Incidence of hip pain in a prospective cohort of asymptomatic volunteers: is the cam deformity a risk factor for hip pain?
BACKGROUND
Although cam-type femoroacetabular impingement is commonly associated with labral chondral damage and hip pain, a large proportion of asymptomatic individuals will have this deformity.


OBJECTIVE
To determine the incidence of hip pain in a prospective cohort of volunteers who had undergone magnetic resonance imaging (MRI) of their hips.


METHODS
Case control study; Level of evidence, 3.


METHODS
A total of 200 asymptomatic volunteers who underwent an MRI of both hips were followed for a mean time of 4.4 years (range, 4.01-4.95 years). Thirty were lost to follow-up, leaving 170 individuals (77 males, 93 females) with a mean age of 29.5 years (range, 25.7-54.5 years). All patients were blinded to the results of their MRI. All completed a follow-up questionnaire inquiring about the presence of hip pain or a history of hip pain lasting longer than 6 weeks since the original MRI. Each patient was asked to draw where the pain was on a body diagram.


RESULTS
Eleven patients (5 males, 6 females; 6.5% of sample; mean age, 29.9 years; range, 25.7-45.6 years) reported hip pain, of which 3 (1 male, 2 females) had bilateral pain for a total of 14 hips. Seven of the 14 painful hips had a cam-type deformity at the time of the initial MRI versus 37 of the 318 nonpainful hips (P = .0002). This gave a relative risk of 4.3 (95% confidence interval [CI], 2.3-7.8) of developing hip pain if cam deformity was present. Those 14 painful hips had a significantly greater alpha angle at the radial 1:30 clock position than did those who did not develop pain with a cam deformity: 61.5° (range, 57.3°-65.7°) versus 57.9° (range, 56.9°-59.1°), respectively (P = .05). A significantly greater proportion of patients (12%) with limited internal rotation ≤20° (versus 2.7% with internal rotation >20°) went on to develop hip pain (P = .009; relative risk = 3.1 [95% CI, 1.6-6.0]).


CONCLUSIONS
The presence of a cam deformity represents a significant risk factor for the development of hip pain. An elevated alpha angle at the 1:30 clock position and decreased internal rotation are associated with an increased risk of developing hip pain. However, not all patients with a cam deformity develop hip pain, and further research is needed to better define those at greater risk of developing degenerative symptoms.
Paul E. Beaulé, Division of Orthopedic Surgery, University of Ottawa, 501 Smyth Road, CCW 1646, Ottawa, ON, Canada K1H 8L6. pbeaule@ottawahospital.on.ca.
Vickas
V
Khanna
Anthony
A
Caragianis
Gina
G
Diprimio
Kawan
K
Rakhra
Paul E
PE
Beaulé
D000328:Adult; D000368:Aged; D016022:Case-Control Studies; D005260:Female; D057925:Femoracetabular Impingement / Q000473:pathology*; D005500:Follow-Up Studies; D006615:Hip; D006621:Hip Joint / Q000473:pathology*; D006801:Humans; D015994:Incidence; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D010146:Pain / Q000209:etiology*; D011446:Prospective Studies; D012307:Risk Factors; D012399:Rotation; D011795:Surveys and Questionnaires; D014838:Volunteers
cam; hip deformity; internal rotation; pain