HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Abstract Full Text (PDF) All Versions of this Article: ptj.20050391v1 87/12/1669    most recent Submit a response Alert me when this article is cited Alert me when Rapid Responses are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lin, H.-T. Articles by Su, F. C. Search for Related Content PubMed PubMed Citation Articles by Lin, H.-T. Articles by Su, F. C. Related Collections Kinesiology/Biomechanics Social Bookmarking                      What's this?

Determining the Resting Position of the Glenohumeral Joint in Subjects Who Are Healthy

HT Lin, PT, PhD, is Assistant Professor, Department of Physical Therapy, I-Shou University, Kaohsiung County, Taiwan
AT Hsu, PT, PhD, is Professor, Department of Physical Therapy, College of Medicine, and Professor and Chair, Institute of Allied Health Sciences, National Cheng Kung University, 1 Ta-Hsueh Rd, Tainan 701, Taiwan
GL Chang, PhD, is Professor, Institute of Biomedical Engineering, College of Engineering, National Cheng Kung University
J Chang Chien, PhD, is Assistant Professor, Department of Electronic Engineering, National Kaohsiung First University of Science and Technology, Kaohsiung, Taiwan
KN An, PhD, is Professor, Biomechanics Laboratory, Division of Orthopedic Research, College of Medicine, Mayo Clinic, Rochester, Minn
FC Su, PhD, is Professor, Institute of Biomedical Engineering, College of Engineering, National Cheng Kung University

Address all correspondence to Dr Hsu at: arthsu{at}mail.ncku.edu.tw

Submitted December 16, 2005; Accepted July 27, 2007

	Abstract

 
Background and Purpose: The resting position is frequently used by clinicians in the examination and early treatment of patients with joint impairments. However, there is a lack of research on the kinematic characteristics of the resting position of the glenohumeral (GH) joint. The aim of this study was to define the resting position of the GH joint by quantifying the humeral head translation and axial rotational range of motion (ROM).

Subjects and Methods: The anterior and posterior translation of the humeral head and the rotational ROM of the dominant arm were assessed in the seated position at multiple abduction positions in 15 subjects who were healthy by use of an electromagnetic tracking device. A force of 80 N and a torque of 4 N·m were applied during the measurement procedures for the translation of the humeral head and the rotational ROM, respectively.

Results: The mean resting position determined by rotational movement was located at 49.8 degrees of GH abduction. However, the mean resting position determined by translational movement was located at 23.7 degrees of GH abduction and was significantly lower than the resting position determined by rotational movement (t=5.45, P=.000).

Discussion and Conclusion: The mean resting position for rotational movement is consistent with the already accepted range of 30 to 60 degrees for a "loosely packed" position of the GH joint. The mean resting position for translational movement appears to be lower than 30 to 60 degrees. The results of this study suggest that, at least for the GH joint, different resting positions should be assessed with different movement criteria (accessory or physiological movement).

	Introduction

Top Abstract Introduction Method Results Discussion Conclusion References

 
The resting position is the position of a joint in which the joint tissues are under the least amount of stress and in which the joint capsule has its greatest laxity.^1–4 It is also called the "maximal loosely packed position" or "loosely packed position" as opposed to the "closely packed position."^4,5 The resting position also is regarded as the position of minimal congruence between joint surfaces allowing the greatest passive separation between articular surfaces.^3–5 Clinically, the resting position of a joint is usually considered to be a single position and to be located in the middle of its full range of motion (ROM). For the in vivo glenohumeral (GH) joint, the resting position is generally considered to be located at a position in neutral rotation between 55 and 70 degrees of shoulder abduction with respect to the trunk in the plane of the scapula (commonly defined as the plane 30° anterior to the frontal plane).^2,4,5 Because the resting position allows joint surface movements such as glide, roll, and spin to occur easily, it is frequently chosen as one of the positions for the initial evaluation and early treatment of a painful and inflammatory joint or a joint with hypomobility or hypermobility.^2,4,5 Despite frequent use in clinics, there is no specific rationale for the methods currently used for determining the resting position of the GH joint. These methods were based not on experimental studies but on clinical experience and anecdotal information.

The resting position is generally considered to be the position of maximal mobility. Because the evaluation of GH joint mobility usually includes both accessory (humeral head translation) and physiological (ROM) joint mobility,^6,7 many translational or laxity tests and angular mobility tests are potentially useful clinically for the determination of the resting position. For the GH joint, the most common mobility or laxity tests used in the clinical setting are related to the assessment of anterior, posterior, or inferior instability and the ROM for internal rotation (IR) or external rotation (ER).^8–11 Therefore, the translational and rotational laxity of the GH joint may be useful for determining the resting position in vivo.

Noninvasive quantitative measurements of GH joint laxity in vivo are still difficult because of the complex movement of the shoulder and the difficulty of fixation of the scapula. Several studies^9,12–14 have attempted to quantify passive GH joint movements, including translational and rotational laxity. Translation can be defined as the amount of linear movement between the humeral head and the glenoid fossa when stress is applied by the examiner, whereas rotational laxity refers to humeral rotational ROM relative to the scapula at the applied rotational torque.

Tibone et al¹² measured shoulder translation by holding one electromagnetic tracking sensor beneath the thumb directly on the anterior aspect of the proximal shoulder and applying manual forces to the humerus in the anterior-posterior (A-P) direction. The direction of humeral head translation and the force applied by the examiner were not reported. Borsa and colleagues^15,16 measured A-P and posterior-anterior (P-A) GH joint laxity in subjects who were healthy by using a shoulder arthrometer. A mechanical restraining system stabilized the trunk and scapula to prevent scapular retraction or protraction. Two linear displacement transducers were affixed to the skin surface of the acromion and the lateral portion of the humeral head to measure the translation of the humeral head resulting from an applied force of up to 134 N. However, the position of the humeral cuff wrapped around the proximal humerus and the direct use of linear displacement transducers on the skin to measure GH laxity may have affected the accuracy of humeral head translation.

