CHAPTER 128 Bone and Joint Infections Neha P. Raukar | Brian J. Zink PRINCIPLES examinations and helps guide management, including antibiotic therapy and surgical intervention. Background Anatomy and Physiology Historically, bone and joint infections (BJIs) have been described in grim terms. Aids to Surgery, written in 1919, noted that “acute Histologically, bone tissue is classified as compact or spongy. infective osteomyelitis … is a very fatal disease.” With septic Compact bone forms the shaft of long bones and outer shell of arthritis, “the patient becomes exhausted from toxaemia or all bone. Spongy bone is found at the ends of long bones and pyemia,” and “ankylosis is the usual most favourable termina- makes up irregular bones. Compact bone is dense and without tion.”1 Advances in diagnostic methods, antibiotic therapy, and cavities and consists of longitudinally running Haversian systems, surgical techniques have resulted in better patient outcomes; which contain Haversian canals that house vasculature and nerves. however, new challenges are arising. Antibiotic resistance is evolv- Spongy bone, conversely, consists of a bony lattice, the trabeculae, ing, and many patient subsets have reduced host immunity. This which contains marrow, is more metabolically active, and is less combination results in greater complexity in the management of dense than compact bone. The central Haversian canals run paral- BJIs than has ever been encountered. The emphasis of modern lel to the long axis of the bone and contain the blood supply and management of BJIs has shifted from prevention of sepsis and reticular connective tissue for the Haversian system. Spongy bone, death to prompt diagnosis, initiation of treatment, and avoidance also called cancellous or medullary bone, has numerous cavities, of the complications and morbidity associated with chronic bone is located within the medullary cavity, and consists of extensively or joint infections. connected trabeculae. The overall occurrence of BJIs appears to have remained The gross structure of long bones can be divided into several constant during the past 4 decades.2 In hospitalized patients in the sections. The diaphysis is the shaft of the bone and contains the United States, the incidence is approximately 1%. Osteomyelitis compact cortical bone with an overlying periosteum and a medul- in children younger than 13 years occurs in 1 in 5000, whereas the lary canal containing marrow. The metaphysis is the junctional incidence of septic arthritis ranges from 5.5 to 12/100,000 indi- region between the epiphysis and diaphysis. The metaphysis viduals.2 In contrast to the rest of the world, there is no correlation contains abundant trabecular bone, but the cortical bone thins between socioeconomic factors or race and the incidence of BJI here relative to the diaphysis. Finally, the epiphysis is the area at in the United States. Both bone and joint infections show a either end of a long bone and is made up of abundant trabecular bimodal age distribution, occurring most commonly in people bone and a thin shell of cortical bone (Fig. 128.1). In the skeletally younger than 20 years or older than 50 years. In children, BJIs mature individual, the epiphysis of most bones is involved in usually occur in previously healthy individuals, with boys having articulation and, instead of being covered by a periosteum, is a slightly increased susceptibility to bone infections. In adults, covered with a thin layer of articulating cartilage, a very thin layer there are several known risk factors that lead to a higher risk of secretory cells sitting on a loose fibrous stroma that allows of BJIs. frictionless movement of the bones. Orthopedic infections can be classified according to the site of Joints are enclosed by a synovial capsule, which consists of a involvement and include osseous (osteomyelitis), articular (septic, dense fibrous connective tissue that offers structural integrity and pyogenic, or suppurative arthritis), bursal (septic bursitis), subcu- is lined with synovial cells that secrete synovial fluid. This forms taneous (cellulitis or abscess), muscular (infectious myositis or a sleeve around the articulating bones to which it is attached. In abscess), and tendinous (infectious tendinitis or tenosynovitis) some joints, such as the shoulder, hip, and knee, the synovial varieties. The terms osteomyelitis literally means inflammation of membrane extends beyond the epiphysis and attaches to the the marrow of the bone, but it is colloquially used to refer to metaphysis. This anatomic relationship allows bacteria to spread infection in any part of the bone. directly from the metaphysis into the joint. Infectious processes can also be categorized by their onset and are generally