Osteonecrosis, Childhood

Synonyms

Avascular necrosis (Perthes disease = Legg–Calvé–Perthes disease = idiopathic avascular necrosis of the hip in childhood); Bone infarction; Chondrolysis (of cartilage)

Definitions

Arterial or venous ischemia leading to cell death and/or disturbance of growth in bone. Historically, several (eponymous) variations in skeletal growth, now known not to be due to necrosis, were once so considered and are still often discussed in the context of true necrosis states. Death or disturbance of the zone of resting cartilage leads to delay, deformity, or cessation of enchondral growth; other conditions such as frostbite and Kashin–Beck disease may locally impair enchondral growth as well. The conditions in infancy known as multiple stippled epiphyses may well be secondary to necrosis of growth cartilage not yet in a growth plate.

Pathology/Histopathology

Clinical bone necrosis is usually more dynamic than mere death of osteocytes. The body has ways of repairing damage, so that the histopathologic pattern may be composed of both destruction and rebuilding. In Perthes disease, for example, the first step is impairment of vascular supply. The first irreversible structural change is a crumbling fracture of bone just below the lateral zone of provisional calcification, seen on frog leg radiographs. Then waves of bone necrosis appear with lack of viable osteocytes, followed by waves of overlying new bone (creeping substitution). Years later, a viable but deformed head is usually formed, more or less congruent with its acetabulum. However, because the shape is less spherical than normal and does not fully fit in its acetabulum, secondary arthrosis tends to appear relatively early in adulthood. Because of avascularity in the femoral neck and primary spongiosa in Perthes’ disease, cartilage from the physis persists in the otherwise ossified neck, giving gouges of lucency on X‐ray images. Both the head and neck of the femur widen transversely compared to normal as the disease progresses—perhaps related to increased periosteal formation in the neck from the processes of healing. An adverse event in the progress of Perthes is tethering across the physis in some patients. The greater trochanter growth is generally not impaired in Perthes, so it is relatively overgrown, leading to varus deformity of the hip, which is further exaggerated if tethering of the main physis occurs.

Osteochondrosis (some still refer to it as osteochondritis) dissecans is an injury to bone and overlying cartilage, which is painful and more severe, indeed unstable, whenever joint fluid enters the space between the lesion and normal bone.

Schmorl nodes are protrusions of normal vertebral disk substance through weak areas in the vertebral end plates (zones of provisional calcification). Schmorl nodes are often a component of Scheuermann disease of the spine.

In frostbite and Kashin–Beck disease ( 1), portions or the entire involved physis or acrophysis becomes nonviable, leading to local lack of growth (and perhaps early physeal fusion). A cone epiphysis is a result of a similar loss of viability of the central (more senior) portion of a physis, whether due to injury, infection, or genetic causes.

Clinical Presentation

Pain (in the groin, thigh, or referred to a knee), limping, and favoring a limb may reflect Perthes disease; however, Perthes may be clinically silent for months and discovered serendipitously on radiographs acquired for other reasons. Symptoms for avascular necrosis from other causes and at other sites are similar. In Gaucher disease, the spleen is often quite large; in sickle cell anemia, the spleen is usually small or absent. Traumatic avascular necrosis occurs after hip dislocation. For steroid‐induced hip necrosis, other symptoms of steroid use could be sought. The incidence of osteochondrosis dissecans rose when teenagers were dancing The Twist, which indicates that certain challenging repetitive motions might be a predisposing factor. For frostbite, the history of severe cold exposure if available is helpful for the diagnosis (although the pattern of involvement on X‐ray images is virtually diagnostic—especially if the thumb is spared by being held in the fist during the exposure). Kashin–Beck disease is geographically limited to China, Mongolia, and Tibet, where thousands of cases have occurred.

Imaging

In Perthes disease, magnetic resonance imaging (MRI) and nuclear images show avascularity earlier than the first plain image finding, which, in turn, appears first on the frog‐leg view (Fig. 1). However, unilateral retarded maturation of one femoral head might be appreciated on the frontal radiograph as well. Ultrasound shows associated hip effusion easily; plain images do not. As Perthes disease progresses, computer tomography (CT) images show the current integrity of bone, extent of involvement, and nonosseous components; however, MRI is preferred because it does not use radiation and also displays the femoral head and neck and acetabulum throughout the long course of Perthes ( 2).

Figure 1

Perthes disease lucent crescent ( arrowhead) of the outer femoral head on frog‐leg view in an 8‐year‐old boy. From Oestreich AE, Crawford AH (1985) Atlas of Pediatric Orthopedic Radiology. Thieme Verlag, Stuttgart p 190.

Osteochondrosis dissecans of the distal femur is usually situated posteriorly in the involved condyle, and thus is better seen on a notch (angled) view tangential to it. Evaluation for instability or fluid between the osteochondrosis and adjacent healthy bone could be made with MRI or a CT arthrogram.

When there is doubt about whether a normal variant of ossification or an osteonecrotic bone is present, a display of the osseous and cartilaginous elements on MRI may help one decide, with overlying normal cartilage favoring the normal variant. For example, Meyer dysplasia of the hip ( 3) can be distinguished from Perthes disease by the finding of normal cartilage and normally vascularized bone. Ultrasound can show the findings in Osgood–Schlatter condition of the patellar tendon and anterior tibial apophysis.

