Infection of bone and Joint

Osteomyelitis and septic arthritis remain a significant cause of morbidity in paediatric practice. Prompt and adequate treatment is needed to reduce the risk of complications. In some parts of the world tuberculosis is still a serious problem; indeed there are signs it may be on the increase in the Western hemisphere.

Bone and joint infection is usually described in terms of acute, subacute or chronic. No age is exempt from any type. Although there are classical forms of presentation at different ages, skeletal infection can pose great problems in terms of differential diagnosis. For example, trauma or sickle cell crisis can be confused with acute osteomyelitis, benign or malignant bone tumours can mimic subacute or chronic infection (Fig. 28.15) and other causes of inflammatory joint disease, such as juvenile arthritis or irritable hip syndrome, have to be distinguished from septic arthritis (Fig. 28.16).

Thus, bone and joint infection my present in many guises, from an acute life-threatening condition to a painless deformity manifesting many years after an unrecognised infection damaged the growth plate.

The treatment of skeletal infection is based on the following principles:

   • rest;

   • elevation;

   • surgical drainage;

   • antibiotics;

   • nutrition.

In every case, all must be considered although not all may need immediate implementation. For example, an early osteomyelitis may not require surgical drainage or, in another case, antibiotics should be withheld until adequate surgical clearance has removed infected, dead tissue and provided specimens for culture and sensitivity. It is also vital to remember that when surgeons are considering which antibiotic to give or whether a bone should be explored, the importance of resting and elevating a limb, along with correction of nutritional deficiency, including anaemia, must not be forgotten.

The cause of skeletal infection is usually haematogenous spread from without the body or from a septic focus within. In acute osteomyelitis the metaphysis is the common site. Involvement of epiphysis or diaphysis is more often seen in subacute or chronic infections.

Acute infections

Septic arthritis

The hip and knee are the commonest joints affected but the principles of management apply to any joint.

It is difficult to distinguish between septic arthritis of the hip and osteomyelitis of the upper femur. The growth plate and metaphysis are intracapsular and an early osteomyelitis can rapidly progress across the metaphysis directly into the joint. In practice, especially in the neonate, osteomyelitis and septic arthritis of the hip should be considered a single entity.

The usual cause of septic arthritis in any joint is haematogenous spread but direct inoculation can occur, e.g. penetration of the hip during femoral venepuncture. Neo­nates, the immunosuppressed and children with sickle cell disease are more susceptible.

Bones and joints can be involved as part of septicaemia, e.g. meningococcal. Diagnosis is often delayed in the serious­ly ill child where attention is directed towards the septicaemia.

Clinical features. The diagnosis is straightforward when there are typical signs such as tenderness, reluctance to move a limb (pseudoparalysis) and fever. In superficial joints an effusion can be demonstrated and the joint is warm. In the hip, ultrasonography is useful to show an effusion. Plain X-rays show this as widening of the joint space (Fig. 28.17) and in severe cases there may be a septic dislocation of the hip.

Treatment. Blood should be taken for blood count, ery­throcyte sedimentation rate (ESR) and C-reactive protein. The joint should be aspirated. If pus is obtained or there is any doubt, open surgical drainage and decompression of the joint is indicated. In the hip, this is most easily done through an anterior approach. A section of capsule is excised to ensure free drainage and the joint copiously irrigated. Once material has been taken for culture, intravenous antibiotics are commenced. The guidance of a microbiologist is recommended.

The most common organisms are staphylococci and streptococci. In children under 4, Haemophilus influenzae may be found.

If the hip was subluxated or dislocated a hip spica should be applied to keep it reduced. Otherwise bed rest is appropriate until the signs of infection, combined with blood tests, are seen to be settling. In this regard it is easier to monitor and treat a superficial joint, e.g. knee. Pus in a joint is destructive. If treatment is delayed chondrolysis occurs. In the hip, this is followed by avascular necrosis of the femoral head and ultimately limb shortening due to dislocation (Fig. 28.18). A hip thus affected may come to arthrodesis or trochanteric arthroplasty in which the unaffected greater trochanter is placed in the acetabulum to stabilise the hip. Minor damage to the growth plate may not show until late after the infection (Fig. 28.19).

Osteomyelitis

  As with septic arthritis, the usual cause is haematogenous spread to the metaphysis and most frequently involves the most rapidly growing ends of long bones. There is often a history of antecedent trauma and osteomyelitis may follow a subperiosteal haematoma. The initial inflammatory reaction is followed by an abscess which tracks laterally to lift the periosteum. This deprives the cortex of its blood supply and it may die; a sequestrium. Subperiosteal new bone produces the involucrum (Fig. 28.20). Pus may continue to rupture through the involucrum via cloacae and reach the skin (Fig. 28.21a and b).

