Symptoms of sciatic nerve damage

The sciatic nerve (n. ischiadicus) is a long branch of the sacral plexus, contains nerve fibers of neurons located in the spinal cord segments LIV - SIII. The sciatic nerve is formed in the pelvic cavity near the greater sciatic foramen and leaves it through the infrapiriformis foramen. In this foramen, the nerve is located more laterally; above and medially from it go the inferior gluteal artery with its accompanying veins and the inferior gluteal nerve. Medially passes the posterior cutaneous nerve of the thigh, as well as the vascular-nerve bundle, consisting of the internal gluteal artery, veins and pudendal nerve. The sciatic nerve can exit through the suprapiriformis foramen or directly through the thickness of the piriformis muscle (in 10% of individuals), and in the presence of two trunks - through both foramina. Due to this anatomical location between the piriformis muscle and the dense sacrospinous ligament, the sciatic nerve can often be subject to compression at this level.

Upon exiting through the gap under the piriformis muscle (infrapiriformis opening), the sciatic nerve is located more externally than all the nerves and vessels passing through this opening. The nerve here is located almost in the middle of the line drawn between the ischial tuberosity and the greater trochanter of the femur. Coming out from under the lower edge of the gluteus maximus, the sciatic nerve lies in the area of the gluteal fold near the broad fascia of the thigh. Below, the nerve is covered by the long head of the biceps femoris and is located between it and the adductor magnus muscle. In the middle of the thigh, the long head of the biceps femoris is located across the sciatic nerve, it is also located between the biceps femoris and the semimembranosus muscle. The division of the sciatic nerve into the tibial and common peroneal nerves most often occurs at the level of the upper angle of the popliteal fossa. However, the nerve often divides higher - in the upper third of the thigh. Sometimes the nerve even divides near the sacral plexus. In this case, both portions of the sciatic nerve pass as separate trunks, of which the tibial nerve passes through the lower part of the greater sciatic foramen (infrapiriformis foramen), and the common peroneal nerve passes through the suprapiriformis foramen, or it pierces the piriformis muscle. Sometimes, not from the sacral plexus, but from the sciatic nerve, branches extend to the quadratus femoris, gemelli, and obturator internus muscles. These branches extend either at the point where the sciatic nerve passes through the infrapiriformis foramen or higher. In the thigh, branches extend from the peroneal part of the sciatic nerve to the short head of the biceps femoris, from the tibial part to the adductor magnus, semitendinosus, and semimembranosus muscles, as well as to the long head of the biceps femoris. Branches to the last three muscles separate from the main trunk of the nerve high in the gluteal region. Therefore, even with fairly high damage to the sciatic nerve, the flexion of the limb at the knee joint is not impaired.

The semimembranosus and semitendinosus muscles flex the lower limb at the knee joint, rotating it slightly inward.

Test for determining the strength of the semimembranosus and semitendinosus muscles: the subject, lying on his stomach, is asked to bend the lower limb at an angle of 15° - 160° at the knee joint, rotating the shin inward; the examiner resists this movement and palpates the tense tendon of the muscles.

The biceps femoris flexes the lower limb at the knee joint, rotating the lower leg outward.

Tests to determine biceps femoris strength:

1. the subject, lying on his back with the lower limb bent at the knee and hip joints, is asked to bend the limb at the knee joint at a sharper angle; the examiner resists this movement;
2. The subject, lying on his stomach, is asked to bend his lower limb at the knee joint, rotating it slightly outward; the examiner resists this movement and palpates the contracted muscle and tense tendon.

In addition, the sciatic nerve innervates all the muscles of the leg and foot with branches that extend from the trunks of the tibial and peroneal nerves. From the sciatic nerve and its branches, branches extend to the bags of all the joints of the lower extremities, including the hip. From the tibial and peroneal nerves, branches extend that provide sensitivity to the skin of the foot and most of the leg, except for its inner surface. Sometimes the posterior cutaneous nerve of the thigh descends to the lower third of the leg, and then it overlaps the innervation zone of the tibial nerve on the back surface of this leg.

The common trunk of the sciatic nerve can be affected by wounds, trauma with a fracture of the pelvic bones, inflammatory processes in the pelvic floor and buttocks. However, most often this nerve suffers from the mechanism of tunnel syndrome when the piriformis muscle is involved in the pathological process.

The mechanisms of the development of piriformis syndrome are complex. The altered piriformis muscle can compress not only the sciatic nerve, but also other branches of SII-IV. It should also be taken into account that between the piriformis muscle and the trunk of the sciatic nerve there is a vascular plexus, which belongs to the system of the inferior gluteal vessels. When it is compressed, venous congestion and passive hyperemia of the sheaths of the trunk of the sciatic nerve occur.

Piriformis syndrome can be primary, caused by pathological changes in the muscle itself, and secondary, caused by its spasm or external compression. This syndrome often occurs after an injury to the sacroiliac or gluteal region with subsequent formation of adhesions between the piriformis muscle and the sciatic nerve, as well as with ossifying myositis. Secondary piriformis syndrome can occur with diseases of the sacroiliac joint. This muscle reflexively spasms with spondylogenic damage to the roots of spinal nerves. It is the reflex effects on muscle tone that can occur with a focus of irritation of nerve fibers remote from the muscle.

The presence of a spasm of the piriformis muscle in discogenic radiculitis is confirmed by the effect of novocaine blockades of this muscle. After an injection of 0.5% novocaine solution (20-30 ml), the pain stops or significantly weakens for several hours. This is due to a temporary decrease in spasticity of the piriformis muscle and its pressure on the sciatic nerve. The piriformis muscle is involved in external rotation of the thigh with the lower limb extended at the hip joint, and in hip abduction with its flexion.

