Mechanical Leg Research Articles

New Insights for the Design of Bionic Robots: Adaptive Motion Adjustment Strategies During Feline Landings

Felines have significant advantages in terms of sports energy efficiency and flexibility compared with other animals, especially in terms of jumping and landing. The biomechanical characteristics of a feline (cat) landing from different heights can provide new insights into bionic robot design based on research results and the needs of bionic engineering. The purpose of this work was to investigate the adaptive motion adjustment strategy of the cat landing using a machine learning algorithm and finite element analysis (FEA). In a bionic robot, there are considerations in the design of the mechanical legs. (1) The coordination mechanism of each joint should be adjusted intelligently according to the force at the bottom of each mechanical leg. Specifically, with the increase in force at the bottom of the mechanical leg, the main joint bearing the impact load gradually shifts from the distal joint to the proximal joint; (2) the hardness of the materials located around the center of each joint of the bionic mechanical leg should be strengthened to increase service life; (3) the center of gravity of the robot should be lowered and the robot posture should be kept forward as far as possible to reduce machine wear and improve robot operational accuracy.

Real-time adaptive leg-stiffness for roll compensation via magnetorheological control in a legged robot

Over the recent few decades, the evolving research-field of legged robotics has seen various mechanical and control-based developments. Inspired by biological species, a significant adaptation in modern mechanical leg designs has been the implementation of adjustable stiffness, shifting from what were previously simple linkages to more-complex variable stiffness actuators. Physiological studies previously demonstrated leg-stiffness modulation was not only a common trait in multiple biological locomotors, but also played a key role in disturbance recovery for humans. Guided by this, recent robotics research has shown that this can also be applied to legged robots to achieve similar locomotion adaptations, albeit often limited by the tuning time of leg stiffness in such circumstances. This study proposes real-time adaptive stiffness robot legs which are governed by fast-response magnetorheological fluid dampers, enabling stiffness adjustment upon a single step. Through experimental characterisation and model validation, these legs are shown to achieve a maximum stiffness shift of 114%. Enabled by real-time control during locomotion, improved performance and roll-angle stability is experimentally demonstrated for a bipedal robot test platform. Such improvement to locomotion is found through typical legged locomotion scenarios, with the platform encountering: obstacles, valleys, and coronal gradients in a comprehensive series of experiments.

No relevant mechanical leg axis deviation in the frontal and sagittal planes is to be expected after subtrochanteric or supracondylar femoral rotational or derotational osteotomy.

The purpose of this study was to investigate if one level of corrective femoral osteotomy (subtrochanteric or supracondylar) bears an increased risk of unintentional implications on frontal and sagittal plane alignment in a simulated clinical setting. Out of 100 cadaveric femora, 23 three-dimensional (3-D) surface models with femoral antetorsion (femAT) deformities (> 22° or < 2°) were investigated, and femAT normalized to 12° with single plane rotational osteotomies, perpendicular to the mechanical axis of the femur. Change of the frontal and sagittal plane alignment was expressed by the mechanical lateral distal femoral angle (mLDFA) and the posterior distal femoral angle (PDFA), respectively. The influence of morphologic factors of the femur [centrum-collum-diaphyseal (CCD) angle and antecurvatum radius (ACR)] were assessed. Furthermore, position changes of the lesser (LT) and greater trochanters (GT) in the frontal and sagittal plane compared to the hip centre were investigated. Mean femoral derotation of the high-antetorsion group (n = 6) was 12.3° (range 10-17°). In the frontal plane, mLDFA changed a mean of 0.1° (-0.06 to 0.3°) (n.s.) and -0.3° (-0.5 to -0.1) (p = 0.03) after subtrochanteric and supracondylar osteotomy, respectively. In the sagittal plane, PDFA changed a mean of 1° (0.7 to 1.1) (p = 0.03) and 0.3° (0.1 to 0.7) (p = 0.03), respectively. The low-antetorsion group (n = 17) was rotated by a mean of 13.8° (10°-23°). mLDFA changed a mean of -0.2° (-0.5° to 0.2°) (p < 0.006) and 0.2° (0-0.5°) (p < 0.001) after subtrochanteric and supracondylar osteotomy, respectively. PDFA changed a mean of 1° (-2.3 to 1.3) (p < 0.01) and 0.5° (-1.9 to 0.3) (p < 0.01), respectively. The amount of femAT correction was associated with increased postoperative deviation of the mechanical leg axis (p < 0.01). Using multiple regression analysis, no other morphological factors were found to influence mLDFA or PDFA. Internal rotational osteotomies decreased the ischial-lesser trochanteric space by < 5mm in both the frontal and sagittal plane (p < 0.001). In case of femAT correction of ≤ 20°, neither subtrochanteric nor supracondylar femoral derotational or rotational osteotomies have a clinically relevant impact on frontal or sagittal leg alignment. A relevant deviation in the sagittal (but not frontal plane) might occur in case of a > 25° subtrochanteric femAT correction. IV.

