1. INTRODUCTION:

Although the shoulder joint has a wide range of motion for our body to make big and delicate movements, it has low stability because it consists of a shallow labrum between acromion and humeral head1. In the anatomic structure of the shoulder joint, humerus, scapula, clavicle, and sternum exists, and within the subacromial space formed by the scapula and humerus exists the subacromial bursa, supraspinatus tendon, and capsular ligament.

Within the subacromial space, there are the tendons of the rotator cuff muscles, and as a boundary part between the coracoacromial arch and the humeral head, it is composed of complex structures2.

Shoulder joints with complex structures have the annual damage occurrence rate of 20%-50%. The causes of the damage are age, gender, occupation, repetitive work, and changes in posture3-5. The damages of the shoulder joint includes the damage of the rotator cuff muscle, bursitis, shoulder impingement syndrome, and tendinosis, and among them, the rotator cuff muscle damage is the most frequent6,7. The rotator cuff muscle can be divided into partial rupture and complete rupture, and often the partial rupture is reported to cause more pain compared to complete rupture8, and it was reported that the patients with the rotator cuff muscle reported higher pain in the abduction of shoulder joint9. The patients with the shoulder damaged, in abduction, the subacromial space decreases to cause pain due to the pressurization of the rotator cuff muscle10-12. The physiological damages of the rotator muscle occurs frequently in the injuries of the supraspinatus and in overuse, and the pathological status of the rotator cuff is the result of the possibility of collision in the acromion and the result of the humeral head moving upward, and the rotator cuff muscle is pressurized to cause damages to the muscle13. Also, the collision syndrome of the shoulder is caused from the sack beneath the acromion between the coracoacromial arch and the humerus being rubbed, or the rotator muscle being jammed, leading to the damages of the coraco- acromial ligament14. Such collision syndromes weaken the shoulder muscle, and causes pain and decrease of range of motion leading to difficulties in daily life15. The subacromial space distance is related to scapula movement and posture16. On the other hand, an abnormal abduction of the shoulder joint, from a kinematics perspective, is the cause of a pain in the shoulder joint17-19.

Thomspon et al (2011) conducted the research regarding the decrease of the subacromial space regarding the abduction degree of the shoulder joint in radiography of the subacromial space in shoulder joints, and argued that according to the pressure of the hand, the value of the distance of the subacromial space differed20. Escamilla et al (2009) researched the changes of muscle activation according to the degree of the shoulder joint. They argued that among the muscles, the muscle activation of deltoid increased21. While previous researches measured the subacromial space based on loading amount and angle, researches on interaction between loading amount and angle are still insufficient. Therefore, this study intends to find out, targeting those with an intact shoulder joint, the effect that a change in the shoulder joint abduction angle and load has on the subacromial space.

2. MATERIALS AND METHODS:

2.1. Research subject:

The subjects of this research were the students of S University at Asan, Chungnam. Plenty of education regarding the research purposes and methods were conducted before the experiment. The research subjects were those who had agreed to research participation, and healthy 20s who had no disorders of the neck bone, shoulder, the musculoskeletal diseases or neural diseases in the past, those who show the abduction of the shoulder joint of 90° or more, and do not complain the pain of the cervical, shoulder and upper extremity. This research was approved by the ethical board of the IRB(Institutional Review Board). The overall research process is as [Figure 1]. Also, total of 30 research subjects were selected by utilizing G*Power3.1, and the general characteristics of the research subjects areas [Table 1].

Figure 1. Research process

Table 1. General characteristics (n=30)

Characteristic	Male
Age (years)	21.33 ± 1.51a
Height (cm)	174.70 ± 5.37
Weight (kg)	68.73 ± 7.88
amean ± standard deviation

