6 Gross Anatomy J.W

Home , Intertrochanteric line, Ischiofemoral ligament, Pubofemoral ligament

6 Gross Anatomy J.W. Thomas Byrd

he four distinguishing features of a diarthrodial ciate these landmarks and understand their relation- (synovial) joint are (1) a joint cavity, (2) articu- ship to the deep soft tissue structures. The principal T lar cartilage, (3) synovial membrane producing landmarks include the greater trochanter, anterior su- synovial fluid, and (4) a ligamentous capsule. Ball-and- perior iliac spine, pubic symphysis, iliac crest, poste- socket joints demonstrate multiaxial articulations and rior iliac spine, and the ischium (Figure 6.1). are one of six types of diarthrodial joints. Hip motion Two and perhaps three of these landmarks are crit- most closely represents the true ball-and-socket con- ical for proper orientation during arthroscopy (Fig- figuration. This configuration has significant impli- ure 6.2).3–5 The principal landmark is the greater cations for the technical ability to assess this joint trochanter; its superior margin as well as its anterior arthroscopically. and posterior borders must be noted. The anterior su- Additionally, the hip is the joint most densely en- perior iliac spine is the second important landmark cased by its soft tissue envelope, necessitating extra- for determining the position of the anterior portal. The length arthroscopic instruments. More importantly, it surgeon needs to be careful not to compromise the ex- requires significant skills in localization and triangu- posure of these areas during draping of the patient. lation techniques to instrument the joint, challenging The pubic symphysis has been used by some au- the surgeon’s proprioceptive abilities. thors as a landmark for establishing the position of Distraction is usually employed to separate the ar- the anterior portal.6,7 Palpation and orientation are re- ticular surfaces sufficiently to allow for introduction producible, but must be done before draping the pa- of the arthroscope and operative instruments. Dis- tient, as it is difficult to incorporate this area into the traction must overcome the powerful musculature operative field. surrounding the hip as well as the dense ligamentous capsule. Adequate relaxation, whether through gen- eral or epidural anesthesia, negates the dynamic mus- MUSCULATURE cle compressive forces, leaving only minimal static muscle effects. However, the dense capsule, measur- The hip musculature can be conceptualized as a su- ing more than 0.5 cm in thickness in some areas, rep- perficial layer and a deep layer. The fascia lata covers resents a formidable static restraint to distraction, the entire hip region including the three muscles that necessitating the magnitude of traction forces often make up the superficial layer: the tensor fascia lata, required in hip arthroscopy. With maintained tension, sartorius, and gluteus maximus (Figure 6.3). The fas- even this dense, relatively noncompliant structure can cia lata also splits to cover the deep and superficial relax through the process of physiologic creep, often surface of the tensor fascia lata and gluteus maximus allowing the ability to adequately distract the hip with- encasing these muscles. The tensor fascia lata and the out having to rely on excessive force. Understanding gluteus maximus insert as a continuation, forming the these anatomic and structural principles is important iliotibial band. The gluteus maximus also partly in- in the ability to perform effective arthroscopy. serts into the proximal femur at the gluteal tuberos- The surgeon must be properly oriented and aware ity. This fibromuscular sheath was described by of the important extraarticular structures, as with any Henry8 as the “pelvic deltoid,” reflecting the fashion joint.1,2 This preparation begins with proper knowl- in which it covers the hip much as the deltoid mus- edge of the topographic anatomy, which is critical to cle covers the shoulder. Interestingly, the gluteus max- interpreting the spatial relationship of deep structures. imus is the largest muscle in the body, and the sartorius, which crosses two joints, although quite weak, is the longest. TOPOGRAPHIC ANATOMY The gluteus medius has a transitional relationship between the superficial and deep musculature layers Palpation of the bony landmarks about the hip is (Figures 6.3, 6.4). Its origin from the iliac crest is rel- straightforward. It is nonetheless important to appre- atively superficial and covered by a portion of the

100 CHAPTER 6: GROSS ANATOMY 101

Iliac crest

Anterior superior Posterior superior Iliac spine Iliac spine

Pubic symphysis Greater trochanter

Ischial tuberosity

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

Anterior Portal FIGURE 6.2. The lateral two portals (anterolateral 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 Anterolateral Portal a sagittal line drawn distally from the anterior superior iliac spine and a transverse line across Posterolateral Portal the tip of the greater trochanter. 102 J . W . THOMAS BYRD

Sartorius

Tensor fascia lata Iliotibial band

Gluteus medius

Gluteus maximus

FIGURE 6.3. Superficial muscular layer of the hip.

