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PHYS THER
Vol. 85, No. 7, July 2005, pp. 636-647
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Research Reports

Correlation of 3-Dimensional Shoulder Kinematics to Function in Subjects With Idiopathic Loss of Shoulder Range of Motion

Peter J Rundquist and Paula M Ludewig

PJ Rundquist, PT, PhD, is Assistant Professor, DPT Program, Krannert School of Physical Therapy, University of Indianapolis, 1400 E Hanna Ave, Indianapolis, IN 46227 (USA) (prundquist{at}uindy.edu)
PM Ludewig, PT, PhD, is Associate Professor, Program in Physical Therapy, University of Minnesota, Minneapolis, Minn

Address all correspondence to Dr Rundquist


Submitted June 18, 2004; Accepted January 10, 2005


   Abstract
 
Background and Purpose. People with idiopathic loss of shoulder range of motion (ROM) have difficulty completing activities of daily living. This investigation was performed to determine the association between active glenohumeral ROM and function and to develop a multiple regression equation to explain variation in function in people with idiopathic loss of shoulder motion. Subjects and Methods. This was a comparative study of 21 subjects (18 female, 3 male), using measurements of shoulder kinematics and administration of the Shoulder Rating Questionnaire (SRQ). Electromagnetic tracking sensors monitored the 3-dimensional position of the scapula and humerus throughout active shoulder motions. Correlations were performed between the active ROMs of interest and various demographic factors and the SRQ. A multiple regression equation was generated. Results. A multiple regression equation including scapular-plane abduction, external rotation at the side, external rotation at 90 degrees of abduction, and weight explained 69% of the variation in the SRQ scores. Discussion and Conclusion. The results suggest that active ROM can be used to predict function in people with idiopathic loss of shoulder ROM.

Key Words: Articular • Glenohumeral joint • Kinematics • Range of motion • Upper-extremity function


   Introduction
Top
 Abstract
 Introduction
Method
 Results
 Discussion
 Summary and Conclusions
 Appendix
 References
 
Idiopathic loss of shoulder range of motion (ROM), the loss of shoulder motion without discernable etiology, is a descriptive label for a set of symptoms.1,2 All patients with idiopathic loss of shoulder ROM complain of decreased motion.2–10 Additional complaints include disturbed sleep2–9 and difficulty accomplishing personal hygiene, donning and doffing clothing,3 and overhead movement, reaching, or rotation activities.10

There have been multiple alternative attempts to label this condition. None have been all-inclusive. Codman2 initially coined the term "frozen shoulder" in 1934. It is the most frequently referred to term labeling the condition found in the literature.4,5,7–9,11–35 However, usage of the term has not been universal.

Terminology has been based on assumed etiology. Terms based on inflammation include "adhesive capsulitis,"3,10,36–46 "adhesive subacromial bursitis,"7,38,47 "biceps tenosynovitis,23 "scapulohumeral periarthritis,"1,7,38,47–51 "subdeltoid bursitis,"2,47 "obliterative bursitis,"23 and "tendinitis of the short rotators."38 Noninflammation-based terms include "stiff and painful shoulder,"2,38,52–54 "calcification of the supraspinatus tendon,"47 "periarticular adhesions,"38 "Duplay disease,"38 "an algodystrophic process,"55 and "checkrein shoulder."14,56

Up to 3% of the general population is affected by idiopathic loss of shoulder ROM.57 Bridgman48 reported that up to 7% of outpatients seen at a community hospital had symptoms of periarthritis, and Bunker and Anthony14 reported that more than 5% of all patients in their study who were seen at shoulder clinics were diagnosed with frozen shoulder. Age and sex distributions reported in the literature have been widely variable, with ages ranging from 22 years43 to 85 years58 and with the percentage of female subjects ranging from 48%14 to 84%.59

Codman2 was the first person to publish the opinion that idiopathic loss of shoulder ROM is a self-limiting condition. Grey17 investigated his belief that frozen shoulder is self-limited. He utilized reassurance, analgesics, and hypnotics as his sole interventions. He concluded that symptoms resolved and full movement returned in 21 of 22 patients within 2 years. Several investigators have presented less favorable prognoses.4,60

Binder et al60 followed 40 patients with frozen shoulder for an average of 44 months. They found that 16 patients still had pain or movement restriction at follow-up and that 5 patients had greater than 25% reduction in total range of movement. Shaffer4 followed 62 patients for an average of 7 years. Thirty-one patients reported shoulder pain or stiffness, or both, at their final evaluation. Therefore, despite the relatively low percentages of the general population affected by idiopathic loss of shoulder ROM, the long-term limitations experienced by these people suggest that a greater understanding of the condition and more effective intervention approaches are needed.

