Symptoms of saphenous nerve damage

The saphenous nerve (n. saphenus) is the terminal and longest branch of the femoral nerve, a derivative of the LII - LIV spinal roots. After leaving the femoral nerve at the level of the inguinal ligament or above it, it is located lateral to the femoral artery in the postero-medial part of the femoral triangle. Then it enters together with the femoral vein and artery into the adductor canal (subsartorial, or Gunter's canal), which has a triangular cross-section. Two sides of the triangle form muscles, and the roof of the canal is formed by a dense intermuscular fascia sheet, which is stretched between the vastus medialis muscle of the thigh and the adductor longus muscle in the upper part of the canal. In the lower part of the canal, this fascial sheet is attached to the adductor magnus muscle (it is called the subsartorius fascia). The sartorius muscle is adjacent to the roof of the canal from above and moves relative to it. It changes the degree of its tension and the size of the lumen for the nerve depending on the contraction of the medial vastus and adductor muscles of the thigh. Usually, before exiting the canal, the subcutaneous nerve divides into two branches - the infrapatellar and descending. The latter accompanies the long hidden vein and goes down to the shin. The nerves can penetrate the subsartorius fascia together or through separate openings. Then both nerves are located on the fascia under the sartorius muscle and then exit under the skin, spirally bending around the tendon of this muscle, and sometimes piercing it. The infrapatellar branch changes direction more sharply than the descending one. It is located along the long axis of the thigh, but in the lower third of the thigh it 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 internal capsule. The descending branch gives off branches to the skin of the inner surface of the shin and the inner edge of the foot. Of practical interest is the small branch that passes between the superficial and deep parts of the tibial (inner) collateral ligament. It can be injured (compressed) by a fallen meniscus, hypertrophied bone spurs along the edges of the joint, during surgical interventions,

Damage to the saphenous nerve occurs in individuals over 40 years of age without previous trauma. They have significant fatty deposits on the thighs and some degree of O-shaped configuration of the lower limbs (genu varum). Internal torsion (rotation around the axis) of the tibia is often associated with the syndrome of damage to this nerve. Intra-articular and periarticular changes in the knee joint are not uncommon. Therefore, these symptoms are often explained only by damage to the joint, without assuming a possible neurogenic nature of the pain. Direct trauma to the thigh with this neuropathy is rare (only in football players). Some patients have a history of damage to the knee joint, usually caused not by direct trauma, but by the transfer of a combination of angular and torsional effects to the joint. This type of injury can cause a tear of the internal meniscus at the site of its attachment or a rupture of the cartilage. Usually, when musculoskeletal disorders or joint hypermobility impede movement, a neurogenic basis for persistent pain and dysfunction is not assumed. However, such changes may be an anatomical cause of chronic trauma to the saphenous nerve.

The clinical picture of the saphenous nerve lesion depends on the combined or isolated lesion of its branches. When the infrapatellar branch is affected, the pain and possible sensory disturbances will in most cases be limited to the area of the inner part of the knee joint. When the descending branch is affected, similar symptoms will relate to the inner surface of the shin and foot. Neuropathy is characterized by increased pain when extending the limb at the knee joint. The symptom of finger compression is very important for diagnosis if, when performing it, the upper level of provocation of paresthesia or pain in the area of supply of the saphenous nerve corresponds to the point of exit of the nerve from the adductor canal. This point is located approximately 10 cm above the internal condyle of the femur. The search for this point is performed as follows. The fingertips are placed at this level on the anterior-inner part of the medial vastus muscle of the thigh and then slide backwards until they touch the edge of the sartorius muscle. The exit opening of the saphenous nerve is located at this point.

In differential diagnosis, the area of distribution of painful sensations should be taken into account. If pain (paresthesia) is felt on the inner surface of the lower limb from the knee joint down to the 1st finger, a high level of femoral nerve damage should be differentiated from neuropathy of its terminal branch - the saphenous nerve. In the first case, the pain also spreads to the anterior surface of the thigh, and a decrease or loss of the knee reflex is also possible. In the second case, the sensation of pain is usually localized no higher than the knee joint, there is no loss of the knee reflex and sensory disturbances on the anterior surface of the thigh, and the point of pain provocation with finger compression corresponds to the place where the saphenous nerve exits the canal. If painful sensations are limited to the inner part of the knee joint, neuropathy of the saphenous nerve should be differentiated from, for example, a position of the knee joint, such as inflammation of the tibial collateral ligament or acute meniscus injury. The presence of these disorders and dysfunction of the joint is easy to assume based on intense pain, tenderness of the inner surface of the knee joint and sharp pain when moving it. The final diagnosis of neuropathy of the infrapatellar branch of the saphenous nerve is facilitated by identifying the upper level of provocation of painful sensations with digital compression. This level corresponds to the site of nerve compression. Of diagnostic value is at least a temporary weakening of pain after an injection of hydrocortisone at this point, as well as the identification of sensory disorders in the skin zone of the inner surface of the knee joint.

Prepatellar neuralgia is characterized by: a history of direct trauma to the patella, usually from falling on the knees; immediate or delayed for several weeks from the moment of injury occurrence of neuralgic pain under the patella; detection by palpation of a painful point only at the level of the middle of the inner edge of the patella; inability due to increased pain to kneel, bend the lower limbs at the knee joints for a long time, climb stairs and, in some cases, walk at all; complete cessation of pain after surgical removal of the neurovascular bundle supplying the prepatellar bursae. All these symptoms are not characteristic of damage to the subcutaneous nerve.

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