Plain Radiographs

A line along the upper margin of the neck of the femur transects the femoral head in anteroposterior (AP) and lateral radiographs. This alignment is changed when the epiphysis is slipped.

A line along the inferior margin of the neck of the femur forms a continuous arc with the superior and medial margin of the obturator foramen of the pelvis. This line, known as Shenton’s line (see Fig. 8.8 ), is disrupted in congenital dislocation of the hip.

On an AP radiograph a line between the lowermost part of each condyle , although parallel to the upper tibia, lies at an angle of 81 degrees to the shaft of the femur. This amount of genu valgum is normal.

Radiography

The neck of the femur is anteverted approximately 10 degrees. In AP radiography of the neck , therefore, the leg must be internally rotated 10 degrees to position the neck of the femur parallel to the film.

In a lateral view of the neck , a film and grid placed vertically and pressed into the patient’s side must be positioned at an angle of 127 degrees to the shaft of the femur because of the angulation of the neck to the shaft.

Views of the intercondylar fossa (tunnel views) are taken with the knee flexed at an angle of about 135 degrees with a vertical beam and with a beam angled at 70 degrees to the lower leg.

Sesamoid Bones

A sesamoid bone called the fabella is frequently seen in the lateral head of the gastrocnemius muscle. On radiographs, this is projected on the posterior aspect of the lateral ­femoral condyle.

Blood Supply of the Head of the Femur

The head of the femur receives its blood supply mainly via the neck, as described above. Thus fracture of the neck, especially subcapital fracture , disrupts this blood supply and results in ischaemic necrosis of the head in 80% of cases.

Ossification of the Femur

The primary centre in the shaft appears in the seventh fetal week. A secondary centre is present in the lower femur at birth (this is a reliable indicator that the fetus is full term) and another appears in the head between 6 months and 1 year of age. Secondary centres appear in the greater ­trochanter at 4 years and in the lesser trochanter at 8 years of age. All fuse at 18–20 years of age.

Trabecular Markings in the Neck of the Femur and Bone Density

Additional biomechanical integrity of the neck of the femur is provided by an ordered internal trabecular network with a combination of primary compressive trabeculae, primary tensile trabeculae and secondary compressive trabeculae. These trabeculae, readily identified on conventional radiographs, surround a triangular area where there is a relative paucity of trabecular markings, termed Ward’s triangle. The integrity of these described trabeculae reflects relative osteoblastic activity and stress. In osteoporosis, the disappearance of secondary compressive trabeculae prior to the disappearance of primary tensile trabeculae prior to subsequent disappearance of primary compressive trabeculae forms the basis of the Singh index ( Fig. 8.2 ).

Diagrammatic representation of the trabecular markings of the femoral neck.

Plain Radiographs

The outer surface of the patella as seen on tangential (skyline) views is irregular owing to the entry of nutrient vessels here.

Occasionally, the upper outer segment of the patella is separate from the remainder of the bone. Such a patella is called a bipartite patella and must be recognized as normal and not fractured.

Dislocation of the Patella

Lateral dislocation of the patella is more common than medial dislocation and occurs following valgus injury with associated imposed bowstringing of the extensor mechanism over the knee joint. Anatomical structures have evolved to prevent dislocation, including relative hypertrophy of the vastus medialis muscle and overgrowth of the lateral femoral condyle.

Wiberg describes three shapes of the patella:

• ■
  

  Type 1, in which the medial and lateral articular facets of the patella are equal in size and dimension.

  
  
• ■
  

  Type 2, in which the lateral facet is slightly larger than the medial facet.

  
  
• ■
  

  Type 3, in which the lateral facet is dominant and the medial facet is atretic and redundant. The type 3 configuration is more commonly associated with tracking disorders and transient subluxation.

Evaluation of patellofemoral alignment is routinely achieved using the skyline position with the beam centred on the patellofemoral joint from below. Patellofemoral tracking is best achieved using the Merchant views, with the beam directed from above down to a cassette held over the tibia. The Merchant views can therefore be acquired in weightbearing and in varying degrees of flexion and extension.

Ossification

This begins at 3 years and is complete by puberty.

Plain Radiographs

The tibial tuberosity is very variable in appearance, ­particularly during the growth period. Asymmetry and irregularity on radiographs may be quite normal.

