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Original Research Articles

Effects of Home Exercises on Shoulder Pain and Pathology in Chronic Spinal Cord Injury

A Randomized Controlled Trial

Cardenas, Diana D. MD, MHA; Felix, Elizabeth R. PhD; Cowan, Rachel PhD; Orell, Melanie F. MSPT, DPT, NCS; Irwin, Robert MD

Author Information
American Journal of Physical Medicine & Rehabilitation: June 2020 - Volume 99 - Issue 6 - p 504-513
doi: 10.1097/PHM.0000000000001362

Abstract

What Is Known

  • Shoulder pain impacts the majority of persons with chronic spinal cord injury (SCI). A home exercise program (HEP) that includes strengthening and stretching exercises can be used to decrease shoulder pain.

What Is New

  • This investigation evaluated whether a 12-wk HEP aimed at reducing shoulder pain could also induce changes in supraspinatus tendon pathology as measured by quantitative ultrasound (QUS) techniques. Overall, although improvements in shoulder pain and function were present after HEP, significant changes in QUS metrics of supraspinatus tendon pathology were not evident. Long-term maintenance of a HEP may be needed to demonstrate improvements in shoulder pathology coincident with pain reduction.

Shoulder pain is the most common musculoskeletal problem after spinal cord injury (SCI), reported as occurring in 30%–78% of such individuals.1–4 The cause of shoulder pain in SCI is often multifactorial. Loss of lower limb function leads to excessive stress on the arms during activities, such as wheelchair propulsion, weight-bearing during transfers, and activities of daily living (ADLs). In one study of persons with paraplegia seen during routine annual clinic visits, 71% of 26 symptomatic shoulders revealed rotator cuff tears on magnetic resonance imaging, 57% with full-thickness supraspinatus tears.5 Rotator cuff tears and shoulder pain without a tear can have a significant impact on ADLs and wheelchair mobility. Shoulder pain also increases in prevalence with increased duration of SCI.6 Biomechanical studies have demonstrated that a higher radial force on the pushrim of the wheelchair is associated with progression of abnormal magnetic resonance imaging findings over time, although radial force explained only part of the risk of pathologic changes.7 Other factors contributing to shoulder pain after SCI include overuse, tightening of anterior shoulder muscles associated with weak and stretched posterior shoulder stabilizers in paraplegia, and weakness, chronic subluxation, spasticity, and contractures in tetraplegia. Secondary injury from falls or minor trauma, degenerative joint changes associated with aging, and obesity may also contribute to shoulder pain and pathology after SCI.8

Strengthening exercises of the shoulder girdle muscles, particularly the rotator cuff muscles, are commonly prescribed as a major component of treatment programs for shoulder pain and are recommended for persons with SCI by the Clinical Practice Guidelines: Preservation of Upper Limb Function Following Spinal Cord Injury.9 Several studies have documented that a strengthening and stretching program can decrease shoulder pain in persons with chronic SCI.10–12 One such study by Mulroy et al.12 found a significant decrease in shoulder pain after 12 wks of a home exercise program (HEP) that was sustained at 4-wk postintervention. However, no studies to date have included imaging of the shoulder to examine potential changes in shoulder pathology associated with a HEP for shoulder pain. Therefore, we were interested in using objective measures of the rotator cuff tendon (i.e., quantitative ultrasound [QUS]), to examine potential changes in tendon pathology after the completion of the same 12-wk HEP as used by Mulroy et al.12

Ultrasound (US) is a cost-effective approach to identify gross rotator cuff pathology, being equal or superior to magnetic resonance imaging for the diagnosis of rotator cuff tears or disorders of tendons.13,14 Recently, US has been used to quantify mild tendinosis in the supraspinatus tendon of persons with chronic SCI using first- and second-order statistical descriptions of the dispersion and pattern of the greyscale tendon image.15 Metrics generated by this approach are termed QUS measures. It is proposed that QUS parameters objectively quantify tendonopathy15 and could serve as preclinical, pretear markers of tendon health. However, no single QUS measure has been identified as a standalone index of tendon health. Instead, a broad array of QUS measures are often reported.15–19

Tendon width/thickness has been the most commonly measured QUS parameter to assess tendon health,19–23 but the correlation between QUS measures and pain has not been clearly elucidated. Tendon width is also a more commonly used measure in clinical practice and may have the best clinical application at this time.

