Shoulder pain is one of the most common musculoskeletal complaints for which people seek treatment.1,2 Typical signs and symptoms include pain during reaching, weakness, and interrupted sleep.3 Often called Shoulder Impingement Syndrome (SIS), this condition is associated with several biomechanical and impairment-level factors including altered scapula or humerus kinematics, range of motion (ROM) and strength deficits, soft tissue tightness, and peripheral or central sensitization.4-10

Loss of glenohumeral joint internal rotation (IR) ROM is common in individuals with shoulder pain, in particular overhead throwing athletes,6,7,11,12 but also in the general population.4,8,13-15 Loss of glenohumeral IR is attributed to posterior shoulder muscle or posterior capsule tightness (PCT).7,8,16-18 Importantly, PCT is also associated with decreased rotator cuff strength,7 altered scapula and humerus kinematics,8,13,19-21 and sensitization8 – the same alterations noted in those with SIS. This interaction among PCT, SIS, and biomechanical and impairment-level factors suggests that an intervention specifically targeting PCT may reduce symptoms and improve movement in those with shoulder pain.

Treatment specificity, aimed to directly influence the structure contributing to symptoms, should result in better outcomes over less time. Interventions targeting PCT have demonstrated improved shoulder ROM, pain, and function,11,12,14 and there is moderate22 and weak23 evidence that posterior shoulder muscle stretching improves IR ROM deficits. Combining muscle stretching with targeted PCT mobilization improves IR ROM in those with shoulder pain,24 but the effects of specific interventions targeting PCT in individuals who also have shoulder pain has not been reported. Because PCT is regularly associated with SIS, evaluating an intervention that is specific to PCT in the presence of shoulder pain has the potential to provide valuable and clinically relevant information for those treating individuals with shoulder pain.

This study provides treatment to individuals with both PCT and shoulder pain, randomized to specific intervention (Experimental) or general intervention (Comparison) groups. To broadly explore the influence of this targeted treatment approach, the study evaluated shoulder function, kinematics, strength, ROM, and sensitization before and after the two different interventions. We hypothesized that the group receiving treatment specific to common impairments (PCT and external rotation (ER) strength deficit) would demonstrate improved kinematics and decreased impairments compared to the non-specific treatment group.

Table 1 reports descriptive data for both groups. Seven individuals were lost to postintervention assessment because of undisclosed personal reasons (Fig. 1). The average number of treatment sessions was 11.3 ± 1.4 and 11.3 ± 1.1 for the EIG and CIG, respectively. Two individuals from EIG received fewer than 12 sessions because they achieved the pre-determined pain and LFT thresholds to stop treatment.

3DScapular Kinematics and Humeral Translations

For scapular IR and PT, triple and double interactions were not significant (P>.05) and there was no main effect of time (P>.05).

For scapular UR, there was no significant triple interaction (P=.68). However, there was a significant group x time interaction (P=.03), with the EIG having greater UR than the CIG at postintervention (3.1°) (Fig. 3B). An angle x time interaction was also found (P<.01) with increased UR at postintervention compared to preintervention at 90° (3.2°) and 120° (4.8°) of elevation (Fig. 3B).

Fig. 3.

Pre and Postintervention scapular internal rotation (A), upward rotation (B), and tilt (C); and humeral anterior translation (D) and superior translation (E) during elevation of the arm in the sagittal plane for both groups. Values are mean (standard error). Abbreviations: EIG, experimental intervention group; CIG, comparison intervention group.

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For humeral anterior and superior translations, there was no significant triple interaction (P>.05) or significant group x time or angle x time interactions (P>.05). However, a main effect of time was demonstrated for both translations (P<.01). Less anterior and superior humerus translation (-0.7mm and -0.6mm, respectively) was found at postintervention when compared to preintervention (Fig. 3D-E).

This study showed that a specific intervention targeting PCT was successful in improving PCT and scapula UR, two factors commonly noted in those with shoulder pain. The magnitude of increased scapula UR was not considered to be clinically meaningful. Our findings also demonstrated improved humeral translations, SPADI scores, ROM, strength, and PPT outcomes in both the specific and the non-specific intervention groups, with no between-group differences in these factors.

For scapular kinematics, the EIG showed increased UR after intervention. However, the improvement was below the minimal clinically important difference (MCID=5°) described in the literature.28,30,56,58 Other studies evaluating the effects of different treatment approaches on scapular kinematics in individuals with shoulder pain,9,29-31,33,59-62 have shown inconsistent results. Some studies have demonstrated no scapula UR differences,30,33,61,62 while others have noted increased scapula UR that was not clinically meaningful,9,29,31,60 consistent with the present study. The variability in scapular UR described in individuals with shoulder pain44,63,64 may contribute to the lack of clinically important changes. Although reliability of scapula kinematics was not estimated for the present study, we believe the standardized data collection methods, broadly used in many previous studies,9,29-31,33,56,58 allow us to assume consistency of kinematic data.

