What is normal femoral head/neck anatomy? An analysis of radial CT reconstructions in adolescents.
BACKGROUND
Cam morphology in femoroacetabular impingement has been implicated in the development of osteoarthritis. The alpha angle and femoral head/neck offset are widely used to determine femoral head asphericity. To our knowledge, no study has evaluated the alpha angle circumferentially using three-dimensional imaging in a population of healthy individuals of adolescent age.


OBJECTIVE
We sought to (1) determine normal values for the alpha angle in adolescents, (2) define the location along the neck with the highest alpha angle, and (3) determine normal femoral head and neck radii and femoral head/neck offset.


METHODS
Fifty CT scans from a database of scans obtained for reasons not related to hip pain were studied. The average age of the subjects was 15 years (range, 14-16 years). Alpha angle and femoral head/neck offset were measured circumferentially.


RESULTS
The alpha angle averaged 40.66 ± 4.46 mm for males and 37.77 ± 5.65 mm for females. The alpha angle generally was highest between the 11:40 and 12:40 o'clock and between the 6:00 and 7:40 o'clock positions. The femoral head radius was 24.53 ± 1.74 mm for males and 21.94 ± 1.13 mm for females, and the femoral neck radius was 16.14 ± 2.32 mm for males and 13.82 ± 2.38 mm for females. The mean femoral head/neck offset was 8.39 ± 1.97 mm for males and 8.13 ± 2.27 mm for females.


CONCLUSIONS
In this healthy population of 14- to 16-year-old subjects, the highest alpha angle was at the superior and inferior aspects of the heads rather than at the anterosuperior aspect. This information will provide benchmark values for distinction between normal and abnormal morphologic features of the femoral head.
Joint Preservation Institute, Orthopaedic Surgery, 2825 J Street, #440, Sacramento, CA, 95816, USA, contactus@jointpreservationinstitute.com.
Amir A
AA
Jamali
Walter
W
Mak
Ping
P
Wang
Lynn
L
Tai
John P
JP
Meehan
Ramit
R
Lamba
D000293:Adolescent; D000367:Age Factors; D005260:Female; D005270:Femur Head / Q000000981:diagnostic imaging*; D005272:Femur Neck / Q000000981:diagnostic imaging*; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D011857:Radiographic Image Interpretation, Computer-Assisted; D012016:Reference Values; D012737:Sex Factors; D014057:Tomography, X-Ray Computed