Introduction
Intervertebral disk disease is the most common neurosurgical condition in dogs, with an overall prevalence of 3.5%, and surgical decompression of the spinal cord via hemilaminectomy is recommended to alleviate signs associated with intervertebral disk disease in most cases.1,2 Complications associated with thoracolumbar hemilaminectomy are uncommon but can include surgical site infections (SSIs), iatrogenic trauma to neuronal structures, hematoma, and worsening of neurological function.2 Surgical site infections occur in 0.6% to 4.2% of canine hemilaminectomy cases and are associated with increased morbidity, extended hospitalization, and substantial economic burden to owners.3,4
Prophylactic methods of surgical site prevention include preoperative bathing protocols with an antimicrobial-based shampoo, preoperative antiseptic skin preparation with isopropyl alcohol combined with either chlorhexidine gluconate or povidone-iodine to minimize skin colonization, perioperative antibiotic prophylaxis, maintaining normothermia, administering increased fraction of inspired oxygen, and minimizing anesthesia time.3–5 Perioperative antibiotic prophylaxis for the prevention of SSI generally includes a preoperative dose of a broad-spectrum antibiotic administered a minimum of 30 minutes prior to the creation of a surgical incision, with subsequent doses administered every 1 to 2 half-lives of the prescribed antibiotic for the duration of the surgical procedure to maintain tissue concentrations above the minimum inhibitory concentration for most sensitive skin flora.5 The CDC recommends against the use of postoperative prophylactic antibiotics in clean procedures due to the potential for increased antimicrobial resistance with the indiscriminate use of antibiotherapy.5 Antibiotic prophylaxis has not been reported to decrease the rate of SSIs; however, the results of some reports6–9 support postoperative prophylaxis because of their protective effects in orthopedic surgeries.
There are limited data on the role of prophylactic postoperative antibiotics in veterinary neurosurgery, though recent studies3,4 have evaluated the use of antibiotic prophylaxis following various surgical conditions with mixed results. The objective of this study was to determine the influence of prolonged antibiotic prophylaxis on SSI rates after hemilaminectomy compared with cases that did not receive postoperative antibiotic prophylaxis. The null hypothesis was that there would be no difference in hemilaminectomy SSI rates in dogs receiving postoperative antibiotics compared to those that did not.
Methods
Study population
Electronic medical records of dogs treated with thoracolumbar hemilaminectomy in a single tertiary hospital between January 2018 and October 2023 were retrospectively reviewed. Dogs were included if they were treated with decompressive hemilaminectomy at 1 or more thoracolumbar disk sites (T10 through L7) and had an in-person follow-up documented at least 30 days after the procedure.
Data collection
The electronic medical records of 672 dogs were reviewed from 2018 to 2023. The study population was retrospectively categorized into 2 groups according to the presence (group A) or absence (group B) of postoperative antibiotic prescription. Preoperative case data including signalment, body weight (kg), documentation of confirmed or suspected endocrinopathies, and information regarding preoperative antibiotic administration were recorded. Perioperative case data including hemilaminectomy disk site(s), total anesthetic time (including advanced imaging and surgical procedures), total surgical time, primary surgeon, type of perioperative antibiotic administration, and method of skin closure were recorded. Postoperative case data including prescription of oral prophylactic postoperative antibiotic (or not), dates of all postoperative evaluations, outcome data from physical and neurological examinations at postoperative evaluations, and all information regarding treatment and outcome when SSI was diagnosed were recorded. Dogs were excluded if they were given postoperative antibiotics to treat an existing infection (eg, dermatitis or urinary tract infections), had comorbidities that delayed wound healing leading to the addition of postoperative antibiotics (such as diabetes mellitus, hypothyroidism, and hyperadrenocorticism), or did not have a minimum of 30 days of follow-up or if medical records were incomplete.
