Standardization of study design and outcome parameters would help to compare different studies evaluating various novel therapeutic concepts. Comparison to the human clinical counterpart during study design may help increase the predictive value of preclinical research using animal models and improve the process of developing efficacious therapies.

Nucleus pulposus (NP) cells of the intervertebral disc reside in an environment that has a limited vascular supply and generate energy through anaerobic glycolysis. The goal of the present study was to examine the expression and regulation of HIF-1alpha, a transcription factor that regulates oxidative metabolism in nucleus pulposus cells. Nucleus pulposus cells were isolated from rat, human, and sheep disc and maintained at either 21% or 2% oxygen for various time periods. Cells were also treated with desferrioxamine (Dfx), a compound that mimics the effects of hypoxia (Hx). Expression and function of HIF-1alpha were assessed by immunofluorescence microscopy, Western blot analysis, gel shift assays, and luciferase reporter assays. In normoxia (Nx), rat, sheep, and human nucleus pulposus cells consistently expressed the HIF-1alpha subunit. Unlike other skeletal cells, when maintained under low oxygen tension, the nucleus pulposus cells exhibited a minimal induction in HIF-1alpha protein levels. Electromobility shift assays confirmed the functional binding of normoxic HIF-1alpha protein to its putative DNA binding motif. A dual luciferase reporter assay showed increased HIF-1alpha transcriptional activity under hypoxia compared to normoxic level, although this induction was small when compared to HeLa and other cell types. These results indicate that normoxic stabilization of HIF-1alpha is a metabolic adaptation of nucleus pulposus cells to a unique oxygen-limited microenvironment. The study confirmed that HIF-1alpha can be used as a phenotypic marker of nucleus pulposus cells.

The goal of this mini-review is to address the long standing argument that the pathogenesis of disc disease is due to the loss and/or the replacement of the notochordal cells by other cell types. We contend that although cells of different size and morphology exist, there is no strong evidence to support the view that the nucleus pulposus contains cells of distinct lineages. Based on lineage mapping studies and studies of other notochordal markers, we hypothesize that in all animals including human, nucleus pulposus retains notochordal cells throughout life. Moreover, all cells including chondrocyte-like cells are derived from notochordal precursors and that variations in morphology and size are representative of different stages of maturation, and or, function. Thus, the most critical choice for a suitable animal model should relate more to the anatomical, and mechanical characteristics of the motion segment than concerns of cell loss and replacement by non-notochordal cells.

Study Design Experimental measurement and normalization of in vitro disc torsion mechanics and collagen content for several animal species used in intervertebral disc research and comparing these to the human disc. Objective To aid in the selection of appropriate animal models for disc research by measuring torsional mechanical properties and collagen content. Summary of Background Data There is lack of data and variability in testing protocols for comparing animal and human disc torsion mechanics and collagen content. Methods Intervertebral disc torsion mechanics were measured and normalized by disc height and polar moment of inertia for 11 disc types in 8 mammalian species: the calf, pig, baboon, goat, sheep, rabbit, rat, and mouse lumbar, and cow, rat, and mouse caudal. Collagen content was measured and normalized by dry weight for the same discs except the rat and mouse. Collagen fiber stretch in torsion was calculated using an analytical model. Results Measured torsion parameters varied by several orders of magnitude across the different species. After geometric normalization, only the sheep and pig discs were statistically different from human. Fiber stretch was found to be highly dependent on the assumed initial fiber angle. The collagen content of the discs was similar, especially in the outer annulus where only the calf and goat discs were statistically different from human. Disc collagen content did not correlate with torsion mechanics. Conclusion Disc torsion mechanics are comparable to human lumbar discs in 9 of 11 disc types after normalization by geometry. The normalized torsion mechanics and collagen content of the multiple animal discs presented is useful for selecting and interpreting results for animal models of the disc. Structural composition of the disc, such as initial fiber angle, may explain the differences that were noted between species after geometric normalization.

The bony remodeling observed in this model system appears to be a biological phenomena and not a result of altered mechanical loading, with the depth of the focal chondral defect (partial vs. full thickness) dictating the bony remodeling response. The type of cartilage injury should be carefully controlled in studies utilizing this model to evaluate TE approaches for cartilage repair.

Biofilm-associated implant-related bone and joint infections are clinically important due to the extensive morbidity, cost of care and socioeconomic burden that they cause. Research in the field of biofilms has expanded in the past two decades, however, there is still an immense knowledge gap related to many clinical challenges of these biofilm-associated infections. This subject was assigned to the Biofilm Workgroup during the second International Consensus Meeting on Musculoskeletal Infection held in Philadelphia USA (ICM 2018) (https://icmphilly.com). The main objective of the Biofilm Workgroup was to prepare a consensus document based on a review of the literature, prepared responses, discussion, and vote on thirteen biofilm related questions. The Workgroup commenced discussing and refining responses prepared before the meeting on day one using Delphi methodology, followed by a tally of responses using an anonymized voting system on the second day of ICM 2018. The Working group derived consensus on information about biofilms deemed relevant to clinical practice, pertaining to: (1) surface modifications to prevent/inhibit biofilm formation; (2) therapies to prevent and treat biofilm infections; (3) polymicrobial biofilms; (4) diagnostics to detect active and dormant biofilm in patients; (5) methods to establish minimal biofilm eradication concentration for biofilm bacteria; and (6) novel anti-infectives that are effective against biofilm bacteria. It was also noted that biomedical research funding agencies and the pharmaceutical industry should recognize these areas as priorities. ß

Bacterial invasion of synovial joints, as in infectious or septic arthritis, can be difficult to treat in both veterinary and human clinical practice. Biofilms, in the form of free-floating clumps or aggregates, are involved with the pathogenesis of infectious arthritis and periprosthetic joint infection (PJI). Infection of a joint containing an orthopedic implant can additionally complicate these infections due to the presence of adherent biofilms. Because of these biofilm phenotypes, bacteria within these infected joints show increased antimicrobial tolerance even at high antibiotic concentrations. To date, animal models of PJI or infectious arthritis have been limited to small animals such as rodents or rabbits. Small animal models, however, yield limited quantities of synovial fluid making them impractical for in vitro research. Herein, we describe the use of ex vivo equine and porcine models for the study of synovial fluid induced biofilm aggregate formation and antimicrobial tolerance. We observed Staphylococcus aureus and other bacterial pathogens adapt the same biofilm aggregate phenotype with significant antimicrobial tolerance in both equine and porcine synovial fluid, analogous to human synovial fluid. We also demonstrate that enzymatic dispersal of synovial fluid aggregates restores the activity of antimicrobials. Future studies investigating the interaction of bacterial cell surface proteins with host synovial fluid proteins can be readily carried out in equine or porcine ex vivo models to identify novel drug targets for treatment of prevention of these difficult to treat infectious diseases.

Overall rate of POI was 28%. Fracture classification, method of repair, gender, and surgical duration were significant risk factors.