Comment on: “L3 paravertebral block combined with retro-psoas compartment block versus femoral nerve block for postoperative analgesia in total knee arthroplasty”

Dear Editor, We read with great interest the study by Li et al.[1] comparing the L3 paravertebral block (PVB) combined with retro-psoas compartment block (RPCB), versus femoral nerve block (FNB) for postoperative analgesia in total knee arthroplasty (TKA). We congratulate the authors for publishing this study and wish to present our reflections on the same. Li et al.[1] have used the retro-psoas compartment block with injection of local anesthetic posterior to the psoas major muscle with the needle tip anterior to the lumbosacral ligament. This compartment contains the femoral (L2–L4), obturator (L2–L4) nerves, and the lumbo-sacral trunk (L4–L5).[2] Li et al.’s[1] claim that this method “offers complete sensory anesthesia across dermatomes L3–S3” is found to be incorrect. The article by Bendsten et al.[2] provided for reference shows only moderate sensory coverage at L5 and S1 and poor sensory coverage at S2 and S3 segments. Thus, it is surprising that 27/32 patients achieved a sensory block of S2, given the anatomical location of the block. Li et al.[1] performed an additional paravertebral block at L3 to improve the sensory coverage of the L2 and L3 dermatomes. However, this technique is inadequate to block the branches of the sciatic nerve that supply the posterior part of the knee joint. Li et al.[1] also performed periarticular infiltration with a mixture of local anesthetic, opioid, and steroid in all patients at the end of the surgery. Thus, it would be difficult to assess the exact efficacy of the blocks performed, making the conclusions questionable. The focus of regional anesthesia for TKA has been to provide good analgesia with preservation of motor function to facilitate faster mobilization and recovery. The knee joint has a complex innervation. Whereas the anterior portion is innervated by branches of the femoral nerve and common fibular nerves (L4–S2), the posterior portion is innervated by branches from the posterior divisions of the obturator and tibial (L4–S3) nerves in addition to articular branches from common fibular and sciatic nerves.[3,4] A comprehensive block with minimal motor impairment can be obtained by performing an adductor canal block combined with the iPACK block (interspace between the Popliteal Artery and Capsule of the posterior Knee).[5] These blocks are easy to perform and are selective to the knee joint. However, the L3 PVB and RPCB used by Li et al.[1] are proximally performed blocks that would result in high degrees of motor weakness of the quadriceps muscles. Our main contention is that these blocks are suitable for analgesia in hip surgeries; their role in knee surgeries is questionable. In their conclusion, Li et al.[1] state that “the modified SQLB is a compelling and optimistic block technique,” which is probably a typing mistake. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.