People with idiopathic loss of shoulder ROM have difficulty completing activities of daily living (ADL). The shoulder ROM necessary to complete certain ADL tasks has been investigated in subjects without shoulder pathology.61–64 O'Neill et al62 found that male subjects needed 127.2 degrees of humerus-to-trunk elevation to reach their occiput, 68.7 degrees to reach their opposite shoulder, 86.6 degrees to reach their mouth, and 31.3 degrees to reach their sacrum.

Several investigators have correlated shoulder motion to function. Triffitt63 utilized Spearman rank correlation coefficients (rs) to determine that humerus-to-trunk elevation (rs=.72) and abduction (rs=.68) had the highest correlation with hair combing in patients seen at shoulder clinics. Internal rotation (IR) (rs=.65) and abduction (rs=.62) had the highest correlation with washing the back. Humerus-to-trunk elevation (rs=.58), IR (rs=.53), and abduction (rs=.55) had the highest correlation with reaching a high shelf.63 Bostrom et al64 utilized Spearman rank correlation coefficients to find that humerus-to-trunk flexion and external rotation (ER) correlated moderately well with hand-to-neck (rs=.60 for flexion, rs=.50 for ER), hand-to-opposite shoulder (rs=.59 for flexion, rs=.50 for ER), and hand-behind-back (rs=.52 for flexion, rs=.50 for ER) activity-related tasks in women with rheumatoid arthritis. Twenty-four percent of the variation in personal hygiene ability and 11% of the variation in dressing ability were explained by humerus-to-trunk movement impairment.64

Determining the relationship between impairment-based measures such as ROM and patient function is a priority area in physical therapy research.65 Limitations in ROM are known to be substantial and are the focus of rehabilitation interventions for idiopathic loss of shoulder ROM. However, little is known regarding the relationship between function and ROM limitations or demographic factors for these subjects. Knowledge of this relationship may affect the choice of the most appropriate scientifically based interventions for this condition. Glenohumeral motion was chosen for this investigation as a more accurate representation of the actual joint where the idiopathic motion loss is believed to originate, rather than humerus-to-trunk motion, which is a function of multiple joints. This approach allows interpretation relative to actual glenohumeral joint motion deficits and relationships to function, but does not include compensatory motions that might occur at other shoulder joints.

The purposes of this investigation were: (1) to determine the relationship between glenohumeral ROM and function based on Shoulder Rating Questionnaire (SRQ) scores and (2) to develop a multiple regression equation utilizing glenohumeral ROM and demographic factors to explain functional variation in subjects with idiopathic loss of shoulder ROM.


   Method
Top
 Abstract
 Introduction
 Method
Results
 Discussion
 Summary and Conclusions
 Appendix
 References
 
Subjects

This study was a component of a comprehensive investigation of shoulder ROM and function.66,67 All subjects consented to participate.

Twenty-one volunteers were investigated. Nineteen subjects were recruited from 4 physical therapy practices and 2 orthopedists. Two subjects were recruited through local newspaper contacts. Fourteen of the 21 subjects had a physician's diagnosis consistent with frozen shoulder or adhesive capsulitis, 4 subjects had rotator cuff–related diagnoses, and 3 subjects had no physician's diagnosis, but all diagnoses and symptoms were considered consistent with frozen shoulder or adhesive capsulitis based on our clinical examination. The subjects were 18 years of age or older. Subjects were screened for inclusion if they had had symptoms for at least 1 month and had not had symptomatic exacerbation over the last month.

Three subjects (14%) were male, and 18 subjects (86%) were female. The subjects' ages ranged from 40 to 67 years (X=52.8, SD=6.5). Their height ranged from 1.6 to 1.9 m (X=1.7, SD=0.1). Their weight ranged from 61.4 to 86.4 kg (X=71.7, SD=9.4). The length of symptoms ranged from 2 to 120 months (X=13.6, SD=24.9). Four subjects had experienced idiopathic loss bilaterally. Three subjects reported that their opposite shoulder had returned to normal. The involved shoulder distribution in the subjects with unilateral involvement was 11 right dominant (52%), 4 right nondominant (19%), and 6 left nondominant (29%).

