Saphenous neuropathy or saphenous nerve entrapment can be the result of nerve compression or traction injury of the saphenous nerve a pure sensory nerve terminal branch and the longest cutaneous branch from the femoral nerve that supplies the medial thigh, lower leg and foot 1-3.
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Epidemiology
Saphenous neuropathy is quite frequent and can be associated with surgery 4.
Diagnosis
The diagnosis can be made on clinical grounds and might be confirmed with electrodiagnostic tests like nerve conduction studies 1. Differential diagnoses as femoral neuropathy or radiculopathy should be ruled out. Imaging studies such as ultrasound might help to identify the location of the entrapment and provide clues about the etiology 2.
Clinical presentation
Clinical symptoms include pain and paresthesia along the medial aspect of the leg, medial foot and great toe 1,2.
Sometimes a positive Tinel sign at the entrapment site might be elicited or a neuroma might be palpated 1. Since it is a pure sensory nerve it should not cause any weakness 1.
Pathology
The nerve can be injured at several levels as a result of direct traumatic injury, chronic compression or traction injury 1,4.
Etiology
Common causes of saphenous neuropathy include the following 1-5:
- traumatic injury in the adductor canal or degloving injury of the knee
- stretching injury due to posterolateral instability
- space-occupying lesions
- knee orthosis
- iatrogenic injury
- knee surgery such as meniscectomy, tendon graft harvest or knee arthroplasty
- knee arthroscopy
- varicose vein stripping
- saphenous vein harvest
- ankle arthroscopy
Location
Locations of saphenous nerve injury or entrapment include the following 4:
- adductor canal
- anteromedial knee joint
- lower leg contusion
Radiographic features
Ultrasound
In the thigh, the saphenous nerve travels with the femoral vessels in the adductor tunnel beneath the sartorius muscle to the knee and travels further together with the saphenous vein down the lower leg to the foot 3-5.
Similar to other neuropathies the saphenous nerve might be thickened and hypoechoic with loss of its normal fascicular pattern 3. Local compression with the ultrasound probe might reproduce pain 5. Comparison with the contralateral side might be helpful in the case of suspected pathology 3.
MRI
MRI might visualize compression or displacement of the saphenous nerve due to space-occupying lesions 1. The saphenous nerve is purely sensory and therefore there will not be any denervation changes 1.
Radiology report
The radiology report should include a description of the following:
- abnormal appearance of the saphenous nerve and location
- neuroma formation
- space-occupying lesions compressing the nerve
- knee instability
Treatment and prognosis
Management includes conservative measures including physiotherapy, local anesthetics, anti-inflammatory non-steroidal drugs. Surgery might be required for the removal of space-occupying lesions and involves decompression and neurolysis.
Differential diagnosis
The differential diagnosis of superficial sural nerve entrapment includes 1,2:
- femoral neuropathy
- lumbar plexopathy
- L4 radiculopathy
- peripheral nerve sheath tumor
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