Surgical site infection (SSI) is one of the most common and devastating complications of orthopaedic surgical procedures. The Centers for Disease Control and Prevention (CDC) estimates that 22% of all healthcare-associated infections are SSIs. More than 290,000 SSIs occur annually in the United States, resulting in $1 billion to $10 billion in direct and indirect medical costs. In 2002, there were more than 43 million procedures in the United States, of which more than 600,000 included open reduction and internal fixation.
Although advances in infection prevention have occurred over recent years, SSIs remain a substantial cause of morbidity and mortality. Patients with SSIs are 60% more likely to spend time in an intensive care unit, twice as likely to die, and five times more likely to be readmitted compared with patients without an SSI. In surgical patients with an SSI who died, 89% of the deaths were attributable to the infection. These statistics translate not only into significant losses for the individual patient but also a dramatic burden on societal healthcare costs as a whole.
The pathogens involved in SSIs did not change much between 1986 and 1996. Staphylococcus species, including Staphylococcus aureus, are the leading nosocomial pathogens in hospitals worldwide. Coagulase-negative staphylococci, Enterococcus species, and Escherichia coli are also commonly isolated pathogens. Gram-negative organisms are reported to account for approximately 30% of SSIs in cardiac surgery and total joint arthroplasty. More recently there has also been an increase in infections related to antimicrobial-resistant pathogens such as methicillin-resistant S. aureus (MRSA) and vancomycin-resistant enterococci, both of which colonize the skin and are spread by direct contact. In the United States, it has been estimated that 94,360 invasive MRSA infections occurred in 2005 and that 86% of these were healthcare associated. The death rate from MRSA is 2.5 times greater than from nonresistant S. aureus, and more than 18,000 MRSA deaths were documented in 2005.
In the United States, prevention and treatment of these infections has become a national priority. The Healthcare Infection Control Practices Advisory Committee (HICPAC) is a federal advisory committee that consists of 14 external infection control experts. The HICPAC works together with the CDC and the Secretary of the Department of Health and Human Services to formulate best practices for health care–associated infection prevention, control, and surveillance. The CDC’s National Nosocomial Infections Surveillance System (NNIS), established in 1970, monitors nosocomial infection trends.
In an effort to make evidence-based recommendations on infection prevention, the CDC published the “Guideline for Prevention of Surgical Site Infection, 1999.” In 2002, the CDC collaborated with the Centers for Medicare and Medicaid Services (CMS) to implement the Surgical Site Infection Project. The goal of the project was to decrease mortality and morbidity associated with SSIs by promoting appropriate prophylactic antibiotic choice and timing. Effective July 1, 2006, The Joint Commission expanded the Surgical Site Infection Project to the Surgical Care Improvement Project (SCIP). SCIP is a partnership of many organizations dedicated to improving surgical care. The American Academy of Orthopaedic Surgeons (AAOS) is one of more than 30 organizations represented. The goal of SCIP was to reduce the incidence of surgical complications nationally by 25% by the year 2010. Some of the SCIP target areas pertinent to orthopaedic surgery are shown in Table 22-1 .
| Infection |
|---|
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| Venous Thromboembolism |
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| Global |
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Defining Surgical Site Infections
The National Nosocomial Infections Surveillance System (NNIS) has provided standardized surveillance criteria for defining SSIs ( Fig. 22-1 and Table 22-2 ). These definitions, applied consistently by surveillance personnel, have become a national standard. SSIs are classified as superficial if they involve only the skin and subcutaneous tissue and deep if the infection is within the fascia or muscle. Organ/space SSIs involve any part of the anatomy other than incised body wall layers that were manipulated during surgery. Septic arthritis, septic bursitis, diskitis, epidural abscess, and osteomyelitis are considered organ/space SSIs. Infection occurs within 30 days after the procedure if no implant is left in place or within 1 year if an implant is in place and the infection appears to be related to the operation.
| Superficial Incisional SSI |
|---|
| Infection occurs within 30 days after the operation and infection involves only skin or subcutaneous tissue of the incision and at least one of the following: |
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| Do not report the following conditions as SSI: |
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| Note : Specific criteria are used for identifying infected episiotomy and circumcision sites and burn wounds. |
| Deep Incisional SSI |
| Infection occurs within 30 days after the operation if no implant * is left in place or within 1 year if the implant is in place and the infection appears to be related to the operation and infection involves deep soft tissues (e.g., fascial and muscle layers) of the incision and at least one of the following: |
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| Notes |
|
| Organ/Space SSI |
| Infection occurs within 30 days after the operation if no implant * is left in place or within 1 year if the implant is in place and the infection appears to be related to the operation and infection involves any part of the anatomy (e.g., organs or spaces) other than the incision, which was opened or manipulated during an operation and at least one of the following: |
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* National Nosocomial Infection Surveillance definition: a nonhuman-derived implantable foreign body (e.g., prosthetic heart valve, nonhuman vascular graft, mechanical heart, or hip prosthesis) that is permanently placed in a patient during surgery.