A gyroscope-based system for intraoperative measurement of tibia coronal plane alignment in total knee arthroplasty

Coronal plane alignment in total knee arthroplasty (TKA) is an important predictor of clinical outcomes including patient satisfaction and device longevity. Radiography and computer assisted navigation are the two primary technologies currently available to surgeons for intraoperative assessment of alignment; however, neither is particularly well-suited for use in this increasingly high volume procedure. Herein we propose a novel gyroscope-based instrument for intraoperative validation of tibia coronal plane alignment, and provide initial analytical and experimental performance assessments. The gyroscope-based alignment estimate is derived from simplified joint geometry and verified experimentally using a custom tibial trial insert containing a consumer-grade inertial measurement unit (IMU). Average accuracy of the gyroscope-based tibia coronal angle estimate was found to be within ±1° in mechanical leg jig and cadaver testing. These results indicate that the proposed gyroscope-based method shows promise for low cost, accurate intraoperative validation of limb alignment in TKA patients. Integrating IMU technology into the TKA surgical workflow via low-cost instrumentation will enable surgeons to easily validate implant alignment in real time, thereby reducing cost, operating room time, and future revision burden.

Three-dimensional analysis for quantification of knee joint space width with weight-bearing CT: comparison with non-weight-bearing CT and weight-bearing radiography

To compare computer-based 3D-analysis for quantification of the femorotibial joint space width (JSW) using weight-bearing cone beam CT (WB-CT), non-weight-bearing multi-detector CT (NWB-CT), and weight-bearing conventional radiographs (WB-XR). Twenty-six participants prospectively underwent NWB-CT, WB-CT, and WB-XR of the knee. For WB-CT and NWB-CT, the average and minimal JSW was quantified by 3D-analysis of the minimal distance of any point of the subchondral tibial bone surface and the femur. Associations with mechanical leg axes and osteoarthritis were evaluated. Minimal JSW of WB-CT was further compared to WB-XR. Two-tailed p-values of <0.05 were considered significant. Significant differences existed of the average medial and lateral JSW between WB-CT and NWB-CT (medial: 4.7 vs 5.1mm [P=0.028], lateral: 6.3 vs 6.8mm [P=0.008]). The minimal JSW on WB-XR (medial:3.1mm, lateral:5.8mm) were significantly wider compared to WB-CT and NWB-CT (both medial:1.8mm, lateral:2.9mm, all p<0.001), but not significantly different between WB-CT and NWB-CT (all p≥0.869). Significant differences between WB-CT and NWB-CT existed in participants with varus knee alignment for the average and the minimal medial JSW (p=0.004 and p=0.011) and for participants with valgus alignment for the average lateral JSW (p=0.013). On WB-CT, 25% of the femorotibial compartments showed bone-on-bone apposition, which was significantly higher when compared to NWB-CT (10%,P=0.008) and WB-XR (8%,P=0.012). Combining WB-CT with 3D-based assessment allows detailed quantification of the femorotibial joint space and the effect of knee alignment on JSW. WB-CT demonstrates significantly more bone-on-bone appositions, which are underestimated or even undetectable on NWB-CT and WB-XR.

