Development of an in-vitro passive and active motion Simulator for the investigation of wrist function and Kinematics

This thesis outlines the design and development of an active motion simulator for the investigation of wrist kinematics in multiple gravity loaded positions. Using optical trackers on the third metacarpal, radius, and ulna, the position of the wrist was monitored in real time without introducing material incompatibilities as present for electromagnetic tracking systems. Performance of the system was performed using a series of five cadaver upper limbs that compared the ability to produce repeatable trials using unrestrained active motion techniques over passive manipulation methods. Comparisons to achieve static positions as well as motion trials in flexion-extension and radial-ulnar deviation planes proved the superior performance of computer controlled motion over that of passive manipulation. Investigation into the application of tendon portioning to model in-vivo conditions more accurately suggest that they may improve overall quality of motion

An Image-Based Tool to Examine Joint Congruency at the Elbow

Post-traumatic osteoarthritis commonly occurs as a result of a traumatic event to the articulation. Although the majority of this type of arthritis is preventable, the sequence and mechanism of the interaction between joint injury and the development of osteoarthritis (OA) is not well understood. It is hypothesized that alterations to the joint alignment can cause excessive and damaging wear to the cartilage surfaces resulting in OA. The lack of understanding of both the cause and progression of OA has contributed to the slow development of interventions which can modify the course of the disease. Currently, there have been no reported techniques that have been developed to examine the relationship between joint injury and joint alignment. Therefore, the objective of this thesis was to develop a non-invasive image-based technique that can be used to assess joint congruency and alignment of joints undergoing physiologic motion. An inter-bone distance algorithm was developed and validated to measure joint congruency at the ulnohumeral joint of the elbow. Subsequently, a registration algorithm was created and its accuracy was assessed. This registration algorithm registered 3D reconstructed bone models obtained using x-ray CT to motion capture data of cadaveric upper extremities undergoing simulated elbow flexion. In this way, the relative position and orientation of the 3D bone models could be visualized for any frame of motion. The effect of radial head arthroplasty was used to illustrate the utility of this technique. Once this registration was refined, the inter-bone distance algorithm was integrated to be able to visualize the joint congruency of the ulnohumeral joint undergoing simulated elbow flexion. The effect of collateral ligament repair was examined. This technique proved to be sensitive enough to detect large changes in joint congruency in spite of only small changes in the motion pathways of the ulnohumeral joint following simulated ligament repair. Efforts were also made in this thesis to translate this research into a clinical environment by examining CT scanning protocols that could reduce the amount of radiation exposure required to image patient’s joints. For this study, the glenohumeral joint of the shoulder was examined as this joint is particularly sensitive to potential harmful effects of radiation due to its proximity to highly radiosensitive organs. Using the CT scanning techniques examined in this thesis, the effective dose applied to the shoulder was reduced by almost 90% compared to standard clinical CT imaging. In summary, these studies introduced a technique that can be used to non-invasively and three-dimensionally examine joint congruency. The accuracy of this technique was assessed and its ability to predict regions of joint surface interactions was validated against a gold standard casting approach. Using the techniques developed in this thesis the complex relationship between injury, loading and mal-alignment as contributors to the development and progression of osteoarthritis in the upper extremity can be examined

Application of biomechanical techniques to improved design of products and environments for an ageing population

This work describes the development of a technique for the evaluation of the performance of a product's physical user interface. The technique is intended to combine the best features cat conventional user group testing with those of computer based biomechanical modelling. A requirement for the new technique exists as social pressure demands that consumer products he optimised for users with a wide range of physical capabilities, while shortening product lifecycles leave less time for extensive user evaluation programmes. A demonstration system was developed, based upon the use of an electromagnetic tracking system to gather upper limb motion data and a two segment, rigid link biomechanical model. Experimental work was carried out to test the effectiveness of the system at following limb movements and average error in reconstruction of hand position from segment angle data was 62mm (Standard deviation 41 mm) The modelling system was applied to the assessment of two types of product: cutlery and drinking vessels and the effectiveness of various statistical techniques in allowing the rapid identification of important design parameters was assessed. The use of Taguchi's smaller-the-better signal to noise ratio was found to be effective for the measurement of the effect of product design on shoulder and elbow forces. Cutlery with enlarged handles designed to reduce grip strength requirements tended to increase forces at the shoulder. The method was also applied to an interface optimisation problem involving the design of a lever mechanism. Partial factorial design was used to minimise experimental cost during the assessment of multiple factors, but strong interactions were detected between interface parameters, reducing the value of the analysis. The overall height of the lever handle relative to the user's shoulder was found to be the most significant design factor, with an optimum operating situation existing where the lever was low enough to require almost full extension of the elbow during use. The work concludes that biomechanical analysis holds further promise for the optimisation of interface parameters, provided the high experimental cost involved with present techniques can be reduced

