JBJS | Position of Immobilization After Dislocation of the Glenohumeral Joint : A Study with Use of Magnetic Resonance Imaging

The Journal of Bone & Joint Surgery, Volume 83, Issue 5

Articles | May 01, 2001

Position of Immobilization After Dislocation of the Glenohumeral Joint : A Study with Use of Magnetic Resonance Imaging

Eiji Itoi, MD; Ryuji Sashi, MD; Hiroshi Minagawa, MD; Togo Shimizu, MD; Ikuko Wakabayashi, MD; Kozo Sato, MD

Investigation performed at the Departments of Orthopedic Surgery and Radiology, Akita University School of Medicine, Akita, Japan
Eiji Itoi, MD Ryuji Sashi, MD Togo Shimizu, MD Ikuko Wakabayashi, MD Kozo Sato, MD Departments of Orthopedic Surgery (E.I., T.S., I.W., and K.S.) and Radiology (R.S.), Akita University School of Medicine, Hondo 1-1-1, Akita 010-8543, Japan. E-mail address for E. Itoi: itoi@med.akita-u.ac.jp
Hiroshi Minagawa, MD Department of Orthopedic Surgery, Ugo Municipal Hospital, Ugo-machi, Ogachi-gun 012-1131, Japan
No benefits in any form have been received or will be received from a commercial party related directly or indirectly to the subject of this article. No funds were received in support of this study.
A commentary is available with the electronic versions of this article, on our web site (www.jbjs.org) and on our CD-ROM (call 781-449-9780, ext. 140, to order).

The Journal of Bone & Joint Surgery. 2001; 83:661-667

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Abstract

Background: Glenohumeral dislocations often recur, probably because a Bankart lesion does not heal sufficiently during the period of immobilization. Using magnetic resonance imaging, we assessed the position of the Bankart lesion, with the arm in internal and external rotation, in shoulders that had had a dislocation.

Methods: Coaptation of a Bankart lesion was examined with use of magnetic resonance imaging, with the arm held at the side of the trunk and positioned first in internal rotation (mean, 29°) and then in external rotation (mean, 35°), in nineteen shoulders. Six shoulders (six patients) had had an initial anterior dislocation, and thirteen shoulders (twelve patients) had had recurrent anterior dislocation. Fast-spin-echo T2-weighted axial images were made when the dislocation had occurred less than two weeks earlier, and spin-echo T1-weighted axial images after intra-articular injection of gadolinium-diethylenetriamine pentaacetic acid were made when the dislocation had occurred more than two weeks earlier. Separation and displacement of the anteroinferior portion of the labrum from the glenoid rim were measured on the axial images, and coaptation of the anterior part of the capsule to the glenoid neck was assessed by measurement of the detached area, opening angle, and detached length.

Results: Separation and displacement of the labrum were both significantly less (p = 0.0047 and p = 0.0017, respectively) when the arm was in external rotation than when it was in internal rotation. The detached area and the opening angle of the anteroinferior portion of the capsule were both significantly smaller (p = 0.0003 and p < 0.0001, respectively), and the detached length was significantly shorter (p < 0.0001) with the arm in external rotation.

Conclusion: Immobilization of the arm in external rotation better approximates the Bankart lesion to the glenoid neck than does the conventional position of internal rotation.

Figures in this Article

Introduction

Introduction | Materials and Methods | Results | Discussion | References

Dislocation of the glenohumeral joint is the most common traumatic dislocation in the human body¹. After reduction, the shoulder is usually immobilized to the trunk, with the arm in adduction and internal rotation. Dislocation of the glenohumeral joint is notorious for its high recurrence rate, which has ranged from 47% (forty-eight of 102) to 100% (twenty-one of twenty-one) among young patients^2-11. Recurrence can occur regardless of the type or duration of immobilization^3,4,6-9. If the capsulolabral structures that are detached by the dislocation heal and are in contact with the glenoid, both the method and the duration of immobilization should affect the recurrence rate. Immobilization in adduction and internal rotation has been performed since the era of Hippocrates but without knowledge as to which position is most suitable for the healing of the lesion. In a recent study, we showed that a Bankart lesion created in cadaveric shoulders, with the surrounding muscles removed, remained coapted regardless of arm rotation as long as the arm was in adduction¹². However, in vivo coaptation may be affected by the rotation of the arm because of the change in muscle tone in different positions. We hypothesized that the tight anterior soft-tissue structures with the arm in external rotation would help a Bankart lesion to be coapted. The purpose of the present study was to determine, with use of magnetic resonance imaging, the effect of arm rotation on in vivo coaptation of a Bankart lesion.