The purposes of this study were to (a) replicate the effectiveness of a 12-wk home exercise intervention based on the study by Mulroy et al.12 to improve symptoms of shoulder pain in persons with chronic SCI and (b) use QUS to aid in the assessment of potential changes in rotator cuff pathology, specifically of the supraspinatus tendon, associated with pain reduction. The primary hypothesis was that supraspinatus tendon width would decrease after the HEP compared with no change in the control group. Secondary outcomes of interest were changes in other QUS metrics and self-reported shoulder pain and function.

METHODS

The study was approved by the University of Miami Internal Review Board and registered at ClinicalTrials.gov (NCT 03521856). Study participants were recruited primarily from the University of Miami’s South Florida SCI Model System, a comprehensive, interdisciplinary service delivery model system, and the SCI Clinic at Jackson Memorial Hospital, a large public hospital affiliated with the University of Miami. Medical record screenings were completed by research staff and individuals meeting initial screening criteria were approached to assess their interest in the study. In addition, participants were solicited via posted flyers throughout the University of Miami Miller School of Medicine campus, through the Web site of The Miami Project to Cure Paralysis, and from a community SCI support group. Potential participants were asked to contact the study investigators whether they were interested in learning more about the study. Enrollment occurred between May 1, 2012, and June 1, 2016. The study conforms to all Consolidated Standards of Reporting Trials (CONSORT) guidelines and reports the required information accordingly (see Supplemental Checklist, Supplemental Digital Content 1, http://links.lww.com/PHM/A929). We certify that all applicable institutional and governmental regulations concerning the ethical use of human volunteers were followed during the course of this research.

Inclusion criteria were as follows: men or women at least 20 yrs of age; SCI of at least 1 yr of duration; use of a manual or power wheelchair of more than 50% of the time and the ability to transfer without help of others; and the presence of at least moderate shoulder pain (≥4 on a 0–10 numerical rating scale for average pain intensity) for at least the past 3 mos. Each participant gave written informed consent. Participants were excluded if they had a history of rotator cuff tears or traumatic injury to either shoulder or were currently undergoing physical therapy for shoulder pain.

Sample size estimation was based on previous research on the effect of a HEP on shoulder pain by Mulroy et al.12 in which measures of shoulder pain were significantly decreased after the exercise program. We calculated the needed sample size so that we would have at least a 90% chance of detecting a similar effect size for changes in shoulder pain, to examine the potential for clinically significant changes in supraspinatus tendon metrics. This resulted in the need for at least 13 participants per study arm.

Study Design and Intervention

A parallel, randomized, controlled trial was conducted. Enrolled participants were randomly assigned (1:1) to a 12-wk standardized HEP or an education-only control condition (CON). Random assignment was generated using an online freely available program, which was set to randomize in blocks of four (two in each group). Block randomization was used so that, for every four consecutive participants, two were assigned to the HEP group and two were assigned to the CON group, thus preventing the possibility of having those in the HEP intervention clustered mostly at one time point during the study. The randomization sequence was kept by the study coordinator and was consulted after each new subject was enrolled to determine their group assignment. Although the research participants could not be feasibly blinded to which arm of the study they were randomized, the physician performing the shoulder US examination and image capture was blinded to the participant’s assignment, as was the QUS image analyst.

The HEP and the education content for the CON group were based on those published by Mulroy et al.12 The HEP included stretching and strengthening exercises and, after one-to-one instruction by a physical therapist regarding proper performance of exercises, subjects were instructed to perform them 3 days per week using therapy bands and hand weights. Those in the HEP were seen again at 4 wks after initiation of HEP to confirm proper technique of each exercise and to reassess the resistance of the bands to meet the intended 8–15 repetition maximum for each exercise. During the baseline visit, the CON group received printed materials on the shoulder and viewed a 1-hr video of shoulder anatomy, mechanisms of injury, and general information for dealing with shoulder pain but did not contain recommendations for specific shoulder exercises.

