Sage Journals: Discover world-class research

Abstract

Background:

Excessive external rotation of the glenohumeral joint during the late cocking phase of throwing is a factor in internal impingement; however, the relationship between maximum external rotation (MER) of the glenohumeral joint and morphological changes in the shoulder joint is unclear.

Purpose:

To clarify whether glenohumeral MER is associated with quantified assessment of morphological changes in the throwing shoulder joint.

Study Design:

Descriptive laboratory study.

Methods:

This study included 15 male university and adult baseball players from a competitive team. The posterior glenohumeral distance (mm) and area of impingement (mm²), reflecting morphological changes in the shoulder joint, were measured using open magnetic resonance imaging. The percent posterior glenohumeral distance (%PGHD) and percent area of impingement (%AOI) were calculated as these values of the throwing shoulder divided by those of the nonthrowing shoulder. With a 3-dimensional motion analysis system, bar markers were affixed to the acromion and humerus, and the glenohumeral MER angle was measured.

Results:

Simple linear regression analysis revealed that the glenohumeral MER angle was associated with the %PGHD (β coefficient = 0.685; P = .005) and %AOI (β coefficient = 0.754; P = .001).

Conclusion:

The glenohumeral MER angle was associated with the %PGHD and %AOI, which reflects morphological shoulder-joint changes.

Clinical Relevance:

Assessment of excessive external rotation of the glenohumeral joint during the late cocking phase contributes to the understanding of morphological changes in the shoulder joint and related throwing injuries.

Keywords

posterior glenohumeral distance rotator cuff impingement throwing shoulder joint internal impingement baseball player

The late cocking phase of the throwing motion leads to a maximum external rotation (MER) of the glenohumeral joints.^26,27 Internal impingement occurs as a result of the contact between the posterior glenoid rim and the humeral greater tuberosity^{‖ ‖} and causes posterior labral lesions, humeral head cysts, and rotator cuff tears, which result in throwing shoulder disabilities.^{2,3,14,15,19,22,37} Excessive shoulder external rotation during the late cocking phase represents the most common mechanism underlying the development of internal impingement.^17,19,24,32 Therefore, accurate measurement of the glenohumeral MER angle during the late cocking phase is crucial for understanding internal impingement. With respect to the shoulder-joint position during the late cocking phase, previous studies using a 3-dimensional motion analysis system have reported approximately 90° of abduction, with 145° to 180° of external rotation of the shoulder.^5-7,30,33 Miyashita et al^26,27 were concerned that this measurement method was a shoulder-joint complex that included posterior tilt of the scapula and thoracic extension, and that it did not reflect the MER angle identified for the glenohumeral joint. Thus, a new method was developed to measure the glenohumeral MER angle using a bar with markers at both ends in the acromion and distal humerus, and it was reported to be reliable and valid.

Additionally, cadaveric studies have shown that contact pressure and strain in the joint are associated with an increase in the external rotation angle of the glenohumeral joint.^24,32 Nevertheless, because the subject of these studies was a cadaver, the association between the external rotation motion of the shoulder during the late cocking phase and the morphological changes caused by internal impingement has not been clarified.^10,38 As repeated microtrauma to musculoskeletal structures contributes to throwing shoulder disabilities,⁴ Takahashi et al^34,35 used open magnetic resonance imaging (MRI) to determine the posterior glenohumeral distance, defined as morphological changes in the posterior glenoid rim, and focused on the area of the rotator cuff inserted between the humeral greater tuberosity and the posterior glenoid rim. However, the association between morphological changes in the shoulder joint and the MER of the glenohumeral joint angle during the late cocking phase has not been determined. Clarifying the association between morphological changes in the shoulder joint and the glenohumeral MER angle during the late cocking phase is important to understand internal impingement.

Therefore, the present study aimed to investigate whether the glenohumeral MER angle is associated with morphological changes in the shoulder joint. The results of the present study may contribute to the establishment of evidence-based treatment strategies for internal impingement, which relates to throwing shoulder disabilities. We hypothesized that an increase in the glenohumeral MER angle during the late cocking phase would be associated with morphological shoulder-joint changes.

Methods

The study team for this laboratory study was formed between 2021 and 2023.

Participants

Data were collected from September 2022 to May 2023. The inclusion criteria were as follows: university baseball players or adult baseball players who have played university baseball and belong to a competition-level team. The exclusion criteria were previous shoulder surgery and shoulder pain during measurement in this study.

The present study was conducted in accordance with the ethical guidelines and regulations of the Declaration of Helsinki, and the study protocol was approved by the Ethics Committee of the Ibaraki Prefectural University of Health Sciences (approval No. 1041). Written informed consent was obtained from all participants for their inclusion in the study.

