Relationship Between Patient-Reported Assessment of Shoulder Function and Objective Range-of-Motion Measurements

Matsen, Frederick A. III MD; Tang, Anna BS; Russ, Stacy M. BA; Hsu, Jason E. MD

Journal of Bone & Joint Surgery - American Volume: 1 March 2017 - Volume 99 - Issue 5 - p 417–426
doi: 10.2106/JBJS.16.00556
Scientific Articles
Disclosures
Commentary

Background: Assessment of function is the cornerstone of clinical shoulder research. This purpose of this study was to answer 3 relevant questions: How does subjective patient assessment of shoulder function correlate with objectively measured active shoulder range of motion? What is the difference in active motion between shoulders that can and those that cannot be used to perform each of the functions of the Simple Shoulder Test (SST)? Does the relationship between subjective and objective assessment of shoulder function differ between male and female patients?

Methods: We analyzed the relationship between objective range-of-motion measurements recorded by the observer-independent Kinect motion capture system and SST patient self-assessments of shoulder function of 74 male and 30 female patients with osteoarthritis.

Results: There was poor correlation between objective measurements of active abduction and total SST scores of osteoarthritic shoulders of patients seen before shoulder surgery: the coefficients of determination (R2) were 0.29 for the osteoarthritic shoulders of women and 0.25 for those of men. The relationships between active abduction and total SST score were closer for the contralateral shoulders (R2 = 0.54 for women and R2 = 0.46 for men). The difference in active abduction between the osteoarthritic shoulders that allowed and those that did not allow the patient to perform the individual SST functions was significant (p < 0.05) for only 4 of the 12 functions in the female group and 5 of 12 in the male group because of the highly variable relationship between self-assessed function and active abduction. In contrast, when the contralateral shoulders were assessed, this difference was found to be significant for 10 of the 12 functions in the female group and all 12 of the functions in the male group. The relationship between objective motion and subjective function did not differ significantly between male and female subjects.

Conclusions: The self-assessed function of osteoarthritic shoulders of women and men is only partially determined by the active range of abduction. Both subjective and objective measurements are important in characterizing the clinical status of shoulders. Studies of treatment outcomes should include separate assessments of these 2 complementary aspects of shoulder function.

Level of Evidence: Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

1Department of Orthopaedics and Sports Medicine, University of Washington Medical Center, Seattle, Washington

E-mail address for F.A. Matsen III: matsen@uw.edu

E-mail address for A. Tang: annat9@uw.edu

E-mail address for S.M. Russ: stacyr5@uw.edu

E-mail address for J.E. Hsu: jehsu@uw.edu

Article Outline

In order to determine what treatment works best for which patients, individual practitioners and clinical investigators need to understand the tools used for assessing the functional status of shoulders before and after treatment. Some assessment approaches are “subjective” because they rely on the patient’s evaluation of his or her shoulder function1-6. Others are “objective” in that surgeons or their designees make measurements of passive motion, active motion, stability, or strength7,8. However, these objective measurements are difficult to standardize and are subject to intraobserver and interobserver variability9-20. Some instruments, such as the commonly used Constant score, include both subjective and objective assessments with weights arbitrarily assigned to each21-23, leading authors to conclude that the high percentage of objective data in the Constant-Murley scale introduces interobserver variability in this metric6,23,24. A few tools have been used to perform objective measurements that are essentially independent of the observer; however, many of these are impractical for routine clinical use because of their size, complexity, hardware requirements, and expense14,23,25-29. A recent article demonstrated that an inexpensive operator-independent objective shoulder motion measurement system based on the Microsoft Kinect can serve as a practical tool in the clinical examination room26. Several other authors have used Kinect for the measurement of shoulder motion30-35. The accuracy of Kinect, which does not require the attachment of markers to determine limb position, has been validated in comparison with marker-based systems36-41.

The present study was undertaken to explore the relationship between subjective and observer-independent objective measures of shoulder function. We specifically sought to answer 3 questions: How does subjective patient assessment of shoulder function correlate with objectively measured active shoulder range of motion? What is the difference in active motion between shoulders that can and those that cannot be used to perform each of the functions of the Simple Shoulder Test (SST)? Does the relationship between subjective and objective assessment of shoulder function differ between male and female patients?

