Biomechanics and clinical measurement of functional wrist motion

Abstract

Despite of the anatomical complexity of the wrist, its motion is usually decomposed into two rotations: flexion-extension and radioulnar deviation. However, during many activities of daily living the wrist follows an oblique plane, known as the dart throwing motion (DTM). During DTM, the relative motion between the carpals in the proximal row is minimised, making this plane essential for designing early post-surgical rehabilitation protocols following ligament tears and carpal fusion surgeries. Despite its importance, clinical integration of the motion remains a challenge. Therefore, the first objective of this thesis was to investigate the accuracy of clinical measurement of the DTM and the variability of the DTM within a healthy cohort. For this purpose, wrist kinematics of a healthy cohort were measured using an optical motion capture system and goniometry. This analysis identified the need to determine a person-specific DTM plane, the orientation of which cannot be quantified based only on goniometry measurements. The effects of wrist injury and rehabilitation on the definition of the DTM were investigated across a patient cohort, together with the relationship of DTM with a standard clinical tool, the Patient-Rated Wrist/Hand Evaluation (PRWE) score. As a result of this study it was shown that although the injury has a significant effect on range of motion, it does not have any significant effect on the DTM plane orientation. Moreover, the normalised DTM range of motion was correlated with PRWE scores and normalised grip strength of the patients. The abovementioned findings highlighted the need for improving the accuracy of the quantification of the DTM plane. Thus, a mathematical correction method was designed that used parameters based on the geometrical relationships derived from the anatomy and the planar nature of the DTM. The corrected DTM plane estimation reduced differences from the motion capture estimation to non-significant levels in both healthy participants and patients. Although, better adjustment was achieved for the healthy cohort. Synchronised measurements of muscle activation and wrist kinematics during the DTM revealed similar patterns of co-activation of flexor and extensor wrist muscles in healthy participants and patients. This is in agreement with previous findings and supports the 10 consistency of the DTM plane through injury and rehabilitation. The conclusions of this work support and provide an insight into the clinical importance of the functional plane of the DTM, as well as address the problem of its quantification by standard clinical assessment procedures