Imaging Examination

MRI was performed using a 0.3-T whole-body MRI scanner (AIRIS Vento; Fujifilm Medical Ltd). The imaging conditions were as follows: T2* with gradient echo, horizontal section centered on the glenohumeral joint, and 90°, 100°, and 110° of external rotation from a 90° of abduction of the shoulder-joint position to simulate the late cocking phase.³⁴ Because the 110° of external rotation position was difficult to maintain for the nonthrowing shoulder, the range of motion (ROM) was not obtained and only the 90° and 100° of external rotation positions were assessed. A 10° or 20° tilt board was used to set the shoulder external rotation angle, and 2 examiners (M.M. and M.T.) changed the shoulder external rotation positions to prevent changes in the imaging section.

To achieve approximate shoulder-joint position in the late cocking phase, MRI values were evaluated on the basis of the external rotation ROM of the nonthrowing shoulder to determine the 90° or 100° of external rotation measurement position. Thus, nonthrowing shoulder-joint external rotation ROM <95° was measured at a 90° of external rotation position and external rotation ROM ≥95° was measured at a 100° of external rotation position. Additionally, the measurement position was fixed with a belt to prevent compensatory motion of the scapulothoracic joint and thoracic vertebrae.

Posterior Glenohumeral Distance of the Throwing Shoulder Normalized by That of the Nonthrowing Shoulder

The posterior glenohumeral distance was defined depending on the measurement method: (1) measurement of the posterior glenohumeral distance of the noncorresponding side-to-side limbs at the same external rotation angle quantified morphological changes in the posterior glenoid rim of the throwing shoulder, and (2) measurement of the corresponding ipsilateral limb at different external rotation angles quantified the interosseous proximity of glenohumeral joint alignment changes associated with internal impingement. The posterior glenohumeral distance had an intraclass correlation coefficient (ICC[1,2]) of 0.942 (95% CI, 0.912-0.962) for intraexaminer reliability (Figure 1A).³⁵

Figure 1.

Methods for measuring the posterior glenohumeral distance (mm) and area of impingement (mm²). (A) Posterior glenohumeral distance: draw a line from the anterior to posterior glenoid rim (a) and a vertical line from the posterior glenoid rim to the humeral head (b), and measure the distance from the posterior glenoid rim to the humeral head (a-b). (B) Area of impingement): determine the area of the triangle connecting the posterior glenoid rim (a’), humeral greater tuberosity (b’), and rotator cuff depth (c’).

With respect to the first definition of this measurement, the percent posterior glenohumeral distance (%PGHD) was calculated as the posterior glenohumeral distance value of the throwing shoulder divided by that of the nonthrowing shoulder (%PGHD = posterior glenohumeral distance of the throwing shoulder/posterior glenohumeral distance of the nonthrowing shoulder × 100). A %PGHD >100% indicates a greater expansion of posterior interosseous distance of the throwing shoulder than that of the nonthrowing shoulder.

Area of Impingement of the Throwing Shoulder Normalized by That of the Nonthrowing Shoulder

The area of impingement was measured as the rotator cuff tendon area depicted by a low signal between the humeral greater tuberosity and the posterior glenoid rim. The area of impingement was defined depending on the measurement method: (1) measurement of the area of impingement of the noncorresponding side-to-side limbs at the same external rotation angle quantified the degreed of insertion of the rotator cuff tendon in the throwing shoulder, and (2) measurement of the corresponding ipsilateral limb at different external rotation angles quantified the degree of compression of rotator cuff tendons involved in internal impingement. The area of impingement had an ICC(1,2) of 0.925 (95% CI, 0.876-0.955) for intraexaminer reliability (Figure 1B).³⁴

With respect to the first definition of this measurement, the percent area of impingement (%AOI) was calculated as the area of impingement value of the throwing shoulder divided by the area of impingement value of the nonthrowing shoulder (%AOI = area of impingement of the throwing shoulder/area of impingement of the nonthrowing shoulder × 100). A %AOI >100% indicated a large side-to-side difference in morphological changes in the shoulder joint and a greater insertion of the rotator cuff tendon in the throwing shoulder.

