Hip

Hip

Normal Acetabular Angles* (Caffey)
AP radiograph of pelvis

Age	Acetabular Angle --Female (Degrees)	Acetabular Angle--Male (Degrees)
Newborn	28.8 ± 4.8	26.4 ± 4.4
3 Month Old	25 ± 3.5	22 ± 4
Six Month Old	23.2 ± 4.0	20.3 ± 3.7
One Year Old	21.2 ± 3.8	19.8 ± 3.6
Two Year Old	18 ± 4	19 ± 3.6

*Acetabular angle defined as the angle made from line through the Y synchondroses and another line through the superior and inferior points of the iliac portion of the acetabulum.
from Caffey in Ozonoff MB. Pediatric Orthopedic Radiology. W.B. Saunders Company: Philadelphia. 1992. p181. (Used with permission from M.B. Ozonoff; publisher's permission requested)

Normal sonographic appearance of Infant Hip

Sonographic Hip Type	Alpha angle*
I Normal	> 60°
2A Physiologic Immaturity < 3 months old	50 - 59°
2B Delayed ossification > 3 months old	50 - 59°

*The alpha angle is the geometric complement of the acetabular angle, derived from a line drawn along the lateral bony margin of the ilium and from a line drawn across the bony acetabular roof.

Source: Modified from Graf R, Schuler P. in Sonography of the infant hip: an atlas. Weinheim: VCH Verlagsgesellschaft, 1986 and Schlesinger AE, Hernandez RJ. Diseases of the musculoskeletal system in children: imaging with CT, sonography, and MR. AJR 1992; 158: 729-741.

Medial Joint Space
AP radiograph of pelvis

The medial joint space is used to determine lateral displacement of the femoral head. It is defined as the distance measured from the medial edge of the femoral ossific nucleus (where it is broadest just above the growth plate) to the adjacent acetabular wall. When the ossific nucleus is absent or asymmetric, measurement is made from the femoral neck metaphysis just below the growth plate. This measurement is best made on the frog-lateral projection.
Normal range: 6 months to 11 years = 5-12 mm. From side to side, the medial joint space of both hips should be within 1.5 mm of each other.
Source: Eyring et al., 1965 in reference: Ozonoff MB. Pediatric Orthopedic Radiology. W.B. Saunders Company: Philadelphia. 1992. p181. (Used with permission from M.B. Ozonoff; publisher's permission requested)

Medial joint space = distance from widest portion of femoral head to adjacent acetabulum

Center-Edge Angle (Wiberg)
AP radiograph of pelvis

The center edge angle is used to evaluate the relationship of the femoral head to the acetabulum. It is defined as the angle formed by a line drawn through the center of the femoral head and the edge of the acetabulum and another line perpendicular to a line drawn through the center of the femoral heads. The value of this is limited if the femoral head is deformed or if the ossific center is small or eccentric.

Normal Center-Edge Angles

Age	Center Edge Angle (Degrees)
3 months	18-20
2 years	30
Lowest limit of normal, age 5 to 8 y	19
Lowest limit of normal, age 9 to 12y	25
Lowest limit of normal, age 13 to 20 y	26-30

Reference: Ozonoff MB. Pediatric Orthopedic Radiology. W.B. Saunders Company: Philadelphia. 1992. p181. (Used with permission from M.B. Ozonoff; publisher's permission requested) Back to Table of Contents