The CFL fails before the ATFL immediately after combined ligament repair in a biomechanical cadaveric model.

PURPOSE: To assess the impact on ankle stability after repairing the ATFL alone compared to repairing both the ATFL and CFL in a biomechanical cadaver model. METHODS: Ten matched pairs of intact, fresh frozen human cadaver ankles (normal) were mounted to a test machine in 20.0° plantar flexion and 15.0° of internal rotation. Each ankle was loaded to body weight and then tested from 0.0° to 20.0° of inversion. The data recorded were torque at 20.0° and stiffness, peak pressure and contact area in the ankle joint using a Tekscan sensor, rotation of the talus and calcaneus, and translation of the calcaneus using a three-dimensional motion capture system. Ankles then underwent sectioning of the ATFL and CFL (injured), retested, then randomly assigned to ATFL-only Broström repair or combined ATFL and CFL repair. Testing was repeated after repair then loaded in inversion to failure (LTF). RESULTS: The stiffness of the ankle was not significantly increased compared to the injured condition by repairing the ATFL only (n.s.) or the ATFL/CFL (n.s.). The calcaneus had significantly more rotation than the injured condition in the ATFL-only repair (p = 0.037) but not in the ATFL/CFL repair (n.s.). The ATFL failed at 40.3% higher torque than the CFL, at 17.4 ± 7.0 N m and 12.4 ± 4.1 N m, respectively, and 62.0% more rotation, at 43.9 ± 5.6° and 27.1 ± 6.8°, respectively. CONCLUSIONS: There was a greater increase in stiffness following combined ATFL/CFL repair compared to ATFL-only repair, although this did not reach statistical significance. The CFL fails before the ATFL, potentially indicating its vulnerability immediately following repair. LEVEL OF EVIDENCE: III, case-control therapeutic study.

Biomechanical Comparison of Low-Profile Contoured Locking Plate With Single Compression Screw to Fully Threaded Compression Screws for First MTP Fusion.

BACKGROUND: Open metatarsophalangeal (MTP) arthrodesis using locked plates produces good clinical outcomes. However, arthroscopic fusion with new-generation fully threaded compression screws is emerging as an alternative. The purpose of this study was to compare low-profile contoured locked plates with fully threaded compression screws for first MTP fusion, in a biomechanical cadaveric model. METHODS: The first rays of 8 matched pairs of fresh frozen cadaveric feet underwent dissection and dual-energy x-ray absorptiometry (DEXA) scanning to measure bone mineral density (BMD). The "plate" group was prepared with cup-and-cone reamers, and fixation of the MTP joint with 1 compression screw and low-profile dorsal locked plate. The matched-pair "screws" group was prepared through a simulated arthroscopic technique, achieving fixation with 2 new-generation fully threaded compression screws. The plantar MTP gap was recorded with an extensometer during 250 000 90-N cyclic loads followed by a single load to failure. RESULTS: The screw group demonstrated significantly greater stiffness, 31.6 N/mm (plates) and 51.7 N/mm (screws) (P = .0045). There was no significant difference in plantar gapping or load to failure, 198.6 N (plates) and 290.1 N (screws) (P = .2226). Stiffness and load to failure were highly correlated to BMD for the screw group, r =0.79 and r = 0.94, respectively, but less so for the plate group, r = 0.36 and r = 0.62, respectively. The maximum metatarsal head height measured on the lateral view was strongly correlated with load to failure for both the plate- and screw-only groups (r > 0.9). CONCLUSION: These data demonstrate that hallux MTP arthrodesis utilizing fully threaded compression screws had similar plantar gapping and load to failure when compared with the low-profile locking plate, but with significantly more stiffness. These results support an increased role of fully threaded screws for MTP arthrodesis using either the arthroscopic or open technique. However, with decreased BMD plate fixation may remain the better fixation choice. CLINICAL RELEVANCE: Our data suggest that with regard to construct stability, fully threaded headless compression screws may be just as effective as low-profile locking plates, but BMD and MTP joint fluoroscopic measurements should be considered in the decision-making process for fixation.

The Role of Calcaneofibular Ligament Injury in Ankle Instability: Implications for Surgical Management.

