History
Presenting symptoms of subacute osteomyelitis include mild-to-moderate localized pain. Pain is the most consistent complaint in most patients; it may at times become more intense or remit, and it is frequently exacerbated following a period of unusual activity. Night pain that is relieved with aspirin is frequently reported. Minimal loss of function is another common symptom (eg, limping in a patient with a lower-limb lesion), with no history of systemic toxicity.
Because the symptoms of subacute osteomyelitis are vague, an accurate diagnosis is usually delayed. The bone lesion may also not be readily apparent on plain radiographs for some time (see Workup). The average duration of symptoms before diagnosis is 1-6 months, but symptoms may be present for a longer period before the diagnosis is made.
Physical Examination
On clinical examination, localized tenderness may only occasionally be associated with warmth, redness, and soft-tissue swelling with the involvement of subcutaneous bone. This finding seems to increase and subside with activity. Pain may occur with movement of the adjacent joint, and some joint effusion may be present, but the pain and effusion are usually mild. The surrounding muscles may occasionally demonstrate some wasting.
Classification
Ross and Cole categorized these lesions either as aggressive or as cavities in the area of the metaphysis and epiphysis. [30] This categorization helps in the treatment plan, in that aggressive lesions should be treated surgically for diagnosis. Subsequently, in 1973, Gledhill proposed a radiologic classification for primary subacute osteomyelitis that consisted of four types on the basis of his review of eight patients, as follows [31] :
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Type I – Solitary lesion with surrounding sclerosis, classic Brodie abscess
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Type II – Metaphyseal radiolucent lesion with an associated loss of cortical bone
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Type III – Diaphyseal cortical hyperostosis without onion-skinning
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Type IV – Diaphyseal lesions associated with onion-skin layering
In 1982, Roberts et al modified and expanded Gledhill's classification to include six forms on the basis of morphology, location, and similarity to neoplasms, as follows [32] :
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Type Ia lesions present as a punched-out radiolucency that is often suggestive of eosinophilic granuloma
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Type Ib lesions are similar to type Ia lesions but have a sclerotic margin and appear as a classic Brodie abscess
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Type II lesions erode the metaphyseal cortex and may appear similar to osteogenic sarcoma
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Type III lesions are observed as a localized diaphyseal cortical and periosteal reaction simulating osteoid osteoma
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Type IV diaphyseal lesions most often resemble Ewing sarcoma, with onionskin periosteal reaction
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Type V lesions occur in the epiphysis and appear as a concentric radiolucency
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Type VI lesions involve the vertebral body with an erosive or destructive process
This classification system has been the most widely used in the literature, and several reports have advocated modifying it to include flat-bone involvement, tarsal bones, and lesions affecting both the metaphysis and the epiphysis. This scheme is useful for reporting the results of treatment according to the site but is not a prognosis or treatment plan.
The authors have modified Roberts's classification system to include four main types, each of which has subtypes (see the image below).
Modified classification of subacute osteomyelitis. Type I is metaphyseal. Type Ia is a punched-out central metaphyseal lesion. Type Ib is an eccentric metaphyseal cortical erosion. Type II is diaphyseal. Type IIa is a localized cortical and periosteal reaction. Type IIb is a medullary abscess in the diaphysis without cortical destruction but with onionskin periosteal reaction. Type III is epiphyseal. Type IIIa is a primary epiphyseal osteomyelitis. Type IIIb is a lesion that crosses the epiphysis and involves both the epiphysis and the metaphysis. Type IV is a metaphyseal equivalent. Type IVa involves the vertebral body with an erosive or destructive process. Type IVb involves the flat bones of the pelvis. Type IVc involves the small bones, such as the tarsal bones.
The types and subtypes are defined as follows (see Workup):
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Type I (metaphyseal lesion) - Type Ia is a central metaphyseal lesion that is seen as a punched-out radiolucency, often suggestive of Langerhans cell histiocytosis; type Ib is a metaphyseal lesion eccentrically located with cortical erosion, which may give the appearance of osteogenic sarcoma
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Type II (diaphyseal lesion) - Type IIa is a localized cortical and periosteal reaction that simulates osteoid osteoma; a type IIb lesion is a medullary abscess in the diaphysis without cortical destruction but with onionskin periosteal reaction that resembles Ewing sarcoma
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Type III (epiphyseal lesion) - Type IIIa is a primary epiphyseal osteomyelitis and appears as a concentric radiolucency, usually seen in children younger than 4-5 years; type IIIb is a subacute infection that crosses the epiphysis and involves both the epiphysis and metaphysis
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Type IV (metaphyseal-equivalent lesion, defined as the portion of a flat or irregular bone that borders cartilage [apophyseal growth plates, articular cartilage, or fibrocartilage], such as the vertebrae, the pelvis, and small bones [eg, tarsal bones and clavicle]) [22] - Type IVa involves the vertebral body with an erosive or destructive process; type IVb involves the flat bones of the pelvis and is mostly sclerotic, with neither erosion nor destructive processes [33, 34] ; type IVc involves the small bones (eg, tarsal bones, clavicle)
In all reported series of primary subacute osteomyelitis, the classic Brodie abscess (central metaphyseal lesion with well-defined sclerotic margins, classified as type Ia according to the authors' system) has accounted for the largest number of cases.
