Biomedical subjects

Antony J Hodgson

Publications and source records attributed to Antony J Hodgson.

7 recordsLinked to original sources

PubMed2006

Assessing cognitive & motor performance in minimally invasive surgery (MIS) for training & tool design.

The objective of this paper is to present the development of a new modelling diagram (MCMD) to represent MIS procedures in terms of both motor and cognitive actions. Through observation and analysis of several laparoscopic cholecystectomy procedures and based on task analysis techniques, we created a diagram language composed of six primary symbols: processes, decisions, interrupt service routines (ISRs), options points and AND and OR gates. We then tested and refined them during 10 new cases until no further changes seemed necessary, we have since applied this approach to 6 laparoscopic colorectal surgeries and have found that no further symbols were necessary though the procedural representation was naturally different. This modelling diagram allowed us to represent both cognitive and motor performance aspects of surgical procedures in a unified framework and will in future allow us to assess motor performance on particular surgical tasks at particular points in the procedure (i.e., the surgical context).

Computer Simulation↗

PubMed2005

Saturated muscle activation contributes to compensatory reaching strategies after stroke.

The control and execution of movement could potentially be altered by the presence of stroke-induced weakness if muscles are incapable of generating sufficient power. The purpose of this study was to identify compensatory strategies during a forward (sagittal) reaching task for 20 persons with chronic stroke and 10 healthy age-matched controls. We hypothesized that the paretic anterior deltoid would be maximally activated (i.e., saturated) during a reaching task and that task completion would require activation of additional muscles, resulting in compensatory movements out of the sagittal plane. For reaching movements by control subjects, joint motion remained largely in the sagittal plane and hand trajectories were smooth and direct. Movement characteristics of the nonparetic arm of stroke subjects were similar to control subjects except for small increases in the abduction angle and the percentage that anterior deltoid was activated. In contrast, reaching movements of the paretic arm of stroke subjects were characterized by increased activation of all muscles, especially the lateral deltoid, in addition to the anterior deltoid, with resulting shoulder abduction power and segmented and indirect hand motion. For the paretic arm of stroke subjects, muscle and kinetic compensations increased with impairment severity and weaker muscles were used at a higher percentage of their available muscle activity. These results suggest that the inability to generate sufficient force with the typical agonists involved during a forward reaching task may necessitate compensatory muscle recruitment strategies to complete the task.

Adaptation, Physiological↗

PubMed2003

Linear spring-damper model of the hypertonic elbow: reliability and validity.

Hypertonia of the elbow joint complex is common in individuals with stroke and is related to the magnitude of the torque response (described by position dependent parameters) during constant velocity extensions. The objective of this study was to model position and velocity dependent characteristics of hypertonia. For both the more and less affected arms in 17 persons with chronic stroke, we measured the torque response to constant velocity stretches (30-180 degrees/s). The responses were combined in position-velocity space and parameters of stiffness, damping, and offset angle were determined from a linear spring-damper model of the torque profile. The model was assessed at three levels: (1) ability to describe the combined torque profile variance, (2) reliability of parameters, and (3) validity of parameters (i.e. clinical correlation). Model parameters fit the torque profiles of both arm groups well and exhibited day-to-day reliability. Stiffness (r=0.820), damping (r=0.816), and 'viscoelasticity' (r=0.909), a composite parameter index developed posthoc, were highly correlated to a manual assessment of hypertonia (Modified Ashworth Scale). Mechanically determined parameters of hypertonia graded along a continuum may have better discriminatory power than manual assessments and thus, may be better at tracking recovery and evaluating interventions.

Aged↗

PubMed2003

Time and magnitude of torque generation is impaired in both arms following stroke.

Muscle strength, usually measured as the peak torque during maximal contraction, is impaired in persons with stroke. Time-dependent properties of muscle contraction may also be altered but have not been quantified. We quantified both magnitude (peak torque) and time-dependent parameters (times to develop and reduce torque) in eight different isometric joint actions. Parameters were compared among the more and less affected arms of 20 persons with chronic stroke and the nondominant arms of 10 similarly aged healthy persons. Torque-generation parameters were independent from one another (i.e., low correlations) and highly reliable between trials and days. All parameters were impaired in the more affected arm, whereas peak torque and time to develop torque were impaired in the less affected arm. Following stroke, torque-generation impairments include both magnitude and time-dependent properties and exist not only in the more affected but also in the less affected arm. Clinicians attempting to improve upper-extremity function should employ therapeutic exercises that challenge patients to improve both their strength and speed of muscle contraction.

Aged↗

PubMed2002

Bone cutting errors in total knee arthroplasty.

Although achieving precise implant alignment is crucial for producing good outcomes in total knee arthroplasty, the contribution of the bone-cutting process to overall variability has not been measured previously. Eight orthopaedic surgeons with varying amounts of total knee arthroplasty experience performed 85 resections on 19 cadaver femora and tibiae, and the planes of the resulting cut surfaces were compared with the guide planes. Varus-valgus alignment variability ranged from 0.4 degrees to 0.8 degrees SD for expert and trainee surgeons. Sagittal variability was approximately 1.3 degrees SD for both surgeon groups. Slotted cutting guides reduced the variability and eliminated the bias in the sagittal plane for experienced surgeons but did not improve significantly frontal plane alignment variability. Guide movement contributed 10% to 40% of the total cutting error, depending on cut and guide type.

Arthroplasty, Replacement, Knee↗

PubMed2002

Quantitative methodology of evaluating surgeon performance in laparoscopic surgery.

Quantitative performance and skill assessments are critical for evaluating the progress of surgical residents and the efficacy of different training programs. Current evaluation methods are subjective and potentially unreliable, so there is a need for objective methods to evaluate surgical performance. We identify a feasible method to measure kinematic data in the live operating room setting and to assess the repeatability of an analysis method based on a hierarchical decomposition of surgical tasks. We used an optoelectronic motion analysis system to acquire postural data and tool tip trajectories of one expert surgeon over a period of four months. To assess repeatability of performance measures, we created a hierarchical decomposition diagram describing the procedure in terms of surgical tasks, tool sequences and fundamental tool actions. From the kinematic data, we extracted characteristic measures of individual tool actions and compared these measured distributions using the Kolmogorov-Smirnov statistic. The comparisons of distributions show consistent performance over time by a trained surgeon and little effect from patient variability, and so are likely reliable measures of performance. An expanded set of reliable kinematic measures will form the basis for quantifying surgical skill and should be useful in validating surgical simulations for use in training, certifying surgeons and designing and evaluating new surgical tools.

Biomechanical Phenomena↗

PubMedDate not supplied

Computer-assisted femoral head resurfacing.

Femoral head resurfacing is re-emerging as a surgical option for younger patients who are not yet candidates for total hip replacement. However, this procedure is more difficult than total hip replacement, and the mechanical jigs typically used to align the implant produce significant variability in implant placement and take a significant amount of time to position properly. We propose that a computer-assisted surgical (CAS) technique could reduce implant variability with little or no increase in operative time. We describe a new CAS technique for this procedure and demonstrate in a cadaver study of five paired femurs that the CAS technique in the hands of a novice surgeon markedly reduced the varus/valgus variability of the implant relative to the pre-operative plan (2 degrees standard deviation for CAS versus 5 degrees for a mechanical jig operated by an expert surgeon). We also show that the mechanical jig resulted in significantly retroverted implant placement. There was no significant difference in operative time between the two techniques.

Arthroplasty, Replacement, Hip↗