Comparison of scapular position in elite tennis players with and without shoulder impingement: A case-control study

Abstract

BACKGROUND:

To maximize the ball velocity in the tennis sever, the shoulder plays a key role in the kinetic chain. But shoulder inefficiency leads to shoulder injuries such as shoulder impingement syndrome (SIS). Thus, to verify the scapular movements during the tennis serve could help prevent shoulder injury in tennis players.

OBJECTIVE:

This case-control study aimed to verify the scapular movements during flat first serve for elite tennis players with shoulder impingement syndrome compared to those without it.

METHODS:

Eight elite tennis players (4 males and 4 females) with SIS and 8 elite healthy players (4 males and 4 females) performed flat first serves, and the three-dimensional scapular kinematic data was recorded using the Qualisys motion capture system through spherical reflective markers including the acromion marker cluster.

RESULTS:

The scapula was more internally rotated (median difference: 10.40 ${}^{\circ}$ ) in the male players with SIS than in those without it at the maximally externally rotated humerothoracic joint during flat first serve, and female players with SIS (median difference: 7.16 ${}^{\circ}$ and 11.28 ${}^{\circ}$ , respectively) had more internally rotated scapula at the maximally externally rotated humerothoracic joint and ball impact.

CONCLUSION:

Increased scapular internal rotation may be something that affects shoulder injuries in the overhead sports, and it may help to prevent and rehabilitate overhead injuries including SIS.

Keywords

Tennis overhead activity scapular kinematic shoulder injury

1. Introduction

Participation in tennis, especially at the elite level, exposes players to a risk for musculoskeletal injury [1]. A review article reported that all-level players have an injury incidence of 0.04 to 3.0 injuries per 1000 h tennis played [2]. In particular, high-level tennis players under 18 years of age have injury rates ranging from 2 to 20 injuries per 1000 h of play [1]. Most tennis injuries occur in the lower extremity, ranging from 31% to 67%, but up to 50% of all tennis injuries occur in the upper extremity [1]. Shoulder pain was especially present in 24% and 50% of high-level tennis adolescent and middle-aged players, respectively [3]. The majority of shoulder pain is commonly due to repetitive lifting and overhead arm movements [4]. The risk factors for upper extremity injuries in tennis players are exposure to tennis, muscle fatigue, skill level, bad skill or technique, shoulder kinetic or kinematic, and scapular dyskinesis [4].

During overhead arm movements, the scapula is expected to rotate upwardly, tilt posteriorly, and move towards internal or external rotation [5]. Visible alterations in these scapulothoracic motions and position, which are defined as scapular dyskinesis, have been previously associated with various shoulder pathologies including shoulder impingement syndrome [6]. A previous study showed that overhead athletes with scapular dyskinesis accounted for 61%, and athletes with scapular dyskinesis have about 50% greater risk of developing shoulder pain compared to those without scapular dyskinesis [7]. However, some researchers mentioned that no direct relationship between the scapular motion deficit and shoulder pain or risk factor for shoulder injury has been shown [6].

The tennis serve, which is a typical overhead arm movement, accounts for 45 to 60% of total strokes in the game [8]. The maximum ball velocity in tennis sever requires a kinetic chain that efficiently transfers linear momentum from the foot to the arm-racket complex [8]. The shoulder in particular, which is the link between the trunk and the arm-racket complex, plays a key role in the kinetic chain [9]. Shoulder efficiency depends on coordination between the humerus and scapula, and as the arm moves to maximum elevation, the scapular moves in three motions (upward/downward rotation, internal/external rotation, and anterior/posterior tilting) [9]. However, inappropriate scapular movement leads to shoulder injuries such as shoulder impingement syndrome [9]. Thus, verifying scapular movements during the tennis serve could help prevent shoulder injury in tennis players [8].

Previous studies mentioned that it was difficult to analyze the three-dimensional scapula movements using cutaneous marker-based methods because the scapula glides and rotates underneath layers of soft tissue and skin, unlike the upper and lower extremities [10]. However, the acromion marker cluster (AMC) has recently been a valid and reliable method to estimate dynamic scapular orientation and has been shown to be a reliable and valid measurement of scapular orientation at end-range clavicle movements, independent of humeral movements [11]. The aims of this study were to verify the scapular movements during flat first serve for elite tennis players with shoulder impingement syndrome compared to those without it and to provide useful information on the prevention of shoulder injury in tennis players.

