Determining the Ratio of Wedge Height to Degree of Correction for Anterior Tibial Closing Wedge Osteotomies for Excessive Posterior Tibial Slope

Background: Anterior closing wedge osteotomy of the proximal tibia may be considered in revision anterior cruciate ligament (ACL) reconstruction surgery for patients with excessive posterior tibial slope (PTS). Purpose: (1) To determine the ratio of wedge thickness to degrees of correction for supratubercle (ST) versus transtubercle (TT) osteotomies for anterior closing wedge osteotomies and (2) to evaluate the accuracy of ST and TT osteotomies in achieving slope correction. Study Design: Controlled laboratory study. Methods: The computed tomography (CT) scans of 38 knees in 37 patients undergoing revision ACL reconstruction were used to simulate both ST and TT osteotomies. A 10° wedge was simulated in all CT models. The height of the wedge along the anterior tibia was recorded for each of the 2 techniques. The ratio of wedge height to achieved degree of correction was calculated. ST and TT osteotomies were performed on 3-dimensional (3D)–printed tibias of the 12 patients from the study group with the greatest PTS, after the desired degree of correction was determined. Pre- and postosteotomy slopes were measured for each tibia, and the actual change in slope was compared with the intended slope correction. Results: According to CT measurements, the ratio of wedge height to degree of correction was 0.99 ± 0.07 mm/deg for the ST osteotomy and 0.83 ± 0.06 mm/deg for the TT osteotomy ( P < .001). When these ratios were used to perform simulated osteotomies on the twelve 3D-printed tibias, the mean slope correction was within 1° to 2° of the intended slope correction, regardless of osteotomy location (ST or TT) or whether slope was measured on the medial or lateral plateau. The ST technique tended to undercorrect and the TT technique tended to overcorrect. Conclusion: When anterior tibial closing wedge osteotomies were removed to correct excessive PTS, removing a wedge with a ratio of 1 mm of wedge height for every 1° of intended correction for an ST technique and a ratio of 0.8 mm to 1° for a TT technique resulted in overall average slope correction within 1° to 2° of the target. Clinical Relevance: The calculated ratios will allow clinicians to more accurately correct PTS when performing anterior closing wedge tibial osteotomy.

Evaluation of P-Band SAR Tomography for Mapping Tropical Forest Vertical Backscatter and Tree Height

Low-frequency tomographic synthetic aperture radar (TomoSAR) techniques provide an opportunity for quantifying the dynamics of dense tropical forest vertical structures. Here, we compare the performance of different TomoSAR processing, Back-projection (BP), Capon beamforming (CB), and MUltiple SIgnal Classification (MUSIC), and compensation techniques for estimating forest height (FH) and forest vertical profile from the backscattered echoes. The study also examines how polarimetric measurements in linear, compact, hybrid, and dual circular modes influence parameter estimation. The tomographic analysis was carried out using P-band data acquired over the Paracou study site in French Guiana, and the quantitative evaluation was performed using LiDAR-based canopy height measurements taken during the 2009 TropiSAR campaign. Our results show that the relative root mean squared error (RMSE) of height was less than 10%, with negligible systematic errors across the range, with Capon and MUSIC performing better for height estimates. Radiometric compensation, such as slope correction, does not improve tree height estimation. Further, we compare and analyze the impact of the compensation approach on forest vertical profiles and tomographic metrics and the integrated backscattered power. It is observed that radiometric compensation increases the backscatter values of the vertical profile with a slight shift in local maxima of the canopy layer for both the Capon and the MUSIC estimators. Our results suggest that applying the proper processing and compensation techniques on P-band TomoSAR observations from space will allow the monitoring of forest vertical structure and biomass dynamics.

First steps to bridging the gap between CryoSat-2 and ICESat2: retrackers and slope induced error.

&lt;p&gt;Satellite radar altimetry is one of the most important tools for monitoring changes in the mass balance of the world's ice sheets. Different altimetry techniques however, come with their own pitfalls. In radar altimetry, signal penetration into the snowpack introduces ambiguity in the origin of reflected echo, a major issue not present in laser altimetry. Fine tuning the developed processing algorithms for the CryoSat-2 radar altimetry data, using the IceSat2 laser altimetry data as a benchmark, may allow for a more precise surface elevation and snowpack depth estimations. Furthermore, bridging the gap between radar and laser altimetry will result in larger spatial and temporal data coverage when the two data sets are combined. &amp;#160;Focusing on Greenland Ice Sheet (GIS), we have developed a processing chain for the estimation of surface elevations and elevation changes from the ESA level-1 product (L1b) Baseline D. We investigated the importance of a retracker type, retracker threshold, Digital Elevation Model (DEM) in the slope correction, and how these affect the estimated surface elevation as compared to the ICESat2 data.&lt;/p&gt;&lt;p&gt;Firstly, ESA L1b Baseline-D data was processed at several different thresholds and with various waveform retracker algorithms, including threshold first maxima&amp;#160;retracker&amp;#160;algorithm (TFMRA) (Helm, 2012; Nilsson, 2015) and the offset center of gravity (OCOG) retracker algorithm (Bamber, 1994; Ricker et al. 2014). We then apply slope correction to adjust for the slope induced error in the radar altimetry data (Hurkmans, 2012), the correction was applied using three different DEMs, ArcticDEM Release 7 (Porter et al., 2018), Greenland Ice Mapping Project (GIMP) DEM (Howat et al., 2017) and &amp;#8216;Helm&amp;#8217; DEM (Helm, 2014). We checked all of the produced data sets against IceSat-2 data (Smith et al., 2019) corresponding to the same time period, and selected by nearest neighbor calculation for specified maximum distance. We analyze and discuss the differences between IceSat-2 data and CryoSat-2 data and their dependence on several radar altimetry processing parameters and methodologies.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

