Cam impingement causes osteoarthritis of the hip: a nationwide prospective cohort study (CHECK).
OBJECTIVE
To determine the association between cam impingement, which is hip incongruity by a non-spherical femoral head and development of osteoarthritis.


METHODS
A nationwide prospective cohort study of 1002 early symptomatic osteoarthritis patients (CHECK), of which standardised anteroposterior pelvic radiographs were obtained at baseline and at 2 and 5 years follow-up. Asphericity of the femoral head was measured by the α angle. Clinically, decreased internal hip rotation (≤20°) is suggestive of cam impingement. The strength of association between those parameters at baseline and development of incident osteoarthritis (K&L grade  2) or end-stage osteoarthritis (K&L grades 3, 4, or total hip replacement) within 5 years was expressed in OR using generalised estimating equations.


RESULTS
At baseline, 76% of the included hips had no radiographic signs of osteoarthritis and 24% doubtful osteoarthritis. Within 5 years, 2.76% developed end-stage osteoarthritis. A moderate (α angle>60°) and severe (α angle>83°) cam-type deformity resulted in adjusted OR of 3.67 (95% CI 1.68 to 8.01) and 9.66 (95% CI 4.72 to 19.78), respectively, for end-stage osteoarthritis. The combination of severe cam-type deformity and decreased internal rotation at baseline resulted in an even more pronounced adjusted OR, and in a positive predictive value of 52.6% for end-stage osteoarthritis. For incident osteoarthritis, only a moderate cam-type deformity was predictive OR=2.42 (95% CI 1.15 to 5.06).


CONCLUSIONS
Individuals with both severe cam-type deformity and reduced internal rotation are strongly predisposed to fast progression to end-stage osteoarthritis. As cam impingement might be a modifiable risk factor, early recognition of this condition is important.
Department of Orthopaedics, Erasmus MC University Medical Centre, Rotterdam, The Netherlands. r.agricola@erasmusmc.nl
Rintje
R
Agricola
Marinus P
MP
Heijboer
Sita M A
SM
Bierma-Zeinstra
Jan A N
JA
Verhaar
Harrie
H
Weinans
Jan H
JH
Waarsing
D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000706:statistics & numerical data; D015331:Cohort Studies; D018450:Disease Progression; D005260:Female; D057925:Femoracetabular Impingement / Q000150:complications / Q000000981:diagnostic imaging*; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D015207:Osteoarthritis, Hip / Q000000981:diagnostic imaging* / Q000209:etiology; D011379:Prognosis; D011446:Prospective Studies; D011859:Radiography; D012399:Rotation; D012720:Severity of Illness Index