March 2016

Out on a limb: An analgesic assist

1Limb-JordanaJordana Bieze Foster, Editor

When it comes to improving outcomes after anterior cruciate ligament (ACL) recon­struction, lower extrem­­ity practitioners need all the help they can get. Fortunately, a recent study suggests they might be able to get some valuable assistance from their colleagues in anesthesiology.

Increasing numbers of studies have underscored the importance of quadriceps strength—and, in particular, quadriceps strength symmetry between limbs—in determining functional outcomes after ACL surgery. In fact, a number of orthopedic surgeons say the need to maximize quadriceps strength after ACL reconstruction is an important consideration in their choice of graft type, surgical technique, and rehabilitation protocols (see “Outcomes after ACL surgery: The importance of graft type,” page 18).

But a smaller body of literature is starting to indicate the type of analgesia used in ACL reconstruction procedures also affects postoperative quadriceps strength—which could, in turn, affect functional outcomes.

Femoral nerve blocks, for example, have been widely reported to cause immediate postoperative quadriceps weakness, particularly in patients undergoing total joint arthroplasty, but also in those undergoing ACL reconstruction. One might not think analgesia-induced weakness in the first day or two after surgery would have longer-term implications, especially in athletes, but research from the Mayo Clinic in Rochester, MN, suggests it might.

The type of analgesia used in ACL surgery can affect patients’ quadriceps strength, which could influence functional outcomes.

The Mayo Clinic team reported last February in the Journal of Knee Surgery that ACL reconstruction patients who received a postoperative femoral nerve block (FNB) had significantly weaker quadriceps at six months than patients who did not receive a FNB. Vertical jump and single-leg hop performance was also significantly poorer in the FNB group.

Given the obvious downsides to the conventional FNB approach, surgeons and their anesthesiologist colleagues have been looking for alternatives. These include the adductor canal block (ACB), a more distal block of the femoral nerve, positioned in the midthigh to preserve quadriceps femoris strength.

Early studies on ACB use in total knee arthroplasty patients have been positive. And, in a study epublished in early March by Anesthesiology, researchers from the University of Toronto in Canada found that an ACB administered prior to ACL reconstruction was associated with significantly less quadriceps strength loss than a preoperative FNB, while providing equal or better pain relief.

Granted, the findings are preliminary, and we can’t connect all the dots yet. The Toronto study only assessed strength loss preoperatively, so we can’t assume those effects would be evident postoperatively. The Mayo Clinic results suggest they might, but we can’t yet assume the findings of that study can be extrapolated beyond six months, or that they would have any impact on rerupture rates or cartilage degeneration.

Still, the findings are intriguing enough that lower extremity practitioners should at least be asking questions about analgesia when planning an ACL reconstruction or a postoperative rehab protocol.

And, when facing a clinical challenge as complicated as an ACL injury, lower extremity practitioners should also be encouraged to know that it’s a battle being fought on multiple fronts.

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