Osteomyelitis and septic arthritis are uncommon diseases in the neonate. When they occur, however, they can cause significant morbidity and permanent disability. The exact incidence of these two diseases is difficult to determine because most centers see only a few cases per year. A preponderance of male infants is affected, and newborns subjected to invasive monitoring are at increased risk.

In most cases, no precipitating factors are noted. Osteomyelitis of the newborn has been reported, however, after heel punctures, umbilical vessel catheterization, exchange transfusion, total parenteral nutrition, fetal monitoring, femoral venipuncture, suprapubic aspiration, and other needle punctures. Osteomyelitis also has been described as a complication of infected cephalohematoma. Broad-spectrum antibiotic therapy, prematurity, central venous catheters, and total parenteral nutrition are risk factors for fungal bone and joint infections.

Hematogenous dissemination is the most frequent source of suppurative bone and joint infections in the newborn period, but skeletal infection can occur after direct inoculation or as an extension from a contiguous site. The long bones are affected most commonly. The pathogenesis of osteomyelitis differs in the neonate compared with the older child. In the neonatal period, a communication between epiphyseal and metaphyseal vessels exists through sinusoidal vessels that transverse the growth plate. The sluggish flow in the sinusoidal loops of the metaphysis near the growth plate predispose to bacterial sequestration and the development of hematogenous osteomyelitis. The infection can spread through the transphyseal vessels and extend to the epiphysis. Infection of the epiphysis may rupture through the periosteum and enter the joint space, with secondary suppurative arthritis, especially for such joints as the hip and shoulder, where the epiphysis is intraarticular.

Another unique feature of neonatal osteomyelitis is the frequency of multiple-bone involvement and contiguous joint involvement. This is particularly true for skeletal infections caused by Staphylococcus aureus. The destruction of the hyaline cartilage and the growth plate can lead to long-term sequelae.

The mechanisms of infection secondary to umbilical vessel catheterization may be related to multiple septic embolization through an infected umbilical stump and catheter and to decreased blood flow that might predispose to infection by altering the host defense mechanisms. The infection is generally in the ipsilateral inferior limb, distal to the tip of the catheter.

In group B streptococcal osteomyelitis, the right proximal humerus tends to be affected more frequently. The predilection for this site seems related to minor trauma to the shoulder while passing beneath the pubic bone during delivery.

Osteomyelitis of the os calcii may result from the direct introduction of bacteria at the time of heel puncture for blood sampling; improper site and techniques have been reported as causative events. Osteomyelitis of the skull is associated with the use of fetal scalp monitoring and rarely as a result of extension from an infected cephalhematoma.

Candida species can cause neonatal osteomyelitis and suppurative arthritis in those newborn who require invasive monitoring. Bones and joints are frequent secondary foci of infection in infants with disseminated candidiasis.

The leading pathogen causing osteomyelitis is S. aureus; and the group B streptococci, especially serotype III, have been reported with an increased frequency. In some centers, group B streptococcus is the most frequently isolated pathogen in neonatal osteoarticular infections. Neisseria gonorrhoeae, as well as gram-negative bacilli such as Klebsiella pneumoniae, Haemophilus influenzae (type b and nontypable), Proteus species, and Escherichia coli are infrequent pathogens (Box 73.1).

The pathogens causing suppurative arthritis in the neonate are the same as those causing osteomyelitis; differences in etiology are influenced principally by whether the infection is acquired in the hospital. In a review of 92 cases, Dan reported that the pathogens involved for hospital-acquired infections were Staphylococcus species (62%), Candida species (17%), gram-negative enteric bacilli (13%), Streptococcus species, and H. influenzae (4%). For community-acquired infections, the pathogenic organisms were streptococci, mainly group B (52%), Staphylococcus species (26%), gonococci (17%), and gram-negative bacilli (4%).