Intramuscular Degloving Injuries to the Rectus Femoris: Findings at MRI

Musculoskeletal Imaging Clinical Perspective Kassarjian et al. Rectus Femoris Degloving Injuries Musculoskeletal Imaging Clinical Perspective ra Kassarjian 1 Rosa Monica Rodrigo 2 Juan Maria Santisteban 3 Kassarjian, Rodrigo RM, Santisteban JM Keywords: football (soccer), MRI, muscle injury, rectus femoris, soccer, sports medicine DOI:10.2214/JR.13.10931 Received March 20, 2013; accepted after revision November 1, 2013. 1 Musculoskeletal Radiology LLC, Corades, Madrid, Spain and rookline, M. ddress correspondence to. Kassarjian (akassarjian@gmail.com). 2 Resonancia Magnética ilbao, ilbao, Spain. 3 Medical Services, thletic Club ilbao Spain and Department of Physiology, Faculty of Medicine and Odontology, University of the asque Country, ilbao, Spain. WE This is a web exclusive article. JR 2014; 202:W475 W480 0361 803X/14/2025 W475 merican Roentgen Ray Society JR:202, May 2014 Intramuscular Degloving Injuries to the Rectus Femoris: Findings at MRI OJECTIVE. The purpose of this study was to describe the MRI characteristics of intramuscular degloving injuries to the rectus femoris whereby the inner bipennate component of the indirect head is dissociated from its superficial unipennate component. CONCLUSION. Injuries to the rectus femoris muscle are common in athletes, especially European football (soccer) players. The complex muscle-within-a-muscle anatomic configuration of the rectus femoris makes it susceptible to various types of injuries. I njuries to the thigh muscles, specifically the rectus femoris, are common in many sports, especially football (soccer) and rugby. fter hamstring strains, rectus femoris strains are the second or third most common thigh muscle strains [1, 2]. Previous articles have elegantly described the complex anatomy of the rectus femoris muscle. The descriptions include unique characteristics such as a double tendinous origin (indirect and direct tendons) and long intramuscular extension of the indirect tendon, occasionally referred to as the intramuscular septum or central aponeurosis [3]. These complex anatomic features result in a muscle-withina-muscle configuration in which an outer unipennate muscle surrounds an inner bipennate muscle [4 8]. unipennate muscle is one in which the muscle fibers originate from one side of the tendon and that tendon remains on one side of the muscle, sometimes blending with an aponeurosis on the surface of the muscle, as is the case for the direct portion of the rectus femoris. bipennate muscle is one in which the muscle fibers originate from two sides of a tendon, as is the case of the indirect portion of the rectus femoris, and form an intramuscular central tendon or central aponeurosis (Fig. 1). ecause of the complex anatomy, injuries to the rectus femoris muscle may not always fit nicely into the traditional 3-point grading system of describing muscle injuries [6]. For instance, myofascial injuries, which are not rare in the rectus femoris, are difficult to classify with the traditional strain grades. In addition, the complex anatomic features, including the muscle-within-a-muscle configuration of the rectus femoris, make the muscle susceptible to an uncommon type of injury whereby the inner bipennate intramuscular portion of the indirect myotendinous complex is separated from the surrounding outer unipennate portion of the muscle [8, 9]. This separation results in dissociation of the inner muscle belly from the outer belly and in some cases results in retraction of the inner muscle belly. This combination of dissociation and potential retraction of the inner muscle is analogous to a finger in a glove, which is why the injury is called intramuscular degloving of the rectus femoris. The purpose of this study was to describe the MRI characteristics of these injuries. Materials and Methods Institutional review board approval was obtained from the sites collaborating on this project, both of which waived the requirement for patient consent for this retrospective study. The imaging databases of two private imaging sites were searched for MRI examinations of the hip, pelvis, or thigh that revealed injuries to the rectus femoris muscle. For one of the sites, this was a textbased search of reports from the previous 3 years that mentioned injuries (keywords: injury, strain, or tear) to the rectus femoris. For the other site, the clinical database of the elite youth academy of a first division football (soccer) team was searched for players with recorded rectus femoris injuries who had undergone MRI examination for that injury over the past three seasons. The reports of the MRI examinations were reviewed by one of two musculoskeletal radiologists (10 and 15 years of experience in musculoskeletal W475

