Can Normal Fracture Healing Be Achieved When the Implant Is Retained on the Basis of Infection? An Experimental Animal Model

Background

Infection after open fractures is a common complication. Treatment options for infections developed after intramedullary nailing surgery remain a topic of controversy. We therefore used a rat fracture model to evaluate the effects of infection on osseous union when the implant was maintained.

Questions/purposes

In a rat model, (1) does infection alter callus strength; (2) does infection alter the radiographic appearance of callus; and (3) does infection alter the histological properties of callus?

Methods

An open femoral fracture was created and fixed with an intramedullary Kirschner wire in 72 adult male Sprague-Dawley rats, which were divided into two study groups. In the infection group, the fracture site was contaminated with Staphylococcus aureus (36 animals), whereas in the control group, there was no bacterial contamination (36 animals). No antibiotics were used either for prophylaxis or for treatment. We performed biomechanical (maximum torque causing failure and stiffness), radiographic (Lane and Sandhu scoring for callus formation), and histologic (scoring for callus maturity) assessments at 3 and 6 weeks. The number of bacteria colonies on the femur, wire, and soft tissue inside knee were compared to validate that we successfully created an infection model. The number of bacteria colonies in the soft tissue inside the knee was higher in the infection group after 6 weeks than after the third week, demonstrating the presence of locally aggressive infection.

Results

Infection decreased callus strength at 6 weeks. Torque to failure (299.07 ± 65.53 Nmm versus 107.20 ± 88.81, mean difference with 95% confidence interval, 192 [43–340]; p = 0.007) and stiffness at 6 weeks (11.28 ± 2.67 Nmm versus 2.03 ± 1.68, mean difference with 95% confidence interval, 9 [3–16]; p = 0.004) both were greater in the control group than in the group with infection. Radiographic analysis at 6 weeks demonstrated the fracture line was less distinct (Lane and Sandhu score of 2–3) in the infection group and complete union was observed (Lane and Sandhu score of 3–4) in the control group (p = 0.001). Semiquantitative histology scores were not different between the noninfected controls and the rats with infection (score 10 versus 9).

Conclusions

Retaining an implant in the presence of an underlying infection without antibiotic treatment leads to weaker callus and impedes callus maturation compared with noninfected controls in a rat model. Future studies might evaluate whether antibiotic treatment would modify this result.

Clinical Relevance

This model sets the stage for further investigations that might study the influence of different interventions on fracture healing in implant-associated osteomyelitis. Future observational studies might also evaluate the histological properties of callus in patients with osteomyelitis.     

Beneficial effect of methylprednisolone on cardiac myocytes in a rat model of severe brain injury

Cardiac injury, occurred after traumatic brain injury (TBI), has been recognized for more than a century. Bcl-2 is a key regulatory component of the mitochondrial cell death pathway, and its overexpression is cytoprotective in many cell types. The therapeutic agents, which induce the expression of bcl-2 protein, might provide a new therapy to prevent cardiac myocyte damage following TBI. In this study, we investigated whether methylprednisolone sodium succinate (MPSS) influences the expression of bcl-2 in the heart. Wistar-Albino female rats underwent TBI (300 g/cm) generated by the weight-drop method, and were left untreated (n = 6) or treated with either MPSS (30 mg/kg) (n = 6) or vehicle (albumin solution) (n = 6). The heart was isolated from each animal with TBI. For comparison, the hearts were isolated from sham-operated (n = 6) and control rats (n = 6). The relative expression of bcl-2 mRNA in the heart was quantitated by real-time polymerase chain reaction. We also assessed lipid peroxidation in the heart tissue by determining the concentration of thiobarbituric acid-reactive substances (TBARs) as an indicator of tissue damage. The bcl-2 expression level was significantly higher in the hearts of MPSS-treated rats compared to that of other TBI groups (p < 0.0001). Moreover, TBI increased the lipid peroxidation in the heart, which was significantly reduced by the treatment with MPSS (p < 0.0001). These findings provide evidence for the efficacy of MPSS in protection of cardiac myocytes to achieve optimal heart donation after TBI in heart transplantation.     

Can a b value of 500 be substituted for a b value of 1000 in the characterization of focal liver lesions?

Purpose

Comparison of two different b values in diffusion-weighted magnetic resonance imaging (DWI) for characterization of focal liver lesions.

Methods

A total of 174 focal liver lesions from 100 patients were analyzed using two different b values (500 and 1000 s/mm²). The DWI with b values of 500 s/mm² (DWI500) and 1000 s/mm² (DWI1000) were analyzed using the Mann–Whitney test, kappa statistic, and paired t test with respect to image quality. The statistically significant differences between DWI500 and DWI1000 in the characterization of the lesions with respect to the cutoff ADC values were evaluated via χ ² test.

Results

DWI500 had the highest mean score in the qualitative evaluation of image quality (p < 0.0001) and the highest signal-to-noise ratio (8.7 ± 2.1; p < 0.0001). The sensitivity, specificity, and AUC for discriminating malignant from benign focal lesions on DWI500 and DWI1000 using cutoff ADC values of 1.54 × 10^?3 and 1.38 × 10^?3 s/mm² were 95.8%, 92.3%, 0.98, and 93.8%, 92.3%, 0.97, respectively. There was no statistically significant difference in sensitivity, specificity, and AUC values between DWI500 and DWI1000 with respect to the cutoff ADC values (p > 0.05).

Conclusions

The image quality of DWI500 was better than that of DWI1000, and there was no significant difference between DWI500 and DWI1000 in the characterization of the lesions with respect to the cutoff ADC values. The b value of 500 s/mm² can be substituted for the b value of 1000 s/mm² in the characterization of focal liver lesions.     

Docking for fragment inhibitors of AmpC β-lactamase

Fragment screens for new ligands have had wide success, notwithstanding their constraint to libraries of 1,000–10,000 molecules. Larger libraries would be addressable were molecular docking reliable for fragment screens, but this has not been widely accepted. To investigate docking's ability to prioritize fragments, a library of >137,000 such molecules were docked against the structure of β-lactamase. Forty-eight fragments highly ranked by docking were acquired and tested; 23 had K_i values ranging from 0.7 to 9.2 mM. X-ray crystal structures of the enzyme-bound complexes were determined for 8 of the fragments. For 4, the correspondence between the predicted and experimental structures was high (RMSD between 1.2 and 1.4 Å), whereas for another 2, the fidelity was lower but retained most key interactions (RMSD 2.4–2.6 Å). Two of the 8 fragments adopted very different poses in the active site owing to enzyme conformational changes. The 48% hit rate of the fragment docking compares very favorably with “lead-like” docking and high-throughput screening against the same enzyme. To understand this, we investigated the occurrence of the fragment scaffolds among larger, lead-like molecules. Approximately 1% of commercially available fragments contain these inhibitors whereas only 10⁻⁷% of lead-like molecules do. This suggests that many more chemotypes and combinations of chemotypes are present among fragments than are available among lead-like molecules, contributing to the higher hit rates. The ability of docking to prioritize these fragments suggests that the technique can be used to exploit the better chemotype coverage that exists at the fragment level.