Anatomy Of The Hip

Question 1

Osteology of the hip bones

Answer 1

The left and right hip bones (innominate bones) are two irregularly shaped bones that, together with the sacrum, form part of the pelvic girdle – the bony structure that attaches the axial skeleton to the lower limbs.

The hip bones have three main articulations:

Question 2

Composition of the hip bone

Answer 2

The hip bone is comprised of three parts: the ilium, pubis and ischium.

In the child, these are separated by the triradiate cartilage; fusion begins between the ages of 15 and 17 years and is complete by age 20-25 years.

Together, the ilium, pubis and ischium form a cup-shaped socket known as the acetabulum

The head of the femur articulates with the acetabulum to form the hip joint.

Question 3

The ilium

Answer 3

The ilium is the widest and largest of the three parts of the hip bone and is located superiorly.

The body of the ilium forms the superior part of the acetabulum (acetabular roof). Immediately above the acetabulum, the ilium expands to form the wing

The wing of the ilium has two surfaces:

Question 4

The Pubis

Answer 4

The pubis is the most anterior portion of the hip bone. It consists of a body, a superior ramus and an inferior ramus (ramus = branch).

Pubic body: Located medially, the pubic body articulates with the opposite pubic body at the pubic symphysis. Its superior aspect is marked by a rounded thickening (the pubic crest), which extends laterally as far as the pubic tubercle.

Superior pubic ramus: This extends laterally from the pubic body to the acetabulum.
Inferior pubic ramus: This extends laterally from the pubic body join with the inferior ischial ramus. Together they form the ischiopubic ramus.

Together, the superior and inferior rami enclose part of the obturator foramen, through which the obturator nerve, artery and vein pass through to reach the lower limb

Question 5

The ischium

Answer 5

The ischium forms the posteroinferior part of the hip bone.

Like the pubis, it is composed of a body, an inferior ramus and superior ramus.

The posteroinferior aspect of the ischium forms the ischial tuberosity. When you are sitting upright in a chair, it is your ischial tuberosities that you are sitting on.

Near the junction of the superior ramus and body is a posteromedial projection of bone; the ischial spine.

Two important ligaments attach to the ischium:

Question 6

The hip joint

Answer 6

The hip joint is a ball and socket synovial joint consisting of an articulation between the head of femur and the pelvic acetabulum

Its primary function is to enable mobility of the lower limbs without weakening the ability of the lower limbs to support the weight of the body.

The acetabulum forms a cup-like socket on the inferolateral aspect of the pelvis.

A fibrocartilaginous collar, the acetabular labrum, encircles the acetabulum, deepening it and providing a more secure fit for the hemispherical femoral head.

The acetabular labrum increases the articular contact area by 10% so that more than 50% of the femoral head is in contact with the socket at any one time.

It is therefore a very stable joint, at the expense of some mobility

Both the acetabulum and head of femur are covered in hyaline cartilage.

The articular surface of the acetabulum is shaped like a horseshoe; it is incomplete inferiorly in the region known as the acetabular notch. The acetabular notch contains fibroelastic fat covered with synovial membrane.

Question 7

Osteology of the femur

Answer 7

The femur articulates with the acetabulum of the pelvis proximally to form the hip joint, and with the tibia and patella distally to form the knee joint. It is the longest bone in the human body.

The femoral head is covered with hyaline cartilage. In the centre of the hemispherical femoral head, there is a small depression called the fovea capitis.

The ligamentum teres (or ligament of the head of the femur) attaches here. This ligament contains the artery of the ligamentum teres.

The neck connects the head of the femur to the femoral shaft. It passes inferiorly, posteriorly and laterally, making an angle of approximately 125° with the long axis of the femoral shaft. This angle is slightly smaller in females.

The greater and lesser trochanters are large bony prominences at the proximal end of the femoral shaft. On the anterior aspect, they are connected by the intertrochanteric line and on the posterior aspect by the intertrochanteric crest

The femoral shaft is smooth and rounded. Posteriorly, there is a ridge called the linea aspera to which the intermuscular septa and many muscles of the thigh attach.

