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DOI:10.2214/AJR.04.1929
AJR 2006; 187:1457-1461
© American Roentgen Ray Society

Clinical Observations

Sonography and MRI of Rectus Abdominis Muscle Strain in Elite Tennis Players

David Connell1, Kaline Ali1, Malika Javid1, Phil Bell2, Mark Batt3 and Simon Kemp4

1 Department of Radiology, Royal National Orthopaedic Hospital, Brockley Hill, Stanmore, London HA7 4LP, United Kingdom.
2 BUPA Wellness, Barbican, United Kingdom.
3 Centre for Sports Medicine, Queens Medical Center, Nottingham, United Kingdom.
4 Football Union Rugby House, Twickenham, United Kingdom.

Received December 20, 2004; accepted after revision July 10, 2005.

 
Address correspondence to D. Connell (david.connell{at}rnoh.nhs.uk).


Abstract
Top
 Abstract
Introduction
 Subjects and Methods
 Results
 Discussion
 References
 
OBJECTIVE. The objective of this study was to describe the imaging findings at sonography and MRI of rectus abdominis muscle strain in tennis players.

CONCLUSION. Asymmetrical hypertrophy of the recti is seen in elite tennis players. The muscle belly hypertrophies on the side opposite the dominant arm and is subject to muscle tears of its deep fibers below the umbilicus. Imaging can be used to show these injuries.

Keywords: MRI • muscle strain • rectus abdominis • sports medicine • sonography


Introduction
Top
 Abstract
 Introduction
Subjects and Methods
 Results
 Discussion
 References
 
Anterior abdominal wall and groin injuries in athletes, including tennis players, have been described in several studies [1-4]. Injury to the anterior abdominal wall results in pain, tenderness, and forced withdrawal of the athlete from play and may lead to prolonged exclusion from competition [3].

The length and cross-sectional area of muscle injury and the amount of hematoma are prognostic factors that have been implicated in convalescence and return to play after muscle injury [5]. Experimental data suggest that, after strain injury, muscle is weaker and at increased risk for further injury compared with normal muscle [6]. These considerations make the diagnosis of any potential strain or muscle tear important so that appropriate early rehabilitation and subsequent functional rehabilitation can be instituted promptly.

In this study, we describe the imaging findings of rectus abdominis muscle strain in a group of tennis players who presented with anterior abdominal wall injury. To the best of our knowledge, the imaging findings of rectus abdominis strain have not been previously reported.


Subjects and Methods
Top
 Abstract
 Introduction
 Subjects and Methods
Results
 Discussion
 References
 
Subjects
From January 2003 to January 2005, 11 elite tennis players were referred by sports physicians to our institution for sonography to evaluate anterior abdominal wall pain and muscle spasm. There were eight males and three females with an age range of 15-28 years (mean age, 21 years). There were nine right-handed tennis players, and two were left-handed. Six players complained of sudden onset pain and point tenderness that occurred while serving, four while playing a forehand ground stroke, and one while performing an overhead smash. The symptoms were on the contralateral side of the dominant (racquet) arm in all cases. Three of the 11 patients reported similar episodes in the past (3, 5, and 10 years ago, respectively). Informed consent was obtained from all 11 players, and institutional board consent for the study was granted.

After clinical assessment, sonography was performed by a trained musculoskeletal radiologist (10 years of experience) with emphasis on the area of point tenderness and pain. The scanner used (HDI, ATL) had a 5-12 MHz linear probe. The presence or absence of a tear was noted as was the location within the muscle belly, and the craniocaudal length was measured. The patient lay supine and the recti were scanned separately by passing the transducer in a transverse sweep from the cranial-to-caudal direction, followed by longitudinally scanning in the left-to-right direction. The abdominal wall musculature was evaluated, and a comparison was made of rectus abdominis thickness on either side by measuring the distance from the posterior to the anterior margin at the level of the umbilicus. Any alteration in echotexture or fibril disruption was noted as was the length of any tear measured. The longitudinal length of the tear was measured because it was the greatest dimension in all cases. Color Doppler sonography was performed to assess for neovascularity. The presence or absence of echogenic foci characterizing scar tissue was noted.

