Constraints to hydraulic acclimation under reduced light in two contrasting Phaseolus vulgaris cultivars.

Two cultivars of Phaseolus vulgaris L. were grown under three light levels to determine if hydraulic acclimation to light occurs in herbaceous annuals and whether intraspecific trade-offs constrain hydraulic traits. Acclimation occurred in response to reduced light and included decreased stomatal density (SD) and increased specific leaf area (SLA). Reduced light resulted in lower wood density (WD); decreased cavitation resistance, measured as the xylem pressure causing a 50 % reduction in stem conductivity (P50); and increased hydraulic capacity, measured as average leaf mass specific transpiration (E(LM)). Significant or marginally significant trade-offs between P50 and WD, WD and E(LM), and E(LM) and P50 reflected variation due to both genotype and environmental effects. A trade-off between WD and P50 within one cultivar indicated that morphological adjustment was constrained. Coordinated changes in WD, P50, and E(LM) within each cultivar in response to light were consistent with trade-offs constraining plasticity. A water-use efficiency (WUE, measured as δ(13)C) versus hydraulic capacity (E(LM)) trade-off was observed within each cultivar, further indicating that hydraulic trade-offs can constrain acclimation. Larger plants had lower hydraulic capacity (E(LM)) but greater cavitation resistance, WD, and WUE. Distinct hydraulic strategies were observed with the cultivar adapted to irrigated conditions having higher stomatal conductance and stem flow rates. The cultivar adapted to rain-fed conditions had higher leaf area and greater cavitation resistance. Hydraulic trade-offs were observed within the herbaceous P. vulgaris resulting from both genotype and environmental effects. Trade-offs within a cultivar reflected constraints to hydraulic acclimation in response to changing light.

Ultrasound assessment of dorsal lisfranc ligament strain under clinically relevant loads.

BACKGROUND: Pure Lisfranc ligament injuries have a varied clinical presentation, making them difficult to diagnose. This study seeks to understand in vivo strain characteristics of the dorsal Lisfranc ligament under clinically relevant stress loads and foot orientations measured by ultrasound. METHODS: Randomized ultrasound imaging trials were performed on 50 asymptomatic feet of 20-to-32-year-old individuals who were free of lower-extremity abnormalities. The dorsal Lisfranc ligament was ultrasound imaged under low, medium, and high stress while at 0° and 15° abducted foot orientations. Load was applied using a seated calf-raise apparatus, and a single examiner performed all of the tests. Two-way repeated-measures analysis of variance was used to determine any significant load or position main effects or load × position interaction. RESULTS: Position main effect for dorsal Lisfranc ligament length demonstrated a significant overall increase in ligament length of 0.21 mm (P < .001), which reflects a 4.03% change in ligament length between the rectus and 15° abducted orientations. Furthermore, low and medium loads demonstrated significant length increase with position effect (P = .03 and P < .001, respectively). No significant load main effect or interaction was determined. CONCLUSIONS: Dorsal Lisfranc ligament length undergoes more strain in an abducted foot position at the same load compared with in a rectus foot. We advocate measuring under a medium load if possible and comparing foot positions for the maximum length changes. The participant stress loads and foot positions used are clinically feasible, which makes it possible to perform this ultrasound procedure in the clinical setting.

Reliability of ultrasound imaging in the assessment of the dorsal Lisfranc ligament.

BACKGROUND: The Lisfranc ligament plays an integral role in providing stability to the midfoot. Variable clinical presentations and radiographic findings make injuries to the Lisfranc ligament notoriously difficult to diagnose. Currently, radiographic evaluation is the mainstay in imaging such injuries; however, ultrasound has been suggested as a viable alternative. The objective of this study was to evaluate the intra-rater and inter-rater reliability in the measurement of the length of the dorsal Lisfranc ligament using ultrasound imaging in healthy, asymptomatic subjects. METHODS: The dorsal Lisfranc ligaments of fifty asymptomatic subjects (n = 100 feet) were imaged using a Siemens SONOLINE Antares Ultrasound Imaging System© under low, medium, and high stress loads at 0° and 15° abducted foot positions. The lengths of the ligaments were measured, and Interclass correlation coefficients were used to calculate within-session intra-rater reliability (n = 100 feet) as well as between-session intra-rater reliability (n = 40 feet) and between-session inter-rater reliability (n = 40 feet). RESULTS: The within-session intra-rater reliability results for dorsal Lisfranc ligament length had an average ICC of 0.889 (min 0.873 max 0.913). The average ICC for between-session intra-rater reliability was 0.747 (min 0.607 max 0.811). The average ICC for between-session inter-rater reliability was 0.685 (min 0.638 max 0.776). CONCLUSIONS: The measurement of the dorsal Lisfranc ligament length using ultrasound imaging shows substantial to almost perfect reliability when evaluating asymptomatic subjects. This imaging modality methodology shows promise and lays the foundation for further work in technique development towards the diagnostic identification of pathology within the Lisfranc ligament complex.

Ultrasound assessment of bilateral symmetry in dorsal Lisfranc ligament.

Bilateral symmetry of the ligaments is a common assumption used as an intrasubject control for clinical diagnosis. The present study investigated the bilateral symmetry of the dorsal Lisfranc ligament (dLL) using ultrasound. Data were acquired from 50 asymptomatic subjects in a seated position at a loaded calf raise machine equipped with a force plate. The testing conditions included low, medium, and high stress at 0° and 15° abducted foot positions. Images of the dLL were captured and measured using a 10.0-MHz ultrasound transducer and custom written MATLAB software, respectively. The data were analyzed using paired t tests to compare the bilateral measurements of the dLL length under all test conditions. The bilateral pooled dLL length was 7.01 ± 1.38 mm and showed a moderate correlation with the foot length and width. No bilateral differences were found in the dLL length under any of the stress loads in the abducted position or under the medium and high stress load in the rectus position. However, the low stress load rectus position demonstrated a significant bilateral difference in the dLL length (p = .005). The smallest bilateral difference was observed at the 15° abducted position under medium stress (measurement error mean -0.062 mm). Our data suggest that the contralateral dLL length can be used as an intrasubject control for clinical purposes. However, we recommend that the dLL length measurements should be taken in weightbearing position with the foot in the abducted position under medium stress (bilateral stance), reducing potential strain-induced asymmetry.