2. Method

2.1 Study design

A case-control study was designed and approved by the research ethics committee of Pukyong National University (1041386-20180710-HR-023-03). Tennis players enrolled in a Korean university that volunteered to participate in this study and were Korean national level players, were included.

2.2 Participants

Eight elite tennis players (4 males and 4 females) with shoulder impingement syndrome (SIS) and 8 elite healthy players (4 males and 4 females) were selected to participate in this study. All participants had been playing tennis since elementary school and trained twice a day except to weekend. The SIS group experienced pain during elevation of the dominant arm and tested positive for at least 3 of the following tests: (a) pain during supraspinatus empty can test, (b) Neer impingement sign, (c) Hawkins-Kennedy impingement sign, and (d) painful arc between 60 ${}^{\circ}$ and 120 ${}^{\circ}$ . Subjects in the healthy (CON) group had full arm elevation in both the sagittal and frontal planes without pain and tested negative in all 4 tests. An experienced physician, with additional training in musculoskeletal examination, carried out all the tests, and exclusion criteria for both groups were having a history of shoulder: fractures, dislocation or instability, surgery, or clinical treatment for frozen shoulders. Table 1 showed the demographic characteristics and visual analog scale (VAS) of the players who participated in this study, and there were no differences between the groups in age, height, weight, career, and VAS.

Table 1
Demographic characteristics of the participants

Gender	Group	Age (yrs.)	Height (cm)	Weight (kg)	Career (yrs.)	VAS (points)
Male	SIS ( $n=$ 4)	21.50 (20.25, 22.75)	177.50 (168.00, 184.75)	72.50 (69.25, 78.75)	11.50 (10.25, 12.00)	3.60 (0.60, 4.95)
( $n=$ 8)	CON ( $n=$ 4)	22.00 (20.25, 23.00)	187.00 (177.00, 188.75)	74.50 (70.50, 82.25)	12.00 (9.50, 16.00)	1.90 (0.40, 5.20)
Female	SIS ( $n=$ 4)	21.50 (20.25, 22.75)	165.00 (160.25, 166.00)	55.50 (52.00, 59.00)	10.00 (8.25, 11.75)	6.20 (3.75, 6.55)
( $n=$ 8)	CON ( $n=$ 4)	21.00 (20.00, 22.00)	160.00 (155.50, 170.50)	65.00 (63.50, 67.25)	11.00 (10.00, 12.00)	2.80 (0.70, 4.45)

Values express as median (1 ${}^{\text{st}}$ quartile, 3 ${}^{\text{rd}}$ quartile). SIS: shoulder impingement syndrome group, CON: control group, VAS: visual analog scale.

2.3 Outcome measures

The Qualisys motion capture system (Qualisys AB, Sweden) consisted of 10 infrared cameras (7+, Qualisys AB, SWE) and 1 color video camera (Oqus 2c, Qualisys AB, SWE), which were used to collect the three-dimensional scapular kinematic data through 15 spherical reflective markers and interfaced with the Qualisys Track Manager 2.15 (Qualisys AB, Sweden). Eleven markers were attached to the players’ skin on the thorax, humerus, and scapula of their dominant arm according to the International Society of Biomechanics (ISB) recommendations [25]; the spinous processes of the 7th cervical and 8th thoracic vertebrae, suprasternal notch, xiphoid process, acromioclavicular joint, middle of scapular spinae, root of the scapular spine, inferior angle of scapula, acromial angle of the scapula, glenohumeral rotation center, and elbow medial and lateral epicondyles (Fig. 1). An additional acromion marker cluster was attached to the meeting point between the acromion and scapula spine.

Table 2
Difference of downward/upward rotation in tennis players with and without shoulder impingement syndrome (SIS and CON) at the five key-events of the flat first serve

Event	Gender	SIS		CON		$Z(p)$
E1	Male	$-$ 8.24	( $-$ 12.51, $-$ 5.45)	$-$ 4.77	( $-$ 6.92, $-$ 3.46)	$-$ 1.443	(0.149)
	Female	1.01	( $-$ 4.98, 12.71)	4.07	( $-$ 5.38, 7.48)	$-$ 0.354	(0.857)
E2	Male	$-$ 3.56	( $-$ 9.02, 7.61)	3.15	( $-$ 3.51, 6.07)	$-$ 0.866	(0.486)
	Female	8.96	( $-$ 2.53, 10.88)	8.04	( $-$ 7.80, 15.56)	$-$ 0.354	(0.857)
E3	Male	0.69	( $-$ 3.68, 8.76)	4.96	( $-$ 2.02, 10.40)	$-$ 0.866	(0.486)
	Female	7.90	( $-$ 1.61, 10.90)	17.09	( $-$ 2.92, 26.04)	$-$ 0.001	(0.999)
E4	Male	$-$ 3.88	( $-$ 6.26, 4.42)	0.72	( $-$ 5.87, 7.63)	$-$ 0.577	(0.686)
	Female	5.84	( $-$ 1.09, 9.24)	10.98	( $-$ 8.32, 19.70)	$-$ 0.354	(0.857)
E5	Male	$-$ 5.84	( $-$ 13.49, $-$ 3.79)	$-$ 3.54	( $-$ 12.76, $-$ 0.13)	$-$ 0.866	(0.486)
	Female	4.68	( $-$ 3.36, 7.14)	5.14	( $-$ 15.07, 10.53)	$-$ 0.354	(0.857)