Each subject was examined using a cervical and shoulder clinical screening to eliminate alternative potential causes of loss of shoulder ROM. Specific exclusion criteria are listed in Figure 1. Loss of passive ROM of at least 25% in at least 2 of the following motions was an inclusion criterion: abduction, ER, and IR. Supine passive abduction, ER, and IR side-to-side comparisons were made for the 17 subjects with unilateral involvement. Seven subjects (41%) had at least 25% losses in abduction, ER, and IR; 6 subjects (35%) had losses in abduction and ER; 1 subject (6%) had losses in abduction and IR; and 3 subjects (18%) had losses in ER and IR. The person with current bilateral symptoms had 25% or greater loss in IR as compared with the less involved side.


Figure 1
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[in a new window] 		Figure 1. Exclusion criteria.

 
Instrumentation

A number of functional scales based on shoulder function are available.68–72 None were specifically designed to evaluate the shoulder function of subjects with idiopathic loss of shoulder ROM. The SRQ was chosen for this investigation. It contains elements designed to assess global function, pain, ADL, leisure activities, and work-related activities. Subjects with idiopathic loss of shoulder ROM were included in its psychometric properties evaluation. The SRQ has demonstrated acceptable validity, reliability, and responsiveness.70 Because global glenohumeral function was the overall outcome of interest in this investigation, the total SRQ score was used rather than domain scores. Specific information on the administration and psychometric properties of the SRQ is shown in the Appendix.

Technical advances over the last 20 years allow for accurate and reliable 3-dimensional (3-D) analysis for the evaluation of shoulder ROM.73–76 Utilizing 3-D kinematic analysis to evaluate scapulohumeral ROM in subjects with idiopathic loss of shoulder ROM has several advantages. It allows for analysis of glenohumeral motion specifically. It is more accurate than goniometry. Finally, errors from evaluating the 3-D movement of the shoulder with a 2-dimensional (2-D) technique are likely.

The Polhemus FASTRAK electromagnetic motion capture system* was used to track the 3-D kinematics of each subject's humerus, scapula, and thorax at a 40-Hz sampling rate per sensor. The FASTRAK system consists of a stationary electromagnetic transmitter and up to four 3-D sensors. An additional sensor attached to a stylus is used to digitally determine the 3-D orientation and position of anatomical landmarks relative to their respective segment sensor. The sensors track the orientation of the segments in reference to the transmitter throughout motion over time.

The manufacturer of the FASTRAK system has reported root-mean-square (RMS) accuracy of 0.15 degree for orientation and 0.3 to 0.8 mm for position within a source-to-sensor separation of 76 cm.77 Accuracy described as RMS identifies the level of error expected for an average measurement or subject while adjusting for the normal positive and negative distribution of errors by taking the square root of average squared errors. Within-day and within-subject test-retest RMS variability of peak flexion for the primary investigator (PJR) without removing the sensors was less than 1 degree when previously evaluating 4 subjects without shoulder symptoms.66 Between-day within-subject test-retest RMS variability of peak flexion for the primary investigator was less than 3 degrees when previously evaluating 2 subjects without shoulder symptoms.66

Experimental Procedure

Three FASTRAK sensors were used. Each sensor was 2.3 cm in length, 2.8 cm in width, 1.5 cm in height, and weighed 17 g.77 One sensor was attached to the sternum and one sensor was attached to the skin overlying the flat superior bony surface of the scapular acromion with adhesive tape. The third sensor was attached to a thermoplastic cuff that was secured to the distal humerus with Velcro straps.{dagger} In order to minimize movement error caused by deltoid muscle contraction, the scapular sensor was placed as medially as possible while remaining on the acromion. Figure 2 illustrates the subjects' experimental setup.


Figure 2
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[in a new window] 		Figure 2. Experimental setup.