BACKGROUND: Acute inversion ankle sprains are among the most common musculoskeletal injuries. Higher grade sprains, including anterior talofibular ligament (ATFL) and calcaneofibular ligament (CFL) injury, can be particularly challenging. The precise effect of CFL injury on ankle instability is unclear. HYPOTHESIS: CFL injury will result in decreased stiffness, decreased peak torque, and increased talar and calcaneal motion and will alter ankle contact mechanics when compared with the uninjured ankle and the ATFL-only injured ankle in a cadaveric model. STUDY DESIGN: Descriptive laboratory study. METHODS: Ten matched pairs of cadaver specimens with a pressure sensor in the ankle joint and motion trackers on the fibula, talus, and calcaneus were mounted on a material testing system with 20° of ankle plantarflexion and 15° of internal rotation. Intact specimens were axially loaded to body weight and then underwent inversion along the anatomic axis of the ankle from 0° to 20°. The ATFL and CFL were sequentially sectioned and underwent inversion testing for each condition. Linear mixed models were used to determine significance for stiffness, peak torque, peak pressure, contact area, and inversion angles of the talus and calcaneus relative to the fibula across the 3 conditions. RESULTS: Stiffness and peak torque did not significantly decrease after sectioning of the ATFL but decreased significantly after sectioning of the CFL. Peak pressures in the tibiotalar joint decreased and mean contact area increased significantly after CFL release. Significantly more inversion of the talus and calcaneus as well as calcaneal medial displacement was seen with weightbearing inversion after sectioning of the CFL. CONCLUSION: The CFL contributes considerably to lateral ankle instability. Higher grade sprains that include CFL injury result in significant decreases in rotation stiffness and peak torque, substantial alteration of contact mechanics at the ankle joint, increased inversion of the talus and calcaneus, and increased medial displacement of the calcaneus. CLINICAL RELEVANCE: Repair of an injured CFL should be considered during lateral ligament reconstruction, and there may be a role for early repair in high-grade injuries to avoid intermediate and long-term consequences of a loose or incompetent CFL.

Temperature-dependent deliquescent and efflorescent properties of methanesulfonate sodium studied by ATR-FTIR spectroscopy.

Modeling of aerosols and cloud formation processes in the marine boundary layer (MBL) require extensive data on hygroscopic properties of relevant methanesulfonate particles, which are currently scarce. In this work, methanesulfonate sodium (CH3SO3Na, MSA-Na), the most abundant methanesulfonate salt, was selected, and its deliquescent and efflorescent properties at temperatures relevant to the lower troposphere were studied using an ATR-FTIR flow system. To validate the approach, we investigated hygroscopic properties of NaCl particles, and our measured deliquescent relative humidity (DRH) and efflorescent relative humidity (ERH) of the NaCl particles obtained from the changes in integrated absorbance of water peaks in infrared spectra agreed with literature data well. We then reported DRH and ERH of MSA-Na particles as a function of temperature for the first time using both the changes in integrated absorbance of water peaks and the changes in peak position and shape of CH3SO3(-) symmetric and asymmetric vibrational modes. Our experiments showed that MSA-Na particles present quite different temperature-dependent hygroscopic behaviors from NaCl. Both the DRH and ERH of MSA-Na particles increase with decreasing temperatures. Due to the significant differences in temperature-dependent DRH and ERH, NaCl particles, if processed in MBL by methanesulfonic acid, are expected to deliquesce slightly earlier during a hydration process but effloresce at a much earlier stage during a dehydration process, especially at lower temperatures. This could considerably influence phase, size, and water content of sea salt aerosols and consequently their reactivity, lifetime, and impacts on atmospheric chemistry and climate systems.

Kinetics study of heterogeneous reactions of ozone with erucic acid using an ATR-IR flow reactor.

