Protrusio Acetabuli

► [Intrapelvic bulging of the medial acetabular wall]

Protrusio acetabuli most commonly occurs as a secondary event in disorders characterized by osteoporosis and osteomalacia, or in association with degenerative osteoarthritis, rheumatoid arthritis, and Paget disease. A special type of protrusio acetabuli is that occurring with acetabular fractures and medial dislocation of the hip (Fig. 4.18). Protrusio acetabuli in degenerative osteoarthritis is seen with cartilage loss, and migration of the femoral head, at the super-omedial aspect of the acetabulum. Inward bulging of the acetabulum is most commonly mild and unilateral. A more severe degree of protrusion can be observed in advanced rheumatoid arthritis: axial migration of the femoral head, bilateral and symmetrical loss of the interosseous space, and erosions about the femoral head are common in this condition. A similar pattern is seen in ankylosing spondylitis, although the presence of osteophytosis as a collar around the femoral head-neck junction is a distinctive feature of the last condition. Protrusio acetabuli can be a complication of severe Paget disease (OMIM 167250, 601530, 603499, 606263). Osteoarthritic changes, with narrowing of the joint space most prominent at the medial or axial portion of the acetabulum, are often associated findings. Whether protrusio acetabuli in Paget disease occurs as a secondary event after osteoarthritis or represents a primary manifestation of the disease is unknown (Guyer and Dewbury 1978). Intrapelvic protrusion of the acetabulum has been reported among the late complications of radiation therapy applied to pelvic organs. Although obliterative endarteritis (Hall et al. 1979) and aseptic necrosis of the acetabulum (Hasselbacher and Schumacher 1977; Csuka et al. 1987)

Protrusio Acetabuli With Trauma
Fig. 4.18. Trauma in an adult female patient. Multiple fractures involving the left acetabular fossa and ischial and pubic rami of both sides are apparent. The left femoral head has moved upward and inward, resulting in protrusio acetabuli

have been implicated as potential mechanisms of protrusion in such cases, the exact pathogenesis has not yet been elucidated. Protrusion of the acetabulum is relatively frequent in patients with sickle cell anemia. Again, the ultimate cause is unknown, but impaired growth of the triradiate cartilage and diffuse chondrolysis of the articular cartilage, both possibly related to vaso-occlusive episodes, are putative mechanisms (Hernigou et al. 1991; Schumacher et al.

1993). Idiopathic chondrolysis of the hip is a monoar-ticular disease most commonly affecting adolescent girls, manifesting with hip pain, restriction of motion, and stiffness in the absence of any previous history of trauma. Diffuse loss of the acetabular and femoral articular cartilage occurs. Radiographs show joint space narrowing, irregular and eroded subchondral bone, regional osteoporosis, and mild protrusio acetabuli (Hughes 1985). The condition can mimic juvenile chronic arthritis, septic arthritis, transient osteoporosis of the hip, os-teonecrosis of the femoral head, and pigmented vil-lonodular synovitis (Resnick and Niwayama 1995; Sherlock 1995).

Protrusio acetabuli associated with Marfan syndrome (OMIM 154700) and Ehlers-Danlos syndromes has been linked with intrinsic weakness of the bone (Fast et al. 1984; Yule et al. 1999). As discussed in more detail elsewhere in this book, the skeleton is diffusely osteoporotic in patients with osteogenesis imperfecta, owing to defective synthesis of the collagen matrix coupled with deficient mineralization of the matrix. Bilateral protrusio acetabuli resulting in a 'trefoil' appearance of the pelvis occurs in association with severe coxa vara in teenagers with severe osteogenesis imperfecta (Hanscom et al. 1992) (Fig. 4.19). In Bruck syndrome (OMIM 259450), features of osteogenesis imperfecta and arthrogryposis multiplex congenita occur in combination (Fig. 4.20). The molecular defect underlying this syndrome is a deficiency of bone-specific telopeptide lysyl hydroxylase mapped to 17p12, resulting in aberrant crosslinking of bone collagen (Bank et al. 1999). The disorder manifests at birth with symmetrical contractures of large joints and pterygia, and in subsequent weeks with multiple rib and long bone fractures resulting in bone deformities, osteoporosis, vertebral wedging, kyphoscol-iosis, and persistent wormian bones (Leroy et al. 1998; McPherson and Clemens 1997; Viljoen et al. 1989).

Primary protrusio acetabuli (Otto's pelvis, OMIM 177050) occurs in the absence of any recognizable cause. Failure of ossification or premature fusion of the Y-cartilage and failure of normal acetabular remodeling have been tentatively proposed as etiologic factors (Hooper and Jones 1971). Familial cases, with affected individuals in successive generations, have been observed (Ventruto et al. 1980). The disorder is more common in American Blacks, in the Bantu population of South Africa, and in females (Friedenberg 1953; Crichton and Curlewis 1962). In most cases both hips are affected. Symptoms can appear in ado-

Trefoil Pelvis Osteomalacia

Fig. 4.19. Osteogenesis imperfecta in a 16-year-old girl. Note intrapelvic protrusion of the medial acetabular wall most prominent at the left side. The pelvis displays a 'trefoil' overall appearance. Observe intense osteoporosis, severe coxa vara deformity, and dislocated fracture of the right femoral shaft

Fig. 4.19. Osteogenesis imperfecta in a 16-year-old girl. Note intrapelvic protrusion of the medial acetabular wall most prominent at the left side. The pelvis displays a 'trefoil' overall appearance. Observe intense osteoporosis, severe coxa vara deformity, and dislocated fracture of the right femoral shaft

Bruck Syndrome

Fig. 4.20. Bruck syndrome in a male patient at the ages indicated. Note progressive protrusion of left acetabular region in pelvic wall. Protrusio acetabuli of milder degree is also becoming evident on the right side with increasing age. Observe also osteopenia and bilateral coxa valga. (From Leroy et al. 1998)

Fig. 4.20. Bruck syndrome in a male patient at the ages indicated. Note progressive protrusion of left acetabular region in pelvic wall. Protrusio acetabuli of milder degree is also becoming evident on the right side with increasing age. Observe also osteopenia and bilateral coxa valga. (From Leroy et al. 1998)

lescence or adulthood, and range from none to severe hip pain, limitation of hip motion, flexion contracture, and abnormal gait. Radiographic manifestations include diminution of the joint space, with axial or medial migration of the femoral head and osteoarthritic changes. An estimate of the direction of femoral head migration with respect to the acetabulum - whether axial and medial, as in primary protrusion acetabuli, or superior, as in degenerative joint disease - is helpful in the differential diagnosis against the latter disorder. Axial migration of the femoral head occurs in rheumatoid arthritis, anky-losing spondylitis, chondrolysis, disuse cartilage atrophy following paralysis, and calcium pyrophosphate dihydrate crystal deposition disease (Resnick 1995).

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Responses

  • ivana
    Is acetabular protrusio genetic?
    8 days ago

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