The gut microbiota may be a novel pathogenic mechanism in loosening of orthopedic implants in rats.

Particles released from implants cause inflammatory bone loss, which is a key factor in aseptic loosening, the most common reason for joint replacement failure. With the anticipated increased incidence of total joint replacement in the next decade, implant failure will continue to burden patients. The gut microbiome is increasingly recognized as an important factor in bone physiology, however, its role in implant loosening is currently unknown. We tested the hypothesis that implant loosening is associated with changes in the gut microbiota in a preclinical model. When the particle challenge caused local joint inflammation, decreased peri-implant bone volume, and decreased implant fixation, the gut microbiota was affected. When the particle challenge did not cause this triad of local effects, the gut microbiota was not affected. Our results suggest that cross-talk between these compartments is a previously unrecognized mechanism of failure following total joint replacement.

Skeletal consequences of preterm birth in pigs as a model for preterm infants.

Preterm birth affects about 10% of all live births with many resultant health challenges, including metabolic bone disease of prematurity (MBDP) which is characterized by elevated alkaline phosphatase, suppressed phosphate, and deficient skeletal development. Because of the lack of an animal model, very little is known about bone structure, strength, and quality after preterm birth. This study investigated the utility of a pig model to replicate clinical features of preterm birth, including MBDP, and sought to determine if early postnatal administration of insulin-like growth factor (IGF)-1 was an effective treatment. Preterm pigs, born by caesarean section at 90% gestation, were reared in intensive care facilities (respiratory, thermoregulatory and nutritional support) and compared with sow-reared term pigs born vaginally. Preterm pigs were systemically treated with vehicle or IGF-1 (recombinant human IGF-1/BP-3, 2.25 mg/kg/day). Tissues were collected at postnatal days 1, 5, and 19 (the normal weaning period in pigs). Most bone-related outcomes were affected by preterm birth throughout the study period whereas IGF-1 supplementation had almost no effect. By day 19, alkaline phosphatase was elevated, phosphate and calcium were reduced, and the bone resorption marker CTX-1 was elevated in preterm pigs compared to term pigs. Preterm pigs also had decrements in femoral cortical cross-sectional properties, consistent with reduced whole-bone strength. Thus, the preterm pig model replicates many features of preterm bone development in infants, including features of MBDP, and allows for direct interrogation of skeletal tissues, enhancing the field's ability to examine underlying mechanisms.

Premature birth interrupts a critical period of skeletal development as the majority of fetal bone mineral accumulation occurs during the last gestational trimester, leaving preterm infants at increased risk for low bone mineral density and fractures. While there are some data on growth in bone mass in preterm infants, very little is known about bone structural properties, quality, and strength during development after preterm birth. In this study we sought to evaluate the pig as a model for postnatal skeletal development after premature birth. Preterm pigs born after approximately 90% of the full gestation period were compared to full-term control pigs through day 19 of life. Levels of two blood markers used to diagnose osteoporosis of prematurity were replicated in the pig model. Bone properties related to strength were reduced even when accounting for their smaller body size, possibly suggesting elevated fracture risk in preterm infants. Based on the similarities between the preterm pig model and preterm human infants, the pig model may prove to be useful to study factors and interventions affecting postnatal bone development after preterm birth.

CXCR4 mediates the effects of IGF-1R signaling in rodent bone homeostasis and fracture repair.

Non-union fractures have considerable clinical and economic burdens and yet the underlying pathogenesis remains largely undetermined. The fracture healing process involves cellular differentiation, callus formation and remodeling, and implies the recruitment and differentiation of mesenchymal stem cells that are not fully characterized. C-X-C chemokine receptor 4 (CXCR4) and Insulin-like growth factor 1 receptor (IGF-1R) are expressed in the fracture callus, but their interactions still remain elusive. We hypothesized that the regulation of CXCR4 by IGF-1R signaling is essential to maintain the bone homeostasis and to promote fracture repair. By using a combination of in vivo and in vitro approaches, we found that conditional ablation of IGF-1R in osteochondroprogenitors led to defects in bone formation and mineralization that associated with altered expression of CXCR4 by a discrete population of endosteal cells. These defects were corrected by AMD3100 (a CXCR4 antagonist). Furthermore, we found that the inducible ablation of IGF-1R in osteochondroprogenitors led to fracture healing failure, that associated with an altered expression of CXCR4. In vivo AMD3100 treatment improved fracture healing and normalized CXCR4 expression. Moreover, we determined that these effects were mediated through the IGF-1R/Insulin receptor substrate 1 (IRS-1) signaling pathway. Taken together, our studies identified a novel population of endosteal cells that is functionally regulated through the modulation of CXCR4 by IGF-1R signaling, and such control is essential in bone homeostasis and fracture healing. Knowledge gained from these studies has the potential to accelerate the development of novel therapeutic interventions by targeting CXCR4 signaling to treat non-unions.

