STATS block – Selective Tibial Approach To Sciatic – A Novel Approach to the Sciatic Nerve: A Cadaver Study
The ultrasound-guided selective tibial nerve (TN) block was originally described as an alternative to sciatic blocks in total knee arthroplasties using a low volume technique to spare the peroneal nerve (PN) while still providing analgesia to the posterior knee. However, in our experience some “selective” tibial block patients still displayed signs of an undesired peroneal block resulting in foot drop post operatively. While a PN block is undesirable for knee surgery, both TN and PN blocks are necessary to provide postoperative analgesia for foot and ankle surgery. Using this information, the STATS block was born: we successfully began using a higher volume injection in the paraneural sheath of TN at a location distal to the split from the PN for our foot and ankle cases that required a sciatic block. We hypothesized this approach was effective in blocking both nerves because local anesthetic tracks up the tibial sheath to where PN and TN meet.
Material and Methods
The cadaveric specimen was obtained by Andrews Research and Education Foundation. Approval was obtained from the foundation to perform our study. To test our hypothesis, TN and PN were identified in the popliteal fossa, using ultrasound, where both nerves were distinctly separate. Using a medial to lateral approach, 30 mL of injectate was deposited in the paraneural sheath of TN. A medial to lateral approach completely avoided any inadvertent contact with PN. The limb was dissected immediately to determine spread of the dye.
On our dissection, we identified TN and PN with injectate distinctly around both nerves. Additionally, the injectate traveled 12 cm distally from the initial injection to where the two nerves combine. Most of the dye, however, was concentrated at the level of injection, suggesting some connective tissue between TN and PN that allowed spread between both nerve sheaths.
The spread to PN from our TN injection appears primarily from connective tissue at the level of injection even though some spread was seen distally to where the two nerves combine. Historically, post-op neuropraxia cases after sciatic blocks are in the PN distribution. This may be from needle to nerve trauma, intraneural injection, or from direct local anesthetic toxicity to nerves. Regardless, PN appears to be more susceptible to injury then TN. Therefore, the advantages of the STATS block technique versus classic popliteal sciatic block are several-fold. First, the STATS approach does not necessitate direct needling around the PN, eliminating needle to nerve trauma or peroneal intraneural injection. Second, TN is superficial near the popliteal crease making it easier to identify with ultrasound then the more proximal approach. We have performed more than 100 STATS blocks successfully with only one patient requiring a rescue peroneal block. Further areas for research are needed to determine the optimal volume needed for effective spread and to determine the incidence of neuropraxia. The STATS blocks- Selective Tibial Approach to the Sciatic. A new innovative way to perform a sciatic block with the STATS (and results) to prove it!