Effect of Hamstring-to-quadriceps Ratio on Knee Forces in Females During Landing.

ACL injuries in the athletic population are a common occurrence with over 70% associated with non-contact mechanisms. The hamstring to quadriceps ratio is a widely used clinical measure to assess an athlete's readiness to return to sport; however, its relationship to knee forces and ACL tension during landing is unknown. Baseline isokinetic testing was completed on 100 college-aged females. Subjects with strength ratios 0.4 (n=20) and those with ratios of 0.6 (n=20) returned for an assessment of their drop landing. A sagittal plane knee model determined the low ratio group demonstrated 16.6% larger ligament shear (p=0.000), a 26% increase in tibiofemoral shear force (p=0.026) and a 6% increase vertical force between the femur and tibial plateau (p=0.026) compared to the high hamstring ratio group within 100 ms upon impact. The lower ratio group also demonstrated 9.5% greater maximal quadriceps (p=0.028) force during landing. These findings suggest that the hamstring to quadriceps ratio may be related to knee forces and ACL loading during landing. This metric may augment clinical decision making regarding an athlete's readiness to return to sport or relative risk for re-injury.

Comparison of estimates of Achilles tendon loading from inverse dynamics and inverse dynamics-based static optimisation during running.

Tendon stress may be one of the important risk factors for running-related tendon injury. Several methods have been used to estimate Achilles tendon (AT) loading during a human performance such as inverse dynamics (ID) and inverse dynamics-based static optimisation (IDSO). Our purpose was to examine differences between ID and IDSO estimates of AT loading during running. Kinematic data were captured simultaneously with kinetic data. Imaging of the AT cross-sectional area was performed with ultrasound for 17 healthy runners (height: 170.2 ± 6.2 cm, mass: 63.9 ± 11.0 kg, age: 21.8 ± 1.4 years). AT stress, strain, and force were estimated from both ID and IDSO approaches. The two methods resulted in minimal differences (3.6-4.7%) in estimated peak AT stress, strain, and force (P = 0.051-0.054); however, IDSO estimates were greater (32.7-36.8%) during early-stance phase of running (P = 0.000-0.008). This difference in AT load during early-stance may be due to the inability of the ID to account muscle coactivation. The similarity between the peak AT loading for ID and IDSO methods revealed that the advantage of IDSO used to estimate muscle forces had little effect on the ankle plantar flexor peak forces during running. Therefore, the use of IDSO with a higher computational cost compared with ID may not be necessary for estimating AT stress during running.

Effects of Foot Strike and Step Frequency on Achilles Tendon Stress During Running.

Achilles tendon (AT) injuries are common in runners. The AT withstands high magnitudes of stress during running which may contribute to injury. Our purpose was to examine the effects of foot strike pattern and step frequency on AT stress and strain during running utilizing muscle forces based on a musculoskeletal model and subject-specific ultrasound-derived AT cross-sectional area. Nineteen female runners performed running trials under 6 conditions, including rearfoot strike and forefoot strike patterns at their preferred cadence, +5%, and -5% preferred cadence. Rearfoot strike patterns had less peak AT stress (P < .001), strain (P < .001), and strain rate (P < .001) compared with the forefoot strike pattern. A reduction in peak AT stress and strain were exhibited with a +5% preferred step frequency relative to the preferred condition using a rearfoot (P < .001) and forefoot (P=.005) strike pattern. Strain rate was not different (P > .05) between step frequencies within each foot strike condition. Our results suggest that a rearfoot pattern may reduce AT stress, strain, and strain rate. Increases in step frequency of 5% above preferred frequency, regardless of foot strike pattern, may also lower peak AT stress and strain.

Two- and Three-Dimensional Relationships Between Knee and Hip Kinematic Motion Analysis: Single-Leg Drop-Jump Landings.

CONTEXT: Hip- and knee-joint kinematics during drop landings are relevant to lower-extremity injury mechanisms. In clinical research the "gold standard" for joint kinematic assessment is 3-dimensional (3D) motion analysis. However, 2-dimensional (2D) kinematic analysis is an objective and feasible alternative. OBJECTIVE: To quantify the relationship between 2D and 3D hip and knee kinematics in single-leg drop landings and test for a set of 3D hip and knee kinematics that best predicts 2D kinematic measures during single-leg drop landings Design: Descriptive, comparative laboratory study. PARTICIPANTS: 31 healthy college-age women (65.5 kg [SD 12.3], 168.1 cm [SD 6.7]). METHODS: Participants performed five 40-cm single-leg landings during motion capture at 240 Hz. Multiple regressions were used to predict relationships for knee and hip between 2D frontal-plane projection angles (FPPA) and 3D measurements. RESULTS: 2D knee FPPA had a strong relationship with 3D frontal-plane knee kinematics at initial contact (IC) (r2 = .72), which was only minimally improved with the addition of knee sagittal-plane and hip transverse-plane positions at IC (r2 = .77). In contrast, 2D knee FPPA had a low relationship with 3D knee-abduction excursion (r2 = .06). The addition of knee sagittal-plane and hip transverse-plane motions did not improve this relationship (r2 = .14). 2D hip FPPA had a moderate relationship with 3D frontal-plane hip position at IC (r2 = .52), which was strengthened with the addition of hip sagittal-plane position (r2 = .60). In addition, hip 2D FPPA into adduction excursion had a strong association with 3D hip-adduction excursion (r2 = .70). CONCLUSION: 2D kinematics can predict 3D frontal-plane hip and knee position at IC during a single-leg landing but predict 3D frontal-plane knee excursion with far less accuracy.

