Radiographic Techniques Of The Lower Limb

RADIOGRAPHIC TECHNIQUES OF THE LOWER LIMB

FOOT (POSTIONING TERMINOLOGY)

Dorsal surface: the superior surface of the foot is known as the dorsal surface and slopes downwards, at a variable angle, from the ankle to the toes and from medial to lateral.

• Plantar aspect: the inferior surface of the foot is known as the plantar aspect.
• Medial aspect: the surface nearer the midline of the body is the medial aspect.

Lateral aspect: the surface further from the midline of the body is the lateral aspect .

Radiographic Techniques Of The Lower Limb

Medial rotation: the lower limb is rotated inwards, so that the anterior surface faces medially. This will produce internal rotation of the hip joint.

Lateral rotation: the lower limb is rotated outwards, so that the anterior surface faces laterally. This will produce external rotation of the hip joint.

Ankle flexion: of the ankle joint occurs when the dorsal surface of the foot is moved in a superior direction.

Ankle extension: of the ankle joint occurs when the plantar surface of the foot is moved in an inferior direction.

Inversion: inversion of the foot occurs when the plantar surface of the foot is turned to face medially – with the limb extended.

Eversion: eversion of the foot occurs when the plantar surface of the foot is turned to face laterally – with the limb extended.

Flexion of the knee joint: the degree of flexion of the knee joint relates to the angle between the axis of the tibia when the knee is extended and the angle of the axis of the tibia when the knee is flexed.

Basic projections

• Two projections are routinely taken,
• a dorsi-plantar (DP)

a DP oblique

DORSI-PLANTAR

Position of patient and image receptor

• The patient is seated on the X-ray table, supported if necessary, with the hip and knee flexed.
• The plantar aspect of the foot is placed on the image receptor and the lower leg is supported in the vertical position by the other knee.
• The receptor can be raised by 15° to aid positioning, with a vertical central beam.

This will improve the visualization of the tarsal and tarso-metatarsal joints.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated central beam is centred over the cuboid– navicular joint midway between the palpable navicular tuberosity and the tuberosity of the 5th metatarsal.
• The X-ray tube is angled 15° cranially when the receptor is parallel to the table.
• Alternatively, the X-ray beam is vertical if the receptor is raised by 15°.

DORSI-PLANTAR OBLIQUE

Position of patient and image receptor

• From the basic DP position, the affected limb is leaned medially, bringing the plantar surface of the foot to approximately 30–45° to the image receptor.
• A non-opaque angled pad is placed under the foot to maintain the position, with the opposite limb acting as a support.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated central beam is directed over the cuboid–navicular joint.

LATERAL

This is used in addition to the routine DP projection to locate a foreign body.

It may also be used to demonstrate a fracture or dislocation of the tarsal bones, or base of metatarsal fractures or dislocation.

Position of patient and image receptor

• From the DP position, the leg is rotated outwards to bring the lateral aspect of the foot in contact with the receptor.
• A pad is placed under the knee for support.
• The position of the foot is adjusted slightly to bring the plantar aspect perpendicular to the receptor.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated central beam is centred over the navicular-cuneiform joint if the whole foot is to be examined.

LATERAL – ERECT (WEIGHT-BEARING)

This projection is used to demonstrate the condition of the longitudinal arches of the foot, usually in pes planus (flat feet).

Both feet are examined for comparison.

It is important that the full weight of the patient is placed on the feet, to allow an accurate evaluation of the effect of normal weight on the longitudinal arch and bony alignment.

Position of patient and image receptor

• The patient stands on a low platform with the receptor placed vertically between the feet.
• The feet are brought close together.

The weight of the patient’s body is distributed equally.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated central beam is centred to the tubercle of the 5th metatarsal.

TOES

• Basic projections

It is common practice to obtain two projections, a DP and a DPO.

A lateral projection is taken for fractures of the phalanges of the hallux (great toe) such as hyperflexion avulsion fractures of the distal phalanx, which could be missed on an oblique projection.

DORSI-PLANTAR

Position of patient and image receptor

• The patient is seated on the X-ray table, supported if necessary, with hips and knees flexed.
• The plantar aspect of the affected foot is placed on thereceptor. A CR cassette may be raised by 15°.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated central beam is directed over the 3rdmetatarso-phalangeal joint (MTPJ).