The gluteal tuberosity lies between the upper end of the linea aspera and the intertrochanteric crest; this is the site of insertion of the gluteus maximus muscle of the buttock

The lines aspera diverges to form the lateral and medial supracondylar lines

Question 8

The capsule and capsular ligaments

Answer 8

The capsule of the hip joint is strong and tough.

Proximally, it attaches to the edge of the acetabulum, 5-6mm outside the acetabular labrum.

Distally, it attaches to the intertrochanteric line of the femur anteriorly and the femoral neck posteriorly

Anteriorly, the capsular fibres ascend along the neck as longitudinal retinacula, containing blood vessels for the femoral head and neck

The iliofemoral ligament is the strongest ligament in the body. It has an inverted Y shape, the base of the Y is attached to the anterior inferior iliac spine of the ilium and the limbs of the Y are both attached to the intertrochanteric line of the femur.

In the standing position, it ‘screws the head of the femur into the acetabulum’ and prevents the trunk from falling backward without the need for muscular activity i.e. prevents hyperextension of the hip. When seated, it becomes relaxed, permitting the pelvis to tilt backward into its ‘sitting position’.

The pubofemoral ligament lies inferior and anterior to the hip joint. It is triangular in shape. Its base is attached to the superior pubic ramus and its apex to the inferior part of the intertrochanteric line anteriorly. Its roles are to prevent excessive abduction and extension of the hip joint.

The ischiofemoral ligament is spiral-shaped and is attached to the body of the ischium posteriorly. Its inferior fibres spiral superolaterally from the body of the ischium to attach to superolateral end of the intertrochanteric line of the femur, anteromedial to the base of the greater trochanter. It is the weakest of the three ligaments. It prevents excessive internal (medial) rotation of the hip joint.

There is also a small transverse acetabular ligament, which is formed by the acetabular labrum as it bridges the acetabular notch

This converts the notch into a tunnel through which blood vessels and nerve enter the hip joint.

The synovial membrane lines the capsule and is attached to the margins of the articular surfaces. It ensheathes the ligamentum teres (round ligament) and covers the pad of fat contained in the acetabular fossa.

Question 9

Stabilising factors

Answer 9

There are several factors that act to increase stability of the hip joint:

Question 10

Movements and muscles

Answer 10

Flexion - uses the muscles: Iliopsoas (iliacus + psoas major) Assisted by rectus femoris, sartorius, pectineus

Extension - uses the muscles: Gluteus maximus Hamstrings: semimembranosus, semitendinosus, biceps femoris (long head)

Abduction - uses the muscles: Gluteus medius, gluteus minimus Assisted by sartorius, tensor fascia lata

Adduction - uses the muscles: Adductor longus, adductor brevis, adductor magnus Assisted by pectineus, gracilis, obturator externus

Lateral rotation - uses the muscles: Obturator externus, piriformis, obturator internus, superior and inferior gemelli, quadratus femoris Assisted by gluteus maximus, sartorius

Medial rotation - uses the muscles: Anterior fibres of gluteus medius and minimus, tensor fascia lata. Assisted by adductor brevis, adductor longus, superior portion of adductor magnus, pectineus

Question 11

The blood supply of the femoral head and neck

Answer 11

There is an extracapsular arterial ring at the base of the femoral neck that is formed posteriorly by large branch of the medial femoral circumflex artery (MFCA; which is a branch of the profunda femoris artery) and anteriorly by smaller branches of the lateral femoral circumflex artery (LFCA; also usually a branch of the profunda femoris artery)

As the ascending cervical arteries cross the surface of femoral neck, they send numerous small branches into the metaphysis of the femoral neck.

The ligamentum teres (ligament of the head of the femur or round ligament) contains within it the artery of the ligamentum teres, which arises most commonly from the obturator artery.

Question 12

The lumbosacral plexus

Answer 12

The lower limb receives its nerve supply via the lumbosacral plexus.

The lumbar component of the lumbosacral plexus is formed from the anterior rami of the L1-4 spinal nerves.