Some irregularity of the tibia at the upper part of the interosseous border may simulate a periosteal reaction here.

Ossification of the Tibia

The primary ossification centre for the shaft of the tibia appears in the seventh fetal week. A secondary ossification centre is present in the upper end at birth and in the lower end at 2 years. The upper centre fuses with the shaft at 20 years, the lower sooner at 18 years.

Ossification of the Fibula

Ossification of the primary centre in the shaft begins in the eighth fetal week, in the lower secondary centre in the first year and in the upper at 3 years. The lower epiphysis fuses with the shaft at 16 years and the upper at 18 years.

The tibia in adulthood . In adulthood, the tibia, like all other long bones, is characterized by thick compact bony cortex in the tubulated diaphysis, in contrast to cortical thinning in the flared metaphysis. Biomechanical integrity of the tibial metaphysis, in contrast to the diaphysis, is provided by an additional internal ordered trabecular network, cancellous bony matrix.

The Talus

The long axis of the talus points forwards and medially so that its anterior end is medial to the calcaneus. The talus has a:

• ■
  

  Body between the malleoli, with a superior articular surface called the trochlear surface;

  
  
• ■
  

  Neck grooved inferiorly as the sulcus tali which, with the sulcus calcanei, forms the sinus tarsi;

  
  
• ■
  

  Head anteriorly that articulates with the navicular;

  
  
• ■
  

  Posterior process , which is sometimes separate as the os trigonum.

The inferior surface of the talus (see also the subtalar joint) has a large facet posteriorly for articulation with the calcaneus. Separated from this by the sinus tarsi are three facets, separated by ridges, as follows:

• ■
  

  The middle talocalcaneal facet for the sustentaculum tali of the calcaneus

  
  
• ■
  

  A facet for the plantar ligament

  
  
• ■
  

  The anterior talocalcaneal articular surface

These, in turn, are continuous with the talonavicular facet on the head of the talus. The talus has no muscular attachments.

The Calcaneus

This is the largest tarsal bone. It lies under the talus with its long axis pointing forward and laterally. It is irregularly cuboidal in shape with a shelf-like process anteromedially to support the talus – known as the sustentaculum tali. Its upper surface has three facets for the talus (the middle one is on the superior surface of the sustentaculum tali), which correspond with the facets under the talus.

The plantar surface has a large calcaneal tuberosity posteriorly which has medial and lateral tubercles. There is a small peroneal tubercle on the lateral surface.

The Arches of the Foot

The longitudinal arch is more pronounced medially. It has two components:

• ■
  

  The medial arch, formed by the calcaneus, the talus, the medial three cuneiforms and the first three metatarsal bones.

  
  
• ■
  

  The lateral arch, formed by the calcaneus, the cuboid and the fourth and fifth metatarsals.

A series of transverse arches are formed and are most marked at the distal part of the tarsal bones and the proximal end of the metatarsals. Each foot has one half of the full transverse arch.

The arches are maintained by the shape of the bones of the foot, the ligaments and muscles, particularly of the plantar surface.

Plain Radiographs

Boehler’s critical angle of the calcaneus (see Fig. 8.6A ) is the angle between a line drawn from the posterior end to the anterior end of its superior articular facet and a second line from the latter point to the posterosuperior border of the calcaneus. It is normally 30–35 degrees, with an angle less than 28 degrees occurring when there is ­significant structural damage to the bone.

Radiological features of the bones of the foot. (A) Boehler’s calcaneal angle and heel pad thickness. (B and C) Orientation of the talus in a child. (D and E) Styloid process of the fifth metatarsal: epiphyseal line and fracture. (F and G) Sesamoid bones of the foot.

Heel pad thickness (see Fig. 8.6A ) is measured on a lateral radiograph of the calcaneus between the calcaneal tuberosity posteroinferiorly and the skin surface. Normal thicknesses are 21 mm in the female and 23 mm in the male. Thickening of the heel pad occurs in patients with gigantism or acromegaly.

On a lateral radiograph of the foot in children over 5 years old the long axis of the talus points along the shaft of the first metatarsal. In the younger child the talus is more vertical and its long axis points below the first metatarsal (see Fig. 8.6B and C ).