Measurement Method of Human Lower Limb Joint Range of Motion Through Human-Machine Interaction Based on Machine Vision.

To provide stroke patients with good rehabilitation training, the rehabilitation robot should ensure that each joint of the limb of the patient does not exceed its joint range of motion. Based on the machine vision combined with an RGB-Depth (RGB-D) camera, a convenient and quick human-machine interaction method to measure the lower limb joint range of motion of the stroke patient is proposed. By analyzing the principle of the RGB-D camera, the transformation relationship between the camera coordinate system and the pixel coordinate system in the image is established. Through the markers on the human body and chair on the rehabilitation robot, an RGB-D camera is used to obtain their image data with relative position. The threshold segmentation method is used to process the image. Through the analysis of the image data with the least square method and the vector product method, the range of motion of the hip joint, knee joint in the sagittal plane, and hip joint in the coronal plane could be obtained. Finally, to verify the effectiveness of the proposed method for measuring the lower limb joint range of motion of human, the mechanical leg joint range of motion from a lower limb rehabilitation robot, which will be measured by the angular transducers and the RGB-D camera, was used as the control group and experiment group for comparison. The angle difference in the sagittal plane measured by the proposed detection method and angle sensor is relatively conservative, and the maximum measurement error is not more than 2.2 degrees. The angle difference in the coronal plane between the angle at the peak obtained by the designed detection system and the angle sensor is not more than 2.65 degrees. This paper provides an important and valuable reference for the future rehabilitation robot to set each joint range of motion limited in the safe workspace of the patient.

Design and Analysis of a Multi-Legged Robot with Pitch Adjustive Units

The paper proposes a novel multi-legged robot with pitch adjustive units aiming at obstacle surmounting. With only 6 degrees of freedom, the robot with 16 mechanical legs walks steadily and surmounts the obstacles on the complex terrain. The leg unit with adjustive pitch provides a large workspace and empowers the legs to climb up obstacles in large sizes, which enhances the obstacle surmounting capability. The pitch adjustment in leg unit requires as few independent adjusting actuators as possible. Based on the kinematic analysis of the mechanical leg, the biped and quadruped leg units with adjustive pitch are analyzed and compared. The configuration of the robot is designed to obtain a compact structure and pragmatic performance. The uncertainty of the obstacle size and position in the surmounting process is taken into consideration and the parameters of the adjustments and the feasible strategies for obstacle surmounting are presented. Then the 3D virtual model and the robot prototype are built and the multi-body dynamic simulations and prototype experiments are carried out. The results from the simulations and the experiments show that the robot possesses good obstacle surmounting capabilities.

Femoral morphology affects postoperative alignment of the lower extremities in hybrid closed-wedge high tibial osteotomy.

This study aimed to determine correction error predictors of lower extremitiy alignment after hybrid closed-wedge high tibial osteotomy (HCWHTO). From 2011 to 2015, 102 knees in 75 patients with medial compartment knee osteoarthritis of the knee and varus knee deformities who underwent HCWHTO were evaluated in this retrospective study with a minimum 2-year follow-up. Preoperative radiological parameters including weight-bearing line ratio (WBL ratio), mechanical leg axis angle, mechanical lateral distal femoral angle (mLDFA), medial proximal tibial angle (MPTA), joint line convergence angle (JLCA), and JLCA under varus or valgus stress were measured. The knees were divided into the following three groups based on the WBL ratio on average 54months after procedure: acceptable (WBL crossing the tibial plateau between 50 and 70%), under-correction (< 50%), and overcorrection (> 70%). A multiple regression analysis was performed to evaluate predictors that could influence postoperative WBL ratio and cut-off values of predictive preoperative factors was analysed. Significant differences in pre- and postoperative WBL ratios and mechanical leg axis angles were found. Preoperative mLDFA in the under-correction group (89.4° ± 2.1°) was significantly higher than that in the overcorrection group (87.4° ± 2.2°) (p = 0.015), while other preoperative parameters revealed no significant differences. The postoperative MPTA in the under-correction group (92.1° ± 3.7°) was significantly lower than that in the other two groups (p = 0.005 and p = 0.0001, respectively), while there was no significant change between the acceptable (94.6° ± 3.4°) and the overcorrection (96.7° ± 3.2°) groups. Multiple regression analysis revealed that mLDFA (β = - 0.316; p = 0.010) had a significant impact on postoperative WBLR. The cut-off value for under-correction of mLDFA was 89.5°and sensitivity and specificity were 53.6 and 71.6%, respectively (p = 0.014). Preoperative mLDFA is significantly associated with postoperative alignment in HCWHTO. While postoperative MPTA is important, disregarding the preoperative mLDFA may bears a high risk of malcorrection. Varus alignment of the knee with larger mLDFA may be an indication for not only HCWHTO, but also for distal femoral osteotomy.

