Comparison of Two Multimodal Analgesia Regimens for Total Knee Arthroplasty : a Randomized Controlled Trial

The improvement of postoperative analgesia is an important issue in orthopedic surgery, especially after total knee arthroplasty. The early postoperative mobilization of these patients is crucial to ensure a favorable functional evolution, and this goal can't be accomplished without effective analgesia. Opioids offer an efficient pain relief, but their consumption can result in side effects that can increase the length of hospital stay. The use of a peripheral nerve block, such as the adductor canal block (BCA) is a widely favored alternative since it allows postoperative analgesia superior to opioids while preserving the strength of the quadriceps.

For a long period of time, the femoral block has been the most popular peripheral nerve block for patients after a knee arthroplasty. However, this perineural block is associated with an important rate of quadriceps' weakness, which could impair the post-operative mobilization and expose the patient to a risk of falling. It has now been widely replaced by the adductor canal block. The latter has the advantage of providing analgesia at rest and during movement equivalent to the femoral block, while preserving the quadriceps strength and offering a better mobility in the first 24 hours after surgery. In opposition to the femoral block, the adductor canal block does not increase the risk of falling since it is mainly a sensitive block.

The adductor canal block is an advantageous analgesic modality for patients after TKA, but it is limited since it offers only analgesia to the anteromedial aspect of the knee, sparing the lateral and posterior faces. It is common to combine this block with a periarticular knee infiltration with local anesthetics, performed by the surgical team at the end of the surgery. The two modalities combined make it possible to achieve very low pains scores at rest and during walking, compared to both techniques used separately.

The adductor canal block can be administered in one unique injection or with a perineural continuous infusion, to extend the block's analgesic duration. However, it is uncertain whether there is an advantage to use a continuous infusion. There is a significant rate of catheter migrating out of the adductor canal and losing effect. There is also the possibility that the continuous infusion results in a proximal extent of local anesthetic in the femoral canal, generating quadriceps weakness that invalidates the benefits for ACB in the context of postoperative mobilization.

Indeed, the location of the catheter near the surgical site predisposes it to be dislodged out of the adductor canal during surgical manipulations in a significant proportion of patients. A rate as high as 30% of catheter dislodgement on postoperative day 1 was observed. It is possible to perform the block after surgery, before the dressing is applied, but this practice tends to create delays, which are not desirable in the actual context of optimization of the OR time.