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Fig. 1-A:: Figs. 1-A and 1-B Magnetic resonance images with the arm in internal and external rotation. Fig. 1-A With the arm in internal rotation, there is an abnormal cavity between the glenoid neck and the anterior tissue structures because of a displaced Bankart lesion.

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Fig. 1-B:: With the arm in external rotation, the anterior joint cavity is closed and the labrum lies against the glenoid rim (white arrow).

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Fig. 2:: Measurements of the labrum. Separation (S) was defined as the distance (in millimeters) between the inner margin of the labrum and the anterior aspect of the glenoid neck. Displacement (D) was defined as the distance (in millimeters) between the tip of the labrum and the tip of the glenoid rim. The value was positive when the labrum was displaced medial to the rim of the glenoid, and it was negative when the labrum was displaced laterally, toward the humeral head.

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Fig. 3:: Measurements of the capsule. The detached area (lined area) is the area between the anterior aspect of the glenoid neck and the detached anterior part of the capsule (in square millimeters). The opening angle (q) is the angle between the anterior aspect of the glenoid neck and a line tangential to the capsule at the glenoid insertion (in degrees). The detached length (A to B) is the length between the anterior glenoid rim and the anterior capsular attachment (in millimeters).

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Fig. 4-A:: Figs. 4-A and 4-B Magnetic resonance images made with the arm in internal and external rotation. Fig. 4-A In internal rotation, the subscapularis muscle (asterisk) is lax and the labrum is displaced medially on the neck of the glenoid (white arrow).

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Fig. 4-B:: Figs. 4-A and 4-B Magnetic resonance images made with the arm in internal and external rotation. Fig. 4-B In 47 of external rotation, the subscapularis muscle becomes tight and the labrum returns to the glenoid rim. Because of the tight subscapularis, the effusion shifted to the posterior joint cavity in external rotation.

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TABLE I: Normalized Measurements of the Shoulders

*ND = labrum not detectable.

