Introduction

The gluteal region is an anatomically important area at the posterior aspect of the pelvis, which contains muscles critical to dynamic movements and upright stability of humans.[1][2] It is a key conduit for several important neurovascular structures passing into the lower limb.[3] The major muscles in this region are the gluteus maximus, medius, and minimus, of which the former is the largest and most superficial (see Image. Gluteus Maximus). Owing to its position, the gluteus maximus muscle has importance in surgical approaches to the hip joint.[4] See Image. Muscles of the Hip and Thigh.

Structure and Function

The gluteal muscles are a group of muscles that make up the buttock area; the muscle group consists of the gluteus maximus, gluteus medius, and gluteus minimus. The gluteus maximus is the most superficial and largest of the three muscles and makes up the bulk of the shape and form of the buttock and hip area. The gluteus maximus is a thick fleshy muscle with a quadrangular shape, sloping across the buttock at approximately 45 degrees to its distal insertion. 

The gluteus maximus arises from the posterior part of the ilium behind the posterior gluteal line and the lateral mass of the sacrum as well as having soft tissue origins from the sacrotuberous ligament and the lumbar fascia.[5]

The gluteus maximus has two insertion points. The superficial fibers insert into the iliotibial tract, and the deep fibers insert into the gluteal tuberosity of the femur between the adductor magus and vastus lateralis.[6]

The gluteus maximus also has associations with three bursae: the trochanteric, ischial, and gluteofemoral bursae.[7][8][9] The trochanteric bursa separates the gluteus maximus from the greater trochanter, the ischial bursa separates the gluteus maximus from the ischial tuberosity, and the gluteofemoral bursa separates the iliotibial tract from the vastus lateralis. See Figure. Structures of the Gluteal Region.

The principal function of the gluteus maximus is as the chief antigravity muscle during sitting by counteracting and controlling the flexion of the hip. Its main actions are to extend and externally rotate the thigh. Although a powerful extensor, it only acts in this capacity when force is necessary; it works in conjunction with semitendinosus and semimembranosus to achieve this. Examples of activities requiring the gluteus maximus to act as an extensor include rising from a seated position, straightening from a bending position, walking upstairs or on a hill, and running.[2]

To externally rotate the hip, the gluteus maximus works synergistically with the iliopsoas, piriformis, and obturator muscles. It also acts on the bony pelvis, supporting it and the trunk, which is vital when standing on one leg. By attaching to the tensor fascia lata, the gluteus maximus also steadies the femur.[10][11]

Embryology

Like all limb muscles, the gluteus maximus develops from the somites; these are bilaterally paired blocks of the paraxial mesoderm. The myoblasts migrate into the limb buds during the fifth week of development. There, these cells condense into either the dorsal or ventral limb bud. The dorsal limb buds of the lower extremity compose the extensors and abductors, which include the gluteus maximus.[12]

Blood Supply and Lymphatics

The gluteus maximus receives vascular supply from both the inferior and superior gluteal arteries. These vessels enter the gluteus maximus at the center of the muscle. The inferior gluteal artery proceeds to descend along the greater trochanter of the femur. It accompanies the descent of the sciatic nerve, which proves to be critical as rupture of the inferior gluteal artery can cause gluteal compartment syndrome and sciatic nerve palsy.[13] The artery supplies the superficial skin and anastomoses with the perforating arteries of the lower limb. The inferior gluteal artery is also susceptible to pseudoaneurysm formation following intramuscular injection.[14]

Nerves

The innervation of the gluteus maximus muscle is from the inferior gluteal nerve, the only muscle this nerve innervates. The inferior gluteal nerve originates from the ventral rami of L5, S1, and S2. The nerve emerges from the inferior border of the piriformis. In contrast, its counterpart, the superior gluteal nerve, emerges from the superior border of this muscle along with the superior gluteal artery.[15] Classically, the inferior gluteal nerve was thought not to provide cutaneous innervation. However, the recent literature describes findings of cutaneous branches of the nerve, which might contribute toward gluteal pain during lumbar disk herniation. Surgeons must also be aware of this nerve as an injury might result in compression ulcers and various pain syndromes.[16][17]

Physiologic Variants

The literature documents anatomical and biomechanical variations of the gluteus maximus. For example, one study focused on the muscle’s variability regarding its movement arms (the length between the joint axis and line of force acting on that joint) in a sample population. The study demonstrated high variability in the gluteus maximus muscle and attributed these results to the variation in insertion points along the iliotibial tract and gluteal tuberosity.[18]

