Janet L. Ronsky

Gait characteristics as a function of age and gender

Abstract Sixty male and fifty-eight female subjects ranging in age from 20 to 79 years performed walking at a controlled pace barefoot, wearing standard shoes, and wearing their personal shoes. Additionally these subjects performed walking in the standard shoe at a freely selected speed. Selected kinematic variables for the knee and ankle joint complexes and ground reaction forces were measured in three dimensions to determine differences with respect to age and gender. Additionally a comparison of the path of motion during ground contact and the active range of motion measured in a range of motion fixture were made. A multivariate analysis revealed a number of the kinematic and kinetic variables which were significantly different although the absolute differences were generally small. The comparison of path of motion and range of motion revealed a high correlation for abduction and adduction and plantarflexion and dorsiflexion. It is speculated that changes in gait pattern with increasing age are associated with decreasing muscle strength and a need for increased stability during locomotion with increasing age. The high correlation between path of motion and range of motion is associated with the decrease in muscle strength with increasing age, which is assumed to influence both path of motion and range of motion.

Reliability of trunk shape measurements based on 3-D surface reconstructions

This study aimed to estimate the reliability of 3-D trunk surface measurements for the characterization of external asymmetry associated with scoliosis. Repeated trunk surface acquisitions using the Inspeck system (Inspeck Inc., Montreal, Canada), with two different postures A (anatomical position) and B (‘‘clavicle’’ position), were obtained from patients attending a scoliosis clinic. For each acquisition, a 3-D model of the patient’s trunk was built and a series of measurements was computed. For each measure and posture, intraclass correlation coefficients (ICC) were obtained using a bivariate analysis of variance, and the smallest detectable difference was calculated. For posture A, reliability was fair to excellent with ICC from 0.91 to 0.99 (0.85 to 0.99 for the lower bound of the 95% confidence interval). For posture B, the ICC was 0.85 to 0.98 (0.74 to 0.99 for the lower bound of the 95% confidence interval). The smallest statistically significant differences for the maximal back surface rotation was 2.5 and 1.5° for the maximal trunk rotation. Apparent global asymmetry and axial trunk rotation indices were relatively robust to changes in arm posture, both in terms of mean values and within-subject variations, and also showed a good reliability. Computing measurements from cross-sectional analysis enabled a reduction in errors compared to the measurements based on markers’ position. Although not yet sensitive enough to detect small changes for monitoring of curve natural progression, trunk surface analysis can help to document the external asymmetry associated with different types of spinal curves as well as the cosmetic improvement obtained after surgical interventions. The anatomical posture is slightly more reliable as it allows a better coverage of the trunk surface by the digitizing system.

Alterations in Knee Joint Laxity During the Menstrual Cycle in Healthy Women Leads to Increases in Joint Loads During Selected Athletic Movements

Background It has been speculated that the hormonal cycle may be correlated with higher incidence of ACL injury in female athletes, but results have been very contradictory. Hypothesis Knee joint loads are influenced by knee joint laxity (KJL) during the menstrual cycle. Study Design Controlled laboratory study. Methods Serum samples and KJL were assessed at the follicular, ovulation, and luteal phases in 26 women. Knee joint mechanics (angle, moment, and impulse) were measured and compared at the same intervals. Each of the 26 subjects had a value for knee laxity at each of the 3 phases of their cycle, and these were ordered and designated low, medium, and high for that subject. Knee joint mechanics were then compared between low, medium, and high laxity. Results No significant differences in knee joint mechanics were found across the menstrual cycle (no phase effect). However, an increase in KJL was associated with higher knee joint loads during movement (laxity effect). A 1.3-mm increase in KJL resulted in an increase of approximately 30% in adduction impulse in a cutting maneuver, an increase of approximately 20% in knee adduction moment, and a 20% to 45% increase in external rotation loads during a jumping and stopping task (P < .05). Conclusion Changes in KJL during the menstrual cycle do change knee joint loading during movements. Clinical Relevance Our findings will be beneficial for researchers in the development of more effective ACL injury prevention programs.

Indices of torso asymmetry related to spinal deformity in scoliosis.