In a study by McQuade and Murthi,¹⁴ the internal humeral head center was determined for translation tracking, and the true scapular reference frame was used to define GH head translation relative to scapular orientation. The scapular sensor compressed by body weight was assumed to have been placed stably. For rotational laxity, Novotny et al⁹ quantified the IR and ER ROM values at an applied torque of 4 N·m in subjects who were healthy. The scapula and clavicle of the subjects were immobilized with a clamp, and the defined IR-ER ROM of the GH joint was 139.4 degrees at 45 degrees of abduction in the plane of the scapula.

Few studies have quantitatively investigated the resting position.^1,13,17 Helmig et al¹⁸ reported that maximal inferior excursion of a GH joint specimen during an inferior humeral head translation test occurred at 20 degrees of abduction. Debski et al¹⁷ proposed that there was less translation of the humeral head in both the anterior and the posterior directions at the extreme range of abduction (0° and 90°) than in the midrange (30° and 60°) in the scapular plane under a maximum load of 89 N. They reported that the resting position of the in vitro GH joint was located between 30 and 60 degrees of abduction in the plane of the scapula (the plane 30° anterior to the frontal plane). However, no detailed data for anterior or posterior translation between 30 and 60 degrees of abduction were reported, nor was the rotational laxity of the GH joint reported.

Hsu et al¹ defined the resting position of the GH joint by using an in vitro model. A materials testing system was used to simulate translational and rotational movements performed by physical therapists. The use of the materials testing system and a GH joint specimen allowed rigid fixation of the scapula and precise control of repeated movements during the translational and rotational movement testing. According to the data reported by Hsu et al, the resting position was located at an average of 39 degrees of GH abduction in the plane of the scapula (45% of the maximal GH abduction ROM). However, there was no active muscle tension, and the core temperatures in their cadaver specimens were inconsistent. Moreover, the material properties of living tissue may differ from those of cadaver tissue.

To our knowledge, no previous study has determined the resting position of the GH joint in vivo. Such information is necessary to clarify whether the resting position of the GH joint is the same in vivo as it is in cadaver specimens. In addition, recent advances in 3-dimensional (3-D) motion analysis techniques have improved the precision and accuracy of estimates of the center of rotation (COR) during GH joint motion.^9,13,19 The use of a computed internal humeral head center for translation tracking and a true scapular reference frame to define GH translation and GH joint rotational movement relative to scapular orientation enables GH movement to be measured with reasonable accuracy and reliability. Therefore, the purpose of this study was to define the resting position of the GH joint in subjects who are healthy by investigating the magnitude of anterior and posterior translation of the head of the humerus and the rotational ROM of the humerus at different GH abduction angles. The clinical relevance of this study was to provide physical therapy clinicians with important quantitative information regarding the resting position of the GH joint as well as the translational and rotational mobility of this joint at different abduction positions. Such information is important during the evaluation and treatment of patients with GH joint problems.

	Method

Top Abstract Introduction Method Results Discussion Conclusion References

 
Subjects

Fifteen volunteers with no shoulder symptoms were recruited. Subjects with histories of shoulder impairment as a result of any orthopedic or neurological disorder or any surgery associated with the shoulder girdle were excluded from the study. All subjects read and signed informed consent forms before participating in this study.

Basic information on the subjects, such as sex, age, and health status, was recorded. Because the ranges of translational and rotational movements of the humeral head are known to be different between the dominant shoulder and the nondominant shoulder, we tested only the shoulder on the dominant side. The shoulder ipsilateral to the dominant hand (the writing hand) of each subject was tested. The maximal values for active range of motion (AROM) and passive range of motion (PROM) for the shoulder were assessed with a goniometer, and joint play was assessed with a 7-point scale proposed by Kaltenborn²⁰ to rule out subjects with inadequate or excessive mobility of the shoulder. For these procedures, participants were tested in the supine position on the examination table. Throughout the duration of testing for GH joint rotational ROM, the arm of each subject was placed at 90 degrees of GH abduction. Scapular stabilization was provided by the examiner applying a posteriorly directed force against the subject's coracoid process and clavicle with the hand. From the anatomical zero rotation in 90 degrees of abduction, the rotational AROM and PROM values of each subject were determined until the subjects achieved a stable end-point position. The IR and ER angles then were recorded from the goniometer. Demographic data for the subjects are shown in Table 1.

A force sensor (MLP-50) and a torque transducer (SWS-100) were used to detect the force and the torque applied by the examiner to ensure good repeatability and reliability. Signals from the force sensor and torque transducer were sampled at 20 Hz. A custom-made remote control device was used to synchronize the acquisition of kinematic data from the FASTRAK system and data from the force sensor and torque transducer.

Experimental Procedure

Digitization.
Prior to testing, the FASTRAK system, the force sensor, and the torque transducer were calibrated. Each subject was seated on a specially designed, sturdy chair with clamps grasping the spine of the scapula superiorly and posteriorly and the clavicle anteriorly. The lateral borders of the scapula were blocked with another clamp. The subject was instructed to sit relaxed while the trunk was stabilized with pelvis and chest belts. An adjustable elbow brace was applied to the elbow to immobilize the elbow joint at 90 degrees of flexion. Three sensors were attached to the sternal notch, the flat surface of the acromion, and a thermoplastic cuff secured to the distal humerus with straps. While subjects sat with their dominant arms hanging relaxed at the sides with the forearm pointing forward and the elbow braced at 90 degrees of flexion (neutral position), 9 bony landmarks (Fig. 1) were palpated and digitized. With these digitized points and the estimated GH joint COR (center of glenoid [CG]/center of humeral head [CH]; described in the next paragraph), the local coordinate systems of the trunk, humerus, and scapula were determined according to the suggestions of the International Shoulder Group²² (Fig. 1).

