Prevalence of Associated Deformities in Patients with Cam Type Femoroacetabular Impingement (SS-30)

Abstract

Femoroacetabular impingement (FAI) has recently been described as a cause of hip pain in young adults and a cause of osteoarthritis of the hip. Cam type impingement is due to a non-constant radius of curvature of the femoral head, usually due to a prominence at the anterosuperior head-neck junction. The surgical treatment of FAI may be able to prevent or retard the progression of degeneration within the hip. One critical aspect in the understanding of the natural history of any hip condition is determining the prevalence of bilateral disease. This clinical information can also be very useful for patient counseling, development of treatment strategies as well as patient follow up care. The purpose of this study was to determine the prevalence of bilateral deformity in patients with cam type FAI as well as the presence of associated acetabular abnormalities. All patients less than 56 years of age seen by the senior author for hip pain with at least one antero posterior pelvic radiograph and lateral view were included. All patients with dysplasia and/or arthritis were excluded. One hundred and thirteen patients with symptomatic cam impingement deformity (alpha angle greater than 55.5 degrees) of at least one hip were evaluated. There were 82 males and 31 females with an average age of 37.9 years (range 16-55). Cam type impingement deformity was defined by measuring the a angle of Notzli on the lateral views (either cross-table lateral with leg in 15 degrees of internal rotation or Dunn view). On the AP pelvic radiograph, hips were assessed for signs of pincer type impingement and lateral centre-edge angle of Wiberg. Pincer type impingement was defined as acetabular retroversion, coxa profunda or coxa protrusio. Out of the 113 patients, only 27 patients had bilateral hip symptoms. The average a angle measured was 67.10, sd 10.60, range 39-920. 88 patients had an a angle greater than 55.50 in both hips (77.8%). The average a angle value amongst the cam impinging hips was 69.50, sd 8.50, range 56-920. The average a angle in the female hips was significantly lower than the male hips - 62.10, sd 9.60 versus 69.10, sd 10.40 respectively (p<0.001). 11 out of 31 females (35.5%) and 14 out of 82 (17.1%) males had unilateral impingement. This difference was significant (p=0.03). Patients with unilateral impingement had a significantly lower average a angle on their impingement side than for hips in patients who had bilateral impingement - 63.60, sd 6.70 and 70.40, sd 6.80 respectively, p<0.001. Of patients who complained of unilateral pain, the average a angle of painful hips was 69.90, sd 8.20, whilst that of the non-painful side was 63.1.10, sd 11.70. This difference was statistically significant (p<0.001). Comparing hips with a angles of 610-700 with those less than 600 found an odds ratio of being painful of 2.59 (95% CI: 1.32-5.08, p=0.006). Similarly hips with a angles greater than 710 had an odds ratio of being painful of 2.54 (95% CI: 1.3-4.96, p=0.007). Of these 113 patients, 88 had bilateral cam deformity and 25 unilateral, i.e. 201 of 226 hips had cam type deformity. Ninety-eight hips had pincer impingement, 84 of these occurring in hips with a cam type deformity (42%). 53 hips had retroversion of the acetabulum (21 patients had bilateral retroversion and 11 unilateral). The strong bilateral prevalence and the correlation between the side to side a angles may suggest a predisposition in some patients to an acquired deformity. A post slip deformity is similar in morphology, male predominance and bilateral prevalence. Our study would suggest that patients with alpha angles less than 60 degree are less likely to develop symptoms which can be used when counseling patients with minor deformities with associated labral pathology as well as those with bilateral deformities. In conclusion, most patients with cam type FAI have bilateral deformities and an associated acetabular deformity almost fifty percent of the time, although most will not be symptomatic at the time of presentation. This is important information in terms of better defining the natural history of this deformity as well as devising effective treatment strategies. Physicians should consider getting appropriate x-rays of the contralateral hip when diagnosing a patient with FAI.