients two times with six weeks interval between interpretations in random order. Semi-quantitative and quantitative measurements were compared in terms of reliability. In addition, the values were correlated using Pearson`s correlation. A factorial cluster analysis of BTU was performed to identify clinically relevant regions, which should be grouped and analysed together.ResultsThe localization scheme showed high inter- and intra-observer reliabilities for all femoral and acetabular regions independent of the measurement method used (semiquantitative versus 3D volumetric quantitative measurements). A high to moderate correlation between both measurement methods was shown for the distal femur, the proximal femur and the acetabular cup. The factorial cluster analysis showed that the anatomical regions might be summarized into three distinct anatomical regions. These were the proximal femur, the distal femur and the acetabular cup region.ConclusionsThe SPECT/CT algorithm for assessment of patients with pain after THA is highly reliable independent from the measurement method used. Three clinically relevant anatomical regions (proximal femoral, distal femoral, acetabular) were identified.

Increase in physical activity after resurfacing hip arthroplasty is associated with calcar and acetabular bone mineral density changes.

Bone preservation is an important advantage of the resurfacing hip arthroplasty (RHA) concept. We hypothesised that patients' increase in physical activity level after RHA would positively relate with periprosthetic bone mineral density (BMD) changes and thus facilitate bone preservation. BMD-changes were prospectively recorded in 38 patients after RHA. Dual-energy absorptiometry was used to quantify BMD-changes in 6 periprosthetic regions of interest preoperatively, at 6 months, 1, 2 and 3 years postoperative. The effect estimates of patients' physical activity, according to their Harris Hip Score (HHS) and University of California at Los Angeles (UCLA) Activity Score, on these BMD changes were assessed in linear mixed models. The UCLA (coefficient = 0.02 (95% CI, 0.010-0.034); p<0.001) and HHS (coefficient = 0.002 (95% CI, 0.001-0.003); p<0.001) were associated with the BMD in the calcar region. As for BMD changes in the femoral neck only the HHS was associated (coefficient = 0.0006 (95% CI, <0.0001-0.001); p = 0.04). Both the UCLA and the HHS were inversely associated with BMD in the medial acetabular region (UCLA: coefficient = -0.02 (95% CI, -0.038 to -0.007); p = 0.005, HHS: coefficient = -0.002 (95% CI, -0.003 to -0.001), the same accounted for the HHS to BMD-change cranial to the acetabulum (-0.001 [95% CI, -0.0018 to -0.0001]; p = 0.03). For the caudal acetabular and femoral subtrochanteric region no relation with BMD-changes was found. The increase in activity scores after RHA was indeed associated with an increase in BMD in the calcar region, however unexpectedly also with a BMD decrease on the acetabular side. Stress shielding from the implant is the most likely causative factor.

Anatomic Hip Center Decreases Aseptic Loosening Rates After Total Hip Arthroplasty with Cement in Patients with Crowe Type-II Dysplasia: A Concise Follow-up Report at a Mean of Thirty-six Years.

We previously reported the two to twenty-two-year results of 145 total hip arthroplasties (THAs) with cement performed from 1969 to 1980 in 117 patients with Crowe type-II dysplasia. The purpose of the present study was to update the long-term effects of a nonanatomic hip center on component loosening and aseptic revision in this cohort. Forty-nine patients (sixty hips) were alive at a mean of thirty-six years. The overall cumulative incidence of aseptic revision at thirty-five years was 32% for acetabular cups and 21% for femoral stems. Acetabular loosening was less likely with a hip center placed within the true acetabular region (TAR), <15 mm superior to the approximate femoral head center (AFHC), <35 mm superior to the interteardrop line (ITL), or within zone 1. Femoral loosening and revision were less likely with the hip center placed <35 mm superior to the ITL and within zone 1. An anatomic hip center was associated with significantly lower loosening and aseptic revision rates for both acetabular and femoral components. The current study supports the placement of acetabular components in an anatomic position to promote long-term durability after THA with cement. Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Importance of revision- and tumor-endoprosthetics in the treatment of periprosthetic fractures of the lower extremity

Periprosthetic fractures of hip and knee prostheses are gaining clinical significance due to the increasing numbers of of primary arthroplasties. Additionally, these fractures are often associated with poor bone quality or present in patients after multiple revision procedures and concomitant excessive bone defects precluding those patients to be adequately treated by conventional osteosynthesis. Revision implants provide a wide range of options for the treatment of these fractures in order to achieve good clinical results. In the acetabular region cavitary defects associated with periprosthetic fractures can be treated by the use of megacups. Extensive segmental defects and pelvic discontinuity necessitate the use of cups with additional iliac support or even customized implants. Proximal femoral fractures can usually be fixed with modular stems and diaphyseal anchorage. Periprosthetic knee joint fractures can be treated with revision implants with modular sleeves or augment-combinations allowing sufficient bridging of bony defects. Functional reconstruction or refixation of the extensor mechanism is of crucial importance.