† If the area around a stab wound becomes infected, it is not an SSI. It is considered a skin or soft tissue infection, depending on its depth.
It is important to note that other organizations have also formulated evidence-based definitions of orthopaedic infections. The AAOS and the Musculoskeletal Infection Society have specific recommendations and definitions for diagnosing periprosthetic joint infections (PJIs) ( Table 22-3 ). Although these definitions are not currently used by government agencies, it is anticipated that they will be used in the future during data collection for the American Joint Replacement Registry (AJRR).
Based on the proposed criteria, definite Periprosthetic Joint Infection exists when:
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* A periprosthetic joint infection may be present if fewer than four of these criteria are met.
Preoperative Interventions
Infection control is best integrated into a clinical practice using an outside-to-inside methodology. The AAOS Patient Safety Committee has identified a variety of modifiable risk factors for SSI ( Fig. 22-2 ). Certainly, not all of these risk factors can be applied to the acute trauma setting. Many orthopaedic patients, however, are unhealthy hosts, and optimizing these patients as best possible before surgery may be the most important and tangible aspect of SSI prevention. Although direct scientific evidence showing that risk factor modification will lead to a lower SSI rate is lacking in some instances, extrapolating data from other fields such as cardiac surgery has been helpful in raising awareness among orthopaedists and mobilizing future orthopaedic research on this topic.
Smoking is a well-known risk factor for multiple surgical complications, including infection. A recent large prospective report has confirmed the significant association between smoking and organ/space SSI in orthopaedic surgery with implants. Tobacco products cause microvascular vasoconstriction via the effects of nicotine on the sympathetic nervous system. Tissue hypoxia is caused by carbon monoxide binding to hemoglobin and creating carboxyhemoglobin. Smoking intervention programs, even when instituted as briefly as 4 weeks before surgery, can diminish the risk of complications. A patient in an external fixator who is awaiting definitive fixation of a pilon fracture, for example, would be an ideal patient to enroll in a smoking cessation program.
Obesity, defined as a body mass index of 30 kg/m 2 or greater, is a known risk factor for orthopaedic postoperative infections. The pathogenesis by which many obese patients go on to have a postoperative infection is multifactorial. The diet many of these patients follow is devoid of essential nutrients. Surgical time is often longer for these patients, and hematoma or seroma formation leading to prolonged drainage is more common. The subcutaneous layer in these patients is often poorly vascularized, and they require a significantly greater fraction of inspired oxygen (FiO 2 ) to reach an arterial oxygen tension of 150 mm Hg. Meticulous treatment of soft tissues and expedited surgeries by experienced surgeons should be considered whenever possible. Obese patients should have properly dosed prophylactic antibiotics and nutritional counseling perioperatively. Last, these patients need to be counseled never to try to lose weight while healing their surgical wounds because this may lead to a catabolic state.
Patients with rheumatoid arthritis have an increased risk of infection after orthopaedic procedures such as joint replacement. Many of these patients are treated with complex drug regimens that have an effect on wound healing. Antiinflammatory medications should be held perioperatively both because of wound healing complications that can lead to infection as well as their potential effects on wound healing. Although corticosteroids have been shown to increase infection rates and affect wound healing, these medications should be continued. Although the use of steroid stress doses remains controversial, they should probably not be routinely administered. Rather, each patient should be dealt with individually, keeping in mind the chronicity and dose of steroid usage, anticipated stress level of the surgery, and the presence of other risk factors for infection. Methotrexate should not be discontinued perioperatively except in patients with renal insufficiency, poorly controlled diabetes, lung or liver disease, or a history of alcohol abuse. One study has described serious postoperative orthopaedic infections in patients taking tumor necrosis factor (TNF). Another study, however, did not show an increased risk of infection in patients undergoing foot and ankle surgery while taking TNF inhibition therapy. Perioperative consultation with a rheumatologist who has experience with these medications is recommended.
