Poster Number-67 - Posterior femoral cutaneous nerve neuropathy post marathon: a case report

Posterior femoral cutaneous nerve neuropathy post marathon: a case report

Purpose:

Posterior femoral cutaneous nerve (PFCN) neuropathy is an uncommon, potentially under-recognized cause of low back, buttock, perineal, and posterior and lateral thigh pain and numbness (1). Since there is overlap with the innervation of the sciatic and pudendal nerve, pathology of the PFCN is often under-diagnosed due to the more common pathologies of these other nerves (2).  Most reports of nerve injuries regarding the PFCN are caused by intramuscular injections (1), although there are also reports due to hematoma (3), tumor formation (4), prolonged cycling (4), entrapment in the facia lata (1), piriformis hypertrophy (5), operations such as an above-knee amputation from the thigh pressure cuff (6) or a posterior hip replacement (7) abnormal venous formations (8) pressure injuries against the sciatic tuberosity or the inferior margin of the gluteus maximus due to sitting on hard surfaces or falls (2) (4), and hamstring injuries due to the proximity to the origin of the hamstring muscle (9) (10). PFCN injury due to hamstring pathology have been reported, mostly due to hamstring tears as well as vaginal, pudendal and sciatic nerve surgery, childbirth, car accident, biking accident, and falls (10). However, this is the first reported case of a PFCN injury of hamstring pathology due to tendonitis caused by long-distance running.

Methods:

A 42-year-old male with no relevant past medical history developed right lower buttock pain two weeks post marathon. He is an avid runner and does not recall a discrete injury. The pain was located medial and superior to the ischia tuberosity and extended distally to the right scrotum with no testicular pain. Pain was worse with flexion of right hip. On physical examination there was no sensory changes in the skin itself and no increased pain with deep pressure. The pain progressed such that he was unable to sit down or flex his hip for over a year. The patient was able to modify his car seat to a 45-degree angle to still be able to drive.

An initial MRI showed a small amount of increased T2 signal adjacent to the ischial tuberosities at the hamstring origins bilaterally suggesting hamstring tendinitis. Consults with sports medicine and hip orthopedics provided no clear diagnosis. He failed to improve with NSAIDS, physical therapy, massage, PRP injection, two Ganglion of Impar Nerve blocks, and trial of Pregabalin. The diagnosis was confirmed with temporary relief following a PFCN block. He was then advised to have the nerve resected because of failure of non-surgical treatment. Intraoperatively, the PFCN was found to be adherent to the ischial tuberosity secondary to scar tissue in the proximity of the hamstring tendonitis, which confirmed the mechanism of the injury.

Following surgical resection of the nerve, he experienced posterior buttock numbness initially which gradually resolved over a year. He progressed in sitting tolerance and was able to return to walking and running.

Results:

The Posterior femoral cutaneous nerve (PFCN) arises from the ventral primary rami of S1, S2, and S3 of the lumbosacral plexus (11) and provides the sensory innervation for the inferolateral gluteal region, the superomedial aspect of the perineal region, the posterior aspect of the thigh, and the skin at the popliteal fossa (1).

PFCN neuropathy presentation varies, due to the level and location of the abnormality along the different branches. The Perineal Branch innervates the lateral perineum, proximal medial thigh, posterolateral aspect of the scrotum/labium majus, and a portion of the penis/clitoris (12). Neuropathy of the cluneal branches can cause clunealgia, which present as pain and paresthesia referred to the inferior lateral buttock area (13). Neuropathy to these nerves along with the other terminal branches of the PFCN are responsible for the common complaint of “pain with sitting.” (10). Neuropathy of the Cutaneous Branch typically manifests as pain and paresthesia of the skin over the inferior buttocks, posterior thigh, and popliteal region (14).

Diagnostic assessment is currently restricted to clinical findings and a diagnostic nerve block of the PFCN.  Techniques for diagnostic blocks have been reported using anatomic landmarks (14), high resolution ultrasound (1), computed tomography guidance (13), and with high-resolution magnetic resonance imaging (12). A fluoroscopic technique is difficult due to no good fluoroscopic landmarks, other than the ischium (2). The landmark recommended by Hughes to target the whole nerve is one quarter of the distance between the ischial tuberosity and the greater trochanter. To target the perineal branch, Hughes recommends directly at the ischial tuberosity (14). In contrast, Fritz recommends targeting the pathologic branches. He recommends 2 cm below the ischial tuberosity for the perineal branch, under the gluteus maximus muscle for the cluneal nerves, and between the gluteus maximus and the long head of the biceps femoris for symptoms in the posterior thigh (12). Tubbs recommends 4 cm below the ischial tuberosity for the perineal branch (16). A somatosensory-evoked potential (SSEP) evaluation of the PFCN has been used in the literature as well (15).

Initial treatment starts with conservative therapy. If this fails, selective diagnostic nerve blocks of the PFCN can be helpful to assess the location of the pathology of the nerve and to identify potential surgical targets for a surgical neurectomy (1). Cryoablation of the posterior femoral cutaneous nerve resulting in successful treatment of PFCN-mediated sitting pain has also been reported.

Conclusion:

After excluding the more common etiologies of buttock pain and sitting intolerance such as: hamstring tendinitis, sacroiliac dysfunction, gluteal myofascial syndrome, piriformis syndrome, pudendal nerve impingement, ischial stress reaction, and hip pathology, practitioners should consider the rarer condition of PFCN neuropathy in runners. 

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