Normal Anatomy and Strains of the Deep Musculotendinous Junction of the Proximal Rectus Femoris: MRI Features

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1 Musculoskeletal Imaging Clinical Observations Gyftopoulos et al. MRI of the Proximal Rectus Femoris Musculotendinous Junction Musculoskeletal Imaging Clinical Observations Soterios Gyftopoulos 1 Zehava Sadka Rosenberg 2 Mark E. Schweitzer 2 Marcelo ordalo-rodrigues 2 Gyftopoulos S, Rosenberg ZS, Schweitzer ME, ordalo-rodrigues M Keywords: hip, MRI, musculotendinous junction injuries, rectus femoris, sports medicine, trauma DOI: /JR Received July 26, 2007; accepted after revision September 26, Department of Radiology, eth Israel Medical Center, First ve. at 16th St., New York, NY ddress correspondence to S. Gyftopoulos (soterios20@gmail.com). 2 Department of Radiology, NYU Hospital for Joint Diseases, New York, NY WE This is a Web exclusive article. JR 2008; 190:W182 W X/08/1903 W182 merican Roentgen Ray Society Normal natomy and Strains of the Deep Musculotendinous Junction of the Proximal Rectus Femoris: MRI Features OJECTIVE. The MRI features of the proximal rectus femoris musculotendinous junction have scarcely been described in the literature. The purpose of our study, based on a review of 50 asymptomatic and 20 symptomatic MRI studies, was to define the normal MRI anatomy and MRI features of intrasubstance injury of deep musculotendinous tears of the proximal rectus femoris. CONCLUSION. xial and coronal MR images are optimal for visualizing the direct and indirect heads, the conjoined tendon, and the deep musculotendinous junction of the proximal rectus femoris. Tears of the deep musculotendinous junction are longitudinal, involving a long segment of the muscle. MRI features include a bull s-eye sign, longitudinal scar, retraction, pseudocyst, and hematoma. I njuries of the deep proximal musculotendinous unit of the rectus femoris are infrequent and can be difficult to diagnose. The injuries, defined as intrasubstance tendinous tears of the proximal rectus femoris, occur in young, athletic individuals during activities such as sprinting and kicking [1]. Predisposing factors include muscle fatigue, insufficient warm-up exercises, overall poor muscle conditioning, and a previous tear [2]. The rectus femoris is a long, fusiform muscle forming the anterior superficial portion of the quadriceps muscle group [3] (Fig. 1). Its main functions include knee extension and hip flexion. The proximal rectus femoris has two tendinous origins: the direct (straight) head, arising from the anterior inferior iliac spine, and the indirect (reflected) head, arising slightly more inferiorly and posteriorly from the superior acetabular ridge and hip joint capsule. The two heads form a conjoined tendon a few centimeters below their origins. The direct head, making up most of the superficial component of the conjoined tendon, blends more distally with the anterior fascia of the rectus femoris. The indirect head, forming most of the posterior component of the conjoined tendon, becomes intrasubstance and forms a long, deep musculotendinous junction extending approximately two thirds of the length of the muscle. To the best of our knowledge, only a few reports in the literature focus on the MRI features of the proximal rectus femoris muscle [4 6]. The purpose of our study, based on a review of 50 asymptomatic and 20 symptomatic patients, was twofold: first, to define the normal MRI anatomy of the proximal rectus femoris musculotendinous unit; and, second, to describe the MRI features of proximal deep rectus femoris musculotendinous junction tears. Materials and Methods MRI Technique MR examinations of the hip were performed at 1.5 T (Magnetom, SP4000, Siemens Medical Solutions) with a phased-array torso coil. The field of view was cm, and the matrix was xial T1-weighted images (TR range/te range, /12 14), coronal T1-weighted images ( /12 14), coronal turbo spin-echo fat-suppressed fluid-weighted images (5,000 6,000/45 65; echotrain length, 8), and sagittal fluid-weighted images (5,000 6,500/50 65) were obtained. The slice thickness was 4 5 mm with a 10% gap. Institutional review board approval was obtained, and informed consent was waived for this retrospective HIP-compliant study. symptomatic Population retrospective review of the normal MRI anatomy of the proximal rectus femoris was performed in 50 MRI studies of 47 patients (23 men, 24 women; age range, years; mean age, 44 years). The studies were obtained from a W182 JR:190, March 2008

