Torsional Measurements Research Articles

Torsion sensor based on inter-core mode coupling in seven-core fiber.

We proposed a novel torsion sensor based on inter-core mode coupling in seven-core fiber (SCF). The torsion sensor is fabricated by tapering a commercially available SCF spliced with two single mode fibers. Waist diameter and length of the taper structure were experimentally optimized to achieve good transmission spectrum. Based on this structure, the torsion measurement was conducted, and the experimental results demonstrated that the transmission spectrum shows a red shift with the fiber twist. The torsion sensitivity increases with the twisting angle, which can achieve as high as 1.00 nm/°. The direction of wavelength shift was observed to be opposite when twisting the tapered SCF in clockwise and counter-clockwise direction, demonstrating its capability to discriminate the rotation orientation. Moreover, all the measurements were repeated in attempts to confirm its stable performance as well as high accuracy. Mode coupling dynamics and theory of optical anisotropy in twisted fiber are adopted to discuss the sensitivity performance, which agrees well with experimental results. The novel torsion sensor could provide a promising candidate for the applications requiring accurate rotation.

Experimental Study of the Shaft Penetration Factor on the Torsional Dynamic Response of a Drive Train

Typical rotating machinery drive trains are prone to torsional vibrations. Especially those drive trains that comprise one or more couplings which connect the multiple shafts. Since these vibrations rarely produce noise or vibration of the stationary frame, their presence is hardly noticeable. Moreover, unless an expensive torsional-related problem has become obvious, such drive trains are not instrumented with torsional vibration measurement equipment. Excessive levels can easily cause damage or even complete failure of the machine. So, when designing or retrofitting a machine, a comprehensive and detailed numerical torsional vibration analysis is crucial to avoid such problems. However, to accurately calculate the torsional modes, one has to account for the penetration effect of the shaft in the coupling hub, indicated by the shaft penetration factor, on the torsional stiffness calculation. Many guidelines and assumptions have been published for the stiffness calculation, however, its effect on the damping and the dynamic amplification factor are less known. In this paper, the effect of the shaft penetration factor, and hence coupling hub-to-shaft connection, on the dynamic torsional response of the system is determined by an experimental study. More specifically, the damping is of major interest. Accordingly, a novel academic test setup is developed in which several configurations, with each a different shaft penetration factor, are considered. Besides, different amplitude levels, along with both a sweep up and down excitation, are used to identify their effect on the torsional response. The measurement results show a significant influence of the shaft penetration factor on the system’s first torsional mode. By increasing the shaft penetration factor, and thus decreasing the hub-to-shaft interference, a clear eigenfrequency drop along with an equally noticeable damping increase, is witnessed. On the contrary, the influence of the sweep up versus down excitation is less pronounced.

운전금지 구역 통과 시 선박용 중간축의 피로강도와 수명

Recent innovations on low-speed two-stroke ship propulsion engines include higher power rating with lower nominal engine speed for increased propeller efficiency and reduced fuel consumption. Additionally, 5~6 cylinder engines are preferred for having reduced dimension freeing up cargo spaces and lower repair and maintenance costs as well. Likewise, the barred speed range (BSR) protects the shafting system from increased torsional vibration stresses by passing in a shortest possible time at this critical speed. Considering above-mentioned engine specifications, shaft breakage accidents can occur from the accumulated fatigue stress due to the prolonged barred speed range passing and shafting design. This paper evaluates the propulsion shafting system fatigue strength and lifecycle of a 6G70ME model engine through theoretical analysis and torsional vibration measurement data.

Derotational Osteotomy of the Distal Femur for the Treatment of Patellofemoral Instability Simultaneously Leads to the Correction of Frontal Alignment: A Laboratory Cadaveric Study.

