How can I determine if a suture tract or sinus still contains retained suture material when it is not visible?

Detecting Retained Suture Material in Non-Visible Tracts

Ultrasound is the imaging modality of choice for detecting retained suture material in a spitting suture tract when the material is not visible on examination, with a reported sensitivity of 95% for foreign body detection. 1, 2

Imaging Algorithm for Non-Visible Retained Sutures

First-Line Imaging: Ultrasound

• Ultrasound should be performed immediately when clinical suspicion exists for retained suture material despite negative visual inspection. 1, 2
• All foreign bodies, including suture material, appear hyperechoic on ultrasound with posterior acoustic shadowing, allowing reliable detection even when deeply embedded. 1, 2
• Ultrasound provides real-time characterization of the foreign body's morphology, depth, and relationship to adjacent structures such as tendons and neurovascular bundles. 1, 2
• This modality offers the additional advantage of real-time guidance during surgical removal procedures. 1, 2

Second-Line Imaging: CT Scanning

• If ultrasound is unavailable or technically limited, CT with 1 mm thin slices should be obtained, as it is 5-15 times more sensitive than plain radiography for foreign body detection. 3, 1, 4
• CT provides precise three-dimensional localization of retained suture material and can identify associated complications including sinus tracts, abscesses, cellulitis, and fascial edema. 3, 1
• Suture material composition can sometimes be characterized based on attenuation and Hounsfield unit values on CT. 3
• Intravenous contrast administration should be considered to differentiate abscess from phlegmon and to evaluate for vascular complications such as pseudoaneurysms. 3

Third-Line Imaging: MRI

• MRI has lower sensitivity compared to ultrasound and CT for foreign body detection but may be useful when osteomyelitis or deep soft tissue infection is suspected. 3, 2
• MRI excels at detecting complications surrounding retained suture material, including surrounding edema, inflammation, abscess formation, and bone marrow signal abnormalities. 3, 2
• One significant disadvantage is that bone marrow signal abnormalities may persist for months following surgery, potentially confounding interpretation. 3

Clinical Context and Complications

Why Retained Sutures Cause Persistent Problems

• Chronic surgical site infections commonly arise from bacterial biofilms that invest retained suture material and associated soft tissue surfaces. 5
• Suture material provides a nidus for polymicrobial biofilm formation, which can cause culture-negative infections that persist despite antibiotic therapy. 5
• Granulomatous soft tissue reactions develop around retained foreign bodies, with superimposed infections including cellulitis, abscess, myositis, septic arthritis, or chronic sinus tracts. 3, 1

Management Principles

• To achieve wound healing, the chronic sinus tract and all retained suture material must be surgically removed. 6
• Exploration of a suture sinus should be performed under general anesthesia with secondary intention healing of the resulting wound. 7
• Monofilament suture material and associated knots are particularly implicated in suture sinus formation, with 26 of 31 suture sinuses in one series associated with monofilament material. 7

Critical Pitfalls to Avoid

• Never rely solely on visual inspection or negative plain radiographs to exclude retained suture material. 1, 4
• Do not assume that absence of purulent drainage or negative cultures excludes retained foreign body infection, as biofilm-associated infections are frequently culture-negative. 5
• Avoid closing suture sinus tracts primarily, as this markedly increases infection risk; secondary intention healing is required after foreign body removal. 7
• Do not delay advanced imaging when clinical signs persist (ongoing drainage, erythema, pain, or failure to heal) despite initial negative findings. 1, 6