Variations in the high division of the sciatic nerve and relationship between the sciatic nerve and the piriformis.

OBJECTIVE: The sciatic nerve (SN) separates into its branches, the tibial and common fibular nerves, outside the pelvis. However, it may rarely be separated within the pelvis. In such cases, the tibial nerve and the common fibular nerve may leave the pelvis through different routes. These variations may cause nerve compressions under other anatomic structures, resulting in non-discogenic sciatica. The aim of this study was to define the level of the SN exit and of the SN division.

MATERIAL AND METHOD: 50 gluteal regions were examined in 25 formalin-fixed adult male cadavers.

RESULTS: In 52% of the cases, the SN exited the pelvis as a whole nerve without any division, whereas in 48% a high division was observed. Branches of the SN left the pelvis through the infrapiriform foramen (IP) as two separate nerves In 24%. One branch of the SN left the pelvis through the IP and other through a different route in another 24%.

CONCLUSION: The differences in the exit routes of these two nerves are important in clarifying the clinical etiology of nondiscogenic sciatica. These variations require reviewing the piriformis syndrome.