These anterior rami divide into several cords which combine to form the major peripheral nerves of the lumbar plexus.

These nerves descend on the posterior abdominal wall to the lower limb, where they innervate their target structures (e.g. skin, muscle).

The L4 anterior ramus also gives off a branch which combines with the L5 anterior ramus to form the lumbosacral trunk. This contributes axons to the sacral plexus (hence the combined term, lumbosacral plexus).

The ilioinguinal nerve has the root L1. Amongst other functions, it innervates the skin of the genitalia and the upper medial thigh

The genitofemoral nerve has the roots L1 and L2. It divides into a genital branch and a femoral branch ( Femoral B innervates the skin on the upper anterior thigh

The lateral cutaneous nerve of the thigh (also known as the lateral femoral cutaneous nerve) is formed from the posterior divisions of the L2 and L3 roots. It has a purely sensory function and enters the thigh at the lateral aspect of the inguinal ligament, where it provides cutaneous sensation to the anterolateral thigh as far inferiorly as the knee.

The obturator nerve is formed from the anterior divisions of the L2, L3 and L4 roots. It innervates the skin over the medial thigh and is the nerve of the medial compartment of the thigh.

The femoral nerve is formed from the posterior divisions of the L2, L3 and L4 roots. It innervates the skin of the anterior thigh via its anterior femoral cutaneous branch and via its saphenous branch it also innervates the skin of the medial leg.

I Get Leftovers On Friday 
Ilioinguinal (L1)
Genitofemoral (L1+L2)
Lateral femoral cutaneous (L2+L3)
Obturator (L2+L3+L4)
Femoral (L2+L3+L4)

Question 13

The sacral plexus

Answer 13

The sacral plexus is formed from the anterior rami of S1, S2, S3, S4 and S5.

It also receives a contribution from L4 and 5 via the lumbosacral trunk.

The nerves of the sacral plexus have two main destinations: the lower limb; and the pelvic muscles, organs and perineum.

The branches of the sacral plexus that you need to know the root values:

Question 14

Greater and lesser sciatic foramina

Answer 14

The sacrospinous ligament runs from the sacrum to the ischial spine of the pelvis and the sacrotuberous ligament runs from the sacrum to the ischial tuberosity.

The greater and lesser sciatic foramina are formed by the sacrospinous and sacrotuberous ligaments and the greater and lesser sciatic notches of the pelvis

The greater sciatic foramen is bounded inferiorly by the ischial spine and sacrospinous ligament, posteromedially by the upper fibres of the sacrotuberous ligament and anterolaterally the greater sciatic notch of the ilium.

The superior gluteal nerve and vessels exit the pelvis through the greater sciatic foramen superior to the piriformis muscle

The following structures all exit the pelvis via the greater sciatic foramen inferior to the piriformis muscle:

Question 15

The sciatic nerve in the gluteal region and thigh

Answer 15

The sciatic nerve is the largest nerve in body, measuring approximately 2cm in diameter. It has the root values L4, L5, S1, S2, and S3.

The sciatic nerve emerges horizontally from the pelvic cavity, inferior to the piriformis muscle, mid-way between the posterior superior iliac spine and the ischial tuberosity.

In the gluteal region, the sciatic nerve lies successively on the bone of the ischium, then on the superior gemellus, obturator internus, inferior gemellus and quadratus femoris muscles

It passes midway between the greater trochanter of the femur and the ischial tuberosity of the pelvis to enter the posterior
compartment of the thigh.

In the posterior thigh, the sciatic nerve lies on the posterior surface of the adductor magnus muscle and is crossed by the long head of the biceps femoris muscle

The sciatic nerve usually divides into the tibial nerve and common perineal nerve at the superior end of the popliteal fossa (above the knee). The common peroneal and tibial nerves are both mixed sensory and motor nerves.

The sciatic nerve has no branches in the gluteal region.

The tibial nerve supplies all of the hamstring muscles i.e. semitendinosus, semimembranosus, biceps femoris (long head) and the hamstring (ischial) part of adductor magnus in the posterior thigh.

