Pyogenic Arthritis Pyarthrosis

Pyogenic arthritis is a septic condition of a joint. As in acute osteomyelitis, acute pyarthrosis may result from: (a) hematogenous spread of bacteria with direct synovial lodgment, (b) transphyseal (across the growth cartilage) spread of a primary infective focus in the long-bone metaphysis, (c) contiguity, or (d) penetration or operation. The most common offenders are micrococci and gram-negative bacilli.

In children, pyarthrosis has a predisposition for the large joints of the limbs, whereas bacterial spondylitis and diskitis (equivalent to the infection of a diarthrosis joint) is more common in adults. Often, the sternoclavicular joint and sacroiliac joint are afflicted in drug abusers.

The acute pathological responses of the synovial membrane to bacterial invasion include edema, swelling, and hypertrophy with pus formation. After a few days the articular carti-

Sternoclavicular Joint Arthritis

Fig. 8.10 A, B Protrusio acetabuli complicating an advanced hip joint pyarthrosis and concurrent osteomyelitis in the innominate bone. A Anteroposterior radiograph reveals mottled lysis in the supra-acetabular bone with acetabular protrusion (white arrow). The articular space is completely closed at the centromedial aspect (arrowheads). B Anterior pinhole scintigraph of the left hip in a 60-year-old woman with pyarthrosis shows extremely intense tracer uptake in the hip joint and supra-acetabular bone (arrows). There is minimal bulging of the pelvic border, the sign of early acetabular protrusion or pathological fracture (middle arrow).

Fig. 8.10 A, B Protrusio acetabuli complicating an advanced hip joint pyarthrosis and concurrent osteomyelitis in the innominate bone. A Anteroposterior radiograph reveals mottled lysis in the supra-acetabular bone with acetabular protrusion (white arrow). The articular space is completely closed at the centromedial aspect (arrowheads). B Anterior pinhole scintigraph of the left hip in a 60-year-old woman with pyarthrosis shows extremely intense tracer uptake in the hip joint and supra-acetabular bone (arrows). There is minimal bulging of the pelvic border, the sign of early acetabular protrusion or pathological fracture (middle arrow).

Acetabulum And Hemorrhagic Fluid
Fig. 8.11 Pediatric pyohip caused by direct extension of adjacent acute osteomyelitis (the same case as Fig. 8.15). Anteroposterior radiograph of the left hip in an 11-year-old girl after aspiration shows an infective focus in the ipsilateral femoral neck (open arrow)

lage begins to melt and lysis extends to the subchondral bone if the infection is uncontrolled. Without cartilage the joint is narrowed, collapsed, and eventually ankylosed.

Radiographically, the acute infected joint shows capsular distension, joint space narrowing, and periarticular bone erosions (Fig. 8.8A). The infective arthritis aborted by the early institution of proper treatment may also show similar findings but with a relatively well-preserved joint space (Fig. 8.9A). In the chronic phase the joint is deformed with ebur-nation and bony ankylosis may ensue (Fig. 8.10A). In children, pyohip can occur as an extension of acute osteomyelitis in the ipsi-lateral femoral neck, and both conditions can be diagnosed by radiography (Fig. 8.11).

Ordinary planar scintigraphy simply reveals intense tracer uptake in the joint. However, pinhole scintigraphy shows the intense uptake to be localized to markedly narrowed joint, reflecting the destruction of the articular cartilages and subchondral bones (Fig. 8.12). The articular narrowing tends to be conspicuous in the hips, the knees, and the spine that bear body weight. In contrast, the tracer uptake and articular narrowing are not so conspicuous in the glenohumeral joint (Fig. 8.13) and elbow, which are out of the main weight-bearing axis

Pyarthrosis

Fig. 8.12 Pyarthrosis of the hip. Anterior pinhole scinti-graph of the right hip in a 25-year-old man shows extremely intense tracer uptake diffusely in the acetabular fossa and the femoral head with total obliteration of the joint (arrow). Some tracer uptake is seen also in the femoral neck, probably at the site of the subcapital capsular and synovial attachment (arrowheads)

Fig. 8.12 Pyarthrosis of the hip. Anterior pinhole scinti-graph of the right hip in a 25-year-old man shows extremely intense tracer uptake diffusely in the acetabular fossa and the femoral head with total obliteration of the joint (arrow). Some tracer uptake is seen also in the femoral neck, probably at the site of the subcapital capsular and synovial attachment (arrowheads)

of the body. In pyarthrosis of the hip, tracer accumulates more extensively in the acetabular fossa than in the femoral head (Fig. 8.12). The uptake is concentric and symmetrical, reflecting uniform chondrolysis. A similar change can be seen in rheumatoid arthritis that is attended by more or less generalized cartilage destruction by pannus (see Chap. 10). In inadequately managed patients, the acetabulum may become fractured, resulting in protrusio acetabuli that avidly accumulates tracer (Fig. 8.10B). Pyarthroses of the knee and the ankle manifest as prominent uptake in the entire joint so that all of the bones forming the respective joint are silhouetted (Fig. 8.14). Pathological uptake appears to conform to the synovial lining. Understandably, the tracer uptake in pyarthrosis is far more intense than in simple synovitis. The intensity of uptake in an infective arthritis seems to be related to the severity of infection. In pediatric pyarthrosis, pinhole scintigraphy can occasionally detect the primary focus of infection in the adjacent bone (Fig. 8.15).