Glenohumeral Joint and Shoulder-Joint MER Angles During the Late Cocking Phase

Three-dimensional motion analysis was performed using an 8-camera VICON system (Oxford Metrics Ltd) at a sampling frequency of 200 Hz. On the basis of methods reported by Miyashita et al,^26,27 bars with markers at both ends were affixed to the acromion process, dorsal humerus, and dorsal forearm of the throwing side. Moreover, 7 other markers were affixed to the acromion process of the nonthrowing side, C7 spinous process, Th8 spinous process, L1 spinous process, sternum, and posterior superior iliac spine (Figure 2A). Pitching plates were set up indoors on an artificial turf, and full-effort throws were made 3 times to a target located 5 m away. In accordance with previous studies,^26,27 the throw perceived by the player as the most accurate one was used to determine the representative values for the glenohumeral and shoulder MER angles. Three high-speed cameras were used for the throws and were synchronized with the VICON motion system using a trigger. Motion data were analyzed using VICON Nexus software (Version 2.0.1; VICON Motion Systems Ltd), and coordinate axes were obtained using Excel (Microsoft) data.

Figure 2.

Marker attachment position and neutral position. (A) Marker attachments required for the maximum external rotation (MER) angle: the glenohumeral MER angle was calculated using the acromion bar and humerus bar, and the shoulder MER angle was calculated using the L1, acromion, humerus, and forearm bar midpoints. (B) Neutral position: shoulder joint at 90° of abduction and 0° of rotation.

The glenohumeral MER angle was calculated as the normal vector from (1) the 3-point coordinate axes of the acromion bars (2 anterior and posterior) and humerus bar (1 lateral) and (2) the 3-point coordinate axes of the humerus bars (2 medial and lateral) and acromion bar (1 posterior). The shoulder MER angle was calculated as the normal vector from (1) the 3-point coordinate axes of L1, acromion bar midpoint, and humerus bar midpoint and (2) the 3-point coordinate axes of the humerus bar midpoint, forearm bar midpoint, and acromion bar midpoint. The MER angle was calculated by determining the inner product of these calculated normal vectors, and the angle between 2 planes was calculated from the cosine of these vectors. Additionally, the glenohumeral and shoulder MER angles were estimated using the normalized neutral position at 90° of abduction and 0° of rotation of the shoulder joint (Figure 2B). One examiner (M.T.) securely affixed the markers so that accurate data could be collected, even with a quick throwing motion.

Physical Assessment

An examiner measured the external and internal rotations, and horizontal flexion passive ROM in the supine position. External rotation gain was calculated as the external rotation of the throwing shoulder minus the external rotation of the nonthrowing shoulder, with higher values indicating more anterior shoulder laxity.^3,24,28 Glenohumeral internal rotation deficit was calculated as the internal rotation of the nonthrowing shoulder minus the internal rotation of the throwing shoulder, with higher values indicating posterior shoulder tightness.^{3,11,13,20,24,28} Horizontal flexion deficit was calculated as the horizontal flexion of the nonthrowing shoulder minus the horizontal flexion of the throwing shoulder, with higher values indicating posterior shoulder tightness.^14,28

Statistical Analysis

A simple linear regression analysis was conducted to identify factors contributing to morphological changes in the shoulder joint, with the %PGHD and %AOI as the dependent variables and age, height, weight, body mass index, years of competition, external rotation gain, glenohumeral internal rotation deficit, horizontal flexion deficit, glenohumeral MER angle, and shoulder MER angle as the independent variables. Additionally, to clarify the state of proximity of the humeral head to the posterior glenoid rim with increasing shoulder external rotation, comparison of the posterior glenohumeral distances in the throwing shoulder at external rotation angles of 90°, 100°, and 110° was performed using a 1-way repeated-measures analysis of variance and subsequently a Bonferroni multiple comparison test. The posterior glenohumeral distances in the nonthrowing shoulder at external rotation angle of 90° and 100° was compared using a dependent t-test. Finally, the intraobserver reliabilities of the glenohumeral and shoulder MER angle were determined between the most and second accurate throws using the ICC.

Power analysis for the 1-way analysis of variance was conducted using G*Power software (Heinrich Heine University, Germany). With an alpha level of .05 and effect size f of 0.48, a sample size of 45 shoulders (15 participants in each external rotation position) was deemed to be sufficient to achieve a statistical power of 0.80. In the power analysis of the simple linear regression analysis, 13 research participants were required to obtain a statistical power of 0.8 when α and effect size f² were set to .05 and 0.8, respectively. Statistical analyses were performed using SPSS Statistics (Version 29.0.2; IBM Corp) with a significance level of 5%.

Results

The participants were 15 male baseball players (right dominant, 15; shoulder joints, 30) who did not have throwing pain and belonged to a competition-level university baseball team (n = 12) or the top-prefecture-level adult baseball team (n = 3) of the Japan Amateur Baseball Association. Participants had a mean age of 20.5 ± 1.6 years, height of 173.7 ± 3.1 cm, weight of 71.5 ± 6.9 kg, body mass index of 23.7 ± 2.0 kg/m², baseball experience of 12.1 ± 2.7 years, and practice frequency of 4.4 ± 1.8 practices per week. There were 5 pitchers, 2 catchers, and 8 fielders.

