What is a sinus tract in a wound, particularly in patients with chronic conditions such as diabetes or vascular disease?

What is a Sinus Tract in a Wound

A sinus tract is an abnormal, narrow channel that extends from a wound surface into deeper tissues, connecting the skin to an underlying infection, abscess, foreign body, or infected bone—it represents a pathological communication pathway that allows drainage of infected material from deep structures to the skin surface. 1

Clinical Definition and Pathophysiology

• A sinus tract forms as a tubular pathway lined by granulation or epithelial tissue that connects a deep-seated infection or inflammatory process to the body surface 2
• The tract develops when chronic infection creates a path of least resistance for purulent drainage, typically originating from infected bone (osteomyelitis), infected prosthetic material, chronic abscesses, or retained foreign bodies 1
• The presence of a sinus tract is pathognomonic (definitively diagnostic) of deep infection, particularly prosthetic joint infection or chronic osteomyelitis 1

Clinical Presentation

• The most obvious clinical sign is persistent drainage from a nonhealing wound, often with purulent or serosanguineous discharge 1, 3
• Physical examination reveals a small surface opening with a tract that can be probed to significant depth, often reaching bone or prosthetic material 1
• In vascular graft infections, sinus tracts present with painful erythematous swelling, with or without active drainage, and are highly suggestive of underlying graft infection 1
• The tract may be straight and short (84% in anterior mandibular locations) or long and curved (75% in posterior locations), depending on anatomic location 3

Diagnostic Significance in Chronic Conditions

In Diabetic Patients and Osteomyelitis

• Sinus tracts in diabetic foot wounds strongly indicate underlying osteomyelitis, with studies showing 96% specificity and 90% predictive value when cultures from sinus tracts are compared to bone specimens 1
• The "probe-to-bone" test through a sinus tract is highly specific for diagnosing diabetic foot osteomyelitis 1, 4
• Cultures from sinus tracts have variable concordance with bone cultures (ranging from 30-90% depending on the organism), with highest accuracy when Staphylococcus aureus is isolated 1

In Prosthetic Joint Infections

• A draining sinus tract overlying a prosthetic joint is pathognomonic of prosthetic joint infection (PJI), requiring urgent surgical intervention 1
• Sinus tracts in PJI typically develop months after surgery and indicate treatment failure when they appear after initial wound healing 1

Critical Clinical Pitfalls

• Do NOT culture superficial swabs from sinus tracts, as they are often misleading and contaminated with skin flora, promoting unnecessarily broad antimicrobial treatment 1, 4
• Deep tissue specimens must be obtained from the tract base or underlying infected tissue via curettage or biopsy for accurate microbiologic diagnosis 1, 4
• Sinus tracts require treatment of the underlying pathology (infected bone, foreign body, or prosthesis)—antibiotics alone cannot cure the infection without addressing the source 1, 5
• The small surface opening belies extensive deep tissue involvement, making visual assessment inadequate without imaging (MRI, CT) to define the tract's full extent 1, 2, 6

Anatomic Characteristics

• Sinus tracts have a small surface defect but large, deep basement that extends to the infection source 2
• Imaging (MRI preferred) can demonstrate the tract pathway, identify abscesses, detect bone involvement, and reveal communication with deeper structures 1, 6
• In 55% of head and neck cases, sinus tracts originate from dental pathology; 20% from infected implants or bone grafts; and 11% from chronic osteomyelitis 3