2.2.1 Breed, Sex, and Body Weight

Several host factors identified as risk factors for SSI development are beyond the control of the veterinary team, such as breed, sex, and body weight. Bulldogs and German Shepherds have been identified as having an increased risk for development of SSI following TPLO surgery [21, 27]. Labrador Retrievers and mixed‐breed dogs have been identified as having a lower SSI development risk following TPLO surgery [4, 3]. Both Fitzpatrick and Solano and Nicholson et al. identified intact male dogs to be at higher risk of SSI; however, sex was not identified as a risk factor in other studies [3, 4, 17, 28]. Increased body weight has been significantly associated with an increased SSI risk in several studies [2, 4, 10, 15,28–30]. In one study, each 1 kg increase in body weight resulted in 1.03 times increased odds of developing an SSI, while a second study noted that for each 1 kg increase in body weight, the odds of developing an SSI increased by 4.7% [28, 29]. As these factors are inherent to the patient and cannot be specifically controlled, this information can be utilized to distinguish those animals at higher risk of developing an SSI and thus requiring greater preventive measures.

2.2.2 ASA Status and Endocrinopathies

Preoperative ASA score (Table 2.3) has been correlated with risk for developing an SSI, such that the risk for SSI increases with each increment in ASA score [2]. As ASA scores take into consideration the overall health status of a patient, the higher the ASA score, the more systemically ill the patient. Animals with endocrinopathies have also been identified to be 8.2 times more likely to develop an SSI, likely due to alterations in immune function [3]. Logically, if an animal has a chronic illness, such as an unmanaged or poorly controlled endocrinopathy, postponement of elective orthopedic procedures until these illnesses are adequately addressed should be considered, when possible.

2.2.3 MRSP Carrier Status

As Staphylococcus spp. have been identified as one of the most common bacteria contributing to the development of SSIs following TPLO, and MRSP SSIs are increasing in frequency, monitoring for carriers of MRSP has been investigated [4, 13, 21,31–34]. In one study, 4.4% of animals were identified to be MRSP carriers preoperatively and carriers were 6.72 times more likely to develop an SSI. While screening for MRSP may help to determine those animals at higher risk for SSI, current screening tests are time‐consuming and not practical for routine implementation as this would result in delaying surgery [21]. Additionally, in human medicine, the goals of methicillin‐resistant Staphylococcus aureus (MRSA) screening are to allow for decolonization preoperatively [35–38]. In veterinary medicine, preoperative decolonization of MRSP is a challenge, due to not only the limited number of effective antimicrobials against MRSP, but also the inherent challenges of topical treatment of the sites most commonly colonized – the nasal passages, pharynx, and rectum [21].

While decolonization may not be feasible, it is reasonable to alter perioperative antimicrobial prophylaxis in MRSP carriers undergoing higher risk procedures like TPLO. This may include measures such as adding a single dose of amikacin preoperatively to the typical (e.g., cefazolin) antimicrobial regime, assuming renal health has been evaluated.

2.2.4 Dermatitis, Clipping, and Skin Preparation

As mentioned, Staphylococcus spp. are amongst the most common bacteria causing SSIs. S. pseudintermedius is a commensal bacteria within the normal microbiome of dogs [39]. Assessment of the animal’s skin for evidence of local or distant dermatitis is recommended, to reduce the risk of contamination of the surgical site (Figure 2.1). Despite this logical recommendation, 17.5% of all animals undergoing TPLO in one study had evidence of active local or distant dermatitis. Of those with local dermatitis, 16.7% developed an SSI and 10.2% with distant dermatitis developed an SSI [27]. As there was no significant difference identified between local and distant dermatitis resulting in SSI, the risk for SSI development should not be considered lower for animals with dermatitis not affecting the direct surgical site, as anecdotally thought, and postponement of elective orthopedic surgeries with local or distant dermatitis should be considered [27].

Identifying the underlying cause of the skin disease is paramount for improving the skin barrier and reducing the risk for SSI development. Depending on the type and severity of the dermatitis, cleansing with medicated shampoos, application of topical antimicrobials or antifungals and/or systemic antimicrobials or antifungals may be required. When managing bacterial dermatitis, local to or distant from the surgical site, culture and susceptibility testing is recommended to guide antimicrobial therapy and determine if MRSP is present. While awaiting these results, empirical treatment is recommended with cephalexin (22–30 mg/kg, PO q8h) or clindamycin (11 mg/kg, PO q12h). Antimicrobials should be continued for 1 week beyond resolution of clinical signs.

