This study investigated (1) the effect of repetitive weight-relief raises (WR) and shoulder external rotation (ER) on the acromiohumeral distance (AHD) among manual wheelchair users (MWUs) and (2) the relationship between shoulder pain, subject characteristics, and AHD changes. Twenty-three MWUs underwent ultrasound imaging of the nondominant shoulder in an unloaded baseline position and while holding a WR position before and after the WR/ER tasks. Paired
Subacromial impingement syndrome (SIS) is a common shoulder dysfunction in manual wheelchair users (MWUs). The mechanisms of SIS can be divided into intrinsic and extrinsic factors. [
MWUs commonly experience overuse because their upper extremities are used extensively for mobility and activities of daily living (ADL). The weight-relief raise (WR) is an ADL that requires heavy and frequent shoulder loading. During a WR, MWUs need to lift and support the weight of the body to reduce pressure on the buttocks. This activity results in excessive shoulder joint loading and requires rotator cuff muscles to maintain glenohumeral joint stability [
Shoulder external rotation (ER) is a commonly prescribed training among MWUs to strengthen the shoulder external rotators to act against potentially injurious forces during wheelchair activities [
We recently described a reliable method to quantify the subacromial space by using ultrasound while holding a WR position [
Study participants were a convenience sample recruited during the 2011 National Veterans Wheelchair Games (NVWG). For a power of 0.95, an
Basic demographic information including age, height, weight, and date of injury/diagnosis was collected using self-report. All subjects completed the Wheelchair Users Shoulder Pain Index (WUSPI) [
The OMNI pain scale is a numerical rating scale ranging from 0 to 10 [
Shoulder circumference and upper arm length were obtained from all subjects at the beginning of testing. The shoulder circumference and upper arm length were measured while the subjects were in the seated anatomical position. The shoulder circumference was measured from the superior portion of the acromion to the axilla. The upper arm length was measured from the most lateral and superior portion of the acromion to the tip of the olecranon. A single investigator conducted all of the measurements using a standard tape measure. Using this method to record similar anthropometrical measures has been found to be reliable [
Subjects transferred to a Biodex System 3 dynamometer (Biodex Medical System, Inc., Shirley, NY) with custom-made adjustable height armrests. Armrests were fitted to each subject to allow pushing straight up with full elbow extension to off load the buttock tissue. The seat height was fixed during the entire testing. The WR entailed lifting and holding the buttocks off the seat with an elbow locked position [
The ER task followed a similar protocol to a previous study involving neurologically intact individuals without shoulder disorders and was designed to overuse the shoulder external rotators [
The subacromial space was quantified by measuring the AHD using ultrasound techniques as described in a previous reliability study [
The nondominant side was chosen for all the AHD measures in order to minimize the effects caused by performing other types of activities of daily living on the dominant shoulder. The muscular demand of the nondominant shoulders among manual wheelchair users was also examined in previous studies [
Ultrasonographic image of the acromiohumeral distance (AHD).
An investigator who was blinded to the timing of the video (e.g., pre or post) used a custom developed Matlab program to manually review each frame of the video and mark the inferior edge of acromion and superior margin of the humeral head. (Figure
Twenty-three MWUs (twenty-two men and one woman) participated in this study. Sixteen MWUs had a spinal cord injury (five cervical and eleven thoracic), one had a unilateral transfemoral amputation, three had bilateral transtibial amputations, and three had multiple sclerosis. Twenty-two participants were right hand dominant. Descriptive data are provided in Table
Subject demographics (
Demographic | Mean ± standard deviation | Range |
---|---|---|
Age | 46 ± 12 | 26–64 |
Height (m) | 1.78 ± 0.08 | 1.65–1.93 |
Weight (kg) | 81 ± 18 | 55–130 |
Time since injury (year) | 15 ± 10 | 1.5–33.5 |
Number of WR | 34 ± 16 | 10–61 |
Number of ER | 39 ± 18 | 6–60 |
WUSPI | 14.08 ± 18.07 | 0–60, median 12.6 |
OMNI pain scale baseline | 1.04 ± 1.58 | 0–5 |
OMNI pain scale after WR | 2.09 ± 2.56 | 0–8 |
OMNI pain scale after ER | 2.30 ± 2.42 | 0–7 |
There were no significant differences in the AHD before and after performing WR (
AHD for each subject.
