Diagnostic ultrasound ( PDFDrive )

CHAPTER 40 The Fetal Musculoskeletal System 1379
TABLE 40.3 Normal Extremity Long-Bone Lengths and Biparietal
Diameters at Different Menstrual Ages a
Menstrual Age
(Weeks)
Biparietal
Diameter
BONE
Femur Tibia Fibula Humerus Radius Ulna
13 2.3 (0.3) 1.1 (0.2) 0.9 (0.2) 0.8 (0.2) 1.0 (0.2) 0.6 (0.2) 0.8 (0.3)
14 2.7 (0.3) 1.3 (0.2) 1.0 (0.2) 0.9 (0.3) 1.2 (0.2) 0.8 (0.2) 1.0 (0.2)
15 3.0 (0.1) 1.5 (0.2) 1.3 (0.2) 1.2 (0.2) 1.4 (0.2) 1.1 (0.1) 1.2 (0.1)
16 3.3 (0.2) 1.9 (0.3) 1.6 (0.3) 1.5 (0.3) 1.7 (0.2) 1.4 (0.3) 1.6 (0.3)
17 3.7 (0.3) 2.2 (0.3) 1.8 (0.3) 1.7 (0.2) 2.0 (0.4) 1.5 (0.3) 1.7 (0.3)
18 4.2 (0.5) 2.5 (0.3) 2.2 (0.3) 2.1 (0.3) 2.3 (0.3) 1.9 (0.2) 2.2 (0.3)
19 4.4 (0.4) 2.8 (0.3) 2.5 (0.3) 2.3 (0.3) 2.6 (0.3) 2.1 (0.3) 2.4 (0.3)
20 4.7 (0.4) 3.1 (0.3) 2.7 (0.2) 2.6 (0.2) 2.9 (0.3) 2.4 (0.2) 2.7 (0.4)
21 5.0 (0.5) 3.5 (0.4) 3.0 (0.4) 2.9 (0.4) 3.2 (0.4) 2.7 (0.4) 3.0 (0.4)
22 5.5 (0.5) 3.6 (0.3) 3.2 (0.3) 3.1 (0.3) 3.3 (0.3) 2.8 (0.5) 3.1 (0.4)
23 5.8 (0.5) 4.0 (0.4) 3.6 (0.2) 3.4 (0.2) 3.7 (0.3) 3.1 (0.4) 3.5 (0.2)
24 6.1 (0.5) 4.2 (0.3) 3.7 (0.3) 3.6 (0.3) 3.8 (0.4) 3.3 (0.4) 3.6 (0.4)
25 6.4 (0.5) 4.6 (0.3) 4.0 (0.3) 3.9 (0.4) 4.2 (0.4) 3.5 (0.3) 3.9 (0.4)
26 6.8 (0.5) 4.8 (0.4) 4.2 (0.3) 4.0 (0.3) 4.3 (0.3) 3.6 (0.4) 4.0 (0.3)
27 7.0 (0.3) 4.9 (0.3) 4.4 (0.3) 4.2 (0.3) 4.5 (0.2) 3.7 (0.3) 4.1 (0.2)
28 7.3 (0.5) 5.3 (0.5) 4.5 (0.4) 4.4 (0.3) 4.7 (0.4) 3.9 (0.4) 4.4 (0.5)
29 7.6 (0.5) 5.3 (0.5) 4.6 (0.3) 4.5 (0.3) 4.8 (0.4) 4.0 (0.5) 4.5 (0.4)
30 7.7 (0.6) 5.6 (0.3) 4.8 (0.5) 4.7 (0.3) 5.0 (0.5) 4.1 (0.6) 4.7 (0.3)
31 8.2 (0.7) 6.0 (0.6) 5.1 (0.3) 4.9 (0.5) 5.3 (0.4) 4.2 (0.3) 4.9 (0.4)
32 8.5 (0.6) 6.1 (0.6) 5.2 (0.4) 5.1 (0.4) 5.4 (0.4) 4.4 (0.6) 5.0 (0.6)
33 8.6 (0.4) 6.4 (0.5) 5.4 (0.5) 5.3 (0.3) 5.6 (0.5) 4.5 (0.5) 5.2 (0.3)
34 8.9 (0.5) 6.6 (0.6) 5.7 (0.5) 5.5 (0.4) 5.8 (0.5) 4.7 (0.5) 5.4 (0.5)
35 8.9 (0.7) 6.7 (0.6) 5.8 (0.4) 5.6 (0.4) 5.9 (0.6) 4.8 (0.6) 5.4 (0.4)
36 9.1 (0.7) 7.0 (0.7) 6.0 (0.6) 5.6 (0.5) 6.0 (0.6) 4.9 (0.5) 5.5 (0.3)
37 9.3 (0.9) 7.2 (0.4) 6.1 (0.4) 6.0 (0.4) 6.1 (0.4) 5.1 (0.3) 5.6 (0.4)
38 9.5 (0.6) 7.4 (0.6) 6.2 (0.3) 6.0 (0.4) 6.4 (0.3) 5.1 (0.5) 5.8 (0.6)
39 9.5 (0.6) 7.6 (0.8) 6.4 (0.7) 6.1 (0.6) 6.5 (0.6) 5.3 (0.5) 6.0 (0.6)
40 9.9 (0.8) 7.7 (0.4) 6.5 (0.3) 6.2 (0.1) 6.6 (0.4) 5.3 (0.3) 6.0 (0.5)
41 9.7 (0.6) 7.7 (0.4) 6.6 (0.4) 6.3 (0.5) 6.6 (0.4) 5.6 (0.4) 6.3 (0.5)
42 10.0 (0.5) 7.8 (0.7) 6.8 (0.5) 6.7 (0.7) 6.8 (0.7) 5.7 (0.5) 6.5 (0.5)
a Mean values (cm); value of 2 SD in parentheses.
With permission from Merz E, Kim-Kern MS, Pehl S. Ultrasonic mensuration of fetal limb bones in the second and third trimesters. J Clin
Ultrasound. 1987;5(3):175-183. 12
Foot length is measured from the skin edge overlying the
calcaneus to the distal end of the longest toe (the irst or second
toe) on either the plantar or the sagittal view 22-24 (Fig. 40.3). he
ossiied FL is almost equivalent to the foot length, resulting in a
normal femur-to-foot length ratio of approximately 1.0. his
ratio remains relatively constant from the 14th week of gestation
onward. If the fetus is constitutionally small or there is symmetrical
IUGR, the ratio is generally 0.9 or greater. In most skeletal dysplasias
characterized by short limbs, the ratio is generally less
than 0.9 because of the relative sparing of the hands and feet. he
greater the deviation is from the lower limits of the norm, the
greater is the disproportion and usually also the severity.
SONOGRAPHIC EVALUATION OF
FETUS WITH SKELETAL DYSPLASIA
A prenatal evaluation of a skeletal dysplasia is indicated if there
is a positive family history or an abnormal length or appearance
of the bones at ultrasound.
Assessment of Skeletal Dysplasias: Key
Features
Family history
Serial measurements
Degree of limb shortening
Pattern of limb shortening
Presence of bowing, fractures, and angulations
Spine
Thoracic measurements
Hands and feet
Calvarium and facial features
Positive Family History
A positive family history of a sibling or parents afected by a
skeletal dysplasia or consanguineous parents should prompt an
intensive ultrasound investigation with a focus on targeted