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BACKGROUND: Although many research studies investigating subsidence of intervertebral fusion cages have been published, to our knowledge, no study has comprehensively compared cage subsidence among all lumbar intervertebral fusion (LIF) techniques. This study aimed to review the literature reporting evidence of cage subsidence linked to LIF. The amount of subsidence was compared and associated with the procedures and corresponding implants used, and the effect of cage subsidence on clinical outcomes was investigated. METHODS: For this systematic review, the MEDLINE and PubMed databases were used to identify relevant studies. Search terms included lumbar, lumbar vertebrae, lumbar spine, cage, spinal fusion, prosthesis, prosthesis implantation, implantation, implants, interbody, spacer, and subsidence. Studies included in this review were those having more than 10 patients and reporting the amount of subsidence observed using computed tomography or x-ray imaging after surgery and at follow-up visits after a minimum of 6 weeks postsurgery. Data and scale definitions related to subsidence were extracted from articles for comparison of subsidence prevalence between the 5 LIF surgical procedures. RESULTS: Forty articles were identified for inclusion. The review included data from 390 anterior lumbar intervertebral fusions (ALIFs), 2130 lateral lumbar intervertebral fusions (LLIFs), 560 posterior lumbar intervertebral fusions (PLIFs), 245 oblique lumbar intervertebral fusions (OLIFs), and 1634 transverse lumbar intervertebral fusions (TLIFs) for a total of 4959 patients who underwent LIF surgery. The minimum and maximum percentages of the number of patients having subsidence for each procedure in the included studies were as follows: ALIF stand-alone, 6% and 23.1%; LLIF stand-alone, 8.7% and 39.6%; LLIF with posterior fixation, 3.3% and 20.7%; OLIF with posterior fixation, 4.4% and 36.9%; PLIF with posterior fixation, 7.4% and 31.8%; and TLIF, 0.0% and 51.2%. CONCLUSIONS: The number of patients experiencing subsidence varied between studies within each fusion procedure. Our findings indicate that all 5 surgical methods are at risk of subsidence. Overall, ALIF without posterior fixation resulted in the lowest reported subsidence occurrence among the 5 surgical approaches. There is conflicting evidence on the association between subsidence and negative clinical outcomes. CLINICAL RELEVANCE: This review defines and compares subsidence incidence between all LIF procedures and investigates the risk of symptomatic clinical outcomes. LEVEL OF EVIDENCE: 4.

Metal-cored wire provides material selection diversity for applications where there are no commercially available solid wires. This is becoming more desirable with additive manufacturing in particular. This paper investigates the application of a Stellite 6 metal-cored wire in a Wire and Arc Additive Manufacturing of thin-wall structures with a thickness of ~ 3.5 mm using the Gas Tungsten Arc Welding (GTAW) process. Preliminary experiments by continuous travel of the GTAW torch and constantly feeding the wire showed an unreliable deposition of consecutive layers. A new method was developed featuring a Coordinated Heat and Feed (CHF) printing strategy. This method provided improved control of the weld pool and minimized the nonuniform spread of the molten material. The CHF printing strategy was implemented by dividing the print path into small segments, each of which underwent three sequential steps: (1) the weld pool formation, (2) the wire insertion into the weld pool, and (3) the cooling of the molten pool. A 7-layer thin-wall structure fabricated by this CHF printing strategy was compared with a continuously printed specimen. The results showed that the CHF specimen presented a better geometrical quality and macrostructure uniformity. Both samples had similar microstructural features and properties.

To manage osteoporotic hip fracture risk, it is necessary to understand failure mechanisms of bone at both the material and organ level. The structural response of bone is dependent on load history. Repeated loading causes progressive microstructural cracking, resulting in reduced apparent-level stiffness and, if damage is significant, reductions to peak load bearing capability. However, the effect of previous damage accumulation has not been well explored at the organ level. It was hypothesized that femoral fracture load and fracture pattern may be sensitive to damage accumulation from previous loading events. Six cadaveric specimens were used to develop patient specific finite element (FE) models from quantitative tomographic (qCT) scans. Material properties were assigned from qCT intensity at each element location, and damage evolution was predicted using a previously validated quasi-brittle FE model. Three scenarios were investigated: stumble followed by another stumble (S-S), fall followed by another fall (F-F), and stumble followed by a fall (S-F). Fracture load and pattern were compared to FE predictions for a single stumble (S) or single fall (F) loading event. Most specimens were resilient to accumulated damage, showing little (

This paper discusses the effects of process parameters in TIG based WAAM for specimens created using Hastelloy X alloy (Haynes International) welding wire and 304 stainless-steel plate as the substrate. The Taguchi method and ANOVA were used to determine the effects of travel speed, wire feed rate, current, and argon flow rate on the responses including bead shape and size, bead roughness, oxidation levels, melt through depth, and the microstructure. Travel speed and current were found to have the largest effect on the responses. Increasing travel speed or decreasing current caused a decrease in melt through depth and an increase in roughness. Printing strategies were tested using specimens of multiple layers and no significant difference was found between printing layers in the same direction and printing layers in alternating directions. No observable interface between the layers was present suggesting a complete fusion between layers with no oxidation. Three distinct zones were identified within the three- and eight-layer samples. The zones were characterized by the size and distribution of the molybdenum carbide formations within the matrix grain formations.

