Nutritional Status

Malnutrition adversely affects the following humoral and cell-mediated immune functions: neutrophil chemotaxis, bacterial phagocytosis, neutophil bactericidal function, delivery of inflammatory cells to infectious foci, and serum complement components. Nutritional status of a patient can be determined by anthropometric measures (such as muscle mass, triceps skin fold thickness, weight-height ratio, arm muscle circumference), measurement of cell types (lymphocyte count <1500/mm is associated with increased risk for infection ), serum albumin levels (levels <3.5 g/dL have been shown to increase wound complications), and serum transferrin levels (have been shown to be a very sensitive indicator of wound complications ). The additive history of recent weight loss of greater than 10% has also been associated with increased wound complication rate and should be asked by the physician on interviewing the patient.

The nutritional index of Rainey-MacDonald is a useful screening tool for determining the nutritional index of a patient. The formula is (1.2 × serum albumin) + (0.013 × serum transferrin) − 6.43. If the sum is 0 or a negative number, the patient is nutritionally depleted and is thus at a higher risk for sepsis. Jensen et al. determined that 42% of the patients undergoing elective orthopedic surgery were malnourished and that the number of comorbidities that patients possess were positively correlated to the rate of infection and incidence of complications. Length of stay has also been positively correlated to these same higher incidences of infection and complications.

Immunologic Status

Our ability to fight infection is directly correlated to our ability to initiate an inflammatory (cell mediated) and immune (antibody-mediated) response to the invading organism. The mechanisms involved are (1) neutrophil response, (2) humoral immunity, (3) cell-mediated immunity, and (4) the reticuloendothelial system. Any malfunction of the above, from either congenital or acquired causes, would predispose the patient to an infection by specific groups of opportunistic organisms. Abnormal humoral and cell-mediated immune deficiencies can lead to infections by encapsulated bacteria in infants and elderly subjects, pseudomonas infections in heroin addicts, and Salmonella and pneumococcal infections in patients with sickle cell anemia. Neutrophil counts of less than 55/mm are associated with increased risk for infections with Staphylococcus aureus, gram-negative bacilli, Aspergillus, and Candida . Diabetes, alcoholism, malignancy, and chemotherapy are all causes for neutrophil abnormalities that need to be taken into consideration for risks of infection.

Immunoglobulin and complement factors play crucial roles in humoral immunity. Splenectomy or hypogammaglobulinemia predispose to infections by encapsulated bacteria such as Streptococcus pneumoniae, Haemophilus influenzae , and Neisseria. Defects in the complement cascade predispose patients to S. aureus and gram-negative bacillus, while hypogammaglobulinemia also predisposes to infections by rare organisms like Mycoplasma pneumoniae and Ureaplasma urealyticum.

Cell-mediated immune response is a result of interaction between T-lymphocytes and macrophages. Although primary cell–mediated immune deficiencies are rare, secondary cell–mediated immune deficiencies are common. Steroid therapy, malnutrition, lymphoma, systemic lupus erythematosus, immune deficiencies in elderly, and autoimmune deficiency syndromes can all predispose to fungal, mycobacterial, herpes, and Pnemocystis carinii infections.

Anesthetic agents also have an immunosuppressive effect on the patient, and the use of regional anesthesia may have a slightly lower incidence of infection. Transfusion of homologous blood products has been associated with a slightly lower incidence of postoperative infection compared to autologous blood transfusion (less immunologic modulation of the recipient).

Ectopic Sources of Infection

Many of these sources of infection are targeted for discovery during the preoperative workup of the patient. Dental caries, infections of the genitourinary tract infections, pulmonary infections, and skin ulcers are common potential source for seeding of the primary total knee replacement in the postoperative period. Psoriatic plaques adjacent to the operative site, thin atrophic skin, abrasions/folliculitis, venous stasis ulcers, toe web space ulcers, and infected toenails can be associated with a higher rate of infection, and these must be identified and treated appropriately before surgery. Recognition of many of these sources involves a thorough history and physical examination prior to the operative procedure. The surgeon must remember that other primary care physicians may not realize the importance of these listed sources of bacterial seeding, nor may the patient. Therefore, it is the surgeon’s obligation to make sure all of these issues are addressed in the preoperative time period.

Skin Preparation

Although it may not be possible to completely disinfect the skin, significant reduction in the number of pathogens can be achieved before surgery. The skin and hair can be sterilized by application of the most common substances, including alcohol, iodine, hexachlorophene, or chlorhexidine. One must remember that it is not possible to sterilize the hair follicles and sebaceous glands, which normally harbor bacteria. Hair removal or shaving should be done only in the operating room immediately before surgery to minimize bacterial contamination and reproduction, and electronic shaving devices are better than mechanical blades so that the hair follicles and glands are not invaded prior to surgery.

