The impact of cryosolution thermal contraction on proteins and protein crystals: volumes, conformation and order.

Cryocooling of macromolecular crystals is commonly employed to limit radiation damage during X-ray diffraction data collection. However, cooling itself affects macromolecular conformation and often damages crystals via poorly understood processes. Here, the effects of cryosolution thermal contraction on macromolecular conformation and crystal order in crystals ranging from 32 to 67% solvent content are systematically investigated. It is found that the solution thermal contraction affects macromolecule configurations and volumes, unit-cell volumes, crystal packing and crystal order. The effects occur through not only thermal contraction, but also pressure caused by the mismatched contraction of cryosolvent and pores. Higher solvent-content crystals are more affected. In some cases the solvent contraction can be adjusted to reduce mosaicity and increase the strength of diffraction. Ice formation in some crystals is found to cause damage via a reduction in unit-cell volume, which is interpreted through solvent transport out of unit cells during cooling. The results point to more deductive approaches to cryoprotection optimization by adjusting the cryosolution composition to reduce thermal contraction-induced stresses in the crystal with cooling.

Laboratory predictors for risk of revision surgery in pediatric septic arthritis.

BACKGROUND: Reported complications of pediatric septic arthritis range from minor growth abnormalities to potentially life-threatening conditions and death; some children require multiple surgeries for eradication of infection. The purpose of this study is: (1) to determine the failure rate of a single surgical incision and drainage (I&D) in pediatric septic arthritis, (2) to identify risk factors for failure which are detectable at the time of initial presentation, and (3) to trend post-operative C-reactive protein (CRP) values to see if there is a difference between children who fail a single I&D and those who do not. METHODS: The medical records for 105 children who underwent operative management of septic arthritis were retrospectively reviewed. Single and multivariate analyses were performed. RESULTS: Eighty-four children required one surgical intervention [mean age 5.18 years (±4.01); 38 females (45 %), 46 males (55 %)], 21 children required revision surgery [mean age 8.16 years (±4.54); 4 females (19 %), 17 males (81 %)], and the overall rate of revision surgery was 20 %. Delayed diagnosis (p = 0.015), elevated CRP at presentation (p = 0.000), positive blood culture (p = 0.000), and age (p = 0.009) were all associated with revision surgery in bivariate analysis. In multivariate analysis, CRP at presentation and positive blood culture were significant risk factors for revision surgery (p = 0.005 and p = 0.025, respectively). Additionally, markedly elevated CRP levels on post-operative days (POD) 1-4 were each independently significant risk factors for requiring multiple surgeries (all p < 0.000). Fever, elevated erythrocyte sedimentation rate, and leukocyte count were not risk factors for multiple surgeries. CONCLUSIONS: In this study, a positive blood culture or marked elevation in CRP at presentation or on POD 1-4 were associated with revision surgery. These findings may help improve surgical planning for both the initial surgery in order to avoid revisions, as well as revision surgery, should it be indicated. LEVEL OF EVIDENCE: III.