Knee arthroscopy and anterior cruciate ligament (ACL) repair are very common procedures, with an increasing incidence. They usually concern young and athletic patients.¹ ACL is considered as painful surgery.² while knee arthroscopy remains much less painful. These procedures are very often performed on outpatient basis.³

Regional anaesthesia (RA) and local anaesthetic infiltration are used to ensure effective postoperative analgesia with significant opioid sparing effect. It is frequently associated with a multimodal analgesia and allows a return home the day of surgery.

Knee innervation and surgical procedures Knee innervation is complex and depends on both lumbar plexus and sacral plexus.⁴ Lumbar plexus, through femoral nerve, innervates anterior thigh muscles, anterior side of femoral bone, tibial head and patella. Knee’s medial side is innervated by the obturator nerve. Finally, sacral plexus innervates thigh’s posterior side and knee’s posterior capsule and bone. However, there are numbers of anatomical variations. Futhermore, terminal branches constitute nervous networks that run directly in contact with the bone to insure knee innervation. These networks are made by branches from both lumbar and sacral plexus.

If surgical procedures are standardized for knee arthroscopy and menisectomy, many techniques are possible for ACL repair corresponding to different incision sites and innervation areas. Graft can be harvested from the semitendinous and gracilis muscles innervated by sciatic nerve and obturator nerve. It can also be harvested from patellar tendon (Kenneth jones) innervated by saphenous nerve, terminal branch of the femoral nerve. ACL repair could be associated with a lateral ligament knee repair with an incision related to the lateral cutaneous nerve of the thigh area. Thereby, the choice of RA could be impacted by the type of surgical technique.

Regional anaesthesia (RA) RA can be used alone as an anaesthetic technique, or in association with spinal anaesthesia or general anaesthesia as an analgesic procedure. To be effective on its own, RA must associate a femoral nerve block, an obturator nerve block and a sciatic nerve block. RA ensures a significantly more effective postoperative analgesia than either spinal anaesthesia or general anaesthesia during the 12 first postoperative hours,⁵ and can be prolonged by the use of many adjuvants (dexamethasone, dexmedetomidine).^{6 7} The use of very diluted local anaesthetic leads to decrease in the duration of analgesia.⁸ Finally, RA decreases significantly the duration of hospital stay.⁹

Femoral nerve block is the basic technique for postoperative analgesia after knee surgery, but allows only a partial analgesia according to knee innervation. To complete analgesia coverage, femoral nerve block must be associated with obturator nerve block and/or sciatic nerve block, even if the obturator nerve block’s role is still debated.

Distal peripheral nerve blocks have gained popularity for several years with the objective of achieving analgesia without motor block.

Sciatic nerve block can be substituted by local anaesthetic infiltration of the posterior side of knee’s capsule. This infiltration is performed by the surgeon himself at the end of surgery under arthroscopic visualisation,¹⁰ and enhances analgesic level compared to femoral nerve block alone.

Adductor canal block is an alternative to femoral nerve block. It ensures analgesia for moderate to severe pain at rest, at 45 degrees flexion and on walking.¹¹ Injection site has been debated, between inferior corner of femoral triangle and adductor canal. In the first case, local anaesthetic surrounds both the saphenous nerve and the nerve of vastus medialis and thus insures effective analgesia but with a risk of proximal spread to the femoral nerve. Injecting at the adductor canal induces an isolated saphenous nerve block, but with possible diffusion spread toward the posterior knee’s side ensuring also posterior side analgesia.

Local anaesthetic infiltration Intraarticular infiltration of local anaesthetics is an alternative to peripheral nerve blocks. In some countries, It can be used as an anaesthetic technique for simple arthroscopy without tourniquet.¹² The surgeon injects 20 ml of local anaesthetics inside the knee joint, and 20 ml subcutaneously on the incision sites, 30 min before the surgery.

However, this technique is most commonly used as an analgesic procedure. The injection is performed by the surgeon at the end of the surgery. Intraarticular injection induces a short and moderate analgesic effects which can be extended by adding adjuvants (dexamethasone, dexdemetomidine, magnesium…).^13–15 Nevertheless, the superiority of local anaesthetic infiltration, compared to multimodal analgesia has not been proved yet. Local anaesthetic chondrotoxicity has been and is still debated in some joints such as shoulder or ankle, but never reported in the knee joint.¹⁶ The use of intraarticular catheter is no more recommended.

Which strategy?The therapeutic strategy must be guided by analgesic efficacy, ability to return home and deambulation. Futhermore, rehabilitation after ACL repair does not require early mobilization and motion, compare to total knee replacement. The use of crutches is necessary, according to partial weight-bearing. In these conditions, return home with nerve block is feasible.¹⁷

Concerning analgesic efficacy, RA is superior to local anaesthetic infiltration [18] for painful surgeries such as ACL repair. It could be nuanced for knee arthroscopy and menisectomy which are much less painful. In these cases, multimodal analgesia associating paracetamol and non steroid antiinflammatory drugs can be as effective.

For ACL repair, the choice of peripheral nerve block depends on the type of surgical procedure. If femoral nerve block is the basic analgesic technique, sciatic nerve block and obturator nerve block enhance analgesia when hamstring graft technique is used. For patellar tendon graft, obturator nerve block and sciatic nerve block are not essential.

Conclusion Knee surgery can be divided into painful surgeries (ACL repair and arthrolysis) and non painful surgeries (knee arthroscopy, menisectomy).

Concerning painful surgeries, peripheral nerve blocks remain the best choice. They provide high analgesic level with poor morphine consumption and allow same-day hospital discharge. Motor block induces by these blocks is easily manageable by young and athletic patients who are able to move with crutches without weight-bearing. Distal peripheral nerve blocks (Adductor canal block) could be also an interesting alternative.

For non painful surgery, local anaesthetic infiltration could be proposed, but is not superior to multimodal analgesia associating paracetamol and non steroid anti-inflammatory drugs.

References

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