This study investigated impact-induced strain fields within brain tissue surrogates having different cortical gyrification. Two elastomeric surrogates, one representative of a lissencephalic brain and the other of a gyrencephalic brain, were drop impacted in unison at four different heights and in two different orientations. Each surrogate contained a radiopaque speckle pattern that was used to calculate strain fields. Two different approaches, digital image correlation (DIC) and a particle tracking method, enabled comparisons of full-field and localized strain responses. The DIC results demonstrated increased localized deviations from the mean strain field in the surrogate with a gyrified cortex. Particle tracking algorithms, defining four-node quadrilateral elements, were used to investigate the differences in the strain response of three regions: the base of a sulcus, the adjacent gyrus, and the internal capsule of the surrogates. The results demonstrated that the strains in the cortex were concentrated at the sulcal base. This mechanical mechanism of increased strain is consistent with neurodegenerative markers observed in postmortem analyses, suggesting a potential mechanism of local damage due to strain amplification at the sulcal bases in gyrencephalic brains. This strain amplification mechanism may be responsible for cumulative neurodegeneration from repeated subconcussive impacts. The observed results suggest that lissencephalic animal models, such as rodents, would not have the same modes of injury present in a gyrencephalic brain, such as that of a human. As such, a shift toward representative mild traumatic brain injury animal models having gyrencephalic cortical structures should be strongly considered.

The dynamic response of the human brain subjected to impulsive loading conditions is of fundamental importance to the understanding of traumatic brain injuries. Due to the complexity of such measurements, the existing experimental datasets available to researchers are sparse. However, these measurements are used extensively in the validation of complex finite element models used in the design of protective equipment and the development of injury mitigation strategies. The primary objective of this study was to develop a comprehensive methodology to measure displacement in specific anatomical regions of the brain. A state-of-the-art high-speed cineradiography system was used to capture brain motion in post-mortem human surrogate specimens at a rate of 7500 fps. This paper describes the methodology used to capture these data and presents measurements from these tests. Two-dimensional displacement fields are presented and analyzed based on anatomical regions of the brain. These data demonstrated a multi-modal displacement response in several regions of the brain. The full response of the brain consisted of an elastic superposition of a series of bulk rotations of the brain about its centre of gravity. The displacement field could be linked directly to specific anatomical regions. The methods presented mark an improvement in temporal and spatial resolution of data collection, which has implications for our developing understanding of brain trauma.

This article reviews a body of work performed by the investigators over 9 years that has addressed the significance of cam morphology in the development of hip osteoarthritis (OA). Early hip joint degeneration is a common clinical presentation and preexisting abnormal joint morphology is a risk factor for its development. Interrogating Hill's criteria, we tested whether cam-type femoroacetabular impingement leads to hip OA. Strength of association was identified between cam morphology, reduced range-of-movement, hip pain, and cartilage degeneration. By studying a pediatric population, we were able to characterize the temporality between cam morphology (occurring 1st) and joint degeneration. Using in silico (finite element) and in vivo (imaging biomarkers) studies, we demonstrated the biological plausibility of how a cam deformity can lead to joint degeneration. Furthermore, we were able to show a biological gradient between degree of cam deformity and extent of articular damage. However, not all patients develop joint degeneration and we were able to characterize which factors contribute to this (specificity). Lastly, we were able to show that by removing the cam morphology, one could positively influence the degenerative process (experiment). The findings of this body of work show consistency and coherence with the literature. Furthermore, they illustrate how cam morphology can lead to early joint degeneration analogous to SCFE, dysplasia, and joint mal-reduction post-injury. The findings of this study open new avenues on the association between cam morphology and OA including recommendations for the study, screening, follow-up, and assessment (patient-specific) of individuals with cam morphology in order to prevent early joint degeneration. Statement of significance: By satisfying Hill's criteria, one can deduct that in some individuals, cam morphology is a cause of OA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3125-3135, 2018.

A cam deformity is proposed as a cause of idiopathic osteoarthritis. Increased subchondral bone mineral density (BMD) is associated with this degenerative process of osteoarthritis, and the patient’s activity level may contribute to it. Therefore, the correlation between activity level and subchondral BMD in subjects with cam deformity FAI was studied. In this study, 26 asymptomatic cam deformity subjects (Bump) were compared with 18 subjects with a normal alpha angle (Control). Anterosuperior subchondral femoral neck and acetabular rim BMD were measured using quantitative computed tomography. Activity level was determined using the UCLA activity score. The correlation between BMD and UCLA activity were analysed. The result was a significantly higher BMD for Bump subjects in almost all measured sections. The UCLA score of the Bump versus Control subjects were comparable (8.96 versus 8.77, P = 0.740). While the controls showed no correlation between UCLA and BMD, a positive correlation was found for the Bump subjects on several femoral and acetabular impingement locations. These results support the conclusion that mechanical loading causes subchondral stiffening at the anterosuperior head–neck junction of the femur and anterosuperior acetabular rim. The absence of a correlation between BMD versus UCLA in the Controls supports the hypothesis that activity level may serve as a predictor for higher subchondral BMD in a cam deformity hip joint.