Gluteus medius

Gluteus minimus

Greater trochanter Cut end of gluteus medius

Obturator externus

Quadratus femoris

Gluteus maximus cut end elevated Piriformis

Superior gemellus Ischial spine

Obturator internus

Inferior gemellus

Ischial tuberosity

FIGURE 6.4. Deep structures (posterior view). CHAPTER 6: GROSS ANATOMY 103 fascia lata, whereas its insertion into the greater NEUROVASCULAR STRUCTURES trochanter corresponds with the deep muscles. Posteriorly, the deep muscle layer includes the pir- The femoral neurovascular structures (nerve, artery, iformis, the obturator internus with a common tendi- and vein) exit the pelvis under the inguinal ligament nous insertion including the superior and inferior halfway between the anterior superior iliac spine and gemelli, the obturator externus, and the quadratus the pubic tubercle (Figure 6.6). They are relatively an- femoris (see Figure 6.4). Laterally, the gluteus min- terior to the hip joint, with the nerve being the most imus lies on the deep surface of the gluteus medius. lateral. These structures lie on the anterior surface of Anteriorly, the origin of the rectus femoris, including the iliopsoas muscle, and thus the muscle separates its direct and reflected heads, covers the anterior cap- the femoral neurovascular structures from the hip. sule (Figure 6.5). Just anterior to this is the iliopsoas The lateral femoral cutaneous nerve originates tendon, formed from the muscles of the iliacus and from the lumbar plexus and exits the pelvis under the psoas major inside the pelvis, coursing on the way to inguinal ligament close to the anterior superior iliac its insertion on the lesser trochanter. spine (see Figure 6.6). This nerve is known to be sen- Medially, the hip is bordered by the adductor sitive to external compression (meralgia paresthetica). muscle group including the adductor longus, mag- It is also known to be vulnerable to injury during har- nus, and brevis, and the gracilis (see Figure 6.5). vesting of iliac crest bone graft when the harvest site These muscles are of limited clinical significance is carried too close to the anterior superior iliac spine for hip arthroscopy except when considering a me- and to damage by improperly placed arthroscopic dial approach to the joint, which has been described portals. as a technical entity, but has thus far found limited The lateral circumflex femoral artery arises from clinical application.9 the profunda femoris (deep femoral artery) shortly af-

Rectus femoris reflected & direct heads

Pectineus

Iliopsoas

Adductor magnus

Adductor longus

Adductor brevis

Gracilis

FIGURE 6.5. Deep structures (anterior view). 104 J . W . THOMAS BYRD

Femoral nerve artery & vein

Psoas major muscle

Iliacus muscle

Lateral femoral cutaneous nerve

Ascending branch of the lateral circumflex femoral artery

Iliopsoas muscle

FIGURE 6.6. Neurovascular structures (anterior view).

ter it takes off from the femoral artery (see Figure 6.6). CAPSULAR AND The ascending branch of the lateral circumflex JOINT ARCHITECTURE femoral artery has an oblique course along the direction of the intertrochanteric line. The ilium, ischium, and pubic bones unite at the The superior gluteal nerve and artery are the most acetabulum, forming the innominate bone. During superior of 10 neurovascular structures that exit childhood, these bones are separated within the ac- through the sciatic notch (Figure 6.7). They course etabulum by the triradiate cartilage, which fuses at transversely in a posterior to anterior direction be- skeletal maturity. tween the deep surface of the gluteus medius and the The acetabulum has an inclined abduction angle superficial surface of the gluteus minimus, innervat- of approximately 35 degrees from the horizontal and ing and supplying blood to both. The sciatic nerve ex- a forward flexed position of approximately 20 de- its the notch under the piriformis tendon and then lies grees (Figure 6.8A,C). The articular surface of the posterior to the other short external rotators in a ver- acetabulum has a horseshoe or lunate shape (Figure tical direction as it courses distally (see Figure 6.7). 6.9). The central inferior acetabular fossa is devoid An intricate vascular anastomosis converges at the of articular surface. It is occupied by a fat pad cov- lower border of the quadratus femoris consisting of ered with synovium called the pulvinar. Addition- the ascending branch of the first perforating artery, the ally, it contains the acetabular attachment of the descending branch of the inferior gluteal artery, and ligamentum teres. The socket of the acetabulum is transverse branches of the medial and lateral circum- completed inferiorly by the transverse acetabular flex femoral arteries (see Figure 6.7). ligament. CHAPTER 6: GROSS ANATOMY 105

Descending branch of inferior gluteal artery

Superior gluteal nerve & artery

Inferior gluteal nerve & artery

Pudendal nerve

Posterior femoral cutaneous nerve 1st perforating artery Sciatic nerve

Medial circumflex femoral artery

FIGURE 6.7. Neurovascular structures (posterior view).