The common peroneal (common fibular) nerve supplies the short head of biceps femoris in the posterior thigh.

Question 16

Administering intramuscular injections in the gluteal region

Answer 16

When administering an intramuscular injection in the gluteal region, it is essential to avoid injury to the sciatic nerve.

The dorsogluteal site is used in children between the ages of three and seven years, whereas the ventrogluteal site is usually preferred in children over seven years of age or in adults. The ventrogluteal site is further from the neurovascular structures but requires better patient compliance.

To locate the ventrogluteal site, you should place the palm of your hand over the greater trochanter of the femur, point your thumb towards the inguinal region and your index finger toward the anterior superior iliac crest

Spread your index and middle fingers to make a V and carefully inject between the proximal

Question 17

The Facia lata, tensor facia lata and the iliotibial tract

Answer 17

The deep fascia of the thigh is called the fascia lata

It encloses thigh muscles and is a site of attachment for the intermuscular septae which divide the thigh into three compartments: the anterior, medial and posterior section). compartments.

Superiorly, it is continuous with the fascia of the abdominal wall and perineal region; inferiorly it is continuous with the deep fascia of the leg (crural fascia).

The fascia lata is thinnest medially over the adductor muscles of the thigh.

Question 18

The Gluteal muscles

Answer 18

The gluteal region is an anatomical area located posterior to the pelvic girdle, at the proximal end of the femur.

The muscles in this region move the lower limb at the hip joint.

The muscles of the gluteal region can be broadly divided into two groups:

Question 19

The superficial muscles of the gluteal region

Answer 19

Gluteus Maximus
The gluteus maximus is the largest of the gluteal muscles. It is also the most superficial, producing the rounded shape of the buttocks.

Gluteus maximus originates from the gluteal (posterior) surface of the ilium, sacrum and coccyx. It crosses the buttock at a 45° angle. The superior and most superficial fibres insert into the iliotibial tract and the inferior and deeper fibres insert into the gluteal tuberosity of the femur.

Actions: Gluteus maximus is the main extensor of the thigh and also assists with lateral (external) rotation at the hip. As a powerful extensor of the hip joint, the gluteus maximus is most suited to powerful lower limb movements such as stepping onto a step, climbing or running but is not used much during normal walking.

Gluteus maximus and the hamstrings work together to extend the trunk from a flexed position by tilting the pelvis backwards, for example when standing up from a sitting position. The superior fibres of the gluteus maximus can also assist in extension of the knee through their attachment to the iliotibial tract.

If the gluteus maximus is paralysed, climbing stairs and running will become very difficult but other muscles can still extend the hip.
Innervation: Inferior gluteal nerve (L5, S1, S2).

Gluteus Medius
The gluteus medius muscle is fan-shaped and lies between the gluteus maximus and gluteus minimus muscles. It is similar in shape and function to the gluteus minimus

Gluteus medius originates from the gluteal surface of the ilium and inserts into the lateral surface of the greater trochanter

Actions: Gluteus medius abducts and medially (internally) rotates the lower limb. Whilst walking, it secures the pelvis in a horizontal alignment, preventing a downward tilt towards the unsupported limb

Innervation: Superior gluteal nerve (L4, L5, S1).

Gluteus Minimus
The gluteus minimus is the deepest and smallest of the superficial gluteal muscles. It is similar is shape and function to the gluteus medius.

Gluteus minimus originates from the ilium and inserts onto the anterior aspect of the greater trochanter

Actions: Like gluteus medius, it abducts and medially (internally) rotates the lower limb. Whilst walking, it secures the pelvis in a horizontal alignment, preventing a downward tilt towards the unsupported limb

Innervation: Superior gluteal nerve (L4, L5, S1).

Question 20

Superior gluteal nerve injury

Answer 20

The superior gluteal nerve supplies the abductors of the hip: gluteus medius and minimus. A superior gluteal nerve lesion therefore leads to weakness in abducting the thigh at the hip.

The superior gluteal nerve can be injured as a complication of hip surgery, injections to the buttock, fractures of the greater trochanter (site of insertion of gluteus medius) and dislocation of the hip joint.

