Normal Force Vector Research Articles

Spontaneous Correction of External Tibiofemoral Rotational Deformity and Tibial Tuberosity-Trochlear Groove Measurements Occurs After Medial Patellofemoral Ligament Reconstruction in Fixed or Obligatory Dislocators

Objectives:Tibial tubercle to trochlear groove distance (TT-TG) and external tibiofemoral rotation (TFR) through the knee joint have been identified as potential contributing factors to patellar instability. In patients with a fixed or obligatory lateral patella dislocation (FOD), the normal force vector of the extensor mechanism is altered, so instead of a direct axial pull to cause extension, it exerts a lateralizing and external rotatory force on the tibia via the tibial tubercle. The purpose of this study is to investigate postoperative changes in TT-TG and TFR after medial patellofemoral ligament reconstruction (MPFLR) in two clinical cohorts: standard traumatic patellar instability (SPI) patients and FOD patients. We hypothesized that by surgically relocating the patella in the trochlea, and re-establishing medial sided soft tissue tension, the increased medializing force vector on the patella may exert enough force to alter resting rotation of the tibia in relation to the femur in the FOD group.Methods:A retrospective study was performed from April 2009 to February 2019. FOD and SPI patients under 18 years with available magnetic resonance imaging (MRI) of the knee before and after MPFLR were eligible. All FOD patients in the time frame were analyzed and SPI patients were randomly selected. Exclusion criteria were outside institution MRI, concomitant alignment procedures done at the time of MPFLR, and prior MPFLR or tibial tubercle osteotomy. TT-TG and TFR (using the posterior femoral and tibial condylar lines) were measured blindly on initial axial MRI. Statistical analysis using a paired sample t-test was performed with significance set at p<0.05.Results:A total of 30 patients were included, 14 in the FOD group and 16 in the SPI group. The mean age at time of surgery was 13.9 years (range 10-17 years), 53% of the cohort was female, and the mean time from surgery to follow-up MRI was 2.0 years. Demographics by group are shown in Table 1. TT-TG and TFR were not significantly different preoperatively versus postoperatively in the SPI group (Table 2). In the FOD group, both TT-TG (17.7 vs 13.7, P=.019) and TFR (8.6 vs 3.1, P=.025) decreased significantly on postoperative MRI.Conclusions:The postoperative decrease in TT-TG and TFR in the FOD group suggests that MPFLR in fixed or obligatory dislocators can improve the external rotation deformity through the level of the joint, and thus may help normalize the forces acting through the extensor mechanism.

SPONTANEOUS CORRECTION OF EXTERNAL TIBIOFEMORAL ROTATION AND TIBIAL TUBEROSITY-TROCHLEAR GROOVE DISTANCE OCCURS AFTER MEDIAL PATELLOFEMORAL LIGAMENT RECONSTRUCTION IN FIXED OR OBLIGATORY DISLOCATORS

Background:Tibial tubercle to trochlear groove distance (TT-TG) and external tibiofemoral rotation (TFR) through the knee joint have been identified potential contributing factors to patellar instability. In patients with a fixed or obligatory lateral patella dislocation (FOD), the normal force vector of the extensor mechanism is altered, so instead of a direct axial pull to cause extension, it exerts a lateralizing and external rotatory force on the tibia via the tibial tubercle.Hypothesis/Purpose:The purpose of this study is to investigate postoperative changes in TT-TG and TFR after medial patellofemoral ligament reconstruction (MPFLR) in two clinical cohorts: standard traumatic patellar instability (SPI) patients and FOD patients. We hypothesized that by surgically relocating the patella in the trochlea, and re-establishing medial sided soft tissue tension, the increased medializing force vector on the patella may exert enough force to alter resting rotation of the tibia in relation to the femur in the FOD group.Methods:A retrospective study was performed from April 2009 to February 2019. FOD and SPI patients under 18 years with available magnetic resonance imaging (MRI) of the knee before and after MPFLR were eligible. All FOD patients in the time frame were analyzed and SPI patients were randomly selected. Exclusion criteria were outside institution MRI, concomitant alignment procedures done at the time of MPFLR, and prior MPFLR or tibial tubercle osteotomy. TT-TG and TFR (using the posterior femoral and tibial condylar lines) were measured blindly on initial axial MRI. Statistical analysis using a paired sample t-test was performed with significance set at p<0.05.Results:A total of 30 patients were included, 14 in the FOD group and 16 in the SPI group. The mean age at time of surgery was 13.9 years (range 10-17 years), 53% of the cohort was female, and the mean time from surgery to follow-up MRI was 2.0 years. Demographics by group are shown in Table 1. TT-TG and TFR were not significantly different preoperatively versus postoperatively in the SPI group (Table 2). In the FOD group, both TT-TG (17.7 vs 13.7, P=.019) and TFR (8.6 vs 3.1, P=.025) decreased significantly on postoperative MRI.Conclusion:The postoperative decrease in TT-TG and TFR in the FOD group suggests that MPFLR in fixed or obligatory dislocators can improve the external rotation deformity through the level of the joint, and thus may help normalize the forces acting through the extensor mechanism.Tables/ Figures