Sesamoid Bones

The commonest sesamoid bones seen in foot radiographs (see Fig. 8.6F and G ) are as follows:

• ■
  

  Two sesamoids are found in the tendon of flexor hallucis brevis at the base of the metatarsophalangeal joint of the hallux. These may be bipartite. The sum of the two parts in a bipartite patella is larger than the size of the asso­ciated unipartite sesamoid, in contrast to a fracture where the sum of the two parts equals the size of the associated intact sesamoid.

  
  
• ■
  

  Sesamoid bones are often found at other metatarsophalangeal joints or at the interphalangeal joints of the first and second toes.

  
  
• ■
  

  Os trigonum posterior to the talus.

  
  
• ■
  

  Os vesalianum at the base of the fifth metatarsal.

  
  
• ■
  

  Os peroneum between the cuboid and the base of the fifth metatarsal within the tendon of the peroneus brevis muscle.

  
  
• ■
  

  Os tibiale externum medial to the tuberosity of the navi­cular within the tendon of the tibialis posterior muscle.

Ossification of the Bones of the Foot

Except for the calcaneus, the tarsal bones ossify from one centre each – the calcaneus and talus ossify in the sixth fetal month and the cuboid is ossified at birth; the cuneiforms and navicular ossify between 1 and 3 years of age.

The secondary centre of the calcaneus ossifies in the posterior aspect of the bone at 5 years and its density may be very irregular in the normal foot. It fuses at puberty.

The navicular may ossify from many ossification centres. This should not be confused with fragmentation of osteochondrosis or with fracture. Similarly, the epiphysis at the base of the proximal phalanx of the hallux may be bipartite in the normal foot.

Coalition of the bones of the foot . Tarsal coalition represents abnormal fusion between two or more tarsal bones and is a frequent cause of foot and ankle pain. Coalition results from abnormal differentiation and segmentation of primitive mesenchyme preventing the development of a normal joint.

Type

The hip joint is a synovial ball-and-socket joint, the femoral head functioning as a ball with the acetabular cavity or socket. The normal acetabulum is obliquely oriented from lateral to medial, from front to back and is inclined such that the outer margin of the roof is lateral to the outer margin of the floor. Such acetabular angulation is an evolutionary modification to accommodate bipedalism without repeated dislocation. Loss of normal acetabular obliquity and inclination in acetabular dysplasia predisposes to repeated subluxation and abnormal stress on the acetabular labrum, which becomes degenerate and torn. Similar to angulation of the acetabulum, the femoral neck is anteverted to 10 degrees relative to the shaft, which decreases the likelihood of posterior hip subluxation and leads to further stability at the hip joint.

Hip joint: coronal section.

Articular Surfaces

These are the head of the femur apart from the fovea, which is a horseshoe-shaped articular surface on the acetabulum. The articular surface is deepened by a fibrocartilaginous ring, the acetabular labrum. The acetabulum has a central nonarticular area for a fat pad and the ligamentum teres and an inferior notch bridged by the transverse acetabular ligament, from which this ligament arises.

Capsule

This is attached to the edge of the acetabulum and its labrum and the transverse acetabular ligament; at the femoral neck it is attached to the trochanters and the intertrochanteric line anteriorly; posteriorly it is attached more proximally on the neck at the junction of its medial two-thirds and its lateral third. From its insertion on the femoral neck, the capsular fibres are reflected back along the neck as the retinacula along which blood vessels reach the femoral head.

Synovium

Synovium lines the capsule and occasionally bulges out anteriorly as a bursa in front of the psoas muscle where this muscle passes in front of the hip joint.

Ligaments

These are as follows:

• ■
  

  The iliofemoral ligament (Y-shaped ligament of Bigelow) is an anterior thickening of the capsule between the anteroinferior iliac spine and the neck of the femur to the intertrochanteric line.

  
  
• ■
  

  The ischiofemoral ligament is a posterior thickening of the capsule.

  
  
• ■
  

  The pubofemoral ligament is a thickening of the capsule inferiorly.

  
  
• ■
  

  The transverse acetabular ligament bridges the acetabular notch.

  
  
• ■
  

  The ligamentum teres lies between the central nonarticular part of the acetabulum and the fovea of the head of the femur.

Plain Radiographs

On radiographs of the hip joint pads of fat , seen as linear lucencies, outline the capsule of the hip joint and closely applied muscle. Bulging of these is an early sign of joint effusion.

