Aaron L. Souza

Shoulder magnetic resonance imaging abnormalities, wheelchair propulsion, and gender.

OBJECTIVE To investigate the relationship between pushrim forces and the progression of shoulder injuries in manual wheelchair users. DESIGN Longitudinal case series. SETTING Biomechanics laboratory and magnetic resonance imaging (MRI) facility at a Veterans Health Administration medical center and university hospital, respectively. PARTICIPANTS Fourteen individuals with spinal cord injury (8 men, 6 women) who used manual wheelchairs. INTERVENTION Subjects propelled their own wheelchairs on a dynamometer at 0.9 and 1.8m/s. Bilateral biomechanical data were obtained by using force and moment sensing pushrims at time 1. Bilateral shoulder MR images were also completed on 2 occasions, at time 1 and, approximately 2 years later, at time 2. MAIN OUTCOME MEASURES The peak pushrim forces in a pushrim coordinate system were calculated, weight normalized and averaged over 5 strokes (presented as % body weight). MRI abnormalities were graded by using a summated scale. Differences between scores between times 1 and 2 were calculated. RESULTS Subjects were divided into 2 groups based on change in MRI score. Seven subjects were in the group with worsening scores (MRI+; mean, 8.14 points; range, 5-16), and 7 were in the group with improving or unchanging scores (MRI-; mean, -1.00 point; range, -5 to 1). There was no significant difference between groups with respect to age, body mass index, or years from injury. There were significantly more women in the MRI+ group (6 women, 1 man) than in the MRI- group (7 men) (P=.001). The MRI+ group used significantly greater weight-normalized radial force, or force directed toward the axle at time 1, to propel their wheelchairs at each speed (P<.01): MRI+ at 0.9m/s (mean radial force +/- standard deviation, 5.2%+/-1.0%) and MRI- at 0.9m/s (mean radial force, 3.2%+/-1.7%) (P=.028); and MRI+ at 1.8m/s (mean radial force, 6.6%+/-1.2%) (P=.023) and MRI- at 1.8m/s (mean radial force, 4.1%+/-2.2%). In a separate analysis, women were found to propel with a significantly higher radial force. A logistic regression found a significant relationship between radial force at time 1 and increased risk of progression of MRI findings over time. CONCLUSION Individuals who propel with a greater percentage of force directed toward the axle were at increased risk of progression of MRI findings over time. Most people in this group were women. Clinicians should instruct wheelchair users in effective propulsion techniques and should pay particular attention to women who use wheelchairs. Reducing forces during wheelchair propulsion may minimize the likelihood of developing shoulder injuries.

Biomechanics and strength of manual wheelchair users.

Abstract Background/Objective: Previous investigations have identified muscular imbalance in the shoulder as a source of pain and injury in manual wheelchair users. Our aim was to determine whether a correlation exists between strength and push rim biomechanical variables including: tangential (motive) force (Ft), radial force (Fr), axial force (Fz), total (resultant) force (FR), fraction of effective force (FEF), and cadence. Methods: Peak isokinetic shoulder strength (flexion [FLX], extension [EXT], abduction [ABD], adduction [ADD], internal rotation [IR], and external rotation [ER]) was tested in 22 manual wheelchair users with a BioDex system for 5 repetitions at 60°/S. Subjects then propelled their own manual wheelchair at 2 speeds, 0.9 m/s (2 mph) and 1.8 m/s (4 mph), for 20 seconds, during which kinematic (OPTOTRAK) and kinetic (SMARTWHEEL) data were collected. Peak isokinetic forces in the cardinal planes were correlated with push rim biomechanical variables. Results: All peak torque strength variables correlated significantly (P = 0.05) with Ft, Fr, and FR, but were not significantly correlated with Fz, FEF, or cadence. Finally, there were no relationships found between muscle strength ratios (for example, FLX/EXT) and Ft, Fr, FR, Fz, or FEF. Conclusion: There was a correlation between strength and force imparted to the pushrim among wheelchair users; however, there was no correlation found in wheelchair propulsion or muscle imbalance. Clinicians should be aware of this, and approach strength training and training in wheelchair propulsion techniques separately.

Upper limb strength in individuals with spinal cord injury who use manual wheelchairs.

Abstract Introduction: Manual wheelchair users have been found to be at risk for secondary upper extremity injuries. Purpose: The primary goal of this study was to compare shoulder strength and muscle imbalance of individuals with paraplegia to case-wise matched unimpaired controls (UC). A secondary goal was to evaluate the impact of age and neurologic level of injury (NLI) on weight-normalized strength (WNS). Methods: The SCI group (n = 28) and the UC group (n = 28) completed bilateral shoulder isokinetic strength testing in the sagittal, frontal, and horizontal plane at 60 degrees/second using the BioDex system. Strength ratios, an indicator of muscle imbalance, were also calculated. Results: No significant difference was seen in shoulder strength or strength ratios between the SCI group and the UC group. However, NLI was significantly related to WNS on several planes in the SCI group. Therefore, we dichotomized the SCI group into equal groups based on an NLI. The Low-SCI group was significantly stronger than the High-SCI group in most planes (P < 0.05). The High-SCI group was significantly weaker than the UC in extension (P < 0.01) and a trend (P < 0.01) was seen in flexion, abduction, and external rotation. The Low-SCI group was significantly stronger in abduction than the UC. Conclusion: WNS at the shoulder correlated with NLI. It is likely that this is related to contributions of the trunk and abdominal muscles during testing, since proximal trunk strength aids in generating forces distally. This study and others of strength in individuals with paraplegia may overestimate shoulder strength.

The effects of wheelchair-seating stiffness and energy absorption on occupant frontal impact kinematics and submarining risk using computer simulation.

Many wheelchair users must travel in motor vehicles while seated in their wheelchairs. The safety features of seat assemblies are key to motor vehicle occupant crash protection. Seating system properties such as strength, stiffness, and energy absorbance have been shown to have significant influence on risk of submarining. This study investigated the effects of wheelchair seat stiffness and energy absorption properties on occupant risk of submarining during a frontal motor vehicle 20 g/30 mph impact using a validated computer crash simulation model. The results indicate that wheelchair-seating stiffness and energy absorption characteristics influence occupant kinematics associated with the risk of submarining. Softer seat surfaces and relatively high energy absorption/permanent deformation were found to produce pelvis excursion trajectories associated with increased submarining risk. Findings also suggest that the current American National Standards Institute/Rehabilitation Engineering and Assistive Technology Society of North America (ANSI/RESNA) WC-19 seating integrity may not adequately assess submarining risk.

Effects of cross slopes and varying surface characteristics on the mobility of manual wheelchair users.

ABSTRACT Surface characteristics of a cross slope can impact the ease with which a manual wheelchair (MWC) user propels across a surface. The purpose of this research was two-fold. Phase I of this research surveyed MWC users to identify cross slope scenarios that they reported to be more difficult to traverse compared to other common driving obstacles. Our survey results showed that, overall, cross slopes were harder to propel across than narrow and manual doors, and cross-slopes in inclement weather conditions were equal or more difficult than gravel and rough-surfaces. Cross slopes with severe angles and those with compound angles (slope with cross-slope) were the most difficult to traverse. Phase II focused on identifying the responses (e.g., avoid, explore alternative, experience a sense of insecurity, no effect) people had when viewing pictures of various cross-slopes scenarios (e.g., narrow space, compound angles, extreme weather) that wheelchair users encounter. These results showed that people reported that they would avoid or feel insecure on some cross-sloped surfaces, like the weather, that are not within our control, others, like compound angle and curb-cuts on slopes, that can be addressed in the construction of pathways or sidewalks.