Background:Derotational osteotomy of the distal femur allows the anatomic treatment of patellofemoral maltracking due to increased femoral antetorsion. However, such rotational osteotomy procedures have a high potential of intended/unintended changes of frontal alignment.Purpose/Hypothesis:The purpose of this study was to perform derotational osteotomy of the distal femur and to demonstrate the utility of a novel trigonometric approach to address 3-dimensional (3D) changes on 2-dimensional imaging (axial computed tomography [CT] and frontal-plane radiography). The hypothesis was that 1-step single-cut osteotomy can simultaneously correct torsion and frontal alignment based on preoperatively calculated cutting angles.Study Design:Controlled laboratory study.Methods:Eight human cadaveric whole legs (4 lower limb torsos) underwent derotational osteotomy of the distal femur of 20°. A straight leg axis, determined as a mechanical femorotibial angle (mFTA) of 0°, was chosen as a goal for postoperative frontal alignment. The inclination of the cutting angle from the lateral view was calculated individually for each cadaveric leg and was represented by a simple 3D-printed cutting guide for surgery. Specimens underwent CT for the measurement of torsion, while the frontal leg axis was determined on an upright radiograph preoperatively and postoperatively. Preoperative and postoperative angles were compared with the mathematical prediction model.Results:The preoperative mFTA ranged from –3.9° (valgus) to +3.4° (varus) (mean, –0.2° ± 2.6°). A postoperative mean mFTA of 0.37° ± 0.69° (95% CI, –0.22° to 0.95°) was achieved (P = .01). Derotation showed a mean of 19.1° ± 2.1° (95% CI, 17.3°-20.8°). The oblique cutting plane for the correction of valgus legs showed a mean of 5.9° ± 6.8° and, for the correction of varus legs, a mean of –10.0° ± 4.5° projected on the perpendicular plane to the virtual anatomic shaft axis from the sagittal view.Conclusion:Single-cut distal femoral osteotomy can be performed to simultaneously address rotational as well as frontal alignment using a preoperatively defined oblique cut, as determined by the presented reproducible calculation model.Clinical Relevance:This study adds important knowledge to the technique of derotational osteotomy. This approach provides an individual, oblique single cut for the correction of torsion and frontal axis within a clinically insignificant margin. Simplified tables for calculation and a surgical reference make this model reproducible and safe.

Regional cardiac function analysis from tagged MRI images. Comparison of techniques: Harmonic-Phase (HARP) versus Sinusoidal-Modeling (SinMod) analysis

Cardiac MRI tagging is a valuable technique for evaluating regional heart function. Currently, there are a number of different techniques for analyzing the tagged images. Specifically, k-space-based analysis techniques showed to be much faster than image-based techniques, where harmonic-phase (HARP) and sine-wave modeling (SinMod) stand as two famous techniques of the former group, which are frequently used in clinical studies. In this study, we compared HARP and SinMod and studied inter-observer variability between the two techniques for evaluating myocardial strain and apical-to-base torsion in numerical phantom, nine healthy controls, and thirty diabetic patients. Based on the ground-truth numerical phantom measurements (strain = −20% and rotation angle = −4.4°), HARP and SinMod resulted in overestimation (in absolute value terms) of strain by 1% and 5% (strain values), and of rotation angle by 0.4° and 2.0°, respectively. For the in-vivo results, global strain and torsion ranges were −10.6% to −35.3% and 1.8°/cm to 12.7°/cm in patients, and −17.8% to −32.7% and 1.8°/cm to 12.3°/cm in volunteers. On average, SinMod overestimated strain measurements by 5.7% and 5.9% (strain values) in the patients and volunteers, respectively, compared to HARP, and overestimated torsion measurements by 2.9°/cm and 2.5°/cm in the patients and volunteers, respectively, compared to HARP. Location-wise, the ranges for basal, mid-ventricular, and apical strain in patients (volunteers) were −8.4% to −31.5% (−11.6% to −33.3%), −6.3% to −37.2% (−17.8% to −33.3%), and −5.2% to −38.4% (−20.0% to −33.2%), respectively. SinMod overestimated strain in the basal, mid-ventricular, and apical slices by 4.7% (5.7%), 5.9% (5.5%), and 8.9% (6.8%), respectively, compared to HARP in the patients (volunteers). Nevertheless, there existed good correlation between the HARP and SinMod measurements. Finally, there were no significant strain or torsion measurement differences between patients and volunteers. There existed good inter-observer agreement, as all measurement differences lied within the Bland-Altman ± 2 standard-deviation (SD) difference limits. In conclusion, despite the consistency of the results by either HARP or SinMod and acceptable agreement of the generated strain and torsion patterns by both techniques, SinMod systematically overestimated the measurements compared to HARP. Under current operating conditions, the measurements from HARP and SinMod cannot be used interchangeably.

