Novel CT-based three-dimensional software improves the characterization of cam morphology.
BACKGROUND
Incomplete correction of femoral offset and sphericity remains the leading cause for revision surgery for symptomatic femoroacetabular impingement (FAI). Because arthroscopic exploration is technically difficult, a detailed preoperative understanding of morphology is of paramount importance for preoperative decision-making.


OBJECTIVE
The purposes of this study were to (1) characterize the size and location of peak cam deformity with a prototype CT-based software program; (2) compare software alpha angles with those obtained by plain radiograph and CT images; and (3) assess whether differences can be explained by variable measurement locations.


METHODS
We retrospectively reviewed the preoperative plain radiographs and CT scans of 100 symptomatic cam lesions treated by arthroscopy; recorded alpha angle and clockface measurement location with a novel prototype CT-based software program, CT, and Dunn lateral plain radiographs; and used ordinary least squares regressions to assess the relationship between alpha angle and measurement location.


RESULTS
The software determined a mean alpha angle of 70.8° at 1:23 o'clock and identified 60% of maximum alpha angles between 12:45 and 1:45. The CT and plain radiographs underestimated by 5.7° and 8.2°, respectively. The software-based location was anterosuperior to the mean CT and plain radiograph measurement locations by 41 and 97 minutes, respectively. Regression analysis confirmed a correlation between alpha angle differences and variable measurement locations.


CONCLUSIONS
Software-based three-dimensional (3-D) imaging generated alpha angles larger than those found by plain radiograph and CT, and these differences were the result of location of measurement. An automated 3-D assessment that accurately describes the location and topography of FAI may be needed to adequately characterize preoperative deformity.
University of Pennsylvania, Philadelphia, PA, USA.
Michael T
MT
Milone
Asheesh
A
Bedi
Lazaros
L
Poultsides
Erin
E
Magennis
J W Thomas
JW
Byrd
Christopher M
CM
Larson
Bryan T
BT
Kelly
D000077:Acetabulum / Q000000981:diagnostic imaging; D000328:Adult; D000704:Analysis of Variance; D001182:Arthroscopy; D005260:Female; D057925:Femoracetabular Impingement / Q000000981:diagnostic imaging* / Q000601:surgery; D005270:Femur Head / Q000000981:diagnostic imaging; D005272:Femur Neck / Q000000981:diagnostic imaging; D006621:Hip Joint / Q000000981:diagnostic imaging* / Q000601:surgery; D006801:Humans; D021621:Imaging, Three-Dimensional; D008297:Male; D011237:Predictive Value of Tests; D011857:Radiographic Image Interpretation, Computer-Assisted; D012189:Retrospective Studies; D012984:Software; D014057:Tomography, X-Ray Computed; D055815:Young Adult