Symptoms of involvement of the subcutaneous nerve

The subcutaneous nerve (n. Saphenus) is the terminal and longest branch of the femoral nerve, derived from LII - LIV spinal roots. After moving away from the femoral nerve at the level of the inguinal ligament or above it, it is located lateral to the femoral artery in the posterior part of the femoral triangle. Further, it enters together with the femoral vein and artery into the leading canal (subarital, or Gunther's canal), which has a triangular cross-section. The two sides of the triangle form the muscles, and the roof of the canal forms a dense intermuscular fascia leaf that is stretched between the medial broad thigh muscle and the long leading muscle in the upper canal section. In the lower part of the canal, this fascial leaf is attached to the large adductor muscle (it is called the sub-tripod fascia). The tailor muscle is attached to the top of the canal and moves relative to it. It changes the degree of its tension and the magnitude of the lumen for the nerve, depending on the contraction of the medial broad and leading hip muscles. Usually, before the exit from the canal, the subcutaneous nerve is divided into two branches - podnakolennikovuyu and descending. The latter accompanies a long veiled vein and is sent down to the lower leg. Nerves can penetrate the peri-cap fascia together or through separate apertures. Further, both nerves are located on the fascia under the sartorius muscle and then go under the skin, screw-like around the tendon of this muscle, and sometimes perforating it. More dramatically changes the direction of the podnakolennikovaya branch than the descending one. It is located along the long axis of the thigh, but in the lower third of the thigh can change its direction by 100 ° and go almost perpendicular to the axis of the limb. This nerve supplies not only the skin of the medial surface of the knee joint, but also its inner capsule. From the descending branch branch off to the skin of the inner surface of the shank and the inner edge of the foot. It is of practical interest to have a small twig that passes between the superficial and deep part of the tibial (internal) collateral ligament. It can be injured (squashed) by the dropped meniscus, hypertrophied bone spurs along the edges of the joint, with surgical interventions,

The defeat of the subcutaneous nerve occurs in people over 40 years old without previous trauma. In this case, they reveal significant fat deposits on the hips and a certain degree of O-shaped configuration of the lower limbs (genu varum). With the syndrome of this nerve, internal torsion (rotation around the axis) of the tibia often combines. Numerous intra-articular and periarticular changes in the knee joint area are common. Therefore, these symptoms are often explained only by joint damage, without suggesting a possible neurogenic nature of the pain. Direct trauma to the thigh with this neuropathy is rare (only for soccer players). Some patients have a history of knee joint damage, usually caused not by direct injury, but by the transfer to the joint of a combination of angular and torsion effects. This type of injury can cause a detachment of the inner meniscus at the site of attachment or rupture of the cartilage. Usually, with the musculoskeletal disorders or hypermobility of the joint, which impedes movement, the neurogenic basis of persistent pain and impaired function is not expected. However, such changes can be an anatomical cause of chronic traumatization of the subcutaneous nerve.

The clinical picture of the lesion of the subcutaneous nerve depends on the joint or isolated lesion of its branches. When the subpalatine branch is affected, pain and possible sensitivity disorders will in most cases be limited to the area of the inner part of the knee joint. If the descending branch is affected, these symptoms will refer to the inner surface of the shin and foot. When neuropathy is characterized by increased pain when extending the limb in the knee joint. It is very important for diagnosis of the symptom of digital compression if, at its implementation, the upper level of provocation of paresthesia or pain in the zone of supply of the subcutaneous nerve corresponds to the point of nerve exit from the leading channel. This point is approximately 10 cm above the inner condyle of the thigh. Search for this point is as follows. The tips of the fingers are superimposed on this level on the anterior-inner part of the medial broad thigh muscle and then slide backward until it comes into contact with the edge of the sartorius muscle. The opening of the hypodermic nerve is at this point.

When differential diagnosis should be considered the area of distribution of pain. If the pain (paresthesia) is felt along the inner surface of the lower limb from the knee joint down to the 1st finger, it is necessary to differentiate the high level of femoral nerve damage from the neuropathy of its terminal branch - the subcutaneous nerve. In the first case, the pain also extends to the anterior surface of the thigh, and also the knee reflex may decrease or fall out. In the second case, the sensation of pain is usually localized no higher than the knee joint, there is no ablation of the knee reflex and sensitive disorders on the front surface of the thigh, and the point of provocation of pain in finger compression corresponds to the place of the exit of the subcutaneous nerve from the canal. If the pain is limited to the inner part of the knee joint, the neuropathy of the subcutaneous nerve should be distinguished from, for example, the position of the knee joint, such as inflammation of the tibial collateral ligament or acute meniscus damage. The presence of these disorders and disorders of the function of the joint is easy to assume based on intense pain, tenderness of the inner surface of the knee joint and sharp soreness with movements in it. The final diagnosis of the neuropathy of the podnakolennikovaya branch of the subcutaneous nerve is facilitated by the detection of the upper level of provocation of painful sensations in finger compression. This level corresponds to the site of compression of the nerve. Diagnostic value has at least temporary relief of pain after injection of hydrocortisone at this point, as well as the detection of sensitive disorders in the cutaneous zone of the inner surface of the knee joint.

Prepathel neuralgia is characterized by: a history of direct injury to the patella, usually when it falls to the knees; immediate or delayed for several weeks from the moment of injury the occurrence of neuralgic pain under the patella; the palpation of a painful point only at the level of the middle of the inner edge of the patella; the impossibility, due to the intensification of pain, to kneel, bend the lower limbs for a long time in the knee joints, climb up the stairs and, in some cases, generally walk; complete cessation of pain after surgical removal of the neuromuscular bundle, supplying pre-implant bags. All these symptoms are not characteristic for the defeat of the subcutaneous nerve.

[1], [2], [3], [4], [5], [6], [7], [8]