designated as acute, subacute, or chronic. An acute Pathophysiology infection is one that lasts less than 2 weeks, a subacute infection is one that lasts 2 to 6 weeks, and chronic infections are those that Osteomyelitis is an infection of the bone and medullary cavity. last longer than 6 weeks. Chronic osteomyelitis is also used to Bone is typically resistant to infection unless it is subjected to define a bone infection that fails to respond to a a normal course trauma, disruption of blood flow that deprives the bone of normal of antibiotic therapy. A histologic diagnosis of chronic osteomy- host immunity, a large inoculum of blood-borne or external elitis depends on the presence of necrotic bone. microorganisms, or a foreign body. Hematogenous inoculation For the emergency clinician, the most practical way to classify usually starts in the metaphysis, given the slow flow of blood in osteomyelitis is as hematogenous, which is more common, or the sinusoidal blood vessels. Acute inflammatory cells migrate to contiguous, with the contiguous type further subdivided based on the area, causing edema, vascular congestion, and small vessel the presence or absence of vascular insufficiency. This method of thrombosis, which then leads to an increase in the intraosseous classification assists in the interpretation of diagnostic imaging pressure compromising blood flow to the bone. Eventually, lack 1693 Downloaded for dr.Rahmat Dani Satria, M.Sc, Sp.PK ([email protected]) at Universitas Gadjah Mada from ClinicalKey.com by Elsevier on July 28, 2018. For personal use only. No other uses without permission. Copyright ©2018. Elsevier Inc. All rights reserved. 1694 PART III Medicine and Surgery | SECTION TWELVE Infectious Diseases Compact bone Epiphysis Spongy bone Haversian canals Trabeculae Enlarged below Haversian Diaphysis canals Volkmann’s canals Lamellae Metaphysis Marrow Epiphysis or medullary A B cavity Lacunae Haversian canal Canaliculi C Fig. 128.1. Schematic drawing of long bone. A, Regions of long bone. B, Cross-sectional structure of long bone. C, Microscopic structure. of blood supply to the medullary canal and periosteum leads to are at varying stages of metabolism—some are active, some are areas of necrotic bone termed sequestra. Bony tissue attempts to slow-growing, and some are dormant. Antibiotics target meta- compensate for the tensile stresses caused by infection by creating bolically active bacteria, such as those in the single cell state new bone around the areas of necrosis. This new bone deposition (planktonic state), but bacteria in other stages in the biofilm com- is called an involucrum. Given that there is significantly reduced munity are more resistant to the effects of antibiotics. Further- blood supply to this necrotic bone tissue, bacterial infection is more, Gram staining only identifies planktonic bacteria, which often difficult to eradicate with medication alone and, frequently, helps explain why Gram stains of aspirated synovial fluid in a chronic osteomyelitis requires a combination of surgical débride- suspected septic joint are often negative; therefore, a definitive ment and antibiotic therapy. diagnosis is made only by culture of the synovial fluid aspirate or The evolution of blood flow patterns at the metaphyseal- synovial tissue. Biofilm formation also explains why optimal treat- epiphyseal junction and development of vascular anatomy explain ment of a septic joint, especially of prosthetic joints, involves the pathologic features of hematogenous osteomyelitis in the complete surgical débridement. different age groups. In neonates and infants, osteomyelitis readily Hematogenous spread of bacteria causes almost all cases of advances from the metaphysis to the epiphysis and adjacent joint osteomyelitis in children and in the subset of adults who have space, leading to septic arthritis. After the first year of life, the vertebral osteomyelitis. In the appendicular skeleton of adults, infection usually spreads laterally through Volkmann’s canals, such as in the foot, hand, skull, maxilla, and mandible, osteomy- breaks through the cortex, and lifts the periosteum to form a elitis usually occurs by spread of the pathogens from a contiguous subperiosteal abscess. In the adult, after the epiphyseal plate source of infection or direct implantation. Head and neck ossifies, anastomoses form between the metaphyseal and epiphy- osteomyelitis is usually caused by sinus disease and odontogenic seal blood vessels and infection can once again spread from the infection. metaphysis to the epiphysis and eventually into the synovium Infections from direct implantation of bacteria are caused by and joint space. In addition, the periosteum becomes firmly deep puncture wounds, such as by an animal bite, and