Archives of Physical Medicine and Rehabilitation
Volume 89, Issue 5 , Pages 890-893, May 2008

Expert Opinion and Controversies in Musculoskeletal and Sports Medicine: Femoroacetabular Impingement

  • Christopher J. Standaert, MD

      Affiliations

    • Department of Rehabilitation Medicine, University of Washington, Seattle, WA
    • Department of Orthopaedic and Sports Medicine, University of Washington, Seattle, WA
    • Department of Neurological Surgery, University of Washington, Seattle, WA.
    • Corresponding Author InformationReprint requests to Christopher J. Standaert, MD, 325 9th Ave, Box 359721, Seattle, WA 98104
    • ,
  • Paul A. Manner, MD

      Affiliations

    • Department of Orthopaedic and Sports Medicine, University of Washington, Seattle, WA
    • ,
  • Stanley A. Herring, MD

      Affiliations

    • Department of Rehabilitation Medicine, University of Washington, Seattle, WA
    • Department of Orthopaedic and Sports Medicine, University of Washington, Seattle, WA
    • Department of Neurological Surgery, University of Washington, Seattle, WA.

Article Outline

Abstract 

Standaert CJ, Manner PA, Herring SA. Expert opinion and controversies in musculoskeletal and sports medicine: femoroacetabular impingement.

Femoroacetabular impingement (FAI) has been proposed as a distinct clinical entity that may be a potentially significant cause of hip osteoarthritis (OA). There is a growing body of literature on this condition, including descriptions of biomechanic mechanisms of impingement, anatomic and radiographic findings, and surgical interventions. Although a connection between anatomic abnormalities of the hip and the development of OA has been recognized for some time, there are limited data on the natural history of FAI and no long-term studies on the effect of surgical treatment. Thus, the diagnosis engenders a degree of controversy in multiple regards, including the diagnostic criteria and the role of operative intervention.

Key Words: Osteoarthritis, hip, Pain, Rehabilitation

 

FEMOROACETABULAR IMPINGEMENT (FAI) is a relatively new clinical diagnosis thought by some to be a cause of hip pain and a significant factor in the development of hip osteoarthritis (OA).1, 2, 3, 4, 5, 6 Although a connection between abnormal hip morphology and OA has been noted for some time, the condition of FAI has predominantly been recognized as a clinical problem in the last 5 or 10 years. Ganz et al2 have described the clinical presentation, radiographic findings, and mechanisms of FAI, along with presenting a surgical approach to management, based on their experience with over 600 surgical dislocations of the hip. In the last several years, a significant number of other articles on the subject have been published, including reviews, radiographic descriptions, small treatment studies, and surgical descriptions of open, arthroscopic, and mixed surgical approaches.

The conceptual model of FAI implies that there is abnormal contact between the femur and acetabular rim at the end range of hip motion, particularly flexion, resulting in the development of chondral lesions, labral tears, and progressive OA.2, 4, 5 The basis for the abnormal contact is related to anomalies of the femur, the acetabulum, or both. Two distinct types of FAI have been described (fig 1), predominantly based on whether the anomalous morphology occurs in the femur (cam impingement) or acetabulum (pincer impingement), although mixed impingement with a combination of both cam and pincer mechanisms is also recognized. In cam impingement, it is believed that there is either a nonspherical femoral head or abnormalities at the femoral head-neck junction that results in an increased femoral head radius. In full flexion, the prominence on the femoral head-neck junction is forced into contact with the acetabular rim, causing abrasion of the acetabular cartilage and/or avulsion of the labrum at the anterosuperior rim of the acetabulum. This type of impingement is described as being most common in young active males and has been associated with a prior slipped capital epiphysis, Legg-Calvé-Perthes disease, osteonecrosis, and malunited femoral neck fractures.1, 2, 3, 5, 6

  • View full-size image.
  • Fig 1. 

    Depictions of hip morphology and motion in the setting of a normal hip (top), pincer impingement (middle), and cam impingement (bottom). In pincer impingement, note that the acetabulum is deep, with overcoverage of the femoral head. In full flexion, there is contact between the femoral neck and the acetabular rim accompanied by posteroinferior joint subluxation. In cam impingement, an abnormality at the femoral head-neck junction is forced into the acetabular rim in full hip flexion. Reprinted with permission.8(p1541)

In pincer impingement, the abnormal contact between the femoral neck and the acetabulum occurs because of overcoverage of the femoral head by an abnormally deep or retroverted acetabulum. Repetitive contact between the femoral neck and the acetabular rim is thought to result in labral injury with less substantial cartilage involvement, although recurrent leveraging of the femoral neck on the acetabulum can cause injury to the posteroinferior articular cartilage via a contrecoup mechanism. This type of impingement seems to occur most frequently in middle-aged active women.1, 2, 3, 5, 6 By following this model, treatment is directed toward the alleviation of pain and “joint preservation” through elimination of the abnormal contact between the femur and acetabulum.6 Although the diagnosis of FAI and subsequent surgical intervention appear to be increasingly common, there are significant limitations to the available literature and controversy about multiple aspects of this entity.