The number of patients infected with human immunodeficiency virus (HIV) who are undergoing orthopaedic procedures is on the rise. Some studies, many in arthroplasty patients, done on these patients have shown a higher SSI risk, and others have not. A recent study of orthopaedic trauma patients who were HIV positive revealed that CD4 counts less than 300 cells/μL were associated with development of postoperative infection at a higher risk than those without HIV. Routine screening of orthopaedic patients for immunodeficiencies has not been shown to be cost effective and should be reserved for patients with other risk factors. One study suggested that to diminish the risk of SSI in this patient population, we should administer prolonged prophylactic antibiotic therapy and antiretroviral therapy. Eliminating or modifying other risk factors (injection drug use, smoking, serum glucose level, and prolonged wound drainage) and optimizing psychosocial issues are of utmost importance in these patients.
S. aureus continues to be one of the most common organisms in orthopaedic SSI. Nasal carriers of S. aureus are two to nine time more likely to acquire SSIs than noncarriers. One study has shown that 80% to 85% of the time, S. aureus wound isolates in patients with SSIs match those from the nares. One early study suggested that prophylactic treatment with mupirocin in orthopaedic surgery can reduce the infection rate. Rao and colleagues suggested that chlorhexidine baths for 5 days before surgery with mupirocin ointment to the nares twice daily in positive S. aureus nasal carriers will reduce SSIs in joint replacement surgery. Reductions in postoperative rates of SSIs can be achieved with prescreening programs for S. aureus carrier status in patients undergoing elective orthopaedic surgery. Two recent systematic reviews confirmed the value of screening and decolonization. As new technologies evolve, questions remain about the best screening method (traditional cultures vs. rapid polymerase chain reaction) and the most appropriate decolonization medication (antibiotics vs. antiseptics). Whenever possible, at the very least, patients at risk for S. aureus colonization should be screened and decolonized. S. aureus screening and decolonization protocols must be repeated before any readmission, regardless of prior colonization status. Risk factors include previous MRSA infection; being a healthcare worker, nursing home patient, or prisoner; and being in contact with a patient who has MRSA colonization. Patients found to be carriers of MRSA, in addition to either mupirocin or povidone–iodine nasal decolonization, should be considered candidates for vancomycin prophylactic antibiotics in place of (or possibly in addition to) a cephalosporin, although strict guidelines cannot currently be established. Hospitals with antibiograms showing a high percentage of resistant bacteria should also consider altering their prophylactic prophylaxis regimen appropriately.
Diabetes and hyperglycemia have been known risk factors for orthopaedic SSI for some time. Although the pathologic effects of diabetes on surgical hosts are clearly detrimental, the acute effects of perioperative hyperglycemia are both more detrimental and more readily addressed. In fact, a recent registry study examining the effects of diabetes (as coded in the registry) on total knee replacements did not show a higher risk of revision arthroplasty or deep infection. Hyperglycemia is probably more important and more prevalent than the diagnosis of diabetes itself. It has been defined in many studies as blood glucose levels above 200 mg/dL. In the trauma setting, elevated blood glucose level occurs in up to 50% of patients in the intensive care ward, and the etiology of this stress-induced hyperglycemia is multifactorial.
The pathogenesis of hyperglycemia leading to infection has been well described. Chemotaxis, phagocytosis, and oxidative bacterial killing are all diminished by high serum glucose levels. Hyperglycemia leading to glycosylation of complement proteins and immunoglobulin results in overall host immunosuppression. Multiple studies have shown the advantage of tight glycemic control in critically ill patients. Cardiac surgery studies have confirmed that sternal wound infections are more likely to occur in hyperglycemic patients. In these patients, implementation of continuous insulin infusion protocols reduce the rates of deep sternal wound infections. Several recent studies in orthopaedic spine, joint replacement surgery, and ankle fracture surgery support the role of perioperative glycemic control in patients undergoing orthopaedic surgery. Even though studies supporting interventions at multiple points of care are still needed, perioperative tight glucose control is clearly critical in orthopaedic patients.
Malnutrition is a known risk factor as well after orthopaedic procedures. Screening should be done in patients at risk of malnutrition, such as elderly adults and those with gastrointestinal diseases, renal failure, alcoholism, cancer, or any chronic disease. Total lymphocyte count of less than 1500/mm 3 (1.5 × 10 9 /L), serum albumin level less than 3.5 g/dL, or transferrin level of less than 226 mg/dL should prompt caretakers to initiate consultations with an endocrine or nutritional expert.
