Ignoring the implications of wound problems often leads to denial and inaction when surgery is warranted. John Insall stated, “We … condemn procrastination and the prolonged use of oral antibiotics, when infection is only suspected and not confirmed by bacteriological evidence.”7 We should be emboldened by Kant's exhortation during the Enlightenment: “sapere aude” (have the courage to know). Is this knee infected, and does the drainage originate inside the joint? Yes to either question must be followed by surgery-sooner rather than later.
Wound problems may result in calamitous failure of the total knee arthroplasty (TKA)1 or even amputation. Many failures can be prevented. Some wound problems indicate impending sepsis, but others are already septic. All wound problems require immediate attention, and aspiration of the joint before initiating antibiotic therapy will usually indicate if the joint is infected. Treatment depends on whether there is deep sepsis.
The current literature is divided on issues pertaining to wound complications following TKA. These issues include: (1) prevention of wound complications in the previously operated knee; (2) optimal timing of intervention; and (3) mode of treatment (local wound débridement versus open or arthroscopic arthrotomy, soft tissue reconstruction or resection arthroplasty).
Through a selected literature review we attempt to resolve these ambiguities to provide the arthroplasty surgeon with objective guidelines for a systematic approach in dealing with these complications.
Risk Factors for Wound Complications
Previous incisions pose a substantial risk to wound healing in TKA. However, this risk may be mitigated by planning incisions carefully. For example, osteotomies or open reduction and internal fixation (ORIF) of periarticular fractures should be performed with consideration for an eventual TKA. Transverse incisions can later be crossed with impunity, and well-placed longitudinal incisions can be reused. However, extended lateral incisions, lateral arthrotomies, and the lateral hockey stick incision often used in the treatment of tibial plateau fractures may lead to wound complications.
Transcutaneous oxygen tension measurements of the skin after incisions about the knee demonstrate compromised oxygenation to the lateral skin flap.8 Although the skin depends heavily on the terminal branches of the anterior anastomosis, there is a better blood supply originating medially.3 Accordingly, medial incisions result in a larger lateral area with potentially compromised circulation.21 If a lateral incision is followed with a more medially based approach, the area isolated by the two will be in jeopardy of necrosis. A more midline approach to the knee is generally preferred, as it can safely be reentered for TKA.21 If there is a preexisting lateral incision, vascularity will be less likely compromised if the surgeon reopens it and uses a lateral arthrotomy.
Systemic factors affect wound healing: good glycemic control in patients with diabetes,18 adequate nutrition,19 and cessation of smoking.15 Aggressive knee flexion in the early postoperative period and higher tourniquet pressures induce skin hypoxia.9 Less aggressive rehabilitation in the immediate postoperative period and the perioperative administration of systemic oxygen may minimize these problems.
Preventing Wound Complications
Because of the typically long time intervals between patellar surgery or high tibial osteotomy and later TKA, transverse incisions for the earlier surgery typically do not result in later problems with wound complications when using a standard midline knee arthroplasty incision. When lateral incisions are necessary (eg, previous lateral tibial plateau fracture, distal femoral fracture) they should be reused for TKA.10 If there are multiple previous incisions, we recommend choosing the most recently healed or the most lateral incision. Soft tissue reconstruction with expanders12 or a gastrocnemius flap13 are preferred if there are multiple incisions, if the skin and scar tissue are adherent to underlying tissue, or if wound healing appears questionable.
Since the beginnings of TKA in 1971, most surgeons recommend a straight, anterior midline approach for TKAs in patients without previous scars about the knee.6 This replaced the classical medial parapatellar incision that isolates a laterally based flap and increases the risk of anterior skin necrosis. The distal incision can be advantageously placed 1 cm medial to the base of the tubercle as the subcutaneous tissue is scant directly over the tibial tubercle. Approaches over the tubercle risk an arthrotomy that elevates the medial portion of the patellar tendon attachment, increasing the risk of avulsion. Having medialized the distal incision, a slightly oblique angulation proximal to the tubercle (parallel to the quadriceps muscle) decreases the size of the more vulnerable lateral skin edge and facilitates eversion or retraction. Marginal skin necrosis of knee incisions affects the lateral skin edge because of vascular compromise or mechanical stretching.8 We recommend minimizing separation of skin flaps from underlying tissue; those on the medial side (ie, subvastus approach) are safer, and full thickness flaps preserve cutaneous blood supply. Undermining, particularly on the lateral side, should be avoided to prevent skin necrosis.