Assessment of point and line contact stiffness formulations leading to the initiation of hammering type brake squeal

This article proposes a refined nonlinear mathematical model to conceptually investigate the brake pad kinematics and dynamics in order to reveal certain important aspects that have been ignored in prior studies. In particular, the proposed model is formulated as a three degree-of-freedom mass positioned on a rigid frictional surface moving at constant velocity. The mass is assumed to make planar motion in vertical plane, two translations and one rotation. The interfacial contact is first examined by a point contact model with linear translational springs at edges and then the line contact is defined over the entire interface. Furthermore, kinematic and clearance nonlinearities are included. The nonlinear governing equations with point contacts at edges are numerically solved at certain angular arrangements of normal force vectors. Then, the line contact interface is solved again for the same normal force vector arrangements. Comparison reveals that the line contact approach provides more meaningful results. Finally, a linearized system model and the existence of quasi-static sliding motion are examined over a range of the normal force vector arrangements. Overall, inclusion of the rotational degree of freedom in the source model is crucial and the importance of pad-disc separation is clearly explained by the proposed formulation. This leads to a better understanding of the hammering type brake squeal source mechanisms while overcoming the limitation of prior minimal order models

Outcomes of gluteus maximus and tensor fascia lata transfer for primary deficiency of the abductors of the hip.

This study aims to present 3 patients' results after undergoing gluteus maximus and tensor fascia lata (TFL) transfer for chronic abductor tears unable to be repaired primarily. 3 patients were identified intraoperatively as having an abductor tear unable to be repaired primarily. The anterior 1/3 of the gluteus maximus and the posterior 1/3 of the TFL were mobilised and transferred to the greater trochanter in order to reproduce the normal force vector of the gluteus medius and minimus. Data was prospectively collected for changes in gait, abductor strength, and the following patient reported outcomes (PROs): modified Harris Hip Score (mHHS), Nonarthritic Hip Score (NAHS), Hip Outcome Score-Sports Specific Subscale (HOS-SSS), Hip Outcome Score-Activities of Daily Living (HOS-ADL), visual analogue scale (VAS), and satisfaction. The patients were female, 63-75 years old, with BMIs of 23-28. All patients had follow-up at mean 2.1 years (1.25-2.5) with positive Trendelenburg signs preoperatively; 2 patients normalised postoperatively. For 2 patients, abductor strength improved by 2 grades postoperatively; the other patient maintained grade four. 2 patients' PROs all improved; the other patient's PROs all improved except mHHS. Postoperative VAS scores were 0, 0, 1. 2 patients reported maximum satisfaction. This case series suggests that gluteus maximus and TFL transfer for irreparable abductor deficiency may be effective for pain relief, improving abductor strength, and reconstructing abductor function. Although this is a small series, it is to our knowledge the first report of clinical outcomes of this procedure.

Biomechanical Evaluation of Shear Force Vectors Leading to Injury of the Biceps Reflection Pulley

Background The clinical importance of the biceps reflection pulley (BRP), which stabilizes the long head of the biceps tendon (LHB) as it exits the joint, has been shown. However, there is controversy on the pathomechanism of injury to the BRP. The angular orientation of the LHB relative to its origin and distal course changes with joint positions and may place the BRP at risk for injury. Purpose To measure the course of the LHB in common arm positions and to determine the shear and normal (stabilizing) force vectors as well as the excursion of the LHB. Study Design Descriptive laboratory study. Methods The LHBs of 8 fresh-frozen cadaveric shoulders were marked with arthroscopically injected microbeads and mounted in a custom-built shoulder rig. Data for neutral arm position, forward flexion, and abduction were collected in internal, neutral, and external rotation using biplane fluoroscopy. Bone and LHB position were reconstructed in 3 dimensions. Results The shear component of the resulting vector was significantly higher during internal (28.4% ± 18.1%) compared with external rotation (18.9% ± 9.7%; P = .0157) and was highest in neutral arm position with internal rotation (39.2% ± 12.7%) and forward flexion with neutral rotation (36.2% ± 10.7%). The normal force vector, stabilizing the LHB, was significantly higher in abduction (55.2% ± 9.6%) compared with forward flexion (39.1% ± 12.4%; P < .0001) and neutral positions (39.1% ± 11.4%; P < .0001). The LHB excursion was significantly lower for neutral arm positions (0.7 ± 6.0 mm) compared with forward flexion (12.6 ± 8.3 mm; P < .0001) and abduction (12.0 ± 6.5 mm; P < .0001). Conclusion Increased shear load at forward flexion with internal or neutral arm rotation and internal rotation at neutral arm position may cause injury to the BRP. Additionally, a sawing mechanism caused by the 12-mm linear excursion combined with a load of the LHB through the BRP during elevation may also lead to lesions. Clinical Relevance Knowledge of the pathomechanisms of BRP injury may help in developing specific treatment and rehabilitation strategies as well as tests for physical examination.