When walking, this muscle is strained with each step. The sciatic nerve, whose mobility is limited, receives frequent jolts during walking when the piriformis muscle contracts. With each jolt, the nerve fibers are irritated, their excitability increases. Such patients are often in a forced position with their lower limbs bent at the hip joint. In this case, a compensatory lumbar lordosis occurs and the nerve is stretched over the sciatic notch. To compensate for the insufficient stabilization of the lumbar spine, the iliopsoas and piriformis muscles go into a state of increased tonic tension. This can also be the basis for the development of piriformis syndrome. The sciatic nerve at the point where it exits the small pelvis through a relatively narrow infrapiriform opening is subject to fairly strong mechanical effects.

The clinical picture of piriformis syndrome consists of symptoms of damage to the piriformis muscle itself and the sciatic nerve. The first group of symptoms includes:

1. pain on palpation of the upper inner part of the greater trochanter of the femur (the site of muscle attachment);
2. palpatory pain in the lower part of the sacroiliac joint (projection of the attachment site of the piriformis muscle to the capsule of this joint);
3. passive adduction of the hip with its inward rotation, causing pain in the gluteal region, less often in the innervation zone of the sciatic nerve in the leg (Bonnet's symptom);
4. pain when palpating the buttocks at the point where the sciatic nerve emerges from under the piriformis muscle. The latter symptom is caused to a greater extent by palpation of the altered piriformis muscle than of the sciatic nerve.

The second group includes symptoms of compression of the sciatic nerve and blood vessels. Painful sensations during compression of the sciatic nerve by the piriformis muscle have their own characteristics. Patients complain of a feeling of heaviness in the lower limb or a dull, aching pain. At the same time, compression of the spinal roots is characterized by a stabbing, shooting pain with its spread in the area of a certain dermatome. The pain intensifies when coughing and sneezing.

The nature of the loss of sensitivity helps to differentiate between lesions of the lumbosacral spinal roots of the sciatic nerve. With sciatic neuropathy, there is a decrease in sensitivity on the skin of the shin and foot. With a herniated disc involving the LV - SI-II roots, there is lampaceous hypoesthesia. True dermatomes LV - SI extend to the entire lower limb and gluteal region. With sciatic neuropathy, the zone of decreased sensitivity does not rise above the knee joint. Movement disorders can also be informative. Compression radiculopathy often causes atrophy of the gluteal muscles, which usually does not happen with damage to the sciatic nerve.

With a combination of discogenic lumbosacral radiculitis and piriformis syndrome, vegetative disorders are also observed. In most cases, a decrease in skin temperature and oscillographic index are detected on the affected side, which increase after injection of novocaine (0.5% solution, 20 ml) into the piriformis muscle. However, these angiospastic phenomena are difficult to explain by sciatic neuropathy alone. Constrictor effects on the vessels of the extremities can come not only from the compressed and ischemic trunk of the sciatic nerve, but also from nerve roots that are subject to similar irritation. When novocaine is injected into the nerve area, its blockade interrupts vasoconstrictor impulses coming from higher parts of the nervous system.

When the sciatic nerve is damaged at the hip level (below the exit from the small pelvis and up to the level of division into the peroneal and tibial nerves), flexion of the lower limb at the knee joint is impaired due to paresis of the semitendinosus, semimembranosus and biceps femoris muscles. The lower limb is extended at the knee joint due to the antagonistic action of the quadriceps femoris. The gait of such patients acquires a special characteristic - the straightened lower limb is carried forward like a stilt. Active movements in the foot and toes are absent. The foot and toes droop moderately. With gross anatomical damage to the nerve, atrophy of the paralyzed muscles occurs after 2-3 weeks.

A constant sign of sciatic nerve damage is sensory disturbances on the posterolateral surface of the shin, the dorsum of the foot, the toes and the sole. Muscle-articular sensation in the ankle joint and interphalangeal joints of the fingers is lost. Vibration sensation is absent on the lateral malleolus. Painfulness of palpation along the sciatic nerve (at Balle points) is characteristic - on the buttock in the middle between the ischial tuberosity and the greater trochanter, in the popliteal fossa, etc. Lasegue's symptom is of great diagnostic importance - pain in the first phase of its examination. Achilles and plantar reflexes disappear.

In case of incomplete damage to the sciatic nerve, the pain is causalgic in nature, there are sharp vasomotor and trophic disorders. The pain is burning and intensifies when lowering the lower limb. Mild tactile irritation (touching the shin and foot with a blanket) can cause an attack of increased excruciating pain. The foot becomes cyanotic, cold to the touch (at the onset of the disease, the skin temperature on the shin and foot may increase, but subsequently the skin temperature drops sharply compared to the temperature on the healthy side). This is clearly visible when examining the lower limbs. Hyperkeratosis, anhidrosis (or hyperhidrosis), hypotrichosis, changes in the shape, color and growth of the nails are often observed on the plantar surface. Sometimes trophic ulcers may occur on the heel, outer edge of the foot, dorsum of the toes. X-rays reveal osteoporosis and decalcification of the bones of the foot. The muscles of the foot atrophy.

Such patients experience difficulty when trying to stand on their toes and heels, tap their feet to the beat of music, lift their heels, resting their feet on their toes, etc.

Much more often in clinical practice, damage is observed not to the sciatic nerve trunk itself, but to its distal branches - the peroneal and tibial nerves.

The sciatic nerve divides slightly above the popliteal fossa into the tibial and peroneal nerves.

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