Pathology of the Rectus Femoris



Fig. 16.1
Muscle within muscle appearance of the rectus femoris muscle. The indirect head inserts on the anterior inferior iliac spine (black arrow). The muscle fibers arising from the deep tendon of the indirect head (black arrowheads) form a small muscle within the rectus femoris. The grey arrow points to the direct head



On axial magnetic resonance imaging (MRI) both heads appear as linear low-signal structures arising from their respective bony insertions. The deep tendon transfers from a globular structure at its proximal part to a boomerang-like structure located anteriorly and medially to the muscle fibers. The anterior component of the conjoint tendon (superficial tendon) blends more distally with the anterior fascia of the RF muscle. The more posterior portion of the conjoined tendon (deep tendon) gradually becomes embedded within the muscle belly of the RF muscle, forming a deep tendon with a long intrasubstance muscle tendon junction (Fig. 16.2). On coronal images the two origins of the RF tendon are also clearly seen. Anteriorly the origin of the direct head from the AIIS is visualized as a relatively thick, somewhat rectangular low-signal structure. Slightly more posteriorly, the indirect head appears—in very close proximity to the joint capsule—as a linear low-signal structure highlighted by fat and thinner than the direct head [7].

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Fig. 16.2
A healthy 15-year-old male athlete with normal MRI anatomy of the proximal right rectus femoris. (ae) Axial T1-weighted MRI. (a) The direct head inserts at the anterior inferior iliac spine (black arrow) while the indirect head is slightly more posterior inserting at the superior ridge at the anterolateral aspect of the acetabulum (white arrow). (b) The indirect tendon is seen in its full horizontal oblique course (white arrows) and is immediately posterior to the direct tendon (c) Slightly caudally both tendons merge into the conjoint tendon (arrow). (d) The rounded tendon progressively flattens as it travels distally, lying in the most medial aspect of the muscle (arrow). (e) While progressing along the muscle, fibers from the direct tendon form the superficial tendon (black arrows) and those continuing the indirect tendon migrate to a sagittal position (white arrow). (f, g) Coronal T1-weighted MRI show the insertion of the direct head off the anterior inferior iliac spine (black arrow) and the attachment of the indirect head to the superior acetabular ridge (white arrow)

On ultrasound, the insertion of the direct tendon is easily detected in axial scans from the easily-palpated AIIS downward. The indirect head follows an oblique course and is examined with an oblique axial scan at the lateral aspect of the uppermost portion of the thigh. More distal scans reveals the particular internal architecture of the RF with the deep aponeurosis represented by a mildly curved, comma-shaped hyper echoic structure—normally quite distinct from the muscle tissue—extending as far as the lower third of the muscle. The superficial tendon, however, is visualized as a thickening of the muscle fascia [8].



16.3 Mechanisms of Injury


In general there are three main etiopathogenic mechanisms of muscle injury: (1) direct trauma—resulting in contusion; (2) indirect trauma—resulting in strains; and (3) lacerations. The latter mechanism is uncommon in sport related lesions, and is excluded from this chapter. The quadriceps muscle is subject to both direct and indirect energy trauma. It has, however, been shown that the mechanism of injury usually depends on which muscle within the quadriceps is involved: vastus medialis and lateralis muscles are more often exposed to direct trauma while lesions of the RF usually result from indirect energy trauma. Indirect trauma to the RF causes the muscle to rupture at its weakest point, which is the myotendinous junction in adults (strains) and the apophyseal growth cartilage in children [8, 9].

The RF has all the characteristics of frequently injured muscles. It is biarticular, spanning the hip and knee and thus responsible for decelerating both; it has a high proportion of type II muscle fibers which generate more tension on contraction; and it acts in an eccentric manner [6, 1012]. The incriminating role of kicking has been well described [13]. In the final portion of the backswing phase, the hip is hyperextended and the knee is flexed, stretching the biarticular RF muscle and putting it in passive insufficiency, its weakest position, especially at the proximal third. At the onset of the forward swing there is massive eccentric muscular recruitment of the quadriceps and iliopsoas muscles. Forceful muscular contraction in a stretched quadriceps muscle can lead to sprain [6, 9, 13]. This is what typically happens when, for example, soccer or rugby players unexpectedly encounter irregular or slippery turf as they are about to kick the ball, and they try to compensate by extending the hip [8, 14]. It also occurs when one loses one’s footing during abrupt deceleration, an event that is common in all sports that involve running.


