Understanding and Modelling Manual Wheelchair Propulsion and Strength Characteristics in People with C5-C7 Tetraplegia
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
Spinal Cord Injuries (SCIs) are debilitating injuries where damage to the spinal cord causes a loss of mobility and feeling in muscles innervated below the injury point. Tetraplegia refers to an SCI in the cervical region of the spinal cord that impacts on the functionality of all four limbs. ‘Complete’ tetraplegia results in complete paralysis of the legs, partial or complete paralysis of the arms and trunk, and in the most severe cases, the neck. The independence of people living with tetraplegia is heavily dependent on assistive and mobility devices.
Understanding the strength characteristics of people with tetraplegia is crucially important for the suitable and effective design of mobility and rehabilitative devices such as wheelchairs. A study using a stationary dynamometer and video capture measured kinetic and kinematic characteristics of wheelchair propulsion for 15 subjects with C5-C7 tetraplegia. This study differentiated between subjects with different injuries, at two different test resistances, and was more comprehensive than other reported studies on MWC propulsion.
Some of the subjects in the study with C5-C6 injuries had no elbow extension capability, while others had undergone a deltoids-to-triceps tendon transfer procedure called TROIDS, which restores some elbow extension capability. No differences were found in any of the push phase metrics between those who had undergone the TROIDs procedure, and those who had not, suggesting that TROIDs provides no significant benefit for mobility. As expected, subjects with C7 tetraplegia recorded velocity and power outputs significantly higher than those for subjects with C5-C6 tetraplegia.
To better understand the strength characteristics over the full range of motion in the sagittal plane, and thus potentially modify the design of mobility devices to better suit these characteristics, a novel method for gathering strength data in multiple directions and positions was developed. This method had advantages over other commonly used methods. In particular, it was inclusive of complex muscle and joint interactions that would otherwise be very difficult to build into a model.
Sagittal horizontal push strength was measured using this method for 8 able bodied and 4 tetraplegic subjects. There were clear trends in the data from the able-bodied subjects, and a fourth order polynomial (R-squared = 0.8) was fitted to the data for modelling purposes. Data for the tetraplegic subjects varied significantly from the able-bodied data, but inter-individual variation was such that no model would provide a satisfactory fit to the data indicating a very high degree of patient-specific behaviour. One multi-directional data set, consisting 1584 measurements in the sagittal plane, was gathered for an able-bodied subject. The main trends in this measured data were successfully captured by a model consisting of twelve fourth-order polynomials.
Building on these measurements, and employing a human model in the constraint modelling environment, SWORDS, this thesis develops a conceptual design tool for comparing the effectiveness of different hand force paths. Initial simulations using hypothetical hand paths indicated that the proposed method for predicting the direction of the applied force needs to be verified, and likely refined, for hand paths that differ significantly from the traditional wheelchair push-rim path. This proposed procedure has the potential to be a powerful tool for optimising and modifying the design of wheelchairs or human powered devices to utilise previously untapped abilities for any given population.