Along the same lines of consideration, skin barriers also help reduce the contamination during surgery. Plastic surgical adhesive drapes reduce wound contamination by preventing lateral migration of the skin bacteria. One should remember that normal recolonization of the skin occurs within 30 minutes. However, a plastic drape impregnated with slow-release iodophor effectively eliminates any skin colonization for up to 3 hours. Application of povidone-iodine solution to the skin margins to reduce the bacterial colony count is a useful method to reduce contamination. Vigorous scrubbing of the operating site should be avoided during preparing the site, as it may be counterproductive by increasing the bacterial counts by releasing harbored bacteria from follicles and sebaceous glands.

Some of the same issues listed above concerning skin preparation of the surgical site are applicable to hand scrubbing by operating room staff and the surgeon. The optimum antiseptic agent and the proper duration for surgical hand scrub are not clear, but applications of Betadine-Povidone, Avagard, alcohol povidone-iodine, alcohol chlorhexidine, foam alcohol, and hexachlorophene foam compound have all provided excellent bactericidal action.

Prophylactic Antibiotics

A number of studies have shown the efficacy of prophylactic antibiotics in reducing infection rates after orthopedic procedures. During the first 24 hours after surgery, the incidence of an infection depends on the number of bacteria present that the host can successfully mount a response that eradicates the bacterial load. In the first 2 hours, the host defense mechanisms decrease the overall number of bacteria. However, during the next 4 hours, the number of bacteria remains fairly constant, with the bacteria that are multiplying and those that are being killed by the host defenses being roughly equal.

It is the first 6 hours after surgery that is called the golden period, after which the bacteria multiply exponentially. Antibiotics decrease bacteria multiplication and thus expand the golden period. A good prophylactic antibiotic is one that is safe, bactericidal, and effective against the most common organisms responsible for infection— S. aureus, S. epidermidis, Escherichia coli, and Proteus. The first-generation cephalosporins are nontoxic, inexpensive, and effective against the most potential pathogens in orthopedic surgery. In patients who are allergic to penicillin, vancomycin may be the alternative antibiotic of choice. A maximal dose of antibiotic should be administered 30 to 60 minutes before the skin incision and at least 10 minutes before inflation of the tourniquet. During the procedure, antibiotics should be re-dosed every 4 hours or whenever the blood loss exceeds 1000 mL. Many studies have shown that 24 hours of antibiotic therapy is just as effective as 48 or 72 hours, and most authorities recommend a single preoperative dose of antibiotics followed by two or three postoperative doses to reduce the possibility of antimicrobial toxicity and to prevent development of resistant organisms and reduce unnecessary costs.

The role of antibiotic irrigation is still not well established in orthopedics. However, several studies have shown a decrease in colony counts in wounds and a decrease in infection rates with the use of antibiotic irrigation in general surgical procedures. Triple antibiotic irrigation (neomycin, polymyxin, and bacitracin) is currently one of the most favored solutions in use.

Local Wound Environment

Careful preoperative assessment and planning are required to minimize the risk of infection in patients with advanced vascular disease, multiple scars from previous surgeries, history of infection, and psoriatic lesions over operative sites. The relatively subcutaneous position of the knee joint makes infection more common compared to the more deep-seated joints. Meticulous closure and good wound care in the postoperative period help in reducing the overall incidence of infection. Prolonged operative time also has an impact on the rate of deep prosthetic infection.

The well-thought-out use of preexisting scars around the knee is essential to reduce the skin complications, and such preexisting scars should be excised, unless it compromises the wound closure. All attempts should be made to use the lateralmost previous incision for surgery in order to optimize the blood supply to the subcutaneous flap. Gentle handling of the tissues, avoiding prolonged use of self-retaining retractors and racks, as well as avoiding the dissection of subcutaneous tissue from underlying fascia all help to prevent devitalization of the subcutaneous tissues. Faulty placement of sutures strangles the tissue and facilitates infection. Meticulous closure of the joint capsule and subcutaneous tissues to avoid dead space and careful homeostasis both help to reduce the incidence of postoperative hematoma formation.

The routine use of drains for total knee replacements is controversial, and many recent studies suggest equivocal results. Good-layered closure with epidermal apposition provides early sealing of the wound and minimizes wound drainage. Watertight closure of the joint capsule prevents deep seeding from a superficial infection or stitch abscess. Chemical composition of the suture is an important determinant of infection in the presence of wound infection and contamination. Monofilament absorbable synthetic suture is associated with a lower rate of infection than braided absorbable synthetic suture. Although the exact effects of specific physical or chemical properties of implants for total joint arthroplasty are not known, studies suggest that specific biomaterials do influence bacterial adhesion to the implant surface. Coagulase-negative staphylococci exhibit preferential adhesion to polymers, while coagulase-positive staphylococci adhere more readily to metals. Bacteria alter their metabolic characteristics and antibiotic susceptibility after adhering to biomaterials, and bacteria adherent to methylmethaacrylate show very high resistance to antibiotics compared with those that are adherent to metals.