The study participants had a mean representative %PGHD of 178% ± 60%, %AOI of 236% ± 106%, external rotation gain of 18.0°± 10.8°, glenohumeral internal rotation deficit of 21.1°± 6.7°, and horizontal flexion deficit of 7.8°± 5.1°. Details of each parameter for pitchers and fielders are shown in Table 1.

Table 1

Breakdown of Each Parameter in Pitchers and Fielders

	Pitchers (n = 5)		Catchers and Fielders (n = 10)
	Mean	SD	Mean	SD
Age, y	20.4	1.4	20.5	1.7
Height, cm	173.4	1.9	174.0	3.5
Weight, kg	71.8	7.8	72.6	6.9
Body mass index, kg/m²	23.9	2.4	24.0	1.9
Years of competition	12.0	0.9	12.3	3.4
External rotation gain, deg	18.2	5.2	22.7	6.4
Glenohumeral internal rotation deficit, deg	19.2	12.4	16.2	9.6
Horizontal flexion deficit, deg	5.6	5.2	8.1	4.9
% posterior glenohumeral distance	225.2	60.2	163.0	50.7
% area of impingement	307.6	106.3	215.0	94.6
Glenohumeral maximum external rotation, deg	100.6	9.6	98.6	10.6
Shoulder maximum external rotation, deg	139.9	15.9	144.7	14.9

Simple linear regression analysis revealed that the glenohumeral MER angle (β coefficient = 0.685; P = .005) and glenohumeral internal rotation deficit (β coefficient = −0.583; P = .022) were the factors associated with the %PGHD (Table 2), and that the glenohumeral MER angle (β coefficient = 0.754; P = .001), glenohumeral internal rotation deficit (β coefficient = −0.623; P = .013), and external rotation gain (β coefficient = −0.551; P = .033) were the factors associated with the %AOI (Table 3).

Table 2

Simple Linear Regression With Percent Posterior Glenohumeral Distance as the Dependent Variable ^a

Independent Variable	B Coefficient	95% CI		β Coefficient	P Value	R ²	f ²
Independent Variable	B Coefficient	Lower	Upper	β Coefficient	P Value	R ²	f ²
Age, y	−0.085	−0.295	0.125	−0.236	.396
Height, cm	−0.032	−0.146	0.082	−0.162	.559
Weight, kg	−0.022	−0.075	0.030	−0.247	.375
Body mass index, kg/m²	−0.065	−0.250	0.116	−0.214	.445
Years of competition	0.012	−0.111	0.134	0.058	.838
ERG, deg	−0.029	−0.059	0.000	−0.508	.053
GIRD, deg	−0.054	−0.099	−0.009	−0.583	.022 ^b	0.34	0.52
HF deficit, deg	−0.010	−0.084	0.063	−0.085	.762
Glenohumeral MER, deg	0.039	0.014	0.063	0.685	.005 ^c	0.47	0.88
Shoulder MER, deg	−0.002	−0.030	0.026	−0.047	.869

ERG, external rotation gain; GIRD, glenohumeral internal rotation deficit; HF, horizontal flexion; MER, maximum external rotation.

P < .05.

P < .01.

Table 3

Simple Linear Regression With Percent Area of Impingement as the Dependent Variable ^a

Independent Variable	B Coefficient	95% CI		β Coefficient	P Value	R ²	f ²
Independent Variable	B Coefficient	Lower	Upper	β Coefficient	P Value	R ²	f ²
Age, y	−0.194	−0.558	0.169	−0.305	.269
Height, cm	−0.051	−0.253	0.150	−0.151	.591
Weight, kg	−0.059	−0.148	0.031	−0.365	.181
Body mass index, kg/m²	−0.196	−0.505	0.114	−0.355	.195
Years of competition	−0.023	−0.239	0.193	−0.063	.823
ERG, deg	−0.056	−0107	−0.005	−0.551	.033 ^b	0.30	0.44
GIRD, deg	−0.102	−0.178	−0.025	−0.623	.013 ^b	0.34	0.52
HF deficit, deg	0.013	−0.117	0.142	0.058	.837
Glenohumeral MER, deg	0.075	0.036	0.114	0.754	.001 ^c	0.57	1.32
Shoulder MER, deg	−0.005	−0.054	0.044	−0.062	.827

ERG, external rotation gain; GIRD, glenohumeral internal rotation deficit; HF, horizontal flexion; MER, maximum external rotation.

P < .05.