Sampled Bragg gratings formed in helically twisted fibers and their potential application for the simultaneous measurement of mechanical torsion and temperature.

We propose and demonstrate a novel type of sampled Bragg gratings by combining a helically twisted fiber and a Bragg grating. A comb-like spectrum with a series of harmonic narrow resonances is observed, and the influence of geometrical parameters on the resonances is studied. As a special application, the intrinsic nature of the device that contains the Bragg grating and helical fiber spectral responses permits the temperature to be detected from the former, whereas the mechanical torsion is extracted from the latter, suggesting a potential for the simultaneous measurement of these two parameters. The proposed configuration features simplification, easy fabrication, high flexibility, stability, and low cost, and therefore has good prospects for sensor applications, as well as other applications, such as multi-channel filters, distributed Bragg reflectors, etc.

Torsional Oscillator Measurements of Liquid 4He Confined in 2.5-nm Channel of FSM

We measured the superfluid response of liquid 4He confined in 2.5-nm channel under low pressure by means of the torsional oscillator to clarify how the superfluid response varies with decreasing channel diameter. In the previous measurements, in the 2.8-nm channel under 0.13 MPa, the superfluid fraction appears at 1.8 K, and then shows a sharp rise at 0.9 K. On the other hand, in the 2.2-nm channel, no sharp rise is observed although the superfluid fraction appears. In the present measurements for 2.5-nm channel, the superfluid appears at around 1.5 K, and then shows a sharp rise at 0.13 K. By comparison, with decreasing channel diameter, the temperature of superfluid appearance is suppressed with gentle acceleration, which is attributable to the suppression of falling into a BEC-like state. In contrast, the temperature of the rise in the superfluid is suppressed drastically compared with that of superfluid appearance, by decreasing the channel diameter from 2.8 to 2.5 nm.

Posttraumatic torsional deformities of the forearm : Methods of measurement and decision guidelines for correction

Forearm fractures are common in all age groups. Even if the adjacent joints are not directly involved, these fractures have an intra-articular character. One of the most common complications of these injuries is apainful limitation of the range of motion and especially of pronation and supination. This is often due to an underdiagnosed torsional deformity; however, in recent years new methods have been developed to make these torsional differences visible and quantifiable through the use of sectional imaging. The principle of measurement corresponds to that of the torsion measurement of the lower limbs. Computed tomography (CT) or magnetic resonance imaging (MRI) scans are created at defined heights. By searching for certain landmarks, torsional angles are measured in relation to adefined reference line. Anew alternative is the use of 3D reformation models. The presence of atorsional deformity, especial of the radius, leads to an impairment of the pronation and supination of the forearm. In the presence of torsional deformities, radiological measurements can help to decide if an operation is needed or not. Unlike the lower limbs, there are still no uniform cut-off values as to when acorrection is indicated. Decisions must be made together with the patient by taking the clinical and radiological results into account.

Reliability and reproducibility of disc-foveal angle measurements by non-mydriatic fundus photography.

