A syndrome of burning pain (causalgia) and associated symptoms (causalgia) may follow incomplete lesions of the ulnar nerve (or other major nerves of the limbs) and is described further on.
The twelfth thoracic, first to fifth lumbar, and first, second, and third sacral spinal nerve roots compose the lumbosacral plexuses and innervate the muscles of the lower extremities (Fig. 43-6 and Table 43-1). The following are the common plexus and crural nerve palsies.
Extending as it does from the upper lumbar area to the lower sacrum and passing near several lower abdominal and pelvic organs, this plexus is subject to a number of special injuries and diseases. The cause may be difficult to ascertain because the primary disease is often not within reach of the palpating fingers, either from the abdominal side or through the anus and vagina; even refined radiologic techniques may not reveal it. Diagnosis involves exclusion of spinal root (cauda equina) lesions by EMG, examination of CSF if root disease is likely, and MRI of the plexus. The clinical findings help to focus studies on the appropriate part of the lumbosacral plexus.
The main effects of upper lumbar plexus lesions are weakness of flexion and adduction of the thigh and extension of the leg, with sensory loss over the anterior thigh and leg; these effects must be distinguished from the symptoms and signs of femoral neuropathy (see later). Lower plexus lesions weaken the posterior thigh, leg, and foot muscles and abolish sensation over the first and second sacral segments (sometimes the lower sacral segments also). Lesions of the entire plexus, which occur infrequently, cause weakness or paralysis of all leg muscles with atrophy, areflexia, and anesthesia from the toes to the perianal region and autonomic loss with warm, dry skin.
The types of lesions that involve the lumbosacral plexus are rather different from those affecting the brachial plexus. Cancer, diabetes, and an idiopathic variety have dominated our material. Trauma is a rarity except with massive pelvic, spinal, and abdominal injuries because the plexus is so well protected. Occasionally, a pelvic fracture will damage the sciatic nerve as it issues from the plexus. In contrast, some part of the plexus may be damaged during surgical procedures on abdominal and pelvic organs, often for reasons that may not be entirely clear. For example, hysterectomy has on a number of occasions led to neurologic consultation in our hospitals because of numbness and weakness of the anterior thigh. Either the cords of the upper part of the plexus or the femoral nerve were compressed by retraction against the psoas muscle, or in vaginal hysterectomy (when thighs are flexed, abducted, and externally rotated) the femoral nerve was compressed against the inguinal ligament. A similar injury may be associated with vaginal delivery (see further on). Lumbar sympathectomy has also been associated with upper plexus lesions, of which the most disabling sequelae are burning pain and hypersensitivity of the anterior thigh. Appendectomy, pelvic explorations, and hernial repair may injure branches of the upper plexus (ilioinguinal, iliohypogastric, and genitofemoral nerves), with severe pain and slight sensory loss in the distribution of one of these nerves. The pain may last for months or a year or more.