Книги по МРТ КТ на английском языке / MRI for Orthopaedic Surgeons Khanna ed 2010

Fig. 7.5 Zone classification. (A) An artist’s depiction of the left and right hemipelves. The acetabulum has been subdivided into six zones: 1, anterior-inferior; 2, anterior-superior; 3, central superior; 4, posterior-superior; 5, posterior-inferior; and 6, acetabular notch. (B) An artist’s depiction of the left and right proximal femurs. (Left) The frontal view of the femoral head is divided into six zones around the acetabular fossa (there is a dotted line around the ligamentum teres [LT]): 1, anterior-inferior; 2, anterior-superior; 3, central

anatomic zones of labral vascularity. They reported that cadaveric specimens have relatively avascular hip labra, with no statistically significant (p >.05) di erences among the anterior, superior, posterior, or inferior labral lesions, or in torn versus

superior; 4, posterior-superior; 5, posterior-inferior; and 6, area around the ligamentum teres. (Right) The superior view shows the three subdivisions of zones 2, 3, and 4: medial (M), superior (S), and lateral (L). (From Ilizaliturri VM Jr, Byrd JWT, Sampson TG, et al. A geographic zone method to describe intra-articular pathology in hip arthroscopy: cadaveric study and preliminary report. Arthroscopy 2008;24:534–539. Reprinted by permission.)

intact specimens. However, slightly increased vascularity was seen on the capsular compared with the articular side, suggesting that the vascularity usually is supplied by the capsule. Those authors also noted that all labral tears were associated

with increased microvascularity at the labral base, adjacent to the attachment of bone. Such studies have important future implications for labral surgery in terms of determining the type and location of tears that would be amenable to successful repair, as opposed to arthroscopic debridement.

MRI evaluation of the postoperative labrum is similar to that of the postoperative meniscus in the knee. Because labral debridement causes a persistent intralabral signal secondary to abnormally mobile water in the degenerative fibrocartilage, the presence of abnormal signal alone should not serve as a primary indicator of a re-tear. The most reliable indicator of a re-tear of a labral remnant is the presence of a displaced fragment.

Stress Fractures

Stress fractures, which result from cyclic mechanical stress, can be subdivided into one of two groups: fatigue or insufficiency. Military recruits and athletes are more susceptible than the general population to fatigue fractures, given that they occur in normal bone that is exposed to a repetitive mechanical overload that overwhelms the normal remodeling process.18 Insu ciency fractures occur more commonly in the elderly secondary to osteoporosis, osteomalacia, or other processes that weaken the bone, permitting osseous failure to occur after fewer loading cycles than in normal bone. Insu ciency fractures in the athletic population have also been described in female athletes, in association with the female athletic triad.19 Stress fractures can occur on the compression or the tension side of the femoral neck.20 Compression stress fractures are more common and begin at the inferior cortex of the femoral neck. Tension stress fractures begin in the superior cortex, have a greater propensity to displace, and thus require more aggressive treatment. A fracture line with a benign periosteal reaction may be visualized on conventional radiography or CT, and bone scintigraphy may be sensitive but not specific for the diagnosis of femoral neck stress fracture. However, MRI is sensitive and specific to the presence of underlying bone marrow lesions, and a linear fracture line associated with the preservation of fatty marrow should be sought to confirm the diagnosis of a stress fracture.20,21 Fat-suppressed or STIR coronal images show a linear pattern of increased signal intensity, which is compatible with an acute or subacute fracture (Fig. 7.6). MRI is also useful for excluding underlying lesions, such as a tumor, or marrow disorders that may be the cause of a pathologic stress fracture.

Traumatic Posterior Subluxation/

Dislocation/Lateral Impaction

A traumatic posterior hip dislocation most commonly occurs as a result of a motor vehicle accident when the hip and knee are flexed and the knee impacts on the dashboard, producing

Fig. 7.6 A coronal fat-suppressed image obtained with a body coil technique, showing increased signal intensity (arrow) surrounding a stress fracture at the medial aspect of the left femoral neck. (© 2009 Hospital for Special Surgery, New York, NY.)

a posteriorly directed force on the hip. In the acute setting, MRI may aid in the diagnosis of the following22,23:

•Femoral head contusions

•Labral disruptions

•Sciatic nerve injury

•Intraarticular fragments

Hip subluxation usually has a more subtle presentation than does hip dislocation because of its lower energy mechanism of injury, such as a fall on a flexed hip and knee; however, subluxation is a potentially devastating injury that may be misdiagnosed as a simple hip strain or sprain. Traumatic posterior subluxation events in football or other high-level athletic activities may cause symptomatic cartilage-shear- ing injuries and labral tears, but they are not associated with radiographic documentation of a dislocation.24 Depending on the degree of force applied to the hip at the time of translation, the posterior labrum or wall may be displaced and/or combined with anterior labral tears, disruption of the iliofemoral ligament, and parafoveal cartilage shearing injuries; the latter two typically are sustained at the time of reduction (Fig. 7.7). MRI is also a useful tool for detecting the complication of osteonecrosis and for assisting in the determination of when athletes may return safely to sports activity24,25 (see Osteonecrosis, below). Byrd26 described a lateral impaction injury as a direct blow to the greater trochanter, resulting in isolated traumatic chondral injuries in young, physically fit individuals as a consequence of sports

or activity. MRI is useful in this scenario for determining the extent of chondral damage and for evaluating the presence of osteochondral loose bodies.