View larger version (14K): [in this window] [in a new window]   Figure 1. Bony landmarks used to define the local coordinate systems of the thorax, humerus, and scapula according to the suggestions of the International Shoulder Group. AA=acromial angle, AB/AD=abduction/adduction, C7=spinous process of the seventh cervical vertebra, EL=lateral epicondyle, EM=medial epicondyle, Flex/Ext=flexion/extension, GH=glenohumeral rotation center, IA=inferior angle of the scapula, IR/ER=internal rotation/external rotation, MR/LR=medial rotation/lateral rotation, PT/AT=posterior tipping/anterior tipping, PX=xiphoid process, RS=root of the spine of the scapula, SN=suprasternal notch, T8=spinous process of the eighth thoracic vertebra, UR/DR=upward rotation/downward rotation. Xh, Xs, Xt, Yh, Ys, Yt, Zh, Zs, and Zt indicate the humerus (h), scapula (s), and thorax (t) coordinate system in the X, Y, and Z axes, respectively.

The method developed by Gamage and Lasenby²³ was used to calculate the in vivo CH in this study. The basic assumption of this least-squares method is that the electromagnetic sensors on the humerus remained at a constant distance from the COR. The sensor coordinates were recorded during passive small-arc arm movements of the segment to locate the mean COR of the GH joint. During small-arc movements of the GH joint, the glenoid fossa is in full contact with the head of the humerus. Therefore, the electromagnetic sensors on the humerus segment defined part of a sphere and remained at a constant distance from the COR of the GH joint, where the CH and the CG coincide. To evaluate the suitability of this least-squares method for estimating the COR of the GH joint, we collected electromagnetic sensor positions within the PROM of 45 degrees of shoulder abduction/adduction, flexion/extension, and circumduction before the experiment. The standard deviations from the defined joint center were 2.41, 0.61, and 1.16 mm in the x, y, and z axes, respectively. These low standard deviations demonstrated that estimating the GH center by use of the method developed by Gamage and Lasenby²³ should be repeatable.

Computation of translation of the humeral head.
For measuring the translation of the humeral head, we applied A-P and P-A force to the humeral head of each subject at positions from 0 degrees to the end position of GH abduction in 10-degree increments in neutral rotation in the plane of the scapula. An 80-N A-P or P-A force monitored by a force sensor was applied during A-P glide and P-A glide, and the electromagnetic sensors were tracked to assess the mobility of the GH joint at the 10-degree increments of GH abduction (Figs. 2A and 2B). A height-adjustable arm support was designed to prop up the arm during humeral head translation testing. With the scapula stabilized, we adjusted the height of the support at increments of 10 degrees of GH abduction. The magnitude of force (80 N) used in this study was similar to that used by Sauers et al,⁸ Debski et al,¹⁷ and Warner et al²⁴ (89 N) to simulate the amount of force required to reach the clinical end point of the GH joint. This loading was reported to allow steady load-displacement performance of the GH joint after conditioning with a low chance of damage to the capsular ligament and surrounding tissues.^8,17,25,26

View larger version (86K): [in this window] [in a new window]   Figure 2. (A) A posterior-anterior force of 80 N was applied to the head of the humerus. (B) A force sensor was used to monitor the force applied. (C and D) A torque transducer was used during rotational range-of-motion testing to ensure the application of a consistent torque of 4 N·m for the internal rotation (C) and external rotation (D) procedures.

View larger version (14K): [in this window] [in a new window]   Figure 3. (A) Centers of rotation of the glenoid (CG) and the humeral head (CH) in a cocentered condition, which is assumed during small-arc movements. The coordinate relationships between this cocenter and the acromial sensor (and, thus, the scapular local coordinate system) and between this cocenter and the distal humeral sensor (and, thus, the humeral local coordinate system) can be established. (B) When the humeral head is displaced from the cocentered condition, the coordinates for CH and CG can be derived if the orientations and coordinates of the acromial and distal humeral sensors are known.

Calculation of rotation of the humerus.
After the humeral head translation procedures, medial and lateral rotational ROM testing was executed, and ROM was measured. Manual support was used to hold the distal arm of each subject instead of height-adjusted arm support for the sake of smoothness of the movement. A torque transducer was used during rotational ROM testing to ensure a consistent torque of 4 N·m for IR and ER (Figs. 2C and 2D). A torque of 4 N·m has been shown to have reasonable reliability and a stable torque-angle curve.⁹ The change in the orientation of the humerus relative to the scapula was described as the Euler angle, which is a sequence of 3 angles of rotation against the initial position.²⁸ After experimenting with different rotation sequences, we adopted the y-x'-z" rotation sequence (representing transverse-, sagittal-, and frontal-plane movements, respectively) to describe the 3 rotation angles of the GH joint. The same rotation sequence (y-x'-z") was used to derive the 3-D scapular movements of winging, tipping, and upward/downward rotation, respectively (Fig. 1). Coordinates and orientations of sensors were tracked at every 10-degree increment in the plane of the scapula from the neutral position to the end position of GH abduction in neutral rotation during rotational ROM testing. Three tests of translation of the humeral head and rotational ROM were recorded at each angle of GH abduction in the scapular plane.

Data Analysis

All 3 replications of the translational and rotational measurements were used for data analysis. The intraclass correlation coefficient (ICC[3,1]) was used to test the intrasession reliability of the respective translation of the humeral head and rotational ROM. To determine the resting position, we modified the method used by Hsu et al.¹ All 3 trials of total translational and rotational ROM data were used to define the resting position for each subject. Curvilinear regression analyses were performed to derive the relationship between abduction angles and total translational as well as total rotational ROM data. Interpolation was performed to calculate translation (A-P, P-A) and rotation (IR, ER) at exactly 0, 10, 20, 30, 40, 50, and 60 degrees and the end position of GH abduction. The abduction angle at which total translation was maximal was determined. The same procedure was used to find the abduction angle for maximal total rotational ROM. The resting positions for translation and rotational ROM were determined from the location (abduction angle) at which maximal total translation occurred and the position at which maximal total rotation occurred, respectively. A Student paired t test was used to inspect the differences between angles of abduction for maximal total translation and those for maximal total rotation.