Disability | Rest | Multiple weight-relief raises (mm) | Shoulder external rotation activity (mm) | ||
---|---|---|---|---|---|
Pre | Post | Pre | Post | ||
C3 spinal stenosis | 14.07 | 10.85 | 10.85 | 10.67 | 9.31 |
T4 com. SCI | 11.53 | 9.32 | 11.27 | 9.18 | 9.04 |
C6 inc. SCI | 10.96 | 10.14 | 9.03 | 8.77 | 8.90 |
MS | 12.64 | 8.08 | 9.45 | 11.25 | 10.82 |
Amp (LAK) | 12.88 | 12.76 | 10.17 | 10.17 | 10.34 |
T4 com. SCI | 11.51 | 10.00 | 9.31 | 9.72 | 10.82 |
Amp (RBK, LAK) | 12.37 | 9.83 | 11.93 | 9.32 | 10.41 |
T7 inc. SCI | 11.64 | 10.28 | 11.37 | 10.70 | 10.69 |
T9 inc. SCI | 12.50 | 11.64 | 11.51 | 11.67 | 11.10 |
MS | 9.32 | 9.04 | 11.53 | 10.27 | 8.92 |
C3 inc. SCI | 10.96 | 10.55 | 10.83 | 10.00 | 8.45 |
MS | 12.36 | 9.03 | 7.16 | 8.47 | 8.36 |
T12 com. SCI | 9.44 | 10.00 | 9.31 | 10.00 | 9.73 |
T12 inc. SCI | 11.81 | 10.00 | 10.27 | 10.27 | 10.69 |
Amp (RAK, LAK) | 10.00 | 8.38 | 9.31 | 7.95 | 8.08 |
T12 com. SCI | 10.14 | 9.31 | 8.77 | 8.75 | 8.49 |
Amp (RAK, LBK) | 10.14 | 8.49 | 7.36 | 7.50 | 9.04 |
C5 inc. SCI | 13.06 | 11.39 | 10.82 | 11.39 | 10.95 |
C7 inc. SCI | 16.32 | 10.86 | 9.66 | 10.52 | 10.17 |
T10 inc. SCI | 13.83 | 12.71 | 12.28 | 12.41 | 13.10 |
T11 inc. SCI | 11.22 | 10.27 | 9.45 | 10.14 | 10.96 |
T12 com. SCI | 13.84 | 11.10 | 11.51 | 9.73 | 10.41 |
T9 inc. SCI | 8.22 | 6.03 | 6.08 | 6.71 | 5.83 |
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Group mean |
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SCI, spinal cord injury (com., complete; inc. incomplete); Amp, amputee; RAK, right leg above knee; RBK, right leg below knee; LAK, left leg above knee; LBK, left leg below knee; MS, multiple sclerosis. †,‡
Correlation analysis for the AHD in neutral shoulder position with the shoulder circumference (
The results of this study indicate that AHD narrowing occurs when MWUs assume a weight-bearing position with their arms. When our subjects assumed the WR position, a statistically significant reduction in space occurred. In this position, the elbows are in full extension allowing the humeral head to be oriented more directly upward and into the joint while the scapula is anteriorly tilted and internally rotated [
In contrast to our hypothesis, this study did not find differences in the AHD measures before and after isolated repetitive WR. One possible explanation is that not all subjects may have experienced overuse in the targeted rotator cuff muscles. Many individuals in our study were not able to complete two minutes of activity which could have been a result of fatigue or other reasons (e.g., pain onset, discomfort, boredom, etc.). Also, the triceps are the most active muscle group during a WR task and overuse would most likely occur in this muscle first [
The ER activity is an overuse protocol targeting the external rotators and minimizing involvement of other shoulder muscles. Previous studies have shown superior migration of the humeral head occurs after overusing the shoulder external rotators [
Not finding differences in AHD after the isolated repetitive tasks may also result from compensatory scapular motions [
Our study found that more shoulder pain was related to greater AHD percentage narrowing after ER. Not finding the same association after the WR task may point to the effectiveness of the ER task in targeting overuse of the infraspinatus muscle [
Our results were consistent with other studies that found that AHD measures were not significantly correlated with the characteristics commonly linked to SIS such as age and weight [
Our study had several limitations. Because our protocol was conducted at a national wheelchair sporting event, it was difficult to control for the amount of upper limb activity experienced before the testing. We conducted the informed consent process and questionnaires at the beginning of the study (e.g., a process that took 15–20 minutes) which helped to provide some washout period for the participants before starting the protocol. Also the within-subject design helped to control the effects that varying amounts of preactivity may have had on the primary pre-/post-AHD measures. In addition, wheelchair users who participate in sporting events may be considered more active than the general population. However, Tolerico et al. found that veterans who participate in the NVWG are not significantly different with respect to mobility characteristics and activity levels from their community-dwelling wheelchair using counterparts [
Finding significant relationships between AHD changes and pain in our study implies that there is clinical relevancy with the AHD measure. However, because we did not specifically target symptomatic subjects for this study or study the effects of an intervention, more work is needed to define clinically meaningful changes in the AHD for manual wheelchair users. Limited research has been done so far in a wheelchair user population. A previous study on nonwheelchairs found that the ultrasonographic measurement of the AHD in affected shoulders among individuals with SIS (19.4 mm) was significantly narrower than the AHD in their nonaffected shoulder (22.2 mm,
The results of this study suggest that MWUs should limit WR for pressure relief, as placing the shoulder in a WR position led to a significant reduction in the subacromial space. The isolated repetitive shoulder activity did not contribute to the changes of subacromial space in MWUs. This study provides objective evidence that the AHD is associated with pain and long-term use of a wheelchair. Ultrasonographic measurement of the AHD may be useful for identifying interventions that prevent pain. A better understanding of the scapular and humeral kinematics may help to elucidate mechanisms leading to subacromial impingement in wheelchair users.
The authors have no conflict of interests to disclose.
This material is based upon work supported by the Department of Veterans Affairs Rehabilitation Research and Development Service (Grant no. B6789C), the Paralyzed Veterans of America, and US Department of Education (Grant no. H133N110011). This material is the result of work supported with resources and the use of facilities at the Human Engineering Research Laboratories, VA Pittsburgh Healthcare System. The contents of this paper do not represent the views of the Department of Veterans Affairs or the United States Government. An extended abstract was presented in student scientific paper winner session of 2012 Rehabilitation Engineering and Assistive Technology Society in North America annual conference.