Nonlinear finite element (FE) modeling can be a powerful tool for studying femoral fracture. However, there remains little consensus in the literature regarding the choice of material model and failure criterion. Quasi-brittle models recently have been used with some success, but spurious mesh sensitivity remains a concern. The purpose of this study was to implement and validate a new model using a custom finite element designed to mitigate mesh sensitivity problems. Six specimen-specific FE models of the proximal femur were generated from quantitative tomographic (qCT) scans of cadaveric specimens. Material properties were assigned a-priori based on average qCT intensities at element locations. Specimens were experimentally tested to failure in a stumbling load configuration, and the results were compared to FE model predictions. There was a strong linear relationship between FE predicted and experimentally measured fracture load (R2= 0.79), and error was less than 14% over all cases. In all six specimens, surface damage was observed at sites predicted by the FE model. Comparison of qCT scans before and after experimental failure showed damage to underlying trabecular bone, also consistent with FE predictions. In summary, the model accurately predicted fracture load and pattern, and may be a powerful tool in future studies.

Accurate in-vitro orientation of cadaveric hip joints is challenging due to limited available anatomical landmarks. Published hip joint in-vitro investigations commonly lack details on methods used to achieve reported orientations and the accuracy with which the desired orientation has been achieved. The aim of this study was to develop an accurate method for orienting hip joints with limited anatomical landmarks for in-vitro investigations, and to compare this method against orientation using guiding axes and by visual approximation. The proposed orientation method resulted in orientation angles achieved to within one degree (SD ± 0.58°). For most specimens, orientation using physical tools resulted in errors of ±8° and ±12° in at least one of three orientation angles used to place the femur and pelvis in neutral orientation, respectively. Precision was also worse, with SDs ranging from ±1° to ±5° for orientation angles of femoral specimens and SDs ranging from ±1° to ±8° for pelvic specimens. The error in the orientation angles was worse for orientation by visual approximation and the range of SDs were greater for both the femur and pelvis. Finite element modeling was used to assess the effects of observed orientation errors, on prediction of fracture load. In most cases, the largest error in fracture load among all trials exceeded 30%, relative to a femur oriented without any error in the orientation angles.

Cam morphology in association with femoroacetabular impingement (FAI) is a recognized cause of hip pain and cartilage damage and proposed as a leading cause of arthritis. The purpose of this study was to analyze the functional and biomechanical effects of the surgical correction of the cam deformity on the degenerative process associated with FAI.Ten male patients with a mean age of 34.3 years (range, 23.1 to 46.5 years) and a mean body mass index (and standard deviation) of 26.66 ± 4.79 kg/m underwent corrective surgery for cam deformity in association with FAI. Each patient underwent a computed tomography (CT) scan to assess acetabular bone mineral density (BMD), high-resolution T1ρ magnetic resonance imaging (MRI) of the hips to assess proteoglycan content, and squatting motion analysis as well as completed self-administered functional questionnaires (Hip disability and Osteoarthritis Outcome Score [HOOS]) both preoperatively and 2 years postoperatively.At a mean follow-up of 24.5 months, improvements in functional scores and squat performance were seen. Regarding the zone of impingement in the anterosuperior quadrant of the acetabular rim, the mean change in BMD at the time of follow-up was -31.8 mg/cc (95% confidence interval [CI], -11 to -53 mg/cc) (p = 0.008), representing a 5% decrease in BMD. The anterosuperior quadrant also demonstrated a significant decrease in T1ρ values, reflecting a stabilization of the cartilage degeneration. Significant correlations were noted between changes in clinical functional scores and changes in T1ρ values (r = -0.86; p = 0.003) as well as between the BMD and maximum vertical force (r = 0.878; p = 0.021).Surgical correction of a cam deformity in patients with symptomatic FAI not only improved clinical function but was also associated with decreases in T1ρ values and BMD. These findings are the first, to our knowledge, to show that alteration of the hip biomechanics through surgical intervention improves the overall health of the hip joint.Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Summary Objective Morphological deformities of the hip, such as femoroacetabular impingement (FAI) may be responsible for up to 80% of hip osteoarthritis. In cam type FAI, the pathomechanism has been attributed to repeated abnormal contact between the femur and the antero-superior acetabular rim, resulting in cartilage and labrum degeneration. Subchondral bone stiffness likely plays a major role in the process, but little is known of the mechanical properties of the cam deformity. The purpose of this study was to determine tissue modulus and the trabecular micro-architecture of the subchondral bone of the cam deformity of patients undergoing resection surgery as well as comparing these parameters to healthy aged matched controls. Design Twelve osteochondral bone biopsies were obtained from symptomatic FAI patients and ten osteochondral control specimens were harvested from cadaveric femurs. A combination of mechanical testing, micro-CT and finite element (FE) analysis were used to determine tissue modulus, bone volume fraction, trabecular thickness, trabecular and spacing, and trabecular number. Results The mean tissue modulus of the cam-type FAI deformities ( E = 5.4 GPa) was significantly higher than normal controls ( E = 2.75 GPa, P = 0.038), but no statistically significant differences were found in bone micro-architectural parameters. Conclusions The data suggests that subchondral bone of the cam deformity consists of older secondary mineralized bone. This supports the notion that the cam deformity is a primary malformation with intrinsic biomechanical abnormalities rather than a secondary deformity as part of the degenerative process of the covering cartilage or remodeling due to repeated impingement.

