Clifford M. Les

Type I collagen D-spacing in fibril bundles of dermis, tendon, and bone: bridging between nano- and micro-level tissue hierarchy.

Fibrillar collagens in connective tissues are organized into complex and diverse hierarchical networks. In dermis, bone, and tendon, one common phenomenon at the micrometer scale is the organization of fibrils into bundles. Previously, we have reported that collagen fibrils in these tissues exhibit a 10 nm width distribution of D-spacing values. This study expands the observation to a higher hierarchical level by examining fibril D-spacing distribution in relation to the bundle organization. We used atomic force microscopy imaging and two-dimensional fast Fourier transform analysis to investigate dermis, tendon, and bone tissues. We found that, in each tissue type, collagen fibril D-spacings within a single bundle were nearly identical and frequently differ by less than 1 nm. The full 10 nm range in D-spacing values arises from different values found in different bundles. The similarity in D-spacing was observed to persist for up to 40 μm in bundle length and width. A nested mixed model analysis of variance examining 107 bundles and 1710 fibrils from dermis, tendon, and bone indicated that fibril D-spacing differences arise primarily at the bundle level (∼76%), independent of species or tissue types.

Nanoscale structure of type I collagen fibrils: Quantitative measurement of D‐spacing

This article details a quantitative method to measure the D‐periodic spacing of type I collagen fibrils using atomic force microscopy coupled with analysis using a two‐dimensional fast fourier transform approach. Instrument calibration, data sampling and data analysis are discussed and comparisons of the data to the complementary methods of electron microscopy and X‐ray scattering are made. Examples of the application of this new approach to the analysis of type I collagen morphology in disease models of estrogen depletion and osteogenesis imperfecta (OI) are provided. We demonstrate that it is the D‐spacing distribution, not the D‐spacing mean, that showed statistically significant differences in estrogen depletion associated with early stage osteoporosis and OI. The ability to quantitatively characterize nanoscale morphological features of type I collagen fibrils will provide important structural information regarding type I collagen in many research areas, including tissue aging and disease, tissue engineering, and gene knockout studies. Furthermore, we also envision potential clinical applications including evaluation of tissue collagen integrity under the impact of diseases or drug treatments.

Do sacrificial bonds affect the viscoelastic and fracture properties of bone

Sacrificial bonds have been suggested as a toughening mechanism for bone tissue. Ionic bridges formed by divalent calcium ions between collagen molecules have been proposed as candidates for sacrificial bonds. If this mechanism is active at the macroscopic level, we should observe changes in mechanical properties of bone when calcium ions are maintained or removed from the tissue. To test this hypothesis, we measured viscoelastic and monotonic mechanical properties of cortical bone subjected to differing ionic environments. Storage modulus of bone could be changed up to 3.8% by the presence or absence of Na+ or Ca++ in the environment in a reversible fashion when bones were monitored continuously during treatments. A long-term one-time treatment increased the viscoelastic properties of bone soaked in Na+ solutions whereas the viscoelastic properties of bones soaked in Ca++ solutions were maintained. However, the strength and toughness of bone specimens soaked and fractured in treatment solutions were not improved. The presence of Ca++ affected the mechanical behavior of mineralized bone tissue at the macro scale. These effects were reversible, consistent with the original proposal. However, these effects may not necessarily indicate an increase in strength or toughness of the tissue at the macro scale.

Rivaroxaban Versus Enoxaparin for Venous Thromboembolism Prophylaxis after Hip and Knee Arthroplasty

The oral Factor Xa inhibitor rivaroxaban (Xarelto) has been the pharmacologic agent used for venous thromboembolism (VTE) prophylaxis after primary hip and knee arthroplasty (THA/TKA) at our institution since February 2012. The purpose of our study was to compare rates of VTE and major bleeding between rivaroxaban and our previous protocol of enoxaparin after THA/TKA. A retrospective cohort study was performed including 2406 consecutive patients at our institution between 1/1/11 and 9/30/13. Patients who did not have unilateral primary THA/TKA or who received other anticoagulants were excluded. Of the 1762 patients included, 1113 patients (63.2%) received enoxaparin and 649 patients (36.8%) received rivaroxaban. This study found no demonstrable differences between these two anticoagulants in rates of VTE, infection, reoperation, transfusion, or major bleeding. Therapeutic, Retrospective comparative study, Level III.

Comparison of mean bone densities of three preparations of the distal portion of the equine third metacarpal bone measured by use of quantitative computed tomography

OBJECTIVE To evaluate whether cutting equine subchondral bone to demarcate specific regions of interest (ROIs) influences the mean density for that bone as measured via quantitative computed tomography (QCT). Sample population-2 metacarpophalangeal joints from equine cadavers. PROCEDURES The distal portion of the third metacarpal bone of each intact metacarpophalangeal joint was scanned via CT to simulate in vivo conditions. Each joint was subsequently disarticulated and dissected, and the distal portion of the dissected third metacarpal bone in air was scanned. Then, six 1-cm(2) areas representing ROIs were cut into the distal condylar surfaces to depths of approximately 1 cm, and the bone was scanned again. Three-dimensional CT models of the 3 bone preparations were generated for each third metacarpal bone on the basis of data from each set of scan images, and densities of the 6 ROIs were measured. Mean bone densities for the 6 ROIs were compared among models of intact, dissected, and cut third metacarpal bone scans. RESULTS Mean bone density was significantly lower in cut bone preparations, compared with that in intact or dissected bone. Differences between mean bone densities for intact and dissected bone preparations were not significant. CONCLUSIONS AND CLINICAL RELEVANCE Cutting subchondral bone to demarcate specific ROIs prior to CT imaging significantly lowered mean bone density as measured via QCT and thus introduced substantial artifacts. These findings have direct implications on techniques for CT modeling of equine subchondral bone in the characterization of joint diseases in horses.