PurposeAbnormal torsion could be associated with cyclovertical strabismus, but torsion measurements are not reliable in children. To assess an objective fundus torsion evaluation in a paediatric population, we used Non-Mydriatic Fundus photography (NMFP) in healthy and cyclovertical strabismus patients to evaluate the disc-foveal angle over time and observers.MethodsWe used a retrospective set of NMFP including 24 A or V-pattern strabismus and 27 age-matched normal children (mean age 6.4 and 6.7 years respectively), taken during 2 distinct follow-up consultations (separated by 251 and 479 days respectively). Each disc-foveal angle measurement (from which the ocular torsion can be assessed) was performed by 5 different observers, using graphical software and based on reproducible fundus anatomical marks. Statistical analysis was performed with a multivariate ANOVA using group, time and observers as factors, in addition to intraclass coefficient correlation (ICC) to assess measurement reproducibility.ResultsA significant difference of disc-foveal angle measures was observed between groups (p<0,001): 18.73° (SD = 6.42), -3,25° (SD = 5.51) and 6,89° (SD = 4,41) respectively for V-pattern, A- pattern and normal subjects. Neither observers (F = 0,2028 p = 0,9369) nor time between 1st and 2nd NMFP (F = 0,6312 p = 0,4271) seem to influence the measure of disc-foveal angle. The evaluation of disc-foveal angle was very reproducible between observers (ICC>0,97).ConclusionAbnormal amount of objective torsion could be associated with alphabet-pattern strabismus. Disc-foveal angle evaluation by NMFP in a children population appears as a non-invasive, reliable and reproducible method.

Directional torsion and temperature discrimination based on a multicore fiber with a helical structure.

We propose and experimentally demonstrate a directional torsion sensor based on a Mach-Zehnder interferometer formed in a multicore fiber (MCF) with a ~570-μm-long helical structure (HS). The HS was fabricated into the MCF by simply pre-twisting and then heating with a CO2 laser splicing system. This device shows the capability of directional torsion measurement from -17.094 rad/m to 15.669 rad/m with the sensitivity of ~0.118 nm/(rad/m). Moreover, since the multiple interferences respond differently to torsion and temperature simultaneously, the temperature cross-sensitivity of the proposed sensor can be eliminated effectively. Besides, the sensor owns other merits such as easy fabrication and good mechanical robustness.

RhBMP-2 in an injectable Gelfoam carrier enhances consolidation of the distracted callus in a sheep model.

A major problem associated with distraction osteogenesis is the long time required for consolidation. The goal of this study was to determine whether a percutaneous injection of recombinant human bone morphogenetic protein-2 (rhBMP-2) in a Gelfoam carrier would enhance bone consolidation following distraction. A unilateral tibial osteotomy combined with external stabilization was performed in 14 adult sheep. After a latency of four days, distraction was performed at 1.25 millimetres per day for 20 days. On days 23 and 30, the sheep received an injection of rhBMP-2/Gelfoam or buffer/Gelfoam. During the following 50 days, radiographs and in vivo torsional stiffness measurements were obtained weekly. The effect of rhBMP-2 treatment post-mortem was assessed using destructive biomechanical testing, quantitative CT and DXA analysis. The in vivo stiffness measurements of the sheep treated with rhBMP-2 were significantly higher than those of the carrier control group (p< 0.05). These in vivo data were verified by post-mortem biomechanical testing and quantitative CT analysis. The maximum torsional moment observed was 55% greater in the sheep treated with rhBMP-2. These data support the potential use of rhBMP-2 in an injectable carrier for enhancing consolidation, as it may ultimately lead to shorter treatment times for patients undergoing distraction procedures.

3D dynamic displacement-field measurement for structural health monitoring using inexpensive RGB-D based sensor

The advent of inexpensive digital cameras with depth sensing capabilities (RGB-D cameras) has opened the door to numerous useful applications that need quantitative measures of dynamic fields whose simultaneous time history quantification (at many points as dictated by the resolution of the camera) provides capabilities that were previously accessible only through expensive sensors (e.g., laser scanners). This paper presents a comprehensive experimental and computational study to evaluate the performance envelope of a representative RGB-D sensor (the first generation of Kinect sensor) with the aim of assessing its suitability for the class of problems encountered in the structural dynamics field, where reasonably accurate information of evolving displacement fields (as opposed to few discrete locations) that have simultaneous dynamic planar translational motion with significant rotational (torsional) components. This study investigated the influence of key system parameters of concern in selecting an appropriate sensor for such structural dynamic applications, such as amplitude range, spectral content of the dynamic displacements, location and orientation of sensors relative to target structure, fusing of measurements from multiple sensors, sensor noise effects, rolling-shutter effects, etc. The calibration results show that if the observed displacement field generates discrete (pixel) sensor measurements with sufficient resolution (observed displacements more than 10 mm) beyond the sensor noise floor, then the subject sensors can typically provide reasonable accuracy for transnational motion (about 5%) when the frequency range of the evolving field is within about 10 Hz. However, the expected error for torsional measurements is around 6% for static motion and 10% for dynamic rotation for measurements greater than 5°.