This article reviews a body of work performed by the investigators over 9 years that has addressed the significance of cam morphology in the development of hip osteoarthritis (OA). Early hip joint degeneration is a common clinical presentation and preexisting abnormal joint morphology is a risk factor for its development. Interrogating Hill's criteria, we tested whether cam-type femoroacetabular impingement leads to hip OA. Strength of association was identified between cam morphology, reduced range-of-movement, hip pain, and cartilage degeneration. By studying a pediatric population, we were able to characterize the temporality between cam morphology (occurring 1st) and joint degeneration. Using in silico (finite element) and in vivo (imaging biomarkers) studies, we demonstrated the biological plausibility of how a cam deformity can lead to joint degeneration. Furthermore, we were able to show a biological gradient between degree of cam deformity and extent of articular damage. However, not all patients develop joint degeneration and we were able to characterize which factors contribute to this (specificity). Lastly, we were able to show that by removing the cam morphology, one could positively influence the degenerative process (experiment). The findings of this body of work show consistency and coherence with the literature. Furthermore, they illustrate how cam morphology can lead to early joint degeneration analogous to SCFE, dysplasia, and joint mal-reduction post-injury. The findings of this study open new avenues on the association between cam morphology and OA including recommendations for the study, screening, follow-up, and assessment (patient-specific) of individuals with cam morphology in order to prevent early joint degeneration. Statement of significance: By satisfying Hill's criteria, one can deduct that in some individuals, cam morphology is a cause of OA. © 2018 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 36:3125-3135, 2018.

Patient specific quantitative CT (QCT) imaging data together with the finite element (FE) method may provide an accurate prediction of a patient's femoral strength and fracture risk. Although numerous FE models investigating femoral fracture strength have been published, there is little consent on the effect of boundary conditions, dynamic loading and hydraulic strengthening due to intra-medullary pressure on the predicted fracture strength. We developed a QCT-derived FE model of a proximal femur that included node-specific modulus assigned based on the local bone density. The effect of three commonly used boundary conditions published in literature were investigated by comparing the resulting strain field due to an applied fracture load. The models were also augmented with viscoelastic material properties and subject to a realistic impact load profile to determine the effect of dynamic loads on the strain field. Finally, the effect of hydraulic strengthening was investigated by including node specific permeability and performing a coupled pore diffusion and stress analysis of the FE model. Results showed that all boundary conditions yield the same strain field patterns, but peak strains were 22% lower and fracture load was 18% higher when loaded at the greater trochanter than when loaded at the femoral head. Comparison of the dynamic models showed that material viscoelasticity was important, but inertial effects (vibration and shock) were not. Finally, pore pressure changes did not cause significant hydraulic strengthening of bone under fall impact loading.

Femoro-acetabular impingement (FAI) is associated with significant acetabular cartilage damage and degenerative arthritis. To understand the contact stress and thus biomechanical mechanisms that may contribute to degeneration, the material behaviour of the cartilage layer is required. The objective of this study is to determine the fibril-reinforced poroelastic properties and composition of cartilage from cam deformities and to compare to those of normal cartilage. Patients undergoing surgical treatment of a symptomatic cam FAI deformity were recruited from the clinical practice of one of the authors. Osteochondral specimens were retrieved from the deformity during surgery using a trephine. Control specimens were retrieved from the anterior femoral head bearing surface during autopsy procedures. Indentation stress-relaxation tests were performed to determine the modulus ( E S ), Poisson’s ratio ( ν ) and permeability ( k 0 ) of the poroelastic component, and the strain-independent ( E 0 ) and -dependent ( E e ) moduli of the fibril-reinforcement using finite element analysis and optimization. Safranin-O staining was used to quantify proteoglycan content. E S and ν were 71% and 37% lower, respectively, in Cam specimens compared to controls, and k 0 was approximately triple that of Control specimens (p E 0 and E e . Proteoglycan content was substantially depleted in Cam specimens, and was correlated with E S , ν and k 0 . This study showed that cartilage from the cam deformity exhibits severe degeneration in terms of the mechanical behaviour and composition changes, and is consistent with osteoarthritis. This further supports the hypothesis that FAI is a cause of hip osteoarthritis.

Current problems associated with bone allografts include risk of disease transmission, limited availability, and cost. Synthetic scaffolds have been proposed as substitute graft materials to address these issues. Calcium polyphosphate is a novel synthetic scaffold material that has shown good mechanical properties and biocompatibility. Here, we evaluated calcium polyphosphate in terms of its ability to support cell proliferation and differentiation in vivo. Calcium polyphosphate, morsellized cancellous bone, and hydroxyapatite/tricalcium phosphate particles were seeded with marrow stromal cells and implanted subcutaneously in the back of NOD/Scid mice. At 7, 14, and 28 days the samples were harvested and the proliferation characteristics and gene expression were analyzed. All tested graft materials had similar proliferation characteristics and gene expression. The subcutaneous environment had a stronger impact on the proliferation and differentiation of the cells than the scaffold material itself. However, it was shown that calcium polyphosphate is superior to hydroxyapatite/tricalcium phosphate and bone in its ability to support cell survival in vivo. The study confirmed that calcium polyphosphate has potential for replacing morsellized cancellous bone as a graft material for bone regeneration.