P < .01.

A comparison of the posterior glenohumeral distance for the throwing shoulder angles (Table 4) revealed that the posterior glenohumeral distance was significantly lower in the 110° of external rotation position (5.3 mm) than in the 90° of external rotation position (6.7 mm) (P = .011). Additionally, the area of impingement was significantly lower in the 110° of external rotation position (21.0 mm²) than in the 90° of external rotation position (27.6 mm²) (P = .012). In contrast, a comparison of the posterior glenohumeral distance and area of impingement for the nonthrowing shoulder in the 90° and 100° of external rotation positions showed no significant difference (P > .05).

Table 4

Comparison of the PGHD (mm) and AOI (mm²) in the Throwing and Nonthrowing Shoulder ER Positions ^a

Variable	ER Imaging Position, deg	Throwing Shoulder			Nonthrowing Shoulder
Variable	ER Imaging Position, deg	Mean (SD)	P Value	Effect Size, f	Mean (SD)	P Value	Effect Size, d
PGHD	90	6.7 (1.2) ^b	.013 ^d	0.49	4.0 (1.2)	.052	0.62
	100	6.0 (1.1)			6.0 (1.1)	.052	0.62
	110	5.3 (1.1) ^b
AOI	90	27.6 (6.1) ^c	.004 ^e	0.48	13.5 (6.8)	.063	0.58
	100	23.9 (5.8)			12.8 (6.2)	.063	0.58
	110	21.0 (5.6) ^c

PGHD, posterior glenohumeral distance; AOI, area of impingement; ER, external rotation.

PGHD in the 110° of ER position is significantly lower than that in the 90° of ER position (P = .011).

AOI in the 110° of ER position is significantly lower than that in the 90° of ER position (P = .012).

P < .05.

P < .01.

The ICC(1,2) values of the glenohumeral and shoulder MER angles were 0.979 (95% CI, 0.942-0.993) and 0.815 (95% CI, 0.545-0.933), respectively. The qualitative evaluation of kinematic data from stride foot contact to ball release, normalized at 100%, showed almost the same results as a previous study (Figure 3).²⁶

Figure 3.

Glenohumeral and shoulder MER angles. GH, glenohumeral; MER, maximum external rotation; REL, ball release; SFC, stride foot contact; SH, shoulder.

Discussion

This study was designed to determine the effects of glenohumeral and shoulder MER on quantified morphological shoulder-joint changes in baseball players, which had not been investigated in previous studies. We hypothesized that the glenohumeral MER angle might be associated with morphological shoulder-joint changes, and the present study's findings confirmed this hypothesis.

Simple linear regression analysis showed that the glenohumeral MER angle was associated with the %PGHD and %AOI, and that the increasing glenohumeral MER angle may be associated with microtrauma and morphological changes of the throwing shoulder joint. Thus, an excessive glenohumeral MER throwing motion might result in an increased joint gap between the humeral head and posterior glenoid rim and a greater insertion of the rotator cuff tendon. Nevertheless, the present study showed an association between morphological changes and the glenohumeral MER angle, but not with the shoulder MER angle. Miyashita et al^26,27 reported that the shoulder external rotation motion during the late cocking phase was a complex motion that involved the glenohumeral joint as well as scapular posterior tilt and thoracic extension. Thus, external rotation of the shoulder-joint complex with posterior scapular tilt and thoracic extension may be an important factor for internal impingement prevention.

Multiple comparison test results indicated that the posterior glenohumeral distance and area of impingement for the throwing shoulder were lower in the 110° of external rotation position than in the 90° of external rotation position. Furthermore, increased shoulder external rotation motion was a factor for the proximity of the humeral head to the posterior glenoid rim. Previous studies have identified an excessive glenohumeral external rotation motion as a factor contributing to internal impingement,^19,32 which is consistent with the present results, suggesting that throwing at an increased glenohumeral MER angle is associated with contact between the posterior glenoid rim and the humeral head, and impinged rotator cuff tendon. Additionally, this study's results showed no association between the MER angle of the shoulder-joint complex and morphological changes in the shoulder joint, highlighting the importance of preventing regional and excessive glenohumeral external rotation motion during the late cocking phase, including subscapularis muscle training,^21,23 thoracic and scapulothoracic joint mobility exercise,^23,26,27,40 and scapular muscle training.³

