Introduction

The gluteal muscles are a grouping of muscles that make up the buttock area. These muscles include:

• Gluteus maximus
• Gluteus medius
• Gluteus minimus

The gluteus maximus is the most superficial as well as largest of the three muscles and makes up most of the shape and form of the buttock and hip area. The gluteus maximus is a thick fleshy muscle with a quadrangular shape. It is a large muscle and plays a prominent role in the maintenance of keeping the upper body erect. The gluteus maximus attaches to many bony compartments including:

• The inner upper ilium
• Ilium crest
• The lower part of the sacrum
• Coccyx

The gluteus maximus has two insertion points: superficial fibers to the greater trochanter and a band of the fascia lata and the deep fibers that insert into the gluteal tuberosity between the adductor magus and vastus lateralis. It originates in the gluteal surface of the ilium.[1] The gluteus maximus also has associations with three bursae.[2][3][4] These include:

• The trochanteric bursa - separates the gluteus maximus from the greater trochanter
• Ischial bursa - separates the gluteus maximus from the ischial tuberosity
• The gluteofemoral bursa - separates the iliotibial tract from the vastus lateralis

Structure and Function

The principal function of the gluteus maximus is to extend and externally rotate the thigh. Although a powerful extensor, it only acts when force is necessary. These situations include rising from sitting, straightening from a bending position, walking up stairs or on a hill, and running. It also acts on the pelvis, supports it and the trunk which is vital when a person is standing on one leg. By attaching to the tensor fascia lata, the gluteus maximus also steadies the femur.[5][6]

Embryology

Like all limb muscles, the gluteus maximus develops from the somites that are bilaterally paired blocks of paraxial mesoderm. During the fifth week of development, the myoblasts migrate into the limb buds. 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 includes the gluteus maximus.[7]

Blood Supply and Lymphatics

The gluteus maximus receives vascular supply by both the inferior and superior gluteal artery. 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.[8] 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.[9]

Nerves

The innervation of the gluteus maximus muscle is from the inferior gluteal nerve. The inferior gluteal nerve originates from the ventral rami of L5, S1, and S2. 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 injury might result in compression ulcers and various pain syndromes.[10][11]

Muscles

The gluteus maximus works with the semitendinosus and semimembranosus muscles to extend the hip. The muscle also works in conjunction with the iliopsoas, piriformis, and the obturator muscles to externally rotate the hip.

Physiologic Variants

The literature documents anatomical and biomechanical variation of the gluteus maximus. One study focused on the muscle’s variability regarding its moment arms (the of length between the joint axis and line of force acting on that joint) in a sample population. The study results 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.[12]

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 looked at the correlation between gluteus maximus muscle to quadriceps femoris ratio in faster athletes compared to slower athletes. Results yielded that the larger the ratio, the faster the athlete.[13]   

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.[14] Variability in the neuromuscular activity of the gluteus maximus in patellofemoral pain syndrome compared to healthy individuals was also documented.[15]

Surgical Considerations

Posterior Approach to the Hip Joint

The gluteus maximus muscle is involved in many surgical approaches that involve the joints around the muscle. 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 reveal 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 will be able to cut and coagulate them before being avulsed during retraction. The incision does not risk denervation because the muscle receives its supply medial to the split.[16]

Other Approaches

The anterolateral approach to the hip mainly involves retracting muscles such as the gluteus medius and tensor fascia lata to gain access to 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.[17]  

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. First, the gluteus maximus is exposed by an incision along the iliac crest. The muscle is then detached from its origin on the ilium and is reflected downward and laterally.  Two structures that are at risk of injury are inferior gluteal nerve and 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 of importance during the posterior approach to the acetabulum. Much like the approach posterior approach to the iliac crest, it 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.[18]

Uses of the Gluteus Maximus During Surgery

The gluteus maximus also plays an important role in reconstructive surgery, which is especially so for myocutaneous flaps employing the gluteus maximus for the treatment of ischial and sacral ulcers. This procedure allows for a simple procedure that provides adequate thickness to cover bony prominences and to cover the lesion.[19][20]

 The gluteus maximus is also useful to address 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.[21][22] Therefore, using the gluteus maximus advancement flap procedure for hip instability should be on considered a treatment option for surgeons after hip arthroplasty. Reconstruction after resection of tumors has also used myocutaneous gluteus maximus flaps.[23]

Arthroscopy is also important in the case of gluteus maximus dysfunction. Post-op arthroscopic results for the treatment of femoroacetabular impingement have shown to improve function and contraction of the gluteus maximus.[24]

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. The patient tightens the buttocks as much as possible 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 in rising from a seated position, climbing up stairs and loss of hip extension. The most common cause of inferior gluteal nerve dysfunction is a posterior hip dislocation. Another etiology is incorrect intramuscular (IM) injection placement. IM injection placement should be in the upper outer quadrant of the buttock. Otherwise, both the inferior and superior gluteal nerves are at risk of injury.[25]

Other Issues

Paralysis of the gluteus maximus does not affect walking on a plane surface. The gluteus maximus only contracts during a part of the stance phase. This phase occurs when the heal strikes the ground to when the foot is flat. The gluteus maximus works by resisting further flexion of the hip and initiate extension. The gluteus maximus actively functions when climbing upstairs or lifting from a seated position.[26]