Adaptive Fuzzy Robust Control of a Bionic Mechanical Leg With a High Gain Observer

In this paper, an observer-based adaptive fuzzy robust controller is proposed for trajectory tracking control of a bionic mechanical leg (BML) with unmeasured system states, dynamic uncertainties and external disturbances. A high gain observer (HGO) is constructed to estimate the unavailable joint velocities using the joint position feedback signals, while an adaptive fuzzy logic system (AFLS) is employed to address the lumped uncertainties. The nonlinear robust controller is then synthesized via backstepping method to improve the position tracking performance. The stability of the closed loop system is mathematically demonstrated via the Lyapunov’s stability theory. It is proven that under the proposed controller all the closed-loop signals are bounded and the trajectory tracking errors converge to a small neighborhood of the origin with appropriate design parameters. The effectiveness of the proposed control scheme is illustrated by simulation studies.

CT-based patient-specific instrumentation for total knee arthroplasty in over 700 cases: single-use instruments are as accurate as standard instruments

PurposeEfforts in total knee arthroplasty are made to improve accuracy for a correct leg axis and reduce component malpositioning using patient-specific instruments. It was hypothesized that use of patient-specific instruments (vs. computer-navigated and conventional techniques) will reduce the number of outliers. Our second hypothesis was that single-use instrumentation will lead to the same accuracy compared to patient-specific instruments made of metal.Methods708 primary total knee arthroplasties between 2014 and 2018 using computer tomography (CT)-based patient-specific cutting block technique and a preoperative planning protocol were retrospectively reviewed. Preoperative data [hip–knee–angle (HKA), lateral distal femoral angle (LDFA), medial proximal tibial angle (MPTA), tibial slope, femoral component flexion] was compared to postoperative performed standard radiological follow-up X-rays. Differences of > 3° between measurements were defined as outliers.ResultsOverall 500 prostheses using standard instrumentation and 208 prostheses using single-use instruments were implanted. Preoperative HKA axes (− 1.2°; p < 0.001), femoral component flexion (Δ 0.8°, p < 0.001), LDFA (Δ − 1.5°, p < 0.001), MPTA (Δ − 0.5°, p < 0.001) and tibial posterior slopes (Δ 0.5°, p < 0.001), respectively, were different from postoperative axes. More outliers occurred using standard (vs. single-use) instruments (p < 0.001) regarding postoperative HKA (ranges of standard- vs. single-use: instruments: HKA 178.0°–180.5° vs. 178.0°–180.5°, femoral component flexion 0.0°–6.0° vs. 0.0°–4.5°, LDFA 90.0°–91.0° vs. 90.0°–90.0°, MPTA 90.0°–90.0° vs. 90.0°–90.0°, tibial posterior slope − 10° to 10° vs. − 1° to 10°). No differences were seen for other angles measured. Comparing both systems, total number of outliers was higher using standard (8%) vs. single-use instruments (4.3%).ConclusionThis study shows a high accuracy of CT-based patient-specific instrumentation concerning postoperative achieved knee angles and mechanical leg axes. Single-use instruments showed a similar accuracy.Level of evidenceIII.

