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BLOCK AT A GLANCE

Infiltration around the sensory branches that provide innervation to the knee joint (genicular nerves) before they enter the knee capsule.

  • Indications: Chronic knee pain, total knee arthroplasty, or procedures associated with moderate to severe postoperative knee pain

  • Goal: Local anesthetic spread next to the genicular arteries (if visible) or at the junction of the epiphysis and diaphysis of the femur and tibia

  • Local anesthetic volume: 4 to 5 mL per nerve

GENERAL CONSIDERATIONS

The genicular nerve block and radiofrequency ablation therapy were initially described to treat severe chronic pain of the knee. An extended version of the block technique under ultrasound (US) guidance was recently introduced to provide analgesia after knee surgery. The infiltration targets only the sensory branches to the knee joint, preserving quadriceps muscle strength. Thus, this novel analgesic technique could be used as an alternative when the femoral nerve and adductor canal blocks are not indicated or not desirable.

The first reported block of genicular nerves under fluoroscopy guidance was based on bony landmarks. The introduction of US allows for easy recognition of the same landmarks and provides additional visualization of the soft tissues and vessels needed to identify the injection site. The available data is still limited; however, case series show promising results of genicular nerve block in the perioperative setting. Clinical trials are currently ongoing to determine the efficacy of this novel technique to treat acute pain after total knee replacement.

Limitations

The genicular nerves vary in number and trajectory and, because of their small size, they are not visualized with the available US technology. Genicular nerve blocks are based on US landmarks, which may result in inconsistent analgesia, particularly if a low volume of local anesthetic (LA) is used.

Specific Risks

The proximity of the inferolateral genicular nerve (ILGN) to the common peroneal nerve (CPN) is a risk factor for unintended CPN block resulting in foot drop. Thus this nerve is spared if denervation is planned to treat chronic pain. Vascular or intraarticular punctures are other potential risks.

ANATOMY

The innervation of the knee is complex, with branches originating from femoral, obturator, and sciatic nerves (Figure 30-1). The interindividual variability explains the discrepancy in the literature over the nomenclature and the origin of the genicular nerves.

FIGURE 30-1.

Innervation of the knee. The origin of the superomedial and superolateral genicular nerves (from the sciatic nerve or from the femoral nerve) is controversial.

To facilitate understanding of knee innervation, most authors divide the knee into an anterior and posterior compartment, and then further divide the anterior compartment into four quadrants. For the purpose of the technique description, the genicular nerves are called the superolateral (SLGN), ...

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