T Gross Anatomy 6

(1)

1 0 0

6 Gross Anatomy

J.W. Thomas Byrd

T

he four distinguishing features of a diarthrodial (synovial) joint are (1) a joint cavity, (2) articular cartilage, (3) synovial membrane producing synovial fluid, and (4) a ligamentous capsule. Ball-and- socket joints demonstrate multiaxial articulations and are one of six types of diarthrodial joints. Hip motion most closely represents the true ball-and-socket configuration. This configuration has significant implications for the technical ability to assess this joint arthroscopically.

Additionally, the hip is the joint most densely encased by its soft tissue envelope, necessitating extra- length arthroscopic instruments. More importantly, it requires significant skills in localization and triangu- lation techniques to instrument the joint, challenging the surgeon’s proprioceptive abilities.

Distraction is usually employed to separate the articular surfaces sufficiently to allow for introduction of the arthroscope and operative instruments. Dis- traction must overcome the powerful musculature surrounding the hip as well as the dense ligamentous capsule. Adequate relaxation, whether through gen- eral or epidural anesthesia, negates the dynamic muscle compressive forces, leaving only minimal static muscle effects. However, the dense capsule, measur- ing more than 0.5 cm in thickness in some areas, represents a formidable static restraint to distraction, necessitating the magnitude of traction forces often required in hip arthroscopy. With maintained tension, even this dense, relatively noncompliant structure can relax through the process of physiologic creep, often allowing the ability to adequately distract the hip without having to rely on excessive force. Understanding these anatomic and structural principles is important in the ability to perform effective arthroscopy.

The surgeon must be properly oriented and aware of the important extraarticular structures, as with any joint.^1,2 This preparation begins with proper knowledge of the topographic anatomy, which is critical to interpreting the spatial relationship of deep structures.

TOPOGRAPHIC ANATOMY

Palpation of the bony landmarks about the hip is straightforward. It is nonetheless important to appre-

ciate these landmarks and understand their relationship to the deep soft tissue structures. The principal landmarks include the greater trochanter, anterior superior iliac spine, pubic symphysis, iliac crest, posterior iliac spine, and the ischium (Figure 6.1).

Two and perhaps three of these landmarks are critical for proper orientation during arthroscopy (Fig- ure 6.2).^3–5 The principal landmark is the greater trochanter; its superior margin as well as its anterior and posterior borders must be noted. The anterior superior iliac spine is the second important landmark for determining the position of the anterior portal. The surgeon needs to be careful not to compromise the exposure of these areas during draping of the patient.

The pubic symphysis has been used by some au- thors as a landmark for establishing the position of the anterior portal.^6,7Palpation and orientation are re- producible, but must be done before draping the patient, as it is difficult to incorporate this area into the operative field.

MUSCULATURE

The hip musculature can be conceptualized as a superficial layer and a deep layer. The fascia lata covers the entire hip region including the three muscles that make up the superficial layer: the tensor fascia lata, sartorius, and gluteus maximus (Figure 6.3). The fascia lata also splits to cover the deep and superficial surface of the tensor fascia lata and gluteus maximus encasing these muscles. The tensor fascia lata and the gluteus maximus insert as a continuation, forming the iliotibial band. The gluteus maximus also partly in- serts into the proximal femur at the gluteal tuberosity. This fibromuscular sheath was described by Henry⁸ as the “pelvic deltoid,” reflecting the fashion in which it covers the hip much as the deltoid muscle covers the shoulder. Interestingly, the gluteus maximus is the largest muscle in the body, and the sartorius, which crosses two joints, although quite weak, is the longest.

The gluteus medius has a transitional relationship between the superficial and deep musculature layers (Figures 6.3, 6.4). Its origin from the iliac crest is relatively superficial and covered by a portion of the

(2)

Iliac crest

Posterior superior Iliac spine

Anterior superior Iliac spine

Pubic symphysis Greater trochanter

Ischial tuberosity

FIGURE 6.1. Palpation requires thorough knowledge of the topographic anatomy.

Anterior Portal

Anterolateral Portal Posterolateral Portal

FIGURE 6.2. The lateral two portals (anterolat- eral and posterolateral) are placed directly over the superior margin of the greater trochanter at its anterior and posterior borders. The anterior portal is positioned at the site of intersection of a sagittal line drawn distally from the anterior superior iliac spine and a transverse line across the tip of the greater trochanter.

(3)

Sartorius

Tensor fascia lata Iliotibial band

Gluteus medius

Gluteus maximus

FIGURE 6.3. Superficial muscular layer of the hip.