OBJECTIVE To develop indices that quantify 360 degrees torso surface asymmetry sufficiently well to estimate the Cobb angle of scoliotic spinal deformity within the clinically important 5-10 degrees range. DESIGN Prospective study in 48 consecutive adolescent scoliosis patients (Cobb angles 10-71 degrees ). BACKGROUND Scoliotic surface asymmetry has been quantified on the back surface by indices such as back surface rotation (BSR) and curvature of the spinous process line and torso centroid line, though with limited success in spinal deformity estimation. Quantification of 360 degrees torso shape may enhance surface-spine correlation and permit reduced use of harmful X-rays in scoliosis. METHODS For each patient a 3D torso surface model was generated concurrently with postero-anterior X-rays. We computed indices describing principal axis orientation, back surface rotation, and asymmetry of the torso centroid line, left and right half-areas and the spinous process line. We calculated correlations of each index to the Cobb angle and used stepwise regression to estimate the Cobb angle. RESULTS Several torso asymmetry indices correlated well to the Cobb angle (r up to 0.8). The Cobb angle was best estimated by age, rib hump and left-right variation in torso width in unbraced patients and by centroid lateral deviation in braced patients. A regression model estimated the Cobb angle from torso indices within 5 degrees in 65% of patients and 10 degrees in 88% (r=0.91, standard error=6.1 degrees ). CONCLUSION Consideration of 360 degrees torso surface data yielded indices that correlated well to the Cobb angle and estimated the Cobb angle within 10 degrees in 88% of cases. RELEVANCE The torso asymmetry indices developed here show a strong surface-spine relation in scoliosis, encouraging development of a model to detect scoliosis magnitude and progression from the surface shape with minimal X-ray radiation.

Relationship between knee joint laxity and knee joint mechanics during the menstrual cycle

Background: An increase in knee laxity during the menstrual cycle may increase the risk of anterior cruciate ligament injury. Objective: To investigate whether changing knee laxity during the menstrual cycle correlates with changing knee joint loads in a cutting manoeuvre. Design: Cross-sectional study. Setting: Laboratory testing. Participants: 25 healthy women, with a normal menstrual cycle, no history of oral contraceptive use, and no previous knee injury Interventions: Serum hormone concentrations were assessed and knee joint laxity at a load of 89 N was measured during the follicular, ovulation and luteal phases. Participants performed 10 trials of a cutting manoeuvre to quantify knee joint mechanics at each test session. Main outcome measurements: Knee joint laxity (mm), peak knee angle (°) and knee joint moment (Nm) and knee joint impulse (Nms). Results: Increased knee laxity was observed during ovulation compared with the luteal phase, but no significant changes in knee mechanics corresponding to menstrual phases were found. A positive correlation was found between changes in knee laxity and changes in knee joint loads (Δmoment or Δimpulse) from the follicular phase to ovulation, and from ovulation to the luteal phase (p<0.05). Women in whom knee laxity increased showed increased knee loads, and those in whom knee laxity decreased showed decreased knee loads during the menstrual cycle. Conclusions: Knee laxity correlates positively with knee joint loads, and increased knee laxity during the menstrual cycle may be a potential risk factor for anterior cruciate ligament injuries in certain women during sports activity.

Estimation of spinal deformity in scoliosis from torso surface cross sections

Study Design. Correlation of torso scan and three-dimensional radiographic data in 65 scans of 40 subjects. Objectives. To assess whether full-torso surface laser scan images can be effectively used to estimate spinal deformity with the aid of an artificial neural network. Summary of Background Data. Quantification of torso surface asymmetry may aid diagnosis and monitoring of scoliosis and thereby minimize the use of radiographs. Artificial neural networks are computing tools designed to relate input and output data when the form of the relation is unknown. Methods. A three-dimensional torso scan taken concurrently with a pair of radiographs was used to generate an integrated three-dimensional model of the spine and torso surface. Sixty-five scan–radiograph pairs were generated during 18 months in 40 patients (Cobb angles 0–58°): 34 patients with adolescent idiopathic scoliosis and six with juvenile scoliosis. Sixteen (25%) were randomly selected for testing and the remainder (n = 49) used to train the artificial neural network. Contours were cut through the torso model at each vertebral level, and the line joining the centroids of area of the torso contours was generated. Lateral deviations and angles of curvature of this line, and the relative rotations of the principal axes of each contour were computed. Artificial neural network estimations of maximal computer Cobb angle were made. Results. Torso–spine correlations were generally weak (r < 0.5), although the range of torso rotation related moderately well to the maximal Cobb angle (r = 0.64). Deformity of the torso centroid line was minimal despite significant spinal deformity in the patients studied. Despite these limitations and the small data set, the artificial neural network estimated the maximal Cobb angle within 6° in 63% of the test data set and was able to distinguish a Cobb angle greater than 30° with a sensitivity of 1.0 and specificity of 0.75. Conclusions. Neural-network analysis of full-torso scan imaging shows promise to accurately estimate scoliotic spinal deformity in a variety of patients.

