MRI of the Painful Hip in Athletes

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Joel S. Newman, MDa'b'*, Arthur H. Newberg, MDa'b aDepartment of Radiology, New England Baptist Hospital, 125 Parker Hill Avenue, Boston, MA 02120, USA

bDepartment of Radiology, Tufts University School of Medicine, 136 Harrison Avenue, Boston, MA 02111, USA

Hip pain is a common complaint in athletes, and may result from an acute injury or from chronic, repetitive trauma [1-3]. Osseous injuries involving the proximal femur or adjacent acetabulum represent one important subset. Soft-tissue injuries about the hip are varied, including those involving the musculotendinous unit and those specifically localized to entheses, or tendon insertions upon bone. A number of bursae about the hip may result in hip pain in the athlete. Finally, increasing emphasis has recently focused on injuries within the hip joint capsule, including the articular cartilage and the fi-brocartilaginous labrum. Specific underlying anatomic conditions may predispose to labral and hyaline cartilage injury at the hip in the athlete, including femoracetabular impingement (FAI) [4-6] and developmental dysplasia of the hip (DDH) [7-9].

Advances in MRI and the increasing use and optimization of MR arthrogra-phy of the hip have facilitated precise definition of soft-tissue injuries at the hip, both intracapsular and extra-articular in location. Occult osseous injuries and osteonecrosis are rapidly diagnosed with MRI, obviating multiple radiographic examinations and computed tomography (CT) in many cases. MRI uses no ionizing radiation, an additional benefit in an athletic population that is generally young.

TECHNICAL CONSIDERATIONS: MRI OF THE HIP

The MRI examination should be tailored to the clinical indication in all cases. Some patient conditions warrant inclusion of the entire pelvis and both hips, such as in acute trauma or suspected osteonecrosis of the femoral heads. This does not preclude additional dedicated imaging of one hip at the same time, using a technique that offers higher resolution, and hence better anatomic detail. In many cases, one hip alone may be imaged using an appropriate coil,

*Corresponding author. Department of Radiology, New England Baptist Hospital, 125 Parker Hill Avenue, Boston, MA 02120. E-mail address: [email protected] (J.S. Newman).

thin-slice technique and other imaging parameters, all in an effort to maximize anatomic detail.

Tl-weighted scans are essential for evaluation of bone marrow within the hip. T2-weighted scans are fluid-sensitive and are required for the depiction of joint effusion, bursitis, and bone marrow and soft-tissue edema. To improve visualization of edema, whether within bone marrow or muscle, fat-suppression techniques are combined with T2-weighted scans or inversion recovery scans are used. By suppressing fat signal arising within marrow and subcutaneous fat, fluid signal/edema becomes more conspicuous.

MR ARTHROGRAPHY OF THE HIP

MR arthography is the preferred examination for evaluation of joint capsule, labrum, and articular cartilage. Joint distension improves evaluation of femoral and acetabular cartilage surfaces that are normally in direct apposition. Use of a dilute gadolinium solution combined with capsular distension affords superb evaluation of the acetabular labrum. MR arthrography should be used when there are mechanical symptoms suggestive of labral tear, underlying DDH, suspected FAI, and suspected articular cartilage injury in the athlete, including possible loose-body and underlying synovial proliferative disease such as synovial osteochondromatosis [9].

To maximize resolution, the authors use a shoulder-phased-array coil for MR arthrography. Field of view is limited to the hip and immediate surrounding soft tissues. Use of fat suppression with Tl-weighted scans increases conspi-cuity of labral pathology, and when combined with T2-weighted scans, affords differentiation of fluid collections and cysts and bursae that communicate with the joint from those that are extracapsular. Depiction of bone-marrow and soft-tissue edema is limited on fat-suppressed, Tl-weighted scans, and fluid-sensitive sequences must be employed in addition [9].

OSSEOUS INJURY

Stress injury of the femoral neck results from repetitive abnormal stresses on the hip, and may be seen in runners, other endurance athletes, and military recruits. Fatigue fractures represent stress injury developing in structurally normal bone. These injuries often occur on the medial aspect of the femoral neck, where compressive forces are pronounced, but can also develop on the outer aspect, where tensile forces predominate [2,10-14]. Radiographs may be negative, at least early in the clinical course. MRI reveals localized bone marrow edema along the medial femoral neck in early stress injury. With progression, a low signal-intensity line may be visualized perpendicular to the medial cortex, surrounded by bone marrow edema. This reflects the actual fracture with endosteal callus. At this stage, radiographs may reveal a corresponding sclerotic line, perpendicular to the cortex (Fig. 1) [13,15].

