Pathological conditionsInfections of bone and joints
A bacterial infection of bone is called osteomyelitis or osteitis and that of a joint, septic arthritis. Both may be caused by bacterial spread via the blood stream (i.e., hematogenous spread) or by direct implantation
|
Figure 85.
Osteomyelitis, Brodie's abscess: conventional tomography.
There is a large defect in the distal part of the tibia with involvement of the metaphysis, physis, and epiphysis.
|
of bacteria, such as in open fractures or at surgery.
In areas of the world where antibiotics are easily available, osteomyelitis is rare, but the disease still is encountered commonly in many other places. The infection often is caused by staphylococcus, but sometimes also by streptococcus (including Streptococcus pneumoniae), E.coli, Klebsiella, Haemophilus influenzae, and Myeobacterium tuberculosis. It is important to re cover fluid or tissue from the site of inflammation, either by open surgery or by percutaneous techniques. Treatment with antibiotics should be begun after recovery of tissue or fluid, not before. On the basis of the course of the disease, osteomyelitis may be separated into acute, subacute, and chronic stages.
Acute osteomyelitis often is seen in children, localized in the metaphyses. The clinical symptoms and signs are pain, swelling, tenderness, fever, elevated sedimentation rate, and leukocytosis. Conventional radiographic examination initially may be negative, but after a few days or 1 to 2 weeks, irregular osteolytic regions are seen, together with a periosteal reaction. In the early stages of osteomyelitis, diagnosis is better accomplished with scintigraphy and MRI.
In subacute osteomyelitis, an osteolytic area may be seen in the metaphyses close to the physis, termed a Brodie's abscess (Fig. 85). Surrounding bone sclerosis is typical, and channel-like radiolucent
|
a
|
Figure 86.
Chronic osteomyelitis with differential diagnostic features of a tumor.
Frontal (a) and lateral (b) views reveal a sclerotic area with small radiolucent regions. At CT examination (c), cortical violation is seen (arrow). Biopsy showed osteomyelitis.
|
b
|
|
c
|
|
regions are virtually diagnostic of infection.
Chronic osteomyelitis often is the result of previous open comminuted fracture or surgery, or both. Chronic osteomyelitis occurring after previous fracture or osteosynthesis is one of the most difficult conditions to treat in orthopedic surgery. It often causes the formation of sinus tracts leading to the skin surface. A sequestrum (an avascular fragment of bone) almost always is diagnostic of chronic osteomyelitis.
Garré osteomyelitis is difficult to treat and sometimes is difficult to differentiate from malignancy. It is characterized by extensive periosteal new bone formation with cortical thickening, and a positive bacterial culture rarely is obtained (Fig. 86). The differential diagnoses include osteoid osteoma, stress fracture, and osteosarcoma.
 | Figure 87.
Tuberculous arthritis of the ankle. The CT examination reveals widespread destruction. There is increased density in the distal portion of the tibia (Ti) and talus (Ta) compared with the calcaneus (C), representing infection and edema in the spongy bone tissue. |
Septic arthritis
Hematogenous infection may lead to septic arthritis in any joint, but it is most common in the hip and in the sacroiliac joints. In any joint, septic arthritis may be caused by
trauma from an open wound, surgery, or adjacent
osteomyelitis. Septic arthritis occurring in superficial joints generally is easy to diagnose because of joint swelling due to intraarticular pus or synovitis or both (Fig. 87). Septic arthritis in deep joints, such as the hip and sacroiliac joints, and in the
spine is more difficult to diagnose.
Septic arthritis of the hip
Septic arthritis of the hip joint can occur in children as well as in adults, and it causes severe pain in the acute state because of the increased pressure in the joint. This increased pressure may cause circulatory deficiency in the fem oral head, leading to osteonecrosis. The clinical signs of increased intracapsular pressure in the hip joint should be well known to radiologists and other clinicians alike: the patient tries to reduce the pressure in the hip joint by lying down with the leg flexed, abducted, and rotated externally. Extension and internal rotation of the hip aggravate the pain.
In the acute stage, the conventional radiographic examination may be normal. After one week the joint cartilage is reduced and broad erosions in the femoral neck may be observed. Subsequently, the hip joint may
 a | Figure 88.Septic arthritis: ultrasonography and CT.
a) Ultrasonography of a hip joint shows increased distance between the outside of the capsule (white arrow) and the femoral neck (open arrow). It is not possible to judge if this is due to an aseptic effusion (coxitis simplex), pus, or synovial swelling.
b) CT shows an inflammatory thickening of the joint capsule (arrow) without fluid in the joint. |
 b | |
be totally destroyed.
Synovitis in the hip joint leads to joint fluid that can be detected with ultrasonography, but it is not possible to differentiate among aseptic fluid, pus, and hypertrophic synovitis (Fig. 88 a). Fluid also can be identified with CT (Fig. 88 b) and MRI. In a patient with fluid or synovitis in the hip joint and with extensive pain and signs of infection, immediate diagnostic aspiration should be accomplished and, if the result is positive, the joint should be drained and the patient should be treated with antibiotic therapy.
When not treated promptly, septic arthritis may lead to total destruction of the hip joint and osteonecrosis (Fig. 89).Many adult patients with septic arthritis of the hip have RA, osteoarthritis, or malignant disease or drug or alcohol abuse.
Septic arthritis of the hip joint may be missed for the following reasons:
1. Clinical and radiologic examination of the hip joint is incomplete.
2. Lack of knowledge about conditions leading to a joint effusion, including
A. Nonseptic arthritis, which rarely causes a sizeable joint effusion.
B. Osteoarthritis, which also causes small amount of joint effusion, if any is produced at all.
C. Osteonecrosis.
D. Stress fractures.
E. Malignancy.
3. Lack of knowledge of typical scintigraphic patterns:
A. Osteoarthritis (limited localized uptake of radionuclide)
B. Arthritis (general, extensive increase in radionuclide uptake on both sides of the joint space.
C. Malignancy (locally increased uptake on one side of the joint space)
D. Insufficiency fracture and osteonecrosis (localized uptake of the radionuclide)
Discitis and spondylitis
These conditions are described in Chapter 12.
Niels Egund, Kjell Jonsson, Holger Pettersson and Donald Resnick