FIGURE 6.8. (A) Acetabular orientation averages 35 degrees of ab- between the bicondylar axis of the knee and the axis of the femoral duction from the horizontal plane. The neck shaft angle formed be- neck in the transverse plane, averages 14 degrees. (C) The acetabu- tween the axis of the femoral neck and femoral shaft averages 125 lum is also oriented with 20 degrees of forward flexion relative to degrees. (B) Femoral anteversion, determined by the angle created the sagittal plane. 106 J . W . THOMAS BYRD

Ilium

Lunate articular surface

Labrum Ligamentum teres

Acetabular fossa

Fovea capitis Transverse acetabular ligament

Pubis 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 liga- Ischium mentum 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.

The labrum is a fibrocartilaginous structure that The intricate nature and specific design of the capsu- attaches to the bony rim of the acetabulum, effectively lar ligaments has been well defined by various ana- deepening to a socket. The labrum terminates inferi- tomic studies. However, over time, more will be orly at the anterior and posterior margins of the ac- learned about the ligaments as a better appreciation etabular fossa. It then becomes contiguous with the is gained of the arthroscopic appearance of this anat- transverse acetabular ligament, which completes the omy. Perhaps this construct will even be partially circumferential ring of the acetabulum. We are learn- redefined. ing that the labrum is a nonhomogeneous structure Anteriorly, the capsule consists primarily of the il- with considerable variation in different areas of the iofemoral ligament or ligament of Bigelow (Figure acetabulum (see Chapter 8). 6.10). It has an inverted Y shape beginning from its il- Although variable, the proximal femur has a neck iac attachment on the superior aspect of the acetabu- shaft angle that averages 125 degrees, with approxi- lum. It then fans out in a spiraling pattern to its femoral mately 14 degrees of femoral neck anteversion (see attachment along the intertrochanteric line. It is one Figure 6.8A,B). The femoral head has an articular sur- of the strongest ligaments in the body, and the spiral- face that forms approximately two-thirds of a sphere, ing direction of its fibers makes it taut in extension in articulating with the acetabulum (see Figure 6.9). Me- a wringing-out mechanism and relaxed in flexion. dially, on the articular portion of the femoral head, is The ischiofemoral ligament reinforces the poste- a pit called the fovea capitis, the site of the femoral rior capsule (Figure 6.11). It too has a spiraling pattern attachments of the ligamentum teres. as it courses from its ischial attachment on the pos- The bony architecture of the hip provides it with terior acetabular rim to its femoral attachment on the significant intrinsic stability. This stability is further superolateral neck, medial to the base of the greater enhanced by an intricate complex of capsular liga- trochanter. ments. This complex consists of four distinct liga- The pubofemoral ligament, although relatively ments that provide varying contributions to the joint. weak, reinforces the inferior and anterior capsule from CHAPTER 6: GROSS ANATOMY 107

Iliofemoral ligament Pubofemoral ligament

FIGURE 6.10. The iliofemoral ligament (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 ANTERIOR capsule, where it blends with the medial edge of the iliofemoral ligament.