Clinical features. Classically, the child is ill with signs of septicaemia. There is local tenderness erythema and increase in local temperature. In severe cases the whole limb is swollen, tender and hot, making localisation difficult. Radiological appearances in osteomyelitis are normal in the early stages, although a bone scan may be helpful.

Treatment. Once pus is formed it must be surgically released. In the genuinely early case (history less than 24

hours) treatment with antibiotics can be started after blood cultures are taken. Provided there is a prompt response (24-48 hours) surgery may be avoided. This approach may also be justified in early severe cases where generalised swelling and tenderness of the whole limb makes localisation difficult. In such cases it is advisable to take blood cultures, commence resuscitation and' intravenous antibiotics, and wait 24—48 hours when localising features will develop to direct the surgical approach.

When surgery is required the periosteum is incised and any subperiosteal abscess drained. If there is no subperiosteal abscess, the bone should be drilled to drain any intraosseous pus. Postoperatively the limb should be rested in a cast. Prolonged antibiotic therapy is necessary (at least 6 weeks) because it can be very difficult to eradicate the condition permanently: ‘once an osteomyelitis, always an osteomyelitis’.

Apart from chronicity, other possible late effects of osteomyelitis include overgrowth of the limb due to stimulation of the growth plate or deformity due to growth plate damage (Fig. 28.22a and b).

Acute infection can affect the spine in childhood. It is often not suspected in a toddler or child who may be generally well; backache, stiffness and a limp are alerting signs. X-rays show disc space narrowing and an MRI scan will highlight the inflamed area. A CT-guided biopsy will probably show infected tissue but it is common that culture is negative or inconclusive. Rather than exploring and draining the spine it   is usually worthwhile to treat these children with a spinal brace and broad-spectrum antibiotics whereupon the infection usually subsides, with or without spontaneous fusion between affected vertebrae.

  Subacute and chronic infections

The epiphysis is a relatively common site. The diaphysis can also be affected. The clinical features are much less marked than with acute infections and diagnosis is often delayed. Radiographs may show a sclerotic wall around a cyst or in many cases sclerosis may be the only feature. A bone scan may be helpful to distinguish from quiescent harmless bone lesions. In cases where sampling a lesion may be difficult because of its anatomical location or lack of clear definition on radiographs a conservative approach with antibiotics may be indicated. If there is no response, biopsy is indicated to exclude a tumour.

Irritable hip

This is also known as transient synovitis or observation hip. It is essentially a diagnosis of exclusion — most importantly from septic arthritis. It is a common condition in which the child, usually between 4 and 8 years old, presents with pain in the hip of variable severity, reluctance to weight bear and a limp. The cause is usually unknown but there may be a history of preceding trauma or a viral infection. The clinical features vary from a well child with minor loss of movement to the unwell child with a low-grade fever and marked stiffness.

Systemic examination may reveal lymphadenopathy or other evidence of a viral infection, such as a rash. Radio-graphs are normal or may show slight widening of the joint space. The blood count is normal and the ESR may be minimally raised. The presence of fever, effusion and marked stiffness would be an indication to investigate as a septic arthritis. This would only apply to a minority of cases. The great majority settles with bed rest followed by mobilisation as the hip becomes comfortable

Skeletal tuberculosis

This may present as chronic arthritis (Fig. 28.23) or osteomyelitis.

In the spine it usually involves the adjacent parts of the bodies of two vertebrae. The disc is relatively resistant to tuberculosis but eventually undergoes avascular necrosis although it may sequestrate. Abscesses can spread in various directions by stripping the vertebral ligaments. In the lumbar region, a paravertebral abscess may enter the psoas sheath to appear in the femoral triangle. Clinical features include general malaise, backache and stiffness. The principal com­plications of spinal tuberculosis are paraplegia and deformity. Paraplegia may occur early or late in the disease. Early para­plegia is usually due to mechanical pressure on the cord from granulation tissue, pus, sequestrated disc material or oedema; ischaemia can also be a cause. Late paraplegia is usually associated with stretching of the spinal cord over an angular deformity, resulting in ischaemia. The usual deformity in spinal tuberculosis is a kyphosis due to collapse of the vertebral bodies. As with other forms of skeletal tuberculosis, treatment should be with appropriate antibiotics. However, it has been shown that, although conservative treatment is effective, there is a risk of a deterioration in the kyphosis and that this is most likely to occur in children and when several vertebrae are involved. Radical anterior débridement and spinal fusion will usually prevent any progression of the deformity.