Procedures

At enrollment, all participants provided demographic, health, and injury information via self-report and underwent a comprehensive shoulder examination, assessments of pain, and a shoulder US examination. The shoulder examination was performed by an experienced physician (RI) using the Physical Examination of the Shoulder Scale (PESS). After the physical examination, the shoulder US examination was then performed by the same physician, who was blind to group assignment, and scores were recorded for the Ultrasound Shoulder Pathology Rating Scale (USPRS). Lastly, the physician obtained two static images to be used for later calculation of QUS metrics, using procedures fully described previously.15,16 The QUS analysis was performed in a blinded fashion, by someone other than the US examiner and who did not have access to the USPRS or PESS scores.

These evaluations were completed at baseline (before starting either the HEP or CON intervention), 12 wks after initiation of the intervention (i.e., immediately after intervention), and 16 wks after baseline (i.e., 4 wks after intervention follow-up). The Leeds Assessment of Neuropathic Symptoms and Signs was also performed at baseline only to assess whether shoulder pain seemed predominately neuropathic or musculoskeletal (nociceptive) in nature.24 Each subject was paid between US $75 and $150 for completing all study visits.

Shoulder Pain and Functional Outcome Measures

Participants were interviewed with regard to several characteristics of their shoulder pain at baseline, immediately after intervention, and 4 wks after intervention using a standard questionnaire, including the following: ratings of the least, average, and worst intensity of shoulder pain during the past week using an numerical rating scale with anchors of “0,” for “no pain,” and “10,” for “the most intense pain imaginable”; rating of the average unpleasantness of their shoulder pain from 0 (“not unpleasant at all”) to 10 (“most unpleasant pain imaginable”); number of days during the past week that shoulder pain was present (0–7); and categories for duration of shoulder pain episodes (1 min or less, between 1 min and 1 hr, between 1 hr and 24 hrs, at least 24 hrs, constant/continuous; coded from 1 to 5, with a higher score indicating longer duration of pain episodes).

The PESS1 was performed by the study physician (RI). The PESS is scored using 11 common physical examination maneuvers for shoulder pathology. Individual tests are scored from 0, indicating the sign or symptom of pain is absent, to 2, indicating the sign or symptom of pain is definitely present (with 1 indicating the sign or symptom of pain is equivocal).

Participants also completed the Disabilities of the Arm, Shoulder, and Hand (DASH) questionnaire to evaluate functional limitations of the upper limbs.25 The DASH is a self-report questionnaire composed of 30 items on which subjects rate their difficulty and symptoms of pain in accomplishing a specified task. Because we were particularly interested in the impact of shoulder pain specifically, we also included additional questions regarding whether the limitation indicated was due specifically to the shoulder. Therefore, we were able to calculate a score for the traditional administration of the DASH, and we were able to calculate a separate score, using only the shoulder-specific questions, and for the “DASH-Shoulder” score. The validity and reliability of the DASH25 as a measure of upper limb health and function has been supported in a number of patient populations including those with shoulder impingement.25,26 However, the DASH-Shoulder has not previously been used and thus has no validity or reliability information available.

The Interference Subscale of the Multidimensional Pain Inventory27 was used to assess the effect of pain on ADLs, and the Wheelchair User’s Shoulder Pain Index was used to provide an estimate of shoulder pain during transfers, wheelchair mobility, self-care, and other general activities.28 The Patient Health Questionnaire29 and the Beck Depression Inventory (BDI)30 were also collected at each time point to assess overall well-being and depressive symptoms. Lastly, at the end of the 12-wk intervention period and at the 4-wk follow-up visit, participants were asked to complete the Patient Global Impression of Change scale, reflecting their overall status compared with the start of the study, using a seven-choice response scale going from “very much improved” to “very much worse.”