Matrix Concentration of Insulin-like Growth Factor I (IGF-I) is Negatively Associated with Biomechanical Properties of Human Tibial Cancellous Bone Within Individual Subjects

Insulin-like growth factor-I (IGF-I), abundant in bone matrix, is believed to play an important role during bone development and remodeling. To our knowledge, however, few studies have addressed the relationship between the concentration of IGF-I in bone matrix and the biomechanical properties of bone tissue. In this study, forty-five cylindrical specimens of cancellous bone were harvested from six human tibiae and scanned using microcomputed tomography (μCT). The bone volume fraction (BV/TV) was calculated from three-dimensional (3D) μCT images. Mechanical tests were then performed on a servohydraulic testing system to determine the strength and stiffness of cancellous bone. Following mechanical testing, the concentration of IGF-I in bone matrix was measured by using an enzyme-linked immunoabsorbent assay (ELISA). Within each subject, the concentration of IGF-I in bone matrix had significant (P < 0.01) negative correlations with the bone volume fraction, strength, and stiffness of cancellous bone. In particular, the anterior quadrant of the proximal tibia was significantly (P < 0.02) greater in IGF-I matrix concentration and marginally significantly lower in strength (P = 0.053) and stiffness (P = 0.059) than the posterior quadrant. The negative correlations between the cancellous bone matrix concentration of IGF-I and cancellous bone biomechanical properties within subjects found in this study may help us understand the variation of the biomechanical properties of cancellous bone in proximal human tibiae.

Patterns of mouthguard utilization among atom and pee wee minor ice hockey players: A pilot study

Objective:To determine if youth hockey players wear their mouthguards properly, and if not, why? Design:Descriptive cross-sectional study. Setting:Tecumseh Shoreline Minor Hockey Association, Tecumseh, Ontario, Canada, during the 2007-2008 season. Participants:Subjects were 180 travel hockey players of the Tecumseh Shoreline Minor Hockey Association at the Atom or Pee Wee level (aged 9-12 y) or their competitors. Assessment of Risk Factors:Players were asked to complete a survey addressing mouthguard wear under their coachs supervision. Main Outcome Measures:The type of mouthguard, whether mouthguards were worn at all and worn properly, and the reasons for noncompliance. The incidence of concussion and association to mouthguard-wearing tendencies were also assessed. Results:Sixty-eight percent [95% confidence interval (CI), 60.4%-74.5%] of subjects always wore their mouthguards, but only 31.7% (95% CI, 25.0%-39.0%) wore them properly during games and 51.1% (95% CI, 43.6%-58.6%) during practice. Custom-made mouthguards were most likely to be worn properly, followed by boil-and-bite and stock-type guards. Younger players wore mouthguards more consistently than older players (P < 0.01). Reasons for not wearing the guard included the following: 43.0% (95% CI, 35.4%-50.4%) of subjects felt it made talking difficult, 27.4% (95% CI, 20.9%-34.3%) felt it uncomfortable, 23.9% (95% CI, 17.9%-30.8%) felt it made breathing difficult, and 12.4% (95% CI, 8.3%-17.9%) thought it did not fit correctly. The incidence of concussion was 17.8%, but the study was underpowered for any association with mouthguard type. Conclusions:Even when mouthguards are mandated to be worn in a childrens travel hockey league, young players self-report that they routinely fail to wear them properly.

Femoral Cortical Bone Mineral Density and Biomechanical Properties in Sheep Consuming an Acidifying Diet

Dietary acidity is a likely contributor to the development of osteoporosis. Dietary acidosis in an ovine model has effects on trabecular bone that have been previously shown to mimic human osteoporosis. Effects on cortical bone using this model have not been investigated. The objective of this study was to examine the effects of dietary acidosis on cortical bone mineral density and material properties. Skeletally mature ovariectomized (OVX) sheep consumed either a normal diet (ND) or a metabolic acidosis diet (MA) for 6 or 12 months. Whole femoral and cortical bone beam BMD was determined using dual energy x-ray absorptiometry (DEXA). Beams were then subjected to three point flexure monotonically to failure to determine strength and modulus and then ashed to determine percent mineralization. Femoral BMD in adult OVX ND 6 mo sheep was significantly greater than those in the non-OVX ND group. The BMD in the MA groups was lower than the control non-OVX ND group. Cortical beams had significantly decreased modulus in all MA and OVX groups when compared with the non-OVX ND group and a tendency towards decreased strength in all groups with significance only in the OVX ND 6 mo sheep. Percent mineralization increased in MA and OVX groups when compared to the non-OVX ND group and was significantly increased in the OVX ND 6 mo and OVX MA 12 mo groups. A significant correlation was seen between BMD of the beam and breaking strength and modulus. Dietary acidity impacts cortical bone and results in reduced material properties that may contribute to failure.

Use of MicroRNA biomarkers to distinguish enchondroma from low-grade chondrosarcoma

ABSTRACT Establishing a definitive diagnosis between benign enchondroma versus low-grade chondrosarcoma presents a potential challenge to both clinicians and pathologists. microRNAs (small non-coding RNAs) have proven to be effective biomarkers for the identification of tumors and tumor progression. We present analysis, both array and quantitative PCR, that shows consistently and substantially increased expression of two microRNAs, miRs-181a and -138, in low-grade chondrosarcomas compared with enchondromas. The data suggest these microRNAs would provide an analytical distinction between the chondrosarcoma and benign neoplasms that can be performed in formalin-fixed paraffin-embedded specimens. Together with recent publications, these data indicate that miRs-181a and -138 also play a role in tumor development and homeostasis and may provide new targets for the development of much needed therapeutic intervention.