When a healthy person, standing erect, is asked to lift one foot off the ground, the gluteus medius and minimus of the supporting lower limb usually contract, preventing the tilting of the pelvis towards the unsupported side

When a person with a superior gluteal nerve palsy is asked to stand on their injured lower limb, the pelvis on the unsupported side descends. This clinical sign is referred to as a positive Trendelenburg sign.

Question 21

The deep muscles

Answer 21

The deep gluteal muscles are a set of smaller muscles, located deep to the gluteus minimus.

The general action of these muscles is to laterally (externally) rotate the lower limb. They also stabilise the hip joint by ‘pulling’ the femoral head into the acetabulum of the pelvis.

Question 22

Piriformis

Answer 22

The piriformis muscle is a key landmark in the gluteal region because the sciatic nerve emerges from the pelvis inferior to it. It is the most proximal member of the ‘deep muscles’

Piriformis originates from the anterior surface of the sacrum. It travels inferolaterally, through the greater sciatic foramen, to insert into the superior aspect of the greater trochanter of the femur

Actions: Lateral (external) rotation and abduction of the lower limb.

Question 23

Obturator Internus

Answer 23

The obturator internus muscle forms part of the lateral wall of the pelvic cavity.

It originates from the medial surface of the obturator membrane (which fills the obturator foramen) and from the adjacent pubis and ischium, travels through the lesser sciatic foramen, and inserts on the posterior aspect of the greater trochanter below the insertion of the piriformis and superior gemellus muscles.

Actions: Lateral (external) rotation and abduction of the lower limb

Question 24

The Superior and inferior Gemelli

Answer 24

The gemelli are two narrow triangular muscles. They are separated by the obturator internus tendon

The superior gemellus muscle originates from the ischial spine; the inferior gemellus originates from the ischial tuberosity. They insert on the posterior aspect of the greater trochanter of the femur, above and below the insertion of obturator internus respectively.

Actions: Lateral (external) rotation and abduction of the lower limb.

Question 25

Quadratics Femoris

Answer 25

The quadratus femoris is a flat, square-shaped muscle. It is the most inferior of the deep gluteal muscles

It originates from the lateral aspect of the ischial tuberosity and inserts onto the quadrate tubercle (located on the intertrochanteric crest, immediately inferior to the insertion of the inferior gemellus onto the greater trochanter

Actions: Lateral (external) rotation of the thigh.

Question 26

Obturator externus

Answer 26

Obturator externus will also be studied during this session. It is sometimes classed as a member of the deep muscles of the gluteal region and sometimes as part of the medial compartment of the thigh.

Obturator externus originates from external surface of obturator membrane (a membrane that occupies the obturator foramen, and from the adjacent bone. It passes posterior to the neck of femur, inserting onto the posterior aspect of the greater trochanter

Actions: Adduction and lateral (external) rotation of the thigh.

Question 27

The Posterior thigh

Answer 27

The muscles in the posterior compartment of the thigh are collectively known as the hamstrings.

They consist of the biceps femoris, semitendinosus and semimembranosus muscles, which form prominent tendons medially and laterally at the back of the knee

As group, these muscles act to extend the lower limb at the hip and flex it at the knee. They are innervated by the tibial part of the sciatic nerve (except the short head of biceps femoris which is innervated by the common peroneal part of the sciatic nerve).

The adductor magnus muscle has a small hamstring component posteriorly, originating from the ischial tuberosity. This part of the adductor magnus muscle had a common embryonic origin with the hamstring muscles and is therefore innervated by the tibial part of the sciatic nerve.

Question 28

Biceps femoris (long head)

Answer 28

Like the biceps brachii muscle in the arm, the biceps femoris muscle has two heads: a long head and a short head. The common tendon of the two heads can be palpated laterally at the posterior knee.

The long head of biceps femoris originates from the ischial tuberosity of the pelvis. The short head originates from the linea aspera on posterior surface of the femur. The two heads form a common tendon which inserts into the head of the fibula.

