ELECTROMYOGRAPHIC ANALYSIS OF THE SCAPULAR DYSKINESIS TEST IN A BASEBALL PITCHER WITH A SLAP LESION: A CASE REPORT

Abstract

Background and Purpose:

The return to play percentage of baseball pitchers who have undergone isolated superior labrum anterior-posterior (SLAP) repair has been reported to be less than 60%. Scapular dyskinesis (SD), characterized by scapular prominence during dynamic scapulohumeral movements, may be used to assist in diagnosing a baseball pitcher with shoulder pathology including a SLAP lesion. The purpose of this case report was to describe the use of the SD test to assess the scapular muscles and report EMG findings in a college baseball pitcher diagnosed with a Type 2 posterior SLAP lesion.

Case Description:

The subject was a NCAA-D1 senior collegiate baseball right hand 3/4 slot pitcher (21 years old) with a primary complaint of pain in the anterior portion of the shoulder during the entire fall practice season, which was attributed to labral surgery performed when he was a senior in high school. No positive clinical testing of the patient was found including: the sulcus sign, tests of gross instability, and the load & shift test. A Type II posterior SLAP lesion was identified via magnetic resonance imaging. The subject presented with glenohuemral internal rotation deficit (GIRD). The SD test identified moderate to severe prominence of scapular medial boarder in shoulder flexion/extension (FLX/EXT). Furthermore, surface EMG analyses indicated that the lower trapezius (LT) muscle was abruptly inhibited on the dominant side during the descending phase of FLX, compared with the non-dominant side. Additionally, a remarkably higher ratio of upper trapezius to LT muscle EMG activity on the dominant side compared to that of the non-dominant side was identified during the descending phase from flexion.

Discussion:

After identification of SD, an off season conservative treatment program allowed him to compete in his last college baseball season, appearing 22 times out of the bullpen in which he was credited four wins with a 3.70 earned run average (ERA) in 41.1 innings in 57 games. The SD test may play a critical role in identifying rehabilitation potential and guide the focus of the rehabilitation program to improve scapulothoracic stability and mobility for unilateral repetitive overhead athletes. Particularly the descending phase during sagittal plane motion (FLX/EXT) may effectively accentuate the scapular prominence during movement, portentially due to LT muscle activity inhibition.

Level of Evidence:

5 Case Report

INTRODUCTION

The potential risk of shoulder pain in athletes with scapular dyskinesis (SD) has been reported in up to 43% of the 419 athletes in a recent meta-analysis.¹ The 419 athletes included athletes from a variety of sports, including handball, rugby, swimming, baseball, volleyball, tennis, and badminton, in whom the level of symptoms in the shoulder did not necessarily require withdrawal from sports. However, an odds ratio has been reported (1.18) for high school baseball pitchers with SD (who were considered disabled for seven days or more due to shoulder injuries during the course of the season), compared to pitchers without SD.² Furthermore, collegiate baseball pitchers with mild SD showed a significant decrease in their Kerlan-Jobe Orthopaedic Clinic Shoulder and Elbow (KJOC) score during the course of a season, although none of the athletes were considered disabled during the course of season. In contrast, those pitchers without SD did not significantly decrease the KJOC score during the course of season.³

SD can be identified by scapular prominence (typically medial or inferior portions) that is observed during active and dynamic arm motions, such as shoulder flexion and extension, or at rest (in a standing position) with a certain amount of weight, depending on the body weight of a subject.^3,6 SD by itself is not considered a specific injury, rather it is described as the loss of normal neurologically mediated control of motion during scapulohumeral rhythm (SHR), although it may exacerbate shoulder symptoms as a result of a shoulder injury.⁷ Activation sequencing patterns, specifically the ratio of upper trapezius to lower trapezius muscle as measured using surface electromyography (EMG) activity, have been discussed during observation of SHR during the SD test.^6,7 Another factor to consider alongside SD of particular relevance for baseball pitchers is posterior shoulder inflexibility or a decrease in the range of horizontal adduction range of motion.⁷ This is associated with glenohumeral internal rotation deficit (GIRD) and the anterior tilt of the scapular or what is known as “a wind-up effect” of the scapula on the thorax.⁷

SD was originally classified into four types of scapular prominences: Type I involving the scapular inferior angle, Type II involving the scapular medial boarder, Type III involving the scapular superior angle, and Type IV describing normal and symmetrical kinesis.⁸ However, visual dynamic assessment schemes of SD have been suggested to be classified into only two types as ‘yes’ or ‘no’ in order to improve inter-rater reliability.^9,10