Theoretically, conservative management with protected weight bearing may suffice in many cases of compressive side fracture with resultant healing. In practice, many femoral neck stress fractures require more aggressive

Right Hip Mri

Fig. 1. Twenty-seven-year-old military recruit with right hip pain. (A) Coronal T1-weighted image of the pelvis demonstrates a low signal focus in the medial aspect of the right femoral head (arrow). (B) Coronal inversion recovery scan demonstrates osseous edema along the medial aspect of the right femoral neck, along with a low signal intensity line representing a stress fracture (arrow). (C) Coronal reformatted helical CTscan 12 days after the MRI demonstrates the stress fracture with a sclerotic line in the medial femoral neck (arrow). The patient subsequently underwent prophylactic screw fixation.

Fig. 1. Twenty-seven-year-old military recruit with right hip pain. (A) Coronal T1-weighted image of the pelvis demonstrates a low signal focus in the medial aspect of the right femoral head (arrow). (B) Coronal inversion recovery scan demonstrates osseous edema along the medial aspect of the right femoral neck, along with a low signal intensity line representing a stress fracture (arrow). (C) Coronal reformatted helical CTscan 12 days after the MRI demonstrates the stress fracture with a sclerotic line in the medial femoral neck (arrow). The patient subsequently underwent prophylactic screw fixation.

management with prophylactic internal fixation (Fig. 2) to prevent fracture propagation. This is true not only in the setting of tensile side injuries, but in compressive side fractures in athletes who cannot be relied upon to protect the hip from further injury [14]. Bone marrow edema may persist for months after osseous injury [15], and MRI is therefore not optimal for follow-up in these cases. Clinical assessment combined with radiographs and CT with multiplanar reformatted images are preferable for follow-up assessment. CT should be used judiciously, however, because of potential risks of substantial ionizing radiation dose in young patients. Bone marrow edema on MRI presenting for longer than 6 months may reflect new or evolving injury [15]. The consequences of progression to a displaced femoral fracture have been documented in the literature [16].

Insufficiency fractures represent a mechanism of injury whereby repetitive stresses on structurally weakened bone result in fracture [10-12]. Young female

Mri Hip Joint

Fig. 2. Twenty-nine-year-old female aerobics enthusiast and police officer. (A) Coronal inversion recovery scan of the right hip reveals a right hip stress fracture with osseous edema (arrow). (B) Follow up radiograph demonstrates very faint osseous sclerosis consistent with a fracture line (arrow). (C) Prophylactic percutaneous screw fixation.

Fig. 2. Twenty-nine-year-old female aerobics enthusiast and police officer. (A) Coronal inversion recovery scan of the right hip reveals a right hip stress fracture with osseous edema (arrow). (B) Follow up radiograph demonstrates very faint osseous sclerosis consistent with a fracture line (arrow). (C) Prophylactic percutaneous screw fixation.

athletes who have had excessive weight loss may develop amenorrhea and become at risk for osteoporosis [17,18]. These individuals may then be predisposed to osseous injury with increased athletic activities such as running (Fig. 3). Management in these cases would be directed not only toward promoting fracture healing, but to management of underlying dietary and metabolic issues [18].

Pelvic stress injuries in athletes may also occur in the sacrum [19,20] (Fig. 4), and have been reported in the pubic rami [3,21] and in the iliac bone in the supracacetabular region [22]. As in the hip, MRI facilitates rapid diagnosis. In equivocal cases, when the etiology of bone marrow edema on MRI cannot be readily ascertained, CT may be helpful in confirming the presence of a sclerotic fracture line. This is particularly true in the case of sacral stress fractures, when radiographic evaluation is limited.

Acute fractures of the pelvis or hip in athletes are not initially imaged with MRI, but are evaluated with radiographs and CT. Long-term sequelae of acute fracture and hip dislocation, including osteonecrosis, may be evaluated with MRI. Chondral and osteochondral injuries of the femoral head are best assessed with MR arthrography, which is discussed subsequently.

Female Hip Mri

Fig. 3. Twelve-year-old girl with right hip pain after excessive running. (A) Coronal T2 scan demonstrates increased signal intensity along the medial right femoral neck (arrow). (B) Coronal inversion recovery scan shows bright signal consistent with edema and an osseous stress reaction (arrow). A fracture line is not identified.

Fig. 3. Twelve-year-old girl with right hip pain after excessive running. (A) Coronal T2 scan demonstrates increased signal intensity along the medial right femoral neck (arrow). (B) Coronal inversion recovery scan shows bright signal consistent with edema and an osseous stress reaction (arrow). A fracture line is not identified.

MUSCULOTENDINOUS INJURY

Injuries to the musculotendinous unit are very common in athletes. Minor muscle strains generally require no imaging and are managed conservatively. In the competitive collegiate or professional athlete and in the case of severe muscle injury, MRI is invaluable for assessing the severity of injury and for helping to determine subsequent management and time to eventual return to activity. Before the advent of MRI, no available imaging modality afforded the high-contrast resolution required to diagnose most muscle injuries other than large tears and tendon rupture.

