James G. Richards

The measurement of human motion: A comparison of commercially available systems

Field tests were conducted to assess the clinical performance characteristics of seven optical-based and one electromagnetic-based biomechanical measurement system. A device placed in the center of the calibrated volume enabled the analysis of four optical system properties: (1) the ability to measure the distance between two constantly visible markers rotating in the volume, (2) the ability to measure motion associated with a static marker, (3) the ability to reconstruct position-time histories of markers that were visible to alternating sets of two or three cameras, and (4) the ability to measure the motion of a marker that moved in close proximity to a second marker. Results indicated that five of the seven optical systems produced less than 2.0 mm RMS errors when measuring fully visible moving markers, and typically less that 1.0 mm RMS error when measuring the stationary marker. All passive optical systems confused marker identifications when markers moved within 2 mm of each other in a 3 m long volume. The electromagnetic device was tested by mounting two sensors at a fixed distance and orientation, and measuring their variability as they moved in various patterns within a pre-defined volume. The electromagnetic system produced real-time results, but was clearly susceptible to repeatable interference from metal in the volume.

Comparison of surface mounted markers and attachment methods in estimating tibial rotations during walking: an in vivo study

The overall goal of this work was to determine an optimal surface-tracking marker set for tracking motion of the tibia during natural cadence walking. Eleven different marker sets were evaluated. The marker sets differed in the location they were attached to the shank, the method used to attach the marker sets to the segment and the physical characteristics of the marker sets. Angular position during stance for each marker set was expressed relative to the orientation of the tibia as measured using bone anchored markers. A marker set consisting of four markers attached to a rigid shell positioned over the distal lateral shank and attached to the leg using an underwrap attachment yielded the best estimate of tibial rotation. Rotational deviations of+/-2 degrees about the medio-lateral and antero-posterior axes, and+/-4 degrees about the longitudinal axis did occur even when using the optimal set of markers.

Analysis of the reliability and validity of the kinetic communicator exercise device.

The Kinetic Communicator (KINCOM), a microcomputer controlled, hydraulically driven device for the test, measurement, and rehabilitation of human joint function, was tested for the reliability and validity of its operating systems. Testing focused on the three primary functions of the KINCOM: lever arm position, lever arm velocity, and force measuring systems. Measurements of the functions were made via external devices and were compared to measurements simultaneously made by the KINCOM system. Tests were performed for both static and dynamic operation of the unit. Force measurements averaged a difference of 3.2% or less, lever arm speed was within 1.5% of the target speed in all cases, and no difference was found in position measurement. These discrepancies were felt to be due to calibration error and were not considered an indication of inaccuracy in the KINCOM system.

Variability of energy-consumption measures in children with cerebral palsy

Oxygen consumption measurements made on five repeated tests from five children with cerebral palsy (CP) and five nondisabled children of similar age and size were collected using the Cosmed K2 (Cosmed, Rome, Italy) oxygen-analysis system at free-walking velocity. Oxygen cost, oxygen consumption, and physiological cost index (PCI) were measured. There were no statistically significant differences in the percentage of variability of oxygen cost, oxygen consumption, or PCI between the disabled and nondisabled populations. Oxygen cost was the most reliable oxygen-use measurement with an average percentage of variability of 13.2% for the CP population and 13.9% for the nondisabled population. Physiological cost index was found be the least reliable measurement with the average percentages of variabilities of the disabled and nondisabled populations of 20.3 and 20.5%, respectively. Thus because of oxygen costs relatively low variability, it was the most sensitive measurement of change in gait efficiency.

Baseball: Influence of pelvis rotation styles on baseball pitching mechanics

Abstract Efficient, sequential timing is essential for upper level pitching. Interestingly, pitchers vary considerably in timing related elements of pitching style including pelvis rotation, arm cocking, stride leg behaviour, and pitch delivery time. The purpose of this study was to determine whether relationships exist among these elements by examining the overall style of pitchers exhibiting different pelvis rotation patterns. Pitching styles were defined by pelvis orientation at the instant of stride foot contact. Pitchers demonstrating a pelvis orientation greater than 30° were designated as ‘early rotators’, while pitchers demonstrating a pelvis orientation less than 30° were designated as ‘late rotators’. Kinematic and temporal differences were associated with the two styles. During the arm cocking phase, early rotators showed significantly greater shoulder external rotation at the instant of stride foot contact, earlier occurrence of maximum pelvis rotation angular velocity, and shorter time taken to complete the phase. However, by the instant of maximum shoulder external rotation, early and late rotators appeared remarkably similar as no significant difference occurred in pelvis and arm orientations. Therefore, it appears that early and late rotators used different methods to achieve similar results, including throwing velocity. Significant differences in throwing arm kinetics were also found for 10 of the 11 measures in the study. As the pelvis assumed a more open position at stride foot contact, maximum kinetic values were found to both decrease in magnitude and occur at an earlier time within the pitch.