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Materials and Methods

Between July 28, 2014, and March 16, 2016, we enrolled 74 male and 30 female patients with glenohumeral osteoarthritis prior to elective shoulder arthroplasty in a prospective study approved by our institutional Human Subjects Review Committee (Institutional Review Board Approval #38897). The average age (and standard deviation) was 67 ± 9 years (range, 46 to 85 years) for the female patients and 63 ± 9 years (range, 38 to 89 years) for the male patients. The patients completed the SST self-assessment of their ability to perform 12 individual shoulder functions (Table I) using the osteoarthritic shoulder and using the contralateral shoulder. The SST was selected because of its excellent psychometric properties, brevity, low cost, international usage, responsiveness, and high degree of correlation with lengthier and more complex instruments6,14,23,42-47. At the same clinic visit, the active range of abduction of each shoulder was measured using a Kinect sensor (Microsoft)26. An assistant who was not otherwise involved in patient care operated the Kinect, capturing the active range of abduction of each shoulder by pressing a key on a laptop while the patient actively positioned the arm in maximal elevation in the plane of the body (Fig. 1). There was no physical contact between the operator and the patient. The Kinect system recorded the range of active abduction of each shoulder directly without any need for post-capture processing. Complete SST and Kinect data were collected for both the osteoarthritic shoulder and the contralateral shoulder.

The ranges of active abduction of the osteoarthritic and contralateral shoulders of the female and male patients were plotted against the overall SST score; the Pearson correlation coefficients (R) and coefficient of determination (R2) were calculated. For each of the 2 sexes, the data were then analyzed for significant differences in range of motion between shoulders that could and could not be used to perform each of the individual SST functions. Significance was set at p < 0.05.

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Results

Correlation of Subjective Patient Assessment of Shoulder Function with Objectively Measured Active Range of Motion

There was poor correlation between the total number of SST functions that could be performed using the osteoarthritic shoulder and the active range of abduction in both the female and male groups: the coefficients of determination (the square of the Pearson correlation coefficient, or R2) were 0.29 for female patients and 0.25 for male patients (Figs. 2-A and 2-B). There was better correlation between the total number of SST functions that could be performed using the contralateral shoulder and the active range of abduction of the contralateral shoulder in the female and male groups: the coefficients of determination (R2) were 0.54 for female patients and 0.46 for male patients (Figs. 2-A and 2-B). These coefficients of determination can be interpreted as indicating the fraction of the variation in patient-assessed shoulder function that can be attributed to the measured active abduction. It is of note that even though there was some correlation between objective active abduction and subjective shoulder function, many of the shoulders had good motion and poor self-assessed function while others had poor motion and good self-assessed function (Figs. 2-A, 2-B, and 2-C).

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Difference in Active Motion Between Shoulders That Did and Did Not Allow Performance of Each of the SST Functions

The percentage of women who could perform the different functions of the SST using the osteoarthritic shoulder ranged from 0% for one of the more demanding functions (Question 10: Do you think you can throw a softball overhand 20 yards with the affected extremity?) to 40% for one of the less demanding functions (Question 1: Is your shoulder comfortable with your arm at rest by your side?) (Table II). Similarly, the percentage of men who could perform the different functions of the SST using the osteoarthritic shoulder ranged from 8% for SST Question 10 to 78% for Question 8 (Can you carry 20 pounds at your side with the affected extremity?) (Table III).

The differences in active abduction between the osteoarthritic shoulders that did and those that did not allow performance of the individual SST functions were significant (p < 0.05) for 4 of the 12 functions assessed by the women and 5 of the 12 assessed by the men because of the highly variable relationship between self-assessed function and objective active abduction. In contrast, analysis of the contralateral shoulders showed this difference to be significant for 10 of the 12 functions in the female group and all 12 of the functions in the male group (Tables II and III), a result consistent with the less variable relationship between self-assessed function and objective active abduction of the contralateral shoulders.

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Relationship Between Subjective and Objective Assessments of Shoulder Function in Male and Female Groups

While the level of self-assessed function of the osteoarthritic shoulder tended to be lower for women than men (Tables II and III, Figs. 3-A and 3-B), the high degree of variability in the ranges of active motion of the osteoarthritic and contralateral shoulders that did and did not allow performance of the SST functions resulted in no significant difference between the sexes with respect to the active ranges of abduction associated with the different shoulder functions. When the self-assessed function of the osteoarthritic and contralateral shoulders was plotted together against active abduction for female and male patients, the relationships were similar for the two sexes (Fig. 2-C).