Experimental studies and many clinical trials have found no difference in the infection rates between uncemented and cemented implants. Antibiotic-impregnated cement is becoming popular as it has been shown to lower the incidence of infection but has some inherent problems such as weakening of bone cement, promoting emergence of resistant organisms, and possible allergic reaction. The availability of premixed antibiotics such as tobramycin (Simplex Tobramycin; Stryker Orthopaedics, Mahwah, NJ) or gentimicin (Smartset GHV; Depuy, Inc. Warsaw, IN) has led many surgeons to include their use in primary TKA or in patients who have known comorbidities that may increase their chances of infection. Only long-term studies will reveal if this practice will decrease infection rates without increasing the rate of aseptic loosening, however. The Swedish joint registry has now confirmed a decreased incidence of primary TKA infection but has shown a trend to more resistant organisms, which may not be beneficial in the long run.

Clean Air

Airborne bacteria are another source of wound contamination. They are usually gram positive and originate exclusively from the staff in the operating room. Studies have shown that each individual in the operating room sheds 5000 to 55,000 particles per minute. Interestingly, premenopausal females shed significantly fewer bacteria than postmenopausal females and males. A conventional operating room may contain as many as 10 to 15 bacteria per cubic feet and as many as 250,000 particles per cubic feet. A laminar airflow system can reduce this by 80% and the use of a personnel isolator system further reduces the airborne bacterial contamination. Clean air is optimally provided by a combination of laminar flow, vertical airflow systems, use of personal isolator suits, and a room air exchange turnover rate of more than 300 times an hour. Body exhaust suits reduce the bacterial counts in the room air, and vertical laminar airflow system is more effective than horizontal airway systems.

Ultraviolet light has also shown to decrease the incidence of wound contamination by reducing the number of airborne bacteria. This concept although first introduced in 1936 and has not been very popular as there is lack of conclusive evidence about its efficacy and there are concerns regarding personnel exposure in the operating rooms. However, ultraviolet light is very cost effective and a good alternative to laminar airflow systems.

Methods of Reducing Bacterial Contamination and Optimization of Wound Environment

There are several important practices that help in optimizing the wound and the operating room environment, and their application may help in lowering the incidence of infection. Some of these may be obvious, and others have already been alluded to previously in this chapter. Sometimes the initiation of some of these practices is not realized by surgeons as they may be involved with other duties such as dictating while some of these occur. It has been shown that avoiding the use of ward beds in the operating room can affect infection incidence. Along the same lines, restricting traffic in and out of the operating room can decrease bacterial counts as well. This can be accomplished by providing signs and temporary barriers to staff from a main corridor so that personnel can only enter the operating room through a substerile corridor or use a telephone to call into the room ( Fig. 25-2 ). Identification of personnel who are part of the surgical scrub team as bacterial shedders can also aid in decreasing the risk of primary infection as well. Other points that may reduce the incidence of bacterial contamination include clamping off of suction tips to avoid continuous air flow through the sucker tip and increased deposition of airborne pathogens on the tip of the sucker. The use of impervious gowns and drapes over cloth has also been shown to be helpful. It may be beneficial to change sucker tips every 30 to 45 minutes to help prevent this from occurring. Letting the scrub technician know that use of a water basin to keep instruments in that return to and from the operative field is a technique that should be avoided can be helpful as well. Pulsatile lavage can remove as much as 99% of wound contaminants and can be added to the operative regimen to aid in decreasing contamination of the operative site as well.

Temporary barriers and signs can be used in the operating room to keep traffic to a minimum.

There are multiple issues that the anesthesiologist can address during the operation that can decrease the risk of operative site infection as well. One of these is to ensure the proper timing of prophylactic antibiotic administration. This is usually the responsibility of the anesthesia team, and they should be educated on its significant importance.

The monitoring of the patient’s temperature is a concern most orthopedic surgeons are aware of during trauma procedures but not as focused on during elective procedures. Patient temperature and risk of surgical site infection in an elective setting have been determined, however. Hypothermia has been shown to cause vasoconstriction, and this further reduces the blood supply to the operative site and makes it more susceptible to infection.

Diabetes is a relatively common comorbidity in many patients. Well-controlled diabetes with blood glucose level less than 200 mg/dL during the operative procedure to decrease risk of surgical site infection has been reported.

Anesthesia traffic should to be kept to a minimum as well. Explaining the importance of this to the anesthesia team as well as posted reminders and barriers as stated in the previous paragraph can be helpful as well. Ultimately, it takes a multidisciplinary approach to keep all related services involved in patient care on the same page concerning all of these risk factors to minimize the incidence of surgical site infection in primary total knee replacement.