Variation of the gluteus maximus also involves physiological differences. In athletes, the gluteus maximus muscle is among the most important to train due to its action of extension of the hip joint, which translates to explosive movements. A 2018 study examined the correlation between the gluteus maximus muscle to quadriceps femoris ratio in faster and slower athletes. Results yielded that the larger the ratio, the faster the athlete.[19]   

Another 2018 study suggests that associated hip muscles may become more atrophied after hip arthroplasty, but larger cohorts would be needed to clarify the results.[20] Variability in the neuromuscular activity of the gluteus maximus in patellofemoral pain syndrome compared to healthy individuals was also documented.[21]

Surgical Considerations

Posterior Approach to the Hip Joint

The gluteus maximus muscle is involved in many surgical approaches that affect the joints around the muscle.[4] The posterior approach to the hip joint involves the gluteus maximus to a significant degree. An incision near the posterior aspect of the greater trochanter reveals the gluteus maximus. The muscle is then completely incised to expose the posterior aspect of the joint capsule. Due to the anatomy of the superior and inferior gluteal arteries, splitting the muscle will inevitably cause bleeding of the vessels, so bleeding is expected. Incising the vessels might be advantageous as the surgeon can cut and coagulate them before avulsion occurs during retraction. The incision does not risk denervation because the muscle receives its supply medial to the vascular split.[22]

Other Approaches to the Hip Joint

The anterolateral approach to the hip mainly involves retracting muscles such as the gluteus medius and tensor fascia lata to access the anterior capsule of the hip joint. During dislocation of the femoral head from the acetabulum, the fibers of the gluteus maximus are incised to gain greater access to the joint.[23]

The posterior approach to the sacroiliac joint also involves the gluteus maximus. This specific approach allows for open reduction and internal fixation of disruptions of the sacroiliac joint. Although this approach is not used widely due to percutaneous screw fixation techniques, it becomes an important procedure if appropriate imaging is not needed.

The first step of this approach is to expose the gluteus maximus via an incision along the iliac crest. The muscle is detached from its origin on the ilium and reflected downward and laterally. Two structures at risk of injury in this approach are the inferior gluteal nerve and the inferior gluteal artery. Both neurovascular structures penetrate the gluteus maximus and are imperative for its function. Therefore, careful inferior mobilization of the muscle is warranted.

The gluteus maximus is also important during the posterior approach to the acetabulum. Much like the posterior approach to the iliac crest, this approach also involves retracting the gluteus maximus. However, when the muscle is exposed, the muscle is retracted superiorly by removing the insertion point on the proximal femur.[24]

Uses of the Gluteus Maximus During Reconstructive Surgery

The gluteus maximus also plays an important role in reconstructive surgery, particularly when creating myocutaneous flaps to treat ischial and sacral ulcers. This allows for a simple procedure that provides adequate thickness to cover bony prominences and the lesion.[25][26]

The gluteus maximus can be used when addressing surgical complications, particularly after hip arthroplasty. Indications for using the gluteus maximus advancement flap procedure include persistent wound breakdown due to infection leading to soft tissue deficiency, aseptic pseudotumor, and abductor insufficiency with recurrent hip instability. Results for patients that underwent this procedure correlated with no repeat infection or hip instability.[27][28] Therefore, using the gluteus maximus advancement flap procedure for hip instability should be considered as a treatment option for surgeons after hip arthroplasty. Reconstruction after the resection of tumors has also used myocutaneous gluteus maximus flaps.[29]

Arthroscopy is also important in the treatment of gluteus maximus dysfunction. For example, post-operative arthroscopic results for the treatment of femoroacetabular impingement have shown an improvement in the function and contraction of the gluteus maximus.[30]

Clinical Significance

Gluteus maximus function is testable in the clinical setting. The test begins with the patient in the prone position with the lower limb straight. Next, the patient tightens the buttocks as much as possible and extends their hip while the examiner palpates the gluteus maximus and feels for contraction.

Gluteus maximus dysfunction is most likely due to inferior gluteal nerve dysfunction; this would cause difficulty with the patient rising from a seated position or climbing stairs and losing hip extension. The most common cause of inferior gluteal nerve dysfunction is posterior hip dislocation.[31] Another inferior gluteal nerve dysfunction etiology is incorrect intramuscular (IM) injection placement. IM injection placement should be in the upper outer quadrant of the buttock. Otherwise, the inferior and superior gluteal nerves are at risk of injury.[32]

Other Issues

Paralysis of the gluteus maximus does not affect walking on a plane (perfectly flat) surface. The gluteus maximus only contracts during a part of the stance phase of ambulation. This stance phase occurs from when the heel strikes the ground to when the foot is flat. The gluteus maximus works by resisting further flexion of the hip and initiating extension. The gluteus maximus actively functions when climbing up a flight of stairs or lifting from a seated position.[33]