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Discussion

Correlation of Subjective Patient Assessment of Shoulder Function with Objectively Measured Active Range of Motion

The assessment of shoulder function is the cornerstone of clinical research regarding the natural history and treatment outcomes for shoulder disorders. Current approaches to this assessment include patient-reported measures, which are often referred to as “subjective,” and provider-reported measures, which are often referred to as “objective.” Relatively little is known about the relationship between these 2 types of measures in patients with shoulder arthritis. Such an analysis is complicated by the observation that provider-reported measures are subject to intraobserver and interobserver variability6,9-20,23,24,48. The importance of this study lies in its analysis of the relationship between subjective patient-reported assessment of shoulder function and observer-independent objective measurement of active shoulder motion in patients with glenohumeral arthritis presenting for consideration of shoulder arthroplasty. The results indicate a highly variable relationship between the patients’ reported ability to perform the functions of the SST and the range of active abduction measured by the Kinect motion sensor system, particularly for osteoarthritic shoulders.

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Difference in Active Motion Between Shoulders That Did and Did Not Allow Performance of Each of the SST Functions

Whereas there were some differences in active abduction between the shoulders that did and did not allow performance of the different SST functions, these differences were less apparent for the osteoarthritic shoulders than for the contralateral shoulders; this suggests that factors other than the active range of motion had a substantial effect on the patients’ self-assessed ability to perform each function.

Some authors have suggested threshold values for the range of motion of the shoulder required to perform specific daily activities; for example, one study of 40 normal shoulders of 20 volunteers showed that 128° ± 8° of abduction was required to perform 10 functional tasks; the small standard deviation is noteworthy27. However, our study of patients with shoulder arthritis indicates that the range of active motion associated with different shoulder functions varied widely from patient to patient, with standard deviations in the range of 30° to 40°. A set threshold of 128° of abduction would not have been useful in predicting which shoulders would or would not allow the patient to perform each of the 12 SST functions.

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Relationship Between Subjective and Objective Assessments of Shoulder Function in Male and Female Groups

While the osteoarthritic shoulders of the women were less functional overall than those of the men, the high degree of interpatient variability led to a lack of significant differences between the sexes in terms of the active ranges of abduction associated with the different shoulder functions.

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Study Limitations

The results of this study need to be viewed in light of certain limitations. First, we considered only the relationship between active abduction assessed by the Kinect and patient self-assessed shoulder function documented with the SST; analysis of other measures of motion and other methods of functional assessment might have led to different results. Second, we only studied patients with osteoarthritis who presented to a single expert surgeon for shoulder arthroplasty; different findings might have been obtained with different patient populations with different pathological conditions seen in different practices. Third, we selected active abduction as the motion with which patient self-assessed function was compared; it is possible that other active motions would have had a different relationship with self-assessed shoulder function. Fourth, we compared the shoulder that was to undergo surgery for osteoarthritis with the contralateral shoulder; we did not assess the type or degree of pathological involvement or its effect on the contralateral shoulder. Fifth, we did not attempt to assess other factors that might have affected patient self-assessed function, such as pain, motivation, strength, relationship of the shoulder condition to the patient’s work, or radiographic findings. Finally, most “objective” measurements of range of motion are made using some form of handheld goniometer, and the problem of intraobserver and interobserver variability in such “objective” measurements remains unresolved9-20.

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Conclusion

We found highly variable relationships between subjective patient-assessed shoulder function and objectively measured active range of motion, particularly for the osteoarthritic shoulders. These relationships did not differ significantly between the shoulders of men and women. Both subjective and objective measurements are important in characterizing the clinical status of shoulders. Studies of natural history and treatment outcomes should include separate assessments of these 2 complementary aspects of shoulder function.

Investigation performed at the University of Washington, Seattle, Washington

A commentary by Jeffrey S. Abrams, MD, is linked to the online version of this article at jbjs.org.

Disclosure: There was no extramural funding for this investigation. On the Disclosure of Potential Conflicts of Interest forms, which are provided with the online version of the article, one or more of the authors checked “yes” to indicate that the author had a relevant financial relationship in the biomedical arena outside the submitted work (http://links.lww.com/JBJS/A29).

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