Mal-angulation of femoral rotational osteotomies causes more postoperative sagittal mechanical leg axis deviation in supracondylar than in subtrochanteric procedures

PurposeAlteration of the postoperative frontal mechanical leg axis is a known problem in femoral rotational osteotomies. However, the maintenance of the sagittal mechanical leg axis seems also important. Goal of this study was to investigate the impact of femoral rotational osteotomies on the sagittal mechanical leg axis and to identify the degree of mal-angulation of the osteotomy planes that alter the postoperative sagittal alignment relevantly.MethodsUsing 3D bone models of two patients with a pathologic femoral torsion (42° antetorsion and 6° retrotorsion), subtrochanteric and supracondylar rotational osteotomies were simulated first with an osteotomy plane perpendicular to the mechanical femoral axis (baseline osteotomy plane), second with predefined mal-angulated osteotomy planes. Subsequently, five different degrees of rotation were applied and the postoperative deviations of the sagittal mechanical leg axes were analyzed.ResultsUsing the baseline osteotomy plane, the sagittal mechanical leg axis changed by 0.4° ± 0.5° over both models. Using the mal-angulated osteotomy planes, maximum deviation of the sagittal mechanical leg axis of 4.0° ± 1.2° and 11.0° ± 2.0° was observed for subtrochanteric and for supracondylar procedures, respectively. Relevant changes of more than 2° were already observed with mal-angulation of 10° in the frontal plane and 15° of rotation in supracondylar procedures.ConclusionRelevant changes of the postoperative sagittal mechanical leg axis could be observed with just slight mal-angulation of the osteotomy planes, in particular in supracondylar procedures and in cases with higher degrees of rotation. However, osteotomies perpendicular to the femoral mechanical axis showed no relevant alterations.

Anaerobic Power Assessment in Athletes: Are Cycling and Vertical Jump Tests Interchangeable?

Regularly assessing anaerobic power is important for athletes from sports with an explosive strength component. Understanding the differences and overlap between different assessment methods might help coaches or smaller-scale testing facilities maximize financial and temporal resources. Therefore, this study investigated the degree to which cycling sprint and vertical jump tests are interchangeable for determining peak mechanical leg power output in strength-trained athletes. Professional skiers (n = 19) performed unloaded squat jumps (SJ) and other jump forms on a force plate and a six-second cycling sprint (6sCS) test on an ergometer on six occasions over two years. Along with cross-sectional correlations between cycling and jumping power, correlations between longitudinal percent changes and agreement between magnitude-based inferences about individual changes were assessed. Among the tested jump forms, SJ reflected 6sCS best. However, despite extremely large cross-sectional correlation coefficients (0.92) between 6sCS and SJ, and moderate (Pearson’s r = 0.32 for 6sCS with SJ over one-year time spans) to large (r = 0.68 over shorter time spans) correlation coefficients on percent changes, magnitude-based inferences agreed in only around 50% of cases. Thus, for making qualitative assessments about the development of anaerobic power over time in athletes, cycling sprint and squat jump tests are not interchangeable. Rather, we recommend employing the test form that best reflects athletes’ strength and conditioning training.