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Controversies 

The Relationship Between FAI, Hip Pain, and OA 

The diagnosis of FAI is based on clinical observations and imaging studies. Although abnormal morphology of the femoral head has clearly been associated with hip OA, the extent of this relationship is not well defined.7 Absent any prospective data, it is difficult to be definitive about the inter-relationship between the proposed anatomic abnormalities and mechanisms of impingement and the development of OA.

The Effect of Operative Treatment 

There is a clear disparity between the relatively short amount of time that has elapsed since the initial descriptions of surgical intervention for FAI and the total time course of degenerative OA of the hip. The exact outcome measures chosen for study are crucial in establishing the efficacy of any particular intervention, and it may be some time before the clinical outcomes show whether surgical intervention for FAI is a “joint-preserving” approach.

The Optimal Treatment Approach 

There is debate about the relative costs and benefits of open versus arthroscopic procedures for FAI. Significant questions remain on the extent of bony débridement necessary, the long-term viability of the joint after various degrees of intervention, and the role of activity modification and other nonoperative approaches to care.

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Practical Approaches 

What Are the Clinical Findings in Patients Thought to Have FAI? 

Clinically, patients with FAI seem to present with groin pain associated with athletic activities, prolonged walking, or prolonged sitting. The pain may develop gradually or start after minor trauma. The condition typically seems to affect young to middle-aged, active adults, although the diagnosis is being made in adolescents as well.2, 5, 6 Some have noted that pain also can occur in the knee, low back, or buttock, substantially broadening the patient population potentially affected by FAI.5, 6 A physical examination marker is reduced range of motion in the hip, particularly for internal rotation, flexion, and adduction. The impingement test is described as being widely, if not uniformly, positive. In this test, the patient lays supine, and the hip is flexed to 90°, internally rotated, and adducted, resulting in reproduction of the patient's symptoms when positive.2, 3, 5, 6 Unfortunately, despite claims of very high sensitivity, true statistical assessment of the sensitivity and specificity of this maneuver is lacking, and it is difficult to conceptualize what the criterion standard might be for any such analysis at this time.

What Are the Radiographic Findings in FAI? 

Radiographically, a number of findings characterize patients thought to have FAI. Standard imaging with plain radiographs includes a true anteroposterior pelvic view and an axial cross-table view of the proximal femur. It is important to follow standardized techniques for positioning of the patient and the camera.8 Radiographs may show a bony prominence or flattening of the anterolateral femoral head-neck junction, radiolucent cystic changes at the femoral head-neck junction, or abnormalities of the acetabulum, particularly excessive coverage of the femoral head by the acetabulum or acetabular retroversion (figs 2A–C). The abnormalities are frequently described as “subtle” or “normal appearing” at first glance, although methods have been described to quantify the amount of “asphericity” of the femoral head.2, 3, 5, 8 Technical limitations can make it difficult to reliably assess the extent of abnormality on plain films, particularly the effects of pelvic rotation and radiographic beam alignment on assessing acetabular version.8 Given the technical specifications and subjective components to assessment, there may be significant issues with the interrater reliability of some of these findings.

  • View full-size image.
  • Fig 2. 

    Radiographic appearance of the right hip on an anteroposterior view. (A) A normal hip. The acetabular fossa (F) is lateral to the ilioischial line (IIL), and the acetabulum does not completely cover the femoral head (E). The arc of the epiphyseal scar (arrows) lies within the circular contour of the femoral head. (B) Pincer impingement. Overcoverage of the femoral head by the acetabulum is present. Acetabular retroversion is depicted, defined by the anterior wall (AW) of the acetabulum being more lateral than the posterior wall (PW). The anterior wall lies medial to the posterior wall in a normal hip. (C) Cam impingement. Note that the epiphyseal scar (arrows) has an abnormal lateral extension that results in an aspherical femoral head and alters the appearance of the femoral head-neck junction (so-called pistol grip deformity). Reprinted with permission.8(p1544,1545,1548)

