1

Describe the sensory innervation of the lower extremity.

Innervation of the lower extremity is derived from nerves of the lumbar and sacral plexuses, sometimes collectively referred to as the lumbosacral plexuses ( Figure 53-1 ). The lumbar plexus, which lies between the psoas major and quadratus lumborum fascias, is derived from the ventral rami of L1 to L4, with some contribution from T12, and branches into the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous (also known as the lateral cutaneous nerve of the thigh), obturator, and femoral nerves. The saphenous nerve is the largest terminal branch of the femoral nerve. Sensory innervation of the lumbar plexus is shown in Table 53-1 .

Extension of nerves from the lumbosacral plexus. Sciatic nerve (divides in midthigh—tibial division and peroneal division), femoral nerve, and obturator nerve.

(From Miller MD, Chhabra AB, Hurwitz SR, et al., editors. Orthopaedic surgical approaches. Philadelphia: Saunders; 2008. p. 434.)

The sacral plexus is derived from the ventral rami of L4 to S4 and gives off the superior and inferior gluteal nerves, the posterior cutaneous nerve of the thigh, the pudendal nerve, and the sciatic nerve. The sciatic nerve is composed of two nerves, tibial and common fibular (formerly known as peroneal), bound together by a common sheath. The terminal branches of the tibial nerve include the medial and lateral plantar nerves. The terminal branches of the common fibular nerve include the deep and superficial fibular nerves. The union of branches from the common fibular and tibial nerves forms the sural nerve. Sensory innervation of the sacral plexus is shown in Table 53-2 .

2

Which nerves are affected during anterior cruciate ligament surgery?

Postoperative pain after ACL repair originates from skin incisions, tibial periosteum at the bone tunnel site, inflammation and swelling within the knee joint, and the tendon harvest site (if an autograft is used). The nerves involved are the following:

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  Femoral nerve: skin incisions adjacent to the patellar tendon

  
  
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  Tibial nerve: tibial periosteum

  
  
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  Branches of femoral, obturator, sciatic nerves: internal knee joint

  
  
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  Autograft harvest:

  
  
  
  
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    Femoral nerve: patellar tendon

    
    
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    Obturator nerve: gracilis tendon

    
    
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    Tibial nerve: semitendinosus tendon

  
  

3

What are the anesthetic options for anterior cruciate ligament surgery?

ACL surgery may be successfully performed under general anesthesia, neuraxial anesthesia, or peripheral nerve block. Although general anesthesia provides excellent operating conditions during surgery, it does not provide postoperative analgesia. Postoperative pain relief can be accomplished with either intravenous analgesic agents or femoral or lumbar plexus blocks or catheters placed perioperatively.

Spinal or epidural neuraxial anesthesia provides adequate analgesia for the procedure but limited postoperative pain relief. Although placement of an epidural catheter provides the potential for an extended period of postoperative analgesia, it is inappropriate for ambulatory procedures. For optimal postoperative pain control, a single-shot spinal technique should be combined with a femoral nerve catheter. The femoral nerve catheter provides extended postoperative analgesia without motor weakness in the nonoperative leg.

Peripheral nerve blocks alone can provide anesthesia, with or without the addition of sedation. They can also provide postoperative pain relief, either by continuous local anesthetic infusion via a catheter or by administration of a long-acting local anesthetic in the original block. Depending on the surgical plan, options include sciatic nerve block combined with either a lumbar plexus or fascia iliaca block.