On sonography, a muscle tear was diagnosed by disruption of the normal echogenic fibrillar pattern and the presence of anechoic clefts and irregular linear bands. Fluid collections were noted. Scar tissue was diagnosed by focal areas of fibril disruption replaced by echogenic foci with disorganization of adjacent normal muscle.


Figure 1
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  		Fig. 1A —24-year-old professional male tennis player. Transverse sonograms show hypertrophy of left rectus abdominis (A) relative to right rectus abdominis (B).

 


Figure 2
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  		Fig. 1B —24-year-old professional male tennis player. Transverse sonograms show hypertrophy of left rectus abdominis (A) relative to right rectus abdominis (B).

 
In addition, seven players underwent further assessment with MRI at the request of the referring physician. A surface coil (SHOPA, MedRad) was placed over the abdominal musculature and the patient was encouraged to breathe gently. After an axial localizer, axial and coronal STIR (TR/TE, 3,500/30; inversion time, 130 msec) and proton density images (4,000/30) were obtained. The field of view was 28 cm, slice thickness was 6 mm, and matrix was 512 x 256. The MRI examination was interpreted by a trained musculoskeletal radiologist (6 years of experience) who was not aware of the sonography results on either the STIR or proton density images. The sonographer was also blinded to the MRI results. On MRI, a muscle tear was considered to be a focal area of high signal with muscle discontinuity, whereas scar tissue was considered to be a focus of low signal on all pulse sequences. The MRI examination preceded or followed the sonography examination on the same day in all seven cases.

In addition, 10 elite asymptomatic tennis players (five men and five women; mean age, 22.1 years) were recruited for sonographic examination. The recti thickness was measured and the muscle architecture evaluated for each player.

Statistical Analysis
The Kolmogorov-Smirnov test was used to assess the normality of the data. Data that did not follow a normal distribution were analyzed using the Mann-Whitney test. Data that satisfied the assumption of normality were analyzed using a one-way analysis of variance. Comparisons were made between the dominant and nondominant anteroposterior diameter measurements for the symptomatic and asymptomatic tennis players. All statistical analyses were performed using SPSS for Microsoft Windows, version 12.0 (Statistical Package for the Social Sciences) and p values of < 0.05 were considered statistically significant.


Results
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 Abstract
 Introduction
 Subjects and Methods
 Results
Discussion
 References
 
Hypertrophy of the rectus musculature was observed on the side contralateral to the racquet arm in all 10 asymptomatic tennis players (Fig. 1A, 1B). Statistical analysis found a significant difference between the anteroposterior diameter measurements for the dominant (mean = 21.2 ± 1.93 [SD]) and nondominant (mean = 28.2 ± 1.93) hands in the asymptomatic tennis players (df(1,18) = 65.625; p < 0.001). There was also a significant difference between the anteroposterior diameter measurements for the dominant (mean = 7.14) and nondominant (mean = 15.86) hands for the symptomatic patients (Mann Whitney U test = 12.5; group 1, n = 11; group 2, n = 11; p = 0.002, two-tailed). The results of the patient cohort have been summarized in Table 1. There were nine injuries on the left side and two on the right. The location of the muscle injury was below the umbilicus in all cases.


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  		TABLE 1: Patient Data and Imaging Findings

 

At sonography, rectus abdominis muscle injuries were characterized by disruption of the normal echogenic fibrillar pattern with fluid-filled clefts traversing the disorganized muscle (Fig. 2A, 2B). The abnormality was thought to represent disrupted muscle fibrils, edema, and hemorrhage. Only in the presence of discrete anechoic collections of blood-fluid products was the musculoskeletal radiologist able to discriminate between the latter two. In nine of the 11 players, the injury was seen on the deep surface of the muscle belly. In one player the injury occurred on the superficial epimysial boundary and in another, it involved the lateral half of the muscle. The range of muscle tears ranged from 6-72 mm in craniocaudal length (mean, 32.2 mm). Pulsatile blood flow in the region of muscle injury was identified in six of the 11 patients on color Doppler sonography. The MRI findings were compatible with sonography and no additional information was provided by the former.


