Anococcygeal Nerve and Sitting Pain: Differential Diagnosis and Treatment Results

The plastic surgeon is often asked to reconstruct the sacral area related to pilonidal cysts or a tumor, or after other surgery, such as coccygectomy. When sitting pain is not due to the pudendal or posterior femoral cutaneous nerve injury, the anococcygeal nerve (ACN) must be considered. Clinically, its anatomy is not well known. Rather than consider coccygectomy when the traditional nonoperative treatment of coccydynia fails, resection of the ACN might be considered.

A review of traditional anatomy textbooks was used to establish classical thoughts about the ACN. A retrospective cohort of patients with sitting pain related to the coccyx was examined, and those operated on, by resecting the ACN, were examined for clinicopathologic correlations.

When the ACN is described in anatomy textbooks, it is with varying distributions of innervated skin territory and nerve root composition. Most include an origin from sacral 5 and coccygeal 1 ventral roots. Most agree that the ACN forms on the ventral side of the sacrum/coccyx, alongside the coccygeus muscle, to emerge laterally and travel dorsally to innervate skin over the coccyx and lower sacrum. A review of 13 patients with sitting pain due to the ACN, from 2015 to 2019, demonstrated a mean age of 54.6 years. Eleven were female. The etiologies of ACN injury were falls (9), exercise (3), and complication from surgery (1). Six of the 9 patients who had surgery were able to be followed up with a mean length of 36.3 months (range, 11-63 months). Overall, 3 had an excellent result, 2 had a good result, and 1 was not improved. The one with a failed result showed improvement with coccygectomy.

The ACN must be included in the differential diagnosis of sitting pain. It is most often injured by a fall. The ACN can be evaluated with a diagnostic nerve block, can be identified at surgery, and can be resected, and its proximal end can be implanted into the coccygeus muscle. This surgery may prove an alternative to coccygectomy.