Failure of the femoral component of total hip arthroplasty is often accompanied by bone loss that can pose a significant challenge to the orthopaedic surgeon. Femoral impaction allografting has attractive potential for restoring bone stock in deficient femurs. However, there have been reports of problematic postoperative stem subsidence with this procedure. Subsidence is highly variable among patients, and there is disagreement over the mechanisms that cause it. This article reviews the various mechanisms that can contribute to subsidence in femoral impaction allografting. Variables such as graft density, cement penetration profile, use of synthetic graft substitutes, or other graft additives are discussed, as well as their potential impact on subsidence. Finally, recommendations are made for future studies aiming to reduce the risk of excessive subsidence in femoral impaction allografting.

Microtopographic features affect diverse cell behaviors. Adult bone marrow progenitor cells (AMPCs) constitute a multipotent heterogeneous population. We hypothesized that microtopographies could direct AMPCs lineage-specific differentiation. AMPCs isolated from Sprague-Dawley rats were CD45 depleted, expanded, and plated at 105 cells/cm2 on epoxy-microfabricated: (1) 60-μm-deep grooves with 95-μm pitch (D60P95), (2) 55-μm-wide and 10-μm-deep squares (W55D10), (3) 30-μm-deep grooves with 45-μm pitch (D30P45), (4) 17-μm-wide and 10-μm-deep pillars (W17D10), and (5) smooth control. AMPCs were cultured using expansion, chondrogenesis, or osteogenesis supporting media. Cell cultures were examined by scanning electron microscopy, qRT-PCR, and immunostaining at 2, 9, 16, and 23 days after plating. Expressions of osteogenesis-related genes, such as Runx-2, alkaline phosphatase, osteopontin, osteocalcin, and parathyroid hormone–related protein receptor (PTHr), and chondrogenesis-associated genes, such as Sox-9, type II collagen, and aggrecan, were determined. In expansion medium, W55D10 induced a transient increase of Sox9 expression. Compared with smooth surfaces, type II collagen mRNA and protein expressions in chondrogenic medium were significantly upregulated on W55D10 by day 23. In contrast, osteocalcin and PTHr expressions were significantly increased on D30P45 in osteogenic medium. We have demonstrated that W55D10 and D30P45 enhanced AMPCs chondrogenic and osteogenic terminal differentiation with appropriate culture conditions. © 2010 Wiley Periodicals, Inc. J Biomed Mater Res Part A, 2010.

Bone marrow stromal cells (MSCs) differentiation and proliferation are controlled by numerous growth factors and hormones. Continuous parathyroid hormone (PTH) treatment has been shown to decrease osteoblast differentiation, whereas pulsatile PTH increases osteoblast differentiation. However, the effects of PTH treatments on MSCs have not been investigated. This study showed continuous PTH treatment in the presence of dexamethasone (DEX) promoted osteogenic differentiation of rat MSCs in vitro, as demonstrated by increased alkaline phosphatase (ALP) activity, number of ALP expressing cells, and up-regulation of PTH receptor-1, ALP, and osteocalcin mRNA expressions. In contrast, pulsatile PTH treatment was found to suppress osteogenesis of rat MSCs, possibly by promoting the maintenance of undifferentiated cells. Additionally, the observed effects of PTH were strongly dependent on the presence of DEX. MSC proliferation however was not influenced by PTH independent of treatment regimen and presence or absence of DEX. Furthermore, our work raised the possibility that PTH treatment may modulate stem/progenitor cell activity within MSC cultures.

This study explored the relationship between the initial stability of the femoral component and penetration of cement into the graft bed following impaction allografting.Impaction allografting was carried out in human cadaveric femurs. In one group the cement was pressurised conventionally but in the other it was not pressurised. Migration and micromotion of the implant were measured under simulated walking loads. The specimens were then cross-sectioned and penetration of the cement measured.Around the distal half of the implant we found approximately 70% and 40% of contact of the cement with the endosteum in the pressure and no-pressure groups, respectively. The distal migration/micromotion, and valgus/varus migration were significantly higher in the no-pressure group than in that subjected to pressure. These motion components correlated negatively with the mean area of cement and its contact with the endosteum.The presence of cement at the endosteum appears to play an important role in the initial stability of the implant following impaction allografting.

The acetabular labrum is a soft-tissue structure which lines the acetabular rim of the hip joint. Its role in hip joint biomechanics and joint health has been of particular interest over the past decade. In normal hip joint biomechanics, the labrum is crucial in retaining a layer of pressurised intra-articular fluid for joint lubrication and load support/distribution. Its seal around the femoral head is further regarded as a contributing to hip stability through its suction effect. The labrum itself is also important in increasing contact area thereby reducing contact stress. Given the labrum’s role in normal hip joint biomechanics, surgical techniques for managing labral damage are continuously evolving as our understanding of its anatomy and function continue to progress. The current paper aims to review the anatomy and biomechanical function of the labrum and how they are affected by differing surgical techniques. Take home message: The acetabular labrum plays a critical role in hip function and maintaining and restoring its function during surgical intervention remain an essential goal. Cite this article: Bone Joint J 2016;98-B:730–5.