The relationships between impact location and post-impact ball speed, bat torsion, and ball direction in cricket batting

ABSTRACTThree-dimensional kinematic data of bat and ball were recorded for 239 individual shots performed by twenty batsmen ranging from club to international standard. The impact location of the ball on the bat face was determined and assessed against the resultant instantaneous post-impact ball speed and measures of post-impact bat torsion and ball direction. Significant negative linear relationships were found between post-impact ball speed and the absolute distance of impact from the midline medio-laterally and sweetspot longitudinally. Significant cubic relationships were found between the distance of impact from the midline of the bat medio-laterally and both a measure of bat torsion and the post-impact ball direction. A “sweet region” on the bat face was identified whereby impacts within 2 cm of the sweetspot in the medio-lateral direction, and 4.5 cm in the longitudinal direction, caused reductions in ball speed of less than 6% from the optimal value, and deviations in ball direction of less than 10° from the intended target. This study provides a greater understanding of the margin for error afforded to batsmen, allowing researchers to assess shot success in more detail, and highlights the importance of players generating consistently central impact locations when hitting for optimal performance.

3D Modeling of Lower Extremities With Biplanar Radiographs: Reliability of Measures on Subsequent Examinations.

Biplanar radiography with 3-dimensional (3D) modeling (EOS) provides a comprehensive assessment of lower limb alignment in an upright weight-bearing position with less radiation than conventional radiography. A study was performed to assess the consistency and reliability of 2 lower extremity 3D biplanar radiograph models created at least 1 year apart in a pediatric population. All patients who had 2 lower extremity radiographic evaluations with EOS performed at visits a minimum of 1 year apart were reviewed. Digital radiographs, of lower extremities in both frontal and sagittal planes, were acquired simultaneously, using the EOS system. The 3D reconstruction of the images was achieved utilizing the SterEOS software. Pelvic position, femoral and tibial anatomy, and the torsional profile were evaluated and compared using t tests. In total, 53 patients with a mean age of 11.7 years (range, 6.1 to 18.9 y) met inclusion criteria. When comparing 3D models between visits, minimal differences were noted in proximal femoral anatomy and pelvic alignment (pelvic incidence, sacral slope, sagittal tilt, neck shaft angle). Expected differences in femoral and tibial length corresponded with normal longitudinal growth between visits. Sagittal plane knee position varied widely between examinations. Femoral and/or tibial rotational osteotomies were performed in 37% of extremities between examinations. After femoral derotational osteotomy, a significant difference in femoral anteversion was appreciated when comparing preoperative and postoperative 3D models. However, this difference was less than the expected difference based on the anatomic correction achieved intraoperatively. No differences were noted in tibial torsion measures after tibial derotational osteotomy. The 3D modeling based on biplanar radiographs provides consistent and reliable measures of pelvic and hip joint anatomy of the lower extremity. Patient positioning may influence the reproducibility of knee alignment. The torsional profile assessment did not accurately reflect changes obtained by derotational osteotomy. Level III.

A 3-axis torsion quasi-zero-stiffness-based sensor system for angular vibration measurement

In this paper, a novel 3-axis torsion quasi-zero-stiffness (TQZS)-based sensor system is proposed for absolute rotation measurement in vibration systems. Analysis on the applied torque and structural parameters shows that the proposed mechanism with two concentric spheres connected by six symmetry distributed springs could approximately achieve TQZS features in three rotational degrees of freedom simultaneously, thus a remarkable torsional vibration measurement performance can be guaranteed. Although due to high stiffness, the mechanism also has high anti-interference ability about force or vibration in translational directions. Mathematical modeling and numerical simulations are carried out to show the effectiveness of the proposed 3-axis sensor system in different base vibrations. In consideration of its feasibility and high performance, it can be foreseen that the proposed TQZS-based sensor will get more and more implementations in various engineering practices with torsional vibration measurements.

