Long Bone Measurement

Long Bone Measurement

• Orthoroentgenology• A radiographic technique used to determine

the exact length of a child’s limb bones• Usually performed on lower limbs• The purpose is to determine limb length

discrepancy, which occurs primarily in children• Because patients might require regular check-

ups, gonadal protection is essential

Procedures

• As of today there are several ways to perform Long Bone Measurement. We will be covering

• Scanogram (spot film) • CT Technique

• Digital and CR with stitching

Orthoroentgenogram

Procedure

• Three exposures are made of the limb– Unilateral examination is recommended if large

discrepancy exists– Bilateral is accurate if discrepancy is small– Upper limb exposures are made at shoulder,

elbow, and wrist– Lower limb exposures are made at hip, knee, and

ankle

Procedure

• Accuracy is dependent on patient remaining absolutely still throughout the procedure

• Proper immobilization is essential

Procedure

• Both sides are examined for comparison• Requires special metal ruler imaged with limbs• Place between limbs and tape to table to

remain immobile for each of the three projections

Procedure

• Patient position– Supine– If imaging both sides simultaneously, immobilize

ankles 5 to 6 inches (13 to 15 cm) apart– Knees fully extended, if possible– If not, support both knees in the same amount of

flexion– Lower limb rotated medially to anatomic position

Procedure

• Localize joints on each side and mark with skin-marking pencil– Indicates central ray (CR) entrance point

• For upper limb– Shoulder marked over superior margin of humeral

head– Elbow marked ½ to ¾ inch (1.3 to 1.9 cm) below

plane of epicondyles– Wrist marked between styloid processes

Procedure

• For lower limb– Hip marked 1 to 1¼ inches (2.5 to 3.2 cm)

laterodistally and at right angle to midpoint of imaginary line between anterior superior iliac spine (ASIS) and pubic symphysis

– Knee marked at depression between femoral and tibial condyles, just below patellar apex

– Ankle marked directly below depression midway between malleoli

Procedure

• Metal ruler taped to table between limbs• Three exposures made on one image receptor

(IR) centered to each joint, beginning at the most proximal joint

• Use close collimation for improved image quality and radiation protection

• Shield gonads

Scanogram (spot film)

CT Technique

Computed Tomography Technique

• Computed tomography (CT) for long bone measurements has two advantages over conventional radiographs – More consistently reproduced– Less radiation exposure

CT Technique

• A CT “scout” or localizer image is made• Scanogram is term applied to image• CT cursor is placed over joints to obtain

measurements• Accuracy is dependent on proper cursor

placement– Research suggests cursor placement be done

three times and then averaged

CT Technique

• The simple explanation– This technique is less radiation because they only

do a CT scout which is a none diagnostic image but does contain enough info to make accurate measurements

CT Scanogram

CT scanograms

Digital and CR with stitching

One exposure multiple CR cassettes Several exposures on the same digital detectors

CR with stitching

• Must be performed upright due to equipment requirements

• Requires special metal ruler imaged with limbs• Place between limbs and tape to buckey to

remain immobile• Extra SID is required to reduce elongation of

bones • After Exposures are taken films are processed

and stitched together.

CR with stitching

Digital Stitching

• Depending on equipment can be performed upright or supine

• No ruler is required to be taped to buckey due to post processing measurement

• Several images are taken then stitched together digitaly

Digital Stitching