A 15-year-old girl is brought to the hospital due to sudden onset of severe left leg pain. She was practicing for an upcoming gymnastics competition when she felt a popping sensation after landing from a jump and developed anterior left leg pain. Following the injury, the patient was unable to bear weight on the leg. Physical examination shows swelling of the left knee with focal tenderness just above the patella. She is unable to raise the left leg against gravity while in the supine position. Imaging confirms a complete tear of the quadriceps tendon, but no fractures are identified. Surgical repair is planned. Lidocaine injection near which of the following sites is most likely to provide adequate anesthesia for the procedure?

Question

A 15-year-old girl is brought to the hospital due to sudden onset of severe left leg pain.  She was practicing for an upcoming gymnastics competition when she felt a popping sensation after landing from a jump and developed anterior left leg pain.  Following the injury, the patient was unable to bear weight on the leg.  Physical examination shows swelling of the left knee with focal tenderness just above the patella.  She is unable to raise the left leg against gravity while in the supine position.  Imaging confirms a complete tear of the quadriceps tendon, but no fractures are identified.  Surgical repair is planned.  Lidocaine injection near which of the following sites is most likely to provide adequate anesthesia for the procedure?

Quizplus · Accepted Answer

11ec160b_3593_740f_9249_79a6984b7596_MD0001_00 The femoral nerve (L2-L4) innervates the quadriceps muscles (enabling extension at the knee and flexion at the hip) and provides sensation for the arch of the foot, shin, and anteromedial thigh. The nerve emerges between the psoas and iliacus muscles and passes under the inguinal ligament (lateral to the femoral artery) into the thigh before branching in the femoral triangle into an anterior and posterior division. The optimal site for a femoral nerve block is right below the inguinal ligament (ie, in the inguinal crease) at the lateral border of the femoral artery. Injecting at this site anesthetizes the skin and muscles of the anterior thigh, femur, and knee and can be used during repair of the quadriceps tendon. The block also anesthetizes structures supplied by the saphenous nerve (ie, the terminal extension of the femoral nerve) to decrease sensation in the medial leg below the knee. (Choices A and D) The saphenous nerve (a branch of the femoral nerve that supplies sensation to the leg) can be anesthetized directly at the level of the adductor canal in the thigh (ie, adductor canal block) or at the medial tibial condyle in the knee (ie, saphenous nerve block). However, the branches of the femoral nerve that supply the knee arise proximal to the saphenous nerve and would not be anesthetized by injection at these locations. (Choice C) The ischial spine divides the greater and lesser sciatic foramina in the bony pelvis. The ischial spine tip is a landmark for pudendal nerve block, which is used for anesthesia during vaginal deliveries and for minor surgeries of the vagina and perineum. (Choice E) The obturator canal is a small gap in the obturator membrane (ie, the fibrous sheet covering the obturator foramen) that allows the obturator artery, obturator vein, and obturator nerve to travel from the pelvis to the thigh. An obturator nerve block would anesthetize the adductor muscles of the thigh and the skin of the medial aspect of the thigh but would not affect the quadriceps muscles or sensation to the knee. Educational objective: A femoral nerve block below the inguinal ligament (ie, in the inguinal crease) will anesthetize the skin and muscles of the anterior thigh, femur, and knee. This type of block can be used in patients requiring tendon repair after a knee injury (eg, quadriceps rupture). __________ References: Anatomical landmarks for femoral nerve block: a comparison of four needle insertion sites. (http://www.ncbi.nlm.nih.gov/pubmed/10589630)

A 15-Year-Old Girl Is Brought to the Hospital Due to Sudden