12/10/2022
Knowledge bomb 💣
Piriformis Syndrome: The Etiology of Piriformis Syndrome.
“Conventionally, the term “piriformis syndrome” has been used to cover entrapment of the sciatic nerve by the piriformis muscle. https://journals.lww.com/acsm-csmr/Fulltext/2015/01000/Piriformis_Syndrome__A_Cause_of_Nondiscogenic.12.aspx
But the role of the piriformis as a nondiscogenic cause of extra-pelvic sciatica that is due to impingement of the sciatic nerve through or around the piriformis muscle is still controversial. https://pubmed.ncbi.nlm.nih.gov/23684469/, https://pubmed.ncbi.nlm.nih.gov/32246173/.
Novel anatomical findings by Larionov and colleagues based on human cadaveric material describe the most prevalent medial muscle origin pattern of the piriformis with a complete covering of the anterior sacral foramen by the piriformis muscle (most frequent anatomical variation with 43% in males, 70% in females). https://pubmed.ncbi.nlm.nih.gov/36173479/
This pattern may result in the compression of the anterior branches of the sacral spinal nerves when crossing the muscle. The nerve entrapment is thus characterized by: (1) the attachment of the piriformis to the second anterior sacral foramina's medial border and (2) a complete covering and filling up of the corresponding foramen. https://pubmed.ncbi.nlm.nih.gov/36173479/ (s. figure)
In such cases, muscle trauma, hypertrophy and inflammation may -according to the authors - enhance piriformis constriction and nerve compression. The S2 root of the sacral plexus, which is the most frequently affected segment, sends the fibers to somatic and autonomic nerves of the pelvis and the leg (s. figure), including the sciatic nerve, the tibial nerve, the common fibular nerve, the pudendal nerve, the inferior and superior gluteal nerves, the femoral nerve (only partly from the sacral plexus, most from the lumbar plexus), the posterior femoral cutaneous nerves.” https://pubmed.ncbi.nlm.nih.gov/22705377/
- Francesco Rullo
🩻 Picture: Schematic drawing of topographic relationship between the piriformis and the peripheral nervous network in the pelvis.VL5- vertebra lumbalis 5; VS(1–5)- vertebrae sacralis 1–5; S(1–5) sacral segments of sacral plexus. . https://pubmed.ncbi.nlm.nih.gov/36173479/