Postoperative anemia treated with allogeneic blood transfusion is a risk factor for SSI in patients undergoing arthroplasty procedures. It is likely that many patients receive unnecessary transfusions. A recent study enrolled 2016 patients who were 50 years of age or older who had either a history of or risk factors for cardiovascular disease and whose hemoglobin levels were below 10 g/dL after hip fracture surgery. The investigators randomly assigned patients to a liberal transfusion strategy (a hemoglobin threshold of 10 g/dL) or a restrictive transfusion strategy (symptoms of anemia or at physician discretion for a hemoglobin level of <8 g/dL). A liberal transfusion strategy, as compared with a restrictive strategy, did not reduce rates of death or inability to walk independently on 60-day follow-up or reduce in-hospital morbidity. Postoperative risk of transfusion can be diminished with perioperative interventions. Epoetin alfa directly increases preoperative red blood cell mass, hemoglobin concentration, and hematocrit levels. It has been shown to be useful for lowering transfusion requirements in total joint replacement procedures but not in pediatric neuromuscular scoliosis patients. A recent pooled observational analysis of very-short-term perioperative administration of intravenous (IV) iron in patients undergoing major orthopaedic surgery has renewed interest in this important modality. Tranexamic acid, an antifibrinolytic included on the World Health Organization’s list of essential medicines, has been shown to be a useful adjuvant in the prevention of postoperative allogeneic blood transfusions in spinal and joint replacement surgeries.
Poor oral health, urinary tract infections, and local or remote orthopaedic infections have also been identified by the AAOS as being modifiable risk factors for SSI. Whenever possible, decayed teeth, untreated dental abscesses, advanced gingivitis, and periodontitis should be taken care of before surgical intervention; this practice is commonly advocated in cardiac surgery. Urinary tract infections and a subsequent delay in surgical intervention should be handled based on the type of symptoms (obstructive vs. irritative) and bacterial colony count. Although it is not the topic of this chapter to discuss the diagnosis of infection for all types of orthopaedic procedures, one should consider at the very least obtaining a C-reactive protein level and an erythrocyte sedimentation rate in all patients undergoing conversion of previous surgery to total joint replacement and in all patients undergoing nonunion surgery.
It may not always be possible to optimize patients completely in the trauma setting. There is almost always something that can be addressed, however, to improve the surgical host and diminish the risk of SSI.
Prophylactic Antibiotics
All surgical wounds are at risk of bacterial contamination. Normal skin transmits aerobic gram-positive cocci, and body orifices contaminate wounds with enteric bacteria.
Prophylactic antibiotics do not sterilize the wound; rather, their administration allows the host to fight off inevitable bacterial contamination more effectively. The ideal antibiotic should be active against the most common pathogens in wounds, have minimal side effects, achieve adequate concentrations in the tissue during the entire time that the wound is open, and carry the smallest impact possible on the patient’s normal bacterial flora. Poor antibiotic selection and timing will lead to ineffective prophylaxis.
Studies on the topic of antibiotic prophylaxis are mostly seen in the field of joint replacement surgery and closed fracture fixation. The Dutch Trauma Trial, a prospective, randomized, double-blind, placebo-controlled study, looked at 2195 closed fractures. Patients received either preoperative ceftriaxone or placebo. The infection rate was 3.6% in the antibiotic group and 8.3% in the placebo group. A more recent meta-analysis supports these findings. In lower extremity arthroplasty cases and in closed fracture procedures, administration of prophylactic antibiotics is the standard of care in the majority of cases. Routine use of prophylactic antibiotics in spine surgery has also been supported by multiple studies.
Fields such as foot and ankle surgery and nontraumatic upper extremity surgery tend not to advocate routine use of prophylactic antibiotics, although studies are limited. It has been the author’s observation that most surgeons appear to give prophylactic antibiotics for ankle and hand arthroplasty procedures as well as for extensive reconstructive procedures in any field.
Timing of Administration
Burke, building on work of Lister, investigated the effects of parenteral antibiotics on surgical incisions contaminated with S. aureus . This seminal study discovered the importance of adequate tissue levels of antibiotics before incision. Several years later, Stone and colleagues critically evaluated 400 non-orthopaedic patients and clearly showed a reduction of infection rates with preoperative antibiotics. The lowest rate of SSI has been observed with antibiotics given briefly before incision. Classen and colleagues prospectively studied the timing of antibiotic prophylaxis in 2847 patients and found that those receiving antibiotics during the 2 hours before the incision had the lowest risk of wound infection. Cephalosporin and clindamycin infusions should begin within 60 minutes of incision and be completed just before the incision. Vancomycin infusion should begin 1 to 2 hours before the incision because fast administration may result in “red man” syndrome, a condition characterized by hypotension and a rash. Last, tourniquet usage affects tissue concentrations of antibiotics. Johnson studied cefuroxime concentration in bone and subcutaneous fat during knee arthroplasty. Patients were randomized to receive the antibiotics 5, 10, 15, and 20 minutes before tourniquet inflation. Bone concentrations were above the minimum inhibitory concentration (MIC) for S. aureus in all groups. Subcutaneous fat levels were lower than MIC for S. aureus in 86% of patients who received antibiotics at 5 minutes before tourniquet inflation. The authors concluded that at least 10 minutes is needed between administration of antibiotics and tourniquet inflation to achieve adequate tissue levels of cefuroxime. Two other studies support these findings ; investigations in the foot and ankle literature suggest that administration of antibiotics after tourniquet inflation may not be detrimental.
