Gr Johnson

A framework for the definition of standardized protocols for measuring upper-extremity kinematics

BACKGROUND Increasing interest in upper extremity biomechanics has led to closer investigations of both segment movements and detailed joint motion. Unfortunately, conceptual and practical differences in the motion analysis protocols used up to date reduce compatibility for post data and cross validation analysis and so weaken the body of knowledge. This difficulty highlights a need for standardised protocols, each addressing a set of questions of comparable content. The aim of this work is therefore to open a discussion and propose a flexible framework to support: (1) the definition of standardised protocols, (2) a standardised description of these protocols, and (3) the formulation of general recommendations. METHODS Proposal of a framework for the definition of standardized protocols. FINDINGS The framework is composed by two nested flowcharts. The first defines what a motion analysis protocol is by pointing out its role in a motion analysis study. The second flowchart describes the steps to build a protocol, which requires decisions on the joints or segments to be investigated and the description of their mechanical equivalent model, the definition of the anatomical or functional coordinate frames, the choice of marker or sensor configuration and the validity of their use, the definition of the activities to be measured and the refinements that can be applied to the final measurements. Finally, general recommendations are proposed for each of the steps based on the current literature, and open issues are highlighted for future investigation and standardisation. INTERPRETATION Standardisation of motion analysis protocols is urgent. The proposed framework can guide this process through the rationalisation of the approach.

Adaptation of scapula lateral rotation after reverse anatomy shoulder replacement

Scapula motion is significant for support of the arm and stability of the shoulder. The effect of the humeral elevation on scapular kinematics has been well investigated for normal subjects, but there are limited published studies investigating adaptations after shoulder arthroplasty. Scapula kinematics was measured on 10 shoulders (eight subjects) with a reverse total joint replacement. The measurements were performed using an instrumented palpating technique. Every subject performed three simple tasks: abduction, elevation in scapula plane and forward flexion. Results indicate that, lateral scapula rotation was significantly increased (average of 24.42% over the normal rhythm) but the change was variable. Despite the variability, there is a clear trend correlating humeral performance with increased rotation (R 2 0.829). There is clearly an adaptation in lateral scapula rotation in patients with shoulder joint replacement. The reason for this is unclear and may be related to joint pathology or to muscle adaptation following arthroplasty.

KINEMATICS PERFORMANCE ON ACTIVITIES OF DAILY LIVING AFTER REVERSE SHOULDER JOINT REPLACEMENT

INTRODUCTION Every normal shoulder requires basic mechanical characteristics such as motion, stability and strength. Each of these characteristics is commonly compromised in an arthritic shoulder and is often related with strong pain. Shoulder arthoplasty is one of the most common solutions for pain relief and to restore shoulder functionality. Reverse anatomy prostheses like DELTA III [1] are introduced as a solution in challenging pathologies, like arthritic shoulder with massive rotator cuff tear [2]. Clinical reviews show very good post operative results, but despite of the extensive nowadays use of reverse prostheses there are only few biomechanical studies to analyse and exploit the performance of the reverse prosthetic designs.

CMBBE special issue on motion analysis and musculoskeletal modelling

Motion analysis and musculoskeletal modelling has progressed over the last 15 years due to major advances in computer performance, methods, accuracy and the application of sophisticated engineering and dynamic modelling procedures. This is reflected in the growing interest in its application as a practical and reliable tool for use in the field of biomechanical and biomedical modelling. The guest editors thus regard this journal as a highly appropriate publication in which to present a collection of specialised papers reporting current research in this field and the following preface aims to describe the appropriate context within which the papers should be considered by the reader. It is of paramount importance to ensure that new designs of biomedical and biomechanical devices perform to the level expected and required by both the patient and the industry standard, and this requires thorough pre-clinical assessment and clinical trial. A number of state-of-the-art techniques have been developed to help with this process and they have advanced at an extraordinary rate over the last 20 years. Traditional in vitro testing of devices to examine performance and failure criteria has been enhanced by the emergence of in silico techniques that employ mathematical and computer modelling methods to predict performance and lifetimes by simulation of the real-world situation. Applying these techniques with confidence to assess function, strength of components and interaction with their biological surroundings requires thorough validation of either in vitro testing methods or in silico models or simulations. The development and application of in silico techniques is amply reflected in the CMBBE Journal; some of the most common methods used are finite element (FE) analysis, boundary element analysis and rigid body modelling. The range of complexity of the FE modelling techniques reported is vast and emerging applications coupling probabilistic techniques with FE thus allowing multi-parameter studies, provide insight into the influence of patient and surgery related variability on implant performance. FE is used to analyse structural and material parameters within complex 3D environments allowing examination of the variation of response over a range of practical simulations by changing significant parameters. However the models are largely comparative rather than predictive, requiring validation in terms of the loading and boundary conditions, the parameters applied to develop constitutive equations and the subsequent comparison with real-life data. High levels of validation of the FE tools are, therefore, required to provide the user with confidence in their practical application and these can be achieved using combined in vitro and in vivo techniques. In vitro testing techniques are of value as they can be used to investigate the behaviour of the implant or component construct at the interface with biological structures. ISO standard tests tend to focus on assessing the performance of the isolated components and tests assessing the construct performance use either synthetic or cadaveric bones. Such tests produce “real” data that is generally restricted to a small number of variables. However, studies using large numbers of cadaveric samples required to overcome the problems of variability between specimens are both costly and time consuming. Ultimately, the best test bed for new devices and applications is the patient and in vivo studies can monitor performance during the first phases of clinical release, using techniques capable of detecting the early signs of poor function and potential failure. Classical methods of clinical assessment, such as planar X-rays, pain/function scores, gait analysis and survivorship analysis may or may not be sensitive enough to detect poor function soon after surgery. However, by using a combination of these

EFFECT OF BAYLEY-WALKER AND DELTA IMPLANTS ON THE DELTOID MUSCLE MOMENT ARM

INTRODUCTION The deltoid muscle acts as the main abductor for a person with a shoulder joint replacement. The ability of the deltoid to move the joint is partially determined by the torque it generates about the joint centre and hence the muscle moment arm. The Newcastle Shoulder Model (NSM) [1] has been modified to include the Bayley-Walker (B-W) and Delta [2] prosthesis. The moment arms of the deltoid during a wide range of arm positions with the B-W and Delta prostheses and a normal shoulder were compared. The variation in the positioning of the implant was also examined to test the effect of surgical placement.