Colon epithelial cell-specific Bmal1 deletion impairs bone formation in mice.

The circadian clock system regulates multiple metabolic processes, including bone metabolism. Previous studies have demonstrated that both central and peripheral circadian signaling regulate skeletal growth and homeostasis in mice. Disruption in central circadian rhythms has been associated with a decline in bone mineral density in humans and the global and osteoblast-specific disruption of clock genes in bone tissue leads to lower bone mass in mice. Gut physiology is highly sensitive to circadian disruption. Since the gut is also known to affect bone remodeling, we sought to test the hypothesis that circadian signaling disruption in colon epithelial cells affects bone. We therefore assessed structural, functional, and cellular properties of bone in 8 week old Ts4-Cre and Ts4-Cre;Bmal1fl/fl (cBmalKO) mice, where the clock gene Bmal1 is deleted in colon epithelial cells. Axial and appendicular trabecular bone volume was significantly lower in cBmalKO compared to Ts4-Cre 8-week old mice in a sex-dependent fashion, with male but not female mice showing the phenotype. Similarly, the whole bone mechanical properties were deteriorated in cBmalKO male mice. The tissue level mechanisms involved suppressed bone formation with normal resorption, as evidenced by serum markers and dynamic histomorphometry. Our studies demonstrate that colon epithelial cell-specific deletion of Bmal1 leads to failure to acquire trabecular and cortical bone in male mice.

Alcohol and Circadian Disruption Minimally Impact Bone Properties in Two Cohorts of Male Mice While Between-Cohort Differences Predominate: Association With Season of Birth?

Many lifestyle factors affect bone. Sleep deprivation increases risk for fractures and alcohol consumption can lead to alterations in the skeleton. How combined exposure to these two risk factors affects bone is unclear. Thus, we sought to determine the effects of circadian rhythm disruption and chronic alcohol intake on bone structure and mechanical properties in mice. A total of 120 male C57BL/6J mice were used in two cohorts of 60 mice each because of limited availability of light-tight housing cabinets. One cohort was born in winter and the other in summer. Mice were randomly assigned to circadian disruption (weekly shifting of the light/dark cycle) and control (no shifting) groups beginning at 8 to 12 weeks of age for 12 weeks at which time mice were administered an alcohol-containing or control diet for an additional 10 weeks. Bone structure and mechanical properties of the femur were assessed by micro-computed tomography and three-point bending, respectively. The initial data analysis revealed a likely cohort effect. Thus, we used a three-way analysis of variance to assess the effects of circadian rhythm disruption, alcohol intake, and cohort. Circadian rhythm disruption alone had minimal effects on bone structure and mechanical properties. Alcohol intake reduced body mass and had minimal effects on cortical bone regardless of circadian disruption. Alcohol intake resulted in higher trabecular bone volume, but these beneficial effects were blunted when circadian rhythm was disrupted. Cohort significantly affected body size, many cortical bone structure outcomes, some trabecular bone structure outcomes, and tissue-level material properties. Thus, cohort had the predominant effect on bone structure and mechanical properties in this study, with chronic alcohol intake and environmental circadian disruption having less consistent effects. The data indicate that season of birth may affect skeletal phenotypes and that studies requiring multiple cohorts should determine if a cohort effect exists. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Comparison of Bone Turnover Biomarkers in Serum and Urine Measured on an Automated Analytical Platform.

