Aurelio Cappozzo

Position and orientation in space of bones during movement: anatomical frame definition and determination

This paper deals with methodological problems related to the reconstruction of the position and orientation of the human pelvis and the lower limb bones in space during the execution of locomotion and physical exercises using a stereophotogrammetric system. The intention is to produce a means of quantitative description of joint kinematics and dynamics for both research and application. Anatomical landmarks and bone-embedded anatomical reference systems are defined. A contribution is given to definition of variables and relevant terminology. The concept of anatomical landmark calibration is introduced and relevant experimental approaches presented. The problem of data sharing is also addressed. This material is submitted to the scientific community for consideration as a basis for standardization. RELEVANCE: In order to make movement analysis effective in the solution of clinical problems, a structured conceptual background is needed in addition to standardized definitions and methods. Technical solutions which make data sharing and relevant data banks possible are also of primary importance. This paper makes suggestions in this context.

Position and orientation in space of bones during movement: experimental artefacts

This paper deals with the experimental problems related to the reconstruction of the position and orientation of the lower limb bones in space during the execution of locomotion and physical exercises. The inaccuracies associated with the relative movement between markers and underlying bone are analysed. Quantitative information regarding this movement was collected by making experiments on subjects who had suffered fractures and were wearing either femoral or tibial external fixators. These latter devices provided frames that were reliably rigid with the bone involved, and hence the possibility of assessing the relative movement between markers mounted on the skin and this bone. Anatomical frames associated with thigh and shank were reconstructed using technical frames based on different clusters of skin markers and their rotation with respect to the relevant bone evaluated. Marker movement was also assessed in subjects with intact musculoskeletal structures using digital videofluoroscopy.

Validation of a functional method for the estimation of hip joint centre location

The present study assesses the accuracy with which the subject specific coordinates of the hip joint centre (HJC) in a pelvic anatomical frame can be estimated using different methods. The functional method was applied by calculating the centre of the best sphere described by the trajectory of markers placed on the thigh during several trials of hip rotations. Different prediction methods, proposed in the literature and in the present investigation, which estimate the HJC of adult subjects using regression equations and anthropometric measurements, were also assessed. The accuracy of each of the above-mentioned methods was investigated by comparing their predictions with measurements obtained on a sample of 11 male adult able-bodied volunteers using roentgen stereophotogrammetric analysis (RSA), assumed to provide the true HJC locations. Prediction methods estimated the HJC location at an average rms distance of 25-30 mm. The functional method performed significantly better and estimated HJCs within a rms distance of 13 mm on average. This result may be confidently generalised if the photogrammetric experiment is carefully conducted and an optimal analytical approach used. The method is therefore suggested for use in motion analysis when the subjects hip range of motion is not limited. In addition, the facts that it is not an invasive technique and that it has relatively small and un-biased errors, make it suitable for regression equations identification with no limit to sample size and population typology.

Surface-marker cluster design criteria for 3-D bone movement reconstruction

When three-dimensional (3-D) human or animal movement is recorded using a photogrammetric system, bone-embedded frame positions and orientations are estimated from reconstructed surface marker trajectories using either nonoptimal or optimal algorithms. The effectiveness of these mathematical procedures in accommodating for both photogrammetric errors and skin movement artifacts depends on the number of markers associated with a given bone as well as on the size and shape characteristics of the relevant cluster. One objective of this paper deals with the identification of marker cluster design criteria aimed at the minimization of error propagation from marker coordinates to bone-embedded frame position and orientation. Findings allow for the quantitative estimation of these errors for any given cluster configuration and suggest the following main design criteria. A cluster made up of four markers represents a good practical compromise. Planar clusters are acceptable, provided in quasi-isotropic distribution. The root mean square distance of the markers from their centroid should be greater than ten times the standard deviation of the marker position error. The second objective of this paper deals with the identification of the optimal cluster position and orientation on the limb aimed at the minimization of error propagation to anatomical landmark laboratory coordinates. Cluster position should be selected to minimize skin movement artifacts. The longest principal axis of the marker distribution should be oriented toward the relevant anatomical landmark position.

Gait analysis methodology

Abstract This paper reports a discussion on the heuristic and applicative objectives of gait analysis and on the experimental and analytical methods used in this context. In particular, the use of an effective method of description of joint kinematics and kinetics i.e., joint function, as applied to the lower limb joints during normal walking is reported. A methodological hypothesis for the evaluation of gait, as an integrated phenomenon is presented and supported by experimental data concerning normal and pathological walking and sportive gaits.

Skin movement artefact assessment and compensation in the estimation of knee-joint kinematics

In three dimensional (3-D) human movement analysis using close-range photogrammetry, surface marker clusters deform and rigidly move relative to the underlying bone. This introduces an important artefact (skin movement artefact) which propagates to bone position and orientation and joint kinematics estimates. This occurs to the extent that those joint attitude components that undergo small variations result in totally unreliable values. This paper presents an experimental and analytical procedure, to be included in a subject-specific movement analysis protocol, which allows for the assessment of skin movement artefacts and, based on this knowledge, for their compensation. The effectiveness of this procedure was verified with reference to knee-joint kinematics and to the artefacts caused by the hip movements on markers located on the thigh surface. Quantitative validation was achieved through experimental paradigms whereby prior reliable information on the target joint kinematics was available. When position and orientation of bones were determined during the execution of a motor task, using a least-squares optimal estimator, but the rigid artefactual marker cluster movement was not dealt with, then knee joint translations and rotations were affected by root mean square errors (r.m.s.) up to 14 mm and 6 degrees, respectively. When the rigid artefactual movement was also compensated for, then r.m.s errors were reduced to less than 4 mm and 3 degrees, respectively. In addition, errors originally strongly correlated with hip rotations, after compensation, lost this correlation.

