Applied Surgical Anatomy of the Posterior Approaches to the Hip and the Acetabulum
Overview
The muscles covering the posterior aspect of the hip joint form two sheaths or layers. The outer layer consists of the gluteus maximus. The inner layer consists of the short external rotators of the hip, the piriformis, the superior gemellus, the obturator internus, the inferior gemellus, and the quadratus femoris. The sciatic nerve runs vertically between the two layers, down through the operative field (Figs. 8-60 and 8-61).
The gluteus maximus sits on the other structures in the buttock like the front cover of a book. It inserts partly into the iliotibial band and partly into the gluteal tuberosity of the femur. Also inserting into the band, but further anteriorly, is the tensor fasciae latae. Together, the gluteus maximus, the fascia lata (which covers the gluteus medius), and the tensor fasciae latae form a continuous fibromuscular sheath, the outer layer of the hip musculature (see Fig. 8-60). As Henry14 noted, the layer can be viewed as the “pelvic deltoid”: it covers the hip much as the deltoid muscle covers the shoulder.
The outer layer can be breached at different points, each of which changes the posterior approach. The most natural separation, the Marcy– Fletcher approach,15 lies at the anterior border of the gluteus maximus, between the gluteus maximus (inferior gluteal nerve) and the gluteus medius. This approach uses a true internervous plane.
Other more posterior approaches (like the Moore approach9 and the
Osborne approach16) involve splitting the fibers of the gluteus maximus. They are more popular than the Marcy–Fletcher approach even though they do not operate in an internervous plane, mainly because they offer excellent exposure of the hip joint.
Figure 8-60 The superficial musculature of the posterior approach of the hip joint. The gluteus maximus predominates.
Gluteus Maximus. Origin. From posterior gluteal line of ilium and that portion of the bone immediately above and behind it; from posterior surface of lower part of sacrum and from side of coccyx; and from fascia covering gluteus medius. Insertion. Into iliotibial band of fascia lata and into gluteal tuberosity. Action. Extends and laterally rotates thigh. Nerve supply. Inferior gluteal nerve.
Figure 8-61 The gluteus maximus and the gluteus medius have been resected to reveal the gluteus minimus, the piriformis, and the short rotator muscles. Note the relationship of the neurovascular structures to the piriformis.
Gluteus Minimus. Origin. From outer surface of ilium between anterior and inferior gluteal lines. Insertion. Into impression on anterior border of greater trochanter via tendon that gives expansion to joint capsule. Action. Rotates thigh medially and abducts it. Nerve supply. Superior gluteal nerve.
Piriformis. Origin. From front of sacrum via fleshy digitations from second, third, and fourth portions of sacrum. Insertion. Into upper border of greater trochanter via round tendon. Action. Rotates thigh laterally and abducts it. Nerve supply. Branches from first and second sacral nerves.
Obturator Internus. Origin. From inner surface of anterolateral wall of pelvis and from surfaces of greater part of obturator foramen. Insertion. Onto medial surface of greater trochanter above trochanteric fossa. Action. Rotates thigh laterally. Nerve supply. Any nerve from sacral plexus.
Quadratus Femoris. Origin. From upper part of external border of tuberosity of ischium. Insertion. Into upper part of linea quadrata, the line that extends vertically downward from intertrochanteric crest. Action.
Rotates thigh laterally. Nerve supply. Branch from sacral plexus.
Figure 8-62 The gluteus minimus, piriformis, and short rotators have been resected to uncover the posterior aspect of the hip joint.
Landmarks and Incision
Landmarks
The greater trochanter, over which the skin incision is centered, is the easiest bony prominence to palpate around the hip. Its posterior aspect is relatively free of muscles; its anterior and lateral aspects are covered by the tensor fasciae latae and the gluteus medius and minimus muscles and are much less accessible.
The greater trochanter arises from the junction of the neck and the shaft of the femur. From there, it projects both upward and backward (Fig. 8-63). The following five muscles insert into it:
1. The gluteus medius attaches by a broad insertion into its lateral aspect. Below this insertion, the bone is covered by the beginnings of the iliotibial tract. A bursa, occasionally a site of inflammation, lies between the tract and the bone over the relatively bare portion of the trochanter.
The bursa can be the site of bacterial infection (historically, most frequently tuberculosis).
2. The gluteus minimus is attached to the anterior aspect of the trochanter, where its tendon is divided in the anterolateral approach (see Figs. 8-61 and 8-62).
3. The piriformis inserts via a tendon into the middle of the upper border of the greater trochanter. (see Figs. 8-61 and 8-62).
