Symptomatic femoroacetabular impingement: does the offset decrease correlate with cartilage damage? A pilot study.
BACKGROUND
Current measures of the reduced head-neck offset such as residual deformity of slipped capital femoral epiphysis (SCFE) including the alpha angle, which measures the femoral head-neck sphericity but does not account for acetabular abnormalities, do not represent the true magnitude of the deformity and the mechanical consequences. The beta angle (angle between the femoral head-neck junction and acetabular rim) accounts for the morphology of both the acetabulum and femur and, thus, may be the more appropriate parameter for assessing SCFE deformity.


OBJECTIVE
We determined (1) whether the beta angle could be reliably measured on MRI; and (2) whether the beta angle correlates with the cartilage status.


METHODS
We recruited 10 adult patients (mean age, 28 years) with symptomatic cam femoroacetabular impingement and 15 asymptomatic volunteers (mean age, 24 years) to have three-dimensional MRI including delayed gadolinium-enhanced MRI of cartilage (dGEMRIC) for cartilage status assessment. Corresponding alpha angles, beta angles, and acetabular dGEMRIC indices were obtained in seven radial reformats to assess the hip in seven regions (anterior to superior and posterior).


RESULTS
We noted high reproducibility for both alpha and beta angle measurements. The dGEMRIC indices correlated with beta angles in the superoinferior and superior regions but not the alpha angles.


CONCLUSIONS
Beta angle measurement in radial MR images is reproducible and appears to correspond to cartilage damage in the superior regions of the hip. The beta angle may be a useful parameter to assess hip deformity in the followup of SCFE although further confirmation is warranted.
Medical Faculty, Department of Orthopedic Surgery, University of Düsseldorf, Düsseldorf, Germany. christoph.zilkens@med.uni-duesseldorf.de
Christoph
C
Zilkens
Falk
F
Miese
Rüdiger
R
Krauspe
Bernd
B
Bittersohl
D000077:Acetabulum / Q000473:pathology*; D000293:Adolescent; D000328:Adult; D016022:Case-Control Studies; D003287:Contrast Media; D018450:Disease Progression; D005260:Female; D057925:Femoracetabular Impingement / Q000209:etiology* / Q000473:pathology; D005269:Femur / Q000473:pathology*; D006132:Growth Plate / Q000473:pathology*; D006621:Hip Joint / Q000473:pathology*; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008536:Meglumine; D009942:Organometallic Compounds; D015207:Osteoarthritis, Hip / Q000209:etiology / Q000473:pathology; D010865:Pilot Projects; D011237:Predictive Value of Tests; D015203:Reproducibility of Results; D060048:Slipped Capital Femoral Epiphyses / Q000150:complications* / Q000473:pathology; D055815:Young Adult
D003287:Contrast Media; D009942:Organometallic Compounds; D008536:Meglumine; C072417:gadoterate meglumine