Anterior and superior humeral head translations decreased in both groups after intervention (-0.7 mm and -0.6 mm, respectively). The translation change in the present study is within the between-day SEM confidence interval previously reported for humeral translations in individuals with shoulder pain (0.3mm to 2.3mm).50 Without MDC and MCID calculations for humeral translations in individuals with PCT and shoulder pain in the literature, we are unable to suggest that the decrease in anterior and superior translations is clinically meaningful. A recent study8 showed that individuals with shoulder pain only demonstrated less anterior translation (1.7mm) and lower SPADI score (22.4) compared to individuals with pain and PCT. Considering the limited dimensions of the subacromial space (∼7mm),65 the small translation changes noted may have clinical relevance for the pain and function improvement on the SPADI in both groups.

The SPADI scores demonstrated decreased pain and improved function in both groups after intervention. A change of 8-13 points on the SPADI is considered clinically significant53 and the decrease of 23.6 points in this study, combined across groups, suggests a meaningful improvement in pain and function. Although significant between-group differences were not demonstrated, the EIG showed a reduction of nearly 10 points more than the CIG, suggesting that a specific intervention might be better than a non-specific intervention to improve pain and function in those with PCT and shoulder pain.

The EIG LFT increased 4.3° after treatment, which may indicate less tightness of the posterior capsule from the targeted treatment approach. The change in the EIG group surpassed the SEM but not the MDC90 calculated in this study. With no previous studies reporting an MCID for the LFT, we are unable to suggest that the change seen was meaningful to participants. In addition, with two treatments in the EIG protocol targeting PCT, the change in LFT in the EIG cannot be directly attributed to either mobilization or stretching.

Both groups had increased glenohumeral IR ROM at postintervention. This result did not support our hypothesis and is inconsistent with previous studies that demonstrated increased glenohumeral IR ROM after specific posterior shoulder mobilizations and stretching.11,12,14 The different techniques used compared to the previous investigation's technique may explain the divergent results. Cools et al.11 used passive stretching for 15 min and also included cross-body stretching. This protocol11 may apply more stress on the capsule and posterior shoulder muscles to increase IR ROM. The intervention in our study was supervised, but we cannot ensure that the capsule was adequately targeted during the sleeper-stretch. Patient's tolerance to pain might have influenced our results as well. Another study12 included a home care approach in addition to physical therapy sessions to increase IR ROM in individuals with internal impingement and PCT. In this case, the number of sessions (3 times per week with therapist + daily home exercises) may explain the IR ROM increase.

The fact that we did not control mobilization and stretching loads might have contributed to the IR ROM results. Although no techniques were used in the CIG to specifically increase IR ROM, they improved after treatment. This change may relate to decreased SPADI scores in this group, considering that IR ROM was previously associated with shoulder pain and PCT.8 It is important to note that this group also had less IR ROM at preintervention compared to EIG, which may explain the larger, although not significant, change in motion.

Although ER ROM values in the EIG were lower at postintervention, the groups were not statistically different. Because neither intervention included a specific technique to influence ER ROM, this 5.9° decrease in the EIG lacks a direct interpretation. It is possible that while performing ER strengthening the EIG group developed a movement pattern that avoided end-range ER motion, and this influenced the ER measurement. Measurement error at postintervention may also explain this change but we would expect error to be evident in both groups, not only for the EIG.

Shoulder ER strength in the EIG increased mildly after the intervention, as expected with performing resistance exercises, but the increase was not enough for statistical significance between groups. It is possible that the amount of resistance used was not adequate to promote larger strength increases. Participants self-selected the amount of resistance for this exercise and perhaps using a 10-Repetition Maximum as in prior studies66,67 may have resulted in greater and more effective resistance loads being applied.

Both groups had improved UT, infraspinatus, supraspinatus, and deltoid PPT. The long mean duration of pain (∼40 months) for individuals in the present study does not appear to have compromised their ability to improve with treatment. These results also suggest that individuals were mostly free of central sensitization despite the chronic nature of symptoms. It is possible that the active treatments in both interventions explains some PPT improvement, considering the critical role movement has in the rehabilitation of individuals with shoulder pain.9,30 With the MCID for PPT improvements in individuals with shoulder pain unknown, we cannot be certain that a meaningful improvement in sensitivity can be attributed to the interventions.

The natural recovery process, the placebo effect and the real effect of the intervention are potential explanations for the improvement observed in the CIG. Future studies could evaluate natural recovery by including a control group and adding long-term follow-up testing. Although the comparison group received a non-specific intervention, they performed active exercise and stretching, which supports the importance of motion to decrease shoulder dysfunction. The placebo effect could also have contributed to the CIG improvement, with the patient's expectations and the therapist beliefs influencing outcomes.68

This study showed that the specific intervention was more effective for improving PCT in individuals with PCT and SIS, as assessed by LFT. Increased scapular UR was also observed in the experimental group following treatment, but these changes were not considered clinically meaningful. Both interventions were effective in changing humeral translations and improving SPADI scores, IR ROM, and local pain sensitivity in individuals with shoulder pain and PCT, demonstrating that there was no additional benefit to a specific targeted intervention on these variables.