A 3-way analysis of variance (ANOVA) was used to assess the effects of sex, the effects of abduction angles (8 positions), and the effects of the direction of translation (A-P, P-A) and the direction of rotational ROM (IR, ER) on the translation of the head of the humerus and rotational ROM, respectively. To assess the effects of sex and abduction angles on total translation and total rotational ROM, a separate 2-way ANOVA was used. All P values of less than .05 were considered significant.

The electromagnetic sensor attached to the flat surface of the acromion was used to track scapular motion and monitor the status of immobilization of the scapula. We investigated the effectiveness of the scapular immobilization frame by computing the variability of the scapula-trunk angular relationship during translational and rotational testing at different GH abduction positions. The mean values of the scapula-trunk angles for 3 replications were used in the analysis. A 2-way repeated-measures ANOVA was used to evaluate the effects of GH abduction position (8 positions) and direction of translation (2 directions: anterior and posterior) on scapula-trunk angles for the translational procedure. The Friedman test was used to evaluate the effects of GH abduction position on scapula-trunk angles for the rotational procedure.

	Results

Top Abstract Introduction Method Results Discussion Conclusion References

 
The intrarater reliability (ICC[3,1]) values for measurements of humeral head translation (in millimeters) during A-P glide and P-A glide procedures and ROM (in degrees) during IR and ER procedures were .86 to .975, .83 to .977, .98 to .99, and .97 to .99, respectively (Tab. 2). With the scapula restrained by the immobilization frame, the mean maximal excursion for GH abduction was 68.3 degrees (SD=5.9°). Because all subjects were able to achieve at least 60 degrees of GH abduction in neutral rotation, we chose to present data from 0 to 60 degrees of abduction and the end position for the sake of simplicity in reporting. The mean values for humeral head translation at 0 degrees (neutral position), at 10, 20, 30, 40, 50, and 60 degrees, and at the end position of GH abduction are shown in Table 3 and Figure 4. The mean values for rotational ROM at 0 degrees (neutral position), at 10, 20, 30, 40, 50, and 60 degrees, and at the end position of GH abduction are shown in Table 4 and Figure 5. The maximal total translation (mean±SD) occurred at 23.7±8.4 degrees (33.8%±11.2% of the GH maximal abduction ROM), and the maximal rotational ROM occurred at 49.8±16.0 degrees (70.0%±25.3% of the maximal abduction ROM). There was a significant difference between the position in abduction at which the maximal total translation occurred and the position at which the maximal total rotational ROM took place (t=5.45, P=.000).

View larger version (22K): [in this window] [in a new window]   Figure 4. Average values for anterior-posterior (A-P) and posterior-anterior (P-A) translation. (A) Significant differences in A-P translation. (B) Significant differences in P-A translation. (C) Significant differences in total translation. Significant results of the post hoc multiple comparisons are presented as horizontal bars indicating significant differences between the values represented by filled circles () and those represented by open circles (). For example, during P-A glide, the anterior translation of the humeral head at the end position of glenohumeral abduction () was significantly smaller than the anterior translation at 10, 20, 30, and 40 degrees of glenohumeral abduction ().

View larger version (25K): [in this window] [in a new window]   Figure 5. Average values for external rotation (ER) and internal rotation (IR) range of motion (ROM). (A) Significant differences in IR. (B) Significant differences in ER. (C) Significant differences in total rotational ROM. The horizontal bars indicate significant results of multiple comparisons between the values represented by filled circles () and those represented by open circles (). For example, the ER ROM at 60 degrees of glenohumeral (GH) abduction () was significantly greater than the ER ROM at 0 and 10 degrees of GH abduction ().

For rotational ROM, a significant interaction of sex and direction (IR and ER) was found. In comparison with their male counterparts, women had greater IR ROM values at 40, 50, and 60 degrees and at the end position of abduction as well as greater total rotation values at 30, 40, 50, and 60 degrees and at the end position of abduction (Tab. 4). For total rotational ROM (the sum of IR and ER), however, there was no interaction between abduction position and sex. Significant main effects of abduction position (F=13.65; df=7,91; P=.003) and of sex (F=6.85; df=1,13; P=.021) on the magnitude of total rotational ROM were found. The total rotational ROM value at the neutral position was significantly different from those at 10, 20, 30, and 40 degrees of GH abduction (P values ranged from .004 to .001). The total rotational ROM values at 20, 30, and 40 degrees were greater than that at 10 degrees of abduction (P<.005). The total rotational ROM value at 30 degrees of abduction was greater than that at 20 degrees of abduction (P<.005) (Fig. 5).

Even with the application of the scapular immobilization device, the abduction angle had a significant main effect on the scapular upward rotation angle during A-P glide (F=23.48; df=7,98; P=.000), P-A glide (F=35.17; df=7,98; P=.000), and rotation (F=48.05; df=7,98; P=.000) tests, respectively. The magnitude of scapular upward rotation at 0 degrees (neutral position) was significantly different from those at 30 degrees to the end position of abduction for the A-P glide test, from those at 40 degrees to the end position for the P-A glide test, and from those at 20 degrees to the end position for the rotation test (Tab. 5). Nevertheless, there was a main effect of direction on scapular winging and tipping but no effect of direction on scapular upward-downward movement. Greater lateral rotation of the scapula and larger posterior tipping angles were found in the P-A direction than in the A-P direction.

	Discussion

Top Abstract Introduction Method Results Discussion Conclusion References

The findings of the present study indicated that the peak magnitudes of anterior and posterior translation and rotational ROM occurred at 24 and 50 degrees of GH abduction, respectively. As the angular difference between the locations of maximal translational and rotational mobility was quite large, the resting positions were determined separately at the locations at which translation and rotational ROM were maximal. The resting position for rotational ROM in young subjects who are healthy appears to be consistent with the findings of Hurschler et al,²⁹ who reported that rotational ROM values were larger at the midrange (30° and 60° of GH abduction) than at the end positions (0° and 90° of abduction) because of variations in joint laxity and tissue extensibility at different joint positions. The resting position for translation, however, was located at 23.7 degrees of GH abduction in the plane of the scapula; this location is lower than the midrange of 30 to 60 degrees within which greater translational mobility was reported by Debski et al¹⁷ and Hurschler et al.²⁹

In the present study, the resting position was determined on the basis of quantifiable measurements of translational and rotational laxity. However, the position at which maximal translational laxity occurred (23.7° of GH abduction) did not coincide with the location of maximal rotational ROM laxity (49.8° of GH abduction). These findings appear to suggest different resting positions for different accessory and physiological movements of the GH joint.