 
Data collection was performed as outlined in previous investigations.66,67,78 Subjects were tested while standing. Digitization of bony landmarks on the humerus (lateral epicondyle, medial epicondyle, and a calculated point midway between the lateral and medial epicondyles) scapula (inferior angle, posterior aspect of the acromioclavicular joint, and root of the spine of the scapula), and thorax (seventh cervical spinous process, eighth thoracic spinous process, suprasternal notch, and xiphoid process) allowed for transformation of sensor data to local anatomically based coordinate systems75 (Fig. 3).


Figure 3
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[in a new window] 		Figure 3. Anatomical landmarks and glenohumeral motion axes. Humerus landmarks: LE=lateral epicondyle, ME=medial epicondyle, and MP=a point midway between. Scapula landmarks: IA=inferior angle, AC=posterior aspect of the acromioclavicular joint, and RS=root of the spine of the scapula. Thorax landmarks: C7=seventh cervical spinous process, T8=eighth thoracic spinous process, SN=suprasternal notch, and XP=xiphoid process. X,Y,Z=axes of rotation, h=humerus, ER/IR=external rotation/internal rotation, ABD/ADD=abduction/adduction, Ext/Flex=extension/flexion.

 
Kinematic data were collected for each subject's full active ROM in the following order: flexion, abduction, scapular-plane abduction, ER, and IR. Measurements of ER and IR were collected with the subject's arm at the side (ER1 and IR1) and with the arm as close to 90 degrees of abduction as possible (ER2 and IR2). The scapular plane was defined as 40 degrees anterior to the coronal plane.75 A vertical plywood guide that could be moved to guide flexion, abduction, and scapular-plane abduction was used to keep the subject's arm in the appropriate plane of motion. The scapular plane was marked on the floor for either extremity. The subject remained with the fingertips in light contact on the board while performing the elevation motions.

Data were collected from both shoulders. Data from the involved glenohumeral joint were used throughout the analysis. The noninvolved shoulder was tested first to allow the subjects to become familiar with the procedure. For the subjects with a history of bilateral involvement, the currently involved shoulder was tested last. Subjects were instructed to move their arm as far as possible for each motion at a self-selected, slow, steady speed (all subjects moved their arm at a rate of less than 1 Hz). Measurements for 5 repetitions of each motion were collected if the subjects were able to perform that number of repetitions. Subjects were allowed to rest, if needed, between sets of motion repetitions. The SRQ was completed after the ROM data collection.

Data Reduction

The digitized anatomical points were the basis for each shoulder segment's clinically relevant local anatomical coordinate system as previously described.67,75,78 The description of humerus position and orientation related to the scapula and the trunk was calculated through matrix transformations.75,79 Humerus-to-scapula orientation was described as rotation about y (adduction/abduction), x' (flexion/extension), and z'' (long axis IR/ER) (Cardan angles, Fig. 3). The rotation sequences are consistent with those previously published75 and allowed for clinically relevant descriptions of humeral motion.

Data Analysis

The intention of this investigation was to use active peak ROM values to investigate the correlation between glenohumeral ROM and function in subjects with idiopathic loss of shoulder ROM. The peak trial may not have been representative of the motion investigated. This concern could be eliminated if there was no difference between trials. Trial effect was analyzed before further analysis was performed.

Trial effect was initially investigated through one-way repeated-measures analyses of variance (ANOVAs) (repeated trials per subject) of the involved and noninvolved shoulders in 10 of the subjects. The subgroup consisted of the first and last 5 subjects who had completed the full data collection. If a motion demonstrated a trial effect within the subgroup of subjects, further analysis was done with all subjects who had completed all 5 trials. If a trial effect remained after all available subjects' data were reviewed, a final review of trial effects was performed through standard error of the measurement (SEM) analysis. The SEM was calculated directly as the square root of the within-subjects mean square error from a one-way ANOVA with subjects as the factor, rather than indirectly using intraclass correlation coefficients.80

Flexion, abduction, scapular-plane abduction, ER1, IR1, and IR2 did not demonstrate a trial effect. The ER2 demonstrated a trial effect (F ratio=6.42, P=.00) in the subgroup (n=10) analyses. The ER2 trial effect remained in the full analysis (F ratio=6.77, P=.00). Post hoc Bonferroni analyses revealed that repetitions 4 and 5 had greater ER ROM than repetition 1. The SEM for the ER2 data was 2.12 degrees. This magnitude of effect was not judged to be clinically significant. As a result, the peak trial data were used in the remainder of the data analysis.

