Entrapment of the posterior femoral cutaneous nerve and its inferior cluneal branches: anatomical basis of surgery for inferior cluneal neuralgia.

PURPOSE: The apparent failure of pudendal nerve surgery in some patients has led us to suggest the possibility of entrapment of other adjacent nerve structures, leading to the concept of inferior cluneal neuralgia. Via its numerous collateral branches, the posterior femoral cutaneous nerve innervates a very extensive territory including the posterior surface of the thigh, the infragluteal fold, the skin over the ischial tuberosity, but also the lateral anal region, scrotum or labium majus via its perineal branch. METHODS: We described the pathophysiological features of cluneal neuralgia, the surgical technique and our preliminary results. RESULTS: We performed a transmuscular approach leading to the fat of the deep gluteal region. Exploration was continued cranially underneath the piriformis, looking for potential entrapments affecting the posterior femoral cutaneous nerve and the sciatic nerve. Nerve decompression on the lateral surface of the ischial tuberosity was then performed. A constant anatomical finding must be highlighted: the presence of a lateral fibrous expansion from the ischium passing behind the nerves and vessels, especially the posterior femoral cutaneous nerve and its perineal branches. In our patients, release of this expansion allowed decompression of the nerve trapped by this expansion. CONCLUSION: Cluneal neuralgia constitutes a distinct entity of perineal pain, which must be identified and distinguished from pudendal neuralgia. Surgery should be performed via a transgluteal approach. A lateral ischial obstacle must be investigated, in the form of a constant fibrous expansion, which, like a retinaculum, can cause nerve entrapment.