Applied of the RICARDO A. FERNANDEZ, MHS, PT, OCS, CSCS • Northwestern University

The hip is more than just a ball-and- fuse in adults to form the easily recog- socket joint. It supports the weight of the nized “hip” . The , meaning bowl head, , and trunk, and it is the primary in Latin, is composed of three structures: the joint that distributes the forces between the innominates, the , and the pelvis and lower extremities.1 This joint is (Figure 1). formed from the articu- The has a large flare, or , Key PointsPoints lation of the proximal superiorly, with the easily palpable anterior with the innomi- superior iliac spine (ASIS) anterior with the The hip joint is structurally composed of nate at the . anterior inferior iliac spine (AIIS) just inferior strong ligamentous and capsular compo- The joint is considered to it. Posteriorly, the crest of the ilium ends nents. important because it to form the posterior superior iliac spine can affect the spine and (PSIS). With respect to , Postural alignment of the bones and pelvis proximally and the PSIS is often marked as a dimple in the of the hip plays a role in determining the femur and skin. Clinicians attempting to identify pelvic functional gait patterns and forces associ- distally. The biomechan- or hip subluxations, leg-length discrepancies, ated with various supporting structures. ics of this joint are often or postural faults during examinations use There is a relationship between the hip misunderstood, and the these landmarks. joint and muscle strength as it relates hip joint receives less to functional performance. attention than other joints such as the shoul- Key Words: hip functional anatomy, hip der or . We readily biomechanics recognize, for example, that the is also known as the glenohumeral joint and the knee is also known as the tibiofemoral joint. What exactly is the anatomical term used to describe the hip joint? The correct response is the coxofemoral joint.1

Bony and Ligamentous Anatomy The os coxa—or innominate, meaning name-

less in Latin—is composed of the union of Figure 1 The pelvis is composed of the innominates, the ilium, , and bones. These sacrum, and the coccyx.

© 2004 Kinetics • ATT 9(4), pp. 6-10 6  JULY 2004 ATHLETIC THERAPY TODAY ATHLETIC THERAPY TODAY JULY 2004  7 There are four main pelvic joints: the lumbosacral referred to as the acetabular notch. The hip socket is and sacroiliac joints, the pubic , and the further deepened by the fibrocartilaginous acetabu- coxofemoral joint. The is composed lar labrum, which grips the periphery of the femoral of the fifth lumbar , which articulates with head.3 The transverse and the acetabular the superior portion of the sacrum. This is the direct labrum reinforce the stability of this articulation. spinal connection to the bony pelvis. The bony design of the hip favors mobility, and The sacroiliac joints form the bilateral articula- therefore the help provide much-needed tions between the wedgelike sacrum and the adjoining stability. There is only one posteriorly located hip ilium. The C-shaped articular surfaces of the sacrum ligament, the . The main are covered with , and the articular function of this ligament is to limit hip extension as surfaces of the ilia are covered with . it spirals around the femur superiorly. There are two There are five groups of ligaments that support the hip ligaments anteriorly, which also limit hip exten- sacroiliac joints. Anteriorly there is only the anterior sion. These are the (which also sacroiliac ligament; posteriorly there are the supraspi- limits abduction) and the large , nous, posterior sacroiliac, sacrospinous, and sacrotu- or Y ligament of Bigelow, which runs from the AIIS. A berous ligaments to provide stability. person who stands with the fully extended, such The is the articulation between as one with a flat- posture or with a posteriorly the right and left halves of the pubic rami anteriorly. displaced upper trunk and head, might be resting on This joint consists of the two ends of the pubis bones, the Y ligament for stability. which are separated by a fibrocartilaginous disc. The The femur proximally consists of the femoral pubic tubercles are often palpated to help a clinician head, fovea capitus, femoral , greater , identify , alignment, or posture. The “neutral and . The head of the femur is shaped pelvis,” for example, is the position in which the bilat- like two thirds of a large sphere.3 There is articular eral ASIS are in the same transverse plane and the cartilage on almost the entire articulating portion of ASIS and the symphysis pubis are in the same vertical the femur, which is thickest superiorly. The cartilage is plane (Figure 2).2 biphasic, or a solid/fluidlike substance, which increases The coxofemoral joint is the articulation between the area of load distribution to minimize stress on the the proximal femur and the innominate at the acetabu- hip joint. The only portion of the that lum. The acetabulum, or socket, is formed at the union does not have articular cartilage is the fovea capitus, of the ilium, ischium, and pubic bone. The acetabulum the attachment for the ligamentum teres. The ligamen- has a bony horseshoe-shaped rim that is absent infe- tum teres, which provides little stabilizing support, riorly and highest superiorly. This rim supports the houses the that during childhood carries the femur to resist potential dislocating forces. The inferior blood supply to the femoral head through the obtura- region of the acetabulum that is devoid of the rim is tor artery. If damaged during childhood, it can disrupt circulation to the head of the femur. The neck of the femur transmits the forces between the femoral head and the femoral shaft. There is a laterally projecting greater tuberosity and a posteromedially projecting lesser tuberosity, which function as muscle-attachment sites for the powerful muscles of the hip. The femur forms an angle in the frontal plane between the femoral neck and the medial side of the femoral shaft that is called the angle of inclination. A normal hip-inclination angle is about 125º in adults. If the angle is greater than 125° it is referred to as coxa Figure 2 The “neutral pelvis” as seen when the bilateral anterior superior iliac spines are in the same transverse plane and they and valga, meaning the distal segment is abducted. If the the symphysis pubis are in the same vertical plane. angle is less than 125° it is called coxa vara, meaning

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