Actions: The main action of biceps femoris is to flex the knee. It also extends the thigh at the hip, and laterally (externally) rotates the hip and knee.

Innervation: The long head is innervated by the tibial part of the sciatic nerve, whereas the short head is innervated by the common peroneal (common fibular) part of the sciatic nerve.

Question 29

Semitendinous

Answer 29

The semitendinosus is a largely tendinous muscle, hence the name.

It is sited medial to the biceps femoris and superficial to the semimembranosus muscles

Semitendinosus originates from the ischial tuberosity and inserts on the upper medial aspect of the tibia as part of the pes anserinus.

Actions: Semitendinosus flexes the leg at the knee joint. It also extends the thigh at the hip, medially (internally) rotates the thigh at the hip joint and medially (internally) rotates the leg at the knee joint.

Innervation: Tibial part of the sciatic nerve.

Question 30

Semi-membranosus

Answer 30

The semimembranosus muscle has a flat broad tendon of origin, hence its name. It is located deep to the semitendinosus muscle.

Attachments: Semimembranosus originates from the ischial tuberosity and inserts onto the medial tibial condyle. It does not form part of the pes anserinus.

Actions: Semimembranosus flexes the leg at the knee joint. It also extends the thigh at the hip, medially (internally) rotates the thigh at the hip joint and medially (internally) rotates the leg at the knee joint. Its actions are therefore the same as those of semitendinosus.

Innervation: Tibial part of the sciatic nerve.

Question 31

Hamstring injury

Answer 31

A pulled hamstring tends to occur during sudden muscular exertion that results in stretching of the posterior thigh muscles e.g. jumping, sprinting and lunging.

It is relatively common in footballers and athletes, especially if proper warm-up exercises have not been performed beforehand.

Sudden tension on the hamstrings results in either a muscle sprain, a partial tear or a complete tear of the origin of the hamstring muscles from the ischial tuberosity, sometimes accompanied by avulsion of a fragment of bone.

Question 32

Disorders of the Hip - OA

Answer 32

Osteoarthritis (OA) is the most common disease affecting synovial joints worldwide.

It most commonly affects the elderly; 20-30% of people over the age of 70 suffer from OA of the hip.

It is traditionally referred to pathologically as a degenerative disorder arising from the breakdown of articular hyaline cartilage.

The most common joints affected are the hips, knees, cervical spine, lumbar spine and small joints of the hands.

OA can be classified into primary osteoarthritis in which the cause is unknown, and secondary osteoarthritis in which there is a known precipitating cause.

The risk factors for primary osteoarthritis include:

Question 33

Pathology of OA

Answer 33

Precipitating risk factors (e.g. obesity, trauma, malalignment) lead to excessive or uneven loading of the joint. This leads to damage to the hyaline cartilage covering the articular surface.

Initially, the hyaline cartilage becomes swollen due to increased proteoglycan synthesis by chondrocytes, with increased numbers of chondrocytes differentiating from chondroprogenitor cells

This stage reflects an attempt to repair the cartilage damage and can continue for several years.

As the disease progresses however, the proteoglycan content falls, causing the cartilage to soften and lose elasticity.

Microscopically, flaking and fibrillation (vertical clefts) develop along the normally smooth articular surface. Over time,
the cartilage becomes eroded down to the subchondral bone, resulting in loss of joint space.

These surface changes in the cartilage alter the distribution of biomechanical forces and trigger further active changes in the tissues.

The subchondral bone responds with vascular invasion and increased cellularity, becoming thickened and denser at areas of pressure. This process, known as eburnation, manifests as subchondral sclerosis on X-rays.

The traumatised subchondral bone may also undergo cystic degeneration to form subchondral bone cysts.

At areas along the articular margin, osseous metaplasia of connective tissue occurs, leading to irregular outgrowth of new bone (osteophytes).

The four cardinal signs of OA on an X-ray are:

Question 34

OA of the hip

Answer 34

Osteoarthritis of the hip OA of the hip is most common in males over 40 years of age.