4. Obturator externus tendon. Immediately below the insertion of the piriformis lies the trochanteric fossa, a deep pit that marks the attachment of the obturator externus tendon (see Figs. 8-61 and 8-62).
5. The obturator internus tendon inserts with the two gemelli into the upper border of the trochanter, posterior to the insertion of the piriformis (see Figs. 8-61 and 8-62).
Incision
The upper part of the incision crosses the lines of cleavage of the skin at almost 90 degrees, but the resulting scar is always hidden by clothing. Most patients who undergo this approach are elderly and tend not to form exuberant scar tissue, and they heal with a fine line scar.
Figure 8-63 Osteology of the posterior aspect of the hip and pelvis.
Superficial Surgical Dissection and Its Dangers
Superficial dissection consists of cutting through the outer muscle layer by splitting the fibers of the gluteus maximus, the single largest muscle in the body. The fibers of the gluteus maximus are extremely coarse; they run obliquely downward and laterally across the buttock. The muscle’s innervation, the inferior gluteal nerve, emerges from the pelvis beneath the inferior border of the piriformis and almost immediately enters the muscle’s deep surface close to its medial border, its origin. From there, the nerve’s branches spread throughout the muscle. Splitting the gluteus maximus close to its lateral insertion does not denervate significant portions of the muscle, because its main nerve supply passes well medial to the most medial point of splitting (see Fig. 8-60).
The gluteus maximus is quiet during normal walking or standing still; it comes into play during stair climbing or standing up from a sitting position. (During normal walking, hip extension is primarily a function of the hamstrings rather than the gluteus maximus.)
Deep Surgical Dissection and Its Dangers
Deep dissection consists of incising some portion of the inner muscular layer (the short external rotators of the hip) to expose the posterior hip joint capsule (see Fig. 8-55). Five muscles form the inner layer: the piriformis, the superior gemellus, the tendon of the obturator internus, the inferior gemellus, and the quadratus femoris.
Recognizing the relationship of the piriformis to passing structures is the key to understanding the neurovascular anatomy of the area (see Fig. 8-61). All neurovascular structures that enter the buttock from the pelvis pass through the greater sciatic notch, either superior or inferior to the piriformis, which itself passes from the pelvis to the buttock through the notch.
The 10 critical neurovascular structures are as follows:
(These are the only structures to pass above the piriformis, hence, their name “superior.”)
The superior gluteal nerve emerges from the pelvis above the piriformis. It crosses behind the posterior border of the gluteus medius and runs in the space between the gluteus medius and the gluteus minimus, supplying both before sending fibers to the tensor fasciae latae.
The superior gluteal artery, the largest branch of the internal iliac artery, enters the buttock above the upper border of the piriformis and runs with its nerve, supplying the gluteus medius and gluteus minimus and sending a nutrient vessel to the ilium on the gluteal line. The nutrient vessel may bleed when a larger posterior iliac bone graft is taken. The superior gluteal artery also sends branches to the overlying gluteus maximus, forming part of the muscle’s dual arterial supply.
The superior gluteal artery can be damaged in pelvic fractures, especially in those involving the greater sciatic notch. If it retracts into the pelvis, its bleeding must be controlled by an extraperitoneal approach to the pelvis so that its feeding vessel, the internal iliac artery, can be ligated. In pelvic fractures, selective angiography may aid in the diagnosis of a ruptured superior gluteal artery. During the angiography, the artery may be embolized through the diagnostic cannula, avoiding a pelvic exploration.17 If you are using the anterior or posterior approaches to the acetabulum using a trochanteric osteotomy, the superior gluteal vessels must be intact in order to avoid muscle necrosis of the gluteus medius and minimus. This is because the origin and insertion of the muscles is detached in these approaches. If the acetabular fracture involves a displaced fracture of the greater sciatic notch, preoperative angiography is advised to ensure that the neurovascular pedicle to these structures is intact.
The inferior gluteal nerve reaches the buttock beneath the lower border of the piriformis. It enters the deep surface of the gluteus maximus almost immediately.
The inferior gluteal artery, which follows the inferior gluteal nerve, supplies the gluteus maximus. The branch it sends along the sciatic nerve was the original axial artery of the limb. In rare cases, this artery can serve as one guide to the sciatic nerve during surgery. The inferior gluteal artery may also be torn in pelvic fractures, but not as frequently as the superior gluteal artery.
The pudendal nerve is not encountered during the posterior approach to the hip because its course in the buttock is very short. It turns around the sacrospinous ligament before entering the perineum.
