PHYS THER
Vol. 87, No. 12, December 2007, pp. 1684-1686
DOI: 10.2522/ptj.20050391.ar
Author Response
Hui-Ting Lin,
Ar-Tyan Hsu,
Guan-Liang Chang,
Jia-rea Chang Chien,
Kai-Nan An and
Fong Chin Su
We thank Ludewig for her insightful and constructive commentary on our research,1 and we appreciate the opportunity to respond. We are in full agreement with Ludewig's comment that any surface-based testing method is not immune from errors due to sensor and skin motion relative to the underlying bone, and our study was no exception. Such an issue was prominent in our minds during the planning phase of the experiment. Thus, constraints were made with a custom-made wooden frame and clamps applied to the scapula and the clavicle. Consequently, the maximal arm elevation angles for the subjects in our study were limited to an average of 68.3 degrees of arm abduction in the plane of scapula, well within the range reported by Karduna et al2 where the scapular motions recorded by surface sensors were almost the same as those recorded from sensors on bone pins surgically fixed on the scapula. Therefore, we felt that it was appropriate in the present study to represent scapular motion with a sensor on the flat surface of the acromion and use it to derive the center of the glenoid fossa.
The reliability coefficients (intraclass correlation coefficient [3,1], r), standard errors of measurement (SEMs), and standard deviations (SDs) of anteroposterior (A-P) and posteroanterior (P-A) translations of the head of humerus obtained in our study at various abduction angles are presented in Table 1. When rated with the modified criteria proposed by Portney and Watkins3 (poor [r<.50], moderate [.50<r<.75], good [.75>r>.90], and excellent [r>.90]), excellent reliability values were consistently achieved across all abduction positions. Only P-A translation at 20 degrees (r=.83) and its A-P counterpart at the end range (r=.86) of abduction yielded good reliability. The SEM of translation was derived as the product of the SD and the square root of inconsistency (1–r):
where r is the value of reliability. Both SEM and SD values did not show a definite relationship with the angle of abduction. We believe that, in the present study, the differential skin motion artifact across measurement positions tested most likely did not confound the differences in translation values reported in end-range abduction.
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Table 1. Standard Deviation (SD), Standard Error of Measurement (SEM), and Intraclass Correlation Coefficient (ICC[3,1]) Values for the Anterior-Posterior (A-P) and Posterior-Anterior (P-A) Translation of the Head of the Humerus
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As Ludewig has rightly pointed out, the number of subjects involved in the present study is certainly one of the limitations of the present study. However, the use of the average measurements to define the resting position was intended to demonstrate statistically that the resting position defined by the maximal translation and that defined by the maximal rotation were different (mean difference [±SD] was 25.3°±17.5°, and the 95% confidence intervals of the difference were 15.6° and 35.0°, respectively). For about 67% of the subjects, maximal translation occurred anywhere from 15 to 32 degrees and maximal rotation occurred from 34 to 66 degrees of glenohumeral abduction in the plane of the scapula. A box plot is presented in the Figure to demonstrate the distribution of positions where the greatest range of motion (ROM) occurred across individual subjects. More detailed descriptive statistics of the resting positions determined by the positions of maximal translation and maximal rotation ROMs are presented in Table 2.
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Table 2. Descriptive Statistics of the Resting Positions (in Degrees) Determined by the Positions of Maximal Translation and Maximal Rotational Ranges of Motion
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Hsu et al4 investigated the resting position of the glenohumeral joint in a cadaveric study. In the 7 specimens tested, the maximal total translation occurred at 38.53±3.41 degrees and the maximal total rotation occurred at 41.84±4.69 degrees of glenohumeral abduction. The resting position, determined as the midpoint of the shared range of the 95% confidence intervals of the predicted abduction position where the peaks of displacement and rotation occurred, was located at 39.33±4.37 degrees. In the present in vivo study, however, the maximal total translation occurred at 23.7±8.4 degrees, and the maximal rotational ROM occurred at 49.8±16.0 degrees. We felt that the difference in the angular positions between resting positions determined by different criteria was so great that we were obliged to test their difference statistically. Ludewig's comment regarding the choice of presenting the resting position as a range and not a single position is well taken. A more detailed reporting of the resting position data would have been necessary. The detailed relevant information is presented in Table 2 and in the Figure. We would not go so far, however, as to suggest a common range for the glenohumeral positions of maximal translation and rotation because, in every subject tested, the glenohumeral resting position determined by the position with the maximal total rotation range was always greater than the glenohumeral resting position determined by the position of the maximal total translation.