An explanation for such discrepancies in the locations of maximal translational and rotational mobility is that the resting positions might have been movement dependent, that is, 2 different resting positions for translational and rotational movements. Although relatively small differences in flexion and abduction ROM values have been reported for sitting and supine positions, differences in rotational ROM values have not been reported.³⁰ However, the posture of subjects during measurements (sitting) might be an important factor influencing the magnitude of translational mobility because unintentional contractions of the antigravity muscles in abducted positions might result in maximal translational laxity (the resting position) at smaller angles of GH abduction. Such a situation might have occurred in our study.

Further studies should record the electromyographic activity of the involved muscle and address whether sitting and supine positions affect muscle tone and the measurement of GH laxity. Another potential explanation for differences in rotational mobility is humeral retroversion, which might result in discrepancies in the magnitudes of rotational mobility.^31–33 This adaptation of the bony architecture of the GH joint enables ER of the shoulder joint to a greater extent and less IR before constraints are imposed by soft tissue.

Finding the resting position is important to clinicians who want to evaluate the GH joint in a resting position. Maximal A-P and P-A translational mobility in a seated position occurs at approximately 24 degrees of GH abduction. With the scapula and clavicle securely fixed, this position is located at approximately 33% of the total available abduction ROM, which corresponds to about 40 degrees of abduction in a normal GH joint, with the assumption of a 120-degree GH abduction range. Glenohumeral rotation excursions were greatest at approximately 50 degrees of GH abduction (70% of the available ROM or 84° of abduction in a normal GH joint). For other accessory or physiological movements in different directions, such as distraction, inferior glide, and lateral glide, the resting positions may be different from those found in the present study (ie, A-P and P-A translation and rotation). The results of the present study suggest the possibility that, at least for the GH joint, there exists not one but more than one resting position. Therefore, different resting positions may need to be determined for a particular joint, depending on the criterion accessory or physiological movements used for assessment or treatment.

Existing literature did not provide a unified conclusion on the issue of the effect of sex on GH joint mobility.^16,34–38 Many reports^{15,34–37,39} showed no significant differences in translation, rotation angles, and stiffness between male and female subjects, whereas some authors^16,38 found that female subjects had greater anterior GH laxity and rotational ROM than male subjects had. In the present study, we demonstrated that the values for A-P and P-A translation and ER ROM were similar for men and women. Such findings are consistent with the majority of previous reports on this issue. The failure to find sex differences in translational mobility may have arisen from insufficient numbers of participating subjects or insufficient instrumental precision to detect sex differences in translation with our method. However, we found that women had a greater range of IR than men had at positions of greater abduction. This finding is in contrast to previous reports showing no differences in IR and ER ranges between male and female subjects when the scapula was stabilized.³⁴

Comparisons of the translation data obtained in the present study with those reported in the existing literature are difficult because of differences in experimental design and subject status (eg, age, posture [sitting or supine], and status of muscular activation). Hsu et al¹ applied a force of 80 N and a torque of 1 N·m to cadaver specimens at different abduction angles in order to quantify humeral head translation and GH joint rotational ROM, respectively. The values that they obtained for head translation were much larger than those obtained in the present study, possibly because of the absence of muscle tone in cadaver specimens. Sauers et al¹³ reported that at 20 degrees of GH abduction in subjects who were healthy, the total humeral head translation was 20 mm; this value is lower than the value (25 mm) obtained in the present study. During translation tests, we computed the translation of the CH relative to the scapula (CG) rather than directly recording the translation via linear motion sensors affixed to the skin surface. In addition, differences in the scapular immobilization method and the experimental setup might have accounted for this difference. In the present study, the translation values obtained during P-A glide were greater than those obtained during A-P glide at each GH abduction angle, in contrast to those reported by Sauers et al,¹³ who demonstrated equal magnitudes of translation in the A-P and P-A directions.

The roles played by different sectors of the GH joint capsule during anterior and posterior translation of the humeral head have been reported.^40–43 The anterior capsule, especially the anteroinferior sector, is the primary stabilizer for the GH joint during anterior translation; the posterior capsule, especially the posteroinferior sector, primarily constrains the posterior translation of the humeral head.^40,41,43

In a magnetic resonance imaging study, Urayama et al⁴⁴ reported a slightly longer capsule length (34.8±5.6 mm) for the anteroinferior capsule than for its posterior counterpart (31.3±6.6 mm) in unaffected shoulders in a group of subjects with anterior GH instability. The anterior band of the inferior GH ligament was reported to be less stiff than the posterior band of the inferior GH ligament.^42,45 McQuade et al³⁹ also reported slightly less stiffness in the anterior direction than in the posterior direction at GH abduction angles of 45, 90, and 180 degrees in neutral rotation. Therefore, the greater anterior as opposed to posterior translation of the humeral head might have been the result of the interplay of capsule length and mechanical property.