BACKGROUND: Matched serum and urine samples from patients who had total hip replacement were used to assess serum-validated immunoassay reagents for use in urine. METHODS: Samples were evaluated by an automated electrochemiluminescent immunoassay (cobas e411; Roche Diagnostics) for C-terminal telopeptide of type I collagen isoform ß (ß-Crosslaps), osteocalcin N-terminal midfragment (N-MID OC), N-terminal propeptide of type I collagen (PINP), and interleukin 6 (IL-6). Spike and recovery experiments were utilized to assess urinary matrix effects. Correlations between serum and both raw and creatinine-corrected urinary measures were assessed. Short-term precision was assessed. RESULTS: Spike and recovery experiments indicated minimal matrix effects of urine for the ß-Crosslaps assay. Potential matrix effects were observed for the other analytes because N-MID OC and IL-6 tended to be slightly overrecovered, whereas PINP was underrecovered. There were strong correlations between serum ß-Crosslaps and raw (Spearman ρ [rs] = 0.725, P < 0.0001) and creatinine-corrected (rs = 0.793, P < 0.0001) urinary measures and moderate correlations between serum N-MID OC and raw (rs = 0.582, P < 0.0001) and creatinine-corrected (rs = 0.482, P < 0.0001) urinary measures. PINP was not detected in urine, and no significant serum-urine correlations were found for IL-6. Short-term precision for urinary levels of ß-Crosslaps, N-MID OC, and IL-6 were 1.6%, 6.3% and 14.4%, respectively. CONCLUSIONS: Urinary measurements of ß-Crosslaps and N-MID OC assays were correlated with serum measurements and had good short-term precision. Urinary PINP was not detectable. IL-6 can be measured in urine using this technology, but the levels did not correlate with serum levels, and the short-term precision was variable.

The Use of Serum Procalcitonin in the Setting of Infected Ureteral Stones: A Prospective Observational Study.

Introduction: Infected ureteral stones are a urologic emergency and require urgent decompression. We set out to determine whether serum procalcitonin (PCT) could aid in the diagnosis of infected ureteral stones. Methods: All consecutive patients presenting to the emergency room from November 9, 2016, to November 10, 2018, with an obstructing ureteral stone were included. All patients had complete blood count, urinalysis (UA), PCT, and urine culture (UCx). Subgroup analysis was performed in a "clinically equivocal" cohort of afebrile patients defined as a leukocytosis >104/µL and UA with <50 white blood cells (WBCs) per high powered field (hpf). Patients with positive and negative UCx were compared. Results: A total of 231 patients were included, of whom 56 had a positive UCx. Of all covariates, UA WBCs with a cutoff of 9 per hpf performed best at predicting positive UCx with an area under the curve (AUC) of 0.87. PCT did not perform as well with an ideal cutoff of 0.08 ng/mL, having an AUC of 0.77, sensitivity 70.6%, specificity 73.9%, positive predictive value (PPV) 34.3%, and negative predictive value (NPV) 92.9%. When looking at the clinically equivocal cohort, UA WBCs with a cutoff of 6 per hpf appeared to perform best at predicting a positive UCx with an AUC of 0.72. PCT was less predictive in this cohort with an ideal cutoff of 0.3 ng/mL, having an AUC of 0.32, sensitivity 47.1%, specificity 85.2%, PPV 38.1%, and NPV 89.3%. Conclusion: PCT does not appear to be a superior marker for diagnosing urinary tract infection in the setting of obstructing ureterolithiasis when compared with components of the standard work-up.

Correlating Spatial Ability With Anatomy Assessment Performance: A Meta-Analysis.

Interest in spatial ability has grown over the past few decades following the emergence of correlational evidence associating spatial aptitude with educational performance in the fields of science, technology, engineering, and mathematics. The research field at large and the anatomy education literature on this topic are mixed. In an attempt to generate consensus, a meta-analysis was performed to objectively summarize the effects of spatial ability on anatomy assessment performance across multiple studies and populations. Relevant studies published within the past 50 years (1969-2019) were retrieved from eight databases. Study eligibility screening was followed by a full-text review and data extraction. Use of the Mental Rotations Test (MRT) was required for study inclusion. Out of 2,450 screened records, 15 studies were meta-analyzed. Seventy-three percent of studies (11 of 15) were from the United States and Canada, and the majority (9 of 15) studied professional students. Across 15 studies and 1,245 participants, spatial ability was weakly associated with anatomy performance (rpooled  = 0.240; CI at 95% = 0.09, 0.38; P = 0.002). Performance on spatial and relationship-based assessments (i.e., practical assessments and drawing tasks) was correlated with spatial ability, while performance on assessments utilizing non-spatial multiple-choice items was not correlated with spatial ability. A significant sex difference was also observed, wherein males outperformed females on spatial ability tasks. Given the role of spatial reasoning in learning anatomy, educators are encouraged to consider curriculum delivery modifications and a comprehensive assessment strategy so as not to disadvantage individuals with low spatial ability.

