The hip joint is formed like a ball and socket joint, which rotates on more than one axis and is classed as a synovial joint. The ball of the hip joint is comprised of the head of the femur or thigh bone as it is more commonly known, whilst the concavity of the socket is created by the acetabulum, which is a cup-like depression within the pelvic bone.
The main function of the hip joint is to support the body weight in both standing and running or walking. The hips are very important for maintaining balance, and damages of the hip may cause impairments in all the function that this joint has, that can vary from easy to severe impairment.
|Articulation surfaces||Head of the femur and acetabulum of the pelvis|
Outer: iliofemoral, ischiofemoral, pubofemoral
Inner: transverse acetabular, ligament of the femoral head
Flexors: iliopsoas, sartorius, tensor fasciae latae, rectus femoris, gluteus medius
Extensors: gluteus maximus, medius and minimus, biceps femoris, semimembranosus
Abductors: gluteus medius, gluteus minimus, piriformis
Adductors: adductor longus, adductor brevis, adductor magnus, pectineus, gracilis, quadratus femoris
Internal rotators: gluteus medius, gluteus minimus
External rotators: obturator internus, obturator externus, superior gemellus, inferior gemellus, quadratus femoris, piriformis
|Vascularization||Medial and lateral circumflex arteries, artery of the head of the femur (branches of the femoral artery)|
|Innervation||Anteriorly: femoral nerve
Inferiorly: obturator nerve
Laterally: sciatic nerve
Posteriorly: superior gluteal nerve
|Actions||Flexion (140 degrees), extension (15 degrees), abduction (40 degrees), adduction (25 degrees), internal rotation (35 degrees), external rotation (45 degrees)|
|Clinical relations||Perthes disease, fractures, osteoporosis, luxation|
This article will discuss the anatomy and clinical aspects related to the hip joint.
The femur is both the longest and the heaviest bone in the entire human skeleton. It is comprised proximally of a head that contains a fovea or pit shaped depression and a neck which joins the head to the shaft of the bone.
The neck is angled to the long axis of the femur at an average of 126 degrees. Also, the greater and lesser trochanters project laterally and medially respectively, at the junction of the neck and the body of the femur. They are separated by the intertrochanteric line, indicating the exact border of the femoral neck and body.
The acetabulum is the female portion of the hip joint; a concavity which encompasses the head of the femur. It is the part of the pelvis in which the ilium, ischium and pubis merge. While it is a concave structure, its bony rim is partially surrounded by a fibrocartilaginous ring known as the labrum. This structure is completed by the transverse acetabular ligament which stretches across the acetabular notch.
The capsule of the hip joint has been described as strong and fibrous, but loose enough to accommodate a range of movements. It attaches to the anatomical structures known as the acetabular labrum, the transverse acetabular ligament and the intertrochanteric line of the femur.
The proximal two thirds of the neck of the femur are encapsulated by the hip joint, whereas the distal third remains extracapsular. The iliofemoral ligament, the pubofemoral ligament and the ischiofemoral ligament all act to strengthen the mobile capsule.
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- The iliofemoral ligament attaches itself to both the anterior inferior iliac spine and the acetabulum superiorly and the intertrochanteric line inferiorly, creating a ‘Y’ shape. It prevents hyperextension of the hip.
- The ischiofemoral ligament originates in the rim of the acetabulum and turns laterally as it ascends to insert upon the inferomedial aspect of the greater trochanter. It functions in coherence with the iliofemoral ligament and also fixates the femoral head in the acetabulum. Prevents excessive medial rotation of the thigh.
- The pubofemoral ligament arises from the pubic ramus and merges inferolaterally into the iliofemoral ligament, but may also have an attachment to the femoral neck. This ligament tightens during extension and abduction in order to limit the latter movement.
- The transverse acetabular ligament runs over the acetabular notch and joins up with the inferior ends of the labrum. This ligament completes the acetabular ring.
- The ligament of the head of the femur is situated within the capsule but is extrasynovial. It arises from the acetabular notch and inserts upon the fovea of the femur. Within the ligament runs the artery that supplies the head of the femur.
Now a brief overview of the muscle groups, which are organised according to their primary function in relation to the hip joint.
- The iliopsoas muscle, which consists of the psoas major muscle and the iliacus muscle. The psoas major originates from the vertebral bodies of T12- L4, the intervertebral discs between T12-L4 and the costal processes of L1-L5 vertebrae. The iliacus muscle originates from the iliac fossa. These individual muscle fascicles merge together and insert as a whole upon the lesser trochanter of the femur. The iliopsoas acts up the hip joint causing flexion and external rotation of the thigh. The psoas major also contributes to anterior and lateral flexion of the trunk.
- The sartorius muscle; originating from the anterior superior iliac spine(ASIS) and the notch which is situated just below it, the sartorius muscle inserts itself at the medial surface of the proximal tibia via the pes anserinus.
- The rectus femoris starts from the anterior inferior iliac spine and superior margin of the acetabulum. This muscle finds it's insertion at the tibial tuberosity, via the patellar ligament. The rectus femoris functions by extending the leg at the knee joint and flexing the thigh at the hip joint.