2 MRI of the Proximal Rectus Femoris Musculotendinous Junction Fig. 1 Drawing of rectus femoris muscle. Direct head originates from anterior inferior iliac spine (gray arrow) and blends with anterior fascia. Indirect head originates more posteriorly from acetabulum (black arrow) and dives into rectus femoris muscle belly. Modified with permission from [8]. computer data search of MRI examinations of the hips and thighs performed at our institution during a 2-year period. Review of the asymptomatic sides in 47 patients assessed for a variety of unilateral symptoms such as hip or groin pain, avascular necrosis, trauma, tumor, or neurologic conditions was performed. In three patients with sciatic neuropathy, both sides were reviewed. The MR studies were reviewed by one musculoskeletal radiologist with 20 years experience. Symptomatic Population MRI studies of the hip were obtained through a search of our institution s computer data files. The search words included rectus femoris injury, rectus femoris tear, and rectus femoris strain. Only cases with MRI evidence of deep muscu lotendinous junction injury, defined as injuries of the intrasubstance tendon, were included in the study. total of 20 patients with deep muscu lotendinous junction injuries were identified (16 males, four females; age range, years; mean age, 32 years). Two musculoskeletal radiologists, one with 15 years and one with 20 years of musculoskeletal radiology experience, in consensus, reviewed the studies. The following parameters were recorded: grade of injury; presence of bull s-eye sign, retraction, or hematoma; and age of injury. Grading of the tears was based on accepted MRI characteristics of musculotendinous strains [7]. grade I tear is defined as high signal intensity focally or diffusely at the musculotendinous junction on fluid-sensitive images. feathery appearance to the muscle on all pulse sequences is compatible with interstitial hemorrhage and edema. The musculotendinous junction is maintained. grade II tear shows partial disruption of the musculotendinous junction with interstitial feathery high signal intensity or hematoma in the acute setting. Low signal representing either fibrosis or hemosiderin can be seen in chronic or old injuries. grade III tear represents a complete musculotendinous disruption with or without retraction. The bull s-eye sign was defined as bright signal surrounding the low-signal deep tendon on axial T1 or fluid-sensitive sequences (or both) and after administration of IV gadolinium. The age of the injury was categorized as acute when interstitial edema, fluid, and hemorrhage were present; old when there was fibrous encasement of the tendon, muscle atrophy, and fatty replacement; or chronic when there were MRI features of both acute and old injuries. Results symptomatic Population The two tendinous origins of the rectus femoris muscle, the direct and indirect heads, were optimally identified on axial images as linear low-signal structures in all cases (Fig. 2). The direct head originated from the anterior inferior iliac spine (Fig. 2), and the indirect head originated slightly more distally and posteriorly from the acetabulum (Fig. 2). The two heads formed a conjoined tendon approximately 1 cm below their origins. The tendon transformed from a globular structure to a boomerang-like structure located anterior and medial to the muscle fibers. The anterior component of the conjoined tendon blended more distally with the anterior fascia of the rectus femoris. The more posterior portion of the conjoined tendon gradually became embedded within the muscle belly of the rectus femoris, forming a deep tendon with a long, intrasubstance musculotendinous junction (Fig. 2C). The two origins of the rectus femoris tendon and the deep musculotendinous junction were also seen clearly on coronal images, but they were less optimally visualized on sagittal images (Fig. 2D). nterior coronal images depicted the direct head s origin from the anterior inferior iliac spine as a relatively thick, somewhat rectangular low-signal structure (Fig. 2E). The indirect head was visualized on consecutive, slightly more posterior coronal images, in very close proximity to the joint capsule, as a linear, low-signal structure highlighted by fat and thinner than the direct head (Fig. 2F). Symptomatic Population Seventeen (85%) of the 20 symptomatic patients had grade II injuries; one (5%), a grade I tear; and one (5%), a grade III tear. One of the patient s tears could not be accurately graded due to inadequate imaging technique. The injuries were categorized as old (n = 9, 45%) or acute (n = 9, 45%). In two patients (10%), it was difficult to distinguish between a subacute and old injury. In all of our patients, the injuries extended along a long portion of the deep musculotendinous junction. The most common MRI tear pattern was a bull s-eye appearance (n = 13, 65%): a halo of bright signal around the deep tendon, noted on multiple consecutive axial T1 or fluid-sensitive images (Fig. 3). Tendon thickening (n = 6, 30%) and partial muscle retraction (n = 6, 30%) were also seen. Other findings included hematoma (n = 8, 40%); pseudocyst (n = 4, 20%) (Fig. 4); focal fatty muscle