DORSI-PLANTAR OBLIQUE

Position of patient and image receptor

• From the basic DP position, the affected limb is allowed to lean medially to bring the plantar surface of the foot approximately 45° to the receptor.
• A 45°e non-opaque pad is placed under the side of the foot for support, with the opposite leg acting as a support.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated central beam is centred over the 1st MTPJ if all the toes are to be imaged and angled sufficiently to allow the central ray to pass through the 3rd MTPJ.

ANKLE

Two projections are routinely taken, an antero-posterior (AP,mortise) and a lateral.

Each image is acquired using a CR image detector or alternatively within the field of view of a DDR detector.

ANTERO-POSTERIOR (AP) – MORTISE PROJECTION

• Position of patient and image receptor
• The patient is either supine or seated on the X-ray table with both legs extended.
• A pad may be placed under the knee for comfort.
• The affected ankle is supported in dorsiflexion by a firm 90°pad placed against the plantar aspect of the foot.

The limb is rotated medially (approximately 20°) until the medial and lateral malleoli are equidistant from the receptor.

Radiographic Techniques Of The Lower Limb

• If the patient is unable to dorsiflex the foot sufficiently, then raising the heel on a 15° wedge or using 5–10° of cranial tube angulation can correct this problem.
• The mid-tibia may be immobilised using a sandbag

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated vertical beam is centred midway between the malleoli with the central ray at 90° to an imaginary line joining the malleoli.

LATERAL (MEDIO-LATERAL)

Position of patient and image receptor

• A 15° pad is placed under the lateral border of the forefoot and a pad is placed under the knee for support.
• From the supine position, the patient rotates on to the affected side.
• The leg is rotated until the medial and lateral malleoli are
• superimposed vertically.
• A 15° pad is placed under the anterior aspect of the knee
• and the lateral border of the forefoot for support.
• The receptor is placed with the lower edge just below the

plantar aspect of the heel

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated vertical beam is centred over the medial malleolus, with the central ray at right-angles to the axis of the tibia.

CALCANEUM

Two projections are routinely taken – a lateral and an axial.

Each image is acquired using a CR image detector or alternatively within the field of view of a DDR detector.

LATERAL

• Position of patient and image receptor
• From the supine position, the patient rotates on to the affected side.
• The leg is rotated until the medial and lateral malleoli are superimposed vertically.
• A 15° pad is placed under the anterior aspect of the knee and the lateral border of the forefoot for support.
• The receptor is placed with the lower edge just below the plantar aspect of the heel.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The vertical collimated beam is centred 2.5 cm distal to the medial malleolus, with the central ray perpendicular to the receptor.

AXIAL

• Position of patient and image receptor
• The patient sits or lies supine on the X-ray table with both limbs extended.
• The affected leg is rotated medially until both malleoli are equidistant from the receptor.
• The ankle is dorsiflexed.
• The position is maintained by using a bandage strapped around the forefoot and held in position by the patient.
• The receptor (CR) is positioned with its lower edge just distal to the plantar aspect of the heel.

DIRECTION AND LOCATION OF THE X-RAY BEAM

The X-ray tube is directed cranially at an angle of 40° to the plantar aspect of the heel.

• The collimated beam is centred to the plantar aspect of the heel at the level of the tubercle of the 5th metatarsal.

TIBIA AND FIBULA

Two projections are taken of the full length of the lower leg.

The receptor chosen should be large enough to accommodate the entire length of the tibia and fibula.

ANTERO-POSTERIOR

• Position of patient and image receptor
• The patient is either supine or seated on the X-ray table, with both legs extended.
• The ankle is supported in dorsiflexion by a firm 90°pad placed against the plantar aspect of the foot.
• The limb is rotated medially until the medial and lateral malleoli are equidistant from the receptor.
• The lower edge of the receptor is positioned just below the plantar aspect of the heel.

DIRECTION AND LOCATION OF THE X-RAY BEAM

• The collimated beam is centred to the mid-shaft of the tibia with the central ray at right-angles to both the long axis of the tibia and an imaginary line joining the malleoli.

LATERAL

• Position of patient and image receptor
• From the supine/seated position, the patient rotates onto the affected side.
• The leg is rotated further until the malleoli are superimposed vertically.
• The tibia should be parallel to the image receptor.
• A pad is placed under the knee for support.
• The lower edge of the receptor is positioned just below the plantar aspect of the heel.

DIRECTION AND LOCATION OF THE X-RAY BEAM

The collimated beam is centred to the mid-shaft of the tibia, with the central ray at right-angles to the long axis of the tibia and parallel to an imaginary line joining the malleoli.