The symptoms experienced include:

Question 35

Fractures of the Femoral neck

Answer 35

Fractured neck of femur (#NOF) is defined as a fracture of the proximal femur, up to 5cm below the lesser trochanter.
#NOF are classified as:

Question 36

Why with extra capsular fractures the supply to femoral head is likely to remain intact?

Answer 36

NOF is a very common injury with an incidence approaching 100,000 per annum in the UK and approaching 4 billion worldwide. It is a very serious injury, especially in older people, is likely to be life-changing and for some people will be life- threatening.

Intracapsular fractures are more common in the elderly, especially post- menopausal women with osteoporotic bone. They often occur after a minor fall.

Extracapsular fractures tend to affect the young and middle-aged population and are usually the result of significant traumatic force e.g. a road traffic collision.

Due to the high risk of avascular necrosis, a displaced intracapsular fracture in an older person is usually treated by surgical replacement of the femoral head

There is 10% one-month mortality, rising to 20% at one year. This is mostly due to many of the patients being elderly and having multiple co- morbidities. 30% of patients at one-year post-#NOF will have a permanent disability, 40% will be unable to walk independently and 80% will be unable to carry out at least one independent activity of daily living.

The symptoms of #NOF are:

Question 37

Why is hip shortened, abducted and externally rotated in a displaced #NOF

Answer 37

The #NOF allows the shaft of the femur to move independently of the hip joint.

The axis of rotation of the femur that normally passes obliquely through the head and down the neck of the femur, shifts to pass through the greater trochanter and vertically down the long axis of the femoral shaft.

The short lateral rotators of the hip (piriformis, obturator internus, superior and inferior gemelli and quadratus femoris) contract and laterally (externally) rotate the femoral shaft.

The iliopsoas also now acts as a lateral rotator of the femur as it pulls the lesser trochanter anteriorly about the new axis of rotation, so the femoral shaft rotates externally.

The strong abductors that attach to the greater trochanter (gluteus medius and minimus) abduct the femur distal to the fracture site. They also rotate the greater trochanter laterally about the new longitudinal axis of rotation, adding to the external rotation caused by iliopsoas and the short lateral rotators.

Shortening of the limb occurs because the strong muscles of the thigh pull the distal fragment of the femur upwards. These include rectus femoris, adductor magnus and the hamstring muscles.

Question 38

Traumatic dislocation of the hip

Answer 38

Dislocation of the hip is defined as the head of the femur being fully displaced out of the cup-shaped acetabulum of the pelvis (less than complete displacement = subluxation).

Dislocations may be congenital. Developmental dysplasia of the hip (DDH) was formerly known as Congenital Dislocation of the Hip (CDH).

Alternatively, hip dislocation may be traumatic. An acute traumatic hip dislocation is a severe injury, most commonly seen in 16 to 40-year-olds involved in high-speed road traffic collisions.

It takes a massive amount of force to dislocate a normal hip.
In traumatic hip dislocation, the affected hip is extremely painful, and the patient resists any attempt to move the limb.

90% of hip dislocations are posterior. The most common cause is the knee impacting the dashboard during a road traffic collision. The affected limb will be shortened and held in a position of flexion, adduction and internal (medial) rotation. A sciatic nerve palsy is present in 8-20% of cases.

Question 39

Why shortening and internal rotation of the limb after posterior dislocation of the hip

Answer 39

The femoral head is pushed backwards over the posterior margin of the acetabulum and comes to lie on the lateral surface of the ilium.

The head of the femur is then pulled upwards by the strong extensors (gluteus maximus and hamstrings) and adductors of the hip, causing limb shortening.

The anterior fibres of the gluteus medius and minimus pull on the posteriorly- displaced greater trochanter and cause the femur to rotate internally.

In anterior dislocation, the limb is held in a position of external rotation and abduction with slight flexion. Femoral nerve palsies can be present but are uncommon.

In central dislocation, the head of the femur is driven into the pelvis through the acetabulum. It is always a fracture-dislocation. The femoral head is palpable on rectal examination and there is a high risk of intrapelvic haemorrhage due to disruption of the pelvic venous plexuses. This can be a life-threatening injury.