The ischiatic region: normal and MRI anatomy.

AIM: The aim of this study was to describe the anatomy correlated to the normal magnetic resonance imaging (MRI) images of the proximal thigh region and the ischial tuberosity.
METHODS: MRI coronal and axial sequences were obtained from 20 asymptomatic volunteers (10 male and 10 female) aged 20 to 38 years (mean age: 28 years), and then they were compared with 2 anatomical dissections and 7 cryosections of 6 cadaver thighs.
RESULTS: The anatomical specimens were directly correlated with MRI scans. From the comparison it could be seen how the axial MRI sequences well outlined the sciatic nerve, usually observed oval in shape with moderate signal intensity, and thus easily detectable from other surrounding organs. Other structures were also identified by axial images: the ischial tuberosity, the proximal origin of the hamstring muscles arising from the ischium and the related bursae, the gluteus maximus and its bursa, the quadratus femoris and its inconstant bursa, a triangular adipose body and vessels. Coronal scans also showed well the hamstring muscles, both in length and thickness.
CONCLUSIONS: Both MRI images and cadaver dissections showed the ischial tuberosity as an interesting intersection area that could be delimited as follows: on the dorsal border the gluteus maximus and its bursa, on the dorso-medial side the hamstring muscle origin, and on the antero-lateral side the quadratus femoris muscle with its inconstant bursa and the ischial tuberosity. These anatomical and MRI descriptions are very useful to give a contribution to the right explanation of sciatic symptoms caused by those sports specifically overloading the hamstring muscles. Frequently, in fact, in these athletes a sciatic syndrome arise drawing the physician's attention to the lumbosacral joint or to the sciatic nerve course near the piriformis muscle. Another very important site where the sciatic symptoms can rise, indeed, could also be found in the hamstring muscle region, where the nerve run under the gluteus maximus beside the ischiatic bone. Athletes who manifest notorious muscle overload in this anatomical region usually show sciatic pain symptoms that are not to be related with pathologies of the lumbosacral junction nor to relationships of the sciatic nerve with the piriformis muscle but rather to relationships that this nerve acquires with either gluteal muscles as well as with muscles of the underneath ischiatic region.