3D-ANALYSIS OF LOWER LIMB ANATOMY: NORMAL VALUES FOR JOINT ANGLES AND ALIGNMENT

Aims and Objectives:The analysis of lower limb anatomy is mandatory in deformity surgery and total knee replacement. Standard values for joint angles and alignment are only available for 2D images using long standing and lateral radiographs. In contrast, 3D bone models realistically represent the anatomy and are independent of position and projection. Using a self-developed, standardised and validated protocol for 3D analysis of lower limb geometry, standard values for specific joint angles and axes can be obtained in a young cohort for the first time.Materials and Methods:After power and sample size analysis, 60 thin-slice CTs of the entire leg were analysed (30 patients, 13 f, 17 m; age = 33.8 [18-50 years]). After segmentation all 24 relevant bony landmarks were set using our standardised analysis method. Results of joint angles and mechanical axis deviation are calculated automatically. Mean values are stated with standard deviations to describe a possible reference range.Results:The mean neck-shaft angle (NSA) was 133±10° and the mean medial proximal femoral angle (MPFA) 85±9°. Around the knee joint, the mean mechanical lateral distal femoral angle (mLDFA) was 87±4° and the medial proximal tibial angle (MPTA) 88±5°. Medial and lateral slope averaged 12±7° and 9±8°. The deviation of the frontal mechanical leg axis from the knee joint center (MAD frontal) was 7±15mm and the mechanical femoro-tibial angle (HKA) 175±6°. Women showed a smaller mLDFA than men (86.4° vs. 87.8°, p<0.05) and a larger joint line convergence angle (JLCA 2.5° vs. 1.4°, p<0.01) representing a more valgiform anatomy.Conclusion:The standardised 3D analysis enabled reference ranges for the relevant joint angles and axes to be defined on the 3D bone model for the first time. The results redefine reference ranges for 3D measurements similar to existing 2D measurements on long standing radiographs. The systematic analysis of the complex 3D anatomy results in a multitude of new questions and possibilities in preoperative planning.

The Effect of Mechanical Leg Alignment on Cartilage Restoration With and Without Concomitant High Tibial Osteotomy

To assess graft survivorship in patients who underwent autologous chondrocyte implantation (ACI) or osteochondral allograft transplantation (OCA) for the treatment of focal full-thickness cartilage lesions on the medial femoral condyle with and without concomitant high tibial osteotomy (HTO), depending on the preoperative lower-extremity alignment. A secondary purpose was to retrospectively evaluate associated factors for ACI and OCA graft failures. A total of 168 patients who underwent cartilage repair with ACI or OCA with or without HTO for focal chondral defects on the medial femoral condyle by a single surgeon between March 2007 and February 2018 were included. Clinical notes, operative reports, and radiographic imaging were reviewed for each patient. Detailed Kaplan-Meier analyses were performed based on patient's mechanical axis alignment. In a subanalysis, failures and nonfailures in patients treated with ACI or OCA were comparatively evaluated. In ACI, neutral mechanical alignment resulted in a significantly longer graft survival compared with slight valgus alignment (P= .003 and P= .05, respectively). No significant differences in survivorship were seen based on mechanical axis alignment in OCA patients (P > .05). Patients who were considered failures after ACI presented significantly more often with valgus alignment (P= .002), whereas failures in the OCA group were more often female and smokers (P= .025; P= .034). In summary, the results of this study suggest that neutral mechanical axis alignment, regardless if physiologic or through HTO, improves survivorship in patients undergoing medial compartment ACI. Neutral alignment also showed a trend towards improved survivorship in patients after OCA, but this did not reach statistical significance. Case-Series; Level of evidence,4.

Linear influence of distal femur osteotomy on the Q-angle: one degree of varization alters the Q-angle by one degree.

The effect of a distal femur varization osteotomy on patellofemoral biomechanics in genu valgum is unknown. The purpose of this study was to quantify the influence of frontal leg axis correction on the Q-angle with a novel three-dimensional (3-D) measurement method. 3-D surface models of ten lower extremities were generated using patient computed tomography (CT) data. The preoperative 3-D Q-angle was measured using a novel defined and validated 3-D measurement method. Biplanar supracondylar osteotomies were simulated with different degrees of varus correction (from 1° to 15°) in one-degree steps beginning from the preoperative valgus deformity, resulting in a total of 150 simulations. Additionally, mechanical leg axis and 3-D Q-angle measurements were performed on 3-D surface models of the postoperative CT scans of the same individuals. Further, pre- and postoperative TT-TG distance was measured. Mean preoperative Q-angle was 15.8 ± 3.9° (range 10°-21.4°) with a mean preoperative mechanical leg axis of 6.5° ± 2.4 valgus (range 3.8°-11.6° valgus). The Q-angle changed linearly 0.9 ± 0° per 1° of varization. No difference was detected between simulated 3-D Q-angles and effectively corrected postoperative values (n.s.). TT-TG distance changed irregularly and minimally, and with no correlation to the degree of varization. Distal femur varization osteotomy has a linear effect on the Q-angle with a change of 1° per 1° of varization. The difference in TT-TG distance was mainly due to an unintentional rotational component implemented during surgery.