Shoulder US Outcome Measures

The primary outcome of interest with regard to QUS measures of the supraspinatus tendon was the change in tendon width between baseline, immediately after intervention, and at the 4-wk postintervention follow-up. A B-K Minifocus 1402 scanner (B-K Medical, Herlev, Denmark) with a 6- to 15-MHz linear array transducer was used to capture US images. The area of the supraspinatus tendon was visualized in the rotator interval with a clear view of the biceps and supraspinatus tendons, taking care to position the US probe to avoid tendon anisotropy. The US image was downloaded and deidentified for QUS measures to be obtained. The area of interest for the tendon was isolated using a Matlab program that had been modified for our parameters. The QUS measures calculated were tendon width, echogeneity, variance, entropy, contrast, energy, and homogeneity. We used techniques described in a previous study16 but modified the lower border to be the lowest part of the tendon to get the true width of the tendon, thus eliminating the chondral cartilage that was included in that study’s measurement.

The USPRS was used to evaluate overall shoulder pathology.1 The USPRS quantifies the severity of shoulder pathology during US examination using established signs from five tests. Each test is graded on an ordinal scale, with increasing numbers indicating the presence of greater pathology. The following three static tests are conducted: greater tuberosity and cortical surface irregularity (0–3 scale), supraspinatus tendinosis/tendinopathy (0–5 scale), and biceps tendonosis/tendinopathy (0–6 scale); in addition, two dynamic tests are conducted: supraspinatus impingement (0–3 scale) and subscapularis/biceps/coracoid impingement (0–3 scale). An overall shoulder pathology score was computed for each shoulder as the sum of the five test grades (range of 0–20).

Statistical Analysis

Baseline characteristics of participants in the HEP and the CON groups were compared using t tests and χ2 tests. Two primary approaches were used to assess the effect of the HEP on shoulder pain and pathology. First, comparison of measures across time points was made within each group (HEP and CON) separately. Because of the small sample size and the nonnormal distribution of some of the outcome variables, nonparametric tests were used. Intent-to-treat analysis (ITT) with the last observation carried forward method was used to examine overall changes across the three time points (baseline, immediately postintervention, and 4-wk postintervention follow-up) using the Friedman test and including all the participants who were randomized. The per-protocol (PP) analysis approach was used to compare data collected for those who completed the baseline and immediate postintervention measures and, separately, for those who completed the baseline and 4-wk postintervention follow-up (Wilcoxon signed ranks test).

Second, percent changes from baseline were compared between the two groups (HEP and CON), for the immediate postintervention and the 4-wk postintervention follow-up time points separately, using Mann-Whitney U tests (PP approach). Despite random assignment of subjects to intervention groups, some of the outcome variables significantly differed across the groups at baseline; thus, calculation of percent change scores was appropriate for these nonparametric comparisons between groups.

Statistical tests resulting in P values <0.05 were considered significant. No adjustments were made for multiple comparisons.

RESULTS

Participants

Among 343 individual records screened for potential participation, 286 (83%) were excluded from eligibility because they were younger than 20 yrs (n = 20), less than 1 yr after SCI (n = 32), did not use a wheelchair at least 50% of the time and/or did not transfer independently (n = 145), did not have moderate or greater shoulder pain (n = 20), had an existing rotator cuff tear or current medical condition preventing them from completing the HEP (n = 27), could not give independent consent in English (n = 33), or lived too far from the study site to complete follow-up (n = 9). Of those eligible, nine declined to participate. Forty-eight persons with SCI were consented for the study, but 13 did not keep baseline appointments. Thus, a total of 32 persons (56% of those meeting initial eligibility criteria) were randomized for treatment in the study. Of the 35 who completed baseline assessments, three were excluded from further participation because one had a limited range of motion, precluding positioning for US imaging; one had an existing tear in the supraspinatus that was detected at the baseline examination; and one had high-fat body composition making it impossible to fully visualize the supraspinatus tendon during US imaging (excessive obesity and muscularity have been noted to be problematic in assessing the rotator cuff with US31). Thus, 17 participants were allocated to HEP and 15 to CON. Three participants in the CON group and four in the HEP group were lost or withdrew after the baseline assessment. Five participants in the CON group and six participants in the HEP group were unable to return for the immediate postintervention assessment because of difficulty with transportation and scheduling and within the window (1 wk) for this time point. The CONSORT participant flow diagram is presented in Figure 1.

FIGURE 1
FIGURE 1:
The CONSORT Flow Diagram. CONSORT diagram for participant disposition throughout the trial, showing the number of participants included in ITT analyses and PP analyses. 4P, 4-wk postintervention time point; IP, immediate postintervention time point.

