Bone and Joint Infections

(1)

Groningen, The Netherlands

Extremely Painful Immobile Extremity

Complaint: the child cannot move the involved extremity and has a lot of pain.
Assessment: a newborn obviously cannot point to where the pain is localized. What is conspicuous is that the involved extremity is not mobile and feels warmer around the focus of infection. If the bone or joint lies just under the skin, then there is also redness. There is severe local pressure pain at the level of the involved area. There can be an abnormally forced position in the adjacent or involved joint. An older child will refuse to use the arm or leg and will in the case of a leg certainly not stand on it or walk. Older children are usually febrile.
Differential diagnosis:
- acute osteomyelitis
- septic arthritis (bacterial-, pyogenic-, suppurative arthritis)
Explanatory note: acute osteomyelitis and septic arthritis. A distinction must be made between children younger than 9–18 months and older children.

A child younger than 9–18 months is mostly not ill and does not have a temperature. This is due to an under-developed defense system with as a rule gives hardly any reaction to the infection.

In newborns an acute osteomyelitis can occur in more locations at the same time. In those cases there is sufficient stimulation of the defense system and the child will be febrile.

Older children as a rule are ill and are febrile.

The WBC, BSE and CRP are as a rule normal in children younger than 9–18 months of age but are raised in older children. In acute osteomyelitis or septic arthritis in more areas these parameters will be raised not only in newborns but also in older children.

On examination an acute osteomyelitis cannot be distinguished from a septic arthritis. This is partly because a reactive hydrops in the adjacent joint can also be caused by an acute osteomyelitis. Furthermore, the involved or adjacent joint has an abnormal forced position in a septic arthritis and also often in an acute osteomyelitis. The hip will be in flexion, abduction and external rotation (Fig. 18.1) and the knee in 30° of flexion (Bonnet position). Joint aspiration and culture are often necessary to distinguish between an acute osteomyelitis and a septic arthritis. An untreated acute osteomyelitis will result in a chronic osteomyelitis and an untreated septic arthritis may result in a deformity of the joint, or even in resorption of the femoral head.

Fig. 18.1

Newborn with an infected left hip joint. The hip is in flexion, abduction and external rotation

Subacute osteomyelitis (Brodie abscess) (see pp. 222–226 and 228)
Gonococcal arthritis (see p. 220)
Bone and joint tuberculosis (see pp. 221, 222)
Spondylodiscitis (see pp. 45, 48, 49, 51)
Tuberculous spondylitis (see pp. 51, 52)

Incidence

An acute osteomyelitis or septic arthritis can occur at all ages but usually involves children under 10 years of age. It is more frequent in boys than in girls. The incidence is 5–20 per 100,000 children per year.

Pathogenesis of Acute Osteomyelitis

A bone infection occurs because bacteria are spread hematologenously (bacteremia) or lymphogenously to the bone from a source of infection elsewhere in the body. These infections can be from the ear, throat, airways, intestines and urinary passages, sometimes skin infections after chickenpox or infection after a direct wound i.e. due to a nail in the foot and after diverse operations. The focus is usually not known. Bacteremia in children is a daily occurrence for example, there is a bacteremia in 50 % of cases after brushing the teeth.

The parts of the metaphysis, particularly those close to the epiphyseal plate, have an excellent vascularisation. The nutrient artery that is responsible for the vascularisation splits up in the bone marrow into small arterioles which run towards the growth plate. Just before the growth plate they turn around and end up in a venous cavity (sinus), which drains into the marrow cavity (vascular loops). Infection starts where the arterioles turn around (Fig. 18.2). As a result of a reduction in blood circulation the bacteria accumulate here. In children an acute hematogenous osteomyelitis begins in the metaphysis, never in the epiphysis or diaphysis. Some authors suggest that an injury (i.e. a contusion) may play a role in acute hematogenous osteomyelitis in 30–40 %. In the first instance a cellulitis occurs. In the cellulitis stage clinical symptoms and signs may be present such as pain, redness, swelling, joint mobility loss and possibly fever and general malaise.

Fig. 18.2

In otherwise normal children an acute hematogenous osteomyelitis occurs where the vascular loops are situated in the metaphysis. The bacteria accumulate here because of the reduction in blood circulation

If an acute hematogenous osteomyelitis remains untreated, then a subperiosteal abscess will be present after several days. The periosteum will be raised up due to the accumulation of pus (Fig. 18.3).

Fig. 18.3

(a) An acute hematogenous osteomyelitis in the metaphysis. (b) If this is not treated a subperiosteal abscess will develop. The periosteum will be raised up as a result of the accumulation of pus

Pathogenesis of Septic Arthritis

A septic or infectious arthritis often occurs hematogenously:
As a result of a direct hematogenous infection of the synovium (joint capsule) or the synovial fluid (Fig. 18.4).

Fig. 18.4

A septic arthritis can be the result of a direct infection of the synovium not only in newborns (a) but also in older children (b)

Fig. 18.5

(a) In a newborn an acute hematogenous osteomyelitis in the metaphysis spreads by way of the transphyseal vessels to the epiphysis and further into the joint through a piece of bone which does not have an epiphyseal bone core. (b) After the appearance of the bone core in the epiphysis the transphyseal vessels disappear and the epiphysis and metaphysis have their own blood supply. In older children a metaphyseal infection as a rule does not spread from the growth plate to the epiphysis with the exception of meningococcal infections and tuberculosis
In newborns an acute osteomyelitis that starts in the metaphysis can also spread into the epiphysis and then into the joint. In newborns the long bones do not have a bone nucleus in the epiphysis and the blood vessels run from the metaphysis into the epiphysis, the so-called transphyseal vessels. Through these vessels an infection can spread from the metaphysis into the epiphysis and finally into the joint. This causes total destruction of the growth plate and the epiphysis and finally the whole joint. After the appearance of the bony nucleus in the epiphysis transphyseal blood vessels disappear and the epiphysis and metaphysis have a separate blood supply. As a result an acute osteomyelitis in older children cannot spread from the metaphysis through the growth plate into the epiphysis (Fig. 18.6). Exceptions are in case of meningococcal sepsis and in delayed treatment of a serious acute osteomyelitis and in these cases the growth plates can be damaged.

Fig. 18.6

In joints where the growth plate and part of the metaphysis lie inside the joint capsule a metaphyseal infection can occur in the newborns (a) as well as older children (b) in which there is a direct extension into the joint
In joints in which the growth plate and a part of the metaphysis lie within the joint capsule, such as the glenohumeral joint, humeroradial joint, the hip joint and the talocrural joint, a metaphyseal infection can directly spread into the joint (Fig. 18.5).
Apart from this a septic arthritis may be caused by local spread of an infection from adjacent tissues or contamination after an intra articular wound, puncture or operation on the joint (Fig. 18.7).

Fig. 18.7

Apart from a bacteremia a septic arthritis can occur due to local spread from adjacent tissues or through contamination after an intra-articular wound, puncture or operation in newborns (a) or in older children (b)