Despite its presence in orthopaedic infections, Staphylococcus epidermidis's ability to directly induce inflammation and bone destruction is unknown. Thus, we compared a clinical strain of methicillin‐resistant biofilm‐producing S. epidermidis (RP62A) to a highly virulent and osteolytic strain of methicillin‐resistant Staphylococcus aureus (USA300) in an established murine implant‐associated osteomyelitis model. Bacterial burden was assessed by colony forming units (CFUs), tissue damage was assessed by histology and micro‐computed tomography, biofilm was assessed by scanning electron microscopy (SEM), host gene expression was assessed by quantitative polymerase chain reaction, and osseous integration was assessed via biomechanical push‐out test. While CFUs were recovered from RP62A‐contaminated implants and surrounding tissues after 14 days, the bacterial burden was significantly less than USA300‐infected tibiae (p < 0.001). In addition, RP62A failed to produce any of the gross pathologies induced by USA300 (osteolysis, reactive bone formation, Staphylococcus abscess communities, marrow necrosis, and biofilm). However, fibrous tissue was present at the implant‐host interface, and rigorous SEM confirmed the rare presence of cocci on RP62A‐contaminated implants. Gene expression studies revealed that IL‐1β, IL‐6, RANKL, and TLR‐2 mRNA levels in RP62A‐infected bone were increased versus Sterile controls. Ex vivo push‐out testing showed that RP62A‐infected implants required significantly less force compared with the Sterile group (7.5 ± 3.4 vs. 17.3 ± 4.1 N; p < 0.001), but required 10‐fold greater force than USA300‐infected implants (0.7 ± 0.3 N; p < 0.001). Taken together, these findings demonstrate that S. epidermidis is a commensal pathogen whose mechanisms to inhibit osseous integration are limited to minimal biofilm formation on the implant, and low‐grade inflammation. © 2019 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 38:852‐860, 2020

Treatment of implant-associated orthopedic infections remains challenging, partly because antimicrobial treatment is ineffective after a mature biofilm covers the implant surface. Currently, the relative efficacy of systemic mono-and combination standard-of-care (SOC) antibiotic therapies over the course of mature biofilm formation is unknown. Thus, we assessed the effects of cefazoline (CEZ), gentamicin (GM), and vancomycin, with or without rifampin (RFP), on Staphylococcus aureus biofilm formation during the establishment of implant-associated osteomyelitis in a murine tibia model. Quantitative scanning electron microscopy of the implants harvested on Days 0, 3, and 7 revealed that all treatments except CEZ monotherapy significantly reduced biofilm formation when antibiotics started at Day 0 (0.46-to 0.25-fold; p < 0.05). When antibiotics commenced 3 days after the infection, only GM monotherapy significantly inhibited biofilm growth (0.63-fold; p < 0.05), while all antibiotics inhibited biofilm formation in combination with RFP (0.56-to 0.44-fold; p < 0.05). However, no treatment was effective when antibiotics commenced on Day 7. To confirm these findings, we assessed bacterial load via colony-forming unit and histology. The results showed that GM monotherapy and all combination therapies reduced the colony-forming unit in the implant (0.41-to 0.23-fold; p < 0.05); all treatments except CEZ monotherapy reduced the colony-forming unit and staphylococcus abscess communities in the tibiae (0.40-to 0.10-fold; p < 0.05). Collectively, these findings demonstrate that systemic SOC antibiotics can inhibit biofilm formation within 3 days but not after 7 days of infection. The efficacy of SOC monotherapies, CEZ particularly, is very limited. Thus, combination treatment with RFP may be necessary to inhibit implant-associated osteomyelitis.

Background Rheumatoid arthritis (RA) is known to cause secondary osteoporosis and fragility fractures. This study aimed to identify biomarkers predictive of bone mineral density (BMD) change at three anatomical sites in patients with RA. Methods We conducted a prospective longitudinal study in patients with RA. In 2012, we recruited 379 patients from an RA cohort, 329 of whom underwent evaluation of blood and urine biomarkers together with measurement of BMD in the lumbar spine, proximal femur, and distal forearm. The BMD in these three regions was reassessed in 2014. We performed multivariate linear regression analysis to identify those factors associated with BMD change. Results The averages of age, body mass index, and disease activity score in 28 joints (DAS28) at baseline were 63.2 (minimum to maximum, 32–85), 21.3 (12.3–30.0), and 3.2 (0.1–5.9), respectively. Univariate analysis showed that the annual BMD change was significantly associated with the use of steroid, bisphosphonate (BP) or vitamin D (VitD), and serum homocysteine in the lumber spine; DAS28, the use of BP or VitD, CRP, and anti-cyclic citrullinated peptide antibody (ACPA) in the proximal femur; and the dosage of MTX, the use of BP or VitD, and serum tartrate-resistant acid phosphatase 5b (TRACP-5b) in the distal forearm, respectively. Conclusions Predictive biomarkers for BMD change in RA patients differ at each anatomical site. Practitioners should treat each anatomical site with different markers and prescribe osteoporosis drugs to prevent fractures for RA patients.