Figure 3
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  		Fig. 2A —16-year-old elite male tennis player. Sonogram shows focal area of myofibril disruption of deep and lower part of left rectus abdominis after forehand smash.

 

Figure 4
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  		Fig. 2B —16-year-old elite male tennis player. Color Doppler sonogram shows blood vessels infiltrating site of muscle tear.

 
In the seven patients who underwent MRI, abnormal signal was returned in the region of sonographic abnormality (Fig. 3A, 3B). Coronal imaging was found to be useful for assessing the degree of fibril disruption and retraction (Fig. 4). There was some discrepancy in the imaging findings with respect to the time course after injury. In players who presented within the first few days after injury, edema and blood fluid products were prevalent findings—both of which had incompletely resolved in the players who presented at 14 and 28 days after injury.


Figure 5
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  		Fig. 3A —21-year-old male tennis player after serving injury. Axial proton density (TR/TE, 4,000/30) (A) and axial STIR (3,500/30 [B]; inversion time, 130 msec) images show hypertrophy of left rectus abdominis with focal area of hyperintensity (arrow) compatible with muscle edema, hemorrhage, and fibril disruption.

 

Figure 6
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  		Fig. 3B —21-year-old male tennis player after serving injury. Axial proton density (TR/TE, 4,000/30) (A) and axial STIR (3,500/30 [B]; inversion time, 130 msec) images show hypertrophy of left rectus abdominis with focal area of hyperintensity (arrow) compatible with muscle edema, hemorrhage, and fibril disruption.

 

Figure 7
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  		Fig. 4 —Coronal MR image (TR/TE 4,000/30) in 19-year-old elite male tennis player shows left lower rectus abdominis tear (arrow) after forehand injury.

 
In two of the three patients with a history of previous symptoms, there was scar tissue on the affected side in addition to the acute tear. This was manifested as an irregular echogenic focus on sonograms and a discrete focus of low signal on MR images on both the proton density and STIR sequences. These foci were distinct and separate from the acute injuries. There was no neovascularity of these scarred areas on color Doppler sonography.

There was no difference in the location of the muscle injury when comparing MRI and sonography. There was also no discernible difference in the size of the tears; however, a 6-mm slice thickness was used on MRI, and because many of the tears were small, the MR measurement was approximate.

We have limited data on the follow-up and return of players to the tennis circuit. Five players had returned to practice within 4 weeks and four of these were playing competitive tennis within 2 months.


Discussion
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
References
 
The recti are paired straplike muscles that are separated at the midline by the linea alba (Fig. 5). Each muscle has two tendinous origins. A medial head arises from the anterior surface of the pubic symphysis, whereas the larger lateral head originates from the upper border of the pubic crest, and together they form a muscle mass that inserts onto the fifth to seventh costal cartilages [7]. The aponeuroses of the internal and external oblique and transversus abdominis fuse to form the linea alba, a strong midline fibrous structure that is firmly attached to the xiphoid process above and the pubic symphysis below.


Figure 8
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  		Fig. 5 —Transverse section through anterior abdominal wall.

 
Three fibrous bands or tendinous intersections interrupt each muscle and blend inseparably with the anterior layer of the rectus sheath. They are found at the level of the umbilicus, the xiphoid process, and midway between the two. They pass obliquely across the muscle in a zigzag manner but occupy only the superficial part of the rectus and do not penetrate through to the posterior surface of the muscle, which is thus not connected to the posterior layer of the sheath. One or two incomplete intersections are occasionally present below the umbilicus.

In our study, fibril disruption tended to occur on the deep epimysial surface of the muscle below the umbilicus. This part of the muscle is where the tendinous intersections do not extend, and the result may be a longer zone through which strain is transferred and a potential site of weakness. Hence, there may be an anatomic explanation for the site of injury, although this needs to be further evaluated with biomechanical testing.