Piriformis

Obturator externus

Quadratus femoris Gluteus minimus

Greater trochanter

Cut end of gluteus medius Gluteus medius

Gluteus maximus cut end elevated

Ischial spine Obturator internus

Inferior gemellus Ischial tuberosity Superior gemellus

FIGURE 6.4. Deep structures (posterior view).

(4)

fascia lata, whereas its insertion into the greater trochanter corresponds with the deep muscles.

Posteriorly, the deep muscle layer includes the piriformis, the obturator internus with a common tendi- nous insertion including the superior and inferior gemelli, the obturator externus, and the quadratus femoris (see Figure 6.4). Laterally, the gluteus minimus lies on the deep surface of the gluteus medius.

Anteriorly, the origin of the rectus femoris, including its direct and reflected heads, covers the anterior capsule (Figure 6.5). Just anterior to this is the iliopsoas tendon, formed from the muscles of the iliacus and psoas major inside the pelvis, coursing on the way to its insertion on the lesser trochanter.

Medially, the hip is bordered by the adductor muscle group including the adductor longus, magnus, and brevis, and the gracilis (see Figure 6.5).

These muscles are of limited clinical significance for hip arthroscopy except when considering a medial approach to the joint, which has been described as a technical entity, but has thus far found limited clinical application.⁹

NEUROVASCULAR STRUCTURES

The femoral neurovascular structures (nerve, artery, and vein) exit the pelvis under the inguinal ligament halfway between the anterior superior iliac spine and the pubic tubercle (Figure 6.6). They are relatively anterior to the hip joint, with the nerve being the most lateral. These structures lie on the anterior surface of the iliopsoas muscle, and thus the muscle separates the femoral neurovascular structures from the hip.

The lateral femoral cutaneous nerve originates from the lumbar plexus and exits the pelvis under the inguinal ligament close to the anterior superior iliac spine (see Figure 6.6). This nerve is known to be sen- sitive to external compression (meralgia paresthetica).

It is also known to be vulnerable to injury during har- vesting of iliac crest bone graft when the harvest site is carried too close to the anterior superior iliac spine and to damage by improperly placed arthroscopic portals.

The lateral circumflex femoral artery arises from the profunda femoris (deep femoral artery) shortly af-

Rectus femoris reflected & direct heads

Pectineus

Iliopsoas

Adductor longus Adductor magnus

Adductor brevis

Gracilis

FIGURE 6.5. Deep structures (anterior view).

(5)

ter it takes off from the femoral artery (see Figure 6.6).

The ascending branch of the lateral circumflex femoral artery has an oblique course along the direction of the intertrochanteric line.

The superior gluteal nerve and artery are the most superior of 10 neurovascular structures that exit through the sciatic notch (Figure 6.7). They course transversely in a posterior to anterior direction between the deep surface of the gluteus medius and the superficial surface of the gluteus minimus, innervat- ing and supplying blood to both. The sciatic nerve exits the notch under the piriformis tendon and then lies posterior to the other short external rotators in a ver- tical direction as it courses distally (see Figure 6.7).

An intricate vascular anastomosis converges at the lower border of the quadratus femoris 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 circumflex femoral arteries (see Figure 6.7).

CAPSULAR AND

JOINT ARCHITECTURE

The ilium, ischium, and pubic bones unite at the acetabulum, forming the innominate bone. During childhood, these bones are separated within the acetabulum by the triradiate cartilage, which fuses at skeletal maturity.

The acetabulum has an inclined abduction angle of approximately 35 degrees from the horizontal and a forward flexed position of approximately 20 degrees (Figure 6.8A,C). The articular surface of the acetabulum has a horseshoe or lunate shape (Figure 6.9). The central inferior acetabular fossa is devoid of articular surface. It is occupied by a fat pad covered with synovium called the pulvinar. Addition- ally, it contains the acetabular attachment of the ligamentum teres. The socket of the acetabulum is completed inferiorly by the transverse acetabular ligament.

Iliacus muscle

Lateral femoral cutaneous nerve

Ascending branch of the lateral circumflex femoral artery

Psoas major muscle

Iliopsoas muscle Femoral nerve artery & vein

FIGURE 6.6. Neurovascular structures (anterior view).

(6)

Descending branch of inferior gluteal artery

1st perforating artery Superior gluteal

nerve & artery

Inferior gluteal nerve & artery

Pudendal nerve

Posterior femoral cutaneous nerve

Sciatic nerve Medial circumflex femoral artery

FIGURE 6.7. Neurovascular structures (posterior view).