Nonsurgical treatment such as exercise is the preferred method for management of knee osteoarthritis (OA). A combination of aerobic, muscle strengthening, and flexibility exercises is recommended for older adults. However, effects of the exercise intervention on cartilage metabolism remain unclear. This study used biomarkers to investigate the effects of well-rounded exercise program on cartilage metabolism in 42 women (mean age: 59 years). Participants started a weekly supervised exercise program and continued for 12 weeks. Before and after the program, we measured physical performance on the Timed Up-and-Go Test, 3-Minute Walk Test, and 30-Second Chair Stand Test. We collected serum and urine samples at the start of the program until 24 weeks and measured the concentrations of 4 biomarkers related to type II collagen metabolism: serum cartilage type II procollagen carboxy propeptide (sPIICP), urine C-terminal telopeptide of collagen type II (uCTX-II), urine cleavage of type II collagen by collagenases (uC2C), and serum cartilage oligomeric matrix protein (sCOMP). Participants were divided into pre-OA and OA groups based on X-ray findings. The pre-OA group showed significant increases and decreases in sPIICP and uCTX-II concentrations with improved physical performance, respectively. sCOMP concentrations significantly increased in both groups. The exercise also improved physical performance with no detrimental effect on type II collagen metabolism in the OA group. Thus, well-rounded exercise may not only improve physical capacity but also have beneficial effects on type II collagen metabolism, especially in people without radiological OA.

The formation of a biofilm on the implant surface is a major cause of intractable implant-associated infection. To investigate the antibiotic concentration needed to eradicate the bacteria inside a biofilm, the minimum biofilm eradication concentration (MBEC) has been used, mostly against in vitro biofilms on plastic surfaces. To produce a more clinically relevant environment, an MBEC assay against biofilms on stainless-steel implants formed in a rat femoral infection model was developed. The rats were implanted with stainless steel screws contaminated by two Staphylococcus aureus strains (UAMS-1, methicillin-sensitive Staphylococcus aureus; USA300LAC, methicillin-resistant Staphylococcus aureus) and euthanized on days 3 and 14. Implants were harvested, washed, and incubated with various concentrations (64–4096 μg/mL) of gentamicin (GM), vancomycin (VA), or cefazolin (CZ) with or without an accompanying systemic treatment dose of VA (20 μg/mL) or rifampicin (RF) (1.5 μg/mL) for 24 h. The implant was vortexed and sonicated, the biofilm was removed, and the implant was re-incubated to determine bacterial recovery. MBEC on the removed biofilm and implant was defined as in vivo MBEC and in vivo implant MBEC, respectively, and the concentrations of 100% and 60% eradication were defined as MBEC100 and MBEC60, respectively. As for in vivo MBEC, MBEC100 of GM was 256–1024 μg/mL, but that of VA and CZ ranged from 2048–4096 μg/mL. Surprisingly, the in vivo implant MBEC was much higher, ranging from 2048 μg/mL to more than 4096 μg/mL. The addition of RF, not VA, as a secondary antibiotic was effective, and MBEC60 on day 3 USA300LAC biofilm was reduced from 1024 μg/mL with GM alone to 128 μg/mL in combination with RF and the MBEC60 on day 14 USA300LAC biofilm was reduced from 2048 μg/mL in GM alone to 256 μg/mL in combination with RF. In conclusion, a novel MBEC assay for in vivo biofilms on orthopedic implants was developed. GM was the most effective against both methicillin-sensitive and methicillin-resistant Staphylococcus aureus, in in vivo biofilms, and the addition of a systemic concentration of RF reduced MBEC of GM. Early initiation of treatment is desired because the required concentration of antibiotics increases with biofilm maturation.