Demographic and injury characteristics of the study sample are shown in Table 1. Participants included 26 men and 6 women with a mean ± SD age of 44.8 ± 12.5 yrs. There were no significant differences between HEP and CON groups for sex, age, race/ethnicity, body mass index, level of injury (cervical/tetraplegia or thoracic-lumbar/paraplegia), motor completeness, or duration of SCI and shoulder pain.

TABLE 1
TABLE 1:
Demographic and injury characteristics of study groups at baseline

Baseline Differences

Significant baseline differences were found between the two groups for the DASH, the shoulder-specific DASH, the MPI-Interference subscale, and the BDI, which were all higher (worse) in the HEP group compared with CON group (P < 0.05, Mann-Whitney U; signified with “e” in Table 2). With regard to QUS measures (Table 3), the contrast measure of the dominant supraspinatus tendon was significantly higher, and homogeneity significantly lower, in the HEP group compared with the CON group at baseline, whereas all other US measures were not significantly different between groups.

TABLE 2
TABLE 2:
Self-report measures of shoulder pain and functiona
TABLE 3
TABLE 3:
Quantitative ultrasound measures of the shouldera

Adverse Events

Three participants in the HEP group reported study-related adverse events during 12-wk protocol. Two reported mild to moderate increases in shoulder pain that was present during the first 1 to 2 wks of initiating the program, but both reported resolution of this symptom thereafter. One participant also reported a moderate exacerbation of epicondylitis when weight was increased after the first 4 wks of the HEP. No study-related adverse events occurred in the CON group during the 12-wk intervention period.

Within-Group Differences in Shoulder Pain and Function Across Time

Shoulder pain and function results are in Table 2. For the HEP group, the typical duration of shoulder pain episodes (P = 0.020), the nondominant (P = 0.007), and dominant (P = 0.009) PESS scores, and the shoulder-specific DASH (P = 0.04) all improved across time points (ITT analysis, all signified with “c” in Table 2). Per-protocol comparison of baseline to each of the two postintervention evaluations in the HEP group indicated immediate postintervention improvements in intensity ratings of least shoulder pain (P = 0.020), and the number of days during the past week with shoulder pain (P = 0.042), nondominant PESS (P = 0.008), and the shoulder-specific DASH (P = 0.028, all signified with “b” in Table 2). However, only improvements in the number of days of shoulder pain during the past week (P = 0.035) and the nondominant PESS (P = 0.013) persisted at the 4-wk postintervention follow-up (all signified with “b” in Table 2). Additional improvements at the 4-wk postintervention follow-up compared with baseline included average unpleasantness of shoulder pain (P = 0.046), duration of shoulder pain episodes during the past week (P = 0.011), and dominant PESS (P = 0.007, all signified with “b” in Table 2).

In general, the CON group demonstrated fewer changes in shoulder pain and impairment than the HEP group. Intent-to-treat analysis analyses indicated average unpleasantness ratings of shoulder pain during the past week (P = 0.023) and depression symptoms (BDI, P = 0.011) improved across the two postintervention time points (signified with “c” in Table 2). Per-protocol analyses of baseline to each postintervention evaluation in the CON group indicated that there were no significant changes in pain or function at the immediate postintervention time point and that only ratings of average unpleasantness of shoulder pain were reduced at the 4-wk postintervention follow-up (P = 0.049, signified with “b” in Table 2).

Between-Group Differences in Change in Shoulder Pain and Function Postintervention

To determine whether the changes from baseline to each postintervention evaluation differed between the HEP and CON groups, nonparametric Mann-Whitney U tests were performed on percent change calculations for each variable. Significant differences between groups in percent change in self-report pain and function measures are indicated by “d” in Table 2. Using the PP analysis approach, HEP participants had a significantly greater improvement in nondominant PESS scores immediately after intervention (P = 0.026, signified with “d” in Table 2) and significantly greater perceived improvements in shoulder condition at the 4-wk postintervention follow-up (Patient Global Impression of Change scale, P = 0.015; Fig. 2). The CON participants exhibited a significantly greater improvement in depression symptoms (BDI) at the 4-wk postintervention follow-up compared to the HEP participants (P = 0.003, signified with “d” in Table 2).