Antibiotic protocols
All dogs were administered cefazolin (22 mg/kg, IV) or enrofloxacin (10 mg/kg, IV) at least 30 minutes prior to the start of surgery. Dogs prescribed cefazolin were given periodic doses every 90 minutes for the duration of the anesthetic event; dogs prescribed enrofloxacin did not receive follow-up doses due to the method of action and half-life of fluoroquinolones. All incisions were cleaned with saline promptly after closure while still in the operating room, and each incision was then covered with an island barrier dressing that remained in place for the duration of hospitalization. Dogs in group A were prescribed postoperative antibiotic prophylaxis of cefovecin (8 mg/kg, SC, once), cefpodoxime (5 to 10 mg/kg, PO, q 24 h), amoxicillin–clavulanate acid (13.75 mg/kg, PO, q 12 h), metronidazole (5 to 10 mg/kg, PO, q 12 h), or marbofloxacin (2.2 mg/kg, PO, q 24 h), with duration of prophylaxis at the primary surgeon’s discretion. Dogs in group B were not prescribed any prophylactic antibiotics during the postoperative monitoring period.
Surgical site evaluation
Medical record entries were evaluated for any evidence of complication related to the surgical site or incision between the time of surgery and the 4-to-6-week in-person postoperative evaluation prescribed for all hemilaminectomy cases at the study facility. When evaluating the medical records, the CDC’s guidelines for the diagnosis of SSI were employed and cases were designated as no infection, superficial infection, or deep infection.10
A superficial SSI involves the skin and subcutaneous tissues. The diagnosis of a superficial SSI is dependent on the inclusion of at least one of the following factors previously defined by the CDC: the presence of purulent discharge, bacteria cultured from the incision site, or diagnosis of a superficial incisional infection by a surgeon. A deep SSI includes the deeper soft tissues including fascia and muscle. There must be purulent discharge, spontaneous dehiscence deep in the surgical site, or the need for incisional reexploration for wound management to be classified as a deep SSI.10
Statistical analysis
All analyses were performed with SAS, version 9.4 (SAS Institute Inc). A P value below .05 was considered significant. Normality was evaluated via inspection of quantile-quantile and probability-probability plots, histograms, and skewness. Normally distributed variables were summarized descriptively with mean, SD, and range. Nonnormally distributed variables were summarized descriptively with median, IQR, and range. Wilson binomial CIs were calculated for SSI rates. Surgical site infection rates between dogs given or not given antibiotics were analyzed with a Fisher exact test.
Results
A total of 672 dogs were identified as having been treated with hemilaminectomy during the study period. Of these, 397 dogs were excluded (Figure 1). The remaining 275 dogs met all inclusion criteria. Forty-three breeds were represented, with Dachshunds and Dachshund crossbreeds overrepresented (142 of 275 [52%]). There were 95 spayed females, 102 neutered males, 31 intact females, and 48 intact males. Mean age was 6.2 years (SD, 2.7). Median body weight was 7.7 kg (IQR, 6.0 to 11.8). Median time to final in-person evaluation was 45 days (IQR, 41 to 52). Median total anesthetic time and surgical time were 140 minutes (IQR, 120 to 175) and 62 minutes (IQR, 50 to 84), respectively. Skin closure at the surgical site was performed with nylon sutures in 12 cases (4%), intradermal poliglecaprone 25 in 79 cases (29%), and surgical staples in 184 cases (67%). Cyanoacrylate glue was not used in conjunction with any closure methods.
Case exclusion flowchart documenting all case identification steps including total population, included and excluded cases, and reasons for exclusion from this study. UTI = Urinary tract infection.
Citation: Journal of the American Veterinary Medical Association 2025; 10.2460/javma.24.10.0677
Pre/perioperative cefazolin was administered to 271 dogs (99%), and 4 dogs (1%) were administered enrofloxacin. Dogs receiving cefazolin were dosed once (186 of 271 [68.7%]), twice (84 of 271 [31%]), or 3 times (1 of 271 [0.3%]) depending on the duration of surgery. All 4 dogs receiving enrofloxacin were dosed a single time, 30 minutes prior to surgery.
A total of 147 of 275 dogs (53%) were included in group A, and 128 of 275 dogs (47%) were included in group B. Dogs in group A were heavier than dogs in group B (P = .005). There were no statistical differences in sex or age distributions between group A and group B (P = .260 and P = .319, respectively). Dogs in group A were prescribed cefpodoxime (86 of 275 [59%]), cefovecin (51 of 275 [35%]), marbofloxacin (5 of 275 [3%]), amoxicillin–clavulanic acid (3 of 275 [2%]), or metronidazole (2 of 275 [1%]). Median duration of prescribed prophylactic postoperative antibiotics was 7 days (IQR, 7 to 10).
