Robert J. Spinner and Robert L. Tiel

Case Presentation

A 48-year-old male train conductor presented with a 2- to 3-year history of insidious pain in his left ankle. It was a shooting pain that radiated to the medial heel and was worse with movement of the ankle. His past medical history revealed cardiac bypass surgery with left saphenous vein harvesting 6 years earlier. He had not received adequate relief from a regimen of pain medicines, and had had no benefit from steroid injections into the ankle joint and a transcutaneous electrical nerve stimulation (TENS) unit.

Examination revealed normal motor strength, sensation, and reflexes in the lower extremity. Pain was localized just anterior to the medial malleolus, just distal to the termination of the incision on his left ankle, which had been used for harvesting his saphenous vein. Pressure there elicited and reproduced the pain. A rope-like thickening of the nerve could be appreciated.

A diagnostic block performed with 3 mL of 0.5% Marcaine (AstraZeneca Pharmaceuticals LP, Wilmington, DE) provided complete resolution of the symptoms. Surgery was offered in view of the positive nerve block and the patient’ s failure of nonoperative therapy.

The distal extent of the preexisting incision was opened and extended distally over the dorsum of the foot. A distal saphenous neuroma was identified and resected over a 6 cm length. The proximal fascicles were coagulated and allowed to retract under the subcutaneous tissue. The relocation of the neuroma away from the ankle joint minimized the potential irritation with ankle movement.

Postoperatively, he had no pain with ankle movement and experienced complete resolution of the shooting pain across the ankle. He was discharged from the clinic.

Diagnosis

Distal saphenous neuroma

Anatomy

The saphenous nerve is the largest and the longest sensory branch of the femoral nerve. The saphenous nerve arises at the level of the femoral triangle, near the inguinal ligament where the femoral nerve divides into its terminal branches in the proximal anterolateral thigh. It courses obliquely to run along the medial thigh and heads toward the adductor canal, where it passes under the sartorius muscle (Hunter canal; subsartorial canal) along with the femoral artery and vein. It exits the canal by penetrating a thick fascia, the subsartorial fascia, near a branch of the descending geniculate artery, and enters the subcutaneous tissues. The saphenous nerve runs distally beneath the sartorius where it divides into terminal branches, the infrapatellar and descending branches. The infrapatellar branch curves sharply and innervates the medial aspect of the knee joint and the overlying skin. The descending branch travels distally down the leg next to the greater saphenous vein and supplies the medial leg, medial ankle region, and a variable portion of the medial foot.

Characteristic Clinical Presentation

Patients with saphenous nerve injury commonly present with medial knee or leg pain. Symptoms are often exacerbated with walking, especially up stairs, or when standing with the knee fully extended. Rest often alleviates complaints.

Most commonly, branches of the nerve are injured following surgery or trauma anywhere along its course. Specifically, iatrogenic injury of the saphenous nerve in the groin or thigh can occur following femoral arteriography. Injury of the descending branch may follow vein stripping, vein harvesting for arterial repair, or ankle arthroscopy. Injury of the infrapatellar branch is becoming more widely recognized following orthopedic procedures, including knee arthroscopy, arthrotomy, ligament reconstruction, medial meniscal repair, or knee arthroplasty.

Occasionally, the saphenous nerve may also be directly traumatized such as occurs in contact sports (e.g., soccer or rugby). Rare cases of spontaneous saphenous nerve compression have been described within the adductor canal. In addition, the nerve may be compressed where it penetrates the subsartorial fascia by strong contraction of the surrounding musculature, such as may occur with knee extensions or squats. The nerve may also be compressed associated with pes anserine bursitis. Rarely, a mass lesion may involve the nerve (nerve sheath tumor) or compress the nerve (e.g., lipoma) resulting in nerve injury or even resection.

Findings include sensory abnormality in the distribution of the saphenous nerve innervation. The motor examination is normal. Localized point tenderness commonly occurs near a previous incision or, rarely, in the distal thigh, near the nerve’s emergence from the Hunter canal. Percussion over the site of nerve injury reproduces symptoms.

Differential Diagnosis

Saphenous nerve injury is often misdiagnosed as a musculoskeletal or peripheral vascular disorder, and rarely a radiculopathy, based on the symptoms alone. In the foot and ankle region, neuromas of other sensory nerves must be distinguished.

Diagnostic Tests

Electrodiagnostic Studies

Nerve conduction studies are not widely utilized for saphenous nerve injury. Sensory nerve action potentials can be obtained by stimulating over the medial aspect of the forefoot and recording over the medial knee or anteromedial thigh.

Imaging Studies

Patients often arrive with extensive imaging studies, but typically these do not add to the diagnostic evaluation. MRI is the imaging modality of choice if a soft tissue mass lesion is suspected.

Nerve Blocks

The diagnosis can be confirmed by blocking the nerve at its point of maximal irritation. We prefer doing this using a saline block control followed by 1% lidocaine. Alternatively or sequentially, more proximal field blocks may be performed. Blocks also serve the dual purpose of allowing the patient to know what deficit to expect after neurectomy surgery.

Management Options

Nonoperative treatment consists of rest, avoidance of exacerbating activities/positions, pain management with non-narcotic medications (e.g., amitriptyline, carbamazepine, phenytoin, gabapentin, pregabalin, etc.), and local steroid injection.

If this fails, operative intervention may be necessary. For neuromas, we prefer performing a neurectomy along with the attached scar, rather than neurolysis. The proximal stump should retract into a normal bed away from scar tissue, and when possible under the cover of muscle. Some surgeons attempt to repair or reconstruct the nerve. Neurolysis, division of the subsartorial fascia, and partial release of the sartorius tendon may be indicated for the rare case of entrapment.

Outcome and Prognosis

Often nonoperative approach is sufficient for pain control. Neurectomy, when performed prudently, can be an extremely gratifying procedure. A small percentage of patients may require a revision neurectomy.

Conclusions

The saphenous nerve may be injured anywhere along its course, but injury to it must be suspected in patients with localized pain, especially after vascular procedures or knee surgery.