Cement intrusion into cancellous or impacted bone is not well understood. We adopted an engineering mechanics approach to predict the effect of surgical variables on the cement intrusion into impacted cancellous bone, used for the revision of failed total hip replacement with the impaction allografting technique. Specifically, a three-dimensional finite element model was used to determine the effects of cement viscosity, the magnitude and duration of pressurization, and the distribution of the porosity along the femur on cement intrusion. The overall averaged mean intrusion depth difference between the finite element model prediction and the cadaveric measurements was 1.1mm. The depth of penetration increased with higher pressurization pressure, duration of pressurization, and earlier stem insertion (lower viscosity), but maintained a similar profile. The distribution of the porosity along the femur determined the intrusion profile. Cement viscosity, the applied pressure or the duration of the pressurization can be adjusted to limit the cement volume injected into the medullary canal and therefore prevent the cement from reaching the endosteal surface.

Experimental data suggest that lumbar torsion contributes to lumbar disc degenerative changes, such as instability, spondylolisthesis and spinal canal stenosis. However, some basic mechanical characteristics of the lumbar spine under torsional loading have not yet been reported in detail. For example, the function of the facet joints under combined mechanical loads such as torsion with superimposed flexion or extension postures is an area of interest about which little biomechanical data have been reported. In this study, the kinematic response to axial torsion with superimposed axial compression (200 N), compression-flexion (3 and 6 Nm) and compression-extension (3 and 6 Nm) was investigated in 10 cadaveric lumbar functional spinal units. Range of motion (ROM), and helical axes of motion (HAM), were analyzed. There was no difference in ROM between no preload, pure compressive and flexion-compression preload conditions. The ROM was significantly reduced by both extension-compression preload conditions (11% reduction for 3 Nm and 19% reduction for 6 Nm of extension) compared to the pure compressive preload. For no preload, the average HAM position in the transverse plane of the intervertebral disc was near the posteriormost part of the disc and located laterally on the side contralateral to the applied torsional moment. In the transverse plane, the HAM position showed a discrete trend towards the posterior part of the specimens during extension. Kinematic data were visualized using computer animation techniques and CT-based reconstructions of the respective specimens. This information may be used for identifying and characterizing physiologic and pathologic motion and for specifying conservative and surgical treatment concepts and, thus, may find application to identifying indications for spinal fusion or in evaluating the effect of future semi-flexible instrumentation.

Hip resurfacing arthroplasty is an alternative to traditional hip replacement that can conserve proximal bone stock and has gained popularity but bone resorption may limit implant survival and remains a clinical concern. The goal of this study was to analyze bone remodelling patterns around an uncemented resurfacing implant and the influence of ingrowth regions on resorption. A computed tomography-derived finite element model of a proximal femur with a virtually implanted resurfacing component was simulated under peak walking loads. Bone ingrowth was simulated by six interface conditions: fully bonded; fully friction; bonded cap with friction stem; a small bonded region at the stem-cup intersection with the remaining surface friction; fully frictional, except for a bonded band along the distal end of the cap and superior half of the cap bonded with the rest frictional. Interface condition had a large influence on remodelling patterns. Bone resorption was minimized when no ingrowth occurred at the bone-implant interface. Bonding only the superior half of the cap increased bone resorption slightly but allowed for a large ingrowth region to improve secondary stability.

Study design An in vitro biomechanical investigation on human cadaveric specimens was conducted before and after nucleotomy. Endplate and vertebral body deformation patterns were measured under compression and shear loading, in addition to kinematics and disc pressure. Objective The working hypotheses of this study were that in compression, nucleotomy results in an altered deformation pattern of the endplate and that in shear, nucleotomy does not result in an altered endplate deformation pattern or disc pressure. Summary of background data The pressure distributions within the intervertebral disc have been studied in compression loading but not in shear loading. Severe degeneration and surgical nucleotomy result in small nuclear pressure and altered loading distribution in compression. The effect of these changes on the vertebral endplate and the response under shear loads are not well understood. Methods Five L3-L4 and two L4-L5 functional spinal units were tested under compression and shear loading, intact and after nucleotomy. Vertebral body deformations, intradiscal pressure, and intervertebral kinematics were measured. A series of compression-type (maximum 1000 N) and shear-type (maximum 500 N) loads were applied. Results With nucleotomy, the disc pressure and the endplate strains decreased under compression, but the vertebral rim strains did not change. In shear, the vertebral rim and endplate strains did not change with nucleotomy. Disc pressure was lower in shear than in compression. Conclusion Nucleotomy resulted in decreased disc pressure, decreased endplate deformation, and modified loading patterns onto the inferior vertebra in compression loading. However, nucleotomy did not appreciably affect the behavior of the disc in shear loading.

The understanding of load support mechanisms in cartilage has evolved with computational models that better mimic the tissue ultrastructure. Fibril-reinforced poroelastic models can reproduce cartilage behaviour in a variety of test conditions and can be used to model tissue anisotropy as well as assess stress and pressure partitioning to the tissue constituents. The goal of this study was to examine the stress distribution in the fibrillar and non-fibrillar solid phase and pressure in the fluid phase of cartilage in axisymmetric models of a healthy and osteoarthritic hip joint. Material properties, based on values from the literature, were assigned to the fibrillar and poroelastic components of cartilage and cancellous and subchondral compact bone regions. A cyclic load representing walking was applied for 25 cycles. Contact stresses in the fibrillar and non-fibrillar solid phase supported less than 1% of the contact force and increased only minimally with load cycles. Simulated proteoglycan depletion increased stresses in the radial and tangential collagen fibrils, whereas fibrillation of the tangential fibrils resulted in increased compressive stress in the non-fibrillar component and tensile stress in the radial fibrils. However neither had an effect on fluid pressure. Subchondral sclerosis was found to have the largest effect, resulting in increased fluid pressure, non-fibrillar compressive stress, tangential fibril stress and greater cartilage consolidation. Subchondral bone stiffening may play an important role in the degenerative cascade and may adversely affect tissue repair and regeneration treatments.