Two additional potential confounding factors were reviewed as part of the comprehensive investigation of shoulder ROM and function.66 Neither speed of shoulder movement nor order of data collection was found to be a significant covariate in the peak motion found. It was possible that later tested motions could have been progressively less limited as the shoulder "loosened up." This was not found to be the case.

Descriptive statistics (mean, standard deviation, range) were calculated across subjects for each motion. Potential variables included active peak elevation of the humerus in relation to the scapula and trunk in flexion, scapular-plane abduction, abduction, ER1, IR1, ER2, and IR2.

Pearson product moment correlations (r) and point biserial correlations (rpb) were performed to determine the factors that were strongly associated with the overall SRQ score and the factors that were strongly associated with each other. Factors in the Pearson matrix were the 7 glenohumeral motions and the subject's age, duration of symptoms, height, and weight. Factors in the point biserial matrix were whether the dominant shoulder was involved, whether the subject had a history of bilateral involvement, and whether the subject was taking anti-inflammatory medications. A multiple regression also was calculated to explain the variation in the total SRQ scores.

Several steps were involved in determining which factors were used in the multiple regression. The top 10 factors (of 14 possible) from the Pearson and point biserial correlation matrices were used in the all-possible regression. To avoid multicollinearity, if interfactor correlations were higher than .85, only one of the factors was used in the multiple regression.81 Variance inflation factors (VIFs) also were assessed in the models to ensure that they remained below a value of 5.82 Variance inflation factors are direct measures of multicollinearity (the inverse of 1 – the R2). A VIF value greater than 5 indicates an R2 greater than .80, and subsequently multicollinearity may be affecting the results.82

The sample size limits the number of factors that could be considered. The absolute maximum states there must be at least 2 subjects for each factor in the model. The general rule of thumb is that there should be at least 4 times the number of subjects as predictors.83 With 21 subjects, a maximum of 10 predictors could be used. Based on the general rule, 4 predictors would be appropriate with 21 subjects.81 The absolute maximum (2:1) rule was used to determine the 10 factors used in the all-possible regression. The 4:1 rule was utilized to determine the best combination of 4 factors for the multiple regression.

An all-possible regression evaluates all of the possible combinations of factors (allowing for all orders of entry) to determine which factors are significant by themselves or in a group.83 After accounting for multicollinearity, the 10 most highly correlated factors with the total SRQ score were used in an all-possible regression to determine the most predictive group of 4 factors. Those predictors then were used in the multiple regression, with a forced model ordered as the result of the combination determined by the all-possible regression.


   Results
Top
 Abstract
 Introduction
 Method
 Results
Discussion
 Summary and Conclusions
 Appendix
 References
 
Descriptive Statistics

Means, standard deviations, and ranges of peak humerus motion in relation to the scapula across all involved shoulders for the 7 motions investigated are presented in Table 1. The SRQ scores ranged from 35.5 to 91.2 (X=61.9, SD=13.4). Glenohumeral scapular-plane abduction, abduction, flexion, age, ER1, IR1, duration, anti-inflammatory use, bilateral involvement, and dominant involvement were the 10 factors that correlated highest with the total SRQ. Table 2 outlines the Pearson product moment and point biserial correlations. The Pearson product moment correlations between scapular-plane abduction and flexion (r=.97, P=.00) and between scapular-plane abduction and abduction (r=.95, P=.00) were greater than .85. Thus, only scapular-plane abduction was used in the subsequent multiple regression analyses, and ER2 and weight also were considered in the all-possible regression. Scapular-plane abduction had the highest individual correlation to the SRQ.


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[in a new window] 		Table 1. Descriptive Statistics for Humerus-to-Scapula Peak Motion (in Degrees) (N=21)

 

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[in a new window] 		Table 2. Pearson Product Moment (r) and Point Biserial (rpb) Correlations for the Shoulder Rating Questionnaire (SRQ) (N=21)a

 
The all-possible regression analysis determined that scapular-plane abduction, ER1, ER2, and weight were the 4 best predictors (Tab. 3). The all-possible regression analysis determined that scapular-plane abduction alone explained the highest individual amount of variation (R2=.38). The addition of ER1 to scapular-plane abduction resulted in the highest 2-factor variation explanation (R2=.41). The addition of ER2 resulted in the highest 3-factor variation explanation (R2=.59). The addition of weight resulted in the overall explanation of 69% of the variance (P=.001, R2=.69) in SRQ scores. All factors were significant predictors individually at alpha <.05.


