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Increased above the knee symptoms seen with continued femoral nerve block
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A continuous infusion of femoral nerve block analgesia resulted in an increased incidence of patient-reported symptoms above the knee compared with placebo after ACL reconstruction, according to findings presented by Bradley R. Wasserman, MD, at the 2011 Annual Meeting of the American Orthopaedic Society for Sports Medicine.
“Multiple studies have documented the efficacy of femoral nerve blocks for postoperative pain control after ACL reconstruction,” Wasserman said during his presentation. “However, no study has prospectively evaluated the side effects and/or complications following this modality for patients undergoing primary ACL reconstruction.”
Three cohorts
The study included 270 patients with a mean age of 27.4 years. Surgeons selected the graft type and tourniquet use for the reconstruction. The patients were allocated into one of the following groups:
- a placebo group that received a normal saline bolus, followed by a 48-hour normal saline infusion;
- a bolus-only group that received 0.25% levobupivicaine (Chirocaine; Abbott Laboratories) followed by a 48-hour normal saline infusion; and
- a continuous infusion group that received 0.25% levobupivicaine followed by a 48-hour levobupivicaine continuous infusion.
In addition, each group received spinal anesthesia and intravenous sedation.
The femoral nerve catheters were removed after 48 hours. Postoperatively, patients wore compressive cooling devices and hinged knee braces.
Patient surveys
After a minimum of 5 years postoperatively, patients received surveys in the mail inquiring about the presence of numbness, paresthesias, weakness or burning. Patients who did not respond to the mailing were followed up by phone. The survey had a response rate of 61.6%, with 149 patients responding at a mean of 6.9 years postoperatively.
There were no differences among the three treatment groups in terms of patient demographics, graft types, tourniquet use or surgical duration. The researchers found no significant differences among the cohorts regarding numbness, paresthesias, burning or weakness above the knee. However, the investigators found that the continuous infusion group had an increased incidence of patient-reported weakness compared to controls, but this “did not reach significance,” according to Wasserman.
When they combined all neurological symptoms, the investigators found that the continuous infusion group had a significantly higher rate of symptoms compared with the placebo group (37% vs. 12%). The researchers also found no differences among the groups for combined below-the-knee symptoms. The researchers also adjusted the results for graft type and tourniquet use, which had no effect on the results.
“Our study demonstrated significant differences in symptoms above the knee between the placebo group and those who were receiving continuous infusion,” Wasserman said. “However, the clinical significance of our findings is unknown.”
Limitations
Wasserman cited the 61.6% response rate as a study limitation. However, he noted that no differences were found between responders and non-responders to the survey in terms of treatment group, surgeon, graft type and tourniquet use. He also noted that the team did not test the reliability or validity of the survey used to report symptoms after ACL reconstruction. The study also investigated a 0.25% dose of levobupivicaine — double the currently used dose of 0.125%.
“Therefore, we believe that the prevalence of symptoms may be decreased with this current recommended dose, and we recommend that a future study be undertaken to evaluate for the adverse effects with this current treatment dose used today,” Wasserman said. – by Renee Blisard
Reference:
- Wasserman BR, Jordan SS, Mark Z, et al. Adverse effects of femoral nerve block analgesia after anterior cruciate ligament reconstruction. Paper #37. Presented at the 2011 Annual Meeting of the American Orthopaedic Society for Sports Medicine. July 7-10. San Diego.
- Bradley R. Wasserman, MD, can be reached at UPMC Center for Sports Medicine, 3200 S. Water St., Pittsburgh, PA 15203; 412-432-3662; email: wassermanbr@upmc.edu.
- Disclosure: Wasserman has no relevant financial disclosures.