The same pattern regarding the magnitude of humeral head translation has been observed in several research studies.^{1,17,39,40,46–49} However, the relative magnitudes of anterior translation and posterior translation are dependent not only on the types of subjects tested but also on the positions in which tests are conducted. The magnitude of anterior or posterior translation may rely on the stiffness of each portion of the ligament or on the capsular constraint. In the studies of Borsa and colleagues,^50,51 posterior translation was much more lax than anterior translation in baseball pitchers and swimmers. In their studies, the shoulder of each subject during force-displacement measurements was kept at 90 degrees of abduction and 60 degrees of ER. Under these testing conditions, the anterior band of the inferior GH ligament might have acted as the primary constraint and might have limited anterior translation of the head of the humerus.^43,50

In the present study, total rotational ROM values of 147.2 and 147.0 degrees were obtained at 40 and 50 degrees of GH abduction, respectively. Such values are similar to those reported in the literature for the corresponding position (139.4° of rotational ROM at 45° of abduction).⁹ These values are lower than those reported without scapular fixation for subjects who are healthy^11,38 because the accessory scapulothoracic motions necessary for humerus rotational movements are restrained by scapular stabilization.^11,34 In the present study, the ER range increased with increasing angle of abduction. Earlier selective cutting studies indicated that the inferior GH ligament is the most important restraint for humerus ER in both neutral⁵² and abducted^52,53 positions, whereas the coracohumeral ligament provides more restraint to ER only when the arm is in the neutral position.^52–54 In the abducted position, the coracohumeral ligament becomes loose, places less restraint on ER, and allows a greater range of ER in abduction. Our results concur with the findings of Kuhn et al,⁵² who reported a greater range of ER at larger abduction angles than at smaller abduction angles.

In the present study, the angular displacement of the scapula, especially for scapular rotation, varied with the angle of GH abduction. It is difficult to immobilize the scapula with the immobilization frame at larger angles of elevation. However, the maximal arm elevation angles for each subject in our study were within 120 degrees of arm abduction relative to the thorax. According to Karduna et al,⁵⁵ the scapular motions recorded by surface sensors were almost the same as those recorded by sensors on bone pins surgically fixed on the scapula when the humerothoracic elevation was less than 120 degrees. The results of their study indicated that skin motion artifacts are not a significant factor as long as the shoulder joint is maintained at less than 120 degrees of abduction. Therefore, it seems appropriate in the present study to represent scapular motion with the use of a sensor on the acromion when the shoulder is at less than 120 degrees of elevation.

Limitations

The present study had several limitations. Only anterior and posterior translation and rotational ROM were used to define the resting position. Other GH joint accessory movements in various planes and directions, such as distraction, inferior glide, and lateral glide, are potential parameters for determining the resting position.

In the present study, we incorporated the method described by Gamage and Lasenby²³ for the derivation of COR from small-arc movements of the GH joint. This method was originally used for the hip joint. The GH joint, unlike the hip joint, lacks passive stability and requires the GH capsuloligamentous structures and surrounding muscles to act as passive and active stabilizers to constrain humeral head translation. During small-arc movements, however, the influence of the GH joint capsule and muscle was not likely to be significant in the present study because the coaptation of the glenoid and the head of the humerus was ensured by a medially directed compressive force applied to the head of the humerus. Under such conditions, the GH joint acts as an ideal ball-and-socket joint, and the centers of the glenoid and humeral head coincide at the COR of the GH joint during small-arc movements. Even with greater abduction, the amount of translation of the humeral head has been reported to be relatively small.^{47–51,56,57}

The magnitude of translational or rotational laxity may be dependent on factors such as age, sex, race, and the magnitude of the applied load. In the present study, young subjects who were healthy were recruited; therefore, the findings may be specific to the study's subject pool. Furthermore, the scapula was immobilized in our study; this condition resembled clinical testing situations in which the scapula of a subject is constrained manually by a therapist. Thus, generalization of the results obtained from the present study for test conditions in which the scapula is not constrained should be made with caution.

	Conclusion

Top Abstract Introduction Method Results Discussion Conclusion References

 
In the present study, the resting position of the GH joint was determined by measuring A-P and P-A translation and rotational ROM with a fixed scapula in 15 young subjects who were healthy. In the dominant GH joint of the tested population, we found that the mean resting position for A-P and P-A translation was located at 23.7 degrees and that the mean resting position for rotational ROM was located at 49.8 degrees of GH abduction in the plane of the scapula. The position at which maximal translational laxity occurred did not coincide with that of maximal rotational ROM laxity. Our results suggest the possibility that the resting position for each joint may not be a unique position, at least for the GH joint. Although the concept of one resting position for each joint has been universally accepted in clinical practice, on the basis of the findings of the present study, we suggest that multiple resting positions should be determined depending on the criterion accessory or physiological movements used for mobility assessments.

	Footnotes

 
Dr Hsu provided concept/idea/research design. Dr Lin, Dr Hsu, and Dr An provided writing and data analysis. Dr Lin provided data collection and subjects. Dr Chang and Dr Hsu provided fund procurement. Dr Hsu, Dr Chang, Dr Chang Chien, and Dr Su provided facilities/equipment. Dr Chang and Dr An provided consultation (including review of manuscript before submission). The authors acknowledge the assistance of Dr Jia-Hao Chang for consultation in software implementation at the initial stage of the study.

The research protocol used in this study was approved by the Institutional Review Board of the National Cheng Kung University Hospital, Tainan, Taiwan.

This study was supported, in part, by an Allied Health Research Grant from the College of Medicine, National Cheng Kung University.

This research, in part, was presented at the 20th Congress of the International Society of Biomechanics and the 29th Annual Meeting of the American Society of Biomechanics; July 31–August 5, 2005; Cleveland, Ohio.

^* Polhemus Inc, 40 Hercules Dr, Colchester, VT 05446.

Transducer Techniques, 42480 Rio Nedo, Temecula, CA 92590.

	References

Top Abstract Introduction Method Results Discussion Conclusion References

 