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[in a new window] 		Table 3. Regression Resultsa

 

   Discussion
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
Summary and Conclusions
 Appendix
 References
 
Duration of Symptoms

Codman2 has stated his belief that idiopathic loss of shoulder ROM is self-limiting. The average duration of subjects' symptoms in this investigation was 13.6 months. All of the subjects continued to demonstrate ROM and functional deficits. Grey17 found that the frozen shoulder of 21 of 22 subjects spontaneously resolved within 2 years. Although the current investigation was not longitudinal, 2 of the subjects had deficits beyond 2 years after onset of symptoms, supporting the data of other authors4,60 that deficits can be more long-standing.

Associations of Impairment and Functional Status

No shoulder-specific functional status measures have been specifically validated for subjects with idiopathic loss of shoulder ROM. Although only 5% of the subjects who participated in the development of the SRQ had frozen shoulder, its good overall psychometric properties made it appealing for this investigation.70

A correlation of .5 to .75 is generally considered a moderate association, and a correlation over .75 is considered a good-to-strong association.84 The individual correlations between glenohumeral scapular-plane abduction (r=.62), abduction (r=.56), and flexion (r=.53) and the SRQ met the moderate association threshold. They were moderately associated with the SRQ total score. None of the factors met the strong association threshold (Tab. 2). Additionally, association does not equate to causation.

Multiple regression was utilized to explain variation in SRQ scores. Glenohumeral scapular-plane abduction, ER1, ER2, and weight were found to significantly contribute to the variation in overall SRQ score. Together, these factors explained 69% of the variability. Although these data explain 69% of previously unexplained variation for this population, additional factors that were not included in the model are clearly necessary to fully predict functional status.

Both ER1 and ER2 accounted for part of the variation in the total SRQ score. They are correlated to each other at r=.76, which is less than the recommended multicollinearity cutoff of .85.81 Different parts of the capsule are tightened when performing ER at different abduction levels. The coracohumeral ligament limits ER at 0 degrees of humerus-to-trunk abduction,85 whereas the anterior band of the inferior glenohumeral ligament limits ER at 90 degrees of humerus-to-trunk abduction.86

Only 1 subject's motion in the current study was less than the values necessary to complete eating activities described by Safaee-Rad et al.61 This deficit was on the subject's left (nondominant) side. Thirteen of the 21 subjects did not achieve enough scapular-plane abduction to complete reaching the occiput under the parameters outlined by O'Neill et al.62 This motion is necessary for hair combing.

Shoulder motion is not the only factor involved in completing the activities investigated by Safaee-Rad et al61 and O'Neill et al.62 Barker et al87 investigated the upper-extremity joint coordination strategies utilized to complete ADL tasks. They used a triaxial, flexible electrogoniometer to study the upper limbs of 11 right-hand–dominant subjects through 3 ADL tasks. They determined that it is difficult to determine normal versus abnormal upper-extremity joint coordination strategies. As Barker et al stated, "In fact, the mechanical degrees of freedom available to the upper limb system may imply that such a 'normal' description may always be elusive."87(p24)

Although the current study investigated the correlation between active glenohumeral ROM and overall function, Triffitt63 correlated humerus-to-trunk ROM to specific ADL tasks. The Pearson r correlation of .62 between scapular-plane abduction and the SRQ in our study was higher than Triffitt's Spearman rank correlations between humerus-to-trunk elevation and reaching a high shelf (rs=.58) and lower than his correlation between humerus-to-trunk elevation and hair combing (rs=.72). The correlation between abduction and the SRQ (r=.56) in our study was similar to Triffitt's correlation between abduction and reaching a high shelf (rs=.55) and lower than his correlation between abduction and hair combing (rs=.68) and his correlation between abduction and washing the back (rs=.68). The correlation between IR and the SRQ (r=.22) in our study was much lower than Triffitt's correlation between IR and reaching a high shelf (rs=.53) and his correlation between IR and washing the back (rs=.65). Additionally, IR was not a significant factor in the all-possible or multiple regressions. These findings may suggest different functional deficits or different perceptions of contributions of specific activities to overall function in Triffitt's nonhomogenous group of diagnoses (rotator cuff problems, instability, capsulitis, arthropathy, and others) as compared with the current investigation's people with idiopathic loss of shoulder ROM. A difficulty in comparing the studies directly is that Triffitt utilized 2-D goniometry to investigate humerus-to-trunk motion, whereas we utilized 3-D electromagnetic goniometry to investigate glenohumeral motion. The IR that Triffitt cited may not have been solely glenohumeral.