Ideally, the surgical site should be free of skin lesions prior to considering surgery. In circumstances where postponing surgery is not possible, topical treatment is recommended, along with the addition of amikacin to the routine perioperative antimicrobials. When lesions are located at sites other than the surgical site, topical treatment is recommended + systemic medications as determined by the extent of the disease process. Bathing these patients with a chlorhexidine shampoo the night prior to surgery can also be considered [40].

Before skin preparation can occur, hair is clipped from the proposed surgical field to facilitate direct skin preparation and the limb is suspended (Figure 2.2). Clipping should be performed following induction of general anesthesia and not sooner due to the increased risk for SSI development [41, 42]. This risk is likely associated with the greater potential for direct skin trauma that may occur when attempting to clip hair on a conscious patient. Any microtrauma caused by rough clipping or poorly maintained clipper blades may also play a role in increasing the risk for SSI development.

Skin preparation (Figure 2.3) begins with the removal of surface dirt and oils using a neutral, nonmedicated soap as antiseptic agents are not active in the presence of organic material. Antiseptic agents are subsequently applied to reduce the bacterial load present on the skin at the time of surgery. Antiseptic agents commonly used in veterinary medicine include povidone‐iodine and chlorhexidine gluconate (Figure 2.4). These antiseptic solutions are applied to the skin using a scrub technique or a paint or spray technique. Ultimately, contact time, meaning the time the antiseptic solution is in direct contact with the skin, is the most important aspect of skin preparation. Both the World Health Organization and the Centers for Disease Control and Prevention recommend the use of alcohol‐based solutions for surgical skin preparation [43, 44]. However, in veterinary medicine, aqueous solutions of povidone‐iodine and alcohol solutions of chlorhexidine gluconate have been proven to be equally effective in reducing bacterial colony‐forming units on canine skin [45, 46]. As many different antiseptic skin preparation solutions exist, following the instructions for your chosen product to ensure adequate contact time is key for appropriate skin preparation.

The initial skin preparation is carried out using nonsterile gloves and gauze. This initial preparation is performed by alternating antiseptic soap and alcohol, three times, ensuring an appropriate total contact time. A final application of an alcohol‐based antiseptic paint may also be performed. Protection of the prepared surgical site with sterile drapes is recommended prior to transport to the operating room (OR), to decrease the risk of inadvertent contamination.

A final sterile skin preparation is subsequently performed in the OR using sterile gloves and sterile gauze. This final preparation may be performed by a nonsterile assistant wearing sterile gloves or by a sterile assistant or surgeon. The final skin preparation is performed by alternating between the antiseptic solution (Figure 2.4) and alcohol, performed three times, or using an alcohol‐based antiseptic paint alone. Whichever antiseptic soap is used for the initial skin preparation must be the same antiseptic solution used in the final skin preparation.

2.3.1 Sources of Contamination

The perisurgical environment, including the anesthesia prep area, patient transportation, the OR, the radiology suite and surrounding personnel, plays a role as a source of possible bacterial contamination. Bacteria most commonly identified in surgical sites at the time of closure during orthopedic surgeries arise from aersol transmission [47]. One study identified 81% of elective orthopedic procedures as experiencing some form of bacterial contamination [47]. Possible sources identified included surgeon hands, surgeon gloves, animal skin, patient footwrap, sink faucet, transportation gurney, radiology table, and OR computers [47]. Despite this high number of reported contamination events and numerous sources identified, a correlation with SSI could not be made [47]. Historically, scalpel blades have been suspected to be a source of increased bacterial contamination into deeper tissues when the same blade is used for skin incisions and deeper tissue incision; this remains unclear at this time, as conflicting data exist [48–50]. However, with documented potential for bacterial transmission from the skin blade, use of a second surgical blade for deeper tissues is advised. Suction tips have also been identified as sources of contamination in clean surgical procedures. In one study, a positive culture rate of 92% was identified at the end of clean surgical procedures, with a second study identifying a 42% positive culture rate at the end of clean orthopedic procedures [51, 52]. While these sources of contamination cannot necessarily be avoided, hospital surveillance of these known sources of contamination is recommended.

2.3.2 Personnel

As the majority of bacteria identified in contamination of surgical sites with and without SSIs arise from the microbiome of humans and animals within the OR, it is no surprise that an increasing number of OR personnel has been correlated with an increased SSI rate [2]. Reducing traffic in and out of the OR during clean orthopedic procedures may therefore reduce the amount of aerosolized bacterial contaminants and decrease contamination rates [53]. In academic settings, traffic in and out of the OR can anecdotally be higher, therefore in animals with inherent risk factors for SSI, attempts to reduce traffic in the OR are recommended. Both MRSA and MRSP have been identified in small animal hospital environments and among small animal employees [54]. It is possible that hospital personnel carrying MRSA and MRSP may cause direct or indirect transmission to animals [54].