The presences of Type I and II SD alter the ‘safe zone’ of glenohumeral angle, which causes an increase in anterior shear of the glenohumeral (GH) joint or tensile loads on the anterior band of the inferior glenohumeral ligament.¹¹ Chronic labral injuries in overhead athletes can be attributed to GH joint instability due to Type II SD. Superior labral anterior-posterior (SLAP) tears commonly found in baseball pitchers have been identified as occurring near the biceps origin.^12,13 The mechanism of SLAP tears has been described as a “peel back” due to the torsional force of the long head of biceps brachii muscle in the transition of the late cocking phase to acceleration phase.¹⁴ The scapular kinematic angles during late cocking phase of healthy competitive professional baseball pitchers showed the scapula in a position of 15 ° protraction, 23 ° upward rotation, and 11 ° of posterior tilt, while the GH joint was elevated 85 ° and horizontally abducted 6 °, and in 114 ° of external rotation.¹⁵ SLAP tears have also been suggested to be associated with shoulder internal impingement as the undersurface of the supraspinatus and infraspinatus tendons rub at the greater tuberosity of the humerus and posterior superior glenoid at maximum external rotation during the late cocking phase of throwing.¹⁴ This internal impingement or contact pressure has been demonstrated to be increased with increasing internal rotation of the scapula in a cadaveric model.¹⁶ Thus, baseball pitchers with Type II SD may be more vulnerable to SLAP tears. The purpose of this case report was to describe the use of the SD test to assess scapular muscle and report EMG findings in a college baseball pitcher diagnosed with a Type 2 posterior SLAP lesion.¹⁴

CASE DESCRIPTION

A NCAA-D1 senior collegiate baseball right hand 3/4 slot pitcher (height: 186 cm, weight: 84 kg, age: 21 years old) appeared 22 times out of the bullpen during the course of the season from February to May in which the team had 57 games. He was credited four wins with 3.70 earned run average (ERA) in 41.1 innings. The subject agreed and signed the consent form approved by the University's Institutional Review Board prior to data collection.

The subject saw his team physician before the course of the season and with a chief complaint of pain in the anterior portion of the right shoulder after participating in throwing during the entire fall practice season. He disclosed that he had undergone labral surgery in the right shoulder when he was a senior in high school which was reported on the sports medicine health history form. His pain severity was identified as mild to moderate. His pitching velocity and accuracy were affected by the chief complaint. Pain mostly occurred at the early acceleration phase of throwing. A subacromial space cortisone injection was performed, but helped the pain for only a few days.

Glenohumeral Range of Motion

The right (dominant) passive internal rotation (IR) of GH joint (measured in the supine position) was 32 ° whereas the left IR was 51 °, indicating 19 ° deficit. A difference in the total arc of passive ROM (the sum of IR and ER) was 15 ° less for the right side than that of the left side. The distance between the posterior portion of acromion process and the wall in the standing position was 7.4 cm for the right side whereas it was 7.8 cm for the left side. The mean distance for the team pitchers (15) was 7.7 cm for the dominant side whereas it was 7.0 cm for the non-dominant side. Taken together, GIRD was identified for this case pitcher while no anterior tilt of the scapula was identified in the static measurement.¹⁷

Manual Muscle tests and Special Tests

No gross deformity, muscle asymmetry, or ecchymosis was observed. Strength was assessed using manual muscle testing (MMT) and 5 out of 5 strength identified with pain upon testing of the rotator cuff (RC) muscles during external rotation. Other MMTs of the RC were graded at 5 out of 5 with no pain. No specific pinpoint tenderness was identified on palpation. Manual orthopedic special tests were negative including: the sulcus sign, gross instability signs, the load & shift test, and Speed's, Yergason's, and Crank tests.

Imaging

A magnetic resonance image (MRI) was obtained and reviewed by the team physician. The right shoulder showed a Type 2 posterior SLAP lesion¹⁴ as well as intermediate grade signal changes in the distal supraspinatus and infraspinatus tendons combined with tendinopathy without any gross tears. There was also focal increased signal at anteromedial humeral head, leading to a suspicion of a reverse Hill Sachs lesion. No fractures or dislocations were identified. No osteochondral defects or significant osteoarthritic changes were identified at the GH joint. The patient understood the nature of the injury, precautions, prognosis, and recovery time as well as the need for scapulothoracic stabilization and flexibility training which were recommended by the team physician.

Scapular Dyskinesis Test- Procedures

The subject performed active shoulder flexion/extension (FLX/EXT) and abduction/adduction (ABD/ADD) with three different weight loads using a cuff weight at the wrist: 0, 1.8, and 3.2 kg, while undergoing EMG recording. EMG data were collected from the upper trapezius (UT), lower trapezius (LT), and serratus anterior (SA) bilaterally. The subject completed the exercise of elevating and lowering the arms each over 5 seconds smoothly to the sound of a metronome with a frequency of 1 beat per second which was used to standardize the speed of movements.⁶