Early changes in serum osteocalcin and body weight are predictive of implant fixation in a rat model of implant loosening.

Biomarkers are of interest to identify patients at risk for peri-implant osteolysis and aseptic loosening. We used a rat model of particle-induced peri-implant osteolysis to investigate if early changes in biomarkers were associated with subsequent implant fixation strength. Implants were placed in rat femora, which were then challenged with intra-articular knee injections of either clean polyethylene, lipopolysaccharide-doped polyethylene, or cobalt-chromium alloy particles, with particle-free vehicle serving as control (n ≥ 8 per group). Rats were weighed weekly, blood was collected at weeks 0, 3, 5, and 6, and locomotor behavior was assessed 4 days before study conclusion. Rats were euthanized 6 weeks post surgery. Week 6 serum was analyzed for five bone remodeling markers, while longitudinal serum was assessed for osteocalcin. Bone-implant contact, peri-implant trabecular architecture, and implant fixation strength were measured. Rats challenged with cobalt-chromium particles had a significant reduction in implant fixation strength compared with the vehicle-control group (P = .034). This group also had elevated serum osteocalcin (P = .005), depressed weight gain (P = .001) and less frequent rearing behavior (P = .029). Regardless of group, change in serum osteocalcin at week 3 (r = -.368; P = .046), change in weight at week 2 (r = .586; P < .001), as well as weight change at all other time intervals were associated with fixation strength. The finding that early alterations in serum osteocalcin and body weight were predictive of subsequent implant fixation strength supports continued investigation of biomarkers for early detection of peri-implant osteolysis and implant loosening. Further, change in biomarker levels was found to be more indicative of implant fixation status than any single measurement.

Arthrotomy-based preclinical models of particle-induced osteolysis: A systematic review.

We completed a systematic literature review of in vivo animal models that use arthrotomy-based methods to study particle-induced peri-implant osteolysis. The purpose of the review was to characterize the models developed to date, to determine the questions addressed, to assess scientific rigor and transparency, and to identify gaps in knowledge. We probed three literature databases (Medline, Embase, and Scopus) and found 77 manuscripts that fit the search parameters. In the most recent 10 years, researchers mainly used rat and mouse models, whereas in the previous 20 years, large animal, canine, and rabbit models were more common. The studies have demonstrated several pathophysiology pathways, including macrophage migration, particle phagocytosis, increased local production of cytokines and lysosomal enzymes, elevated bone resorption, and suppressed bone formation. The effect of variation in particle characteristics and concentration received limited attention with somewhat mixed findings. Particle contamination by endotoxin was shown to exacerbate peri-implant osteolysis. The possibility of early diagnosis was demonstrated through imaging and biomarker approaches. Several studies showed that both local and systemic delivery of bisphosphonates inhibits the development of particle-induced osteolysis. Other methods of inhibiting osteolysis include the use of anabolic agents and altering the implant design. Few studies examined non-surgical rescue of loosened implants, with conflicting results with alendronate. We found that the manuscripts often lacked the methodological detail now advocated by the ARRIVE guidelines, suggesting that improvement in reporting would be useful to maximize rigor and transparency. © 2017 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2595-2605, 2017.

Selective cues to forget can fail to cause forgetting.

Recent research has found that individuals can selectively forget a subset of items through directed forgetting. The goal of the present study was to replicate this selective directed forgetting effect and elucidate its underlying mechanisms. Unfortunately, results from four experiments failed to find any evidence of selective directed forgetting. Participants failed to forget any items when instructed to forget a subset of items from a first list before learning a second list. Participants were only successful in forgetting items from the first list when they were instructed to forget all items from the first list before learning the second list.