Kassarjian et al. MRI) to determine whether the injuries described involved the intramuscular bipennate portion of the rectus femoris muscle. The MR images of those selected reports were then reviewed individually by both radiologists to confirm that the injury did involve the intramuscular portion of the rectus femoris and to assess whether the injury was an intramuscular degloving injury. Discrepancies were resolved by consensus. The database searches and analysis of the data retrieved resulted in identification of the cases of eight patients with degloving injuries to the rectus femoris muscle according to the previously mentioned imaging criteria. These eight patients formed the basis of this study. The clinical database of the soccer team was reviewed by one author, which found that among the 76 rectus femoris injuries over three seasons, seven were degloving injuries. For the degloving injuries, the following were recorded: mechanism of injury, nature of play at time of injury (match vs practice), dominant versus nondominant lower extremity, Fig. 1 Muscle-within-muscle configuration of rectus femoris. (Courtesy of and drawn by Hennequet L, Universidad del País Vasco, ilbao, Spain), Drawing shows overview of rectus femoris muscle. Direct head tendon (DT, dark blue, bottom long arrow) originates from anterior inferior iliac spine and blends with anterior aponeurosis (). Origin of indirect head tendon (IT, pink, top long arrow) with respect to lateral acetabular margin (superior acetabular ridge) and hip joint capsule is more inferior and posterior than that of DT. IT courses within substance of muscle and forms central aponeurosis (C, light blue). Result is bipennate configuration of inner muscle belly (IM, pink). This inner unit is enveloped by unipennate superficial muscle belly (SM, brown) with fibers that run from to posterior aponeurosis (P, green). This envelopment constitutes muscle-within-muscle configuration (short arrows)., 15-year-old male soccer player with muscle fatigue. xial fat-suppressed T2-weighted MR image (right) shows edematous inner indirect (bipennate) myotendinous complex (C and its surrounding fibers, or IM) enveloped by superficial direct (unipennate) muscle belly (SM). lso evident are and P. xial illustration (left) has been inverted to match conventional orientation of MR images. whether the player continued to play, and interval in days between injury and return to play. For the purposes of this study, the intramuscular bipennate portion of the rectus femoris muscle was defined as the long portion of the indirect myotendinous complex that is located within the muscle, has a sagittal or oblique sagittal tendon orientation, and is covered by muscle fibers on both its medial and lateral aspects. lso for the purposes of this study, intramuscular degloving was defined as separation of the central indirect tendon and the adjacent muscle fibers (i.e., the bipennate myotendinous complex) from the remaining (surrounding unipennate) rectus femoris muscle (Fig. 2). For the MRI examinations of patients with intramuscular degloving injuries to the rectus femoris, the following parameters were recorded on the basis of analysis of the requisitions, MR images, and associated DICOM metadata: age in years, sex, laterality, and activity, when available. For these same cases, the following parameters were recorded independently by each radiologist on the basis of analysis of the MR images (discrepancies were resolved by consensus): maximum length of lesion in centimeters as measured on axial, coronal, or sagittal images acquired with fluid-sensitive sequences; distance in centimeters between the cranial portion of the injury and the acetabular rim (the acetabular rim was chosen because it was visible on all images, whereas the anterior inferior iliac spine, which is the origin of the direct tendon, was not visible on all images); degree of retraction of the tendon, defined as craniocaudal separation in centimeters from the distal point of the involved portion of the inner bipennate muscle to the adjacent intact unipennate outer muscle belly as seen on images obtained with fluid-sensitive sequences (Fig. 3); presence or absence of rectus femoris muscle edema, defined as increased T2 signal intensity in fibers of the rectus femoris; presence or absence of adjacent fascial or perifascial fluid, defined as fluid tracking along the deep or superficial portions of the fascia of the rectus femoris; presence or absence of subcutaneous edema; presence or absence of imaging evidence of previous injury (e.g., scar, focal atrophy) to the ipsilateral rectus femoris or other thigh muscles and the muscles involved; and the presence or absence of edema of other visible muscles and the muscles involved. Results Patient Demographics ll eight patients were male adolescents and young adults (average age, 18 years; range, 15 22 years). Four injuries were on the right, and four were on the left. Of these, four were to the dominant extremity and three were to the nondominant extremity; in one case which extremity was dominant was unknown. ctivity at Time of Injury and Return-to-Play Interval Seven of the eight injuries were sustained while the patient was playing football (soccer). Five occurred during a match, and W476 JR:202, May 2014