Case	External Rotation Angle of the Arm (deg)	Separation* (mm)		Displacement* (mm)		Detached Area (mm²)		Opening Angle (deg)		Detached Length (mm)
Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation
Shoulders with initial dislocation
1	35	0	0	?5.0	3.7	49.9	30.9	7.8	0.1	22.1	5.8
2	81	1.4	0	?7.1	0	302.2	28.9	38.3	13.6	30.6	29.8
3	47	5.7	4.3	?0	0	118.5	57.2	68.8	15.5	14.8	4.7
4	55	1.2	0	12.0	7.3	273.7	126.8	32.9	19.0	26.8	23.6
5	28	0	0	?0	—3.3	164.5	57.7	29.0	16.5	22.7	13.5
6	67	1.3	0	?—1.3	—1.9	59.6	26.5	12.0	1.3	18.3	4.7
Mean	52	1.6	0.7	?3.8	1.0	161.4	54.7	31.5	11.0	22.6	13.7
Standard deviation	20	2.1	1.7	?5.1	3.9	106.9	38.0	21.8	8.2	5.7	10.8
P value		0.0260	0.0527	0.0394	0.0325	0.0146
Shoulders with recurrent dislocation
? 7	60	1.7	1.7	?6.9	0	114.8	31.5	88.2	10.6	7.5	11.9
? 8	19	0	0	?3.2	0	145.6	45.2	26.3	19.0	21.8	5.9
? 9	36	1.2	0	?0	—1.2	246.8	85.8	66.4	12.6	13.3	6.9
10	19	ND	1.4	ND	—2.9	50.8	50.9	26.3	7.5	19.4	4.5
11	—15	—2.8	—4.3	?0	0	88.6	106.4	20.6	20.1	5.2	5.2
12	61	ND	—1.5	ND	0	432.2	28.9	29.2	2.1	11.8	3.3
13	20	—4	—3.4	?0	0	142.3	35.2	65.3	21.0	4.2	4.0
14	14	7.6	0	?0	—3.8	287.3	33.6	83.4	16.9	22.4	8.0
15	7	6.2	0	?0.4	0	61.3	8.7	121.4	42.0	8.4	2.8
16	47	0	0	?3.0	0	86.8	2.3	84.7	11.7	15.4	3.5
17	37	3.6	0	?0	0	89.6	87.2	35.5	8.9	15.5	3.4
18	8	5.6	1.4	?0	0	115.8	58.0	20.1	19.9	24.2	3.1
19	33	3.6	1.2	?9.6	1.2	133.3	26.3	37.2	21.2	39.5	31.0
Mean	27	2.1	—0.3	?2.1	—0.5	153.5	46.2	54.2	16.4	16.0	7.2
Standard deviation	21	3.7	1.8	?3.4	1.4	107.9	31.0	32.7	9.8	9.6	7.6
P value		0.0166	0.0223	0.0054	0.0006	0.0009
All shoulders
Mean	35	1.9	0.1	?2.7	0.0	156.0	48.8	47.0	14.7	18.1	9.2
Standard deviation	24	3.1	1.8	?4.0	2.4	104.6	32.6	31.1	9.4	9.0	9.0
P value		0.0047	0.0017	0.0003	<0.0001	<0.0001

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TABLE I: Normalized Measurements of the Shoulders

*ND = labrum not detectable.

Case	External Rotation Angle of the Arm (deg)	Separation* (mm)		Displacement* (mm)		Detached Area (mm²)		Opening Angle (deg)		Detached Length (mm)
Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation
Shoulders with initial dislocation
1	35	0	0	?5.0	3.7	49.9	30.9	7.8	0.1	22.1	5.8
2	81	1.4	0	?7.1	0	302.2	28.9	38.3	13.6	30.6	29.8
3	47	5.7	4.3	?0	0	118.5	57.2	68.8	15.5	14.8	4.7
4	55	1.2	0	12.0	7.3	273.7	126.8	32.9	19.0	26.8	23.6
5	28	0	0	?0	—3.3	164.5	57.7	29.0	16.5	22.7	13.5
6	67	1.3	0	?—1.3	—1.9	59.6	26.5	12.0	1.3	18.3	4.7
Mean	52	1.6	0.7	?3.8	1.0	161.4	54.7	31.5	11.0	22.6	13.7
Standard deviation	20	2.1	1.7	?5.1	3.9	106.9	38.0	21.8	8.2	5.7	10.8
P value		0.0260	0.0527	0.0394	0.0325	0.0146
Shoulders with recurrent dislocation
? 7	60	1.7	1.7	?6.9	0	114.8	31.5	88.2	10.6	7.5	11.9
? 8	19	0	0	?3.2	0	145.6	45.2	26.3	19.0	21.8	5.9
? 9	36	1.2	0	?0	—1.2	246.8	85.8	66.4	12.6	13.3	6.9
10	19	ND	1.4	ND	—2.9	50.8	50.9	26.3	7.5	19.4	4.5
11	—15	—2.8	—4.3	?0	0	88.6	106.4	20.6	20.1	5.2	5.2
12	61	ND	—1.5	ND	0	432.2	28.9	29.2	2.1	11.8	3.3
13	20	—4	—3.4	?0	0	142.3	35.2	65.3	21.0	4.2	4.0
14	14	7.6	0	?0	—3.8	287.3	33.6	83.4	16.9	22.4	8.0
15	7	6.2	0	?0.4	0	61.3	8.7	121.4	42.0	8.4	2.8
16	47	0	0	?3.0	0	86.8	2.3	84.7	11.7	15.4	3.5
17	37	3.6	0	?0	0	89.6	87.2	35.5	8.9	15.5	3.4
18	8	5.6	1.4	?0	0	115.8	58.0	20.1	19.9	24.2	3.1
19	33	3.6	1.2	?9.6	1.2	133.3	26.3	37.2	21.2	39.5	31.0
Mean	27	2.1	—0.3	?2.1	—0.5	153.5	46.2	54.2	16.4	16.0	7.2
Standard deviation	21	3.7	1.8	?3.4	1.4	107.9	31.0	32.7	9.8	9.6	7.6
P value		0.0166	0.0223	0.0054	0.0006	0.0009
All shoulders
Mean	35	1.9	0.1	?2.7	0.0	156.0	48.8	47.0	14.7	18.1	9.2
Standard deviation	24	3.1	1.8	?4.0	2.4	104.6	32.6	31.1	9.4	9.0	9.0
P value		0.0047	0.0017	0.0003	<0.0001	<0.0001