SummaryObjectiveCam-type femoroacetabular impingement (FAI) deformities have been associated with early osteoarthritic degeneration of the hip. Degeneration depends on many factors such as joint morphology and dynamics of motion. Bone mineral density (BMD) appears to be a manifestation of the above, and may be a potentiator. Thus the goal of this study was to assess subchondral BMD of cam deformities in symptomatic and asymptomatic FAI subjects, and to compare to normal controls.MethodsSubjects undergoing surgical correction of a symptomatic cam-type deformity were recruited (“Surgical”). Asymptomatic volunteers were also recruited and classified as normal (“Control”) or having a deformity (“Bump”) based on their alpha angle measurement. All subjects (n = 12 per group) underwent computed tomography (CT) with a calibration phantom. BMD was determined in volumes of interest around the femoral head and neck to a depth of 5 mm. BMD was compared between groups in each section using spine BMD as a covariate.ResultsNo differences were seen between groups in the peripheral bearing surface. The Bump group exhibited higher BMD than Controls within the head/neck junction (P

SummaryObjectiveFemoroacetabular impingement (FAI) has been associated with significant acetabular cartilage damage and subsequent degenerative arthritis. Subchondral bone, often neglected in osteoarthritis studies, may play an important role in the degenerative cascade. Hence the goal of this study was to assess acetabular subchondral bone mineral density (BMD) in subjects with asymptomatic or symptomatic cam deformities compared to normal control subjects. The relationship between BMD and the alpha angle, a quantitative measure of the deformity, was also analyzed.MethodsPatients diagnosed with symptomatic cam FAI were recruited (‘Surgical’) as well as subjects from the general asymptomatic population, classified from CT imaging as normal (‘Control’) or having a cam deformity (‘Bump’) based on their alpha angle measurement. There were 12 subjects in each group. All subjects underwent a CT scan with a calibration phantom. BMD was calculated in regions of interest around the acetabulum from CT image intensity and the phantom calibration. BMD was compared between groups using spine BMD as a covariate. The relationship between BMD and alpha angle was assessed by linear regression.ResultsIn the antero-superior regions bone density was 15–34% higher in the Bump group (P

Marrow stromal cells (MSCs) are ideally suited for tissue engineered bone grafts since they have the potential to regenerate bone, but may also maintain the homeostasis of the repaired tissue through their ability for self-renewal. An ideal bone graft substitute should support MSC self-renewal as well as differentiation to ensure complete bone defect regeneration and maintenance. The purpose of this investigation was to determine the effect of different substrate materials on MSC expansion and differentiation. Calcium polyphosphate (CPP), bone and hydroxyapatite/tricalcium phosphate (HA/TCP) were seeded with rat MSCs and maintained in culture conditions that promote cell expansion. At 0, 3, 7, 14, and 21 days cell numbers were determined by measuring their metabolic activity using a MTT assay and the frequency of cycling cells by 24 hr BrdU incorporation. Osteogenic, chondrogenic, and adipogenic marker expression in these cultures was measured by qRT-PCR. An initial drop in cell numbers was observed on all substrates. CPP and bone, but not HA/TCP supported an increase in proliferating cells at day 14 and 21. In addition, no upregulation of mature bone markers was observed in cells cultured on CPP and bone, which suggests that these substrates support the expansion of undifferentiated MSCs. In contrast, cell numbers on HA/TCP decreased with time and only rare BrdU positive cells were observed. This decrease in proliferation correlated with the down regulation of osteogenic progenitor markers and the substantial increase in mature osteocyte markers, indicating that HA/TCP favors MSC differentiation and maturation along the osteogenic lineage.

Background. In-vitro mechanical tests are commonly performed to assess pre-clinically the effect of implant design on the stability of hip endoprostheses. There is no standard protocol for these tests, and the forces applied vary between studies. This study examines the effect of the abductor force with and without application of the anterior-posterior hip contact force in the in-vitro assessment of cementless hip implant stability. Methods Cementless stems (VerSys Fiber Metal) were implanted in twelve composite femurs which were divided into two groups: group 1 (N = 6) was loaded with the hip contact force only, whereas group 2 (N = 6) was additionally subjected to an abductor force. Both groups were subjected to the same cranial-caudal hip contact force component, 2.3 times body weight (BW) and each specimen was subjected to three levels of anterior-posterior hip contact load: 0, -0.1 to 0.3 BW (walking), and -0.1 to 0.6 BW (stair climbing). The implant migration and micromotion relative to the femur was measured using a custom-built system comprised of 6 LVDT sensors. Results Substantially higher implant motion was observed when the anterior-posterior force was 0.6BW compared to the lower anterior-posterior load levels, particularly distally and in retroversion. The abductor load had little effect on implant motion when simulating walking, but resulted in significantly less motion than the hip contact force alone when simulating stair climbing. Conclusions The anterior-posterior component of the hip contact load has a significant effect on the axial motion of the stem relative to the bone. Inclusion of the abductor force had a stabilizing effect on the implant motion when simulating stair climbing.

