Kinematic and anatomical measurement for biomechanical finger models

Abstract

Biomechanical models of the fingers are used to gain a greater understanding of their internal loading which will help guide clinicians treat injuries and pathologies. These models require accurate measurement of body kinematics, external reaction forces and anthropometry. The aim of this PhD was to gain a greater understanding of the predicted internal loading using biomechanical finger models and propose improvements in the kinematic and anatomical measurements required as their inputs. Through sensitivity analysis, correlations between uncertainty in the anthropometry and kinematics with predicted internal loading were found. This showed that the predicted internal loading was most sensitive to changes in the moment arm of the flexor digitorum profundus tendon. A new method of motion capture of the fingers using functionally defined joint centres was assessed. This method required the subject to complete a set of calibration movements. Subjects with an injury or pathology may have significantly reduced mobility, therefore an analysis was carried out to quantify the effect of reducing the available movement to that of a subject with pathological mobility. This resulted in errors of less than 5% in the predicted internal loading. It was important to note however, that in the extreme cases of deformity and lack of mobility this functional technique would not be suitable. Finally, a combined method of ultrasound and stereo-photogrammetry to measure the in-vivo moment arm of the flexor digitorum profundus was developed, enabling non-invasive subject specific measurements. Measurement made using this technique found moment arms within the range of previous studies but they were found to alter the predicted internal loading by up to 84%. This demonstrated the importance of subject specific measurement. Although this was only a pilot study with a single subject it showed how this technique could be applied not just to the fingers but to other parts of the body where subject specific measurements of moments arms are important.