Diagnosing Wound Complications
Wound problems can be diagnosed as: (1) superficial without intraarticular sepsis; (2) deep with drainage through a defect in the arthrotomy; or (3) deep as the result of an infected arthroplasty. The approach to each is fundamentally different, but all mandate expeditious diagnosis and treatment. The incidence of superficial wound infection in TKA may exceed 10%,4 and these patients may exhibit no differences in erythrocyte sedimentation rate (ESR), Creactive protein (CRP), or peripheral leukocyte (WBC) counts. Superficial wound infection must be differentiated from joint sepsis by aspiration. Deep infection can be ruled out by an aspirate with a WBC count less than 2000 cells/mL and fewer than 50% polymorphonuclear cells.14 This is to be distinguished from sepsis in a native knee, which is characterized by a WBC count of 80,000 and greater than 75% polymorphonuclear cells.22
Treating Wound Complications
Drainage from the incision or from the drain site in the first few days after surgery can be managed with immobilization and sterile dressing changes. A strategy of immobilization and observation should not exceed 3 to 5 days.20 There is no assurance the flow of drainage may not reverse and inoculate the joint. Antibiotic prophylaxis can only be justified by an aspiration with a culture, WBC count, and differential of the synovial fluid to establish there is no intraarticular sepsis. We believe immediate surgery is necessary if there is intraarticular sepsis.
Necrotic skin must be removed. If the aspiration has yielded a negative culture and cell count, then an arthrotomy may not be necessary. Drainage through the arthrotomy means the joint is infected, or will soon be, and an arthrotomy is imperative. If the drainage and possible sepsis are acute (less than 2 weeks), it may be adequate to perform an arthrotomy, synovectomy, and aggressive irrigation with large volumes of antibiotic solution followed by a primary closure and parenteral antibiotic therapy.2 The modular polyethylene liner may be exchanged at this time. We emphasize such treatment must be reserved for wound drainage or skin necrosis in the absence of established or chronic, deep infection. If the problem has been present for more than 2 weeks, we believe it preferable to remove the arthroplasty and enter the patient into a two-stage protocol. Chronic infections must be eradicated before successful wound management can be anticipated.17 A strategy of multiple débridements in patients with intraarticular sepsis within 30 days of surgery (or < 30 days of symptoms) has been proposed.16 The good results reported 48 months later do not detract from the general recommendation to remove the infected component. Arthroscopy to evaluate problematic knee replacements is rarely useful and may result in infection. It has no role in the treatment of wound problems.11
Should drainage persist after débridement (and deep infection has been ruled out by aspiration), a rotational or free muscle flap is necessary.13 Although the opening in the skin may only measure a few millimeters, the medial capsule often gapes open and cannot heal. The medial gastrocnemius flap has become the most utilitarian of the available reconstructive methods.15 A lateral gastrocnemius flap is a good option in patients with lateral soft tissue deficiency. These flaps may be used in conjunction with a skin graft as needed, but it is futile to turn any flap over an active infection. The problem will not resolve and the flap will be lost.
The intent of our review is to highlight wound problems following TKA. Poor wound healing is a potentially devastating complication of TKA. It is globally accepted early intervention is optimal. However, no consensus exists regarding what constitutes “early” and which intervention is appropriate at what stage. As a result of this ambiguity, surgeons manage wound complications in wide variety of ways. Wound complications may jeopardize the underlying arthroplasty resulting in resection or even amputation. Paradoxically, these high stakes often promote a tendency toward “watchful waiting” and a resultant delay in necessary treatment. We emphasize the importance of Kant's “sapere aude”-have the courage to know. Accordingly, we have outlined objective criteria by which to assess and treat wound problems following TKA.
In summary, there are multiple strategies to optimize healing potential perioperatively from local and systemic perspectives. Postoperative wound complications (draining and/or necrosis) must be differentiated from deep infection because the two problems require distinctly different modes of treatment; this can be objectively achieved by performing an aspiration prior to initiating antibiotic treatment. We believe early recognition followed by expeditious débridement and soft tissue reconstruction is the preferred management of wound complications after TKA.
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