- The tensor fascia latae, like the sartorius muscle also originates from the ASIS, however to a lesser extent it also arises from the anterior part of the outer lip of the iliac crest. It inserts into iliotibial tract along the lateral thigh. It acts to stabilize the trunk on the thigh and also abducts, medially rotates and flexes the thigh at the hip joint, in addition to assisting in extension and external rotation of the leg at the knee joint.
- The gluteus maximus muscle originates the lateroposterior surface of the sacrum and coccyx, the ilium (behind the posterior gluteal line), the thoracolumbar fascia and the sacrotuberous ligament. It inserts into the iliotibial tract as well as into the gluteal tuberosity of the femur.
- The biceps femoris muscle has two heads. The long head arises from the inferomedial impression of the ischial tuberosity, while the short head arises from the lateral lip of the linea aspera and the lateral supracondylar line of the femur. These heads merge and insert as one tendon into the lateral side of the head of the fibula.
- The semimembranosus muscle comes from both the superolateral aspect of the ischial tuberosity and terminates upon the posterior portion of the medial condyle of the tibia.
- The semitendinosis muscle arises from the posteromedial impression of the ischial tuberosity, and inserts at the medial surface of proximal tibia, below the medial condyle, via the pes anserinus.
- The gluteus medius muscle originates between the anterior and posterior gluteal lines on the lateral surface of the ilium and inserts upon the lateral aspect of the greater trochanter of the femur.
- The gluteus minimus muscle passes between the anterior and inferior gluteal lines after arising from the lateral surface of the ilium and terminates upon the anterior surface of the greater trochanter of the femur.
- The piriformis muscle originates upon the anterior surface of the sacrum between S2-S4, and also from the sacrotuberous ligament. It inserts upon the apex of the greater trochanter of the femur.
- The adductor longus muscle originates from the body of the pubis, which is situated just below the pubic crest and inserts into the middle third of the linea aspera of the femur.
- The adductor brevis muscle arises from both the body and the inferior aspect of the pubic ramus and terminates on both the pectineal line as well as the proximal part of the linea aspera of the femur.
- The adductor magnus muscle comes from the inferior pubic ramus, as well as the ramus of the ischium. It also merges with fibers from the ischial tuberosity, which form part of the hamstring complex. These fibers attach themselves to the gluteal tuberosity, the linea aspera of the femur and the medial supracondylar line. The portion that adds to the hamstring fibers inserts upon the adductor tubercle.
- The pectineus muscle starts out at the pectineal line of the pubis and finishes at the pectineal line of the femur.
- The gracilis muscle arises from the body of the pubis and the inferior pubic ramus and terminates upon the superior part of the medial surface of the proximal tibia, via the pes anserinus.
- The quadratus femoris muscle comes from the lateral margin of the ischial tuberosity and inserts into the intertrochanteric crest of the femur.
Internal rotator muscles
The internal rotator muscles include the gluteus medius and the gluteus minimus muscles, in addition to some of the adductor muscles, namely adductor magnus.
External rotator muscles
- The obturator internus muscle originates from the pelvic surface of the obturator membrane and the margins of the obturator foramen. It inserts into the medial surface of the greater trochanter of the femur.
- The obturator externus muscle arises from the margins of the obturator foramen and the obturator membrane. It terminates in the trochanteric fossa of the femur.
- The superior gemellus muscle comes from the outer surface of the ischial spine and stops at the medial aspect of the greater trochanter of the femur.
- The inferior gemellus muscle arises from the upper margin of the ischial tuberosity and terminates upon the medial surface of the greater trochanter of the femur.
- The quadratus femoris muscle (see adductor muscles)
- The piriformis muscle (see abductor muscles)
The range of movements of the hip joint are marked in degrees and are categorised by name:
- Flexion: 140 degrees
- Extension: 15 degrees
- Abduction: 40 degrees
- Adduction: 25 degrees
- Internal rotation: 35 degrees
- External rotation: 45 degrees
These ranges of movement occur when the knee is flexed at a right angle (90 degrees).
There are two sets of arteries that contribute either majorly or minorly to the vascularisation of the joint capsule of the hip. The major contributing set contains the medial and lateral circumflex arteries that arise from the deep branch of the femoral artery. The minor contributing set singularly of the artery of the head of the femur.
The innervation of the hip joint comes anteriorly from the femoral nerve, inferiorly from the anterior division of the obturator nerve, laterally from the articular branch of the sciatic nerve and posteriorly from the nerve that runs to the quadratus femoris as well as the superior gluteal nerve.
Perthes disease, which is correctly termed Legg-Calve-Perthes disease and medically known as avascular necrosis is a disorder that is mostly found in children. The condition affects the head of the femur, when there is inadequate perfusion to the epiphysis, causing the bone to become necrotic.
Eventually the blood flow returns to the area through revascularization and bone remodelling takes place. There are no somatic symptoms for this disease and the main complaint from patients with this condition is an increased risk of hip fracture.