The impact of mal-angulated femoral rotational osteotomies on mechanical leg axis: a computer simulation model

BackgroundSubtrochanteric or supracondylar femoral rotational osteotomies are established surgical treatments for femoral rotational deformities. Unintended change of the mechanical leg axis is an identified problem. Different attempts exist to plan a correct osteotomy plane, but implementation of the preoperative planning into the surgical situation can be challenging. Goal of this study was to identify the critical threshold of mal-angulation of the osteotomy plane and of femoral rotation that leads to a relevant deviation of the postoperative mechanical leg axis using a computer simulation approach.MethodsThree-dimensional (3D) surface models of the lower extremity of two patients (Model 1: 42° femoral antetorsion; Model 2: 6° femoral retrotorsion) were generated from computed tomography data. First, baseline subtrochanteric and supracondylar rotational osteotomies, perpendicular to the femoral mechanical axis were simulated. Afterwards, mal-angulated osteotomies in sagittal and frontal plane followed by different degrees of rotation were simulated and frontal mechanical axis was analyzed.Results400 mal-angulated osteotomies have been simulated. Mal-angulation of ±30° with 30° rotation showed maximum deviation from preoperative mechanical axis in subtrochanteric osteotomies (4.0° ± 0.4°) and in supracondylar osteotomies (12.4° ± 0.8°). Minimal mal-angulation of 15° in sagittal plane in subtrochanteric osteotomies and mal-angulation of 10° in sagittal plane in supracondylar osteotomies altered the mechanical axis by > 2°. Mal-angulation in sagittal plane showed higher deviations of the mechanical axis (up to 12.4° ± 0.8°), than in frontal plane mal-angulation (up to 4.0° ± 1.9°).ConclusionA femoral rotational osteotomy, perpendicular to the femoral mechanical axis, has no considerable influence on the mechanical leg axis. However, mal-angulation of femoral rotational osteotomies showed relevant changes of the mechanical leg axis. In supracondylar respectively subtrochanteric procedures, mal-angulation of only 10° in combination with already 15° of femoral rotation respectively mal-angulation of 15° in combination with 30° of femoral rotation, can lead to a relevant postoperative mechanical leg axis deviation of more than 2°, wherefore these patients probably would benefit from the use of navigation aids.

Convincing long-term results independent from the postoperative leg alignment following cementless total knee arthroplasty

BackgroundCementless primary total knee arthroplasty shows numerous advantages compared with cemented implants (e.g., shorter operation time, preservation of the bone stock). Up to now an increasing number of clinical long-term studies exist. Despite this fact, there is no evidence about the influence of the postoperative leg alignment on the results of cementless knee arthroplasty. There is no work on the clinical outcome of the specific implant, which was used in this study (VANGUARD®, ZimmerBiomet). The purpose of this study was to assess the clinical and radiological long-term results after cementless knee arthroplasty in relation to the postoperative mechanical leg alignment. MethodsClinical and radiological results were retrospectively assessed in 83 patients at 10.3 years (ranging from 9.6 to 11.8 years) after implantation. Hip-knee-ankle angle (HKA) was measured, and the patients were separated into a corrected (HKA between three degrees of varus and three degrees of valgus, n = 60) and a varus/valgus (HKA > 3° of varus and valgus, n = 23) group. ResultsUp to the time of the clinical follow-up, three out of 83 patients already underwent a revision surgery due to a deep infection (3.6%). Tegner–Lysholm Knee scale was 89.1 in the corrected group and 88.8 in the varus/valgus group (p = .94). The mean Knee Injury and Osteoarthritis Outcome score (KOOS) was 81.2 in the corrected group and 82.4 in the varus/valgus group (p = .63). ConclusionsResults of this study showed convincing clinical and radiological results after primary cementless knee arthroplasty. Under- or overcorrected postoperative mechanical leg alignments did not influence the long-term clinical results.