Nuclear Medicine

Nuclear imaging, like MRI, shows findings earlier in Perthes disease than the upper outer lucent crescent found on radiographic frog‐leg images. On bone scans, the earliest finding is a cold defect in the femoral head, a larger zone indicating more extensive disease. This phase, however, is reversible without progression to irreversible definitive Perthes disease. The perthetic femoral head eventually regains scan activity in the reparative phase later in the disease evolution. One week after the onset of sterile infarction of bone, whether from sickle cell disease, Gaucher disease, pancreatitis, or other noninfectious causes, bone scans begin to show high activity (as healing begins) rather than the earlier lower than normal (cold) activity. Lack of bone scan activity is also a sign of avascularity after certain fractures, for example, in the proximal scaphoid following a transverse fracture of the scaphoid waist. The differential diagnosis between infection and infarction of bone in sickle disease can be assisted by dual scanning: in infection, gallium 67 should be much more avidly taken up than technetium in conventional bone scan.

Diagnosis

Bones with osteonecrosis are generally denser than the nearby bones, whether because of the loss of volume putting more bone substance into a smaller space from collapse or because living bones demineralize from local irritation whereas dead bones do not. A classic example is the proximal scaphoid being denser than the distal one when its blood supply is lost from a fracture across the bone’s waist. Infarction of bone shafts can also incite callus, which is denser than the nearby bone.

The early plain image changes of Perthes disease are a smaller epiphysis than contralaterally because of decreased vascularity and, on the frog‐leg view alone, a slit of lucency below the outer femoral head zone of provisional calcification, representing crumbling fracture (Fig. 1). The extent of the slit reflects the severity of involvement. As the disease progresses (with or without surgery to improve position or protect the hip), the head becomes irregularly denser and longitudinally shorter, while the head and neck become transversely wider (and thus incompletely covered by the bony acetabular roof). Gouges of lucency may extend down the metaphysis of the neck from the physis, reflecting avascular zones in the primary spongiosa. Without ultrasound or cross‐sectional imaging, one cannot determine whether effusion accompanies Perthes disease. The perthetic hip through the progress of disease becomes varus as the greater trochanter continues to grow nearly normally, while the femoral physis is slowed, or occasionally tethered, by premature fusion across part of the physis.

Sickle cell infarction of small tubular bones, generally about 1 year of age, is painful accompanied by periosteal reaction and called “hand–foot” syndrome. This may be the presenting symptom of previously unknown sickle cell disease. The typical Lincoln log vertebral bodies in sickle cell disease result from infarction or impairment of the more central portions of the vertebral end plates. Distinguishing infarction from infection in long bones in sickle cell disease by imaging can be quite difficult; dual nuclear scanning with bone scan and gallium scan (or labeled white blood cells) may help by showing especially high activity on the latter.

In frostbite, Kashin–Beck disease, and some sequelae of rat bite ( 1), enchondral bone growth is locally destroyed, so that portions or the entire bones do not grow (Fig. 2). Cone‐shaped epiphyses, fused epiphyses, pumice‐shaped carpal bones, and irregular nonepiphyseal ends of small tubular bones are manifestations. In frostbite the distribution is acral, from the fingertips proximally, because of the nature of the cold injury, often sparing the thumb if it had been protected in the fist. Distribution of enchondral damage in Kashin–Beck disease is more scattered—involvement asymmetrically of the lower extremity bones leads to length discrepancy and hence limp.

Figure 2

Frostbite sequelae: distal phalanges 2 through 5 are short from physeal closure, as are middle phalanges 4 and 5. The distal (acrophyseal) ends of the middle phalanges are also irregular from enchondral damage. As is often the case, the thumb was presumably spared by being protected in the fist during the cold exposure. From Oestreich AE, Crawford AH (1985) Atlas of Pediatric Orthopedic Radiology. Thieme Verlag, Stuttgart p 169.

The apophysis of the posterior calcaneus normally appears denser than the rest of the bone. It is no longer considered “Sever disease” unless localized symptoms occur and the nuclear scan is abnormal. Many diagnoses of “Köhler disease” of the tarsal navicular are actually an overlap of multiple ossification centers rather than true osteonecrosis (Fig. 3). Close perusal of oblique and lateral images will usually solve the question. Similarly, the ossification across the closing inferior ischiopubic synchondrosis is often both vigorous and asymmetric from side‐to‐side. Unless abnormally increased bone scan activity can be shown, van Neck osteonecrosis should not be considered. Kienböck disease or lunatomalacia is a real entity, however, often associated with ulna minus.

Figure 3

Mimic of Köhler disease in a 6‐year‐old patient. Lateral image suggests sclerosis and irregularity of the navicular; but the frontal view shows it results merely from overlap, the bone developing from three normal‐density growth centers. The pain, incidentally, was lateral, not medial.

Meyer dysplasia of the hip in the early years of life is an irregular appearing ossification of the femoral head. However, it has normal vascularity on nuclear scan or MRI and uncommonly progresses to true Perthes disease.