A Biomechanical Investigation into the Effect of Experimental Design on Wrist Biomechanics and Contact Mechanics

The wrist is one of the most commonly injured joints, and injury can have serious sequelae if pathological healing ensues. Strides have been made to understand normal and pathological wrist biomechanics using experimental approaches, which has contributed to improved patient care. The present work advances our understanding of the influence of experimental techniques and joint motion measurement techniques on in-vitro wrist biomechanical cadaveric studies, and applies the knowledge learned to a common clinical entity of scapholunate insufficiency. First, the relative contributions of the carpal rows to wrist motion were assessed, in addition to the identification of limitations of current biomechanical testing techniques. The radiocarpal joint contributed more motion to wrist flexion, the midcarpal joint contributed more to wrist extension, while near neutral wrist position there was a relatively equal contribution from both joints. Passive motion joint simulation, forearm position, and coordinate system selection and joint congruency were all identified as areas needing investigation. In order to assess the effect of joint coordinate system (JCS) selection on resulting wrist angle, four JCS were compared to determine JCS selection on wrist angle characterization. Subtle differences were found between JCSs, and the findings support the use of any of the analyzed methods. Additionally, to quantify joint congruency at the wrist, validation and application of a previously described a non-invasive CT-based technique to measure joint congruency at the wrist is described. The effect of forearm orientation on wrist joint biomechanics was then evaluated. Radioscaphoid joint contact was found to be sensitive to forearm orientation and wrist angle, while radiolunate joint was not sensitive to changes in forearm orientation. Scaphoid angular rotation was found to vary with forearm position, but only at the extremes of wrist flexion-extension. The present work advances wrist biomechanics knowledge and will help to improve the clinical management of acute and chronic wrist injuries

4DCT analysis of in-vivo carpal kinematics during FEM

A consensus, detailed understanding of carpal kinematics remains elusive. 4-dimensional CT (4DCT) is a validated modality capable of accurately studying in-vivokinematic motion. The objective of this work is to quantify normal, in-vivo kinematic motion of the carpus through a flexion-extension arc of motion using 4DCT. Ten healthy, un-injured volunteers underwent a 4DCT scanning protocol through a complete arc of flexion-extension motion. Kinematic changes in motion were quantified using helical axis motion data for each carpal bone. Helical axes were compared between bones and statistical analysis performed using repeated-measures ANOVA to identify difference in kinematic motion between bones (p\u3c0.05). The carpus can be divided into four main kinematic blocks: the distal carpal block, the proximal carpal block and individual scaphoid and trapezial blocks. This work supports an additional segmentation of the trapezium from the distal carpal row, which suggests some modulation between the scaphoid and distal carpal row

The Impact of Scaphoid Malunion on Wrist Kinematics & Kinetics: A Biomechanical Investigation

Scaphoid fractures are very common injuries that can have serious sequelae if pathologic healing ensues. Although there is consensus regarding the importance of a non-united scaphoid, the impact of a malunited scaphoid is less clear. This is based on a paucity in the literature and understanding of the natural history of scaphoid malunion. This study aims to elucidate this study but investigating the impact of scaphoid malunion and joint kinetics, as well as the impact of scaphoid malunion on carpal bone kinematics. This was accomplished using a combination of in-silico, as well as in-vivo modelling based of cadaveric results derived from an active motion. Our results showed that increasing scaphoid malunion was associated with increasing joint contact at the radioscaphoid joint. There was no significant relationship between scaphoid motion and scaphoid malunion severity, however, there was a significant change in lunate motion, as well as motion between the scaphoid and lunate. This work serves as the framework for understanding the complex motion of the carpus and emphasizes the potential importance of establishing a good reduction of the scaphoid following fracture. The clinical importance of this finding has yet to be elucidated, but by understanding this relationship future clinical studies can be target at identifying feature of patients who may benefit from therapy