The lumbosacral plexus corresponds to the leg nerve plexus. This plexus carries spinal nerves from the lumbar and thoracic regions of the spine and innervates the legs motor and sensory. Motor and sensory deficits exist in plexus paresis.
What is the lumbosacral plexus?
Spinal nerves are peripheral spinal cord nerves that are assigned to one side of specific spinal cord segments through their anterior and posterior roots. Between two vertebrae, spinal nerves each emerge from the spinal canal in pairs. The human organism is equipped with 31 paired spinal nerves. Individual spinal nerves are named according to spinal segment. The lumbar region and the thoracic region are such sections of the spinal column. The lumbar region contains five lumbar nerve pairs named L1 through L5. The thoracic region contains twelve thoracic nerve pairs designated Th1 through Th12. Spinal nerve branches meet in different nerve plexuses of the body. One such nerve plexus is the lumbosacral plexus. This lumbar-cruciate plexus carries the abdominal nerve branches (rami ventrales) of spinal nerves from the lumbar and thoracic segments. The lumbosacral plexus nerve plexus is occasionally subdivided by the medical literature into individual plexuses: the lumbar, pudendal, sacral, and coccygeal plexuses.
Anatomy and structure
In the lumbosacral plexus, two lower body nerve plexuses form a functional unit. The first of these plexuses is the lumbar plexus. This nerve plexus carries spinal nerves from segments L1 to L3 and also receives individual fibers from the thoracic segment Th12 and the lumbar segment L4. The second plexus of the lumbosacral plexus is the sacral plexus. This plexus in turn carries spinal nerves from segments L5 to S3 and contains isolated fibers from L4 as well as S4. From the hiatus sacralis the last spinal nerve takes its exit. This nerve corresponds to the coccygeal nerve, which, with the anterior branches of the fourth and fifth. Sacral nerve forms a third nerve plexus: the coccygeus plexus. Basically, the medical literature does not agree on which segments exactly participate in the formation of the lumbosacral plexus. More or less strong deviations occur. What is certain is that within the plexus there is an exchange of nerve fibers from different spinal cord segments. The lumbar nerves show little plexus character. The thoracic nerves show distinct cross connections.
Function and tasks
The lumbosacral plexus is a somatic nerve plexus. This type of plexus always arises from the anterior branches of the spinal nerves and is involved not only in motor but also in sensitive innervation of various structures. Sensory innervation means the delivery of sensitive nerve fibers to individual tissue areas. Stimuli can travel along the sensitive pathways from the tissues to the central nervous system. Motor innervation refers to the sending of motor nerve fibers along which commands from the central nervous system can reach the organs of success. In nerve plexuses such as the lumbosacral plexus, there is an exchange of individual nerve fibers. New nerves emerge from this exchange. The newly formed nerves each contain portions of several spinal cord segments and, in the case of the lumbosacral plexus, innervate the lower extremities, pelvis and abdominal wall. The lower plexus lumbalis uses newly formed nerves to provide motor supply, for example, to the psoas major, psoas minor and quadratus lumborum muscles. The same applies to various extensors and adductors of the thigh muscles. The newly formed sensory nerves supply the front of the thigh as well as the front and inner side of the lower leg. Thus, the lumbar plexus gives rise to the iliohypogastric, ilioinguinal, genitofemoral, cutaneus femoris lateralis, femoralis and obturatorius nerves through the exchange. After fiber exchange, the subplexus sacralis supplies the foot, lower leg, and posterior aspect of the thigh with newly formed nerves of sensitive fiber quality. The motor supply of the hip extensors, knee flexors and all lower leg as well as foot muscles is also a task of the sacral plexus. Thus, through the exchange of individual nerve fibers, the subplexus forms the superior gluteal nerve, inferior gluteal nerve, posterior cutaneus femoris, sciatic nerve and pudendal nerve, as well as the anococcygeal nerves.
Diseases
Paresis of the lumbosacral plexus is a clinical condition that can occur after damage to the leg nerve plexus. The plexus innervates almost the entire foot, lower leg, and thigh motor function. Therefore, the clinical picture after damage to the nerve plexus is characterized by motor deficits. Sensory disturbances in the area of the legs and pelvis also occur as a result of plexus damage. Which leg and foot muscles are paralyzed or limited in motor function depends on the exact localization of the damage. The cause of the plexus damage can be, for example, a trauma after violent impact. Most often these are pelvic fractures, pelvic ring fractures or acetabular fractures. A plexus lesion is usually associated with soft tissue, organ, or vascular injury. Fractures of the anterior pelvic ring or sacroiliac region can also cause plexus injury with subsequent paresis. Sacral fractures just as often result in neurologic deficits due to plexus injury. Less commonly, plexus paresis occurs as a result of surgical intervention, such as after hip replacement or vascular intervention of the abdominal aorta. Ischemic plexus lesions may also occur after renal transplantation. Birth palsies of the lumbosacral plexus are rare. More common are causative tumors such as uterine, prostate, ovarian, or renal carcinomas. Metastatic involvement of the plexus of the leg also causes paralysis. In addition to hemorrhages such as psoas hematomas, aneurysms of the great abdominal artery may also cause plexus palsy. Sacral plexus lesion additionally often occurs in the female population towards the end of pregnancy or during delivery, and in this case is usually related to positional abnormalities of the unborn child. Apart from this, inflammation in the context of idiopathic leg plexus neuritis causes paresis of the nerve plexus due to immunological factors. Diabetes may be another cause of paralysis.