Finally, with respect to the associations of the %PGHD and %AOI with external rotation gain, glenohumeral internal rotation deficit, and horizontal flexion deficit in the throwing shoulder, fewer morphological changes in the shoulder joint were observed with increased external rotation gain and glenohumeral internal rotation deficit values. External rotation gain^8,17,19,33 and glenohumeral internal rotation deficit^{1,3,9,16,28,29,31} have been regarded as factors for throwing shoulder disabilities; nevertheless, no consensus has yet been reached. In particular, Wilk et al³⁹ identified a decreased range of throwing shoulder external rotation as a risk factor, and Tyler et al³⁶ reported that shoulder internal rotation ROM was not associated with throwing shoulder disabilities. Additionally, these physical assessments represent throwing shoulder ROM characteristics based on side-to-side shoulder differences, which are affected by the nonthrowing shoulder ROM. If preexisting anterior laxity or posterior capsular contracture and posterior shoulder tightness are present in the nonthrowing shoulder, even low external rotation gain and glenohumeral internal rotation deficit values may contribute to morphological changes in the shoulder joint.

Limitations

This study has some limitations. First, the study quantified morphological changes in the shoulder joint and revealed a relationship with the glenohumeral MER angle. However, in clinical practice, the external rotation motion is difficult to distinguish between the glenohumeral and shoulder joints, which include the thoracic and scapulothoracic joints. In the future, the development of an assessment tool for clarifying the glenohumeral MER angle during the late cocking phase is warranted. Second, evidence for the %PGHD and %AOI values is limited to a few cross-sectional studies.^34,35 Further prospective cohort research should be conducted on the quantitative assessment of morphological changes in the glenohumeral joint and symptoms of throwing shoulder disabilities. Finally, the side-to-side difference in MRI position and physical assessment may be influenced not only by anterior laxity and posterior tightness of the shoulder joint, but also by humeral retroversion.^12,18

Conclusion

By using a 3-dimensional motion analysis system and open MRI, this study investigated whether the glenohumeral MER angle during the late cocking phase was associated with morphological shoulder-joint changes. Simple linear regression analysis revealed that the glenohumeral MER angle during the late cocking phase was associated with the %PGHD and %AOI. These findings suggest that assessment of excessive external rotation of the glenohumeral joint during the late cocking phase contributes to the understanding of internal impingement and related throwing injuries.

Footnotes

Acknowledgements

The authors thank S. Hanawa and Y. Nakayama of Inter Reha Corporation for their generous support with the measurement method for the VICON motion system.

Final revision submitted December 7, 2024; accepted February 20, 2025.

The authors declared that they have no conflicts of interest in the authorship and publication of this contribution. AOSSM checks author disclosures against the Open Payments Database (OPD). AOSSM has not conducted an independent investigation on the OPD and disclaims any liability or responsibility relating thereto.

Ethical approval for this study was obtained from the Ethics Committee of the Ibaraki Prefectural University of Health Sciences (approval No. 1041).

‖ ‖

References 2, 3, 15, 17, 19, 23 -25, 32, .

References

Agresta

Krieg

Freehill

MT.

Risk factors for baseball-related arm injuries: a systematic review. Orthop J Sports Med. 2019;7(2):2325967119825557. doi:10.1177/2325967119825557

Burkhart

Morgan

Kibler

WB.

Shoulder injuries in overhead athletes. The “dead arm” revisited. Clin Sports Med. 2000;19(1):125-158. doi:10.1016/s0278-5919(05)70300-8

Burkhart

Morgan

Kibler

WB.

The disabled throwing shoulder: spectrum of pathology part I: pathoanatomy and biomechanics. Arthroscopy. 2003;19(4):404-420. doi:10.1053/jars.2003.50128

Chalmers

Wimmer

Verma

, et al. The relationship between pitching mechanics and injury: a review of current concepts. Sports Health. 2017;9(3):216-221. doi:10.1177/1941738116686545

Dillman

Fleisig

Andrews

JR.

Biomechanics of pitching with emphasis upon shoulder kinematics. J Orthop Sports Phys Ther. 1993;18(2):402-408. doi:10.2519/jospt.1993.18.2.402

Fleisig

Andrews

Dillman

Escamilla

RF.

Kinetics of baseball pitching with implications about injury mechanisms. Am J Sports Med. 1995;23(2):233-239. doi:10.1177/036354659502300218

Fleisig

Barrentine

Zheng

Escamilla

Andrews

JR.

Kinematic and kinetic comparison of baseball pitching among various levels of development. J Biomech. 1999;32(12):1371-1375. doi:10.1016/s0021-9290(99)00127-x

Funakoshi

Takahashi

Shimokobe

Miyamoto

Furushima

Arthroscopic findings of the glenohumeral joint in symptomatic anterior instabilities: comparison between overhead throwing disorders and traumatic shoulder dislocation. J Shoulder Elbow Surg. 2023;32(4):776-785. doi:10.1016/j.jse.2022.10.005

Goes

Flores

Damer

Huang

BK.