Comparaison de la densité minérale osseuse acétabulaire au cours des arthroplasties de première intention entre ostéonécrose de la tête fémorale et coxarthrose

BackgroundTotal hip arthroplasty (THA) could be associated with a higher failure rate in patients after osteonecrosis of the femoral head (ONFH) compared to a patient population with primary osteoarthritis prior THA, especially regarding the acetabular component. One major reason could be the compromised acetabular bone quality. Therefore, we performed a retrospective case matched study to assess: (1) is there a difference in periprosthetic bone mineral density between patients with an ONFH prior THA and controls? (2) Do patients with an ONFH prior THA have a lower bone mineral density compared to controls? (3) Which region in the periprosthetic bone stock is more likely to present differences in periprosthetic bone mineral density between both groups? HypothesisWe hypothesized that there is a poorer bone mineral density (BMD) in the periacetabular bone stock in patients with an ONFH prior THA compared to controls receiving a THA due to primary osteoarthritis. Patients and methodsWe compared the BMD of 50 patients with ONFH to 50 controls with primary osteoarthritis prior THA using the same implant in mean 5 years after surgery by means of dual energy X-ray absorptiometry (DXA). We analyzed 3 acetabular regions of interest (ROIs) according to De Lee and Charnley in a modified measurement technique. ResultsIn ROI 3, representing acetabulum's upper aspect, statistically significant lower BMD values for the ONFH group could be found (P<0.05). No difference was found for the modified ROIs 1 and 2 (respectively medial and lower acetabulum). DiscussionThe results indicate a poorer periacetabular BMD in patients with ONFH prior THA which might be responsible for premature loosening of the acetabular cup in THA. Due to a lack of literature, further clinical investigations are required to confirm our results. Level of evidenceLevel III: retrospective case control study.

Shape-based acetabular cartilage segmentation: application to CT and MRI datasets.

A new method for acetabular cartilage segmentation in both computed tomography (CT) arthrography and magnetic resonance imaging (MRI) datasets with leg tension is developed and tested. The new segmentation method is based on the combination of shape and intensity information. Shape information is acquired according to the predictable nonlinear relationship between the U-shaped acetabulum region and acetabular cartilage. Intensity information is obtained from the acetabular cartilage region automatically to complete the segmentation procedures. This method is evaluated using 54 CT arthrography datasets with two different radiation doses and 20 MRI datasets. Additionally, the performance of this method in identifying acetabular cartilage is compared with four other acetabular cartilage segmentation methods. This method performed better than the comparison methods. Indeed, this method maintained good accuracy level for 74 datasets independent of the cartilage modality and with minimum user interaction in the bone segmentation procedures. In addition, this method was efficient in noisy conditions and in detection of the damaged cartilages with zero thickness, which confirmed its potential clinical usefulness. Our new method proposes acetabular cartilage segmentation in three different datasets based on the combination of the shape and intensity information. This method executes well in situations where there are clear boundaries between the acetabular and femoral cartilages. However, the acetabular cartilage and pelvic bone information should be obtained from one dataset such as CT arthrography or MRI datasets with leg traction.

Bone ingrowth around porous-coated acetabular implant: a three-dimensional finite element study using mechanoregulatory algorithm.

Fixation of uncemented implant is influenced by peri-prosthetic bone ingrowth, which is dependent on the mechanical environment of the implant-bone structure. The objective of the study is to gain an insight into the tissue differentiation around an acetabular component. A mapping framework has been developed to simulate appropriate mechanical environment in the three-dimensional microscale model, implement the mechanoregulatory tissue differentiation algorithm and subsequently assess spatial distribution of bone ingrowth around an acetabular component, quantitatively. The FE model of implanted pelvis subjected to eight static load cases during a normal walking cycle was first solved. Thereafter, a mapping algorithm has been employed to include the variations in implant-bone relative displacement and host bone material properties from the macroscale FE model of implanted pelvis to the microscale FE model of the beaded implant-bone interface. The evolutionary tissue differentiation was observed in each of the 13 microscale models corresponding to 13 acetabular regions. The total implant-bone relative displacements, averaged over each region of the acetabulum, were found to vary between 10 and 60 μm. Both the linear elastic and biphasic poroelastic models predicted similar mechanoregulatory peri-prosthetic tissue differentiation. Considerable variations in bone ingrowth (13-88%), interdigitation depth (0.2-0.82 mm) and average tissue Young's modulus (970-3430 MPa) were predicted around the acetabular cup. A progressive increase in the average Young's modulus, interdigitation depth and decrease in average radial strains of newly formed tissue layer were also observed. This scheme can be extended to investigate tissue differentiation for different surface texture designs on the implants.

Comparative analysis of the coxo-femoral joint in hominids in relation to their locomotor behaviour: study of joint correspondence and the degree of congruence between the three-dimensional axes of the two joint components

A comparative study of the hip joint in hominids has important implications for physical anthropology, as new insights could provide additional information for documenting changes associated with the acquisition of habitual bipedalism in the human lineage. In the literature, changes in the shape of both the proximal femur and the acetabular region in hominids have been investigated; however, few analyses have studied joint congruence and even fewer have attempted to quantify the degree of correspondence between the three-dimensional orientations of the two joint components. In humans, the hip joint has a lower degree of correspondence in a bipedal posture than would be expected for such a key joint. Because natural selection is dependent on inherited structure and trade-offs between several functions, it has been suggested in a previous study that the lower degree of correspondence might be partly due to the phylogenetic history of our species. In order to test this hypothesis, an extend sample of hominids was analysed. Our results show that joint architecture changes substantially according to the locomotor behaviour of the taxon considered. In orangutans, the considerable mobility of the lower limbs is ensured in part by a shallow acetabulum and a wide femoral neck-shaft angle. In contrast, the hip joint of gorillas has to support heavy loads and thus needs stability: a deep acetabulum and a narrow femoral neck-shaft angle were observed. Finally, our results provided evidence that the highest congruence between the three-dimensional orientations of the two joint components in all the studied genera, i.e. Homo, Pan, Gorilla and Pongo, was obtained in a quadrupedal posture, further suggesting that the shape of the human hip joint is constrained by its quadrupedal ancestry.