Femoral retroversion in patients with femoroacetabular impingement: A cofactor in the development of hip osteoarthritis

+1Moya L E, 1Molisani D, 1Henn F, 1Ma Y, 1Kelly B T, 1Buly R L +1Hospital for Special Surgery, New York, NY 10021, USA

Senior author BulyR@HSS.EDU Introduction

Femoroacetabular impingement1 (FAI) is, together with dysplasia, one of the main causes of hip osteoarthritis. Clinically, patients complain of hip pain and restricted range of motion of the hip. A positive impingement test is often present during the physical examination (pain associated with a limited internal rotation at 90 º of flexion of the hip). Two main mechanisms of FAI1 have been described: i) Cam-type FAI, when there is a lack of offset at the femoral neck-head junction (i.e. a pistol grip femur) and ii) Pincer-type FAI, an overly prominent anterior wall causing impingement (i.e. acetabular retroversion or coxa profunda).

Femoral retroversion has also been reported2, 3 as a cause of FAI and it is well established that a retroverted femur produces hip pain and alterations in external and internal rotation balance5,6. However no studies of femoral retroversion in patients with FAI have been reported. Furthermore, since the lack of internal rotation is a common feature in patients with FAI, it could be possible that femoral version abnormalities are present in these patients.

The purpose of this study is to describe the femoral version in a group of patients with FAI and assess its relation in the development of hip osteoarthritis. Material ands Methods

The patient history, x-rays and hip CT scans of one hundred and forty-two patients with FAI were reviewed. We defined FAI if the hip had an abnormal alpha angle (>49º) measured on the elongated femoral neck x-ray (Dunn projection), the presence of positive cross-over sign or protrusio acetabuli in the AP pelvis x-ray and the presence of diminished anteversion in the femur (<10º) 5, 6 or a retroverted femur (<0º) measured in the CT scan associated with a positive hip impingement test and lack of internal rotation at 90 degrees of flexion. All the patients presented with persistent hip pain and were evaluated clinically by the senior author, between January 2006 and July 2008. We documented the type of FAI (cam or pincer), the presence of acetabular dysplasia, coxa valga, coxa vara and the femoral version measured on the CT scan. The CT version measurements were performed by a musculoskeletal radiologist as part of the interpretation. The degree of osteoarthritis of the hip using the Tönnis classification was documented as well. This study was done with IRB approval. Results

Two hundred and sixty-five FAI hips from 142 patients (73 females and 69 males) were analyzed. The average age was 36.7 years (15-69). The mean femoral version was 11.4 º (-14.1º to 47º). We found 43 hips (16.6%) of the femora were retroverted and 133 hips (50%) had either diminished anteversion (<10º) or were retroverted (Fig.1). Only 58 hips (22%) were normally anteverted5, 6 (between 12º-20º) and 62 hips (23.3%) had excessive femoral anteversion (>20º). In 12 hips (0.05%) the only cause of FAI was the presence of a diminished anteversion or retroverted femur.

The statistical analysis shown that among these six predictors, both femoral retroversion (p=0.046) and coxa vara (p<0.001) were statistically significant for the presence of osteoarthritis. Compared with those whose do not have a femoral retroversion, patients having a retroverted femur had 1.6-fold odds of osteoarthritis. Compared with those whose did not have coxa vara, patients having coxa vara had 1.6-fold odds of osteoarthritis. The demographic variables age and gender were also significant for hip osteoarthritis (both p-values<0.001). Older patients had higher odds of osteoarthritis. Compared with female patients, male patients had 6.2-fold odds of osteoarthritis (Table I). Statistical Analysis

To account for the high correlation (ρ=0.83) between left hip and right hip within a patient, the generalized estimating equations (GEEs) method4 was considered. Logistic regression based on the GEEs approach was conducted to detect risk factors for the development of hip osteoarthritis using osteoarthritis as the outcome variable. Predictors

are femoral retroversion, coxa vara, coxa valga, pincer-type FAI, cam-type FAI and dysplasia. Age and gender were included as covariates. Regression analysis was conducted using SAS version 9.1.

Table I: Risk factors for the development of hip osteoarthritis based on logistic regression.

C.I.: Confidence interval for Odds Ratio

Figure 1: Histogram showing the frequencies of the femoral version angle measured on CT scans.

Discussion The presence of a retroverted femur is a cofactor in the

development of hip osteoarthritis in patients with FAI. The orthopedic surgeons should be aware of the high frequency of femoral retroversion (16%) during the assessment of patients with hip impingement, in order to make the right diagnosis and choose the correct treatment.

It could be possible that this association between FAI and femoral retroversion is due to the fact that a common hip disease during skeletal maturation (i.e. slipped capital femoral epiphysis) produces both biomechanical alterations, a cam type FAI and a retroverted femur.

Various investigators5, 6, 7 consider normal femoral version to be in the range of 12 and 20 degrees. However, further studies are required in healthy population in order to determine the frequency of femoral retroversion. References 1) Ganz R, Parvici J, Beck M, et al: Femoro-acetabular impingement. An important cause of early osteoarthritis of the hip. Clin Orthop 417:1-9, 2003. 2) Christopher L. Peters and Jill Erickson.The Etiology and Treatment of Hip Pain in the Young Adult.J Bone Joint Surg Am. 2006;88:20-26. 3) Dennis R. Wenger, Shyam Kishan and Maya E. Pring. Impingement and childhood hip disease. Journal of Pediatric Orthopaedics B 2006, Vol 15 No 4. 4) Zeger, S. L. and Liang, K-Y. (1986). Longitudinal Data Analysis for discrete and continuous outcomes. Biometrics 42, 121-130. 5) Tönnis D., Heinecke A. Current Concepts Review - Acetabular and Femoral Anteversion: Relationship with Osteoarthritis of the Hip.J. Bone Joint Surg. Am. 81:1747-70, 1999. 6) Tönnis D, Skamel HJ.,Decreased acetabular anteversion and femur neck antetorsion cause pain and arthrosis. 1: Statistics and clinical sequelae.Z Orthop Ihre Grenzgeb. 1999 Mar-Apr;137(2):153-9. 7) Fabry G, et al. Torsion of the femur: a follow-up study in normal and abnormal conditions. J Bone Joint Surg [Am] 1973;55-A:1726-38.

Parameter Odds Ratio 95% CI p-value Age 1.06 1.03~1.09 <0.001 Sex 6.22 2.71~14.27 <0.001 Femoral Version<0º 1.55 1.01~2.38 0.047 Coxa Valga 0.82 0.6~1.12 0.218 Coxa Vara 1.55 1.12~2.14 0.008

Poster No. 2199 • 55th Annual Meeting of the Orthopaedic Research Society