Pretest

Introduction

Wound healing is critical for the success of any total knee arthroplasty (TKA). Delays in wound healing risk infection and failure. Wound problems are minimized by selecting the proper skin incision, understanding vascular anatomy and patient risk factors, and prompt management should wound complications arise.

Vascular Anatomy

Blood supply to the anterior skin of the knee arises predominantly from the terminal branches of the peripatellar anastomotic arterial ring (Slide 1). In contrast to the skin circulation of the proximal thigh, there is no underlying muscle or intermuscular septae directly anterior to the knee to provide a direct pathway for arterial perforators.^1-3 Skin circulation in this region is dependent on the dermal plexus that originates from arterioles traveling within the subcutaneous fascia. Anterior skin flap elevation about the knee therefore requires dissection deep to the subcutaneous fascia to preserve arteriolar perforators between the subcutaneous fascia and dermal plexus.^1-3

Slide 1

Skin Incision

Vascular anatomy suggests a midline skin incision is less disruptive to the arterial network. Transcutaneous oxygen measurements have demonstrated reduced oxygenation of the lateral skin region.⁴ Medial peripatellar incisions are less desirable as they create a laterally-based skin flap with reduced oxygenation and higher wound complication rates.

Previous skin incisions should be used whenever possible. If long parallel skin incisions exist, a lateral-most skin incision is favored to avoid a laterally-based skin flap, which has been previously compromised at the time of the initial lateral skin incision. In complex situations, such as knees with multiple skin incisions or previously burned or irradiated skin, plastic surgical consultation is wise for the design of the upcoming skin incision or consideration of preoperative muscle flap procedures if the risk of skin necrosis is substantial. Preoperative soft-tissue expansion techniques have also been successfully used to reduce wound complications in high-risk patients.⁵

Technical Factors

The skin incision for TKA should be long enough to avoid excessive tension on the wound edges, especially when the knee is placed in maximum flexion. Gentle retraction is necessary to avoid disruption of perforating arterioles originating in the subcutaneous fascia. Numerous studies have demonstrated that lateral retinacular release reduces lateral skin oxygenation and increases the incidence of wound complications.⁴ If a release of the lateral retinaculum is required, attempts should be made to preserve the lateral superior genicular artery to preserve lateral skin oxygenation. Meticulous hemostasis is required to avoid postoperative hematomas. Wound closure without tension is imperative to minimize skin necrosis.

Patient Risk Factors

Numerous risk factors have been identified in association with an increased incidence of wound complications. Corticosteroid use has been shown to decrease fibroblast proliferation and reduce collagenase clearance from the healing wound,^1,3 decreasing wound tensile strength. The association of higher wound problems in those with rheumatoid arthritis is well documented, although direct evidence demonstrating the scientific etiology of this association is lacking and may be related to the increased incidence of long-term corticosteroid use in many of those with rheumatoid arthritis.^1-3

Extreme obesity can create exposure difficulties, necessitating more vigorous retraction of skin flaps and the subsequent risk of soft-tissue devascularization. Malnutrition (albumin less than 3.5 g/dL, total lymphocyte count less than 1500 cells/mm³) has been associated with delayed wound healing.⁶ Cigarette smoking results in systemic vasoconstriction, reducing skin circulation.⁷ Delayed collagen synthesis resulting in decreased wound tensile strength and reduced early capillary ingrowth have been observed in those with diabetes mellitus.^1,3

Use of high-dose nonsteroidal anti-inflammatory drugs inhibits the acute inflammatory response, an important process in the early phase of wound healing and may enhance wound healing difficulties.^1,3 Hypovolemia can delay wound healing due to reduced oxygen delivery to the healing soft tissues.³ Similarly, early use of continuous passive motion beyond 40° decreases skin oxygen levels.^3,8 Additional risk factors include damaged skin from burns or irradiation and chemotherapy administration.

Wound Complication Management

Wound complications require immediate attention as delay in treatment risks deep infection. Prolonged serous drainage, unassociated with erythema or purulence, can be transiently managed with local wound care and immobilization. If drainage persists beyond 5 to 7 days, spontaneous cessation of drainage is unlikely and surgical debridement is indicated. Subcutaneous or intra-articular hematomas are commonly observed in cases of prolonged drainage. Hematomas threaten the wound by increasing soft-tissue tension, releasing toxic breakdown products of hemoglobin, and serve as a healthy medium for bacterial growth.^1,3

Necrotic skin generally requires surgical debridement. Small areas (less than 3 cm) of superficial necrosis may heal with local wound care or delayed closure. Larger areas of superficial necrosis usually require soft-tissue coverage procedures such as split-thickness skin grafting or fasciocutaneous flaps.

Full-thickness necrosis usually is associated with exposed prosthetic components and requires immediate, aggressive debridement. Secondary closure procedures often fail and soft-tissue transfer, such as cutaneous, fasciocutaneous, or myocutaneous flaps usually is required.⁹ The medial gastrocnemius muscle often is the preferred type of flap reconstruction (Slide 2). It is both larger and 2cm to 3 cm longer than the lateral gastrocnemius muscle. It does not have to traverse the fibula, and therefore, has a larger arc of rotation. This flap provides excellent soft-tissue coverage over the patella and tibial tubercle where the incidence of skin necrosis is highest.¹⁰ Free myocutaneous flaps are reserved for cases that cannot be managed with a gastrocnemius or other local flap reconstruction.

Slide 2

Antibiotics often are required in cases with persistent drainage and wound necrosis but should not be used indiscriminately. Unnecessary antibiotic use risks alteration of bacterial flora and sensitivities, should deep infection occur. Joint aspiration for culture is suggested before antibiotic therapy to maximize culture results. Cultures of superficial drainage often are spurious and have little correlation with deep infecting organisms.

Conclusion

Wound complications after TKA are best avoided by choosing the proper skin incision, gentle handling of the soft tissues, meticulous hemostasis, and closure without excessive tension. Persistent drainage or necrosis requires aggressive, early debridement to reduce the incidence of deep infection.

References

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3. Dennis DA. Wound complications in total knee arthroplasty. Instr Course Lect. 1997; 46:165-169.



4. Johnson DP. Midline or parapatellar incision for knee arthroplasty. A comparative study of wound viability. J Bone Joint Surg Br. 1988; 70:656-658.



5. Gold DA, Scott SC, Scott WN. Soft tissue expansion prior to arthroplasty in the multiply-operated knee. A new method of preventing catastrophic skin problems. J Arthroplasty. 1996; 11:512-521.



6. Dickhaut SC, DeLee JC, Page CP. Nutritional status: importance of predicting wound healing after amputation. J Bone Joint Surg Am. 1984; 66:71-75.



7. Mosely LH, Finseth F, Goody M. Nicotine and its effects on wound healing. Plast Reconstr Surg. 1978; 61:570-575.



8. Johnson DP. The effect of continuous passive motion on wound-healing and joint mobility after knee arthroplasty. J Bone Joint Surg Am. 1990; 72:421-426.



9. Bengston S, Carlsson A, Relander M, Knutson K, Lidgren L. Treatment of exposed knee prosthesis. Acta Orthop Scand. 1987; 58:662-665



10. Gerwin M, Rothaus KO, Windsor RE, Brause BD, Insall JN. Gastrocnemius muscle flap coverage of exposed or infected knee prostheses. Clin Orthop. 1993; 286:64-70.