FIGURE 2
FIGURE 2:
Participant-perceived change in shoulder pain condition. Participants were asked to indicate the degree of change in their shoulder pain condition immediately post intervention (IP) and at the 4-wk postintervention (4P) time point, using the Patient Global Impression of Change scale. The percentage of participants responding in each of the improvement categories is shown for the HEP and CON groups.

Within-Group Differences in Supraspinatus QUS Across Time

All QUS data are presented in Table 3. For the HEP group, there were no significant changes in any QUS metric across the three study time points (ITT analyses) or when comparing baseline to each of the postintervention evaluations separately (PP analyses). The CON group demonstrated significant changes in supraspinatus echogeneity (P = 0.029) and contrast (P = 0.033) of the dominant arm across the three time points (ITT, signified with “c” in Table 3), but these differences were not borne out using the PP pairwise analysis approach for either the immediate or 4-wk postintervention time points (Table 3). The PP pairwise analyses did indicate that for CON, nondominant supraspinatus tendon width was smaller immediately after intervention (P = 0.036, signified with “b” in Table 3). However, this change from baseline did not persist at the 4-wk postintervention follow-up evaluation (P = 0.41).

Between-Group Differences in Change in Supraspinatus QUS Postintervention

To determine whether changes from baseline at each postintervention evaluation differed between HEP and CON, Mann-Whitney U tests were performed on percent change calculations for each variable. The CON participants demonstrated a greater increase in dominant shoulder supraspinatus contrast at 4 wks after intervention (P = 0.040, signified with “d” in Table 3).

Overall, combined across time points, supraspinatus tendon width was smaller in those who had positive biceps tenderness compared with those who did not, based on the PESS assessment (nondominant SS width: P = 0.002; dominant SS width: P = 0.022).

DISCUSSION

The purpose of this study was to compare the potential changes in shoulder pathology, pain, and function after a 12-wk standardized HEP versus an education control condition (CON). The results indicated that shoulder pain was significantly reduced by HEP as measured by the average unpleasantness of shoulder pain (P = 0.046), the average duration of shoulder pain episodes (P = 0.025), the PESS, and the DASH-Shoulder. The PESS, a measure of pain during specific examination maneuvers, was improved unilaterally (nondominant) immediately after the intervention and bilaterally at the 4-wk postintervention follow-up (Table 2). The DASH-Shoulder also improved immediately after the intervention, suggesting that functional activities were less impaired by shoulder pain after treatment, although the traditional DASH (which includes disabilities attributed to the arm, shoulder, and hand) did not show changes. The psychometric properties of the DASH-Shoulder have not been examined, and thus these results should be interpreted with caution.

Although we used the same HEP and CON interventions used by Mulroy et al.,12 the present study did not measure shoulder strength or torque but instead examined the rotator cuff using QUS of the supraspinatus tendon. Unlike the study by Mulroy et al.,12 the present study also included persons with tetraplegia who otherwise met the eligibility criteria (could transfer independently).

Although participants perceived improvements in pain and function after the HEP intervention, the QUS did not show significant differences in pathology. Tendon width decreased in CON participants after 12 wks (i.e., HEP intervention duration); however, the decrease was not apparent at the 4-wk postintervention follow-up. The lack of change in tendon width in our HEP group is consistent with a recent study on patellar tendinopathy in a group of able-bodied athletes, which showed no US changes with an exercise program that reduced symptoms after a 4-wk exercise program.17 It is important to note that although previous studies have shown changes in some QUS tendon metrics after vigorous activity,19,32,33 there are no reports of assessing changes in US for a period of weeks or months. Thus, without evidence of the reliability of these measurement techniques, interpretation of the QUS results in this study is equivocal, and QUS may be found to be suboptimal for assessing subtle, long-term changes.

Another study performed after exercise showed an improvement in shoulder pain, but no change in tendon width on magnetic resonance imaging.34 This study was designed to exclude those with rotator cuff tears; thus, the subject population was more likely to demonstrate milder tendinopathy than in other recent studies. We could find no effect size for QUS to guide the power analysis for change in shoulder pathology after rotator cuff tears were eliminated.

