Pudendal nerve and cluneal nerve entrapment can cause a neuropathic pain syndrome in one, many or all of the sensitive areas innervated by these nerves [1, 2]. Diagnosing this condition can be a challenge, but the Nantes criteria can provide a diagnostic tool [1]. Several techniques for pudendal nerve neurolysis have been described in literature: open approach transperineally or transgluteally and laparoscopically [3-5]. For cluneal nerve neurolysis, an open trans gluteal approach has been proposed [2]. Recently, an anatomical study was published which described a new endoscopic minimal invasive approach for pudendal nerve and inferior cluneal nerve neurolysis (ENTRAMI) [6]. The aim of our study was to describe the feasibility of this new approach on patients and to evaluate the clinical benefits.

Study inclusion criteria:
Patients eligible for inclusion in the study had chronic perineal pain of at least 3 months duration in the area served by the pudendal and/or cluneal nerve. Patients met all 5 of the Nantes criteria for pudendal and / or cluneal nerve entrapment syndrome before surgery was proposed [1]. 

Methodology:
Local ethics approval granted (EC number:2017/78).
From May 2017 until January 2019 patients eligible for pudendal and/or cluneal nerve decompression surgery where offered the ENTRAMI technique for pudendal and/or cluneal nerve release. At all times during the procedure, conversion to the open trans gluteal technique described by R. Robert [7], was possible if necessary.  
Eligible patients gave informed consent after reading written information on the study. Finally, 15 patients, corresponding to 31 nerves, where included in the study and underwent the ENTRAMI technique. All patients were asked to fill out the SF-36 quality of life scoring questionnaire before surgery and 3 months after surgery. Maximum pain VAS (Visual Analogue Scale) score was recorded before and 3 months after surgery. At 3 months after surgery the patient was asked to score a subjective percentage of overall improvement. Operative time, number of trocars needed, perioperative blood loss, per- and postoperative complications (immediate and long term) and hospital stay were also recorded. 

Surgical procedure:
The minimal invasive trans gluteal endoscopic approach used is based on the approach  described in a cadaver study recently [6]. Patients are positioned in a prone position. The first 5mm trocar, used for the 5 mm 0° and 30° optical system, is placed in the upper lateral quadrant of the gluteal region, approximately 10 to 15 cm cranially of an imaginary horizontal line starting at the inferior border of the coccyx (Figure 1). Finger dissection allows to find a plane between the piriformis muscle and the gluteal muscles and insufflation is started through the 5 mm trocar under visual control. The 0° optical system is used to help with the gentle pneumodissection in order to be able to identify the sciatic nerve.  A second 3mm trocar is placed distally from the first trocar, at the level of the horizontal coccygeal line, to insert a 3 mm dissecting grasping forceps. The position of the third 3 mm trocar is determined case specific, depending on the dissected space and anatomy. If clunealgie is suspected, dissection of the posterior femoral cutaneous nerve at the lateral surface of the ischial tuberosity is performed. Dissection expands caudally to the fibrous arcade, which is incised if necessary. The passage through the infra piriformis tunnel can be evaluated and dissected if necessary. In case of associated pudendal neuralgia, dissection is continued medially to be able to identify the pudendal nerve fFigure 2). After clear identification of all nervous, vascular and ligamentous structures, the sacrospinous ligament is cut, and the pudendal nerve transposed as described in the open technique by Robert et all [7].

Between May 2017 and January 2019, 20 patients signed informed consent. In 5 patients, early in our learning curve, the procedure had to be converted to the open approach, mostly because of the inability to create a working space with pneumodissection. So, 15 patients, 8 females and 7 males, age between 21 and 74 years old, corresponding to 31 nerves, underwent the ENTRAMI technique and their results will be discussed.  Patients suffered an average of 5 years (range 1-13 years) before surgery was proposed. Average maximal pain VAS score declared by patients prior to surgery was 9 on a scale of 10 (range 2-10). For bilateral pudendal neurolysis, the average duration of intervention was 164 minutes (range 110 – 270 minutes), 105 minutes (range 100-110 minutes) for unilateral pudendal neurolysis, 120 minutes for bilateral pudendal and cluneal neurolysis, 100 minutes (range 50-130 minutes) for bilateral cluneal neurolysis and 130 minutes for unilateral pudendal and cluneal neurolysis. No perioperative blood loss occurred.  In 11 of 15 patients only 2 trocars were necessary to complete the procedure. There were no immediate postoperative complications, besides a minor gluteal hematoma, and 6 out of 15 patients were discharged on the first postoperative day. All patients were discharged on the second postoperative day. After 3 months, average maximal VAS score declared by patients was 5/10 (range 0-10) with an overall average subjective improvement of pain of 45 %.

The current study describes the feasibility of a new minimal invasive technique for treating patients with chronic pain. Although a learning curve is inevitable, the technique appears feasible after multiple cadaver dissection. No blood loss occurred, and no immediate postoperative complications were recorded, besides one minor gluteal hematoma. Of 20 patients, 5 had to be converted, but this was early in our learning curve, and mostly due to the inability of creating a workspace. At 3 months an average of 45% pain reduction (in terms of maximum VAS score) and subjective improvement was declared by our patients. These results are comparable with the open trans gluteal technique described by R. Robert [7].

If surgery becomes less invasive, then maybe surgery shouldn’t be just the last resort but must be offered more quickly to patients. We can conclude that this technique is feasible and that early results are promising.