2.2. Measurement method:

Before the research, the research subjects were measured of their height and weight by utilizing the automatic BMI measuring stadiometer (BSM 370, Korea, 2011). Sitting on a chair, the participants were told to bend their knee joint and hip joint at 90 degrees and keep their feet touching the ground. Those whose feet did not reach the floor were provided with a stool. Also, by providing them with chairs with backrests, they were fixed in a state with their backs against the backrest. The research subjects were measured in the state of how they normally sit, with stress in their hands, and the stress amount was set as 0lb, 2lb, and 4lb. The scapula head of the subjects were was measured through abduction from the side of the shoulder with the 30°∼40° retroversion regarding the line connected to the epicondyle of the scapula [Figure 2]. To see the subacromial space, using ultrasonic waves, the arm abduction angle was set at 0°, 30°, 60° and 90° in a scaption posture. In measurement of the subject group, while maintaining the stable posture, ultrasonic wave was utilized to measure the distance of the subacromial space of the major band. At this point, random experiment was conducted regarding the stress and degree in experimentation for the research subjects [Figure 3]. After measuring the distance of the subacromial space, the subjects rested for 5 minutes in sitting position, and after resting, they conducted the remainder of the experiment in the same method.

Figure 2. Retroversion of research subjects have loading.

Figure 3. The shoulder angle when the participant have loading.

A: shoulder abduction angle 0°

B: shoulder abduction angle 30°

C: shoulder abduction angle 60°

D: shoulder abduction angle 90°

2.3. Research measurement equipment and measured body part:

In measurement of the shoulder joint’s abduction degree, digital goniometer (digital absolute+axisTM goniometer, USA, 2008) was utilized, and to measure the distance of the subacromial space, ultrasonography (eZono3000, Germany, 2011) was used, and the frequency was 7-10MHz, and after fixing the image depthes 3cm, the measurement was made in B-mode. In the measurement, the position of the probe was linear in the flat part near the acromion between the acromion and the humerus, slightly backward from the upper middle part of the acromion. Here, in the ultrasonic imaging, the distance of the subacromial space was calculated as the vertical distance from the acromion and the humerus head[Figure 4].

A B

Figure 4. Research equipment and measurement

A : position of the ultra sonography probe B : acromiohumeral distance and structure acromiohumeral distance (AHD), acromion (A, humeral head(H), supraspinatus(SSP)

2.4. Analysis method:

All the measured values were calculated through SPSS/PC ver.22.0 for windows program (SPSS INC. Chicago. IL). the research participants used a two-way repeated ANOVA to find out the differences in the subacromial space distance. Also, to find out the difference between each variable, Bonferroni test was conducted. For every statistical verification, the significance level was set as p<.05.

3. RESULTS AND DISCUSSION:

3.1. The interaction between loading and angle

The subacromial space distances seen when 0lb, 2lb or 4lb of loading amount was applied depending on the shoulder joint abduction angle of 0°, 30°, 60° or 90° are presented in [Table 2] and as provided in [Figure 5], interaction between the abduction angles and loading amounts was shown.

Figure 5. The interaction between loading and angle

amean(mm) ± standard deviation, *p<.05

3.2 The changes of the subacromial space according to loading:

As suggested in [Table 3] in the experiment measurement, the subacromial space according to the amount of stress was measured as 8.41mm in 0lb, 7.93mm in 2lb, and 7.66mm in 4lb. The change in the subacromial space depending on the loading amount showed a significant difference (p<.05) between 0lb and 2lb and also between 0lb and 4lb (p<.05). On the other hand, there was no significant difference between 2lb and 4lb (p>.05) [Figure 6].

Figure 6. The changes of the subacromial space according to loading.

Table 3. Subacromial space according to loading

loading (lb)	subacromial space (mm)
0	8.41 ± 1.95a
2	7.93 ± 2.27
4	7.66 ± 2.61
F	14.19*
amean ± standard deviation, *p<.05

3.3 The Changes of subacromial space according to the abduction angle of the shoulder joint:

As suggested in [Table 4] in the experiment measurement, the distance of the subacromial space by the shoulder joint was measured to be 11.27mm in 0°, 7.77mm in 30°, 6.76mm in 60°, and 6.20mm in 90°. There were significant differences in the post-hoc results. As presented in Figure 7, the change in the subacromial space distance depending on the shoulder joint abduction angle showed a significant difference between 0° and 30°, 0° and 60°, 0° and 90°, 30° and 60°, 30° and 90° and 60° and 90° (p<.05) [Figure 7].