Surgical site infection
The overall SSI rate was 3% (8 of 275; 95% CI, 1% to 6%). The SSI rate in group A was 3% (5 of 147; 95% CI, 1% to 8%), which was not statistically different from the 2% SSI rate (3 of 128; 95% CI, 1% to 7%) in group B (P = .728; Table 1). Surgical site infections were confirmed with bacterial culture and sensitivity in 5 of 8 cases (63%). One case had culture and sensitivity performed with no growth observed, but there were sufficient clinical signs of SSI to meet the CDC definition. The remaining 2 cases were diagnosed with SSI based on examination findings alone.
Signalment and relevant case data for 8 dogs that developed surgical site infections (SSIs) following hemilaminectomy.
| SSI No. | Age (y) | Breed | Weight (kg) | Closure method | Prophylactic antibiotic | SSI type | Bacteria |
|---|---|---|---|---|---|---|---|
| 1 | 12 | Dachshund | 6.9 | Staples | Cefovecin | Deep | Citrobacter spp |
| 2 | 7 | Dachshund | 8.4 | Staples | Cefovecin | Deep | Citrobacter freundii |
| 3 | 5 | Dachshund | 5.2 | Staples | Marbofloxacin | Superficial | Staphylococcus epidermis and Staphylococcus warneri |
| 4 | 5 | Dachshund | 9.5 | Staples | Amoxicillin/clavulanate potassium | Superficial | No growth |
| 5 | 5 | Dachshund | 5.7 | Staples | Cefovecin | Superficial | Pseudomonas aeruginosa |
| 6* | 12 | Mixed | 33 | Staples | None | Deep | P aeruginosa and Streptococcus canis |
| 7 | 6 | Dachshund | 5.6 | Staples | None | Superficial | N/A |
| 8 | 9 | Dachshund | 7.1 | Intradermal | None | Superficial | N/A |
*Euthanized due to SSI.
There was not a statistical difference in SSI rates between closure methods (intradermal absorbable, 1% [1 of 79]; cutaneous staples, 4% [7 of 184]; cutaneous nylon, 0% [0 of 12]; P = .611). Additionally, 7 of 8 SSI cases (88%) were Dachshunds. Ten dogs (2 of 8 SSI [25%]) were prescribed 1 of 3 noncephalosporin prophylactic antibiotics (amoxicillin/clavulanate [n = 3; 1 SSI], marbofloxacin [5; 1 SSI], and metronidazole [2; 0 SSI]). When those 10 dogs were excluded from statistical analyses, the SSI rates in dogs prescribed cefpodoxime (0% [0 of 86]), cefovecin (6% [3 of 51]), or no antibiotics (2% [3 of 128]) were not significantly different (P = .067).
Five dogs were diagnosed with superficial SSI and treated with parenteral antibiotics. They were deemed healed after treatment. Three dogs developed deep SSIs and were treated with marbofloxacin as indicated by culture and sensitivity results in all 3 cases along with open-wound management. Two cases with deep SSI were treated successfully, and the SSI was resolved after treatment. The third case with a deep SSI was suspected to have become septic secondary to the deep incisional infection and subsequently euthanized.
Discussion
Clean-procedure neurosurgical site infection rates in dogs are reportedly4 as high as 4.2%. Due to the negative impacts of SSI on patients, surgeons may be inclined to prescribe prophylactic antibiotics following clean surgical procedures. However, the CDC guidelines regarding antimicrobial stewardship recommend against routine antibiotic prophylaxis due to the risk of increasing antimicrobial resistance.5 In this study, there was no association found between the prescription of prophylactic postoperative antibiotics and development of SSI following clean thoracolumbar hemilaminectomy procedures in dogs. Based on these findings, we accepted our hypothesis.
