RESNA 27th International Annual Confence
Upper extremity pain in manual wheelchair users can lead to decreased independence and quality of life (1) . Kinetic propulsion characteristics have been linked to the existence of upper extremity pain and dysfunction in manual wheelchair users (2) . The purpose of this investigation was to determine if spinal cord injury level was associated with kinetic propulsion characteristics. Forty-eight manual wheelchair (MWUs) users participated in this investigation. Average peak resultant force at a self-selected velocity and 1.8 m/s was evaluated, controlling for bodyweight and velocity. Peak resultant force was not associated with injury level. Velocity was an independent predictor of peak resultant force. Documentation of factors that may contribute to upper extremity pain will facilitate interventions to reduce risk of developing pain.
paraplegia; force; pain; injury level; velocity
Upper extremity pain is prevalent among MWUs, affecting an estimated 64% of individuals with paraplegia (3) . Research has linked various parameters of wheelchair propulsion, including peak resultant force and loading rate with shoulder/wrist pain and dysfunction (2) . Kinetic and kinematic differences have been documented between experienced and inexperienced MWUs as well as paraplegics and quadriplegics (4; 5) . Furthermore, paraplegic injury level is associated with upper extremity pain (6) . However, it is unknown whether kinetic propulsion characteristics associated with upper extremity pain differ among various paraplegic injury levels. Identifiable inherent kinetic propulsion differences among individuals with paraplegia could allow rehabilitation practitioners to target at risk groups for early intervention, thus preventing or delaying onset of upper extremity pain and dysfunction.
Forty-eight individuals with spinal cord injury below thoracic level one completed propulsion kinetics evaluation. Participants averaged 37 (+/- 12) years of age, 75.5 (+/- 17.4) kg, with a BMI of 24.7 (+/- 5.4). Over half (71%) the cohort was male.
Participant propulsion kinetics was evaluated via Smart wheels mounted bilaterally to the individual's own chair. Each participant was allowed to acclimate to the dynamometer after their chair was secured by a four-point tie down system. Pushrim kinetics were recorded for 20 seconds once the participant reached the desired steady-state at two speeds; self-selected and 1.8m/s.
Due to a demonstrated relationship between body weight and propulsion force, peak resultant (N) forces were normalized to bodyweight (N) (Boninger et al. 910-915). For the purpose of this study injury level was coded in two ways. For correlational analysis each level was assigned a number such that lower numbers corresponded with higher injury level (i.e. T2 = 1; T3 = 2 …). To allow for group comparisons we divided subjects in to three groups T2-T4, T4.5-T9.5, and T10-L5. A one-way ANOVA with post hoc tests was conducted to determine if group differences in peak resultant force existed at either velocity.
No significant relationship between injury level and peak resultant force was found in either the correlation or group analysis (Tables 1 & 2). As expected, regression analysis demonstrated velocity was a significant determinant of peak resultant force (ß=.694, p=.000), while injury level was not (ß=.186, p=.100).
|
Correlational |
Group comparison |
|
|---|---|---|---|
Peak Force
Self-Select |
r |
.142 |
.038 |
p |
.346 |
.801 |
|
Peak Force
4mph |
r |
.223 |
.130 |
p |
.132 |
.384 |
|
Mean |
Between Groups |
|---|---|---|
Peak Force Self-Select |
||
T1 – T4 |
.084 |
T4.5-T9.5 |
| T10-L5 .668 |
||
T4.5 – T9.5 |
.094
|
T1-T4 |
| T10-L5 1.00 |
||
T10 – L5 |
.094 |
T1-T4 |
| T4.5-T9.5 1.00 |
||
Peak Force 4mph |
||
T1 – T4 |
.126 |
T4.5-T9.5 |
| T10-L5 .242 |
||
T4.5 – T9.5 |
.139 |
T1-T4 |
| T10-L5 .689 |
||
T10 – L5 |
.149 |
T1-T4 |
| T4.5-T9.5 .689 |
||
Pain is associated with decreased strength and functioning, regardless of the population studied (1) . A primary goal of clinicians working with manual wheelchair users should be the prevention of secondary conditions, which compromise an individual's functioning and quality of life. Development of pain and dysfunction in the upper extremity can be considered a chronic condition resulting from extended exposure to multiple risk factors. Documentation of such risk factors and the degree to which they are modifiable will allow practitioners to identify individuals at risk for developing this chronic condition and target interventions to improve risk factor profiles. Lower injury level corresponds with an increase in the amount of voluntary control over musculature. Individuals who have use of postural muscles do not need to utilize the pushrim as a balance tool, may use the trunk to augment propulsive force, and could direct a higher percentage of force towards the pushrim. Consequently we theorized individuals with greater trunk control would exert a lower peak force on the pushrim at any given speed than those with higher impairments.
Contrary to our expectations, injury level was not statistically associated in any manner with peak resultant force. Velocity, as expected, was a significant contributor to peak force. Although peak force at a given speed did not differ among our cohort, a more in depth examination would further clarify force application among individuals with paraplegia. Peak resultant force may represent a point in a propulsive stroke where pushrim contact is not needed to supplement balance. However, individuals possessing limited trunk control may apply greater initial and terminal forces as their trunk approaches its stability limits, thereby increasing the amount of force applied across the duration of pushrim contact. In addition, some individuals may exert greater muscle power to achieve similar pushrim forces due to less efficient kinematics. Over a lifetime, such individuals may incur greater glenohumeral forces, increasing their risk of pain and dysfunction development. While resultant forces may be similar in individuals with paraplegia, tangential and radial force distribution across the duration of pushrim contact may differ. Greater radial forces may help identify which individuals should be monitored for pain development. Future studies should examine force application characteristics in combination with kinematic characteristics across the duration of pushrim contact, focusing on the initial and terminating phases.
Peak resultant force has been associated with the presence of upper extremity pain and dysfunction in MWUs (2) . Although injury level in paraplegics was not associated with peak resultant force, understanding what factors do not contribute directly to the development of upper extremity pain is important. Such documentation will allow practitioners to focus time and efforts on interventions to reduce the presence of identified risk factors.
This study was supported by U.S. Department of Veteran Affairs (project B3057T and B2674-CA) .
Rachel Cowan,
Human Engineering Research Labs,
VA Pittsburgh
Healthcare System,
Pittsburgh, PA 15216
Phone: (412) 365-4850,
Fax: (412) 365-4858,
Email:rec12@pitt.edu.