 So in this video we are looking at the surface anatomy of the sciatic nerve using modern imaging techniques. Michael, what do you know about the sciatic nerve? The sciatic nerve is the largest and longest nerve in the body. It can be up to two centimetres in diameter. It originates from a lumbosacral plexus at L4 to S3, exiting the pelvis through the greater sciatic frame just below periformis muscle. The sciatic nerve innervates all the muscles in the posterior thigh and also all the muscles below the knee. So Tom, what do you know about the surface anatomy of the sciatic nerve? Through reading the textbooks we have found that there are some discrepancies with the surface anatomy of the sciatic nerve. Some of the textbooks state that the surface marking of the sciatic nerve is a midway point from the posterior superior iliac spine down to the ischial tuberosity. Also from a midway point from the ischial tuberosity over to the greater trochanter of the femur. Other textbooks state the surface markings as a point from the ischial tuberosity one third the way up to the posterior superior iliac spine. We've also found that there's been no mention of the surface marking of the sciatic nerve in diagnostic imaging textbooks. So what do you think the surface anatomy of the sciatic nerve is important? It's imperative for intramuscular gluteal injections as these are done on a regular basis for the administration of drugs. It's also important for effective sciatic nerve block and it's important for percutaneous transgluteal drainage of deep pelvic abscesses. So Michael what do you think about the discrepancies between the textbook? Okay well I mean the origins of surface anatomy have historically come from cadaver models with all limitations. For example the distortion of tissue as a result of the embalming process or it may just come from variation between individuals. So the aim of this study is to investigate the surface markings of the sciatic nerve in the gluteal region in living adults using CT scan. Now our radiology resident will explain the method, result and the conclusion of this study. Using CT scans of the abdomen and CT colonographies we were able to identify the sciatic nerve in relation to the bony landmarks. After exclusions including distorting pathology and total hip joint replacements we were left with 100 supine scans and 19 prone scans and supine scans to be analysed by deal consensus. The centre of the sciatic nerve and most superficial parts of the bony landmarks were marked using a Syrex 3.0 software. 3D multi planar reconstructions and 3D volumetric reconstructions were then created and the nerve measured in relation to the bony landmarks. That is the posterior superior iliac spine, greater trachecanta and eschial tuberosity. What we found is that the sciatic nerve was placed on average 5.2 cm below the posterior superior iliac spine and 11.4 cm above the eschial tuberosity along a line between the posterior superior iliac spine and eschial tuberosity. What we also found is that along a line from the greater trachecanta to the eschial tuberosity we found that the sciatic nerve laid 6.2 cm from the greater trachecanta and 5.8 cm from the eschial tuberosity. In conclusion what we found was that all of the sciatic nerves lay in the upper half of a line from the posterior superior iliac spine to eschial tuberosity and that all sciatic nerves lay in the middle third of a line between the greater trachecanta and eschial tuberosity. Our study was the first study to map the course of the sciatic nerve in vivo in relation to bony landmarks. The nerve lies one third of the way from the posterior superior iliac spine and half of the way from greater trachecanta to eschial tuberosity from what we found and the nerve is significantly higher within the gluteal region than currently portrayed.