Comparison of our QUS results to published work is limited to tendon width as variables derived from greyscale cannot be compared across machines. For both groups in both shoulders, baseline tendon width and age (44 yrs vs. 45 yrs) was comparable with values reported by Collinger et al.15,18 This is unexpected, as our participants had been using a wheelchair longer (19.4 yrs vs. 13.8 yrs) and had greater shoulder pain as measured by the Wheelchair User’s Shoulder Pain Index (61 vs. 12). The possible influence of these factors on supraspinatus width might be mitigated by the lower body mass of our group (78 kg vs. 83 kg), as body mass is a strong predictor of supraspinatus width.15,19 Supraspinatus tendon width of our sample is also consistent with values reported by Wang et al.20 for elite college baseball athletes.

The failure of the exercise protocol to achieve robust improvements in QUS variables may indicate supraspinatus degeneration has reached a nonreversible state. The rotator cuff tendinopathy continuum paradigm35,36 proposes three states for an overloaded tendon; reactive tendinopathy, reversible tendon disrepair with possible reactive tendinopathy, and non/limited reversible tendon degeneration with possible reactive tendinopathy. Cook et al.36 suggest that tendons increase their cross-sectional area to compensate for mechanical weakness accompanying structural degeneration. This aligns with validity observation by Collinger et al.15 that more severe shoulder pathology was associated with greater supraspinatus tendon width and greater fibrillary disorganization. In addition to non/limited reversible degeneration, the shoulder tendons of manual wheelchair users, as measured by QUS, are minimally acutely reactive to activity based stimuli. Hogaboom et al.19 reported increased biceps tendon width immediately after wheelchair users with SCI completed a repeated wheelchair transfer protocol with heavier users showing larger changes. No other QUS changes were observed in the biceps and supraspinatus tendon.

Similarly, Collinger et al.15 reported limited QUS changes in the biceps and supraspinatus tendons in a group of manual wheelchair users after a strenuous manual wheelchair propulsion task. Collectively, these results may indicate the presence of nonreversible, nonreactive degenerative tedinopathy in the shoulder tendons of manual wheelchair users with SCI. However, it is unclear the degree to which US greyscale–derived variables are sufficient proxies of collagen fiber structural integrity throughout the tendon cross-section. They may instead capture only superficial integrity. In addition, it remains to be determined whether tendon pathology as measured by QUS greyscale variables provides clinical utility as a predictor of increased risk for onset of serious, functionally limiting degeneration (i.e., full rotator cuff tear).

Study Limitations

Our failure to impart a robust change in QUS variables could be attributed to measurement error,16 insufficient machine sensitivity, insufficient intervention dose (duration/intensity), and/or duration of shoulder pathology.

In addition, the small sample size may have limited our ability to detect changes in QUS. Because we calculated sample size based on a desire to show changes in shoulder pain and function, based on a previous study in the literature,12 we may have underpowered it for detecting changes in pathology using US. Drop-out rate was 24% in the HEP group and 20% in the CON group, and many barriers exist that lead to patients dropping out of studies, transportation being just one of them.37 Other limitations of this study include the midintervention study visit (4 wks after initiation of the intervention) for those in the HEP group that did not occur for those in the CON group, the unblinded nature of exercise as an intervention for the study participants, and the short duration of the exercise intervention; however, the duration of 12 wks was chosen based on the success of others.12,34

CONCLUSIONS

This study confirms a positive result of an HEP in chronic wheelchair users based on “patient global impression of change” and nondominant shoulder evoked pain reports, when compared with an education-only control condition. Although other measures of shoulder pain and function were also demonstrated to improve between baseline assessment and post–home exercise intervention, these changes were not significantly greater than those in the control condition. The study did not find anatomical/pathological changes accompanying these perception changes. Future research might focus on the timing to see whether earlier intervention after SCI could induce anatomic changes. Alternatively, future studies might also verify whether the anatomic/pathologic changes represent progression of disease or whether they signify structural stability in the tendon after chronic wheelchair use.

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Keywords:

Pain; Shoulder Pain; Spinal Cord Injury; Home Exercise Program

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