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Proximal Saphenous Neuralgia After Coronary Artery Bypass Graft

1995; Lippincott Williams & Wilkins; Volume: 80; Issue: 3 Linguagem: Inglês

10.1097/00000539-199503000-00035

1526-7598

Ray J. Défalque, Judy McDanal,

Anesthesia and Pain Management

We have seen nine patients who developed a severe saphenous neuralgia in the thigh after undergoing a venous coronary artery bypass graft (CABG). Although neuropathies of the descending branch of the saphenous nerve after CABG have been reported [1-3], this proximal neuralgia has not been described. Because of its location in the thigh, the pain was not immediately associated with a post-CABG saphenous neuropathy and its treatment was thus delayed. This has prompted us to report the syndrome. Case Reports The nine patients were Caucasian men between the ages of 52 and 78 yr. Three were physicians. Two had well controlled insulin-dependent diabetes mellitus; two others had had successful surgery for carpal tunnel syndrome. The saphenous neuralgia appeared 3 to 10 wk after the cardiac surgery. All patients had made a remarkable postoperative recovery, were highly motivated, and participated in an intensive program of rehabilitative exercises. Their surgeon and cardiologist had been unable to diagnose their puzzling thigh pain. All nine patients complained of a constant, severe, diffuse, burning, and gripping pain in the medio-inferior aspect of the thigh of the operated extremity. When severe, the pain radiated to the groin and, in five patients, caused buckling of the knee and loss of balance. This was a source of anxiety, frustration, and embarrassment to the five patients. The pain was aggravated by walking, running, swimming, stair climbing, and other flexion/extension movements of the foreleg. It was decreased by sitting or lying down but never completely disappeared. One patient, a diabetic, had nightly exacerbations which interfered with his sleep. There were small patches of cutaneous anesthesia or dysesthesia in and around the venectomy scar in the foreleg but no pain nor marked tenderness. All nine patients' venectomy scars were restricted to the foreleg and ended several inches distally to the knee joint. The most distinct and significant finding was a consistent, discrete, exquisitely tender point in the medial aspect of the thigh, situated 8-9 cm above the upper border of the medial femoral condyle in the cleft between the vastus medialis and the adductor magnus. Pressure on that point with the finger tip or the point of a pencil reproduced and exaggerated the pain and its radiation to the groin. This point corresponds to the exit site through the subsartorial fascia of the saphenous nerve from the adductor canal [4-7]. We never elicited a Tinel's sign nor a Valleix phenomenon. The diagnosis was made easily by blocking the saphenous nerve at its fascial exit. The trigger point was located with a pencil point and a skin wheal made over it. A 4-cm 25-gauge needle was introduced through the wheal and slowly advanced perpendicularly until the elastic resistance of the subsartorial fascia was felt at a depth of 2-3 cm. The fascia was then gently probed until painful paresthesiae were felt in the infrapatellar and/or descending branches of the saphenous nerve. Then 0.75% bupivacaine, 8-10 mL, with 1:200,000 epinephrine was slowly injected. The block caused 12-20 h of cutaneous anesthesia and at least 24 h of complete pain relief. The patients were not told the anticipated duration of their numbness. We thus hoped to avoid a placebo effect. No electrodiagnostic studies were done, since the block offered a faster, simpler, and cheaper alternative. All nine patients were much relieved to learn the benign nature of their condition. They were followed for at least 6 mo after their last treatment. Freedom from pain over 6 mo was called permanent relief. 1. Two patients had sufficient relief from their diagnostic block, reassurances, and the occasional use of nonsteroidal antiinflammatory drugs or of a transcutaneous electrical nerve stimulator; they refused further treatment. 2. Three patients had permanent relief after three bupivacaine blocks (0.75% bupivacaine, 10 mL, with epinephrine 1:200,000). The third block also included 40 mg methylprednisolone (Depo-Medrol Registered Trademark). 3. Two patients chose neurosurgery after two consistent diagnostic blocks. A neurectomy was done in the adductor canal. To prevent the formation of a scarentrapped neuroma, the end of the severed nerve was bathed in absolute alcohol, a tight suture (Mersilene) was placed around it, and the nerve was made to retract proximally in the canal. At surgery the nerve showed signs of inflammation at its point of fascial exit. The inflammation was confirmed by the pathologist. Both patients had cutaneous anesthesia in the medial aspect of the knee and foreleg, which they found tolerable. 4. Two patients had recurrence of their pain after three bupivacaine blocks (including a third block with methylprednisolone). The block was repeated with 3 mL of freshly prepared 6% aqueous phenol. Permanent relief was achieved with one block in one patient, and with two blocks in the other. Both had mild cutaneous hypesthesia in the foreleg. Discussion Saphenous neuralgia after venous CABG had been reported [1-3] in 15 patients. In all 15 the pain was confined to the venectomy scar in the distribution of the descending branch of the saphenous nerve in the foreleg. Although retrograde pain is common in entrapment syndromes [5,7], thigh pain has been described in only two reports on saphenous neuralgias: 32 idiopathic cases [4] and 27 cases following femoral arterioplasties [8]. The proximal location of our patients' pain delayed the diagnosis and the treatment of their neuralgia. We hope that our report will help physicians reach a speedier diagnosis and treatment. We postulate that the inelastic [4,5,7] saphenous nerve is trapped by the venectomy scar in its distal end and becomes irritated at its sharp bend in the subsartorial fascia by the repeated leg movements of a very active patient. Inflammatory changes have been described in entrapped nerves, including the saphenous [4-5]. This was confirmed in our two excised nerves. Kopell and Thompson [6] have described knee buckling in one of their patients with saphenous neuralgia, explaining it as a pain reflex. We propose that it may be due to retrograde impulses reaching the femoral nerve and interfering with the tonus of the quadriceps. In conclusion, proximal saphenous neuralgia after saphenous vein CABG is a clinical syndrome seen in patients undergoing intensive postoperative rehabilitation. Its diagnosis should be considered when thigh pain occurs after CABG surgery. Its treatment is highly satisfactory.