The level of the sciatic nerve division and its relations to the piriform muscle

Abstract

Background. The sciatic nerve, as the terminal branch of the sacral plexus, leaves the pelvis through the greater sciatic foramen beneath the piriform muscle. Afterwards, it separates into the tibial and the common peroneal nerve, most frequently at the level of the upper angle of the popliteal fossa. Higher level of the sciatic nerve division is a relatively frequent phenomenom and it may be the cause of an incomplete block of the sciatic nerve during the popliteal block anesthesia. There is a possibility of different anatomic relations between the sciatic nerve or its terminal branches and the piriform muscle (piriformis syndrome). The aim of this research was to investigate the level of the sciatic nerve division and its relations to the piriform muscle. It was performed on 100 human fetuses (200 lower extremities) which were in various gestational periods and of various sex, using microdissection method. Characteristic cases were photographed. Results. Sciatic nerve separated into the tibial and common peroneal nerve in popliteal fossa in 72.5% of the cases (bilaterally in the 66% of the cases). In the remainder of the cases the sciatic nerve division was high (27.5% of the cases) in the posteror femoral or in the gluteal region. Sciatic nerve left the pelvis through the infrapiriform foramen in 192 lower extremities (96% of the cases), while in 8 lower extremities (4% of the cases) the variable relations between sciatic nerve and piriform muscle were detected. The common peroneal nerve penetrated the piriform muscle and left the pelvis in 5 lower extremities (2.5% of the cases) and the tibial nerve in those cases left the pelvis through the infrapiriform foramen. In 3 lower extremities (1.5% of the cases) common peroneal nerve left the pelvis through suprapiriform, and the tibial nerve through the infrapiriform foramen. The high terminal division of sciatic nerve (detected in 1/3 of the cases), must be kept in mind during the performing of popliteal block anesthesia. Conclusion. Although very rare, anatomical abnormalities of common peroneal nerve in regard to piriform muscle are still possible.Uvod. Nervus ishijadikus kao zavrsna grana krsnog zivcanog spleta napusta karlicu prolazeci kroz veliki ishijadikusni otvor ispod piriformnog misica da bi se, najcesce u nivou gornjeg ugla poplitealne jame, zavrsio podelom na tibijalni i zajednicki peroneusni zivac. Visoka podela n. ishijadikusa na tibijalni i zajednicki peroneusni zivac relativno je cesta pojava i moze biti uzrok nekompletnog bloka prilikom izvodjenja poplitealne blok anestezije. Postoji mogucnost da n. ishijadikus ili njegove zavrsne grane imaju atipicne anatomske odnose sa piriformnim misicem (piriformni sindrom). Cilj istrazivanja bio je da se ispita nivo zavrsne racve n. ishijadikusa i njegov odnos sa piriformnim misicem. Istrazivanje je sprovedeno na 100 humanih fetusa (200 donjih ekstremiteta), razlicite gestacijske starosti i pola. Primenjena je metoda mikrodisekcije i svaki slucaj je posebno analizovan i predstavljen shemom, dok su karakteristicni slucajevi fotografisani. Rezultati. N. ishijadikus se u 72,5% slucajeva zavrsio podelom na tibijalni i zajednicki peroneusni zivac u poplitealnoj jami (u 66% slucajeva obostrano). U ostalim slucajevima (27,5%) zavrsna racva n. ishijadikusa bila je visoko, u zadnjoj regiji buta ili pak u sedalnoj regiji. N. ishijadikus napusta karlicu kroz infrapiriformni prostor na 192 donja ekstremiteta (96 %), dok je na 8 donjih ekstremiteta (4 %) nadjen varijabilni odnos prema piriformnom misicu. Na pet donjih ekstremiteta (2,5%) zajednicki peroneusni zivac napusta karlicu prolazeci kroz vlakna piriformnog misica, dok tibijalni zivac prolazi kroz infrapiriformni prostor. Na tri donja ekstremiteta (1,5%) zajednicki peroneusni zivac napusta karlicu kroz suprapiriformni prostor, dok tibijalni zivac napusta karlicu kroz infrapiriformni prostor. Prilikom izvodjenja poplitealne blok anestezije treba voditi racuna o visokoj racvi n. ishijadikusa s obzirom na to da je ona evidentirana u 1/3 slucajeva. Zakljucak. Iako retke, anatomske abnormalnosti zajednickog peroneusnog zivca sa piriformnim misicem su moguce.