Greater Trochanteric Pain Syndrome

Greater trochanteric pain syndrome is a common regional pain syndrome that encompasses greater trochanteric bursitis and tears/tendinosis of the gluteus medius and minimus. The major clinical findings are nonspecific, usually with tenderness localized to the lateral aspect of the hip or thigh. Clinically, distinguishing isolated bursal pathologic changes from tendon abnormalities or other soft-tissue lesions is difficult; therefore, the di erential diagnosis is quite broad and

requires consideration of articular, periarticular, and distant processes as a source of lateral hip pain.27

Trochanteric Bursitis

The surface of the greater trochanter has four distinct facets:

•Anterior

•Posterior

•Lateral

•Superoposterior

The overlying trochanteric bursa is composed of three discrete components27:

Abductor Tears

The gluteus medius inserts onto the superoposterior and lateral facets, and the gluteus minimus inserts onto the anterior facet of the greater trochanter. MRI evaluation of the hip in patients more than 40 years old usually reveals several pathologic processes, including some degree of the following28,29:

•Cartilage degeneration

•Degenerative labral lesions

•Extracapsular abnormalities (including abductor or iliopsoas tendinosis)

Abductor tears have been termed the “rotator cu tears of the hip” and are highly prevalent in patients with osteoarthritis.30,31 Again, the coronal and axial sequences should be evaluated for the presence or absence of such tears. Greater trochanteric bursitis is usually indicated by increased signal on fat-suppressed images (Fig. 7.8A). Partial-thickness tears

Snapping Hip Syndrome (Coxa Saltans)

The snapping hip syndrome, or coxa saltans, is characterized by an audible or palpable snapping of the hip with flexion and extension of the hip, occasionally resulting in pain. The etiology of coxa saltans has been divided into three categories33:

•Intraarticular

•Internal (snapping of iliopsoas tendon against an osseous ridge)

•External (snapping of the ITB or gluteus maximus muscle over the greater trochanter)

It is important to accurately determine the source of the snapping so that the appropriate treatment can be given. MRI is useful for excluding other intraor extraarticular hip abnormalities, but its role in diagnosing coxa saltans is limited because of its lack of dynamic capabilities. With internal coxa saltans, fat-suppressed images may display a hyperintense iliopsoas bursa fluid. With external coxa saltans,

A

Fig. 7.8 Hip abductor tear. (A) A coronal fat-suppressed image of the hip showing a fluid-filled space that should be occupied by the left hip abductors, indicating a tear (arrow). (B) An FSE image showing

B

tendinosis of the gluteus medius tendon (arrow) with dehiscence of its insertion from the greater trochanter. (© 2009 Hospital for Special Surgery, New York, NY.)

Fig. 7.9 An axial FSE image obtained with a body coil technique, showing avulsion of the proximal portion of the rectus femoris from the left anterior inferior iliac spine (left arrow). A normal low signal tendinous insertion is seen on the right (right arrow). (© 2009 Hospital for Special Surgery, New York, NY)

■ Bone Marrow Abnormalities

Osteonecrosis

Osteonecrosis (also termed avascular necrosis or aseptic necrosis) of the femoral head is the cellular necrosis of the bone and bone marrow elements that compromise a part of or the entire femoral head. Osteonecrosis is the preferred term because it makes no reference to the pathophysiology of the disease. There are numerous predisposing causes, including the following39:

•Corticosteroid usage

•Collagen vascular disease

Osteoarthritis

Osteoarthritis is characterized by articular cartilage degenerative change with hip joint space narrowing; the incidence of this process increases with age. There are several conditions that lead to osteoarthritis, including the following46:

•Femoroacetabular impingement

•Previous slipped capital femoral epiphysis

•Developmental dysplasia of the hip

•Legg-Calvé-Perthes disease

•Trauma

•Other anatomic variants

A

The appearance of osteoarthritis on MR images is similar to that on conventional radiographs, including the following:

•Hypointense subchondral sclerosis of the femoral head and acetabulum

•Joint space narrowing

•Osteophyte formation

•Subchondral cysts

Osteoarthritis may also be associated with labral tears, paralabral cysts, synovitis, or osteonecrosis of the femoral head.67

Fig. 7.13 FSE images and sketches of a 41-year-old patient with combined femoroacetabular impingement of the right hip.

(A) The segment prescription (© 2009 Hospital for Special Surgery, New York, NY). The coronal image (© 2009 Hospital for Special Surgery, New York, NY) (B) and associated artist’s sketch

(C) show a torn superior labrum (arrowhead on each) and a cam lesion at the neck–shaft junction (arrow on each). (Adapted from Shindle MK, Foo LF, Kelly BT, et al. Magnetic resonance imaging of cartilage in the athlete: current techniques and spectrum of disease. J Bone Joint Surg Am 2006;88:27–46. Adapted by permission.) (Continued on page 159)

Fig. 7.13 (Continued) The oblique axial view (© 2009 Hospital for Special Surgery, New York, NY) (D) and associated artist’s sketch

(E)(arrow on each) accentuate the osseous defect (cam lesion). The sagittal image (© 2009 Hospital for Special Surgery, New York, NY)

(F)and associated artist’s sketch (G) show full-thickness cartilage loss over the anterior acetabular dome (arrow on each) and partial-

thickness cartilage loss of the anterior femoral head (arrowhead on each). (Adapted from Shindle MK, Foo LF, Kelly BT, et al. Magnetic resonance imaging of cartilage in the athlete: current techniques and spectrum of disease. J Bone Joint Surg Am 2006;88:27–46. Adapted by permission.)