Materials and Methods

Introduction | Materials and Methods | Results | Discussion | References

Patients

We evaluated nineteen shoulders in eighteen consecutive patients with traumatic anterior dislocation of the shoulder. Patients with a glenoid fracture and those without a Bankart lesion were excluded from the study. All of the patients were enrolled in the study after giving their consent. There were fifteen male and three female patients who had a mean age of twenty-three years (range, fifteen to forty-seven years). Six patients (six shoulders) had sustained an initial anterior dislocation, and twelve patients (thirteen shoulders) had had recurrent anterior dislocation. The mean length of time between the last dislocation and the magnetic resonance imaging was four days (range, one to nine days) for the patients who had an initial dislocation and twenty-nine days (range, one to sixty days) for the patients who had a recurrent dislocation.

Magnetic Resonance Imaging

With use of a 1.5-tesla magnetic resonance imager (Signa; General Electric Medical Systems, Milwaukee, Wisconsin), fast-spin-echo T2-weighted axial images (repetition time, 4000 msec; echo time, 92.2 msec) were made when the dislocation had occurred less than two weeks earlier, whereas spin-echo T1-weighted axial images (repetition time, 600 msec; echo time, 23 msec) were made, after injection of 10 mL of saline solution containing 1% gadolinium-diethylenetriamine pentaacetic acid into the glenohumeral joint, when the dislocation had occurred more than two weeks earlier. We chose the two-week point because we assumed that there would be an effusion or hematoma in the glenohumeral joint during the first two weeks after dislocation¹³. The magnetic resonance images were made with 3-mm-thick slices with a 1-mm gap between the slices, a 10-cm field of view, and a matrix size of 256 ¥ 128. The combination of dual-phased array coils and a small field of view achieved high-resolution images¹⁴. The arm was held at the side of the trunk and was positioned first in internal rotation and then in external rotation. The angle of internal rotation was determined such that the forearm rested on the abdomen with the elbow flexed at 90°. Keeping the same rotation, the elbow was extended and the arm was stabilized to avoid movement of the shoulder associated with respiration. This rotation simulated the position of conventional immobilization. The angle of external rotation was the maximum amount of external rotation at which the patient felt comfortable. As the rotation angles were different in each patient, we measured the rotation angles on magnetic resonance images afterward.

