Sacral Plexus: Structure, Function & Diseases

The sacral plexus is the term used to describe the sacral nerve plexus. It is considered the strongest nerve plexus of the organism.

What is the sacral plexus?

Sacral plexus is the name for the strongest nerve plexus within the human body. It is located on the posterior surface of the lesser pelvis. In medicine, it is also called sacral plexus or sacral plexus. The sacral plexus is formed by the anterior branches of the nerve roots belonging to the spinal cord segments L5 to S3. Furthermore, parts of L4 and S4 are present. Together with the lumbar plexus (plexus of lumbar nerves), the sacral plexus forms the nerves of the legs and pelvis. Often, the sacral plexus and lumbar plexus are combined as the lumbosacral plexus.

Anatomy and structure

The sacral plexus is located at the foramina sacralia of the sacrum (Os sacrum). Here, the nerves take their course through the large ischial hole (foramen ischiadicum majus). While the superior gluteal nerve passes through the suprapiriform foramen, the other nerves pass through the infrapiriform foramen. Ventromedial to the sacral plexus are the rectum, the internal iliac vein, and the internal iliac artery. The sacral plexus is subdivided into five main branches. These are the superior gluteal nerve, the inferior gluteal nerve, the posterior cutaneous femoral nerve, the sciatic nerve and the pudendal nerve. The superior gluteal nerve arises from segments L5 through S1. Its functions include motor supply to the tensor fasciae latae muscle (hamstring tensor), the gluteus minimus muscle (small gluteus muscle), and the gluteus medius muscle (middle gluteus muscle). The spinal cord segments L5 to S2 are the origin of the inferior gluteal nerve, from which motor fibers are sent toward the gluteus maximus muscle (large gluteus muscle). The posterior cutaneous femoral nerve originates in segments S1 to S3. It is responsible for sensory supply to the posterior aspect of the thigh and the lower portion of the gluteal region. The strongest and longest peripheral nerve of the sacral plexus and at the same time of the human body is the sciatic nerve, which reaches a diameter of about 1.5 centimeters. It arises from the segments L4 to S3. It supplies all the femoral flexors, all the muscles of the lower leg and foot, and the skin of the lower leg and foot. Another important nerve of the sacral plexus is the pudendal nerve, whose insertion is in segments S1 to S4. From its motor parts, the pelvic floor is supplied, while the sensitive nerve fibers innervate the anal region as well as the external genital organs. An additional branch of the sacral plexus is the musculi obturatorii interni nerve. It provides innervation to the internal hip aperture muscle (Musculus obturator internus).

Function and Tasks

The functions of the sacral plexus include motor supply to the ischiocrural muscles (thigh flexors), gluteal muscles (gluteal muscles), and posterior thigh muscles. Likewise, the foot and lower leg are part of its supply area. In addition, the sacral plexus sends sensitive fibers toward the foot, lower leg, posterior thigh, and anal skin. Within Alcock’s canal, the pudendal nerve gives off a multitude of branches toward the pelvic floor and perineum, which are responsible for innervation of the external sphincter ani muscle and the anal skin. Its terminal branch attends to the sensitive supply of the male penis and female clitoris, respectively.

Diseases

Various complaints and diseases can occur at the different components of the sacral plexus. The sciatic nerve is frequently affected, as it forms the largest nerve of the plexus. In most cases, affected individuals suffer from paralysis caused by dislocations of the sacroiliac joint, as well as fractures of the thigh or pelvis. One of the most common diseases of the sciatic nerve is sciatica, also known as sciatica. In its course, typical sciatic pain occurs due to the stretching of the nerve when bending the hip or stretching the knee. Sciatica can usually be diagnosed using the special Lasegue test.The patient lies on his back and stretches his legs while his feet remain in a neutral position. If the patient then lifts his leg passively, pain is felt in the affected area. The sciatic nerve can also be affected by herniated discs, which also cause sciatica. Health impairments are also possible at the pudendal nerve, another important component of the sacral plexus. First and foremost, this includes pudendal neuralgia, which is most common in women. Due to mechanical causes, the pudendal nerve becomes constricted. A possible reason is the exertion of pressure on the perineal region while cycling. Other causes can be pelvic injuries, fractures, vascular diseases of the pelvis, diabetes mellitus, tumors or a severe birth process. In this case, the pain manifests itself as burning, stabbing, pressing or dull. Furthermore, pudendal neuralgia poses a risk of incontinence. If the superior gluteal nerve fails, this results in a loss of function of the gluteus minimus and gluteus medius muscles, which in turn causes two hip adductors to fail. In this case, physicians speak of a Duchenne limp. In most cases, a weakness of the gluteal muscles or malpositions of the hip joint are responsible. Damage to the inferior gluteal nerve threatens to impair the function of the gluteus maximus muscle. This affects external rotation and extension of the thigh.