two occurred during practice. The activity at the time of injury was not specified for the eighth patient. Four of the seven soccer injuries occurred while the player was kicking, one during sprinting, and one with forced quadriceps extension. The seventh player noticed the injury only after the match. Four of these players continued to play, and three stopped playing. The interval between injury and return to play ranged from 28 to 58 days (average, 38.7 days) (Table 1). Location and Size of Lesions The average length of the degloving injuries was 9.9 cm (range, 3.8 17.9 cm). The average distance between the acetabular rim and the proximal portion of the injury was 15.5 cm (range, 11.3 20.3 cm). The average degree of retraction was 1.2 cm (range, Rectus Femoris Degloving Injuries 0 3.5 cm). ll injuries were associated with edema in the rectus femoris muscle and the presence of fascial or perifascial fluid. Seven injuries were associated with subcutaneous edema (Fig. 4). Three patients had imaging evidence of previous thigh muscle injuries. Of these, one had evidence of previous bilateral rectus femoris injuries, one had evidence of previous ipsilateral rectus femoris injury, and one had evidence of previous bilateral hamstring origin injuries and contralateral rectus femoris injury. Seven patients had associated edema in other thigh muscles. The other muscles involved were variable and included the ipsilateral vastus medialis, vastus lateralis, sartorius, adductors, biceps femoris, semitendinosus, iliopsoas, and tensor fascia lata and the contralateral rectus femoris and vastus lateralis. TLE 1: Patient and Injury Characteristics mong Soccer Players Nature of Play at Time of Injury Dominant vs Nondominant Side Patient No. ge (y) Mechanism Return-to-Play Interval (d) Continued Playing? 1 15 Kicking 31 Match Yes Dominant 2 15 Kicking 58 Match Yes Dominant 3 20 Kicking 30 Match Yes Nondominant 4 17 Sprinting 34 Practice No Nondominant 5 21 Kicking 28 Match No Dominant 6 22 Unknown 37 Match Yes Dominant 53 Practice No Nondominant 7 16 Forced quadriceps extension Note side from age, data were not available for one patient whose sport or activity was unknown. Discussion Given the complexity of the anatomy of the rectus femoris muscle, a variety of lesions can occur, and classification of such lesions is challenging. Many injuries cannot be classified with the traditional muscle strain classification systems. For example, a myofascial injury is difficult if not impossible to clearly classify with the traditional 3-point muscle injury and strain grading system. Other classification systems of acute muscle injuries have been proposed [10, 11] in an attempt to include injuries, such as myofascial and intramuscular injuries, that are not specified in the traditional 3-point grading system. Whether these new classification systems will have clinical utility or prognostic value remains to be seen. In the meantime, it is important to recognize the different types of muscle injuries seen at imaging [6, 12]. ecause the indirect component of the rectus femoris has a long intramuscular myotendinous junction, it is susceptible to unique types of injuries. Unlike the long myotendinous injuries in other muscles, such as the hamstrings, the myotendinous complex of the indirect head of the rectus femoris is susceptible to a more longitudinally oriented injury, which not only results in myotendinous injury but also may result in separation and dissociation of the inner bipennate component of the muscle from the surrounding unipennate muscle. In some cases, this dissociation results in proximal retraction of the inner myotendinous complex, analogous to a C Fig. 2 15-year-old male soccer player with intramuscular degloving injury of rectus femoris. C, Consecutive axial ( and ) and single coronal (C) fat-suppressed T2-weighted fast spin-echo MR images show separation of inner bipennate myotendinous complex (thick arrow) from outer unipennate portion (arrowhead) by fluid (involving 100% of circumference of bipennate portion). Intramuscular edema is present in inner bipennate portion as increased signal intensity. Central aponeurosis (intramuscular septum) is in middle of inner muscle (thin arrow). Retracted inner bipennate muscle (large arrow) is evident in C. JR:202, May 2014 W477

Kassarjian et al. Fig. 3 22-year-old male soccer player with pain in contralateral thigh during match. Patient did not feel pain in imaged thigh. Coronal fat-suppressed T2- weighted fast spin-echo MR image shows craniocaudal separation in centimeters (i.e., degree of retraction) measured by drawing of vertical line from margin of inner bipennate retracted muscle (horizontal line) to more distal intact unipennate outer muscle. finger being withdrawn from a glove. For this reason, we have termed this type of lesion intramuscular degloving injury to the rectus femoris. lthough the ultrasound appearance of the muscle-within-a-muscle configuration of the rectus femoris has previously been described [8, 9], as have myotendinous injuries to the rectus femoris, to our knowledge ours is the first detailed description of the MRI findings of this type of intramuscular degloving injury [6, 9]. It is important to recognize this type of degloving injury as being distinct from the typical myotendinous injury to the indirect portion of the rectus femoris. The more common and previously described typical myotendinous injury to the indirect component of the rectus femoris is a myotendinous injury centered along the long indirect intramuscular tendon. This results in a typical MRI appearance of focal edema and sometimes fluid centered at the true myotendinous junction. Hughes et al. [13] called this injury a bull s-eye lesion (Fig. 5). In contradistinction, with a degloving injury, there is an apparent true dissociation of the inner muscle belly (i.e., the bipennate component) from the surrounding outer muscle (i.e., the unipennate