FIGURE 6.8. (A) Acetabular orientation averages 35 degrees of ab- duction from the horizontal plane. The neck shaft angle formed between the axis of the femoral neck and femoral shaft averages 125 degrees. (B) Femoral anteversion, determined by the angle created

between the bicondylar axis of the knee and the axis of the femoral neck in the transverse plane, averages 14 degrees. (C) The acetabulum is also oriented with 20 degrees of forward flexion relative to the sagittal plane.

(7)

The labrum is a fibrocartilaginous structure that attaches to the bony rim of the acetabulum, effectively deepening to a socket. The labrum terminates inferiorly at the anterior and posterior margins of the acetabular fossa. It then becomes contiguous with the transverse acetabular ligament, which completes the circumferential ring of the acetabulum. We are learn- ing that the labrum is a nonhomogeneous structure with considerable variation in different areas of the acetabulum (see Chapter 8).

Although variable, the proximal femur has a neck shaft angle that averages 125 degrees, with approximately 14 degrees of femoral neck anteversion (see Figure 6.8A,B). The femoral head has an articular surface that forms approximately two-thirds of a sphere, articulating with the acetabulum (see Figure 6.9). Me- dially, on the articular portion of the femoral head, is a pit called the fovea capitis, the site of the femoral attachments of the ligamentum teres.

The bony architecture of the hip provides it with significant intrinsic stability. This stability is further enhanced by an intricate complex of capsular ligaments. This complex consists of four distinct ligaments that provide varying contributions to the joint.

The intricate nature and specific design of the capsular ligaments has been well defined by various anatomic studies. However, over time, more will be learned about the ligaments as a better appreciation is gained of the arthroscopic appearance of this anatomy. Perhaps this construct will even be partially redefined.

Anteriorly, the capsule consists primarily of the iliofemoral ligament or ligament of Bigelow (Figure 6.10). It has an inverted Y shape beginning from its iliac attachment on the superior aspect of the acetabulum. It then fans out in a spiraling pattern to its femoral attachment along the intertrochanteric line. It is one of the strongest ligaments in the body, and the spiraling direction of its fibers makes it taut in extension in a wringing-out mechanism and relaxed in flexion.

The ischiofemoral ligament reinforces the posterior capsule (Figure 6.11). It too has a spiraling pattern as it courses from its ischial attachment on the posterior acetabular rim to its femoral attachment on the superolateral neck, medial to the base of the greater trochanter.

The pubofemoral ligament, although relatively weak, reinforces the inferior and anterior capsule from

Lunate articular surface

Labrum

Acetabular fossa Transverse acetabular ligament

Ischium

Pubis Fovea capitis

Ligamentum teres Ilium

FIGURE 6.9. Formed from portions of the ilium, ischium, and pubis, the lunate-shaped articular surface of the acetabulum surrounds the fossa contain- ing the acetabular attachment of the ligamentum teres and fat, both encased in synovium. The labrum effectively deepens the socket and is contiguous with the transverse acetabular ligament inferiorly. The articular surface of the femoral head forms approximately two- thirds of a sphere. Medially, the ligamentum teres attaches at the fovea capitis. The diameter of the femoral neck is only 65% of the diameter of the femoral head, which allows for freer range of motion without marginal impingement.

(8)

Pubofemoral ligament Iliofemoral ligament

FIGURE 6.10. The iliofemoral liga- ment (ligament of Bigelow) has the shape of an inverted Y as it spirals from its attachment on the iliac portion of the superior acetabulum to its femoral attachment on the anterior neck. It is quite powerful and becomes taut in extension. The relatively weak pubofemoral ligament reinforces the inferior and anterior capsule, where it blends with the medial edge of the iliofemoral ligament.

Ischiofemoral ligament

POSTERIOR

FIGURE 6.11. The ischiofemoral ligament rein- forces the posterior capsule, spiraling from its attachment on the ischial portion of the posterior acetabulum to the superolateral aspect of the femoral neck.

(9)

the pubic part of the acetabular rim where it blends with the medial edge of the iliofemoral ligament (see Figure 6.10). Again, the spiraling nature of this complex tends to screw the femoral head medially into the acetabulum during extension, which has several clinical implications. First, this explains why patients with an irritable hip, whether the result of trauma, disease, or infection, tend to rest with the hip in a slightly flexed position, relaxing the capsule. Second, from a surgical standpoint, it would appear advanta- geous to perform arthroscopy with the hip flexed, further relaxing the capsule. However, this can create po- tential concern for portal placement, as discussed in Chapter 7.