16.4 Risk Factors


The causes of muscle strain injury are multifactorial. Past muscle strain injury is perhaps the most recognized risk factor [15, 16]. Other proposed risk factors include low muscle strength, muscle fatigue, age, lack of warm-up, muscle temperature, and poor flexibility [15, 17]. For quadriceps muscle strains in Australian Rules footballers, Orchard found that both recent (less than 8 weeks) and remote quadriceps strain injury, recent hamstring strain, the dominant kicking leg, short stature, and ground hardness were all associated with increased risk [16]. Orchard described these clinical strains over a 7-year period in the national competition; the injuries were not routinely assessed by MRI, and therefore we do not know what patterns might have been revealed.


16.5 Imaging Techniques


Cross sectional imaging, MRI and ultrasound are commonly indicated for professional and/or elite amateur athletes when both the athlete and others (coach, trainer, manager) need accurate diagnosis and prognosis.


16.5.1 Conventional Radiographs


Conventional x-rays are helpful in detecting osseous fracture in cases of avulsion fracture. Anteroposterior x-rays of the pelvis can be helpful in this case, as can the oblique alar view. X-rays also show mineralization and ossification in chronic lesions of the RF [8].


16.5.2 Ultrasound


The examination is best done with a multifrequency (5–12 MHz) linear transducer. If there is substantial muscle hypertrophy a 5-MHz transducer is preferable as it offers better visualization of the deep planes. A systematic approach will allow complete exploration of the RF and reveal even small lesions that can be easily missed. Axial scans from the AIIS downward are performed first as they offer a panoramic view. They are followed by oblique coronal views at the proximal insertion. Information obtained during the static examination can be supplemented with a dynamic examination performed during isometric contraction. This approach is sometimes more suitable for detecting small partial tears. When the muscle plane has been fully explored, the distal tendon is scanned. During this phase, the knee is flexed approximately 30° to straighten the tendon and to eliminate anisotropy artifacts which result in hypoechoic areas that can be mistaken for focal tendinopathy or even partial ruptures [8].


16.5.3 MRI


Although each patient is unique, certain generalizations are helpful in designing an appropriate MRI protocol. At an absolute minimum, each examination should include at least two orthogonal planes and two different pulse sequences. In addition to the requisite axial plane the second long-axis plane can be either coronal or sagittal. In addition the examination should include a combination of T1-weighted—for high resolution and “anatomical images”—and fat-suppressed fluid-weighted images to detect pathologic changes [7, 18].

Gradient-echo sequences help in detecting the presence of hemosiderin by accentuating certain paramagnetic effects. The administration of gadolinium based contrast material is generally not necessary. Occasionally intravenous gadolinium administration can be helpful, particularly when a clinically suspected muscle injury is not visualized on T2-weighted and inversion-recovery fast spin-echo images. Torn muscle fibers may be more conspicuous after gadolinium administration, particularly when there is extensive hemorrhage and edema. Several cases have been reported in which professional athletes had muscle strains that were not diagnosed on T2-weighted and inversion-recovery fast spin-echo images, but were visualized on contrast-enhanced T1-weighted images [1820].


16.6 Avulsion Fractures at Tendon Insertions


Avulsion fractures can involve any of the three osseous insertions of the RF: the AIIS for the direct head, the superior lateral acetabular ridge for the indirect head, and the patellar sleeve for the distal insertion. Unlike strains, which most commonly involve the indirect head, avulsion fractures usually involve the AIIS, the site of insertion of the direct head [9, 2123]. This type of fracture is also called “sprinter’s fracture” [24]. In children the presence of growth cartilage at the tendon insertion makes the bone-tendon junction more vulnerable to indirect energy trauma than the myotendinous junction. The patient reports a sudden pain and eventually feeling a break when kicking the ball. Pain is usually worst at the site of fracture, which is frequently at the AIIS, or the lateral upper thigh when the indirect head is involved.