The internal pudendal artery runs with the pudendal nerve. The artery is usually well clear of the operative field during posterior approaches, but damage to it has been reported. Local pressure against the ischial spine usually controls bleeding; if not, or if the artery has retracted, an extraperitoneal approach through the space of Retzius18 may be needed to ligate the parent trunk.
The nerve to the obturator internus enters its muscle almost as soon as it emerges from behind the inferior border of the piriformis. The nerve also supplies the superior gemellus.
The massive sciatic nerve, which is formed by roots from the lumbosacral plexus (L4, L5, S1, S2, S3), appears in the buttock from beneath the lower border of the piriformis, just lateral to the inferior gluteal and pudendal nerves and vessels. It is usually surrounded by fat and is often easier to feel than to see. It passes vertically down the buttock together with its artery, lying on the short external rotator muscles of the inner muscular sleeve, the obturator internus, the two gemelli, and the quadratus femoris. Farther distally, it passes deep (anterior) to the biceps femoris and disappears from view, lying on the adductor magnus.
The sciatic nerve is safe during posterior approaches as long as you are aware of its position. It can be injured if it is trapped in the posterior blade of the self-retaining retractor that holds the fascial edge. It also can be damaged if it is not protected during reduction of the prosthetic head into the acetabulum.
The tibial portion of the sciatic nerve supplies all the hamstring muscles except the short head of the biceps femoris and the extensor portion of the adductor magnus in the thigh. All its branches arise from the medial side of the nerve. Dissections around the sciatic nerve in the thigh therefore should remain on the lateral (safe) side, since the only branch coming off that side runs to the short head of the biceps, a muscle that causes few clinical problems if its nerve supply is damaged (see Fig. 8-61).
The common peroneal and tibial nerves, the terminal branches of the sciatic nerve, supply all the muscles below the knee. In addition, they (and other sciatic branches) supply skin over the sole of the foot, the dorsum of the foot (except for its medial side), and the calf and lateral side of the lower leg. Damage to the sciatic nerve at the level of the hip joint injures both tibial and common peroneal elements, resulting in a balanced flaccid paralysis below the knee, together with paralysis of the hamstring muscles. Complete sciatic nerve lesions are relatively rare; more often, the damage seems to affect either the tibial or the common peroneal components. Hence, neurologic findings may vary regardless of the level of the lesion.
Common peroneal nerve palsies do occur after posterior approaches to the hip. The question then arises as to whether the nerve was damaged at the operative site or whether it was compressed by external pressure on the nerve as it winds around the neck of the fibula. The differential diagnosis can be made by doing an electromyogram (EMG) of the short head of the biceps, the only muscle of the thigh that is supplied by the common peroneal division of the sciatic nerve. Lesions in the pelvis or at the level of the hip joint denervate this muscle. Lesions at the level of the fibular head leave it unaffected.
Only 20% of the cross section of the sciatic nerve at the hip joint is formed by nerve fibers. The remaining 80% is made up of connective tissue. Nerve repairs in this area are often unsuccessful, because bundle-tobundle contact is difficult to achieve.
The posterior femoral cutaneous nerve (posterior cutaneous nerve of the thigh) supplies a large area of skin on the back of the thigh. The nerve actually lies on the sciatic nerve until the sciatic passes deep to the biceps femoris. Then the posterior femoral cutaneous nerve continues superficial to the hamstring muscles but deep to the fascia lata, sending out several cutaneous branches.
The nerve to the quadratus femoris emerges from the pelvis behind the sciatic nerve and runs with it on its deep surface as it crosses the tendon of the obturator internus and the two gemelli. The nerve then passes deep to the quadratus femoris before entering its anterior surface. It also gives off muscular branches to the inferior gemellus.
Obturator Internus
The obturator internus is one of the few muscles that make a right-angled turn; it curves round the lesser sciatic notch of the ischium. The muscle has a tricipital tendon that is reinforced at its insertion by the superior and inferior gemelli.
Quadratus Femoris
The quadratus femoris is quadrate, that is, four-sided. Its transversely running fibers form a clear surgical landmark. The muscle has an excellent blood supply. At the lower border of its insertion lies the cruciate anastomosis, consisting of the ascending branch of the first perforating artery, the descending branch of the inferior gluteal artery, and transverse branches of the medial and lateral femoral circumflex arteries (see Fig. 861).
The muscle’s blood supply can be used to revascularize an avascular femoral head and neck.
Vice Dean of the Faculty of Medicine at Sana'a University and a leading consultant in orthopedic and spinal surgery. Learn more about my expertise and achievements.
About the Author: Prof. Dr. Mohammed Hutaif