A small accessory ossicle , the os acetabuli, is sometimes seen at the superior margin of the acetabulum and should not be confused with a fracture here.

Similarly, irregularity of the superior margin of the ­acetabulum in children is a normal variant.

In assessment of radiographs of the hip in infants ( Fig. 8.8 ), the following lines and angles are as described:

• ■
  

  The Y line between the unossified centre of each acetabulum, that is, the Y-shaped cartilage between the pubis, ischium and ilium or the triradiate cartilage.

  
  
• ■
  

  The acetabular angle , normally 15–35 degrees.

  
  
• ■
  

  The iliac angle , normally 44–74 degrees.

  
  
• ■
  

  Shenton’s line along the inferior margin of the femoral neck and along the superior and lateral margins of the obturator foramen of the pelvis should form a continuous arc.

  
  
• ■
  

  Lines along the femoral shafts in Von Rosen’s view (legs abducted at least 45 degrees and internally rotated) should meet in the midline at the lumbosacral junction.

Anteroposterior pelvic X-ray: lines used in assessment (1–4) .

From Carver E, Carver B, Knapp K. Carvers’ Medical Imaging , 3rd ed. Elsevier; 2021.

In assessment of radiographs of the adult hip, routine frontal radiographs allow the identification of six lines (see Fig. 8.8 ). The continuation of the inferior margin of the superior pubic ramus superiorly to the upper outer margin of the acetabular roof forms the outer margin of the anterior column or wall of the acetabulum (line 1). The continuation of the inferior margin of the inferior pubic ramus superiorly to the upper outer margin of the acetabular roof forms the outer margin of the posterior column or wall of the acetabulum (line 2). The continuation of the superior margin of the superior pubic ramus superiorly forms the iliopectineal line (line 3). The continuation of the superior margin of the inferior pubic ramus superiorly forms the ilioischial line (line 4). The roof of the acetabulum forms line 5. The ‘tear drop’ is formed by the reflections of the cotyloid fossa and quadrilateral plate and represents line 6. Disruption of any of the described lines is employed in the localization of disease processes on conventional radiographs.

Radiography

The hip joint is usually investigated by AP and frog lateral (oblique) radiographs. Visualization of the anterior or posterior margins of the acetabulum may be enhanced by oblique or Judet views. The joint space anteriorly, superiorly and posteriorly may be visualized by the false profile lateral view.

Arthrography

Arthrography of the hip joint is achieved by injection of contrast anteriorly just below the head of the femur. The synovial cavity, as described above, is outlined. The ligamentum teres is seen as a filling defect within the joint and the transverse ligament of the acetabulum is seen as a defect near the inferior part of the acetabulum. The labrum is visible as a triangular filling defect around the acetabular rim. A superior acetabular recess is found external to the labrum superiorly. An inferior articular recess is seen at the base of the femoral head.

The synovial cavity is seen to extend along the neck of the femur as described above, and superior and inferior recesses of the neck are seen in the synovial cavity at the upper and lower ends of the intertrochanteric line.

Ultrasound of the Infant Hip ( Fig. 8.9 )

This is useful as visualization of the as-yet unossified femoral head is possible. The ossified parts of the acetabulum, including its roof and the shaft of the femur, are seen as echoic areas, whereas the cartilage of the acetabulum (the triradiate cartilage) and the head of the femur are hypoechoic. The labrum is also visible at the edge of the acetabulum.

Ultrasound scan of the infant hip: coronal view in standard plane.

• 1.
  

  Iliac wing

  
  
• 2.
  

  Acetabulum (iliac part)

  
  
• 3.
  

  Triradiate cartilage

  
  
• 4.
  

  Acetabulum (ischial part)

  
  
• 5.
  

  Labrum of acetabulum

  
  
• 6.
  

  Lower limit of joint capsule as it merges with the femoral neck ­(echogenic focus)

  
  
• 7.
  

  Cartilage of the femoral head

  
  
• 8.
  

  Gluteal muscles

CT of the Hip Joint

In the axial plane, CT allows direct visualization of the margins of the acetabulum. CT scanning allows evaluation of the anterior and posterior walls of the acetabulum, and also allows visualization of the fat-filled cotyloid fossa and of the associated quadrilateral plate.