The abdominal musculature plays a significant role in trunk and core stability for the tennis player, providing a mechanical link between the lower and upper extremities. During the tennis serve, a large amount of angular momentum is transferred to the racquet [8]. Trunk rotation and forward swing after lumbar extension are essential parts of generating the force needed to serve. The lower abdominal muscles function as both stabilizers and prime movers and consequently are vulnerable to injury.

Our study showed that hypertrophy of the contralateral rectus abdominis muscle (the nondominant arm side) is a common finding in tennis players who play at an elite level. High electromyographic activity is seen in the nondominant rectus during the throwing phase of the serving action [9, 10]. We postulate that this is the consequence of increased strain transferred through this muscle, possibly during the serving mechanism or during trunk rotation when hitting forehand ground strokes. Injury most often occurs in the distal rectus (below the umbilicus) on the hypertrophied side.

Sonography appears to be a sensitive and valuable technique in detecting rectus abdominis tears that can be performed courtside if necessary. Acute injuries are easier to diagnose in the presence of blood-fluid products and muscle edema. A high-resolution transducer (7-12 MHz) is necessary to appreciate small areas of fibril disruption and echogenic scar tissue. Color Doppler imaging is useful for depicting neovascularity, which may become apparent in the healing phase of muscle injury and hence a useful adjunct for the identification of muscle tears.

In our study, no additional information was obtained from MRI. However, seven of the 11 players went on to MRI at the request of the tournament medical director because many players would not be returning for further treatment or rehabilitation, and the treating physicians in other countries may not be comfortable with the sonography findings alone. It has been suggested in other muscle injuries that MRI provides better information in chronic injuries and also in documenting the healing process [5]. MRI may be useful in cases that need further evaluation or at institutions where sonographic expertise is not available.

Tears of the rectus abdominal muscles may have an impact on an elite player's career because of a slow recovery time. Professional athletes are under intense pressure to return to play as soon as possible, and rehabilitation programs may be curtailed prematurely. Continued inappropriate loading in the healing phases of this injury may lead to further injury while immature scar tissue is organizing. Our limited follow-up suggests that a return to full competitive play at the elite level after a strengthening rehabilitation program typically takes 4-6 weeks and is dependent on the extent of the muscle injury.


References
Top
 Abstract
 Introduction
 Subjects and Methods
 Results
 Discussion
 References
 

  1. Lacroix VJ, Kinnear DG, Mulder DS, Brown RA. Lower abdominal pain syndrome in national hockey league players: a report of 11 cases. Clin J Sport Med 1998;8 : 5-9[Medline]
  2. Balduini FC. Abdominal and groin injuries in tennis. Clin Sports Med 1988;7 : 349-357[Medline]
  3. Lehman RC. Thoracoabdominal musculoskeletal injuries in racquet sports. Clin Sports Med 1988;7 : 267-276[Medline]
  4. Connell DA, Jhamb A, James T. Side strain: a tear of internal oblique musculature. AJR 2003;181 : 1511-1517[Abstract/Free Full Text]
  5. Connell DA, Schneider-Kolsky ME, Hoving J, Malara F. Longitudinal study comparing sonographic and MRI assessments of acute and healing hamstring injuries. AJR 2004;183 : 975-984[Abstract/Free Full Text]
  6. Garrett WE Jr. Muscle strain injuries. Am J Sport Med 1996; 24[6 suppl]:S2 -S8[Medline]
  7. Sinnatamby CS, ed. Last's anatomy, 10th ed. Edinburgh, Scotland: Churchill Livingstone, 1999:218
  8. CMP Healthcare Web page. Bahamonde R. Net work: trunk biomechanics in tennis. Available at: www.biomech.com/db_area/archives/2003/0310.cover.bio.shtml. Accessed August 18, 2006
  9. Watkins RG, Dennis S, Dillin WH. Dynamic EMG analysis of torque transfer in professional baseball pitchers. Spine1989; 14:404 -408[CrossRef][Medline]
  10. Chow JW, Shim JH, Leon YT. Lower trunk muscle activity during the tennis serve. J Sci Med Sport 2003;6 : 512-518[CrossRef][Medline]

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