A general computing method for the analysis of human locomotion

Abstract This is a study of a method for obtaining a mathematical description of the most significant variables concerning kinematics and dynamics of human locomotion. The method is characterized by a typical approach of system theory. It consists of an analytical procedure for the processing of data obtained by the most common experimental techniques in this area. i.e. photography for recording the movement, and the force platform for measuring the ground reactions. The proposed mathematical algorithms have been designed to obtain the time functions of the variables cited above in an analytical form, and a measurement of the relative indefiniteness induced by experimental errors. The results of the latter allows a critical evaluation of the experimental procedure. In particular, a maximum limit of the number of experimental data to be taken, can be evaluated. The subsystem of the locomotor apparatus which the present work deals with, is the lower limb. The method presented can be applied successfully to all of the gaits having a constant mean direction of progression and periodic time patterns.

Pelvis and lower limb anatomical landmark calibration precision and its propagation to bone geometry and joint angles

Human movement analysis using stereophotogrammetry is based on the reconstruction of the instantaneous laboratory position of selected bony anatomical landmarks (AL). For this purpose, knowledge of an ALs position in relevant bone-embedded frames is required. Because ALs are not points but relatively large and curved areas, their identification by palpation or other means is subject to both intra- and inter-examiner variability. In addition, the local position of ALs, as reconstructed using anad hoc experimental procedure (AL calibration), is affected by photogrammetric errors. The intra- and inter-examiner precision with which local positions of pelvis and lower limb palpable bony ALs can be identified and reconstructed were experimentally assessed. Six examiners and two subjects participated in the study. Intra- and inter-examiner precision (RMS distance from the mean position) resulted in the range 6–21 mm and 13–25 mm, respectively. Propagation of the imprecision of ALs to the orientation of bone-embedded anatomical frames and to hip, knee and ankle joint angles was assessed. Results showed that this imprecision may cause distortion in joint angle against time functions to the extent that information relative to angular movements in the range of 10 degrees or lower may be concealed. Bone geometry parameters estimated using the same data showed that the relevant precision does not allow for reliable bone geometry description. These findings, together with those relative to skin movement artefacts reported elswhere, assist the human movement analysts consciousness of the possible limitations involved in 3D movement analysis using stereophotogrammetry and call for improvements of the relevant experimental protocols.

Effects of hip joint centre mislocation on gait analysis results

Methods to determine the hip joint centre (HJC) location are necessary in gait analysis. It has been demonstrated that the methods proposed in the literature involve large mislocation errors. The choice should be made according to the extent by which HJC location errors distort the estimates of angles and resultant moments at the hip and knee joints. This study aimed at quantifying how mislocation errors propagate to these gait analysis results. Angles and moments at the hip and knee joint were calculated for five able-bodied subjects during level walking. The nominal position of the HJC was determined as the position of the pivot point of a 3D movement of the thigh relative to the pelvis. Angles and moments were then re-calculated after having added to HJC co-ordinates errors in the range of +/-30 mm. Angles and moments at both hip and knee joints were affected by HJC mislocation. The hip moments showed the largest propagation error: a 30 mm HJC anterior mislocation resulted in a propagated error into flexion/extension component of about -22%. The hip abduction/adduction moment was found the second largest affected quantity: a 30 mm lateral HJC mislocation produced a propagated error of about -15%. Finally, a 30 mm posterior HJC mislocation produced a delay of the flexion-to-extension timing in the order of 25% of the stride duration. HJC estimation methods with minimum antero-posterior error should therefore be preferred.

Analysis of the linear displacement of the head and trunk during walking at different speeds

The displacement of points lying on the longitudinal axis of the upper part of the human body at head, shoulder and pelvis level was estimated in the three dimensions of space during level walking on a straight line at speeds ranging from 0.99 to 2.79 m s−1. A stereophotogrammetric technique was used. Forty-one walking trials of five young male subjects with no apparent abnormalities of the locomotor system, were recorded. Harmonic analysis of the displacement functions was carried out. This permitted the identification of two superposed components of the motion pattern of the upper part of the body. One, described as intrinsic to the locomotor act in its essential form, showed characteristics that were remarkably constant both within and between subjects. The other, described as extrinsic, showed erratic features, possibly due to functional or anatomical asymmetries of the locomotor apparatus or to environmental disturbances. The identification of these two components of the motion pattern formed the basis for the definition of a standard average normal walking. Modifications of the motion pattern arising from variations in the speed of progression are identified and discussed also with the help of Lissajouss figures. Emphasis was given to the sources and magnitude of the inaccuracies with which the experimental and analytical results were obtained.