Values express as median (1st quartile, 3rd quartile). Positive ( $+$ ) and negative ( $-$ ) values mean downward and upward rotation, respectively. SIS: shoulder impingement syndrome group, CON: control group. E1: Ball release, E2: First 75% timing of the cocking phase, E3: Maximally externally rotated humerothoracic joint, E4: Ball impact, E5: Minimal height of the tennis racket.

Figure 1.

Position of markers attached to each participant for three-dimensional scapular kinematic.

All trials were conducted in an indoor tennis court, and all players were asked to warm up for 15 min and then to perform 12 flat first serves to land the ball in the service box at their greatest velocity [13]. Kinematic data of 3 successful serves selected from 3 experts were subsequently analyzed. The tennis serve was divided into five key events [13]; the ball release, first 75% timing of the cocking phase, maximally externally rotated humerothoracic joint, ball impact, and minimal height of the tennis racket. The cocking phase defined from the ball release to the humerothoracic joint was maximally externally rotated [13]. Joint kinematics for the thorax, scapula, and humerus were determined by defining local coordinate systems for each rigid body segment according to the ISB recommendations [12]. The previously validated method for measuring the scapular upward/downward rotation, anterior/posterior tilt, and internal/external rotation relative to the thorax was followed at each event [13].

2.4 Statistical analysis

Data were analyzed using SPSS ver. 22 (IBM Corp., Armonk, NY, USA) with significance levels set at 5%. Considering the small sample of this study, the nonparametric Mann-Whitney $U$ test was used to analyze the differences in scapular movements between groups at each event.

3. Results

The scapular kinematic data of male and female tennis players with and without shoulder impingement syndrome are shown in Tables 2 to 4.

Table 3
Difference of posterior/anterior tilt in tennis players with and without shoulder impingement syndrome (SIS and CON) at the five key-events of the flat first serve

Event	Gender	SIS		CON		$Z(p)$
E1	Male	$-$ 4.29	( $-$ 6.95, $-$ 0.32)	$-$ 5.12	( $-$ 7.70, $-$ 2.63)	0.577	(0.686)
	Female	$-$ 6.09	( $-$ 10.78, 1.09)	$-$ 4.42	( $-$ 5.87, $-$ 4.17)	0.001	(0.999)
E2	Male	$-$ 14.11	( $-$ 16.38, $-$ 10.85)	$-$ 13.37	( $-$ 18.43, $-$ 11.29)	0.001	(0.999)
	Female	$-$ 11.93	( $-$ 16.94, $-$ 9.92)	$-$ 11.16	( $-$ 11.91, $-$ 8.98)	$-$ 1.061	(0.400)
E3	Male	$-$ 5.82	( $-$ 7.74, 3.95)	$-$ 4.98	( $-$ 7.86, $-$ 2.46)	0.001	(0.999)
	Female	$-$ 2.88	( $-$ 5.12, 1.47)	$-$ 9.93	( $-$ 10.52, $-$ 6.99)	$-$ 2.121	(0.057)
E4	Male	$-$ 2.42	( $-$ 3.33, 3.82)	$-$ 3.20	( $-$ 4.95, $-$ 1.41)	$-$ 0.866	(0.486)
	Female	$-$ 3.43	( $-$ 4.86, $-$ 1.18)	$-$ 11.89	( $-$ 12.45, $-$ 4.61)	$-$ 1.061	(0.400)
E5	Male	$-$ 1.15	( $-$ 1.70, 5.23)	2.61	(1.68, 4.25)	$-$ 1.155	(0.343)
	Female	$-$ 0.79	( $-$ 2.67, 5.17)	4.86	( $-$ 4.34, 5.87)	0.001	(0.999)

Values express as median (1st quartile, 3rd quartile). Positive ( $+$ ) and negative ( $-$ ) values mean posterior and anterior tilt, respectively. SIS: shoulder impingement syndrome group, CON: control group. E1: Ball release, E2: First 75% timing of the cocking phase, E3: Maximally externally rotated humerothoracic joint, E4: Ball impact, E5: Minimal height of the tennis racket.