Bostrom et al64 correlated humerus-to-trunk ROM and function as measured by the Shoulder Disability Questionnaire and individual functional motions in 63 female subjects with rheumatoid arthritis. The current study's flexion-to-SRQ correlation (r=.53) was similar to their correlations of flexion to hand-to-neck, hand-to-opposite shoulder, and hand-behind-back activity-related tasks. The current study's ER1-to-SRQ correlation (r=.27) was lower than their correlations between ER and hand-to-neck, hand-to-opposite shoulder, and hand-behind-back activity-related tasks. However, the 69% overall SRQ variation explanation in the current study was substantially higher than Bostrom and colleagues' explanation of ROM to personal hygiene and ROM to dressing ability variation (24% and 11%, respectively).

The 3-D investigation of glenohumeral motion should be cautiously compared with the 2-D humerus-to-trunk goniometric techniques that Bostrom et al64 used. In both our study and the study by Bostrom et al, humeral motion deficits were linked to function; however, Bostrom and colleagues' ER measurement may have included a scapulothoracic component. The larger amount of variation explained in the current investigation may have been due to the glenohumeral analysis that more appropriately investigates the true motion of the shoulder joint. Additionally, idiopathic loss of shoulder ROM may not affect ER as much as rheumatoid arthritis, and rheumatoid arthritis is often bilateral. Most of the subjects in the current study had unilateral involvement. One shoulder may not have caused as much functional deficit.

Limitations

Despite the use of an appropriate experimental setup, skin slip may occur with surface sensor techniques. Skin slip has been shown to be worse as end-range shoulder elevation is approached.74 Because end-range shoulder elevation in subjects with idiopathic loss of shoulder ROM does not approach normal values, this may not be a large concern for this population. Additionally, end-range ER and IR values may be under-represented with the methods used in this investigation. Previous validation of this technique comparing data collection though surface sensors to bone pin data found a 7.5-degree average error in rotation measurements.88 Neither ER nor IR had a strong one-factor correlation with the SRQ. Internal rotation was not a significant factor in the multiple regression.

The sample size for this study was small (N=21), because larger sample sizes for this population are difficult to obtain. Such a sample size limited the number of variables that could be considered in the model and did not allow for testing of possible interactions of the independent variables.83 Furthermore, the coefficients are less stable in regression analyses using small sample sizes.83,84

Finally, the investigation may be limited by evaluating only the glenohumeral component of shoulder function. We believe this approach allows for greater interpretation of how the presumed pathology deriving from the glenohumeral joint relates to function. The glenohumeral joint also is primarily targeted with regard to intervention approaches such as joint mobilization. However, people with idiopathic loss of shoulder ROM also may have deficits in the scapulothoracic component of shoulder motion. Alternatively, compensatory increases in scapulothoracic motion are possible. Inclusion of scapulothoracic data may increase the amount of total SRQ explained.

Clinical Implications

Based on the presumed pathology of the underlying capsular restrictions, a rehabilitation focus on managing ER, IR, and abduction is generally advocated.13,44,45,89 This is an impairment-based rehabilitation approach. Justification for such an approach relies on an assumption of a relationship between these ROM impairments and a patient's functional status. Results of the current investigation support such an approach, because impairment measures were significantly associated with functional status and 3 ROM impairment factors could explain 59% of the variance in function. Weight was a demographic factor that cannot be changed directly through physical therapy shoulder rehabilitation, yet it explained an additional 10% of the variance in function. Weight was inversely correlated with the SRQ, suggesting that less body weight may lead to better overall self-perception of shoulder function. Although therapists do, at times, make general health recommendations, including weight loss, to their patients, greater clinical attention to this factor for this population may be warranted.