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Anteroposterior and lateral radiographs of the distal femur. These images depict a type IIIa epiphyseal lesion.
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Anteroposterior radiograph of the left tibia. This image depicts periosteal reaction of the diaphyseal cortex, type IIb.
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Lateral radiograph of the left tibia. This image depicts periosteal reaction of the diaphyseal cortex, type IIb.
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Anteroposterior radiograph of the distal radius. This image depicts a central metaphyseal lesion (punched-out radiolucency), type Ia.
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Lateral radiograph of the distal radius. This image depicts a central metaphyseal lesion (punched-out radiolucency), type Ia.
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Anteroposterior radiograph of the distal tibia. This image depicts an eccentrically located radiolucent lesion crossing the epiphyseal plate, type IIIb.
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Lateral radiograph of the distal tibia. This image depicts an eccentrically located radiolucent lesion crossing the epiphyseal plate, type IIIb.
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Lateral radiograph of the lumbosacral spine. This image depicts destruction of bone and disc space, type IVa.
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Anteroposterior radiograph of the distal tibia. This image depicts an eccentrically located radiolucent lesion crossing the epiphyseal plate, demonstrating the serpentine sign.
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Lateral radiograph of the distal tibia. This image depicts an eccentrically located radiolucent lesion crossing the epiphyseal plate, demonstrating the serpentine sign.
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Total body scan. This image shows increased radionuclide uptake at the distal left tibia.
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Bone scan of both distal legs and feet. This image depicts increased radionuclide uptake at the distal left tibia.
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Computed tomography scan cut of the right lower extremity. This image depicts a sclerotic lesion of the right iliac bone, type IVb.
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Computed tomography scan cut of the right sacrum. This image depicts a round radiolucent lesion with a sclerotic margin.
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Sagittal T1-weighted (time echo = 10 ms, time repetition = 400 ms) magnetic resonance image of the left ankle. This image depicts a well-defined lesion of decreased signal intensity in the anterior aspect of the distal tibial metaphysis, which extends into the adjacent growth plate and epiphysis.
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Axial fast spin echo T2-weighted (time echo = 48 ms, time repetition = 2400 ms) magnetic resonance image through the distal left tibial metaphysis. This image depicts a well-defined lesion of increased signal intensity in the anterolateral aspect of the distal left tibial metaphysis with a rim of decreased signal intensity.
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Sagittal postgadolinium-enhanced T1-weighted (time echo = 10 ms, time repetition = 650 ms) magnetic resonance image with fat saturation. This image shows a hypodense lesion centrally (fluid) with a moderately thick enhancement, which extends through the growth plate into the epiphysis.
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Coronal postgadolinium-enhanced T1-weighted (time echo = 10 ms, time repetition = 650 ms) magnetic resonance image with fat saturation. This image depicts a hypodense lesion centrally (fluid) with a moderately thick enhancement, which extends through the growth plate into the epiphysis.
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Histologic section of bone. This image depicts subacute osteomyelitis with a mixture of polymorphs and plasma cells in an edematous background. Hematoxylin, phloxine, and safranin (HPS) X 440.
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Histologic section of bone. This image shows fibrosis, degenerating bone spicules, and subacute inflammation. Hematoxylin, phloxine, and safranin (HPS) X 10 X 1 X 5.
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Histologic section of bone. This image depicts fibrosis, a mixture of plasma cells, and occasional polymorphs. Hematoxylin, phloxine, and safranin (HPS) X 25 X 1 X 5.
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Modified classification of subacute osteomyelitis. Type I is metaphyseal. Type Ia is a punched-out central metaphyseal lesion. Type Ib is an eccentric metaphyseal cortical erosion. Type II is diaphyseal. Type IIa is a localized cortical and periosteal reaction. Type IIb is a medullary abscess in the diaphysis without cortical destruction but with onionskin periosteal reaction. Type III is epiphyseal. Type IIIa is a primary epiphyseal osteomyelitis. Type IIIb is a lesion that crosses the epiphysis and involves both the epiphysis and the metaphysis. Type IV is a metaphyseal equivalent. Type IVa involves the vertebral body with an erosive or destructive process. Type IVb involves the flat bones of the pelvis. Type IVc involves the small bones, such as the tarsal bones.
