Orthopaedic infections in children

by Anria Horn

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Introduction

Children are particularly prone to developing bone and joint infections. This is because of the unique anatomy around tgrowth plates, leading to sluggish and turbulent blood flow in these areas. Bone and joint infections in children are almost always haematogenous.
The worldwide incidence ranges from 1/800 to 1/5000. The incidence is higher in developing countries.
Boys are more commonly affected than girls, and younger children are more commonly affected than older children. Acute orthopaedic infections in children should be treated as emergencies.

Clinical findings

History

Patients will usually present with a vague history of trauma. This often leads to delayed diagnosis as infection is not considered. There will be a history of limping and pain, inability to weight bear and pseudoparalysis if the upper limb is involved. Ask about a history of an upper respiratory tract infection or recent skin infection, as it is often associated. There may also be a history of fever.

Examination

Start with a general examination including vital signs. Raised temperature and pulse rate is suggestive of infection. Examine the whole body for infectious cutaneous lesions or other obvious sources. Local examination follows the ‘look, feel, move’ principle:
Look:Swelling, erythema, sinus or pustule
Feel:Warmth, fluctuance, effusion (joint), tenderness
Move:Patients with septic arthritis are very reluctant to move their joints. If the joint moves easily, consider adjacent osteitis or cellulitis.

Special investigations

Radiographs of the affected limb should be requested. In acute infections, X-rays are typically normal but may show soft tissue swelling or an effusion. In the case of septic arthritis of the hip, subluxation may be evident. It takes on average 2 weeks for X-ray changes to appear following an acute infection. Blood cultures should be taken in all patients with suspected bone or joint infection.

Full blood count, ESR and CRP should be requested. White cell count and platelets are typically raised, as is the ESR and CRP.

Bone scan is useful to detect occult infections of the spine and pelvis and in the young child where it is difficult to localise the site of the infection. Use is limited by availability.

MRI has a very high sensitivity and specificity for detecting infection, but use is limited by availability and cost.

Kocher Criteria

Originally described to differentiate septic arthritis of the hip from a transient synovitis. Nonetheless useful in determining whether limb pain is caused by infection or something else.

Kocher Criteria
non-weight bearing	or pseudoparalysis
ESR	> 40mm/hr
WCC	< 12 x 10^9/L
Pyrexia	Temp >38.5°C

The number of criteria present predicts the likelihood of infection:
1 = 3%, 2 = 40%, 3 = 93%, 4 = 99%

Bacteriology and antibiotics

The most common infecting organism is staphylococcus aureus in all age groups, which accounts for 80–90% of positive cultures. The table in the chapter ‘Bone and Joint Infections Basics’ shows common organisms of different age groups and patient populations with antibiotic choice, but this should be guided by local trends.

Management

Non-surgical management is seldom indicated. In very early onset osteitis without collection of pus, antibiotic management alone is acceptable. If no infecting organism is identified, empiric antibiotics as listed in the table above should be prescribed for 6 weeks.
Surgical management is nearly always indicated to release the pus. In septic arthritis, a small arthrotomy is performed and the joint irrigated copiously. Pus swabs are taken as well as synovial samples. These are sent for culture and sensitivities as well as TB testing.
In osteitis, the affected bone is surgically approached and any extra-osseus pus is released. If not pus is found in cases with a high suspicion of osteitis, holes may be drilled in the bone to assess for and release intramedullary pus. Following surgery, patients are started on antibiotics as described above: 6 weeks for osteitis and 4 weeks for septic arthritis. Empiric antibiotic treatment can be changed depending on culture results or poor clinical response.

Complications

Untreated septic arthritis will lead to destruction of the joint cartilage and severe arthritis. In the hip and elbow, it may lead to avascular necrosis of the femoral and radial head, respectively.Acute osteitis, even if treated adequately, may lead to pathological fracture, growth disturbance and the development of chronic osteomyelitis.