replacement (n = 3, 15%); and longitudinal, lowsignal scars (n = 6, 30%) (Fig. 5). Scarring either encased the tendon or extended longitudinally into the adjacent muscle. ll of the grade I and II tears were treated conservatively, and the patient with the grade III tear was lost to follow-up. Discussion The tendinous origins of the rectus femoris muscle have been well outlined, but the proximal musculotendinous junction is incompletely defined in most anatomy textbooks [3]. detailed description of the normal anatomy of the rectus femoris was provided by Hasselman et al. in 1995 [8]. They reported that the direct head arises from the anterior inferior iliac spine, while the more posterior and inferior indirect head originates from the superior acetabular ridge and hip capsule. The two heads form a conjoined tendon. The superficial conjoined tendon, made mostly of fibers of the direct head, then blends JR:190, March 2008 W183

3 Gyftopoulos et al. D E F Fig. 2 T1-weighted images show normal MRI anatomy of rectus femoris in multiple patients., xial image (TR/TE, 500/12) shows origin of direct head (arrow) is off anterior inferior iliac spine., xial image (500/12) shows indirect head as it originates, slightly more distally (white arrow), from superior acetabulum and joins direct head to form conjoined tendon (black arrow). C, xial image (500/12) shows blending of direct head, more distally, with anterior fascia of rectus femoris (black arrow). Note that indirect head (white arrow) is now intrasubstance. D, Sagittal T1-weighted image (550/14) shows direct head (black arrow), conjoined tendon (white arrow), and deep tendon (arrowheads). E, Coronal image (500/12) shows origin of direct head off anterior inferior iliac spine (black arrow), conjoined tendon (white arrow), and deep tendon (arrowheads). F, Coronal image (500/12), more posterior than E, depicts indirect head as it originates from acetabular ridge (arrow). with the anterior fascia of the muscle while the posterior conjoined tendon, made mostly of fibers of the indirect head, becomes intrasubstance to form a long, deep musculotendinous junction. We were able to confirm the anatomy described by Hasselman et al. [8] using MRI studies in an asymptomatic patient population. Our findings confirm the MRI anatomic descriptions in two previous reports [5, 6]. The direct and indirect origins of the proximal rectus femoris were best visualized on axial and coronal MR images of the hip. Each head s destination, the anterior fascia for the direct head and the intramuscular substance for the indirect head, was also clearly depicted on sequential axial images. The lengthy, deep musculotendinous junction was well depicted on axial, coronal, and sagittal images. Deep musculotendinous junction injuries of the proximal rectus femoris are difficult to clinically diagnose partly because of the deep location of the injury and partly because of the relatively nonspecific associated physical findings. Typically, patients with acute deep musculotendinous junction injuries present with a sudden onset of thigh pain and a tearing sensation. Persistent pain, tenderness, and rectus femoris asymmetry may be present. discrete anterior thigh mass related to muscle retraction can be mistaken for a soft-tissue neoplasm [4, 5, 8, 9]. C W184 JR:190, March 2008

4 MRI of the Proximal Rectus Femoris Musculotendinous Junction Fig. 3 ull s-eye sign after rectus femoris injury., ull s-eye sign after rectus femoris injury in 19-year-old man after tearing sensation in thigh. xial T2 fatsuppressed image (TR/TE, 5,050/50) depicts halo of increased signal (white arrows) around deep tendon (black arrow)., ull s-eye sign after rectus femoris injury in 35-year-old woman. xial T1-weighted image (600/13) shows halo of increased signal (arrow) surrounding low-signal deep tendon, which is consistent with fatty atrophy due to remote injury. Unlike typical strains that are depicted on MRI as focal, increased signal at the musculotendinous junction [7], strains of the deep musculotendinous junction of the rectus femoris, in our study, showed a longitudinal distribution of increased signal along the involved tendon, optimally seen on sequential axial images. This type of appearance has also been described in hamstring injuries [10]. The most common type of injury noted in our study was a grade II strain (85%). The relatively mild symptoms of a grade I strain, which rarely require MRI examination, may explain its scarcity in our study. We speculate that the length of the deep musculotendinous junction, approximately two thirds of the muscle belly, may protect it from complete tearing and, thus, may explain the rarity of grade III strains in our study. It is important to note that the current grading system of strains was developed for injuries of focal musculotendinous junctions. This grading system may be less applicable