Axial images are routinely employed to determine the axis of the neck of the femur relative to the shaft (normally anteverted to 10 degrees). This can only be achieved by combining axial imaging of the neck and proximal shaft with axial imaging through the condyles of the distal femur. The angle of anteversion is the angle created by the intersection of a line along the neck of the femur and a line drawn between the two distal femoral condyles.

Magnetic Resonance Imaging of the Hip ( Fig. 8.10 )

Magnetic resonance imaging (MRI) of the hip may be ­performed using a body coil and a wide 25–30-cm field of view, allowing simultaneous visualization of both hips and comparison of the normal and abnormal sides. Dedicated imaging of a single hip, to identify the labrum, requires the use of a phased array quadrature surface coil.

Magnetic resonance image (MRI) of the hip. (A–C) Coronal T1-weighted scans from anterior to posterior.

(A–C)

• 1.
  

  Rectus femoris insertion

  
  
• 2.
  

  Gluteus medius muscle

  
  
• 3.
  

  Iliacus muscle

  
  
• 4.
  

  Iliopsoas muscle belly

  
  
• 5.
  

  Tensor fascia lata

  
  
• 6.
  

  Femoral vessels

  
  
• 7.
  

  Conjoined insertion of gracilis and adductor longus muscles

  
  
• 8.
  

  Adductor longus

  
  
• 9.
  

  Pubic symphysis

  
  
• 10.
  

  Pectineus muscle

  
  
• 11.
  

  Bladder

  
  
• 12.
  

  Uterus

  
  
• 13.
  

  Gluteus minimus

  
  
• 14.
  

  Capsule (iliofemoral ligament)

  
  
• 15.
  

  Vastus lateralis muscle

  
  
• 16.
  

  Obturator internus muscle

  
  
• 17.
  

  Obturator externus muscle

  
  
• 18.
  

  Adductor brevis muscle

  
  
• 19.
  

  Adductor longus muscle

  
  
• 20.
  

  Piriformis muscle

  
  
• 21.
  

  Gluteus maximus muscle

  
  
• 22.
  

  Greater trochanter

  
  
• 23.
  

  Ischium

  
  
• 24.
  

  Conjoined tendon of long head of semimembranosus and long head of biceps femoris

  
  
• 25.
  

  Adductor magnus muscle

  
  
• 26.
  

  Semitendinosus muscle

  
  
• 27.
  

  Inferior gemellus muscle

  
  
• 28.
  

  Quadratus femoris muscle

(D–F) Sequential axial T2-weighted scans from superior to inferior (D–F)

• 1.
  

  Rectus abdominis muscle

  
  
• 2.
  

  Bladder

  
  
• 3.
  

  Prostate

  
  
• 4.
  

  Rectum

  
  
• 5.
  

  Quadrilateral plate of the acetabulum (and cotyloid fossa)

  
  
• 6.
  

  Sciatic nerve

  
  
• 7.
  

  Coccyx

  
  
• 8.
  

  Piriformis

  
  
• 9.
  

  Anterior labrum

  
  
• 10.
  

  Ileofemoral ligament (anterior fold of the capsule)

  
  
• 11.
  

  Posterior wall of the acetabulum

  
  
• 12.
  

  Obturator externus muscle

  
  
• 13.
  

  Obturator internus muscle

  
  
• 14.
  

  Ischiorectal fossa

  
  
• 15.
  

  Natal cleft

  
  
• 16.
  

  Gluteus medius

  
  
• 17.
  

  Cotyloid fossa

  
  
• 18.
  

  Femoral vein

  
  
• 19.
  

  Femoral artery

  
  
• 20.
  

  Sartorius

  
  
• 21.
  

  Rectus femoris

  
  
• 22.
  

  Iliopsoas

  
  
• 23.
  

  Tensor fascia lata

  
  
• 24.
  

  Adductor longus

  
  
• 25.
  

  Adductor brevis

  
  
• 26.
  

  Quadratus femoris

  
  
• 27.
  

  Gluteus maximus

Only gold members can continue reading. Log In or Register to continue

Share this:

• Click to share on Twitter (Opens in new window)
• Click to share on Facebook (Opens in new window)

Related posts:

The Breast The Spinal Column and Its Contents The Central Nervous System The Upper Limb The Pelvis 93

Stay updated, free articles. Join our Telegram channel

Join