Shoulder and elbow injuries in adult overhead throwers: imaging review. Radiographics. 2023;43(12):e230094. doi:10.1148/rg.230094

10.

Halbrecht

Tirman

Atkin

Internal impingement of the shoulder: comparison of findings between the throwing and nonthrowing shoulders of college baseball players. Arthroscopy. 1999;15(3):253-258. doi:10.1016/s0749-8063(99)70030-7

11.

Hall

Lewis

Moore

Ridehalgh

Posterior shoulder tightness; an intersession reliability study of 3 clinical tests. Arch Physiother. 2020;10:14. doi:10.1186/s40945-020-00084-w

12.

Hasegawa

Mihata

Itami

Takeda

Neo

Relationship between humeral retroversion and baseball positions during elementary and junior-high school. J Shoulder Elbow Surg. 2021;30(2):290-297. doi:10.1016/j.jse.2020.05.018

13.

Hellem

Shirley

Schilaty

Dahm

Review of shoulder range of motion in the throwing athlete: distinguishing normal adaptations from pathologic deficits. Curr Rev Musculoskelet Med. 2019;12(3):346-355. doi:10.1007/s12178-019-09563-5

14.

Heyworth

Williams

RJ.

Internal impingement of the shoulder. Am J Sports Med. 2009;37(5):1024-1037. doi:10.1177/0363546508324966

15.

Ibounig

Sanders

Haas

, et al. Systematic Review of Shoulder Imaging Abnormalities in Asymptomatic Adult Shoulders (SCRUTINY): abnormalities of the glenohumeral joint. Osteoarthritis Cartilage. 2024;32(10):1184-1196. doi:10.1016/j.joca.2024.06.001

16.

Iida

Taniguchi

Soma

, et al. Posterior shoulder capsule of the dominant arm is stiffer in baseball players than that in nonthrowing population. J Shoulder Elbow Surg. 2022;31(7):1335-1343. doi:10.1016/j.jse.2022.01.119

17.

Ishikawa

Kurokawa

Muraki

, et al. Increased external rotation related to the soft tissues is associated with pathologic internal impingement in high-school baseball players. J Shoulder Elbow Surg. 2022;31(9):1823-1830. doi:10.1016/j.jse.2022.02.021

18.

Ito

Mihata

Hosokawa

Hasegawa

Neo

Doi

. Humeral retroversion and injury risk after proximal humeral epiphysiolysis (Little Leaguer's shoulder). Am J Sports Med. 2019;47(13):3100-3106. doi:10.1177/0363546519876060

19.

Jobe

CM.

Posterior superior glenoid impingement: expanded spectrum. Arthroscopy. 1995;11(5):530-536. doi:10.1016/0749-8063(95)90128-0

20.

Laudner

Moline

Meister

The relationship between forward scapular posture and posterior shoulder tightness among baseball players. Am J Sports Med. 2010;38(10):2106-2112. doi:10.1177/0363546510370291

21.

Lee

Park

Ryoo

Jeong

WK.

Are rotator muscle performance and posterior shoulder capsule tightness related to glenohumeral internal rotation deficit in male college baseball players?

Clin Orthop Surg. 2022;14(4):576-584. doi:10.4055/cios21212

22.

Lin

Wong

Kazam

JK.

Shoulder injuries in the overhead-throwing athlete: epidemiology, mechanisms of injury, and imaging findings. Radiology. 2018;286(2):370-387. doi:10.1148/radiol.2017170481

23.

Mihata

Gates

McGarry

Lee

Kinoshita

Lee

TQ.

Effect of rotator cuff muscle imbalance on forceful internal impingement and peel-back of the superior labrum: a cadaveric study. Am J Sports Med. 2009;37(11):2222-2227. doi:10.1177/0363546509337450

24.

Mihata

Gates

McGarry

Neo

Lee

TQ.

Effect of posterior shoulder tightness on internal impingement in a cadaveric model of throwing. Knee Surg Sports Traumatol Arthrosc. 2015;23(2):548-554. doi:10.1007/s00167-013-2381-7

25.

Mihata

Jun

Bui

CNH

, et al. Effect of scapular orientation on shoulder internal impingement in a cadaveric model of the cocking phase of throwing. J Bone Joint Surg Am. 2012;94(17):1576-1583. doi:10.2106/JBJS.J.01972

26.

Miyashita

Kobayashi

Koshida

Urabe

Glenohumeral, scapular, and thoracic angles at maximum shoulder external rotation in throwing. Am J Sports Med. 2010;38(2):363-368. doi:10.1177/0363546509347542

27.