In impaction allografting, the host bone interface may consist of morsellized allograft alone or as a composite with bone cement. The objective of this study was to investigate the temporal changes in the interface for these two materials in a rat bone chamber model. To simulate the impaired endosteal circulation after impaction allografting, bone chambers were tightened bilaterally to the endosteal surfaces of proximal tibiae of mature rats and filled with pure allograft or cement/allograft composite. The cement/allograft composite-host bone interface strength was significantly higher at 3 weeks and was higher than the allograft construct failure strength. Limited allograft, but extensive periosteal remodeling, was observed at 3 weeks which resulted in a significantly increased cortical porosity and cortical thickness. The allograft porosity decreased significantly at 6 weeks indicating extensive remodeling of the allograft bone. Little or no remodeling of the allograft particles in the cement was found. At 6 weeks a new medullary canal was formed, and the endosteal cortex was partially absorbed. Endosteal absorption resulting in medullary canal widening in revision THR may be responsible for clinically unstable stems after impaction allografting.

In addition to the impact ed allograft -host bone interface, an impact ed allograft -cement composite-host bone interface was identified. Given these variations of interface morphology, we hypothesized that the mechanical characteristics of the impact ed allo graft -host bone interface would exhibit substantial differences along the length of the stem and that the degree of cement penetration of the endosteal cortex would explain a significant percentage of the variation. Methods The femoral necks from six fresh frozen human cadaveric femora were osteotomized. Using a high-speed burr the cancellous bone was removed from the proximal femoral metaphysis and local diaphyseal lytic defects were created. The endosteal surface roughness achieved was similar to that of a femur in a revision total hip arthroplasty as judged by two experienced surgeons. Three surgeons performed the impaction allografting procedure, each on two cadaveric femora using the XChange revision system (Howmedica Inc, Rutherford, NJ, USA). After impaction of the morsellized allograft bone, two packages of low viscosity Simplex cement (Howmedica Inc, Rutherford, NJ, USA) were mixed and injected into the neo-medullary canal. After the canal had been filled in a retrograde manner, a proximal femoral seal was applied and the cement pressurised with a cement gun. The pressure was maintained until the viscosity of the cement was appropriate for the insertion of the double tapered polished collarless Exeter stem (Howmedica Inc, Rutherford, NJ, USA). The femurs were cut in 6mm thick transverse sections with a diamond saw. Anatomical landmarks and the tip of the stem were used to match every other section to seven levels (Figure 2). Push-out tests were performed on these sections to mechanically characterise the impacted allograft/ composite-host bone interface. From the recorded load–displacement curves, the failure load was defined as the point where a zero slope was reached the first time which was, in general, the peak load. The apparent interface shear strength was calculated from failure load and section geometry. The failure modes were determined by macroscopic inspection. Three different failure types were identified (Figure 1): Type I: Pure failure of the allograft/ composite-host bone interface. Type II: Failure of the allograft/ composite-host bone interface with local allograft cement-composite failure. Type III: Failure of the allograft/ composite-host bone interface with local allograft failure.

We studied various aspects of graft impaction and penetration of cement in an experimental model. Cancellous bone was removed proximally and local diaphyseal lytic defects were simulated in six human cadaver femora. After impaction grafting the specimens were sectioned and prepared for histomorphometric analysis. The porosity of the graft was lowest in Gruen zone 4 (52%) and highest in Gruen zone 1 (76%). At the levels of Gruen zones 6 and 2 the entire cross-section was almost filled with cement. Cement sometimes reached the endosteal surface in other Gruen zones. The mean peak impaction forces exerted with the impactors were negatively correlated with the porosity of the graft.

Background: Periprosthetic femoral fractures with well-fixed femoral components can be difficult to manage and internal fixation is usually necessary. This study was designed to determine the effect of cable plate, strut allograft and combined plate and strut allograft fixations of periprosthetic femoral fractures. Methods: A transverse fracture at the level of the tip of the femoral stem was simulated in six cadaveric femurs. The fracture was fixed with a plate–strut graft construct with and without proximal screws, a plate only construct with and without proximal screws and with both anterior and lateral struts grafts of 12 cm or 20 cm in length. The intact femur and the six constructs were tested using anteroposterior and axial loads to simulate the forces at the hip during gait. The interfragmentary motions were measured with an optoelectronic camera system. Findings: The highest median interfragmentary translations were observed with the plate only construct without proximal screws. No significant differences in median translations were found between the combined plate–strut and the strut-graft alone constructs. Median interfragmentary rotations were largest with the plate only construct and lowest with the plate–strut constructs. Interpretation: The best fracture fixation was achieved with the combined plate and strut graft constructs particularly in combination with the two unicortical screws above the fracture. The plate only constructs may not provide sufficient fixation stability in rotation for the simulated transverse fracture. The within-construct interfragmentary motions were not significantly different except for the plate only constructs. This suggests that the fixation construct type is the determining factor of interfragmentary motion.