A New Approach for GNSS-IR Snow Depth Monitoring With Slope Correction and Error Prediction

With the continuous development of GNSS (Global Navigation Satellite System) technology, GNSS-IR (GNSS Interferometric Reflectometry) has become a research hotspot in the field of snow surface monitoring, and the accuracy and reliability have been initially verified. We focus on the reasons for the low accuracy of the existing GNSS-IR snow depth inversion. Therefore, we use the P351 station data in the PBO (Plate Boundary Observatory) network in the United States to monitor the snow depth during the four years from 2011 to 2015. The actual measured snow depth at station 490 in the SONTEL network is used as the true value for accuracy verification. We studied the relationship between the inversion error caused by the slope and the slope angle and the satellite elevation angle, and proposed a slope correction method. The results show that the RMSE (Root Mean Square Error) of snow depth inversion after slope correction is reduced from 12.1 cm to 10.7 cm, the accuracy is improved by 11.6 %. In addition, it is found that there is an apparent correlation between the retrieved snow depth and the inversion error. With the increase of snow depth, the error gradually changes from positive to negative, and the absolute value of error still increases with the increase of snow depth after the error changes to negative. To this end, we introduce BPNN (Back Propagation Neural Network) to train the inversion snow depth and inversion error of the three snowfall periods from 2011 to 2014, then predicts and corrects the snow depth inversion error during the snowfall period from 2014 to 2015. The results show that the RMSE of the corrected GNSS-IR snow depth inversion is reduced from 10.7 cm to 5.7 cm, and the accuracy is increased by 46.7 %. The overall accuracy of the GNSS-IR snow depth inversion is improved by 52.9 % after the slope correction and the BPNN error prediction is performed, which further verifies the accuracy and effective of the approach that proposed by us.

Effect of Slope and Varus Correction High Tibial Osteotomy in the ACL-Deficient and ACL-Reconstructed Knee on Kinematics and ACL Graft Force: A Biomechanical Analysis

Background: Correction of high posterior tibial slope is an important treatment option for revision of anterior cruciate ligament (ACL) failure as seen in clinical and biomechanical studies. In cases with moderate to severe medial compartment arthritis, an additional varus correction osteotomy may be added to improve alignment. Purpose: To investigate the influence of coronal and sagittal correction high tibial osteotomy in ACL-deficient and ACL-reconstructed knees on knee kinematics and ACL graft load. Study Design: Controlled laboratory study. Methods: Ten cadaveric knees were selected according to previous computed tomography measurements with increased native slope and slight varus tibial alignment (mean ± SD): slope, 9.9°± 1.4°; medial proximal tibia angle, 86.5°± 2.1°; age, 47.7 ± 5.8 years. A 10° anterior closing-wedge osteotomy, as well as an additional 5° of simulated varus correction osteotomy, were created and fixed using an external fixator. Four alignment conditions—native, varus correction, slope correction, and combined varus and slope correction—were randomly tested in 2 states: ACL-deficient and ACL-reconstructed. Compressive axial loads were applied to the tibia while mounted on a free-moving X-Y table and free-rotating tibia in a knee testing fixture. Three-dimensional motion tracking captured anterior tibial translation (ATT) and internal tibial rotation. Change of tensile forces on the reconstructed ACL graft were recorded. Results: In the ACL-deficient knee, an isolated varus correction led to a significant increase of ATT by 4.3 ± 4.0 mm ( P = .04). Isolated slope reduction resulted in the greatest decrease of ATT by 6.2 ± 4.3 mm ( P < .001). In the ACL-reconstructed knee, ATT showed comparable changes, while combined varus and slope correction led to lower ATT by 3.7 ± 2.6 mm ( P = .01) than ATT in the native alignment. Internal tibial rotation was not significantly altered by varus correction but significantly increased after isolated slope correction by 4.0°± 4.1° ( P < .01). Each isolated or combined osteotomy showed decreased forces on the graft as compared with the native state. The combined varus and slope osteotomy led to a mean decrease of ACL graft force by 33% at 200 N and by 58% at 400 N as compared with the native condition ( P < .001). Conclusion: A combined varus and slope correction led to a relevant decrease of ATT in the ACL-deficient and ACL-reconstructed cadaveric knee. ACL graft forces were significantly decreased after combined varus and slope correction. Thus, our biomechanical findings support the treatment goal of a perpendicular-aligned tibial plateau for ACL insufficiencies, especially in cases of revision surgery. Clinical Relevance: This study shows the beneficial knee kinematics and reduced forces on the ACL graft after combined varus and slope correction.

Numerical Study of Wind-Tunnel Wall Effects on Lift and Drag Characteristics of NACA 0012 Airfoil

Possible interference effects of the wind tunnel walls play an important role especially for measurements in closed-wall test sections. In this study, a numerical analysis of two-dimensional subsonic flow over a NACA 0012 airfoil at different computational domain heights, angles of attack from 0o to 10o, and operating Reynolds number of 6×106 is presented. The work highlights the role of computational fluid dynamics (CFD) in the investigation of wind tunnel wall effect on lift curve slope correction factor (Ka). The flow solution is obtained using Ansys Fluent software by solving the steady-state continuity and momentum governing equations combined with turbulence model k-v shear stress transport (SST-K?). The numerical results are validated by comparing with the available experimental measurements. Calculations show that the lift curve slope correction results are very close to the published data.