Ischiofemoral ligament

FIGURE 6.11. The ischiofemoral ligament reinforces the posterior capsule, spiraling from its attachment on the ischial portion of the posterior POSTERIOR acetabulum to the superolateral aspect of the femoral neck. 108 J . W . THOMAS BYRD the pubic part of the acetabular rim where it blends A deep layer of fibers within the ligamentous with the medial edge of the iliofemoral ligament (see capsule courses circularly around the neck of the Figure 6.10). Again, the spiraling nature of this com- femur, creating the zona orbicularis (see Figure plex tends to screw the femoral head medially into the 6.12). This layer may serve as a collar to constrict acetabulum during extension, which has several clin- the capsule and help maintain the femoral head ical implications. First, this explains why patients within the acetabulum. 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, VASCULAR SUPPLY TO from a surgical standpoint, it would appear advanta- THE FEMORAL HEAD geous to perform arthroscopy with the hip flexed, further relaxing the capsule. However, this can create po- Intraarticular isolation of the femoral head and neck tential concern for portal placement, as discussed in makes it highly dependent on its tenuous vascular Chapter 7. supply. Its susceptibility to circulatory compromise is The fourth ligament is the ligament of the head of an ongoing source of concern to physicians who treat the femur (ligamentum teres) (Figure 6.12). Coursing hip pathology. Ischemic insult followed by avascular from its attachment in the acetabular fossa to the necrosis (AVN) of the femoral head, similar to other fovea of the femoral head, it is intracapsular, yet en- forms of osteonecrosis, has been clearly linked to cer- cased in synovium, making it extrasynovial. Its rela- tain disease states and types of exposure although it tively weak, redundant nature makes it unlikely that is less clearly associated with others and often purely this has any significant stabilizing effect on the hip. idiopathic.10 AVN has been associated with previous The size and strength of this ligament are variable, trauma including fracture and dislocation and may oc- and it is occasionally absent, the significance of which cur iatrogenically in association with surgical proce- is unknown. dures that violate the vascular pattern.

Ligamentum teres

Zona orbicularis

FIGURE 6.12. The ligamentum teres is redundant and weak and contributes little to the capsular stability of the hip. Encased in synovium, it is intracapsular, yet extrasynovial. CHAPTER 6: GROSS ANATOMY 109

Retinacular arteries superior anterior/posterior inferior

Artery of ligamentum teres (foveolar artery)

Medial circumflex Ascending femoral artery transverse & descending branches of the lateral circumflex Deep femoral artery femoral artery

FIGURE 6.13. The femoral head receives arterial blood flow from branches of the medullary artery from the shaft of the femur; and an anastomosis of three sets of arteries: (1) the retinacular ves- (3) the artery of the ligamentum teres from the posterior division sels, primarily from the medial circumflex femoral artery and, to of the obturator artery. a lesser extent, the lateral circumflex femoral artery; (2) terminal

The poorly defined and uncertain nature of AVN References is reflected in the myriad surgical procedures that have been described in its management, none of which has 1. Anderson JE: Grant’s Atlas of Anatomy, 7th ed. Baltimore: proven to be superior, and few of which have even Williams & Wilkins, 1978. 2. Hoppenfeld S, deBoer P (eds): Surgical Exposures in Or- been shown to be truly effective in altering the natu- thopaedics. The Anatomic Approach. Philadelphia: Lippincott, 11 ral course of the process. 1984. Arterial blood supply to the femoral head is 3. Byrd JWT: Hip arthroscopy utilizing the supine position. Ar- achieved through an anastomosis of three sets of arthroscopy 1994;10:275–280. teries (Figure 6.13). The principal vessels ascend in the 4. Byrd JWT, Pappas JN, Pedley MJ: Hip arthroscopy: an anatomic study of portal placement and relationship to the extrasynovial retinaculum, which is a reflection of the lig- articular structures. Arthroscopy 1995;11:418–423. amentous capsule onto the neck of the femur. These 5. Glick JM: Hip arthroscopy using the lateral approach. Instr vessels arise mainly posterior superiorly and posterior Course Lect 1988;37:223–231. inferiorly from the medial circumflex femoral artery, 6. Johnson L: Hip joint. In: Johnson L (ed). Diagnostic and Surgi- which is supplemented to a lesser extent from the lat- cal Arthroscopy, 3rd ed. St. Louis: Mosby, 1986:1491–1519. 7. Ide T, Akamatsu N, Nakajima I: Arthroscopic surgery of the eral circumflex femoral artery. These vessels anasto- hip joint. Arthroscopy 1991;7:204–211. mose with the terminal branches of the medullary ar- 8. Henry AK: Extensile Exposure, 2nd ed. New York: Churchill tery from the shaft of the femur. The third source is Livingstone, 1973. the anastomosis within the femoral head from the ar- 9. Gross RH: Arthroscopy in hip disorders in children. Orthop tery of the ligamentum teres, which arises from a pos- Rev 1977;6:43–49. 10. Jones JP: Concepts of etiology and early pathogenesis of os- terior division of the obturator artery. This vessel may teonecrosis. Instr Course Lect 1994;43:499–512. persist with advanced age, but in approximately 20% 11. Steinberg ME: Early diagnosis, evaluation and staging of os- of the population it never develops. teonecrosis. Instr Course Lect 1994;43:513–518.