Pinhole scintigraphy is a useful means for the study of acute infection in the irregular joints of the elbow (Fig. 8.16) and the small joints of the hand and foot (Fig. 8.17). Occasi-

Pyogenic Arthritis The Shoulder

Fig. 8.13A, B Inconspicuous scan change in pyarthrosis of the glenohumeral joint. A Anteroposterior radiograph of the right shoulder in a 13-year-old girl with pyogenic arthritis of the shoulder joint shows minimal cortical erosion in the humeral head (arrows). B Anterior pinhole scan reveals increased tracer uptake in the subchondral zone (arrows). Note that the tracer uptake is not so intense

Fig. 8.13A, B Inconspicuous scan change in pyarthrosis of the glenohumeral joint. A Anteroposterior radiograph of the right shoulder in a 13-year-old girl with pyogenic arthritis of the shoulder joint shows minimal cortical erosion in the humeral head (arrows). B Anterior pinhole scan reveals increased tracer uptake in the subchondral zone (arrows). Note that the tracer uptake is not so intense

Uptake Humerus Head

Fig. 8.14A, B Generalized intense tracer uptake in pyar-throsis in the knee and ankle with the "wrapped bone" sign. A Anterior pinhole scintigraph of the right knee in a 29-year-old woman with pyogenic arthritis shows intense tracer uptake in all of the bones about the knee joint, giving rise to the "wrapped bone" appearance. The joint space is narrowed (arrow). B Lateral pinhole scintigraph of the ankle in a young man with acute pyogenic infection shows tracer uptake in the subarticular zones of the distal tibia and fibula (arrow), the trochlea (horizontal arrowheads), and the bones of the subtalar joint (lowermost arrowheads). Note the broadening of the distal tibial phy-seal line and extremely intense tracer uptake in the adjacent metaphysis that represents acute osteomyelitis, the cause of pyarthrosis in this case (arrow)

Fig. 8.14A, B Generalized intense tracer uptake in pyar-throsis in the knee and ankle with the "wrapped bone" sign. A Anterior pinhole scintigraph of the right knee in a 29-year-old woman with pyogenic arthritis shows intense tracer uptake in all of the bones about the knee joint, giving rise to the "wrapped bone" appearance. The joint space is narrowed (arrow). B Lateral pinhole scintigraph of the ankle in a young man with acute pyogenic infection shows tracer uptake in the subarticular zones of the distal tibia and fibula (arrow), the trochlea (horizontal arrowheads), and the bones of the subtalar joint (lowermost arrowheads). Note the broadening of the distal tibial phy-seal line and extremely intense tracer uptake in the adjacent metaphysis that represents acute osteomyelitis, the cause of pyarthrosis in this case (arrow)

Pyarthrosis Knee

Fig. 8.15 Primary infective focus in pediatric pyarthrosis (the same case as Fig. 8.11). Anterior pinhole scan of the left hip in an 11-year-old girl with acute pyarthrosis (open arrows) caused by direct extension of infection from adjacent osteomyelitis in the femoral neck (arrow). Note tracer accumulated in soft-tissue bacterial seeding during aspiration (small arrows)

Fig. 8.15 Primary infective focus in pediatric pyarthrosis (the same case as Fig. 8.11). Anterior pinhole scan of the left hip in an 11-year-old girl with acute pyarthrosis (open arrows) caused by direct extension of infection from adjacent osteomyelitis in the femoral neck (arrow). Note tracer accumulated in soft-tissue bacterial seeding during aspiration (small arrows)

onally, soft-tissue infection caused by bacterial contamination during the aspiration of an infected joint can be diagnosed using bone scin-tigraphy (Fig. 8.15; same joint as shown radio-graphically in Fig. 8.11).

Pyarthrosis and regional osteoporosis of the hip may impose a diagnostic problem because of the great similarity of their symptoms and planar scan findings. With the aid of pinhole scintigraphy, however, tracer uptake in the regional osteoporosis can be clearly differentiated from that of pyarthrosis: the tracer uptake of pyarthrosis is in the joint (Fig. 8.12) and that of osteoporosis is in the femoral head (Fig. 8.18).

Osteoarthritis

Osteoarthritis

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Responses

  • evelyn
    What does intense tracer uptake in left acetabulum mean?
    6 years ago

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