Diabetic foot, ankle patients have fivefold greater risk for postoperative infection

Peripheral neuropathy was the strongest predictor of infection in people with and without diabetes.

A recent study of foot and ankle surgical cases indicates that patients with diabetes mellitus have a significantly greater risk for developing a severe postoperative infection than those without diabetes.

The research also identified factors associated with the development of postoperative infection.

“Diabetic patients have about a fivefold increased risk for developing a severe infection postoperatively than nondiabetic patients,” Dane K. Wukich, MD, said during his presentation at the 25th Annual Summer Meeting of the American Orthopaedic Foot and Ankle Society. “Patients with complicated diabetes have about a fivefold higher infection rate than patients with non-complicated diabetes and about a tenfold increase over people who do not have diabetes. Although people with diabetes who do not have complicated disease have a higher infection rate, we did not find it to be significant.”

Retrospective review

The investigators retrospectively reviewed the charts of 1,000 consecutive surgical cases performed by Wukich. They excluded patients with obvious preoperative infection from the study. They defined postoperative infection as infection that occurred within 30 days of surgery in patients who did not have external fixation, and infection that occurred up to 30 days after removal of the frame in patients who had external fixation.

Dane K. Wukich

They categorized mild infections as cases with less than 2-cm erythema that received outpatient treatment, and deemed cases with greater than 2-cm erythema that received inpatient intravenous antibiotics and/or surgical incision and draining as having a severe infection. The study group included patients with diabetes while the control group consisted of patients who did not have the condition.

The investigators discovered an overall infection rate of 4.8%. They found a 2.8% infection rate for the control group and a 13.2% infection rate for the study group. The investigators categorized two-thirds of the infections in the study group as mild, Wukich said.

Significant factors

A univariate analysis revealed a significant association between the development of a postoperative infection and the following factors:

• Charcot neuropathy;
• diabetes;
• peripheral neuropathy;
• peripheral arterial disease;
• rheumatoid arthritis;
• external fixation;
• longer duration of surgery;
• older age; and
• history of a previous ulcer.

However, the investigators found no significant association between developing a postoperative infection and tobacco use, gender, previous surgical transplantation or whether patients had inpatient or outpatient surgery.

Peripheral neuropathy

A multivariate analysis controlling for the significant univariate factors showed that peripheral neuropathy, history of a previous ulcer and external fixation significantly correlated with high infection rates.

“We found that peripheral neuropathy was the strongest predictor of infection in both diabetic patients and nondiabetic patients with an increased risk factor of 4,” Wukich said.

The investigators also found that external fixation was associated with 40% of infections.

“They were remote from the surgical site and involved pin tracts,” Wukich said. “But, nonetheless, they resulted in a 2.8-fold increase of infection.” A history of a previous ulcer increased the risk of infection 2.5 times.

Secondary analysis

In a secondary analysis that excluded patients who had external fixation, the investigators compared the infection rates among the following groups:

• a control group of patients without diabetes;
• an uncomplicated diabetes group of patients who did not have end organ damage; and
• a complicated diabetes group which consisted of patients who had end organ damage.

The investigators found an overall infection rate of 3.3%. They discovered a 1.8% infection rate for the control group, a 3.5% rate for the uncomplicated diabetes group and a 16.7% rate for the complicated diabetes group.

Wukich cited the retrospective study design, lack of information regarding patients’ body mass index and the potential for investigator bias as study limitations.

“We were unable to determine from records whether the patients had type I or II diabetes and we could not determine the duration of their diabetes,” he said.

Wukich noted that it is important for surgeons to preoperatively document the risk factors for infection. “In this era of pay-for-performance, I think that people are going to get docked in the future if you get a postoperative infection,” he said.

A “Great study”

During the paper discussion, James W. Brodsky, MD, praised Wukich’s research. “This is a great study,” Brodsky said.

“In the United States, this is incredibly important, especially with the new Medicare rule that they do not cover postoperative infection. This shows us that diabetic neuropathy in particular is a very important risk factor.”

For more information:

• James W. Brodsky, MD, can be reached at Baylor University Medical Center, 411 N. Washington St. 7000, LB 14, Dallas, TX 75246-1777; 214-823-7090.
• Dane K. Wukich, MD, can be reached at Comprehensive Foot and Ankle Center, University of Pittsburgh Medical Center, Southside Roesch-Taylor Building, 2100 Jane St., Suite 7100, Pittsburgh, PA 15203; 412-586-1546; e-mail: wukichdk@upmc.edu. Neither source has any direct financial interest in any products or companies mentioned in this article.

Reference:

• Wukich DK. Surgical site infection in foot and ankle surgery: A comparison of patients with and without diabetes mellitus. Presented at the 25th Annual Summer Meeting of the American Orthopaedic Foot and Ankle Society. July 15-18, 2009. Vancouver, British Columbia.