The fourth ligament is the ligament of the head of the femur (ligamentum teres) (Figure 6.12). Coursing from its attachment in the acetabular fossa to the fovea of the femoral head, it is intracapsular, yet encased in synovium, making it extrasynovial. Its relatively weak, redundant nature makes it unlikely that this has any significant stabilizing effect on the hip.

The size and strength of this ligament are variable, and it is occasionally absent, the significance of which is unknown.

A deep layer of fibers within the ligamentous capsule courses circularly around the neck of the femur, creating the zona orbicularis (see Figure 6.12). This layer may serve as a collar to constrict the capsule and help maintain the femoral head within the acetabulum.

VASCULAR SUPPLY TO THE FEMORAL HEAD

Intraarticular isolation of the femoral head and neck makes it highly dependent on its tenuous vascular supply. Its susceptibility to circulatory compromise is an ongoing source of concern to physicians who treat hip pathology. Ischemic insult followed by avascular necrosis (AVN) of the femoral head, similar to other forms of osteonecrosis, has been clearly linked to cer- tain disease states and types of exposure although it is less clearly associated with others and often purely idiopathic.¹⁰AVN has been associated with previous trauma including fracture and dislocation and may oc- cur iatrogenically in association with surgical procedures that violate the vascular pattern.

Ligamentum teres

Zona orbicularis

FIGURE 6.12. The ligamentum teres is redun- dant and weak and contributes little to the capsular stability of the hip. Encased in synovium, it is intracapsular, yet extrasynovial.

(10)

The poorly defined and uncertain nature of AVN is reflected in the myriad surgical procedures that have been described in its management, none of which has proven to be superior, and few of which have even been shown to be truly effective in altering the natu- ral course of the process.¹¹

Arterial blood supply to the femoral head is achieved through an anastomosis of three sets of arteries (Figure 6.13). The principal vessels ascend in the synovial retinaculum, which is a reflection of the ligamentous capsule onto the neck of the femur. These vessels arise mainly posterior superiorly and posterior inferiorly from the medial circumflex femoral artery, which is supplemented to a lesser extent from the lateral circumflex femoral artery. These vessels anasto- mose with the terminal branches of the medullary artery from the shaft of the femur. The third source is the anastomosis within the femoral head from the artery of the ligamentum teres, which arises from a posterior division of the obturator artery. This vessel may persist with advanced age, but in approximately 20%

of the population it never develops.

References

1. Anderson JE: Grant’s Atlas of Anatomy, 7th ed. Baltimore:

Williams & Wilkins, 1978.

2. Hoppenfeld S, deBoer P (eds): Surgical Exposures in Or- thopaedics. The Anatomic Approach. Philadelphia: Lippincott, 1984.

3. Byrd JWT: Hip arthroscopy utilizing the supine position. Ar- throscopy 1994;10:275–280.

4. Byrd JWT, Pappas JN, Pedley MJ: Hip arthroscopy: an anatomic study of portal placement and relationship to the extraarticular structures. Arthroscopy 1995;11:418–423.

5. Glick JM: Hip arthroscopy using the lateral approach. Instr Course Lect 1988;37:223–231.

6. Johnson L: Hip joint. In: Johnson L (ed). Diagnostic and Surgi- cal Arthroscopy, 3rd ed. St. Louis: Mosby, 1986:1491–1519.

7. Ide T, Akamatsu N, Nakajima I: Arthroscopic surgery of the hip joint. Arthroscopy 1991;7:204–211.

8. Henry AK: Extensile Exposure, 2nd ed. New York: Churchill Livingstone, 1973.

9. Gross RH: Arthroscopy in hip disorders in children. Orthop Rev 1977;6:43–49.

10. Jones JP: Concepts of etiology and early pathogenesis of osteonecrosis. Instr Course Lect 1994;43:499–512.

11. Steinberg ME: Early diagnosis, evaluation and staging of osteonecrosis. Instr Course Lect 1994;43:513–518.

Artery of ligamentum teres (foveolar artery)

Medial circumflex femoral artery

Deep femoral artery Retinacular arteries

superior anterior/posterior inferior

Ascending transverse

& descending branches of the

lateral circumflex femoral artery

FIGURE 6.13. The femoral head receives arterial blood flow from an anastomosis of three sets of arteries: (1) the retinacular vessels, primarily from the medial circumflex femoral artery and, to a lesser extent, the lateral circumflex femoral artery; (2) terminal

branches of the medullary artery from the shaft of the femur; and (3) the artery of the ligamentum teres from the posterior division of the obturator artery.