Measurements on Magnetic Resonance Images

An axial slice at the inferior-one-third level of the glenoid was used to assess the degree of coaptation of the Bankart lesion. This level corresponds to approximately the four o’clock position in the right shoulder and the eight o’clock position in the left shoulder. With the arm in internal rotation (Fig. 1-A), the joint cavity anterior to the glenoid was wide open. With the arm in external rotation (Fig. 1-B), the anterior joint cavity was closed and the labrum (which had been displaced inferiorly) lay on the glenoid rim. We assessed the position of the labrum relative to the glenoid with use of two parameters: separation and displacement (Fig. 2). Separation was defined as the distance (in millimeters) between the inner margin of the labrum and the anterior aspect of the glenoid neck. Displacement was defined as the distance (in millimeters) between the tip of the labrum and the tip of the glenoid rim. The labrum was given a positive value when it was displaced medial to the rim of the glenoid, and it was given a negative value when it was displaced laterally, toward the humeral head. We also assessed the coaptation of the anterior portion of the capsule to the glenoid (opening and closing of the anterior joint cavity). The magnetic resonance images were scanned into a personal computer. With use of image-analyzing software (NIH Image; National Institutes of Health, Bethesda, Maryland), the following parameters were measured: (1) the detached area (the area between the anterior aspect of the glenoid neck and the detached anterior part of the capsule), (2) the opening angle (the angle between the anterior aspect of the glenoid neck and a line tangential to the capsule at the glenoid insertion), and (3) the detached length (the length between the anterior glenoid rim and the anterior capsular attachment) (Fig. 3).

The diameter of the humeral head was measured at a slice level close to the center of the humeral head. The rotation of the arm relative to the trunk was also measured on the images. The bicipital groove faces directly anteriorly when the arm is in 10° of internal rotation¹⁵. We drew a line passing through the center of the humeral head and the bicipital groove on the axial image at the level of the center of the humeral head. Then, we measured the angle between this line and the vertical. The angle was positive when the line was inclined internally from the vertical line and negative when the line was inclined externally. By adding 10° to this angle, we obtained the rotation of the arm relative to the trunk. The arm was deemed to be in internal rotation when the angle was positive and in external rotation when it was negative. All of the measurements were performed by one of us (T.S.) in a blinded fashion. For five shoulders, the measurements were repeated twice in order to assess the intraobserver repeatability.

Data Analysis

The measurements of the separation, displacement, and detached length were normalized by dividing the data by the ratio of the measured diameter of the humeral head to the mean diameter of the humeral head. The detached area was normalized by dividing the area data by the ratio of the square of the measured diameter of the head to the square of the mean diameter of the head. Intraobserver repeatability was assessed with use of the correlation coefficient between the measurements at two different times. The precision of the methodology was assessed with use of the coefficient of variation. The measurements of the two rotational positions on magnetic resonance images were compared with use of the paired t test. Significance was set at the 5% level.

Results

Introduction | Materials and Methods | Results | Discussion | References

Reliability of the Methodology

The intraobserver repeatability coefficient ranged from 0.941 to 0.998. The coefficient of variation for the methodology precision was between 0.3% and 3.3%.

Arm Rotation

The mean angle of internal rotation was 29° (range, 4° to 54°), and the mean angle of external rotation was 35° (range, —15° to 81°).

Labral Coaptation

All of the normalized measurements are listed in Table I. Labral coaptation was measurable in all of the shoulders except two (Cases 10 and 12), in which the labrum was not visible with the arm in internal rotation. The shoulders had significantly less separation and displacement of the labrum (p = 0.0047 and p = 0.0017, respectively) when the arm was in external rotation than when it was in internal rotation. When the shoulders with initial dislocation and those with recurrent dislocation were examined separately, the same results were observed—that is, both the separation and displacement were smaller with the arm in external rotation.

Capsular Coaptation

The detached area of the capsule and the opening angle were significantly smaller (p = 0.0003 and p < 0.0001, respectively) and the detached length was significantly shorter (p < 0.0001) with the arm in external rotation than with the arm in internal rotation. The same results were observed when the shoulders were divided into those with initial dislocation and those with recurrent dislocation.

Discussion

Introduction | Materials and Methods | Results | Discussion | References

The present study is the first, as far as we know, to show that labral coaptation in vivo is affected by rotation of the arm and that external rotation increases the amount of coaptation compared with the coaptation achieved with the conventional position of internal rotation. These findings may help to explain the observation in previous studies that the recurrence rate does not depend on the method or the duration of immobilization after glenohumeral dislocation^3,4,6-9. In shoulders with recurrent anterior dislocation, the anteroinferior aspect of the labrum is often inverted and shifted medially. This seems to occur because the anterior part of the capsule is lax in internal rotation. As shown in Figures 4-A and 4-B, the anterior portion of the labrum shifts medially with the arm in internal rotation. The anterior soft-tissue structures are lax and appear to allow the labrum to displace. In external rotation, the subscapularis becomes tight and thereby closes the anterior joint cavity, bringing the labrum back to the glenoid rim.