Table 4

Difference of internal/external rotation in tennis players with and without shoulder impingement syndrome (SIS and CON) at the five key-events of the flat first serve

Event	Gender	SIS		CON		$Z(p)$
E1	Male	10.13	(4.21, 14.07)	6.46	(2.14, 9.54)	$-$ 1.155	(0.343)
	Female	5.27	(2.61, 15.50)	2.37	( $-$ 2.55, 8.21)	$-$ 1.061	(0.400)
E2	Male	$-$ 1.98	( $-$ 4.00, 5.79)	6.23	( $-$ 7.63, 20.68)	$-$ 0.866	(0.486)
	Female	2.49	( $-$ 5.82, 14.52)	3.80	( $-$ 7.57, $-$ 3.28)	$-$ 1.414	(0.229)
E3	Male	26.93	(20.36, 31.52)	16.53	(15.83, 16.71)	$-$ 2.309	(0.029)
	Female	14.90	(11.82, 17.22)	7.74	(2.26, 11.13)	$-$ 2.121	(0.034)
E4	Male	17.98	(13.51, 22.86)	14.16	(8.25, 15.86)	$-$ 1.443	(0.200)
	Female	11.48	(4.41, 16.85)	0.20	( $-$ 1.17, 0.30)	$-$ 2.121	(0.034)
E5	Male	17.54	(12.63, 23.43)	18.84	(10.71, 20.48)	$-$ 0.289	(0.886)
	Female	18.62	(12.71, 26.29)	16.16	(11.52, 19.83)	$-$ 0.707	(0.629)

Values express as median (1st quartile, 3rd quartile). Positive ( $+$ ) and negative ( $-$ ) values mean internal and external rotation, respectively. SIS: shoulder impingement syndrome group, CON: control group. E1: Ball release, E2: First 75% timing of the cocking phase, E3: Maximally externally rotated humerothoracic joint, E4: Ball impact, E5: Minimal height of the tennis racket.

Pairwise comparisons indicated that the scapula was more internally rotated in the male players with SIS than in those without it at the maximally externally rotated humerothoracic joint ( $p=$ 0.029; median difference, 10.40 ${}^{\circ}$ ). Female players with SIS had more internally rotated scapula at the maximally externally rotated humerothoracic joint ( $p=$ 0.034; median difference, 7.16 ${}^{\circ}$ ) and ball impact ( $p=$ 0.34; median difference, 11.28 ${}^{\circ}$ ).

There was no statistically significant difference between the groups during the flat first serve for the scapular upward/downward rotation and anterior/posterior tilt in both males and females.

4. Discussion

The aim of this study was to verify the scapular movements during flat first serve for elite tennis players with SIS compared to those without it. The main results showed that the scapula of male players with SIS rotated internally at the maximally externally rotated humerothoracic joint, while that of female players with it rotated internally at the maximally externally rotated humerothoracic joint and ball impact.

Proper scapular positioning is crucial in allowing full and non-impaired motion of the upper extremities [14]. The resting scapular orientation on the thorax rotated slightly upwardly and internally and tiled anteriorly, and during arm elevation above shoulder level, it moved into more upward rotation, external rotation, and posterior tilting [14]. These scapular movements maintain an adequate size (0 ${}^{\circ}$ of elevation: 11.1 mm, 90 ${}^{\circ}$ of elevation: 5.7 mm) between the greater tuberosity and acromion process during arm elevation, and the changed scapular position or orientation can increase the risk of shoulder injury [15]. During the late cocking phase of throwing, increased scapular internal rotation ( $\geqslant$ 5 ${}^{\circ}$ ) of overhead athletes led to decreased glenohumeral external rotation, increasing the elbow valgus load and shoulder internal impingement [16]. This study also showed that tennis players with shoulder impingement syndrome had increased internally rotated scapula (male: 10.40 ${}^{\circ}$ , female: 7.16 ${}^{\circ}$ –11.28 ${}^{\circ}$ ) during the early cocking and/or late cocking phases of flat first serve. A previous study reported that alternation of scapular kinematics was related to the posterior capsule tightness of the glenohumeral joint [17], and reductions in serratus anterior activation and reduced resting length of the pectoralis minor were also associated with scapular kinematic abnormalities [18]. This study focused on the alteration of scapular movement during flat first serve, but further studies to verify the humeral kinematics, glenohumeral internal rotation limitation, and scapular muscle activation will provide useful information on identifying a possible mechanism for the reduction of scapular external rotation for tennis players during overhead tennis activities.