Due to the risk of antimicrobial resistance in bacteria, the WHO has published guidelines to provide adequate care for patients while minimizing the risk of antimicrobial resistance in human patients.11 However, these guidelines may be extrapolated and adopted for use in veterinary surgical cases. Per the WHO guidelines, antimicrobial prophylaxis in clean procedures should be limited to within the first 24 hours after the procedure. In this study, all dogs were treated with perioperative prophylactic antibiotics roughly 30 minutes before the first surgical incision was made, with some dogs receiving periodic dosing of cefazolin, a first-generation cephalosporin, up to 3 times during the surgical procedure, which is consistent with the WHO guidelines. However, prophylactic antibiotic prescription practices were not heterogeneous in either the perioperative or postoperative periods. While all cases in this study were prescribed perioperative IV antibiotics, 4 dogs were given enrofloxacin instead of cefazolin and the reasoning could not be deduced from the medical records. Additionally, the dogs in group A were prescribed prophylactic antibiotics for 5 to 14 days after surgery. Finally, per antimicrobial stewardship recommendations, when prescribing prophylactic empirical antibiotics, it may be more appropriate to choose first-generation antibiotics, yet 10 dogs in group A were prescribed nontraditional prophylactic antibiotics (eg, marbofloxacin) for reasons that could not be identified due to this study’s retrospective design. Due to the low SSI rate in this study, it was not possible to analyze the potential impact of these variable prescribing practices on antimicrobial resistance.
The impact of surgical site closure method on veterinary orthopedic incisions is unknown.8,12 Atwood et al12 found no difference in risk when tibial plateau leveling osteotomy incisions were closed with either surgical skin staples or poliglecaprone 25. However, Frey et al8 report that use of any incision closure method other than surgical skin staples may be protective against SSI. In the current study, 7 of 8 SSI cases were closed with surgical skin staples and only 1 case was closed with poliglecaprone 25. Surgical staples were used in 67% of all cases compared to 29% of cases closed with poliglecaprone 25, and a statistical difference between the 2 closure methods was not found.
Due to the low incidence of SSIs, associations with other variables could not be made in the current study. There are several known risk factors for SSIs in literature, including procedure-specific and patient-specific variables. There is a direct linear relationship between the duration of anesthesia and SSIs.13,14 Other reported risk factors include age, body weight, the presence of comorbidities, the presence of an implant, preoperative hair clipping more than an hour prior to surgery, American Society of Anesthesiologists status, hypothermia, and hypotension.13,14,15 Body condition scores were not recorded for most dogs in the current study, and this variable could have had a significant impact on SSI rates, as there is evidence that there is a higher prevalence of SSI with increased body weight.15 In this study, most SSIs (88%) were diagnosed in Dachshunds. Though, due to the low number of SSIs and disproportionately high number of Dachshunds, it was unclear whether Dachshunds were at increased risk for SSI following thoracolumbar hemilaminectomy.
Limitations in this study were consistent with limitations inherent to retrospective study designs. Since no standardization of protocols and randomization of case enrollment could be retrospectively achieved, hard conclusions about the findings could not be made. In this study, information about prophylactic antibiotic prescription decisions was based solely on medical record data, with little insight into specific choices made by the prescribing surgeon. It is unclear why 4 dogs were prescribed enrofloxacin instead of cefazolin in the perioperative period, since there were no medical record notes indicating concern about an existing infection or perceived increased risk of infection in those cases. Additionally, the reasoning for and decisions about classes of postoperative prescription of prophylactic antibiotics in the dogs in group A could not be determined retrospectively and it is possible that the surgeon chose to prescribe the antibiotics for reasons other than prophylaxis. Finally, following the CDC’s definition of SSI, we restricted inclusion to require at least 1 evaluation after 30 postoperative days, which prompted exclusion of a relatively large number of cases, which may have introduced bias. Most excluded dogs were presented for suture removal and evaluation after 2 postoperative weeks, but they were not examined again. We assumed that clients would have contacted us or presented their dog if there were clinical signs of infection after the last examination, but we cannot be positive. In conclusion, the results of this study were unable to find an association between postoperative prophylactic antibiotics and decreased risk of SSI in dogs treated with thoracolumbar hemilaminectomy. Based on these findings and the risk of antimicrobial resistance associated with antimicrobial prophylaxis in clean procedures, it may be prudent to discontinue antibiotic prophylaxis within 24 hours of surgery per the WHO guidelines.
Deborah Keys, PhD, performed all statistical analyses for this study.
Disclosures
The authors have nothing to disclose. No AI-assisted technologies were used in the generation of this manuscript.
Funding
The authors have nothing to disclose.
ORCID
S. W. Frederick https://orcid.org/0000-0003-4606-3632
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