MOTOR SPARING KNEE BLOCK: DESCRIPTION OF A NOVEL APPROACH FOR ANALGESIA FOLLOWING KNEE ARTHROPLASTY

Introduction Fast track arthroplasty regimens require preservation of motor power to perform early rehabilitation and ensure early discharge (1). Commonly performed nerve blocks like femoral and Sciatic nerve blocks results in motor weakness thereby interfering with early rehabilitation and may also predispose to patient falls (2, 3). Hence, targeting the terminal branches of the femoral and sciatic nerves around the knee joint under ultrasound is an attractive strategy. The nerve supply of interest for knee analgesia are the terminal branches of the femoral nerve, the genicular branches of the lateral cutaneous nerve of thigh, obturator and sciatic nerves (4). Methods We modified the performance of the adductor canal block and combined it with US guided posterior pericapsular injection and lateral femoral cutaneous nerve block to provide analgesia around the knee joint. The femoral artery is first traced under the sartorius muscle until the origin of descending geniculate artery and the block is performed proximal to its origin. A needle is inserted in-plane between the Sartorius and rectus femoris above the fascia lata and 5 ml of 0.5% ropivacaine (LA) is injected to block the intermediate cutaneous nerve of thigh. The needle is then redirected to enter the fascia of Sartorius to deliver an additional 5ml of LA to cover the medial cutaneous nerve of thigh following which it is further advanced till the needle tip is seen to lie adjacent to the femoral artery under the Sartorius to perform the adductor canal block with an additional 15–20 ml of LA to cover nerve to vastus medialis, saphenous nerve and posterior division of the obturator nerve (Fig 1). The lateral cutaneous nerve of thigh is optionally blocked with 10 ml of LA near the anterior superior iliac spine between the origin of Sartorius and tensor fascia lata (Fig 2). The terminal branches of sciatic nerve to the knee joint is blocked by depositing 25 ml of local anesthetic solution between the popliteal artery and femur bone at the level of femoral epicondyles (Fig 3). Results The initial experience of the block performed on 10 patients reveal the median (IQR) block duration is noted to be around 20 (±6.5) hours. The median (IQR) pain scores in the first 24 postoperative hours ranged from 0 (±0.5) to 3 (±2.5) at rest and 1.5 (±3.5) to 5.5 (±1) on movement. All patients were successfully mobilized on the morning of the first postoperative day. Conclusion Motor sparing from the blocks while providing adequate analgesia can be achieved by selectively targeting the sensory innervation of the knee joint. Future comparative studies are needed to evaluate the performance of the block against other modes of analgesia for knee arthroplasty.

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