AssessmentsVessels and nerves of the gluteal region and posterior thigh
USMLE® Step 1 style questions USMLE
A group of students is studying gluteal and thigh anatomy. The students identify the primary nerve that innervates the gluteus maximus muscle. Which of the following statements regarding this nerve is true?
Content Reviewers:Viviana Popa, MD, Scott Caterine, BSc (Hons.), MSc, MB, BCh, BAO (Hons.)
The gluteal region and posterior thigh contains an abundance of large and small muscles, and coursing through these muscles is a vast network of nerves and vessels.
Ok, so let’s start with the nerves of the gluteal region and posterior thigh.
Most nerves of the lower limb arise from the lumbosacral plexus, a network of nerves derived from the roots of lumbar and sacral spinal nerves that branch out to form the nerves of the lower limb.
However, out of all the resulting nerves, the gluteal region and posterior thigh is only supplied by the cluneal nerves, superior and inferior gluteal nerves, the sciatic and pudendal nerves, the posterior cutaneous nerve of the thigh, and nerves to quadratus femoris and to obturator internus.
Let's start off with the cluneal nerves which innervate the skin of the gluteal region.
The superior cluneal nerves arise from L1-L3, and supply the skin of the superior buttock.
The middle cluneal nerve arises from S1-S3 and supplies skin over the sacrum and adjacent area of the buttocks.
And finally the inferior cluneal nerve is a branch of the posterior cutaneous nerve of the thigh from S2-S3 and supplies skin over the inferior half of the buttocks as far as the greater trochanter.
Next, there’s the superior gluteal nerve which is formed by the L4, L5, and S1 nerve roots.
The nerve courses laterally between the gluteus medius and minimus along the deep branch of the superior gluteal artery, and it exits the pelvis through the greater sciatic foramen above the piriformis muscle.
This nerve doesn’t have any sensory function.
It is also accompanied by multiple branches of the inferior gluteal artery and vein along its trajectory.
The inferior gluteal nerve ultimately divides into several branches, which provide motor innervation to the overlying gluteus maximus but no sensory supply.
Then there’s the sciatic and pudendal nerves, both of which are terminal branches of the sacral plexus,.
Regardless, the roots of the aforementioned spinal nerves converge at the inferior border of the piriformis to form the sciatic nerve, which enters the gluteal region underneath the piriformis and is the most lateral structure through the greater sciatic foramen.
Now, the sciatic nerve supplies no structures in the gluteal region but it does supply the posterior thigh muscles, all leg and foot muscles, and the skin of most of the leg and foot.
It also supplies the articular branches to all joints of the lower limb.
As a side note, it is important to note that the sciatic nerve can have anatomical variations.
As said before, it typically leaves the greater sciatic foramen below the piriformis.
However, in up to 12% of individuals the sciatic nerve divides before exiting the greater sciatic foramen, and its common fibular division pierces the piriformis as it leaves compared to the tibial division which still exits below the piriformis.
A very small 0.5% of individuals the common fibular division will actually leave the greater sciatic foramen above the piriformis, and the tibial division still leaving below the piriformis,
And medial to the sciatic nerve, there’s the pudendal nerve which originates from the S2 to S4 nerve roots and is the most medial structure to exit the pelvis through the greater sciatic foramen.
It descends inferior to the piriformis, posterolateral to the sacrospinous ligament, and enters the perineum through the lesser sciatic foramen.
Within the pudendal canal, an anatomical structure in the pelvis through which the internal pudendal artery, internal pudendal vein, and the pudendal nerve pass, the nerve divides into the inferior rectal nerve at the posterior end of the canal, and two terminal branches - the dorsal nerve of penis or clitoris and perineal nerve.
Now, while the pudendal nerve is the main nerve of the perineum, it supplies no structures in the gluteal region or posterior thigh.
Next up, the posterior cutaneous nerve of the thigh is formed by the S1, 2 and 3 nerve roots.
It lies upon the psoas muscle, from where it travels laterally into the greater sciatic foramen, through which it exits the pelvis below the piriformis muscle.
Within the gluteal region, the nerve is initially situated underneath the gluteus maximus muscle, then it descends superficial to the long head of biceps femoris in the posterior thigh, where it is deep to the fascia lata.
However, it soon pierces the fascia in the popliteal fossa, and it terminates with twigs joining the sural nerve.
Now, this nerve gives off three important branches.
One of them is the inferior cluneal nerve as we said earlier.
Then there’s the cutaneous branch which supplies the skin of the popliteal fossa, and finally the third branch is the perineal branch, which supplies the posterior part of the scrotum or labia majora.
And finally, the nerves to quadratus femoris and obturator internus are both branches arising from the pelvic surface of the plexus.
The nerve to the quadratus femoris is formed by the anterior divisions of L4, L5, and S1, and it leaves the pelvis inferior to the piriformis and deep to the sciatic nerve.
It supplies an articular branch to the hip joint and innervates the inferior gemellus and quadratus femoris muscles.
On the other hand, the nerve to the obturator internus arises from the anterior divisions of the anterior rami of the L5, S1, and S2 and leaves the greater sciatic foramen inferior to the piriformis to parallel the course of the pudendal nerve.
As it passes around the base of the ischial spine, the nerve supplies the superior gemellus, and, after entering the perineum via the lesser sciatic foramen, it supplies the obturator internus muscle.
Before we move on to blood vessels, let’s try and recall the main nerves of the sacral plexuses.
Ok, switching over to arteries, the gluteal region is supplied or traversed by major branches of the internal iliac artery, namely the superior gluteal artery, inferior gluteal artery, and internal pudendal artery.
First, the superior gluteal artery is the largest of the branches, and, from its origin, it passes posteriorly between the lumbosacral trunk and the S1 nerve.
This artery leaves the pelvis through the greater sciatic foramen, superior to the piriformis, and divides immediately into superficial and deep branches.
The superficial branch supplies the gluteus maximus and skin over the proximal attachment of this muscle.