Simulated Y-Site Compatibility of Vancomycin and Piperacillin-Tazobactam.

PURPOSE: To evaluate the physical compatibility of vancomycin with piperacillin-tazobactam during simulated Y-site administration. METHODS: Vancomycin and piperacillin-tazobactam were tested using 2 different diluents: 0.9% sodium chloride and 5% dextrose for injection. Vancomycin concentrations of 2, 5, and 10 mg/mL were tested using 0.9% sodium chloride and 4 and 8 mg/mL in 5% dextrose. Piperacillin-tazobactam was diluted to 16, 30, 40, 80, and 100 mg/mL, representing common concentrations used clinically in hospitals, and concentrations were tested in both 0.9% sodium chloride and 5% dextrose for injection. Medications were reconstituted under USP <797> aseptic technique. Combinations were tested in duplicate and reverse order with control solutions. Compatibility testing for Y-site included visual inspection, inspection with a high-intensity monodirectional light source (Tyndall beam), turbidimeter for turbidity evaluation, pH, and microscopic viewing. Testing occurred immediately after mixing, 15 minutes, 60 minutes, and 4 hours. If inconsistencies were observed between samples, testing was repeated to confirm results. Solutions were deemed incompatible if any one test failed and compatible if all tests were accepted. RESULTS: When dextrose 5% for injection was used as the diluent, vancomycin 4 mg/mL was Y-site compatible with piperacillin-tazobactam 16, 30, and 40 mg/mL and incompatible with 80 and 100 mg/mL. Vancomycin 8 mg/mL was incompatible with all tested concentrations of piperacillin-tazobactam. When 0.9% sodium chloride was used as the diluents, Y-site compatibility was found with vancomycin 2 and 5 mg/mL and all tested concentrations of piperacillin-tazobactam. Vancomycin 10 mg/mL was incompatible with piperacillin-tazobactam 40, 80, and 100 mg/mL. Incompatibilities formed a white precipitate immediately on mixing. CONCLUSION: Y-site incompatibility was greater for the tested concentrations of piperacillin-tazobactam and vancomycin when 5% dextrose was used as the diluent versus 0.9% sodium chloride. Y-site incompatibility was seen immediately in the form of a white precipitate on mixing.

A quantitative evaluation of medication histories and reconciliation by discipline.

BACKGROUND/OBJECTIVE: Medication reconciliation at transitions of care decreases medication errors, hospitalizations, and adverse drug events. We compared inpatient medication histories and reconciliation across disciplines and evaluated the nature of discrepancies. METHODS: We conducted a prospective cohort study of patients admitted from the emergency department at our 760-bed hospital. Eligible patients had their medication histories conducted and reconciled in order by the admitting nurse (RN), certified pharmacy technician (CPhT), and pharmacist (RPh). Discharge medication reconciliation was not altered. Admission and discharge discrepancies were categorized by discipline, error type, and drug class and were assigned a criticality index score. A discrepancy rating system systematically measured discrepancies. RESULTS: Of 175 consented patients, 153 were evaluated. Total admission and discharge discrepancies were 1,461 and 369, respectively. The average number of medications per participant at admission was 8.59 (1,314) with 9.41 (1,374) at discharge. Most discrepancies were committed by RNs: 53.2% (777) at admission and 56.1% (207) at discharge. The majority were omitted or incorrect. RNs had significantly higher admission discrepancy rates per medication (0.59) compared with CPhTs (0.36) and RPhs (0.16) (P < .001). RPhs corrected significantly more discrepancies per participant than RNs (6.39 vs 0.48; P < .001); average criticality index reduction was 79.0%. Estimated prevented adverse drug events (pADEs) cost savings were $589,744. CONCLUSIONS: RPhs committed the fewest discrepancies compared with RNs and CPhTs, resulting in more accurate medication histories and reconciliation. RPh involvement also prevented the greatest number of medication errors, contributing to considerable pADE-related cost savings.

Method for the direct determination of available carbohydrates in low-carbohydrate products using high-performance anion exchange chromatography.