1. 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]
2. Kaltenborn FM. Manual Mobilization of the Joints. Oslo, Norway: Olaf Norlis Bokhandel; 2002.
3. Edmond SL. Manipulation and Mobilization: Extremities and Spinal Techniques. St Louis, Mo: Mosby; 1993.
4. Magee DJ. Orthopedic Physical Assessment. 3rd ed. Philadelphia, Pa: WB Saunders; 1997.
5. Hertling D, Kessler RM. Management of Common Musculoskeletal Disorders: Physical Therapy Principles and Methods. 3rd ed. Philadelphia, Pa: JB Lippincott Co; 1996.
6. Ellenbecker TS, Roetert EP, Bailie DS, et al. Glenohumeral joint total rotation range of motion in elite tennis players and baseball pitchers. Med Sci Sports Exerc. 2002;34:2052–2056.
7. Petty NJ, Maher C, Latimer J, Lee M. Manual examination of accessory movements: seeking R1. Man Ther. 2002;7:39–43.[CrossRef][Web of Science][Medline]
8. Sauers EL, Borsa PA, Herling DE, Stanley RD. Instrumented measurement of glenohumeral joint laxity: reliability and normative data. Knee Surg Sports Traumatol Arthrosc. 2001;9:34–41.[CrossRef][Web of Science][Medline]
9. Novotny JE, Woolley CT, Nichols CE, Beynnon BD. In vivo technique to quantify the internal-external rotation kinematics of the human glenohumeral joint. J Orthop Res. 2000;18:190–194.[CrossRef][Web of Science][Medline]
10. Novotny JE, Beynnon BD, Nichols CE. Modeling the stability of the human glenohumeral joint during external rotation. J Biomech. 2000;33:345–354.[CrossRef][Web of Science][Medline]
11. Ellenbecker TS. Clinical Examination of the Shoulder. Philadelphia, Pa: Elsevier Saunders; 2004.
12. Tibone JE, Lee TQ, Csintalan RP, et al. Quantitative assessment of glenohumeral translation. Clin Orthop Relat Res. 2002;400:93–97.[CrossRef][Medline]
13. Sauers EL, Borsa PA, Herling DE, Stanley RD. Instrumented measurement of glenohumeral joint laxity and its relationship to passive range of motion and generalized joint laxity. Am J Sports Med. 2001;29:143–150.[Abstract/Free Full Text]
14. McQuade KJ, Murthi AM. Anterior glenohumeral force/translation behavior with and without rotator cuff contraction during clinical stability testing. Clin Biomech. 2004;19:10–15.[CrossRef][Medline]
15. Borsa PA, Sauers EL, Herling DE. Glenohumeral stiffness response between men and women for anterior, posterior, and inferior translation. J Athl Train. 2002;37:240–245.[Web of Science][Medline]
16. Borsa PA, Sauers EL, Herling DE. Patterns of glenohumeral joint laxity and stiffness in healthy men and women. Med Sci Sports Exerc. 2000;32:1685–1690.
17. Debski RE, Wong EK, Woo SL, et al. In situ force distribution in the glenohumeral joint capsule during anterior-posterior loading. J Orthop Res. 1999;17:769–776.[CrossRef][Web of Science][Medline]
18. Helmig P, Søjbjerg JO, Kjaersgaard-Andersen P, et al. Distal humeral migration as a component of multidirectional shoulder instability: an anatomical study in autopsy specimens. Clin Orthop Relat Res. 1990;252:139–143.[Medline]
19. McClure PW, Michener LA, Sennett BJ, Karduna AR. Direct 3-dimensional measurement of scapular kinematics during dynamic movements in vivo. J Shoulder Elbow Surg. 2001;10:269–277.[CrossRef][Web of Science][Medline]
20. Kaltenborn FM. Manual Mobilization of the Extremity Joints. Oslo, Norway: Olaf Norlis Bokhandel; 1989.
21. Biryukova EV, Roby-Brami A, Frolov AA, Mokhtari M. Kinematics of human arm reconstructed from spatial tracking system recordings. J Biomech. 2000;33:985–995.[CrossRef][Web of Science][Medline]
22. Van der Helm FCT. A standardized protocol for motion recordings of the shoulder. In: Veeger H, Van der Helm F, Rozing PM, eds. Proceedings of the 1st Conference of the International Shoulder Group; August 26–27, 1997; Maastricht, the Netherlands. Maastricht, the Netherlands: Shaker Publishers; 1997.
23. Gamage S, Lasenby J. New least square solutions for estimating the average center of rotation and the axis of rotation. J Biomech. 2002;35:87–93.[CrossRef][Web of Science][Medline]
24. Warner JJ, Deng XH, Warren RF, Torzilli PA. Static capsuloligamentous restraints to superior-inferior translation of the glenohumeral joint. Am J Sports Med. 1992;20:675–685.[Abstract/Free Full Text]
25. Hsu AT, Ho L, Chang JH, et al. Characterization of tissue resistance during a dorsally directed translational mobilization of the glenohumeral joint. Arch Phys Med Rehabil. 2002;83:360–366.[CrossRef][Web of Science][Medline]
26. Hsu AT, Ho L, Ho S, Hedman T. Joint position during anterior-posterior glide mobilization: its effect on glenohumeral abduction range of motion. Arch Phys Med Rehabil. 2000;81:210–214.[Web of Science][Medline]
27. Lin HT, Hsu AT, An KN, Chang GL. Glenohumeral joint laxity measurement in normal subjects and its validation. In: Proceedings of the 15th International Conference on Mechanics in Medicine and Biology; December 6, 2006; Singapore.
28. An KN, Browne AO, Korinek S. Three-dimensional kinematics of the glenohumeral elevation. J Orthop Res. 1990;9:143–149.[CrossRef][Web of Science]
29. Hurschler C, Wulker N, Windhagen H, et al. Medially based anterior capsular shift of the glenohumeral joint: passive range of motion and posterior capsular strain. Am J Sports Med. 2001;29:346–353.[Abstract/Free Full Text]
30. Sabari JS, Maltzev I, Lubarsky D, et al. Goniometric assessment of shoulder range of motion: comparison of testing in supine and sitting positions. Arch Phys Med Rehabil. 1998;79:647–651.[CrossRef][Web of Science][Medline]
31. Crockett HC, Gross LB, Wilk KE, et al. Osseous adaptation and range of motion at the glenohumeral joint in professional baseball pitchers. Am J Sports Med. 2002;30:20–26.[Abstract/Free Full Text]