The electrodes were placed centrally over the muscle bellies of the UT, LT, and SA muscle, bilaterally. The electrode placements and EMG data collection, reduction, and analysis were in detail described somewhere else.⁶ Input signals of EMG activities were recorded during each of the motions using a data collection system (MP 150 Data Acquisition System; BIOPAC System Inc, Goleta, CA, USA) with a sampling rate of 1000 Hz, and all data were stored in a computer for off-line analyses. All root-mean square values of the EMG signals were normalized to the maximum voluntary isometric contraction (MVIC) of the corresponding muscles. Data for this case report were analyzed for each of the EMG activities as dependent variables which were blocked at every 1000 samples of the EMG activity or every one second during each of the exercises. Consequently, 5000 samples of EMG activity for each exercise were divided into five time blocks of dependent variables from the initial UT EMG activity to the end of the exercise each for upward and descending movement or a total of 10 blocks.

RESULTS

The subject demonstrated (by visual assessment) Kibler's Type II SD classification, in which the medial border of the scapula was prominent during the descending phase of FLX or sagittal plane motion with the wrist cuff weight of 3.2 kg (Figure 1). In contrast, no regions of scapular prominences were visually identified during the upward phase of FLX or either the upward or descending phases of ABD regardless of the weight loads. The findings of the SD test were consistent with the findings of the EMG activities analyzed in the UT and LT muscle (Table 1 and Table 2). Specifically, the EMG activity of the LT muscle on the right side abruptly dropped at 3 sec after the initial movement of descending phase with the weight load of 3.2 kg, compared with those of the left side (3% vs. 10% MVIC) (Figure 1b). In addition, the ratios of UT to LT muscle activity were remarkably greater during the descending phase of FLX for the right side than those of the left side (Figure 2a), while no difference in the ratios was observed during the descending phase of ABD (Figure 2b).

Figure 1.

Kibler's Classification Type II Scapular Dyskinesis

The subject showed visually normal scapular kinesis when he elevated the arms (upward) in shoulder flexion with the weight load of 3.2 kg (a). In contrast, the subject showed the moderate to severe Kibler's classification type II scapular dyskinesis, medial boarder prominence of the scapula, with the same weight load when he lowered the arm (descending) around 90 ° of flexion (b).

Table 1.

Mean Percentage values of Maximum Isometric Voluntary Contraction (% MVIC) during descending phase of abduction (over 5, one second time blocks) with varied loads.

	UPPER TRAPEZIUS						LOWER TRAPEZIUS						SERRATUS ANTERIOR
	RIGHT			LEFT			RIGHT			LEFT			RIGHT			LEFT
Descent	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg
1 sec	37	49	57	37	32	31	11	17	29	14	15	19	24	38	41	17	20	24
2 sec	30	33	51	30	27	29	7	19	35	12	17	22	18	34	32	19	22	27
3 sec	18	31	38	19	25	29	6	17	26	10	15	14	12	25	29	14	25	28
4 sec	16	33	38	18	24	32	6	18	28	10	16	14	12	21	32	14	28	30
5 sec	14	25	32	15	22	26	3	11	15	7	8	9	8	28	27	6	21	15

Table 2.

Mean Percentage values of Maximum Isometric Voluntary Contraction (% MVIC) during descending phase of flexion (over 5, one second time blocks) with varied loads.

	UPPER TRAPEZIUS						LOWER TRAPEZIUS						SERRATUS ANTERIOR
	RIGHT			LEFT			RIGHT			LEFT			RIGHT			LEFT
Descent	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg	0 kg	1.8 kg	3.2 kg
1 sec	20	35	51	14	26	34	12	10	22	15	14	18	23	36	45	17	19	23
2 sec	22	46	55	14	29	37	13	4	8	13	8	10	23	30	36	17	19	26
3 sec	19	40	59	15	35	50	6	2	3	6	4	10	19	27	40	16	22	33
4 sec	20	45	62	16	39	55	2	2	3	5	4	10	18	29	43	17	25	36
5 sec	18	32	57	15	32	44	2	2	3	3	4	11	17	26	44	13	17	26

Figure 2.

a) Ratio of Upper Trapezius to Lower Trapezius Muscle Electromyography (EMG) Activity During the Descending Phase of Adduction. The subject simultaneously lowered both sides of arms from the maximum of flexion to the side of the body (0 ° of flexion) over 5 seconds while following the metronome set at 1 beat per second. The ratio of upper trapezius (UT) to lower trapezius (LT) muscle EMG activity was remarkably higher in the dominant side during the descent phase of flexion, which was progressively greater as the weight load was increased from 0 kg to 3.2 kg.

b) Ratio of Upper Trapezius to Lower Trapezius Muscle Electromyography (EMG) Activity During the Descending Phase of flexion. In contrast to abduction/adduction, no difference in the ratio of UT/LT was found between the dominant and non-dominant side during the descent phase of abduction.

