Fig. 1 A, Popliteal block administration. B, Ankle block being given under ultrasound guidance.
Courtesy of Grace Kunas and the Hospital for Special Surgery

AAOS Now

Published 11/1/2016
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Terry Stanton

Study: Few Complications Seen with Peripheral Nerve Block

Causes for complications that do occur can be difficult to pinpoint
A study on the use of peripheral nerve block (PNB) in foot and ankle surgery revealed an overall low complication rate associated with that anesthetic method. Of postoperative complications that did occur, most were neurological in nature and few were serious or unresolved. The researchers found no clear association in complication rates for popliteal blocks versus ankle blocks.

The study, a 2-year, prospective, blinded analysis involving 2,516 patients undergoing 2,704 foot and ankle procedures, was presented by Grace Kunas, BA, now a medical student at Georgetown University, at the annual meeting of the American Orthopaedic Foot & Ankle Society in Toronto. The senior author was Scott Ellis, MD, of the Hospital for Special Surgery (HSS), in New York City, where the study was conducted.

Ms. Kunas noted that PNBs have become the standard of care for anesthesia in foot and ankle surgery at HSS. Although previous studies have shown low complication rates associated with PNBs, the study was prompted by HSS surgeons' anecdotal perception that more complications may be linked to ankle blocks than popliteal blocks.

According to Dr. Ellis, it seemed as though many patients were "having nerve issues—burning pain and numbness—after peripheral blocks, especially with ankle blocks. We have a large service and wanted to see if this was truly the case. We also wanted to see if there were any factors that led to the cases where there was a problem."

Ms. Kunas noted that "the literature showed that complications from PNBs occur infrequently after lower extremity procedures, but there were no good studies estimating the incidence of neuropathy after ankle blocks, and the extent to which specific anesthesia factors contribute to PNB-related complications was unknown."

Because local anesthetics have been shown to be neurotoxic in proportion to the concentration and duration of exposure, added Ms. Kunas, the researchers hypothesized that these anesthetics  may sometimes be associated with complications.

"Another reason we did the study was to assess whether surgical and patient factors may play a more significant role in the development of neurological complications, since tourniquet use can cause nerve damage and preexisting neurological conditions may increase the risk of complications," she added.

Of the surgeries performed, 75 percent were performed with popliteal block (Fig. 1). Of all patients, 287 (11.4 percent) had a total of 290 complications (10.7 percent). Complications, which were reviewed independently and blindly by a surgeon and anesthesiologist not associated with the case, were rated as follows, based on clinical experience:

  • likely related to PNB
  • possibly related to PNB (indeterminate)
  • definitely not related to PNB

Serious complications were defined as those needing an intervention, having any motor deficit, being unresolved after 6 weeks, or involving pain or neuroplaxia outside the surgical site.

Of the 290 complications, 20 (0.7 percent) were serious, and all were at least possibly related to PNB. Unrelated complications included pin tract infection and suture abscess. One hundred ninety-five total complications (7.2 percent) were deemed possibly related to PNB, and 186 were neurological.

No clear difference between popliteal and ankle block
The number of complications rated as "possibly" due to PNB was significantly higher in patients who received a popliteal block compared with ankle block (P < 0.001), yet no significant difference was seen between the two types of anesthetic methods as relates to complications rated "likely" due to PNB.

Among other findings, dexamethasone additive was a significant predictor in complications that were at least possibly due to the block (P < 0.001), and no demographic factors were associated with complications. And notably, the authors wrote, interrater agreement between the surgeon and anesthesiologist was low, with agreement on 64.6 percent of the complications (0.42, weighted kappa statistic). The authors noted that the relative lack of agreement suggests that the cause of complications is often not obvious.

"Many of the complications are nerve related, and it can be hard to know if it is from the surgery—such as cutting or retracting a nerve or having a tight dressing," said Dr. Ellis. "They can also be due to nerve injury from the anesthetic being injected directly into the nerve. We also tend to attribute causation to somebody else."

Ms. Kunas said the researchers were surprised that they "did not did not see a greater incidence of complications after the ankle blocks compared to popliteal blocks, since that was one of our hypotheses." In addition, noted Dr. Ellis, he and his colleagues were surprised to some extent that "all complications were less common" than they had expected.

The study findings, including the fact that "the small number of complications made it difficult to make conclusions about confounders," point to further avenues of exploration.

According to Dr. Ellis, future studies might involve assessing larger groups of patients to study specific factors that may be associated with complications, such as additives to the blocks.

The authors noted that this was the largest prospective study to date and the first to review complications in a blinded fashion by both an anesthesiologist and an unassociated surgeon.

Coauthors with Ms. Kunas and Dr. Ellis are Jodie Curren, RN; Carey Ford; Kara Fields, MS; Matthew Roberts, MD; Martin O'Malley, MD; David Levine, MD; John G. Kennedy, MD; Jonathan Deland, MD; and Richard Kahn, MD.

The authors' disclosure information can be accessed at www.aaos.org/disclosure

Terry Stanton is the senior science writer for AAOS Now. He can be reached at tstanton@aaos.org

Bottom Line

  • This prospective, blinded analysis of complications following the use of PNBs in 2,516 patients who underwent foot and ankle surgery found that 287 patients (11.4 percent) had a total of 290 complications (10.7 percent).
  • The number of complications rated as "possibly" due to PNB with popliteal block was significantly higher versus those in patients who received ankle blocks, but no difference was seen in regard to complications rated as "likely" related to PNB.
  • Dexamethasone additive was a significant predictor of complications rated as at least "possibly" due to PNB, while no demographic factors were associated with complications.
  • Interrater agreement between surgeon and anesthesiologist was low, suggesting the difficulty of identifying causes of complications associated with anesthetic methods used in foot and ankle procedures.