Even though there is enough evidence showing that preoperative antibiotics should be administered before incision, reports show that this still does not happen routinely. Although educating team members, instituting organized perioperative checklists, and providing feedback to surgeons has raised compliance in some countries, more work remains to be done.
Antimicrobial Choices
Cephalosporins are the most commonly used antibiotics in orthopaedic surgery. First-generation cephalosporins provide excellent bactericidal activity against aerobic gram-positive cocci that usually contaminate these wounds. Second- and third-generation cephalosporins have a broader spectrum but are not as effective against gram-positive bacteria. Cunha and colleagues investigated several antibiotics during total hip replacement and showed that 25 to 40 minutes after injection of cefazolin, a first-generation cephalosporin, the peak bone level was 60 times the MIC of penicillin-resistant staphylococci. The half-lives of cephalosporins are sufficiently long enough that adequate tissue levels remain throughout most orthopaedic procedures. The cost of these agents is relatively low as is the risk of adverse effects. As such, they continue to be widely used and recommended for prophylaxis in orthopaedic surgery. Although patients sometimes have concerns about allergic reactions, it is important to delineate whether these are true allergic reactions or not. The incidence of adverse reactions to cephalosporins in patients with reported penicillin allergy is rare. If skin testing or history points to a true allergy (e.g., hypotension, bronchospasm, pruritus, urticaria), then other agents, such as vancomycin, should be considered. Penicillin allergy testing can decrease prophylactic vancomycin use in patients treated with elective orthopaedic surgery.
Clindamycin and vancomycin are alternative agents that can be used as prophylaxis when cephalosporins are contraindicated. Compared with cephalosporins, bone penetration of vancomycin appears to be inferior, but that of clindamycin is comparable. Clindamycin and vancomycin both exceed the MIC of gram-positive organisms that cause orthopaedic infections. However, increased use of vancomycin leads to increased resistance and emergence of vancomycin-resistant enterococcus infections. Vancomycin should be reserved for patients with known MRSA colonization, those in facilities with recent MRSA outbreaks, and those with known risk factors for MRSA. Risk factors for community- and hospital-acquired MRSA include athletes in contact sports, children at day care centers, homeless patients, IV drug users, men who have sex with men, military personnel, prison inmates, antibiotic use within the preceding year, crowded living conditions, chronic wounds, those who have been recently hospitalized or dialyzed, and those with indwelling catheters or percutaneous medical devices. A cardiac surgery study showed that the choice of antimicrobial used (cefazolin vs. vancomycin) changed the infecting organism and not the rate of SSI. To date, there is insufficient evidence that changing the antibiotic prophylaxis from cephalosporins to vancomycin in institutions with perceived high rates of MRSA will result in fewer SSIs.
Dosing
Because of the historic “one size fits all” strategy, many patients are routinely underdosed with prophylactic antibiotics. Many patients are obese, and this group in particular is at risk for antibiotic treatment failure. Appropriate dosing is most likely one of the contributing factors. Clinicians need to consider the relative risks of overdosing and underdosing. Obesity causes a number of changes, including an increase in volume of distribution and changes in hepatic metabolism and renal excretion. Cefazolin should be dosed at 1 g for patients weighing less than 80 kg and 2 g for patients over that limit. Clindamycin and vancomycin dosing is based on the patient’s body mass, as is pediatric dosing. Consultation with infectious disease and pharmacy experts at the surgeon’s institution is advised. Redosing of antibiotics can lead to suboptimal tissue levels and should be done whenever the procedure exceeds one to two times the half-life of the antibiotic or if there is significant blood loss.
Duration
For a while there has been a trend to administer prophylactic antibiotics for longer periods than necessary. In the recent past, for example, patients undergoing arthroplasty procedures would be given antibiotics until either the drains were removed or the wounds were dry. This has been shown to be unnecessary. In nonorthopaedic procedures, joint replacement surgery, and hip fracture surgery, prolonged prophylaxis has not been shown to be important in reducing SSI rates. Although we do not know the shortest course of antibiotics for prevention of SSI, we do know that prolonged antibiotic usage leads to increased microbial resistance. The current recommendation by the AAOS and SCIP is to discontinue antimicrobial agents within 24 hours postoperatively after elective primary joint replacement.
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