ISoRA: Humanoid Robot Arm for Intelligent Haptic Interaction with the Environment

The paper concentrates on the development and control of the humanoid robot arm iSoRA, intended for operation in a dynamic unstructured environment. Optical torque sensors integrated into each joint enable measurement of contacting forces along the entire manipulator surface. A variable admittance control strategy was elaborated to increase the robot functionality and to achieve the human-like dynamics of interaction. The experimental results show that the proposed approach not only provides safe interaction of the robot arm with a person, but also improves the effectiveness of contact task performance. The paper also presents a novel concept of avoidance of an obstacle of unknown shape. The tactile sensory ability of the developed manipulator allows robot links to follow the object contour and to perform motion planning in the dynamic environment. The information on the applied normal force vector, object shape and target point coordinates is supplied to the motion planning system. The algorithms for contact point detection, object geometry recognition, and estimation of contacting object stiffness are detailed. The numerical simulation elicits a capability of the proposed method to approximate various object shapes precisely. The experimental results showed that the local admittance control and motion planner allowed the end-effector to follow the object contour in a very smooth, consistent manner while reaching the target point.

Characteristics of Vortical Jet Structures of a Hydrofoil

Oscillating foil propulsion, the engineering application of fish-like movement of a hydrofoil, has received in recent decades as a possible competitor for propellers. The oscillating foil produces an effective angle of attack, resulting in a normal force vector with thrust and lift components, and it can be expected to be a new highly effective propulsion system. We have explored propulsion hydrodynamics as a concept in wake flow pattern. The present study has been examined various conditions such as oscillating frequencies and amplitudes in NACA0010 profile. Flow visualizations showed that high thrust was associated with the generation of moderately strong vortices, which subsequently combine with trailing-edge vorticity leading to the formation of a reverse Karman vortex street. Vortex generation was inherent to jet production and playeda fundamental role in the wake dynamics. And it was shown that the strong thrust coefficient obtained as the Strouhal number was larger.

Vectorial analysis of the equilibrium of forces transmitted to TMJ and occlusal biteplane splints.

A mechanical model (link quadrilateral bell crank) is used to demonstrate the equilibrium of normal force vectors transmitted to the masticatory system and maxillary occlusal biteplane splints with different designs. Occlusal contacts were imposed on the proposed models under the action of a masticatory force vector with an arbitrary value of 40 kgf. The consequence of this force action created different responses within the joint and at the level of the dentition. When compared to the intercuspal position in centric occlusion, intra-oral appliances with either smooth contacting surfaces or indentations, both with increased vertical dimension, forced the mandible to assume an anterior position with a concurrent increase of joint forces. The bite-splint that produced the least amount of joint force was the stabilization type with minimal increase of vertical dimension.

Comment on 'Guidance for an aerocapture maneuver'

It is stated that the aerodynamic forces on the vehicle being aerocaptured are controlled by altering the angle of and thereby controlling the lift coefficient. Furthermore, the resulting variation of drag coefficient with angle of attack was ignored. The purpose of this Comment is to point out that an aerodynamic control method that is much more effective than the pitch modulation has been studied and utilized during entries for many years. During aerocapture, it is desirable to have a large range of lift coefficients available, while keeping the vehicle's ballistic coefficients constant. This is accomplished by modulating the vehicle's bank angle, i.e., by rolling the vehicle about its velocity vector. By this method, the angle of attack can be held constant (at the trim angle, if desired), and the C(sub D) and the ballistic coefficient remain constant. Furthermore, the vertical component of the normal force vector (essentially the lift) can be varied over its entire range, from maximum positive to maximum negative values. Reaction controls, rather than aerodynamic ones, are usually utilized to change the bank angle of the vehicle, thus requiring the use of fuel. However, the fuel expenditure that is required to change the bank angle is far less than the amount that would have to be used to continuously hold the vehicle at pitch angles that differ significantly from its trim angle of attack. Also, it has been shown that bank angle modulation to vary the lift can enlarge the entry corridor by increasing the entry angle for the undershoot boundary, where both the heating rate and deceleration reach a maximum. Finally, the crew's deceleration tolerance can be increased somewhat when the bank angle is varied, as opposed to the pitch angle. For bank modulation, the deceleration force vector can be kept at a constant angle with respect to the occupants whose tolerance to g loads is highest when the force is applied in a direction normal to the upper torso. The advantages of bank angle variation to modulate the lift vector were recognized long ago, and this method of control was used successfully on the Apollo command module during lunar return' and, more recently, for the Space Shuttle Orbiter.