Avulsion fractures are readily detected on conventional radiographs. Anterior-posterior x-rays of the pelvis, as well as the oblique alar view, will clearly reveal the avulsion of the cartilage (Fig. 16.3). The degree of retraction and the size of the bone fragment can be evaluated. X-rays taken in athletes years after avulsion fractures show hypertrophy of the AIIS, which appears as a large ossification that projects into the inferior soft tissue. Ultrasound confirms the diagnosis. The avulsed fragment is seen as a hyperechoic structure of variable size lying at some distance from the AIIS [8]. On MRI avulsion fractures appear as hypointense linear abnormalities on T1-weighted imaging of bone underlying the origin of the RF. The osseous fragment and donor site are also evident, as is any hematoma interposed between the avulsed fragment and adjacent bone. The signal intensity of the hematoma depends on the age of the injury, although in the acute phase the hematoma is likely to show decreased signal intensity on T1-weighted images and increased signal intensity on T2-weighted images [9, 25] (Fig. 16.4). Treatment is usually conservative (short period of bed rest followed by progressive weight bearing with crutches) with rapid resolution of pain and return to playing condition in a relatively short period (6 weeks) [26]. Surgery is indicated for long standing symptomatic proximal avulsion after failure of nonoperative treatment [27, 28].

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Fig. 16.3
A 16-year-old female athlete with an old fracture avulsion of the right superior acetabular ridge at the insertion of the indirect head of rectus femoris. (a) Anteroposterior and (b) frog leg lateral x-rays of the right hip show an osseous fragment detached from the superior acetabulum (arrow). (c) Coronal fat-suppressed T2-weighted MRI displays fracture of the superior acetabulum at the insertion of the indirect head (arrow)


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Fig. 16.4
A 14-year-old male athlete with an acute avulsion fracture of the anterior inferior iliac spine. (a) Axial and (b) coronal fat-suppressed T2-weighted MRI show fracture of the anterior inferior iliac spine (black arrow), attachment site of the direct tendon of rectus femoris (white arrow). Note the presence of feathery edema of the iliacus muscle (asterisks)


16.7 Myotendinous Injuries of the RF


The clinical diagnosis of myotendinous injuries is usually based on a three-point scale: (1) for mild; (2) for partial; and (3) for a complete tear [29]. Mild injuries have no discernible loss of strength or motion restriction. Partial tears demonstrate some loss of strength or motion that is not complete, unlike type 3 injuries [2]. Strain injury is associated with inflammation, edema, and sometimes hemorrhage with proliferation of inflammatory cells and fibroblastic activity in the first 24–48 h [2]. Histological animal models of muscle stretch injury have shown that myotendinous injury results in inflammation, bleeding and muscle fiber necrosis initially. This destructive phase is followed by a concomitant repair and remodeling phase involving recruitment of progenitor cells, scar formation, and remodeling of organized tissue [30].

Clinically, the patient may present with sharp pain associated with movement and impaired mobility. The injured area can be located with precision by the patient and verified by a careful examination showing maximal tenderness over the midline of the thigh [3]. Injuries of the origin of the reflected tendon may mimic hip pain or a lesion of the tensor fascia lata. The patient reports a sensation that something in the hip was displaced during the trauma [8]. When the lesion involves disruption of the distal muscle fibers from the posterior tendon of insertion, however, proximal retraction of the entire muscle belly is observed, resulting in a mass that migrates proximally to the groin with muscle activation. This mass is sometimes mistaken for a soft-tissue neoplasm [6, 25, 31]. Other clinical findings include localized swelling, loss of knee extension, thigh asymmetry and a palpable defect with a retracted mass (in complete ruptures). Prompt diagnosis (within a few days of the muscle trauma) is essential to ensure timely and complete healing and to reduce the likelihood of recurrence. Most important at the time of diagnosis is to differentiate benign injuries from serious injuries that may require protracted rehabilitation. Unfortunately, making the distinction is difficult by clinical examination alone, especially in the first week after injury. Imaging studies however show a significant relationship between initial findings and prognosis [3].


16.8 Imaging Findings


RF injuries are commonly classified on MRI as:



  • Grade 1: Bright signal on fluid-sensitive sequences representing fluid and hemorrhage around the myotendinous junction extending into the adjacent muscle, creating a feathery appearance.


  • Grade 2: More severe and may show a thin or irregular appearance of the myotendinous junction itself along with edema and hemorrhage (increased T2 signal intensity) that often tracks along the fascial plane.


  • Grade 3: Complete disruption and discontinuity of muscle typically at the myotendinous junction with complete replacement of organized collagen by fluid signal on fluid sensitive sequences. There is often an associated wavy tendon morphology and retraction of the muscle. Surrounding edema or hemorrhage is usually extensive.

There are also ultrasound classifications for RF injuries [8, 32]. The following were reported by Petroons et al. and modified by Balius et al. [5, 32]:
Jun 25, 2017 | Posted by in MUSCULOSKELETAL MEDICINE | Comments Off on Pathology of the Rectus Femoris

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