The presence of a hematoma or joint effusion is another factor to be considered. The joint effusion usually resolves within three to seven weeks after dislocation¹³. Removing the hematoma from the glenohumeral joint cavity by arthroscopic lavage substantially reduces the rate of redislocation^16,17. Thus, it is likely that a hematoma compromises the healing of the Bankart lesion by pushing the anterior capsulolabral structures off the glenoid. While the hematoma can be removed from the glenohumeral joint by arthroscopic lavage, it is an invasive procedure performed under anesthesia. As shown in the present study, immobilizing the arm in external rotation is a noninvasive and cost-effective method to approximate the disrupted capsular structures.

In our study, we evaluated both shoulders with initial dislocation and those with recurrent dislocation. This approach may be criticized. However, the lesions that cause initial dislocation and recurrent dislocation are morphologically the same¹⁸. The fact that one-third of initial dislocations never recur and that one-fifth of recurrent dislocations stabilize spontaneously⁶ imply that these two entities may be not only morphologically similar but also biologically similar. In fact, separate analysis of the two entities revealed the same results as combined analysis, and we believe that combining the two types of dislocation did not affect the message of this study.

In terms of methodology, one might question how the imaging method affected the measurement. In general, quantitative errors in measurement are much smaller in spin-echo imaging than in gradient-echo imaging¹⁹. As we used only spin-echo and fast-spin-echo imaging, the effects of different imaging methods on the measurements seem negligible. We measured the diameter of the humeral head on both T1-weighted and T2-weighted images. The mean difference was 0.5 mm, which was 1% of the measured diameter. We believe that this value is small enough to validate the data.

In conclusion, treatment of anterior dislocation of the glenohumeral joint with immobilization of the arm in external rotation better approximates the Bankart lesion than does the conventional position of internal rotation.

References

Introduction | Materials and Methods | Results | Discussion | References

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Arciero RA; Wheeler JH; Ryan JB; and McBride JT: Arthroscopic Bankart repair versus nonoperative treatment for acute, initial anterior shoulder dislocations. Am J Sports Med,1994.22: 589-94, 22589 1994 [PubMed]

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Hoelen MA; Burgers AM; and Rozing PM: Prognosis of primary anterior shoulder dislocation in young adults. Arch Orthop Trauma Surg,1990.110: 51-4, 11051 1990 [PubMed]

Hovelius L; Eriksson K; Fredin H; Hagberg G; Hussenius A; Lind B; Thorling J; and Weckstrom J: Recurrences after initial dislocation of the shoulder. Results of a prospective study of treatment. J Bone Joint Surg Am,1983.65: 343-9, 65343 1983 [PubMed]

Hovelius L; Augustini BG; Fredin H; Johansson O; Norlin R; and Thorling J: Primary anterior dislocation of the shoulder in young patients. A ten-year prospective study. J Bone Joint Surg Am,1996.78: 1677-84, 781677 1996 [PubMed]

Marans HJ; Angel KR; Schemitsch EH; and Wedge JH: The fate of traumatic anterior dislocation of the shoulder in children. J Bone Joint Surg Am,1992.74: 1242-4, 741242 1992 [PubMed]

Rowe CR: Prognosis in dislocations of the shoulder. J Bone Joint Surg Am,1956.38: 957-77, 38957 1956 [PubMed]

Ryf C, and Matter P: The initial traumatic shoulder dislocation. Prospective study. Z Unfallchir Versicherungsmed,1993.Suppl 1: 204-12, GermanSuppl 1204 1993 [PubMed]

Vermeiren J; Handelberg F; Casteleyn PP; and Opdecam P: The rate of recurrence of traumatic anterior dislocation of the shoulder. A study of 154 cases and a review of the literature. Int Orthop,1993.17: 337-41, 17337 1993 [PubMed]

