Causes / typical injury mechanism: Total knee arthroplasty (TKA) is a common orthopedic procedure. Wound complications may arise following surgery that can range from mild erythema to wound drainage and severe tissue necrosis. Proper identification of the severity of a postoperative wound complication is important to guide treatment decisions and further specialist consultation.

Classic history and presentation: Patients may present with erythema and swelling around the surgical incision with or without serous or purulent drainage. Patients may have knee effusion due to postoperative hematomas. Skin necrosis is rare but may appear as skin sloughing or eschar in the area of the incision. Visible subcutaneous tissue or knee capsule may be seen in surgical site dehiscence, which may occur after a fall or excessive flexion postoperatively.

Patients may or may not have systemic symptoms such as fever, chills, or nausea. If systemic symptoms are present, expedited assessment is warranted due to the risk of sepsis from a postoperative deep joint infection.

Prevalence: Overall incidence of surgical site problems following a TKA is relatively low, around 0.33%-3%. The risk is greater following revision TKA.

Risk factors: Several risk factors for postoperative TKA wound complications have been described.

• Diabetes mellitus (elevated hemoglobin A1c)
• Vascular disease
• Inflammatory arthritis
• Immunosuppressive therapy
• Poor nutritional status (albumin < 3.5 g/dL, total lymphocyte count < 1500/uL, vitamin D insufficiency)
• Anemia
• Smoking history
• Obesity (body mass index [BMI] > 40 kg/m²)

Patients requiring therapeutic anticoagulation postoperatively are at a greater risk for hematoma and possible subsequent periprosthetic joint infection.

Patients undergoing revision TKA with multiple previous surgeries and preexisting scars or hypotrophic skin are at increased risk for delayed wound healing, postoperative drainage, and tissue necrosis due to compromised vascular supply to the superficial skin.

Pathophysiology: The pathophysiology of wound complications following TKA is complex. Diabetes mellitus and vascular disease may lead to decreased local blood flow, impeding wound healing. Rheumatologic diseases with immunocompromised states may result in a decrease in the patients' inflammatory healing response. Patients with poor nutritional status may not have the capacity to heal a wound without nutrition supplementation.

Falls, excessive knee flexion, or aggressive postoperative physical therapy may lead to rupture of the superficial and/or subcutaneous sutures, causing mechanical wound dehiscence. Although rare, a full thickness wound dehiscence may include the joint capsule exposing the TKA prosthesis.

Therapeutic anticoagulation may cause a joint hematoma, which may present an ideal environment for bacterial proliferation and subsequent periprosthetic joint infection.

Grade / classification system: Laing Classification of Wound Complications (not widely agreed upon but listed for completeness)

1. Simple erythema, no superficial necrosis.
2. Skin necrosis and wound breakdown, no sinus into the joint.
3. Extensive necrosis with a wound sinus into the joint.
4. Deep wound dehiscence with a sinus, little or no prosthetic exposure.
5. Deep wound dehiscence with overt prosthetic exposure.