32. Reagan KM, Meister K, Horodyski MB, et al. Humeral retroversion and its relationship to glenohumeral rotation in the shoulder of college baseball players. Am J Sports Med. 2002;30:354–360.[Abstract/Free Full Text]
33. Pieper HG. Humeral torsion in the throwing arm of handball players. Am J Sports Med. 1998;26:247–253.[Abstract/Free Full Text]
34. 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]
35. Brown GA, Tan JL, Kirkley A. The lax shoulder in females: issues, answers, but many more questions. Clin Orthop Relat Res. 2000;372:110–122.[CrossRef][Medline]
36. Murray MP, Gore DR, Gardner GM, Mollinger LA. Shoulder motion and muscle strength of normal men and women in two age groups. Clin Orthop Relat Res. 1985;192:268–273.[Medline]
37. Emery RJ, Mullaji AB. Glenohumeral joint instability in normal adolescents: incidence and significance. J Bone Joint Surg Br. 1991;73:406–408.[Web of Science][Medline]
38. Barnes CJ, Van Steyn SJ, Fischer RA. The effects of age, sex, and shoulder dominance on range of motion of the shoulder. J Shoulder Elbow Surg. 2001;10:242–246.[CrossRef][Web of Science][Medline]
39. McQuade KJ, Shelley I, Cvitkovic J. Patterns of stiffness during clinical examination of the glenohumeral joint. Clin Biomech. 1999;14:620–627.[CrossRef][Medline]
40. Brenneke SL, Reid J, Ching RP, Wheeler DL. Glenohumeral kinematics and capsulo-ligamentous strain resulting from laxity exams. Clin Biomech. 2000;15:735–742.[CrossRef][Medline]
41. Burkart AC, Debski RE. Anatomy and function of the glenohumeral ligaments in anterior shoulder instability. Clin Orthop Relat Res. 2002;400:32–39.[CrossRef][Medline]
42. Curl LA, Warren RF. Glenohumeral joint stability: selective cutting studies on the static capsular restraints. J Orthop Res. 1996;330:54–65.
43. O'Brien SJ, Schwartz RS, Warren RF, Torzilli PA. Capsular restraints to anterior-posterior motion of the abducted shoulder: a biomechanical study. J Shoulder Elbow Surg. 1995;4:298–308.[CrossRef][Medline]
44. Urayama M, Itoi E, Sashi R, et al. Capsular elongation in shoulders with recurrent anterior dislocation: quantitative assessment with magnetic resonance arthrography. Am J Sports Med. 2003;31:64–67.[Abstract/Free Full Text]
45. Bigliani LU, Pollock RG, Soslowsky LJ, et al. Tensile properties of the inferior glenohumeral ligament. J Orthop Res. 1992;10:187–197.[CrossRef][Web of Science][Medline]
46. Moore SM, Musahl V, McMahon PJ, Debski RE. Multidirectional kinematics of the glenohumeral joint during simulated simple translation tests: impact on clinical diagnoses. J Orthop Res. 2004;22:889–894.[CrossRef][Web of Science][Medline]
47. Wuelker N, Korell M, Thren K. Dynamic glenohumeral joint stability. J Shoulder Elbow Surg. 1998;7:43–52.[CrossRef][Web of Science][Medline]
48. Selecky MT, Tibone JE, Yang BY, et al. Glenohumeral joint translation after arthroscopic thermal capsuloplasty of the posterior capsule. J Shoulder Elbow Surg. 2003;12:242–246.[CrossRef][Web of Science][Medline]
49. Victoroff BN, Deutsch A, Protomastro P, et al. The effect of radiofrequency thermal capsulorrhaphy on glenohumeral translation, rotation, and volume. J Shoulder Elbow Surg. 2004;13:138–145.[CrossRef][Web of Science][Medline]
50. Borsa PA, Wilk KE, Jacobson JA, et al. Correlation of range of motion and glenohumeral translation in professional baseball pitchers. Am J Sports Med. 2005;33:1392–1399.[Abstract/Free Full Text]
51. Borsa PA, Scibek JS, Jacobson JA, Meister K. Sonographic stress measurement of glenohumeral joint laxity in collegiate swimmers and age-matched controls. Am J Sports Med. 2005;33:1077–1084.[Abstract/Free Full Text]
52. Kuhn JE, Huston LJ, Soslowsky LJ, et al. External rotation of the glenohumeral joint: ligament restraints and muscle effects in the neutral and abducted positions. J Shoulder Elbow Surg. 2005;14:39S–48S.[CrossRef][Web of Science][Medline]
53. Urayama M, Itoi E, Hatakeyama Y, et al. Function of the 3 portions of the inferior glenohumeral ligament: a cadaveric study. J Shoulder Elbow Surg. 2001;10:589–594.[Medline]
54. Harryman DT II, Sidles JA, Harris SL, Matsen FA III. The role of the rotator interval capsule in passive motion and stability of the shoulder. J Bone Joint Surg Am. 1992;74:53–66.[Abstract/Free Full Text]
55. 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]
56. Graichen H, Stammberger T, Bonel H, et al. Glenohumeral translation during active and passive elevation of the shoulder: a 3D open-MRI study. J Biomech. 2000;33:609–613.[CrossRef][Web of Science][Medline]
57. Bigliani LU, Kelkar R, Flatow EL, et al. Glenohumeral stability: biomechanical properties of passive and active stabilizers. Clin Orthop Relat Res. 1996;330:13–30.[CrossRef][Medline]

CiteULike

Complore

Connotea

Del.icio.us

Digg

Reddit

Technorati

This article has been cited by other articles:

				P. M Ludewig Invited commentary. Physical Therapy, December 1, 2007; 87(12): 1682 - 1684. [Full Text] [PDF]

				H.-T. Lin, A.-T. Hsu, G.-L. Chang, J.-r. Chang Chien, K.-N. An, and F. C. Su Author Response Physical Therapy, December 1, 2007; 87(12): 1684 - 1686. [Full Text] [PDF]

This Article Abstract Full Text (PDF) All Versions of this Article: ptj.20050391v1 87/12/1669    most recent Submit a response Alert me when this article is cited Alert me when Rapid Responses are posted Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Lin, H.-T. Articles by Su, F. C. Search for Related Content PubMed PubMed Citation Articles by Lin, H.-T. Articles by Su, F. C. Related Collections Kinesiology/Biomechanics Social Bookmarking                      What's this?