Wheeler JH; Ryan JB; Arciero RA; and Molinari RN: Arthroscopic versus nonoperative treatment of acute shoulder dislocations in young athletes. Arthroscopy,1989.5: 213-7, 5213 1989 [PubMed]

Itoi E; Hatakeyama Y; Urayama M; Pradhan RL; Kido T; and Sato K: Position of immobilization after dislocation of the shoulder. A cadaveric study. J Bone Joint Surg Am,1999.81: 385-90, 81385 1999 [PubMed]

Wintzell G; Hovelius L; Wikblad L; Saebo M; and Larsson S: Arthroscopic lavage speeds reduction in effusion in the glenohumeral joint after primary anterior shoulder dislocation: a controlled randomized ultrasound study. Knee Surg Sports Traumatol Arthrosc,2000.8: 56-60, 856 2000 [PubMed]

Sashi R; Terui M; Narita K; Hirano H; Tomura N; Watarai J; and Itoi E: Dual phased array coils for high-resolution MRI of the shoulder. Radiat Med,1997.15: 13-5, 1513 1997 [PubMed]

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Topics

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Fig. 1-B:: With the arm in external rotation, the anterior joint cavity is closed and the labrum lies against the glenoid rim (white arrow).

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TABLE I: Normalized Measurements of the Shoulders

*ND = labrum not detectable.

Case	External Rotation Angle of the Arm (deg)	Separation* (mm)		Displacement* (mm)		Detached Area (mm²)		Opening Angle (deg)		Detached Length (mm)
Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation
Shoulders with initial dislocation
1	35	0	0	?5.0	3.7	49.9	30.9	7.8	0.1	22.1	5.8
2	81	1.4	0	?7.1	0	302.2	28.9	38.3	13.6	30.6	29.8
3	47	5.7	4.3	?0	0	118.5	57.2	68.8	15.5	14.8	4.7
4	55	1.2	0	12.0	7.3	273.7	126.8	32.9	19.0	26.8	23.6
5	28	0	0	?0	—3.3	164.5	57.7	29.0	16.5	22.7	13.5
6	67	1.3	0	?—1.3	—1.9	59.6	26.5	12.0	1.3	18.3	4.7
Mean	52	1.6	0.7	?3.8	1.0	161.4	54.7	31.5	11.0	22.6	13.7
Standard deviation	20	2.1	1.7	?5.1	3.9	106.9	38.0	21.8	8.2	5.7	10.8
P value		0.0260	0.0527	0.0394	0.0325	0.0146
Shoulders with recurrent dislocation
? 7	60	1.7	1.7	?6.9	0	114.8	31.5	88.2	10.6	7.5	11.9
? 8	19	0	0	?3.2	0	145.6	45.2	26.3	19.0	21.8	5.9
? 9	36	1.2	0	?0	—1.2	246.8	85.8	66.4	12.6	13.3	6.9
10	19	ND	1.4	ND	—2.9	50.8	50.9	26.3	7.5	19.4	4.5
11	—15	—2.8	—4.3	?0	0	88.6	106.4	20.6	20.1	5.2	5.2
12	61	ND	—1.5	ND	0	432.2	28.9	29.2	2.1	11.8	3.3
13	20	—4	—3.4	?0	0	142.3	35.2	65.3	21.0	4.2	4.0
14	14	7.6	0	?0	—3.8	287.3	33.6	83.4	16.9	22.4	8.0
15	7	6.2	0	?0.4	0	61.3	8.7	121.4	42.0	8.4	2.8
16	47	0	0	?3.0	0	86.8	2.3	84.7	11.7	15.4	3.5
17	37	3.6	0	?0	0	89.6	87.2	35.5	8.9	15.5	3.4
18	8	5.6	1.4	?0	0	115.8	58.0	20.1	19.9	24.2	3.1
19	33	3.6	1.2	?9.6	1.2	133.3	26.3	37.2	21.2	39.5	31.0
Mean	27	2.1	—0.3	?2.1	—0.5	153.5	46.2	54.2	16.4	16.0	7.2
Standard deviation	21	3.7	1.8	?3.4	1.4	107.9	31.0	32.7	9.8	9.6	7.6
P value		0.0166	0.0223	0.0054	0.0006	0.0009
All shoulders
Mean	35	1.9	0.1	?2.7	0.0	156.0	48.8	47.0	14.7	18.1	9.2
Standard deviation	24	3.1	1.8	?4.0	2.4	104.6	32.6	31.1	9.4	9.0	9.0
P value		0.0047	0.0017	0.0003	<0.0001	<0.0001