In vivo quantification of the cat patellofemoral joint contact stresses and areas

A new method for in vivo measurement of patellofemoral joint contact areas, stresses, and patellar displacements, with joint loading approximating physiologic conditions was developed. Joint contact measurements were obtained using pressure sensitive film inserted directly between articular joint surfaces. Two-dimensional joint kinematics were measured using a high-speed video based motion analysis system. Joint loading, provided by quadriceps muscle stimulation, was measured with an implantable force transducer (IFT). Variations in joint mechanics as a function of joint flexion angle, joint loading and joint stability (anterior cruciate ligament intact or transected) were determined for four adult male cats. The contact measurements obtained with the pressure sensitive film displayed high repeatability with a standard error of +/- 6.8% of the mean value of the median pressure and +/- 4.4% of the mean contact area value. Substantial differences in joint mechanics were reliably detected with the new technique. The influence of experimental procedures, such as incisions in the joint capsule and insertion of pressure sensitive film between the articular surfaces, produced minimal changes in the joint kinematics during muscular contraction.

In Vivo Measurement of the Dynamic 3-D Kinematics of the Ovine Stifle Joint

The ovine stifle joint is a promising animal model for investigation of joint mechanobiology. A method for in vivo measurement of dynamic 3-D kinematics of the ovine stifle joint is described (accuracy: 0.36 +/- 0.39 mm). Inter-subject variability in kinematics is greater than both intra-subject and inter-session variability. For future studies in which joint kinematics are measured prior to and following controlled orthopaedic interventions, pooling of data should be avoided and each subject should act as its own control.

Modeling axi-symmetrical joint contact with biphasic cartilage layers—An asymptotic solution

The articular contact surfaces in human and animal joints are highly variable. Articular cartilage thickness and the material properties of the cartilage vary as a function of location in the joint and may also change in the pathologic state. In order to study practical joint contact problems, we extended the model for the contact of two biphasic cartilage layers proposed by Ateshian et al. [J. Biomechanics 27, 1347-1360 (1994)] by combining the assumption of the kinetic relationship from classical contact mechanics with the joint contact model for biphasic articular cartilage. In order to illustrate the characteristics of the proposed model, the contact problem was solved numerically for different curvatures of the contact surfaces, and for different thicknesses and material properties of the cartilage layers. Each cartilage layer was assumed to have constant thickness within the contact region. The contact radius, the relative displacement between the contacting bodies, contact pressure, and the stress distributions within the cartilage layers were calculated by applying a step load for a time period of 200 s. The contact radius was found to be sensitive to the change in thickness of the cartilage, and was not very sensitive to the change in the material property of the cartilage. The peak effective stress and the maximal shear stress were predicted to occur at the cartilage-bone interface for all simulated cases, which is in agreement with other theoretical research and supports the experimental findings in the literature on the origins of cartilage damage. For articular cartilage layers of different thicknesses, the stresses in the thick layer were found to be higher than those in the thin layer. Compared to other models of joint contact, the present model offers more possibilities for investigating practical applications, such as simulating the effects associated with cartilage degeneration in diseases such as osteoarthritis, and comparing theoretical predictions with experimental measurements of pressure distribution and contact area in joints.

Reconstruction of laser-scanned 3D torso topography and stereoradiographical spine and rib-cage geometry in scoliosis

Assessments of scoliosis are routinely done by means of clinical examination and full spinal x-rays. Multiple exposure to ionization radiation, however, can be hazardous to the child and is costly. Here, we explain the use of a noninvasive imaging technique, based on laser optical scanning, for quantifying the three-dimensional (3D) trunk surface topography that can be used to estimate parameters of 3D deformity of the spine. The laser optical scanning system consisted of four BIRIS laser cameras mounted on a ring moving along a vertical axis, producing a topographical mapping of the entire torso. In conjunction with the laser scans, an accurate 3D reconstruction of the spine and rib cage were developed from the digitized x-ray images. Results from 14 scoliotic patients are reported. The digitized surfaces provided the foundation data to start studying concordance of trunk surface asymmetry and spinal shape in idiopathic scoliosis.