Ultrasound Measurements of Torsions in the Tibia and Femur

BACKGROUND The purpose of the present study was to determine the validity and reliability of using ultrasound to measure tibial and femoral torsion. METHODS In vitro ultrasound measurements of torsion in 118 matched dried tibiae and femora were compared with direct anatomical measurements with use of simple regression. The second part of the study involved repeated in vivo ultrasound measurements made on twenty adult limbs to determine the clinical reliability of our methods. RESULTS The in vitro ultrasound measurements of femoral and tibial torsion were significantly related to the anatomical measurements (p < 0.001 for both). The inter-rater correlation coefficients between three examiners were 0.84 for both the tibial and femoral measurements, and the intra-rater correlation coefficients ranged from 0.86 to 0.98. The in vivo measurements were similar to the in vitro measurements, and the intra-rater correlation coefficients for repeated measures were 0.91 and 0.93 for femoral and tibial torsion, respectively. CONCLUSIONS Ultrasound is a viable tool for measuring torsion of the tibia and femur. In order to minimize measurement errors, the ultrasound measurement should be used to calculate the predicted value of torsion with use of the regression equation.

A method of Dynamic foot-pressure measurement for the evaluation of pediatric orthopaedic foot deformities

Dynamic foot-pressure measurements are time-sensitive measurements of the pressures under the foot while walking. Historically, many methods are used to measure these pressures; however, current medical literature does not contain a method suitable for the evaluation of pediatric orthopaedic foot deformities. A method for the measurement of dynamic foot pressure for the treatment of pediatric orthopaedic foot deformities was defined in this study. We established the dynamic foot-pressure pattern of a normal population using this method. Dynamic foot-pressure measurements were collected from 54 normal subjects (108 feet). These measurements were divided into the following five segments: the heel, the lateral midfoot, the medial midfoot, the lateral forefoot, and the medial forefoot. Standard tables and graphs were created describing the normal progression of pressure across each segment of the foot while walking. These standard tables and graphs can be used as a reference with which clinical measurements can be compared. This method may be useful as a diagnostic measure of foot deformities and may increase the clinicians ability to measure changes in foot deformity resulting from treatment intervention.

The efficacy of tone-reducing features in orthotics on the gait of children with spastic diplegic cerebral palsy.

This study analyzed the effects of tone-reducing features in ankle-foot orthotics (AFOs) on the gait of eight children (ages 4-11 years) with spastic diplegic cerebral palsy. A standard gait analysis was performed on each subject in each of three trial orthotics and in a baseline shoes-only condition. A 4-week accommodation period was allotted for each of the three devices: a standard hinged AFO, an AFO with tone-reducing features, and a supramalleolar orthotic with tone-reducing features. Most significant differences were at the ankle, between free-ankle and plantar flexion-limiting conditions. No significant functional changes in gait were evident with the addition of tone-reducing properties to a standard articulating AFO.

Knee moment profiles during walking: errors due to soft tissue movement of the shank and the influence of the reference coordinate system

The effect soft tissue movement of the shank had on knee joint moments during natural cadence walking was investigated in this study. This was examined by comparing knee moments determined from bone-anchored and surface mounted tracking targets. Six healthy adult subjects participated in this study. The largest difference (3 N m) occurred about the AP axis, with smaller differences of approximately 2 and 1 N m about the flexion/extension (F/E) and longitudinal (Long) axes, respectively. The magnitude of these differences would not likely affect the clinical interpretation of the data. The effect of reporting knee moments in two different orthogonal reference systems was also examined. The peak extension moment was significantly greater when expressed about an anatomical axis following the line of the malleoli than when the moment was reported about an axis parallel to the frontal plane of the shank. In contrast, the first peak abduction moment was significantly greater when expressed about an axis perpendicular to the frontal plane of the shank. Care should therefore be exercised whenever comparisons between studies are made in which the reference axes are not aligned.

Weight Transfer Patterns During the Golf Swing

Abstract Twenty right-handed male golfers participated as subjects in an investigation of the two-dimensional weight transfer pattern produced during the golf swing. Ten subjects possessed handicaps of less than 10 strokes while the remaining 10 subjects had handicaps greater than 20. Center of vertical force locations were sampled during the swing with a computerized forceplate at a rate of 350 Hz. The occurrence of the initiation of the downswing (TOS) was monitored by a vacuum transducer in the club grip while ball contact (CON) was monitored by a laser/photocell system. Variables analyzed consisted of minimum/maximum force distribution ratios from heel to toe and from back foot to target foot as well as distribution ratios at TOS and CON. Intraclass correlation coefficients showed all variables to be reliable for both groups (r > 0.8). A subsequent discriminant function analysis produced one significant function (p < .05) which served to distinguish between the low and high handicap groups. The accura...