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TABLE I: Normalized Measurements of the Shoulders

*ND = labrum not detectable.

Case	External Rotation Angle of the Arm (deg)	Separation* (mm)		Displacement* (mm)		Detached Area (mm²)		Opening Angle (deg)		Detached Length (mm)
Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation	Internal Rotation	External Rotation
Shoulders with initial dislocation
1	35	0	0	?5.0	3.7	49.9	30.9	7.8	0.1	22.1	5.8
2	81	1.4	0	?7.1	0	302.2	28.9	38.3	13.6	30.6	29.8
3	47	5.7	4.3	?0	0	118.5	57.2	68.8	15.5	14.8	4.7
4	55	1.2	0	12.0	7.3	273.7	126.8	32.9	19.0	26.8	23.6
5	28	0	0	?0	—3.3	164.5	57.7	29.0	16.5	22.7	13.5
6	67	1.3	0	?—1.3	—1.9	59.6	26.5	12.0	1.3	18.3	4.7
Mean	52	1.6	0.7	?3.8	1.0	161.4	54.7	31.5	11.0	22.6	13.7
Standard deviation	20	2.1	1.7	?5.1	3.9	106.9	38.0	21.8	8.2	5.7	10.8
P value		0.0260	0.0527	0.0394	0.0325	0.0146
Shoulders with recurrent dislocation
? 7	60	1.7	1.7	?6.9	0	114.8	31.5	88.2	10.6	7.5	11.9
? 8	19	0	0	?3.2	0	145.6	45.2	26.3	19.0	21.8	5.9
? 9	36	1.2	0	?0	—1.2	246.8	85.8	66.4	12.6	13.3	6.9
10	19	ND	1.4	ND	—2.9	50.8	50.9	26.3	7.5	19.4	4.5
11	—15	—2.8	—4.3	?0	0	88.6	106.4	20.6	20.1	5.2	5.2
12	61	ND	—1.5	ND	0	432.2	28.9	29.2	2.1	11.8	3.3
13	20	—4	—3.4	?0	0	142.3	35.2	65.3	21.0	4.2	4.0
14	14	7.6	0	?0	—3.8	287.3	33.6	83.4	16.9	22.4	8.0
15	7	6.2	0	?0.4	0	61.3	8.7	121.4	42.0	8.4	2.8
16	47	0	0	?3.0	0	86.8	2.3	84.7	11.7	15.4	3.5
17	37	3.6	0	?0	0	89.6	87.2	35.5	8.9	15.5	3.4
18	8	5.6	1.4	?0	0	115.8	58.0	20.1	19.9	24.2	3.1
19	33	3.6	1.2	?9.6	1.2	133.3	26.3	37.2	21.2	39.5	31.0
Mean	27	2.1	—0.3	?2.1	—0.5	153.5	46.2	54.2	16.4	16.0	7.2
Standard deviation	21	3.7	1.8	?3.4	1.4	107.9	31.0	32.7	9.8	9.6	7.6
P value		0.0166	0.0223	0.0054	0.0006	0.0009
All shoulders
Mean	35	1.9	0.1	?2.7	0.0	156.0	48.8	47.0	14.7	18.1	9.2
Standard deviation	24	3.1	1.8	?4.0	2.4	104.6	32.6	31.1	9.4	9.0	9.0
P value		0.0047	0.0017	0.0003	<0.0001	<0.0001