component). This deep central unit is a bipennate muscle related to the indirect tendon of the rectus femoris (also called central septum or aponeurosis), which is enveloped by the more superficial unipennate component of the muscle, which is related to the direct tendon of the rectus femoris. This configuration makes up what has been termed the muscle within a muscle. The degloving refers to dissociation (partial or complete) of the inner muscle belly from the outer muscle with or without associated retraction (Figs. 2 and 4). Dissociation of the central bipennate component from the more superficial unipennate component can have a variable length, as seen in our cases, ranging from approximately 4 to 18 cm. In addition, the dissociation appears to occur in the periphery of the fibers of the inner bipennate muscle belly as opposed to the myotendinous junction. For this reason, it may be more appropriate to refer to these injuries as involving the inner muscle belly and not the myotendinous junction per se. C Fig. 4 22-year-old male soccer player with intramuscular degloving injury to rectus femoris. and, xial () and coronal () fat-suppressed T2-weighted fast spin-echo MR images show edema within inner and outer muscle portions of rectus femoris and two components of muscle separated by fluid (small arrow, and ). Fascial fluid tracks medially along rectus femoris (large arrow). C, xial fat-suppressed T2-weighted fast spinecho MR image inferior in location to shows subcutaneous edema anteriorly (arrowhead) and perifascial fluid (arrows) tracking medially along rectus femoris and laterally along vastus lateralis. Defect (asterisk) left by retracted inner bipennate muscle is evident. ll of the injuries in our patients were associated with edema within the rectus femoris muscle and adjacent fascial fluid. Seven of eight patients had mild to moderate subcutaneous edema over the anterior thigh. In addition, mild injuries and edema of other thigh muscles appear relatively common, as seen in most of our patients. Considering the biomechanics of rectus femoris injuries, although some of these other regions of muscle edema may have been directly related to the rectus femoris injury (e.g., those of the ipsilateral sartorius), others may be independent and unrelated lesions. For example, the contralateral vastus lateralis injury may have been from a contusion. Occasionally there may be evidence of previous injuries to other muscles or tendons. However, given the small number of cases in this series, the exact association of previous injuries to other thigh muscles with acute injuries to the intramuscular portion of the rectus femoris is unclear. W478 JR:202, May 2014

Rectus Femoris Degloving Injuries Fig. 5 18-year-old male soccer player with typical indirect myotendinous (central aponeurotic) strain. and, xial () and coronal () fat-suppressed T2-weighted fast spin-echo MR images show edema and fluid along myotendinous junction or central aponeurosis (arrow). The biomechanical implications of this intramuscular degloving injury are not clear and should be the subject of further study. In addition, the natural history and prognostic implications of degloving injuries must be studied in more detail. For example, mild and incomplete lesions may appear merely as edema along the interface Fig. 6 22-year-old male soccer player with injury to rectus femoris muscle. and, Coronal () and axial () fat-suppressed T2-weighted fast spin-echo MR images show edema (arrows) along interface between inner and outer components of rectus femoris muscle without fluid or separation at interface between components. Further investigation is needed to assess whether this is precursor to actual intramuscular degloving injury to rectus femoris. between the inner and outer components of the rectus femoris (Fig. 6). Whether these lesions would progress to an incomplete or complete degloving injury were the player not prevented from training and playing is not known. In our series, the degloving injury represented only 9% of all rectus femoris injuries. Rectus femoris lesions, including degloving lesions, can be difficult to classify according to the traditional 3-point muscle injury grading scheme. However, considering the average return-toplay interval for these lesions and some of their imaging characteristics, their behavior appears similar to grade 2 muscle lesions. Interestingly, for the four players who continued to play a match despite the injury, the initial clinical assessment suggested overuse injury, not an actual muscle tear (strain). The physical examination revealed only increased muscle tension without clinically significant weakness or functional impairment. This study had limitations. First, the number of cases is small. This may be due to a combination of the manner in which we performed our retrospective search, our referral base, and the actual frequency of these lesions. Second, in our small series, most of the injuries were in football (soccer) players because that is an important part of our referral base. These lesions may occur in other sports as well. Third, because these are not typically surgical lesions, we do not have a reference standard for diagnosis. However, most medical professionals treating athletes JR:202, May 2014 W479

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