Table 4. Subacromial space according to the abduction angle of the shoulder joint

Abduction angle of shoulder joint (°)	Subacromial space (mm)
0	11.27 ± 1.32a
30	7.77 ± 1.39
60	6.76 ± 1.11
90	6.20 ± 0.92
F	377.17*
amean ± standard deviation, *p<.05

Figure 7. The Changes of subacromial space according to the abduction angle of the shoulder joint

3.4. DISCUSSION:

The acromion humeral distance is considered to be the three-dimensional space within the human body22. Conversely, the radiography is only feasible in two-dimensional space. In measurement of the acromion humeral distance, as another difference of radiography, the process of changing the posture of the patient is difficult, and also leads to the direct exposure to radiation23, 24. On the other hand, the ultrasonic wave measurement of the acromion humeral distance has the same basis (=.77~.85) 25. Also, the ultrasonic waves do not use special electric coils or imaging, and is able to gain high-quality images without wide space, with low costs, fast diagnosis, and also enabling various postures and images17, 26, 27. Dawes et al (2014) suggested musculoskeletal ultrasonography to cure the sports-related hip joint damages, and Peterson et al (2014) made the conclusion that ultrasonic waves are useful in determining the injuries of the hamstring muscles of the soccer players28. Beekman et al (2003) insisted that the interest regarding the diagnosis of the wrist tunnel syndrome utilizing ultrasonic wave diagnosis machinery is increasing29, supporting the basis for the usefulness of the ultrasonic waves. Therefore, in this research, based on the ultrasonic wave validated of its objectiveness, subacromial space was researched.

In this study, interaction values between shoulder joint abduction angles and loading amounts were significantly measured in a scaption condition. By researching whether the amount of stress reciprocally leads to the decrease of subacromial space, measurements were made with ultrasonic wave imaging machinery. At 0°, the values of 0lb, 2lb, and 4 lb are respectively 10.9mm, 11.24mm, and 11.68mm, and at 30°, the values of 0lb, 2lb and 4 lb are 8.64, 7.72mm, and 6.94mm, and in the abduction of 60°, the value of 0lb, 2lb and 4lb were measured as 7.37mm, 6.67mm, and 6.26mm. Also, in the abduction of 90°, the values of 0lb, 2lb, and 4lb were calculated to be 6.75mm, 6.09mm, and 5.75mm, all showing significant differences. Neumann (2010) suggested that the size of the internal torque and the external torque are identical, and that the void of the rotation movement of the joint is the static rotation parallel1. When the loading amount of 2lb or 4lb is applied onto the hand at 0°, due to the influence of gravity, which is classified as an external force, the subacromial space distance increases than when a loading amount is not applied. On the other hand, when the loading amount of 2lb or 4lb is applied onto the hand in a posture where the shoulder joint abducts at 30°, 60° or 90°, the external torque acting on the area of the hand where the loading amount was applied increases. Therefore, the deltoid that generates internal torque acting on the shoulder joint relatively maintains each angle of the shoulder joint and since static torque equilibrium occurs, the subacromial space distance decreases I believe.

Peter et al (2010) mentioned that as the external torque increases in the shoulder side posture, the muscle activation of the frontal/middle deltoid increases30 and according to the research of Jang et al (2012), when the abduction degree of the shoulder joint is 90°, the value of muscle activation according to the frontal/back deltoid was significantly observed31. Scott et al (2000) expressed the maximum weight that the subjects could hold in proportion (0%, 25%, 50%, 75%, and 90%) in the abduction of the shoulder joint in the shoulder side posture of the research subjects to observe that as the maximum weight changes, the muscle activation of the deltoid increased, and the abduction of the shoulder joint between 0° and 30° increased the muscle activation of the supraspinatus muscle and the infraspinatus muscle, yet in the shoulder joint abduction beyond 30°, the muscle activation of the deltoid was increased32. Also, Graichen et al (2005) observed the muscle activation of the muscles working on the abduction when the shoulder joints are abducted, and the highest muscle activation was shown in the first 30°, and when the muscle activation of the shoulder joint muscle is increased, the humerus head was observed to move 6mm-18mm in the upper direction22. This study suggests that muscle activity increases due to an increase in the amount of load acting on the shoulder joint and that because of this, the subacromial space distance decreases.

