Robert W. Mann

THE FREQUENCY CONTENT OF GAIT

We address amplification of noise in double differentiation of position histories for dynamic analysis of gait. Measurements of the frequency domain characteristics of signal and noise are required to quantitatively assess errors in raw, filtered, and dynamic gait data. The results of a simple technique to determine the frequency content of gait using a population of 12 subjects and a total of 30 gait records is presented.

Limitations of the continuum assumption in cancellous bone

Most existing stress analyses of the skeleton which consider cancellous bone assume that it can be modelled as a continuum. In this paper we develop a criterion for the validity of this assumption. The limitations of the continuum assumption appear in two areas: near biologic interfaces, and in areas of large stress gradients. These limitations are explored using a probabilistic line scanning model for density measurement, resulting in an estimate of density accuracy as a function of line length which is experimentally verified. Within three to five trabeculae of an interface, a continuum model is suspect. When results as predicted using continuum analyses vary by more than 20-30% over a distance spanning three to five trabeculae, the results are suspect.

Mechanics of a constrained chair-rise

A sit-to-stand task is analyzed by a method which estimates the segmental and whole body center of mass (CoM) kinematics and kinetics using bilateral whole body kinematic data from nine healthy young female subjects. The sit-to-stand, or chair-rise, task is constrained with regard to chair height, pace, initial lower limb position and arm use. The chair-rise maneuver is divided into four phases; (1) the flexion momentum phase; (2) the momentum transfer phase; (3) the vertical extension phase; and (4) the stabilization phase; the first three are examined in detail here. The momentum transfer phase, which immediately follows lift-off from the seat of the chair, is the most dynamic portion of the event, demanding a high degree of coordination. This maneuver is analyzed in order to determine if trunk movement is used only to position the body center of gravity or if the trunk motion generates momentum which is important during the brief but critical period of dynamic equilibrium immediately following lift-off from the chair. Our evidence points to the latter case and indicates that inter-segmental momentum transfer is possible during this period.

An evaluation of the approaches of optimization models in the prediction of muscle forces during human gait

Abstract Kinematic data acquisition systems and analytical optimization procedures for the study of human gait have been investigated with the goal of ascertaining individual muscle forces during a walking cycle. Improvements on existing approaches were found to be more crucially dependent on the accurate determination of joint angles and the calculation of joint torques than on the particular optimization criteria employed. Physiologically-based information on the functions of, and constraints on, individual muscles supplemented the optimization procedures. The results of the study elucidate the temporal pattern and quantitative levels of muscle force in a walking cycle for a series of normal persons.

Myoelectric Signal Processing: Optimal Estimation Applied to Electromyography - Part I: Derivation of the Optimal Myoprocessor

This paper (Part I of II) describes the development of a novel technique for processing the electrical activity of muscle which uses multiple channels of myoelectric activity. A phenomenological mathematical model of myoelectric activity is formulated. From this model, a mathematical statement of the optimal myoelectric signal processor is derived, and some of its properties are investigated. This mathematical statement encompasses and places in perspective almost all single-channel myoprocessor developments to date, as well as specifying the optimal multiple-channel myoprocessor. An experimental demonstration of the efficacy of this processor is presented in a subsequent paper (Part II).

Modelling of the biomechanics of posture and balance.

A technique for studying the relationship of posture to balance has been developed. To investigate this relationship quantitatively, the human body was treated as consisting of 11 rigid body segments, each with six degrees of freedom. A bilateral Selspot II/TRACK data acquisition system provides position and orientation kinematic data for estimation of the trajectories of the individual body segment centers of gravity. From these, the whole body center of gravity is estimated and compared to concurrent force plate center of force data. Center of gravity and center of force excursions agree where dynamics are not significant. The technique may be employed to study quiet stance, response to postural disturbances, or the initiation and coordination of complex movements such as gait.

Improved techniques for measuring in vitro the geometry and pressure distribution in the human acetabulum—I. Ultrasonic measurement of acetabular surfaces, sphericity and cartilage thickness

Abstract A unique, highly accurate, non-contacting method for measuring the loaded and unloaded shape and thickness of acetabular articular cartilage employing ultrasound is described. The unloaded cartilage surface is shown to be spherical with localized deviations less than 150 μm. The calcified cartilage interface is quite irregular with deviations from sphericity of 500 μm. The centers of the best-fitting spheres to the cartilage surface and the calcified interface are displaced resulting in decreased cartilage thickness in the anterior medial aspect.

Myoelectric Signal Processing: Optimal Estimation Applied to Electromyography - Part II: Experimental Demonstration of Optimal Myoprocessor Performance

This paper (Part II of two) presents an experimental demonstration of the performance achieved by implementing the mathematically derived optimal myoprocessor described in Part I. Almost an order-of-magnitude improvement over the common myoprocessor is obtained. Excellent agreement of the experimental results with the analytical predictions verifies the mathematical analysis. The relative contributions of each stage of the optimal myoprocessor are examined. A discussion and comparison of several existing and proposed techniques for myoprocessor improvement are presented.

Optical verification of a technique for in situ ultrasonic measurement of articular cartilage thickness

Several investigators have used pulse-echo ultrasonics to measure the thickness of articular cartilage in situ. The underlying assumption in all measurements was that the second reflection used in thickness calculations was from the calcified-cartilage/cartilage boundary (tidemark). To investigate this assumption, the thickness of 24 cartilage plugs excised from a human femoral head was measured both ultrasonically and optically. Measurements established that the second reflection was from the tidemark and validated the ultrasonic technique as a method of mapping the thickness distribution of articular cartilage in synovial joints in situ.

Improved techniques for measuringin vitro the geometry and pressure distribution in the human acetabulum—II. Instrumented endoprosthesis measurement of articular surface pressure distribution

Abstract A technique to measure in vitro the distribution of pressure on the cartilage surface of the human acetabulum using a modified endoprosthesis with fourteen integral pressure transducers is described. Under a constant load vector pressure contour maps are generated for times from shortly after loading until 20 min into cartilage consolidation. The peak pressure decreases with time as the area of contact increases. The pressure distribution is neither uniform nor even axisymmetric about the load vector. We believe that the highly irregular pressure profiles observed are due primarily to cartilage thickness distribution and irregularities at the calcified cartilage interface as described in Part I.