A method for vehicle speed tracking by controlling driving robot

Using a driving robot instead of a human driver to carry out a vehicle emission durability test can effectively improve the accuracy of test. In order to accurately control the speed tracking of driving robot under different working conditions, a speed tracking method of driving robot based on dynamic fuzzy neural network (DFNN) direct inverse control is proposed, which considers the self-learning of vehicle longitudinal performance. Firstly, the kinematics and dynamics models of the driving robot’s mechanical legs are established. Moreover, in order to coordinately control the multi-legs of the driving robot to track the vehicle speed, the longitudinal performance model of the controlled vehicle is established by using performance self-learning data and neural network algorithm. Then, to accurately control the movement of the mechanical leg, a direct inverse controller based on DFNN is designed. The output of direct inverse controller is dynamically compensated by closed-loop control of braking force and throttle opening. Finally, the speed tracking experiments and simulations are carried out by human driver, proportional-integral-derivative (PID) control, fuzzy control and the proposed method under different working conditions. The results show that the proposed method does not have the same large prediction error as human driver. At the same time, it can track the speed quickly in different switching conditions. The fluctuation of the tracking speed is small, and the tracking error remains within ±1km/h. The proposed method avoids the design of complex control law based on model and can coordinately control the multi-legs to complete the tracking of the target speed.

Prototyping of a novel anthropomorphic mechanical leg

This research aims to explore a better kinematic performance and design scheme for a novel mechanical leg using parameter optimization method. Serial structural mechanisms are widely employed in anthropomorphic mechanism legs but with significant disadvantages of the complex structure and large inertia, particularly, for the multi-objective parameter optimization it is hard to select good parameters to achieve excellent performance. In this article, the plane model of the solution space for multiple parameters and a novel statistics parameter optimization method were proposed for a novel mechanical leg. In the position analysis, the structure and workspace for the novel mechanical leg were developed with simple structure, small inertia, and large workspace; and several kinematic performance evaluation indices were also proposed in the kinematics analysis. In the parameter optimization process, the design scheme and prototyping of the mechanical leg have shown a better kinematic performance by considering the assembly technique as compared with the conventional models. The proposed research provides the basis for the applications of the novel mechanical leg, which can be applied in the modern humanoid robot fields to meet the requirements of high stiffness, lower inertia, and good technological efficiency.

Rotation or flexion alters mechanical leg axis measurements comparably in patients with different coronal alignment.

Flexion and rotation of the knee joint are supposed to alter the measurement of the mechanical leg axis on long leg radiographs. However, in patients with varus or valgus alignment it has not been systematically analyzed so far. The hypothesis is that measurement of the mechanical leg axis is more influenced by flexion and rotation in presence of varus or valgus alignment compared to patients with a straight coronal alignment. 3D surface models of the lower extremities of seven individuals with varying degrees of coronal alignment were created based on CT data. The coronal alignment of the seven individuals captured the range between 9° varus and 9° valgus with equal steps of 3°. Combinations of internal and external rotations of 10°, 20°, and 30° with flexion of 5°, 10°, 15°, 20°, and 30° were simulated. The mechanical leg axis was measured for each combination as the antero-posterior (ap)-projected hip-knee-ankle (HKA-) angle. 294 simulations with all combinations of rotation and flexion were performed. Ranges of deviation of HKA never showed a critical deviation of more than 3° from median values. Deviations from baseline appeared normally distributed for all flexion and rotation combinations (p < 0.05) and the probability for a deviation from the mean mechanical leg axis of more than 3° was less than 0.03 for all combinations. Comparability of the models, therefore, could be assumed. Deviations in HKA-angle measurements, caused by rotation or flexion, does not vary relevantly through the range of coronal alignment of 9° varus to 9° valgus. As a clinical relevance, deviations in HKA-angle measurements can be considered as comparable in patients with different coronal alignment. III.