Lumbosacral plexus disorders

**Definition:** The lumbar plexus is formed by the anterior primary rami of lumbar spinal nerves L1 to L4 and the sacral plexus is derived from the anterior primary rami of spinal nerves L4, L5, S1, S2, and S3. The lumbar plexus communicates with the sacral plexus via the anterior division of L4. The lumbosacral plexus can be affected by a variety of diseases like direct invasions by neoplasms (for examples from cervix, prostate, bladder, colorectum, kidney, ovary) or dysfunction due to other causes such as diabetes mellitus, vasculitis and radiation injury. It can also be idiopathic. In lumbar plexus lesions, there is weakness of hip flexion, knee extension and hip adduction. Sensation may be lost in the inguinal region, over the genitalia, the lateral, anterior and medial thigh and on the medial aspect of the lower leg; the knee jerk may be decreased or absent. In sacral plexus lesions, there is weakness of hip extensors and abductors, knee flexors, ankle plantar flexors and dorsiflexors; sensory loss is found over the posterior aspect of the thigh, the anterolateral and posterior aspect of the leg below the knee, and the dorsolateral and plantar surface of the foot. The ankle jerk is reduced or absent.