Osteomyelitis, pyomyositis, and septic arthritis were huge sources of trouble for our orthopaedic ancestors—and their patients. Today, with vastly superior imaging and antibiotics, most orthopaedic infections can be located, identified, and treated in a timely fashion with rare residual sequelae. To stay out of trouble, it is important to recognize several trends over the last couple of decades. Pyomyositis is now the most common musculoskeletal infection, although pyomyositis, osteomyelitis, and septic arthritis occur more commonly together than alone. Bacteria have developed virulence factors and resistance, and we must be vigilant for signs that what seems like a localized musculoskeletal infection is about to “metastasize” and become a life-threatening systemic multiorgan disease (Fig. 18-1). We know a lot more about the acute-phase response (APR) to infection which usually functions efficiently to control infection and allow repair (Fig. 18-2) but can sometimes be “hijacked” by bacterial mechanisms resulting in tissue damage, out-of-control spread of infection and even death (Fig. 18-3).

It is much more likely that the orthopaedist will see a child very early after the start of a bone or joint infection. This can make diagnosis very difficult, because inflammatory markers such as C-reactive protein (CRP) or erythrocyte sedimentation rate (ESR) may initially be normal or only slightly elevated. Inflammatory markers are not the only tests that may be normal initially. An aspiration may not yield any pus early after infection, and radiographs may well be normal also. Repeat the labs if there is any question as the trend can tell a lot about the severity or disease and prognosis (Fig. 18-4).

At the same time, in the modern era, while cases of isolated infections do occur, infections that lead to death or disability are metastatic, involving multiple tissues (e.g., bone, muscle, and joint) with systemic spreading (e.g., lung). Opposed to single isolated infections, the acute phase response to multifocal infections is more exuberant, correlating with the amount of tissue infected and the duration of the infection leading to morbidity and mortality from systemic inflammatory response syndrome and thrombosis. While some have previously argued that knee-jerk
antibiotic administration may blunt the initial picture, current thinking is that early antibiotic administration rarely affects culture results. Holding antibiotics to wait for a culture result can lead to progression of the infection and complications.

As a general rule, be sure to get a medical specialist to help in the management of infants and younger children and in those who show any signs of systemic toxicity.

On first presentation of a child with osteomyelitis, there is often a trauma history. This may lead the orthopaedist down the path of looking for occult fractures, sprains, etc., delaying diagnosis. To stay out of trouble, recognize that if it is an injury, with each passing day, the area looks and feels better; in an infection, with each passing day, it looks and feels worse.

Be aware that children with neuromuscular conditions, especially spina bifida but also cerebral palsy and others, can present with a fracture and have a picture that mimics infection.

Although pain is a key feature, children may not complain of pain. Instead, they may limp or not walk or not move the body part. Don’t forget about referred pain: pain from the back and the psoas area can refer to the hip, and pain that originates in the hip can refer to the distal thigh or knee region. Be sure to get a history of recent infections. A particularly important example is chicken pox: the virus lowers immunity and the skin lesions can be infected. In these cases, the bacterial pathogen is usually Streptococcus but can be Staphylococcus.¹

To stay out of trouble, be alert to how unbelievably unreliable WBCs can be as a marker of infection.² WBC is often normal, although a left shift may be a clue that there is an infection. It is also essential to keep in mind that leukemia may be in the differential diagnosis. If this is a possibility, you will want your primary care doctors or infection consultants to look at a manual differential/smear to rule out leukemia. ESR rises slowly and is unreliable in the early presentation of bone and joint infections. It is also unreliable in the neonate or children with sickle cell disease. CRP can rise after trauma, giving you a false-positive result. It is also usually elevated in otitis media and other childhood infections, so like other markers, specificity is poor.

Blood cultures are good, but the best way to isolate an organism is by aspirating the suspected site of osteomyelitis. When aspirating a potential site of osteomyelitis, do it under conscious sedation with careful localization. A common mistake in aspirating osteomyelitis is to be in the diaphyseal region, too far from the physis. One clue is that if it is hard to penetrate the bone, you are probably in the diaphysis. Use a C-arm if necessary. Localizing the point of maximum tenderness can be very valuable. Most osteomyelitis is in the metaphysis very near the physis. Interventional radiology can be helpful to localize a collection and obtain cultures but is not truly therapeutic with regard to decompressing and sterilizing a larger collection. If there is a large subperiosteal collection, it’s usually better to do an operative irrigation and debridement.

Although imaging is often essential in managing pediatric orthopaedic infections, radiographs can fool you by lagging behind the actual clinical activity. You may encounter imaging that is normal after the disease has started or imaging that looks worse despite rapid clinical resolution (Fig. 18-5). It is well
known that changes in the bone take more than a week to show up on plain radiographs after the start of AHO. To stay out of trouble, look for soft-tissue swelling as an early radiographic sign. For comparison, position both limbs symmetrically and ask for a soft tissue technique. Bone scan with pinhole views have been used in the past but have been largely replaced by MRI (Fig. 18-6). MRI can be incredibly helpful for localizing disease especially in contiguous areas.

In addition to diagnosis, the treatment of AHO can be a significant source of trouble. In the past, while IV antibiotics were generally used until inflammatory markers settle, most centers are finding oral antibiotics to be equally effective and there has been a trend for less IV antibiotic use. Today, most hospitals that would admit a child with AHO have infectious disease specialists on staff. Ask these experts, or the child’s primary care doctor, to help you define the best antibiotic and antibiotic course. Remember that some antibiotics can cause side effects, such as neutropenia and kidney and liver toxicity. You or one of the primary doctors should be following a WBC.

The indications for irrigation and debridement of a potential site of osteomyelitis are not absolute though signs of systemic inflammatory syndrome or thrombosis would warrant emergent surgical treatment. Many orthopaedists use the failure to show clinical improvement after 24 to 36 hours of antibiotics as the main reason to do an irrigation and debridement. Others recommend doing an irrigation and debridement if the CRP is rising, if a significant volume of pus is aspirated, or if there are disruptive changes on radiographs. Extended follow-up may be warranted for young children with osteomyelitis. Because the infection in infants and young children occurs so close to the growth plate, there is a risk for growth arrest, and these kids should be followed for 6 to 12 months after resolution of symptoms with radiographs.

Septic arthritis is a major source of trouble, especially in the hip, where it is a surgical emergency. Surgical irrigation and debridement is also recommended for most other joints, although there is some literature to support the efficacy of repeat aspirations and antibiotics for joints other than the hip.

To stay out of trouble, keep the differential diagnosis of a swollen joint in your head. You should consider Lyme arthritis in endemic areas as well as various rheumatologic conditions. The experienced examiner will note that in both Lyme arthritis and nonbacterial arthritis, there may be a large effusion but no significant short arc tenderness.³ Juvenile rheumatoid arthritis (JRA) can appear suddenly and mimic septic arthritis. Some children with JRA or Lyme arthritis will have a synovial WBC greater than 100,000. Keep gonococcal arthritis in your differential. You won’t see gonococcal arthritis exclusively in sexually active teens; sadly, you may encounter the infection in a younger child who has been sexually abused. As the organism responsible for gonococcal arthritis is notoriously difficult to grow in culture, be sure to obtain proper cultures for the differential diagnosis.