The injured shoulder had decreased scapular upward rotation and posterior tilt during arm elevation in the scapular plane [19]. A 10 ${}^{\circ}$ increase in scapular anterior tilt in subjects with shoulder impingement compared to those without it in shoulder-level elevated arm positions [20]. Subjects with shoulder impingement had approximately 6 ${}^{\circ}$ more anteriorly tilted scapula at 120 ${}^{\circ}$ arm elevation compared to the controls [21]. However, this study showed that there was no significant difference in scapular anterior tilting of players with shoulder impingement syndrome compared to those without it during the flat first serve. In addition, patients with subacromial impingement decreased upward scapular rotation and scapular elevation during arm elevation [20, 21], whereas the players with shoulder impingement syndrome did not. This result may be related to a chronic adaptation of the increased scapular upward rotation to maintain adequate subacromial size during the throwing motion [22]. To further investigate the relationship between scapular kinetic and shoulder injury, the period during which the subject suffers from shoulder pain should be determined. Additionally, because fatigue of the shoulder and scapular muscles may adversely affect scapular movement [23], a difference in scapular position and orientation should exist before and after muscle fatigue will be considered.

For overhead players, the scapula can transmit tremendous force generated in the lower limbs and trunk to the arm, and the changed scapular position or orientation decreases the force transmitted because of alteration of the kinematic chain between the upper and lower extremities, which increases the risk of shoulder injury [24]. Therefore, an in-depth understanding of scapular movements during overhead activities would help to better understand the mechanisms of shoulder injury, and it may improve treatment regimens. In this study, the acromion marker cluster on the meeting point between the acromion and scapula spine [25] and standardized joint coordinate systems by recommended ISB were used to compensate for inaccuracies in the estimated scapular kinematics for tennis players with shoulder impingement syndrome during the flat first serve. However, as it has been reported that deviations of data collected using the acromion marker cluster increased above 100 ${}^{\circ}$ elevation of the humerus [26], the amount of humeral elevation needs to be considered for more players of various sports events in further studies. Also, this study is somehow limited due to the small sample size of only Korean national level tennis player, and further studies should be performed with many athletes of different nationalities.

5. Conclusion

This study found that the scapula of male tennis players with SIS rotated more internally at the maximally externally rotated humerothoracic joint during flat first serve, while that of females rotated more internally at the maximally externally rotated humerothoracic joint and the ball impact during flat first serve compared to those without it. Increased scapular internal rotation may be something that affects shoulder injuries in the overhead sports, and it may help to prevent and rehabilitate overhead injuries including SIS.

Funding

The authors received no financial support for the research, authorship, and/or publication of this article.

Author contributions

Conception: TK, YHK, HC.

Performance of work: JMP, HC.

Interpretation or analysis of data: TK, JMP.

Preparation of the manuscript: TK, YHK, HC.

Revision for important intellectual content: YHK, HC. Supervision: TK.

Ethics statement

The study design was approved by the appropriate ethics review boards at Pukyong National University. All study participants provided informed consent.

Footnotes

Conflict of interest

The authors declare no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.

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Comparison of scapular position in elite tennis players with and without shoulder impingement: A case-control study

Abstract

BACKGROUND:

OBJECTIVE:

METHODS:

RESULTS:

CONCLUSION:

Keywords

1. Introduction

2. Method

2.1 Study design

2.2 Participants

Table 1 Demographic characteristics of the participants

Table 2 Difference of downward/upward rotation in tennis players with and without shoulder impingement syndrome (SIS and CON) at the five key-events of the flat first serve

3. Results

Table 3 Difference of posterior/anterior tilt in tennis players with and without shoulder impingement syndrome (SIS and CON) at the five key-events of the flat first serve

5. Conclusion

Funding

Author contributions

Ethics statement

Footnotes

Conflict of interest

References

Table 1
Demographic characteristics of the participants

Table 2
Difference of downward/upward rotation in tennis players with and without shoulder impingement syndrome (SIS and CON) at the five key-events of the flat first serve

Table 3
Difference of posterior/anterior tilt in tennis players with and without shoulder impingement syndrome (SIS and CON) at the five key-events of the flat first serve