Sacral Edema Lower Back

Fig. 4. Twenty-year-old collegiate hockey player with low back pain and sacral stress fracture. Coronal, oblique, fat-suppressed image through the sacrum demonstrates osseous edema at the right superior sacral ala associated with a fracture line (arrow).

MRI technique must be optimized to depict the entire spectrum of musculotendinous injury. Fluid-sensitive sequences are employed, with the addition of fat suppression. Suppressing background fat signal increases the conspicuity of muscle edema on T2 or proton density scans. Inversion recovery scans are another fat-suppression technique that may be employed. It must be emphasized that mild musculotendinous strains with little alteration of muscle anatomy will be invisible on Tl-weighted scans, and difficult to appreciate on T2-weighted scans performed without fat suppression [23].

Injury to the musculotendinous unit may be categorized into three degrees, or grades, in order of increasing severity [23]. In first-degree musculotendinous strain, muscle edema is apparent on fat-suppressed, fluid-sensitive sequences, accentuating the normal fascicular anatomy with a characteristic ''feathery appearance,'' but without actual muscle tear or hematoma (Fig. 5). Tl-weighted scans are normal. In second-degree injury, an intramuscular tear/hematoma is appreciated. The focally disrupted muscle fascicles manifest as a bright cleavage plane on fluid-sensitive sequences. Hematomas are discrete collections, generally of high signal intensity on T2-weighted scans. In acute or subacute hematomas, intensity on T2-weighted scans may be more heterogeneous, with

Stress Fractures Healing Time
Fig. 5. Professional basketball player with groin pain. (A) Axial T2, fat-suppressed image reveals edema in the adductor brevis (arrow) adjacent to the symphysis pubis. (B) Coronal inversion recovery image shows the muscle edema (arrow) appearing as a feathery pattern typical of Grade I injury.

lower-intensity areas reflecting early breakdown of blood products. T1-weighted scans may reveal muscle swelling and focal fluid collections (hematomas) of varying signal intensity, depending on the time course following injury. Both first-and second-degree injuries are generally managed conservatively [23,24].

Third-degree musculotendinous injuries are the most severe, with tendon rupture [23,24]. It must be emphasized that the muscle and tendon fibers are interwoven. Although tears may present at the distal tendon, they may also occur more proximally, at the so-called ''musculotendinous junction,'' or even at the intramuscular portion of the tendon [25]. Biomechanical factors related to specific muscle and tendon anatomy, and mechanism of injury will dictate the exact location of the tear. On MRI, these injuries are readily apparent on T1-and T2-weighted sequences, with tendon disruption and retraction along with hematomas of varying size. In some cases, such as the hamstring tears, a larger field of view should be included on the MRI study to visualize the extent of the injury including muscle retraction. Third-degree injuries frequently require surgical management [23,24].

Muscle contusions represent another category of musuculotendinous injury about the hip in athletes. These injuries are secondary to direct trauma, commonly in the gluteal region or proximal thigh. Appearances on MRI range from muscle edema with preservation of underlying muscle anatomy, similar to a Grade I strain, to frank hematomas in more severe injuries. The development of myositis ossificans has also been reported following muscle contusion about the hip [3].

Avulsive injuries at pelvic muscle insertions represent another mechanism of injury. Depending on the site, muscle may insert directly onto bone, or attach via tendon. Although not involving the hip per se, some muscle insertions are in close proximity to the hip joint, and these avulsions are a differential consideration in patients who have unilateral hip or groin pain following injury. Commonly encountered muscle avulsions include the relatively broad-based musculotendinous insertions of the rectus femoris (anterior inferior iliac spine) (Fig. 6), sartorius (anterior superior iliac spine), iliopsoas (hip—lesser trochanter), and at the symphysis, the adductor group [26]. The hamstring origins are composed of tendons only; injuries may be confined to the conjoined sem-itendinosus/biceps femoris or to the semimembranosus [25,27].

With mild or partial avulsions, there is elevated signal in the muscle origin on fluid-sensitive sequences. With complete avulsion, fluid signal separates the muscle from underlying bone, and musculotendinous retraction may be appreciated (Fig. 7) [24]. Avulsed osseous fragments or apophyseal avulsion may be overlooked on MRI by virtue of their low signal intensity appearance. These findings can be confirmed on radiographs or CT.

BURSAE

Bursal inflammation is not unique to the athlete population, and is often encountered in older, sedentary individuals. Nevertheless, the iliopsosas and greater trochanteric bursae are closely apposed to the hip and adjacent tendons.

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Responses

  • Donnamira
    What is high signal on fluid sensitive sequences in hip bone?
    8 years ago
  • aatifa
    What are osteochondral fragments of the hip?
    7 years ago
  • leena
    How can an athlete recover from a femoral stress fracture?
    7 years ago

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