Although the 3-D electromagnetic motion analysis technique used in our study is not a clinical tool, it allows for the most precise and objective measurement of the underlying ROM impairment at the glenohumeral joint. Use of a less precise measure such as goniometry would likely introduce greater random error into the measurements and reduce the strength of association. Use of the more precise technique gives the clinician the best possible knowledge of the relationship of the underlying glenohumeral ROM limitations that he or she is trying to improve and the patient's functional status. The data suggest that an expanded clinical focus on scapular-plane abduction in addition to ER ROM might better improve patient function. This expanded focus is consistent with the premise that scapular-plane abduction is a more functional plane of motion than coronal-plane motions of flexion or abduction.88 It is important to consider, however, that flexion and abduction were not included in the overall model because of statistical issues of multicollinearity. The univariate data indicate that flexion and abduction are significantly associated with functional status, although not as strongly as scapular-plane abduction. Abduction ROM deficits receive clinical attention as part of the traditionally described "capsular pattern." When considering patient functional goals, the data of our study support assessment and management of flexion deficits as well. The current results may be used to advocate concentration on glenohumeral elevation, ER1, and ER2 in the treatment of people with idiopathic loss of shoulder ROM. However, because scapulothoracic data are not presented, our data neither support nor refute clinical consideration of the contributions of the scapulothoracic articulation to overall shoulder function.

Research Implications

Although this study provides support for significant associations of ROM impairment and functional status, optimally studies are needed to provide direct evidence of a relationship between improvements in scapular-plane abduction, flexion, and ER and improvements in function. This would require a longitudinal investigation, but would link treatment gains to positive functional improvements.

The SRQ is a self-reported functional status measure. Designing a study that incorporates a functional activity during the collection of ROM data would be insightful. Collection of functional motion data during the investigation would make the motion-to-function analysis more direct. Examples of activities to collect motion data 3-dimensionally include dressing, grooming, and reaching. Collection of data while people perform these activities would allow for more direct comparison with the domains of the SRQ.

Similarly, development of an objective clinical tool that more precisely measures glenohumeral ROM would be beneficial to allow development of more specific interventions for people with idiopathic loss of shoulder ROM. The FASTRAK system is portable and could be used to collect data in the clinic. However, greater ease of use, real-time clinically interpretable data output, and reduced cost are needed prior to such tools being incorporated into clinical practice. Finally, inclusion of scapulothoracic motion in the regression analysis may improve the total SRQ score variation explained. There has been little to no evaluation of the scapulothoracic contribution to idiopathic loss of shoulder ROM thus far in the literature. Scapulothoracic data have been collected as part of the previously completed comprehensive study.66 Data analysis is ongoing.


   Summary and Conclusions
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Summary and Conclusions
Appendix
 References
 
Idiopathic loss of shoulder ROM was the focus of this investigation. Two conclusions can be made from this investigation: (1) active glenohumeral ROM moderately correlates with SRQ-based function in this population, and (2) the combination of glenohumeral scapular-plane abduction, ER1, ER2, and weight can be used to predict 69% of overall shoulder function for these patients. Based on the presumed pathology of the underlying capsular restrictions, a rehabilitation focus on managing ER and IR as well as abduction is generally advocated. Results of the current investigation support an additional focus on scapular-plane abduction in order to expand the pathology-based approach toward additional functional goals.


   Appendix
Top
 Abstract
 Introduction
 Method
 Results
 Discussion
 Summary and Conclusions
 Appendix
References
 


Figure 1
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[in a new window] 		Appendix. Administration and Psychometric Properties of the Shoulder Rating Questionnaire (SRQ)

 


   Footnotes
 
Dr Rundquist's contributions included writing, data collection and analysis, project management, and subject recruitment. The manuscript resulted from his dissertation work. Dr Ludewig's contributions included providing facilities and consultation regarding concept, design, data collection and analysis, and writing. The authors acknowledge the members of Dr Rundquist's PhD dissertation committee for their assistance in project development.

The investigation was approved by the Institutional Review Board of the University of Minnesota.

Preliminary data were presented at the Combined Section Meeting of the American Physical Therapy Association; February 12–16, 2003; Tampa, Fla.

* Polhemus Inc, 40 Hercules Dr, PO Box 560, Colchester, VT 05446. Back

{dagger} Velcro USA Inc, 406 Brown Ave, Manchester, NH 03103. Back


   References
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 Introduction
 Method
 Results
 Discussion
 Summary and Conclusions
 Appendix
 References
 

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