In this research, the value of subacromial space of the stress (0lb, 2lb, 4lb) were calculated to be 8.41mm, 7.93mm, and 7.66mm, having significant values between 0lb and 2lb, 0lb and 4lb. However, there were no significant values between 2lb and 4lb, and this is believed to be because the extent of muscle contraction and the value of muscle vitalization were not even for the each subjects. However, in the stress of the 2lb and 4lb, the figures decreased in subacromial space. Also, the value of the abduction degree(0°, 30°, 60°, 90°) of the shoulder joint were calculated to be 11.27mm, 7.77mm, 6.76mm and 6.20mm, and significant differences in all values existed in subacromial space according to the abduction degree of the shoulder joint (0°, 30°, 60°, 90°).

Silva et al (2010) ascertained that when the shoulder joint is abducted from 0° to 60°, the value at 60° decreased from value at 0° by 1.38mm in the subacromial space33, and Thomson et al (2011) suggested that the distance of the subacromial space decreased as the abduction degree(0°, 30°, 45°, 60°) of the shoulder joint increased20. Want et al (2013) insisted that when the shoulder joint was abducted from 0° to 90° in the shoulder side posture decreased the subacromial space25.

When the shoulder joint is abducted from 0° to 30°, the subacromial space is said to decrease from the upper rotation of the scapula34. When the humerus is abducted beyond 30°, the abduction of the glenohumeral joint and the upper rotation of the interscapulothoracic joint are lapse12. In this experiment, among the abduction degree of the shoulder joint (0°, 30°, 60°, 90°), between 0° and 30°, there was a 3.5mm difference with the sole movement of the humerus, and between 30° and 60°, there was a 0.99mm difference, and 0.56mm difference between 60°and 90°. Compared to the shoulder joint abduction angle between 0° and 30°, the subacromial space distance value was observed to be smaller between 30° and 60° and 60° and 90°. This I believe is because after the shoulder joint abducted at 30°, abduction occurred at the ratio of 1 to 2 due to the scapulohumeral rhythm. Conclusively, the largest decrease of the subacromial space exists between the 0°and 30° of the shoulder joint, deducting the equal result as the prior studies. Therefore, in the measurement of the subacromial space of this experiment, there were gradual differences of the subacromial space according to the various degrees (0°, 30°, 60°, 90°) of the shoulder joint that this research ascertained that the various degrees may affect the subacromial space.

The limitations of this research is that the subjects of the experiment were limited to the healthy men that there were differences in comparison with the subacromial space of the healthy women, and because the subjects were 30 men that the number was small to generalize. Also, only because the shoulder joint of the major hand was conducted of experiment, there were difficulties in ascertaining the difference with the non-major side. Also, by utilizing only the ultrasonic wave diagnosing equipment, there were limitations to explaining the muscle vitalization and the scapulohumeral rhythm mentioned in this research. Thus, the future subacromial space would need the complementation of such limitations.

5. CONCLUSION:

According to the results of this research, when the abduction degree and the stress of the shoulder joint increases, the subacromial space due to the interaction may decrease even further. In this experiment, a remarkable change in the subacromial space distance was shown and it is considered that this result will serve as important basic data for preventing muscular skeletal diseases in the shoulder joint.

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Received on 22.06.2017 Modified on 23.07.2017

Research J. Pharm. and Tech. 2017; 10(8): 2650-2656.

DOI: 10.5958/0974-360X.2017.00471.1

Abduction angle of shoulder joint (°)		loading		F
Abduction angle of shoulder joint (°)	0lb	2lb	4lb	*loadingangle**	loading	angle
0	10.90 ± 1.09a	11.24 ±1.29	11.68 ± 1.48	6.91*	14.19*	377.17*
30	8.64 ± 1.30	7.72 ± 1.18	6.94 ± 1.17
60	7.37 ± 1.19	6.67 ± 0.95	6.26 ± 0.92
90	6.75 ± 0.93	6.09 ± 0.83	5.75 ± 0.71

The comparison of the Subacromial Space according to the difference conditions