Miyashita

Koshida

Koyama

Ota

Tani

Okamune

Biomechanical characteristics of scapular and glenohumeral movements during pitching motion in injury-prone college baseball pitchers. Phys Ther Res. 2023;26(3):89-97. doi:10.1298/ptr.E10254

28.

Myers

Laudner

Pasquale

Bradley

Lephart

SM.

Glenohumeral range of motion deficits and posterior shoulder tightness in throwers with pathologic internal impingement. Am J Sports Med. 2006;34(3):385-391. doi:10.1177/0363546505281804

29.

Norton

Honstad

Joshi

Silvis

Chinchilli

Dhawan

Risk factors for elbow and shoulder injuries in adolescent baseball players: a systematic review. Am J Sports Med. 2019;47(4):982-990. doi:10.1177/0363546518760573

30.

Pappas

Zawacki

Sullivan

TJ.

Biomechanics of baseball pitching. A preliminary report. Am J Sports Med. 1985;13(4):216-222. doi:10.1177/036354658501300402

31.

Park

Jeon

Suh

Lee

Jeong

WK.

Correlation of glenohumeral internal rotation deficit with shear wave ultrasound elastography findings for the posterior inferior shoulder capsule in college baseball players. J Shoulder Elbow Surg. 2021;30(7):1588-1595. doi:10.1016/j.jse.2020.09.036

32.

Rizio

Garcia

Renard

Got

Anterior instability increases superior labral strain in the late cocking phase of throwing. Orthopedics. 2007;30(7):544-550. doi:10.3928/01477447-20070701-03

33.

Sabick

Torry

Lawton

Hawkins

RJ.

Valgus torque in youth baseball pitchers: a biomechanical study. J Shoulder Elbow Surg. 2004;13(3):349-355. doi:10.1016/j.jse.2004.01.013

34.

Takahashi

Iwamoto

Monma

Mutsuzaki

Mizukami

The area of impingement in the throwing versus nonthrowing shoulder of collegiate baseball players: an MRI study of the simulated late-cocking phase of throwing. Orthop J Sports Med. 2021;9(3):2325967121992133. doi:10.1177/2325967121992133

35.

Takahashi

Mutsuzaki

Iwamoto

Monma

Tomita

Mizukami

Morphologic changes in the posterior glenoid rim is independently associated with rotator cuff impingement in baseball players. Heliyon. 2024;10(13):e33064. doi:10.1016/j.heliyon.2024.e33064

36.

Tyler

Mullaney

Mirabella

Nicholas

McHugh

MP.

Risk factors for shoulder and elbow injuries in high school baseball pitchers: the role of preseason strength and range of motion. Am J Sports Med. 2014;42(8):1993-1999. doi:10.1177/0363546514535070

37.

Uchida

Matsuo

Sakata

Yamaguchi

Nishizawa

Sakai

Prevalence of abnormal ultrasonography findings in the posterosuperior humeral head of asymptomatic collegiate baseball pitchers. J Shoulder Elbow Surg. Published online September 7, 2024. doi:10.1016/j.jse.2024.07.026

38.

Walch

Boileau

Noel

Donell

ST.

Impingement of the deep surface of the supraspinatus tendon on the posterosuperior glenoid rim: an arthroscopic study. J Shoulder Elbow Surg. 1992;1(5):238-245. doi:10.1016/S1058-2746(09)80065-7

39.

Wilk

Macrina

Fleisig

, et al. Correlation of glenohumeral internal rotation deficit and total rotational motion to shoulder injuries in professional baseball pitchers. Am J Sports Med. 2011;39(2):329-335. doi:10.1177/0363546510384223

40.

Yoshimi

Maeda

Komiya

, et al. Effect of thoracic expansion restriction on scapulothoracic and glenohumeral joint motion during shoulder external rotation. J Back Musculoskelet Rehabil. 2022;35(6):1399-1406. doi:10.3233/BMR-220006

Association Between Shoulder Morphological Changes and Glenohumeral Maximum External Rotation During Late Cocking Phase

Abstract

Background:

Purpose:

Study Design:

Methods:

Results:

Conclusion:

Clinical Relevance:

Keywords

Methods

Participants

Imaging Examination

Posterior Glenohumeral Distance of the Throwing Shoulder Normalized by That of the Nonthrowing Shoulder

Area of Impingement of the Throwing Shoulder Normalized by That of the Nonthrowing Shoulder

Glenohumeral Joint and Shoulder-Joint MER Angles During the Late Cocking Phase

Physical Assessment

Statistical Analysis

Results

Discussion

Limitations

Conclusion

Footnotes

Acknowledgements

‖ ‖

References