O79: Tibialis anterior muscle in swing phase of gait before and after tendon shortening with simultaneous Achilles tendon lengthening in patients with hemiplegic cerebral palsy

Informed clinical decision making for femoral and/or tibial de-rotation osteotomies requires accurate measurement of patient function through gait analysis and anatomy through physical examination of bony torsions. Validity of gait analysis has been extensively studied; however, controversy remains regarding the accuracy of physical examination measurements of femoral and tibial torsion. Comparison between CT-scans and physical examination measurements of femoral neck anteversion (FNA) and external tibial torsion (ETT) were retrospectively obtained for 98 (FNA) and 64 (ETT) patients who attended a tertiary hospital for instrumented gait analysis between 2007 and 2010. The physical examination methods studied for femoral neck anteversion were the trochanteric prominence angle test (TPAT) and the maximum hip rotation arc midpoint (Arc midpoint) and for external tibial torsion the transmalleolar axis (TMA). Results showed that all physical examination measurements statistically differed to the CT-scans (bias(standard deviation): −2(14) for TPAT, −10(12) for Arc midpoint and −16(9) for TMA). Bland and Altman plots showed that method disagreements increased with increasing bony torsions in all cases but notably for TPAT. Regression analysis showed that only TMA and CT-scan measurement of external tibial torsion demonstrated good (R2 = 57%) correlation. Correlations for both TPAT (R2 = 14%) and Arc midpoint (R2 = 39%) with CT-scan measurements of FNA were limited. We conclude that physical examination should be considered as screening techniques rather than definitive measurement methods for FNA and ETT. Further research is required to develop more accurate measurement methods to accompany instrumented gait analysis.

Anterior and nasal transposition of inferior oblique muscle in cases of superior oblique palsy

To report long-term outcome of inferior oblique anterior and nasal transposition in superior oblique palsy. The medical records of patients with superior oblique palsy who underwent inferior oblique anterior nasal transposition were reviewed retrospectively. A comprehensive ophthalmic evaluation, including prism bar cover test and measurement of torsion, was performed for all cases. One-year postoperative results were evaluated for alignment in primary gaze, contralateral gaze, and upgaze; reduction in inferior oblique overaction and changes in fundus torsion to assess long-term outcome of the procedure. A total of 12 patients were included. Three cases also underwent horizontal muscle surgery. Mean age at the time of surgery was 20.6years. The median preoperative hypertropia was 21.5Δ (range, 12Δ-36Δ), corrected to 4.5Δ (range, 2Δ-10Δ) at 12months postoperatively (P=0.002). Median inferior oblique overaction decreased from +3 (range, +1 to +4) to 0 (range, -1 to +1). Preoperative fundus extorsion was 19.2° ± 6.7°; postoperative, 0.58° ± 1.8° (P<0.001). No consecutive hypotropia or underaction in elevation was observed in 10patients; 1 patient complained of torsional diplopia in upgaze. Extorsion was eliminated and head tilt improved in all patients. Inferior oblique anterior and nasal transposition resulted in good long-term outcomes in our patients with superior oblique palsy presenting with hypertropia, inferior oblique overaction, and extorsion in primary gaze.

Comparative Evaluation of a Positive-Locking Antirotation Mechanism in the Design of Telescopic Nails for Patients in the Growth Phase

The aim of this study is to develop an intramedullary telescopic nail that—in contrast to the current standard—is rotationally stable and firmly anchored in the bone proximally and distally, without containing any extraosseous components that may alter the surrounding soft tissue. Three prototypes for a positive-locking adapted telescopic intramedullary nail (PLATIN) were developed. In a series of biomechanical tests, the prototypes were compared with two Fassier–Duval telescopic nails, which represent the clinical standard. Axial pressure, torsion, and four-point bending measurements were carried out in a materials testing machine, with the telescopic nails implanted into composite bone. Tests were conducted without failure and up to failure. Specifically, the force required for telescoping, as well as torsional stiffness and bending stiffness, was investigated. Taking into account differences that were inherent in the materials, the prototypes showed similar results in the four-point bending tests. In the pressure tests, the prototypes required greater forces than the Fassier–Duval nails. The torsional stiffness was between 0.020 N·m/deg and 0.135 N·m/deg, depending on the diameter of the nail. Positive-locking effect was achieved by a hexagonal shape of an inner rod part and a hexagonal form-fitting outer tube part. Proximal and distal locking of the telescopic nail in the bone was performed by usage of K-Wires in specific arranged drill holes at the end of both parts. Based on these satisfactory results, the future clinical application of positive-locking irrotational telescopic nails can be expected. Furthermore, redesign or development of new designs for existing telescopic nails is recommended.