DISCUSSION

The results of a previous study⁶ of 28 college baseball players including 13 pitchers, all of whom showed no visual evidence of SD bilaterally, indicated that the mean EMG value of the UT on the dominant side was significantly less than that of the non-dominant side during both the ascending and descending phase, whereas the mean EMG value of the LT on the dominant side was significantly greater than that of the non-dominant side. However, no difference was observed in SA muscle activity between the two sides. The subject of this case report activated the SA muscle more on the dominant side than that of non-dominant side likely as a compensation for reduced LT muscle activity during the descending phase. Increased activity of the UT muscle relative to LT muscle may deteriorate and jeopardize optimal upward rotation of the scapula.^18,19 The LT muscle further contributes to the posterior tilt of the scapula during the late cocking phase of the throwing or serving motion.^7,20

Gilliam et al²¹ revealed that only 59% of the pitchers who underwent SLAP repair were able to return to their prior level of performance (RTPP). However, 69% of those pitchers who did RTPP reported a KJOC score that was less than 90 out of 100.²¹ The score below 90 has also been reported for professional pitchers with a history of shoulder or elbow injury²² who had undergone surgical or nonsurgical treatments.²³ Those pitchers returning following a SLAP repair showed a mean KJOC score much less than 90 and often reported scores close to 75/100.^21,24 One retrospective study reported that professional baseball pitchers who had undergone a SLAP repair attained RTPP less than those pitchers who received nonsurgical treatment for their SLAP lesion (15% vs. 33% respectively for AAA/MLB affiliation pitchers; and 0% vs. 15% for Rookie/A/AA affiliation pitchers).²⁵ Ahmad²⁶ also described two kinds of SLAP lesions in baseball pitchers: one was “a beneficial adaptation” while the other was ”a pathologic process.” Thus, the outcomes of SLAP repairs have shown various challenges required for pitchers regardless of their performance level.

The subject of this case report had not pitched in the summer before participating in his team fall practice season. However, he started throwing programs while he was given a rehabilitation exercise program by his team's certified athletic trainer, which included scapular stability exercises using a small dumbbell, such as prone exercises,²⁷ the free-motion kinetic chain exercise²⁸, and rotator cuff strength exercises (Table 3).

Table 3.

Shoulder Exercises for the Pitcher with the SLAP lesion, performed during the pre-season.

Scapular Wall Slide with Elastic Band

Throwing Arm Abduction with Side Lunge

Free Motion Exercise “Lawnmower” Prone Extension, Abduction, External Rotation with 0.9-1.4 kg dumbbell

Prone Scapular Row Exercise with 1.4-1.8 kg dumbell

Supine Scapular Punch Exercise with 6-9 kg dumbell

Side Lying Ext Rot with 0.9-1.4 kg dumbell

Side Step Ext Rot with Elastic Band

Standing Ext Rot 90/90 position with Elastic Band

Standing Extension with Elastic Band

Standing Row Scapular Retraction Exercise with Elastic Band

Standing D1 Parten with Elastic Band

Standing Forward Abduction Exercise with Elastic Band

Manually resisted Side Lying Punch

Manually resisted Supine D2 Pattern

Manually resisted Side Lying Ext Rot

Note: All exercises were performed under the supervision of team athletic trainer. Each exercise volume typically included 2 sets of 15 repetitions, and resistance was dosed for each individual.

He continued to perform his shoulder exercises under the supervision of the team athletic trainer during the course of season, which could have helped him complete his last season. However, this subject had decided to retire after the season and efficaciously completed his career. Thus, a follow-up SD test with EMG analysis was unavailable for this subject to identify the specific outcomes of the exercise intervention. The authors of this study can only recommend that clinicians consider conducting the SD test to identify asymmetrical SD in baseball pitchers with symptomatic shoulders. Since the outcome of labral surgeries to RTPP in baseball pitchers was identified as less than 60%,²¹ the integration of scapular exercises²⁹ might help overhead athletes improve symptomatic shoulders during the course of their athletic career.

Limitations

This report describes only one collegiate baseball pitcher, who was highly trained to prepare for his upcoming season although he had a symptomatic shoulder on his throwing side at the time of data collection. Thus, the findings of results in this study may limit the generalization regarding age and the level of performance to other populations and conditions including other static shoulder and scapular ROMs and symptomatic shoulder.

CONCLUSIONS

The results of this case report indicate that scapular dyskinesis (specifically Kiber's classification Type II) can identified using the SD test in FLX/EXT in a subject with a confirmed Type II SLAP lesion. EMG findings from the SD test further confirm alterations of UT/LT ratios, noted in the descending or lowering phase from flexion. The SD test may play a critical role in identifying SD in symptomatic shoulder who also have a SLAP lesion in a baseball pitcher. Further studies are warranted to investigate the outcome of the SD test compared between pre- and post-rehabilitative intervention, to guide injury prevention and rehabilitation in baseball pitchers.