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Figure. Box plot of the resting positions across individual subjects determined by the positions of the maximal translation and the maximal rotation.
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Ludewig's comment on developing a composite multidirectional measure of translatory and rotational ROM to capture the intended definition of the "overall capsular laxity" in the definition of the resting position is both insightful and constructive. Future studies involving the collection of data from major accessory movements and rotational mobility measures to derive the proposed "overall resting position" of the glenohumeral joint with appropriate statistical techniques similar to those used by Hsu et al4 will be necessary to provide biomechanical bases for transforming clinical impressions of master clinicians into quantifiable measurements. In the clinics, the resting position is frequently assessed and used as the position for evaluating the joint play, for treating joint pain and inflammation, and for initiating treatment of joints with hypomobility. The resting position may change as a result of joint pathology, depending on the location and the extent of the capsuloligamentous structures involved. The direct evidence is still lacking, but in a prior study Hsu et al4 demonstrated a linear relationship between the angle of resting position and the available range of abduction in cadaver glenohumeral specimens. Specimens with smaller available abduction ROM had resting positions located at an abduction angle closer to the neutral position. Further studies in various patient populations are necessary to define their clinical presentations involving changes in the patterns of joint mobility and resting positions.
It would be difficult to replicate the present study in a clinical setting without sacrificing the well-controlled forces and torques and the rigid constraints to the scapulohumeral complex that we had enjoyed in the laboratory. However, therapists or operators could be trained to apply forces and torques during translational and rotational ROM assessments to obtain acceptable consistency and reliability.5 With refinement of the manual stabilization techniques, it would be possible to constrain the movements of scapula and clavicle to limit the arm elevation to well under 120 degrees.6 Thus, it may be possible to complete, within a reasonable length of the patient's time, the translational and ROM mobility assessments of the glenohumeral joint by using electromagnetic devices in the clinical setting to study populations with various shoulder pathologies. Such clinical studies are necessary to provide quantifiable measurements for the advancement of basic and clinical sciences in orthopedics.
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References
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- Lin HT, Hsu AT, Chang GL, et al. Determining resting position of the glenohumeral joint in subjects who are healthy.
Phys Ther.2007;87:1669–1682.[Abstract/Free Full Text]
- Karduna AR, McClure PW, Michener LA, Sennett B. Dynamic measurements of three-dimensional scapular kinematics: a validation study.
J Biomech Eng. 2001;123:184–190.[CrossRef][Web of Science][Medline]
- Portney LG, Watkins MP.
Foundations of Clinical Research: Applications to Practice. 2nd ed. Upper Saddle River, NJ: Prentice Hall Health; 2000.
- Hsu AT, Chang JH, Chang CH. Determining the resting position of the glenohumeral joint: a cadaver study.
J Orthop Sports Phys Ther. 2002;32:605–612.[Web of Science][Medline]
- Chang JY, Chang GL, Chang Chien CJ, et al. Effectiveness of two forms of feedback on training of a joint mobilization skill by using a joint translation simulator.
Phys Ther. 2007;87:418–430.[Abstract/Free Full Text]
- Boon AJ, Smith J. Manual scapular stabilization: its effect on shoulder rotational range of motion.
Arch Phys Med Rehabil. 2000;81:978–983.[CrossRef][Web of Science][Medline]
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Copyright © 2007 by the American Physical Therapy Association.