Correlation of the torsion values measured by rotational profile, kinematics, and CT study in CP patients

BackgroundThe purpose of study was to analyze correlations between bony torsions measured by Staheli’s rotation profile, computed tomography (CT) torsional study, and gait analysis in patients with cerebral palsy (CP). Materials & methodThe study group comprised of 26 children with CP (spastic diplegia, Gross Motor Function Classification System (GMFCS) 1–2, mean age 12.6 years) with torsional deformities. All subjects were assessed by examining: 1) rotational profile [internal rotation (IR) and external rotation (ER)], 2) CT torsional profile [femoral anteversion (FAV) and tibial torsion (TT)], and 3) gait analysis [mean hip rotation (HR) and mean knee rotation (KR)]. Statistical analysis was performed using the Pearson correlation test. ResultsIn the femur, there was good correlation between FAV and Staheli’s rotational profile of IR and ER (Pearson correlation coefficient (PC=0.69, 0.52, p<0.05)). ER correlated very strongly with mean HR during gait (PC=0.8, p<0.05). There was, however, poor correlation between HR and IR (p>0.05), and between HR and FAV (p>0.05).In the tibia, mean KR correlated well with thigh-foot angle (TFA) (PC=0.72) and CT tibia torsion (TT) (PC=0.62). TT also correlated with TFA (PC=0.62). ConclusionGait analysis and Staheli’s rotational profile reflect both static and dynamic factors of gait abnormalities. However, CT study reflect static factor primarily. Dynamic factors tend to influence the measurements of the femoral torsion only due to large rotational arc of hip joint. In surgical planning, it must be considered that HR sometimes does not correlate with CT anteversion angle. Similarly, it must also be considered that KR correlates well with TFA and CT TT angle.

Femoral Torsion: Impact of Femur Position on CT and Stereoradiography Measurements.

The purpose of this study is to evaluate stereoradiographic measurements of femoral torsion with different femoral positions, in comparison with CT measurements, with use of the current standard axial-slice technique. We hypothesize that CT measurements vary with femoral spatial positioning because of the resulting projection onto the CT plane, whereas stereoradiographic measurements, which are derived from a 3D reconstruction of the femur, remain constant. Both in vitro and in vivo studies were conducted. CT and stereoradiographic examinations were performed using 30 dry femurs in the following six femoral positions: neutral position (with the femoral mechanical axis aligned with the longitudinal axis of the CT scanner or stereoradiography system), 10° of abduction, 10° of adduction, 5° of flexion, 10° of flexion, and 5° of extension. The impact of femoral position on torsion measurement was assessed using paired t tests. In addition, 18 patients (mean [± SD] age, 42.3 ± 19.9 years) who underwent both CT and stereoradiography examinations were retrospectively assessed. The correlation between femoral positioning and torsion measurement was determined using the Pearson correlation coefficient. Flexion and extension statistically significantly affected CT measurement of femoral torsion (p < 0.01) but not stereoradiography measurement (p > 0.21). A strong correlation existed between hip flexion and the difference between femoral torsion measured by CT and stereoradiography (r = -0.80). The accuracy of femoral torsion determined by axial CT depends on the position of the femur. Hip flexion significantly reduced the femoral torsion angle measured by CT. Conversely, the accuracy of stereoradiography was independent of femur positioning. Thus, stereoradiography is preferable to CT for accurate measurement of femoral torsion, while it also substantially reduces the radiation dose.