for longitudinally oriented musculotendinous injuries such as those involving the rectus femoris. future prospective study of deep rectus femoris tendon injuries with a larger patient population may be useful to further assess and possibly to modify the present grading system. The bull s-eye sign was seen in 65% of our patients. This sign, coined by Hughes et al. [4] as increased signal around the rectus femoris intrasubstance tendon, was seen in our study in both acute and old injuries and before and after gadolinium injection. We believe this sign represents evolving stages of injury and healing around the deep tendon. Initially, the increased signal on fluidsensitive images likely represents edema and hemorrhage. Subsequently and after IV gadolinium injection, the increased signal may reflect increased vascularity and scarring. bull s-eye sign with secondary atrophy and fatty infiltration of the muscle around the tendon reflects remote injury. The treatment for patients with rectus femoris strains depends on the degree of injury and athletic involvement of the individual. In nonprofessional athletes, conservative management aimed at symptom relief is applied to grade I and II strains. Professional athletes require further intensive physical therapy to avoid reinjury [1, 11]. Surgical intervention is reserved for grade III strains, especially in young, athletic individuals but Fig. 4 Fibrous scarring after remote rectus femoris injury., 19-year-old man who presented with persistent thigh pain after remote rectus femoris injury. Coronal T1-weighted image (TR/TE, 500/14) shows longitudinal scar (arrow) adjacent to deep tendon and scarring and irregularity of distal tendon (arrowhead)., 21-year-old man with fibrous scarring from remote rectus femoris injury. xial T1-weighted image (500/14) shows low signal surrounding left deep tendon (white arrow) representing fibrous encasement. Compare this finding to normal-appearing right deep tendon (black arrow). JR:190, March 2008 W185

5 Gyftopoulos et al. Fig. 5 Pseudocyst in 12-year-old boy with remote rectus femoris injury. xial fat-saturated T1- weighted image after IV gadolinium injection (TR/TE, 600/14) reveals fluid collection with rim enhancement (white arrow); these findings are consistent with pseudocyst adjacent to deep tendon (black arrow). may also be necessary for evacuation of a symptomatic pseudocyst or hematoma. Scar tissue resection has also been recommended to relieve pain and improve elasticity of the rectus femoris muscle [4, 12]. There are a few limitations to our study. The retrospective nature of the study hindered our ability to get a complete clinical history and pertinent follow-up and may have introduced a sample bias. The small sample pool of patients and the lack of surgical correlation were other limitations. One needs to keep in mind, however, that only a small percentage of rectus femoris deep musculotendinous junction injuries require surgery. In conclusion, we have outlined the normal MRI anatomy of the proximal rectus femoris musculotendinous unit and the characteristic MRI features of deep musculotendinous junction injuries. Greater familiarity with these longitudinally oriented MRI findings will expedite accurate diagnosis and appropriate treatment of proximal rectus femoris musculotendinous junction tears. cknowledgment We thank Leon Rybak for providing us with two cases for this study. References 1. Renstrom P. Tendon and muscle injuries in the groin area. Clin J Sports Med 1992; 11: Garrett WE Jr. Muscle strain injuries. m J Sports Med 1996; 24[suppl 6]:S2 S8 3. Standring S, ed. Gray s anatomy: the anatomical basis of clinical practice, 39th ed. New York, NY: Elsevier Churchill Livingstone, Hughes CT, Hasselman CT, est TM, et al. Incomplete, intrasubstance strain injuries of the rectus femoris muscle. m J Sports Med 1995; 23: ordalo-rodrigues M, Rosenberg ZS. MR imaging of the proximal rectus femoris musculotendinous unit. Magn Reson Imaging Clin N m 2005; 13: Ouellette H, Thomas J, Nelson E, Torriani M. MR imaging of rectus femoris origin injuries. Skeletal Radiol 2006; 35: outin RD, Fritz RC, Steinbach LS. Imaging of sports-related muscle injuries. Radiol Clin North m 2002; 40: Hasselman CT, est TM, Hughes CT, et al. n explanation for various rectus femoris strain injuries using previously undescribed muscle architecture. m J Sports Med 1995; 23: Temple HT, Kuklo TR, Sweet DE, et al. Rectus femoris muscle tear appearing as a pseudotumor. m J Sports Med 1998; 26: De Smet, est TM. MR imaging of the distribution and location of acute hamstring injuries in athletes. JR 2000; 174: Cross TM, Gibbs N, Houang MT, Cameron M. cute quadriceps muscle strains: magnetic resonance imaging features and prognosis. m J Sports Med 2004; 32: Rask MR, Lattig GJ. Traumatic fibrosis of the rectus femoris muscle. JM 1972; 221: W186 JR:190, March 2008