Orthopaedic Knowledge Update®: Musculoskeletal Infection 2 Print + Ebook (AAOS - American Academy of Orthopaedic Surgeons)

Chapter 27: Necrotizing Fasciitis and Other Complicated Skin and Soft-Tissue Infections

and 2 ). In 2022, it was reported that nonspecific symp toms including diarrhea, malaise, and loss of appetite can precede the onset of skin manifestations. Fever and other systemic signs of toxicity (such as tachycardia or hemodynamic instability) can develop and then lead to shock and multiorgan failure. 28 Necrotizing cellulitis only affects the skin and spares the fascia and skeletal muscles. Necrotizing fasciitis may be difficult to visualize because it involves the muscle fascia and overlying subcutaneous fat while initially the overlying tissue can look unaffected. One early clue to the presence of necrotizing fasciitis is the development of anesthesia due to destruction of superficial nerves in the subcutaneous tissue. Necrotizing myositis is a rare infection because of the generous blood supply of skele tal muscles; it has been called clostridial myonecrosis or gas gangrene when it is a clostridial infection. Although skin crepitus can be observed in necrotizing cellulitis, its presentation is less severe than gas gangrene. Fournier gangrene is a form of polymicrobial (type I) necrotizing fasciitis affecting the perineum, the second most common site of NSTI after the extremities (lower more often than upper extremities). 7 It occurs more fre quently in men, results from a breach of the urethral or gastrointestinal mucosa integrity, and may rapidly spread to the anterior abdominal wall and the gluteal muscles. A 2018 systematic review of case reports found that NSTIs can affect the head and neck when there is rupture of the oropharynx mucous membrane following surgery or odontogenic infection. 29 A mixture of aerobic and anaer obic bacteria originating from dentition or the pharynx are usually identified. Although most NSTIs of the head and neck are polymicrobial, monomicrobial infection can be due to group A Streptococcus . Necrotizing fasciitis can spread to the lower neck, submandibular space (called Ludwig angina), jugular vein (Lemierre syndrome), and mediastinum. Factors increasing the risk of mediastinitis include prior corticosteroid use, infection due to gas-pro ducing pathogens, and a pharyngeal source of infection. 30 Diagnosis of NSTIs The diagnosis of NSTIs is primarily clinical and sus pected when there are symptoms of soft-tissue infection (such as erythema, edema, or warmth) and signs of sys temic toxicity (such as fever, hemodynamic instability, organ dysfunction) with crepitus, rapid progression of symptoms, or extreme pain (sometimes out of propor tion to skin findings). The definitive diagnosis of NSTIs is established by surgical exploration and direct exam ination of involved tissues including skin, subcutaneous tissue, fascia, and skeletal muscle. NSTIs are diagnosed when there is direct visualization of a swollen and dull gray muscle fascia and easy separation of tissue planes by frank dissection (positive finger test). 31 Intraoperative

that one of the major factors for concluding malpractice in court is the timely diagnosis and management of NSTIs. 21 In addition, although rare, cases of healthcare-associated NSTIs have been cited in malpractice claims. 22,23 Microbiology of NSTIs Almost all NSTIs are polymicrobial (type I) caused by vari ous combinations of anaerobic and aerobic pathogens, with Streptococcus and Bacteroides spp. being the most com mon aerobic and anaerobic bacteria, respectively. 7,24 Other microbes involved in type I NSTIs include Enterobacterales , Clostridium , and Peptostreptococcus spp. NSTIs can also be monomicrobial (type II) caused by group A beta-hemo lytic Streptococcus most commonly, other beta-hemolytic streptococci, or Staphylococcus aureus . Rarely, monomicro bial NSTI can be caused by Vibrio vulnificus , Clostridium spp., Bacteroides spp., Escherichia spp., or other organisms. Most clostridial infections are caused by Clostridium per fringens ; other species causing clostridial infections include Clostridium septicum , Clostridium novyi , and Clostridium histolyticum . Less frequently, NSTIs can be caused by Aeromonas hydrophila and fungi such as Candida spp. and Mucormycosis . 25,26 A systematic review from 2022 reported that necrotizing myositis is usually caused by group A Streptococcus (and other beta-hemolytic streptococci), C perfringens (after penetrating trauma), or C septicum (after hematogenous seeding from the gastrointestinal tract). 27 Clinical Findings in NSTIs NSTIs can manifest with erythema, edema (sometimes extending beyond visible erythema), severe pain (out of proportion compared with physical examination find ings), crepitus, and changes in skin color (such as bullae, necrosis, ecchymosis, and extensive tissue destruction) in the affected area (generally the extremities) ( Figures 1

Section 6: Bone, Joint, and Soft-Tissue Infections

FIGURE 1 Photograph shows necrotizing fasciitis of the lower limb due to Streptococcus agalactiae in an elderly woman with obesity. Copyright © Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. 2023

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Orthopaedic Knowledge Update ® : Musculoskeletal Infection 2