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

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

A

B

FIGURE 2 A and B , Necrotizing cellulitis of the upper limb due to Streptococcus pyogenes in an older man with a chronic underly ing psychiatric disorder and severe malnutrition.

tissue should be sent for analysis by Gram stain, culture, and in vitro susceptibility screening. Although tissue biopsy is the most reliable for diagnosis, it is not required to establish a diagnosis of NSTIs. 18,32 Laboratory Findings The Laboratory Risk Indicator for Necrotizing Fasciitis (LRINEC) score is a tool based on laboratory parameters that has received considerable attention in its ability to discriminate between necrotizing and nonnecrotizing SSTIs, 33 especially those involving the head and neck. 34 The laboratory parameters included in the LRINEC score are C-reactive protein level, creatinine level, glucose level, hemoglobin level, sodium level, and white blood cell count. Because of its variable sensitivity, however, it is not recommended for ruling out NSTI. 34 Before administering antibiotics, two sets of blood cultures (both aerobic and anaerobic bottles) should be drawn. Blood cultures are usually positive in patients with monomicrobial (type II) necrotizing fasciitis and necrotizing myositis, whereas it is not typically the case in patients with polymicrobial (type I) necrotiz ing fasciitis. Imaging Findings A retrospective study from 2022 reported that radio graphic imaging should not delay surgical intervention, especially if there is crepitus on physical examination or rapid progression of symptoms. 35 A 2018 retrospective study showed that, compared with MRI and ultrasonog raphy, CT is the best initial imaging modality. 36 It may show gas in soft tissues, prompting immediate surgical intervention as it is highly specific for NSTI and is most common in clostridial infection or polymicrobial (type I) necrotizing fasciitis. In addition, when a contrast

enhanced CT scan is negative, NSTI can be reliably ruled out in patients with initial suspicion. 36 A 2019 systematic review and meta-analysis of 23 studies was conducted to compare the pooled sensitiv ity and specificity of physical examination, imaging, and LRINEC score in diagnosing NSTIs 37 ( Table 2 ). It demonstrated that the lack of relevant findings on physical examination (eg, fever or hypotension) is not sufficient to rule out NSTI and that LRINEC should not be used to rule out NSTI because it had poor sensitivity. In addition, CT was superior to plain radiography. Thus, a high clinical suspicion justifies prompt surgical consul tation for definitive diagnosis and management of NSTI.

Table 2

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

Accuracy of Some Parameters in Diagnosing Necrotizing Soft-Tissue Infections

Pooled Sensitivity (%)

Pooled Specificity (%)

Parameters

Fever

46.0

77.0 95.8 97.7 93.3 84.8

Hemorrhagic bullae 25.2

Hypotension Copyright © Wolters Kluwer, Inc. Unauthorized reproduction of the content is prohibited. 2023 21.0 88.5 68.2 40.8 CT scan LRINEC score ≥6 LRINEC score ≥8

94.9 LRINEC = Laboratory Risk Indicator for Necrotizing Fasciitis Data obtained from Fernando SM, Tran A, Cheng W, et al: Necrotizing soft tissue infection: Diagnostic accuracy of physical examination, imaging, and LRINEC score – A systematic review and meta-analysis. Ann Surg 2019;269(1):58-65.

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Orthopaedic Knowledge Update ® : Musculoskeletal Infection 2