The ozone initiated heterogeneous oxidation of erucic acid (EA) thin film was investigated using a flow system combined with attenuated total reflection infrared spectroscopy (ATR-IR) over wide ranges of ozone concentrations (0.25-60 ppm), thin film thickness (0.1-1.0 µm), temperatures (263-298 K), and relative humidities (0-80% RH) for the first time. Pseudo-first-order rate constants, kapp, and overall reactive uptake coefficients, γ, were obtained through changes in the absorbance of C[double bond, length as m-dash]O stretching bands at 1695 cm(-1), which is assigned to the carbonyl group in carboxylic acid. Results showed that the reaction followed the Langmuir-Hinshelwood mechanism and kapp was largely dominated by surface reaction over bulk phase reaction. In addition, both the kapp and the γ values showed very strong temperature dependences (∼two orders of magnitude) over the temperature range; in contrast, they only slightly increased with increasing RH values from 0-80%. According to the kapp values as a function of temperature, the activation energy for the heterogeneous reaction was estimated to be 80.6 kJ mol(-1). Our results have suggested that heterogeneous reactions between ozone and unsaturated solid surfaces likely have a substantially greater temperature dependence than liquid ones. Moreover, the hygroscopic properties of EA thin films before and after exposure to ozone were also studied by measurement of water uptake. Based on the hygroscopicity data, the insignificant RH effect on reaction kinetics was probably due to the relatively weak water uptake by the unreacted and reacted EA thin films.

Temperature-dependent Henry's law constants of atmospheric organics of biogenic origin.

There have been growing interests in modeling studies to understand oxidation of volatile organic compounds in the gas phase and their mass transfer to the aqueous phase for their potential roles in cloud chemistry, formation of secondary organic aerosols, and fate of atmospheric organics. Temperature-dependent Henry's law constants, key parameters in the atmospheric models to account for mass transfer, are often unavailable. In the present work, we investigated gas-liquid equilibriums of isoprene, limonene, α-pinene, and linalool using a bubble column technique. These compounds, originating from biogenic sources, were selected for their implications in atmospheric cloud chemistry and secondary organic aerosol formation. We reported Henry's law constants (K(H)), first order loss rates (k), and gas phase diffusion coefficients over a range of temperatures relevant to the lower atmosphere (278-298 K) for the first time. The measurement results of K(H) values for isoprene, limonene, α-pinene, and linalool at 298 K were 0.036 ± 0.003; 0.048 ± 0.004; 0.029 ± 0.004; and 21.20 ± 0.30 mol L(-1) atm(-1), respectively. The fraction for these compounds in stratocumulus and cumulonimbus clouds at 278 K were also estimated in this work (isoprene, 1.0 × 10(-6), 6.8 × 10(-6); limonene, 1.5 × 10(-6), 1.0 × 10(-5); α-pinene, 4.5 × 10(-7), 3.1 × 10(-6); and linalool, 6.2 × 10(-4), 4.2 × 10(-3)). Our measurements in combination with literature results indicated that noncyclic alkenes could have smaller K(H) values than those of cyclic terpenes and that K(H) values may increase with an increasing number of double bonds. It was also shown that estimated Henry's law constants and their temperature dependence based on model prediction can differ from experimental results considerably and that direct measurements of temperature-dependent Henry's law constants of atmospheric organics are necessary for future work.

ATR-IR study of ozone initiated heterogeneous oxidation of squalene in an indoor environment.

There has been a surge of interest in interfacial ozone chemistry for its application in indoor air quality and public health. Squalene, one of the most abundant ozone reactive constituents in an indoor environment, has received increasing attention lately, and a number of studies have been devoted to its heterogeneous interaction with ozone in actual and simulated settings. At present, there is still a large discrepancy in the measurement of the reactive uptake coefficient of ozone onto a squalene surface, and knowledge about this system remains incomplete. In this work, we investigated the ozone initiated heterogeneous oxidation of squalene using attenuated total reflection infrared spectroscopy (ATR-IR). We measured pseudo-first-order rate constants and uptake coefficients based on time dependent absorbance changes in C═C (1668 cm(-1)) and C═O (1730 cm(-1)) vibration bands. The uptake coefficients are (1.7 ± 0.2) × 10(-4) from the C═C band and (5.1 ± 0.7) × 10(-4) from the C═O band. The latter is likely an upper limit of reaction probability for ozone uptake onto squalene. Studies of temperature (5-32 °C) and relative humidity (0 and 80% RH) dependence revealed that indoor temperatures and RHs did not affect reaction kinetics. The insignificant RH effect is probably due to the weak interaction between water and squalene molecules. We quantitatively characterized the hydrophilicity and redox activity of squalene before and after exposure to ozone for the first time, and observed considerable enhancements in both hydrophilicity and redox activity during reaction. This may imply that ozone initiated heterogeneous oxidation could pose a higher public health risk in an indoor environment, and it may help explain some of the adverse health effects associated with elevated indoor pollutants.