An improved method for direct determination of available carbohydrates in low-level products has been developed and validated for a low-carbohydrate soy infant formula. The method involves modification of an existing direct determination method to improve specificity, accuracy, detection levels, and run times through a more extensive enzymatic digestion to capture all available (or potentially available) carbohydrates. The digestion hydrolyzes all common sugars, starch, and starch derivatives down to their monosaccharide components, glucose, fructose, and galactose, which are then quantitated by high-performance anion-exchange chromatography with photodiode array detection. Method validation consisted of specificity testing and 10 days of analyzing various spike levels of mixed sugars, maltodextrin, and corn starch. The overall RSD was 4.0% across all sample types, which contained within-day and day-to-day components of 3.6 and 3.4%, respectively. Overall average recovery was 99.4% (n = 10). Average recovery for individual spiked samples ranged from 94.1 to 106% (n = 10). It is expected that the method could be applied to a variety of low-carbohydrate foods and beverages.

Variation of Anatomical and Physiological Parameters that Affect Estimates of ACL Loading During Drop Landing.

BACKGROUND: Anterior cruciate ligament (ACL) loading during drop landing has been recently studied with a sagittal plane knee model developed by Kernozek and Ragan using mean anatomical and physiological parameters obtained from cadaveric and clinical data. It is unknown how estimates in ACL load may be altered due to variations in anatomical and physiological parameters used from other research. METHODS: USING THE SAME MODEL, THESE PARAMETERS WERE SYSTEMATICALLY VARIED, INCLUDING: tibial slope, moment arms of the patellar tendon, hamstring, and gastrocnemius at the knee and ankle, patellar tendon and hamstring line of force, ACL stiffness, and nonlinear muscle activation parameters. To determine the sensitivity of the model to changes in these parameters, each was varied independently by ±5% and by ranges reported in the literature. Changes in maximum ACL load and shear force components of the patellar tendon, hamstring, and tibio-femoral contact force were calculated from drop landing data of 21 subjects. RESULTS: The variation in ACL load during drop landing from its nominal value was largest (-100% to 176%) when extremes in reported tibial slope values were utilized. Variation in the next most important parameter, patellar tendon line of force, affected ACL load by -72% to 88%. CONCLUSION: Variations in tibial slope and patellar tendon line of force had the greatest influence on estimated ACL loading during drop landing. Differences in these parameters between subjects may be just as important to ACL loading as the kinematic and kinetic performance differences observed in landing.

Estimation of anterior cruciate ligament tension from inverse dynamics data and electromyography in females during drop landing.

BACKGROUND: Recent human performance studies have shown that various kinematic and kinetic parameters may be implicated in non-contact anterior cruciate ligament (ACL) injury during landing and cutting. In this paper, a phenomenological sagittal plane model was used to estimate the ACL tension during drop landing from the net knee moments and forces, obtained from inverse dynamics and electromyography. METHODS: Model parameters were determined with data from anatomical and ACL loading studies of cadaveric specimens. The model was used to process averaged data from 60 cm drop landing trials of sixteen healthy females. FINDINGS: ACL loading during drop landing occurred during the between toe and heel impact with a peak tension of 0.15 body weight. The factors that contributed to ACL tension were the patellar tendon force and the tibial slope in combination with the joint axial loads. Factors responsible for reducing ACL tension were hamstring and ground reaction forces. INTERPRETATION: Sagittal plane results largely confirmed a previous forward dynamics study of landing. The knee appeared to be largely stabilized against abduction moments due to the large axial loads present during drop landing for typical landing trials. Rotational moments were small in drop landing and contributed little to ACL tension. Estimates from this model can be used in human performance studies to determine the relative amount of ACL tension produced in different landing scenarios.

Seat-interface pressures on various thicknesses of foam wheelchair cushions: a finite modeling approach.

OBJECTIVE: To investigate the effect of cushion thickness on subcutaneous pressures during seating by using a finite element modeling approach. DESIGN: Seat-interface pressure measurements were used in a computational model. SETTING: Biomechanics laboratory. PARTICIPANT: A single healthy man (weight, 70 kg). INTERVENTIONS: Subject sat upright either with or without cushions of various heights. Seat-interface pressures measured by using a sensor mat interfaced to a personal computer sampling at 15 Hz. MAIN OUTCOME MEASURES: Peak seat-interface pressure; finite-element software was used to model the buttock, ischial tuberosity, and seat cushion. Subcutaneous stresses were calculated from the model. RESULTS: The region of highest subcutaneous stress in the soft tissue was concentrated within 1 or 2 cm of the ischial tuberosity, with the maximum compressive stress inferior to the bottom surface of the ischial tuberosity. The maximum subcutaneous stress, maximum seat-interface pressure, and maximum subcutaneous shear stress each changed with cushion thickness. Subcutaneous pressures decreased with thicker cushions, but almost all of the reduction was obtained with an 8-cm cushion. The amount of subcutaneous shear stress increased slightly for thicker cushions. The maximum subcutaneous stress was greater than the maximum interface pressure but not by a constant factor. Instead, the former was consistently larger by 0.7 to 0.8 N/cm(2). CONCLUSIONS: Cushion use reduced the maximum subcutaneous stress inferior to the ischial tuberosity. However, increasing the cushion thickness beyond 8 cm was ineffective in further reducing subcutaneous stress. It was also found that seat-interface pressures were a good indicator of the subcutaneous stress reduction in seating.