Abnormalities on magnetic resonance imaging (MRI) with arthrography and computed tomography scans have also been described. MRI athrograms are typically obtained in patients with suspected FAI to assess the labrum and soft tissues.1, 2, 5, 6 Notzli et al9 performed an MRI study on 39 patients with a clinical diagnosis of FAI. The diagnosis was based on symptoms and the presence of less than 10° internal rotation of the hip, a positive impingement test, and a normal acetabulum on radiographs. The findings in these patients were compared with 35 controls with no hip pain, not less than 20° internal rotation of the hip, and a negative impingement test. (Of note, 5 additional asymptomatic controls were excluded because they had decreased internal rotation at the hip and 2 of these had positive impingement tests.) Notzli found a reduced concavity in the area of the femoral head-neck junction in the FAI group compared with the controls. Although useful, this study has limitations, including the exclusion of asymptomatic patients with reduced internal rotation of the hip. Pfirrmann et al10 described the MRI arthrographic findings in 50 consecutive patients diagnosed with FAI at the time of surgery. They identified aspherical changes in the femoral head (as described by Notzli9), cartilage lesions at the anterosuperior acetabulum, and osseous bump formation on the femoral neck in patients with cam impingement and a deep acetabulum and posteroinferior cartilage damage in patients with pincer impingement. One problem with this study is that the patients had already been diagnosed, had had surgery, and had been classified by type of FAI before the MRI findings of the group were characterized, potentially leading to a circular description of the findings that were first used to diagnose the patients.

Clinicians also need to recognize the limitations of MRI arthrography in detecting cartilaginous lesions. In their study comparing MRI arthrography of the hip with arthroscopy, Keeney et al11 found that MRI arthrography identified only 76% of the labral tears found at surgery, with a 5% false-positive rate. Overall, Keeney found that MRI arthrography of the hip had a sensitivity of 71% and a specificity of 44% for labral tears and a sensitivity of 47% and a specificity of 89% for cartilage pathology.

What Is the Relationship Between FAI and OA of the Hip? 

There is a large group of patients with primary (or idiopathic) hip OA, meaning the arthritic changes cannot be attributed to a discrete cause such as trauma, a slipped capital epiphysis, or congenital dysplasia (termed secondary osteoarthritis).7 A number of clinicians believe that primary OA of the hip may be related to an unidentified systemic cause or to less obvious, subclinical dysplasia, slipped capital epiphysis, or FAI.5, 7 A relationship between femur abnormalities and hip OA has been identified for decades.12 In a cadaveric study of the femora of 2665 adult human skeletons, Goodman et al7 assessed the relationship between abnormal femoral head morphology (termed postslip morphology) and primary OA. The prevalence of postslip morphology was 8% in this group. Severe OA was noted in 38% of the hips with postslip morphology compared with 26% of matched controls, representing a statistically significant difference. Tanzer and Noiseux13 found that 100% of their patients undergoing total hip arthroplasty (THA) for primary OA had abnormalities of the femoral head-neck junction (termed pistol grip deformity in this study). Giori and Trousdale14 assessed the prevalence of acetabular abnormalities on radiographs in groups with and without known OA. In those with idiopathic hip arthritis, the prevalence of acetabular retroversion was 20% compared with 5% in the general population.

Overall, the data supporting a connection between abnormalities of the femoral head and/or the acetabulum and primary OA of the hip are relatively strong. The actual definition of what is abnormal or what extent of abnormality is problematic is not as well defined, however. The natural history of those with varying degrees of abnormality and the effect of any intervention on them are also unclear. Further study on the incidence of morphologic abnormalities in the general population and the relative risk for OA posed by these abnormalities would be helpful.

What Are the Treatment Options? 

In general, the role of nonoperative intervention is described as limited and may include activity modification, nonsteroidal anti-inflammatory medications, and injections.2, 5, 6 Physical therapy is described as “counterproductive,”3, 5 and there is concern that any nonoperative care could theoretically result in an increased risk of degenerative change because it does not address the underlying impingement that is suspected of leading to progressive OA.3, 5, 6 The natural logic of this line of thought, however, is that surgery is necessary as an early intervention to avoid progressive degeneration. Absent any prospective data on the natural history of the diagnosis, the long-term outcomes of those undergoing surgery compared with those who do not, and the prevalence of various findings in the asymptomatic population, this reasoning is troublesome.

Surgical intervention may consist of an open procedure, arthroscopy, or both to débride the labrum, remove some of the femur (femoral osteoplasty), and/or perform an acetabular osteotomy. If there is advanced degenerative change, THA may also be considered. The original procedure described by Ganz et al2 involves a lateral hip incision, a trochanteric osteotomy to move the trochanter for access, an incision in the hip capsule, hip dislocation and femoral osteoplasty with débridement of the labrum, osteotomy of the acetabular rim and/or other procedures as necessary to clear the impingement, followed by closure with repinning of the trochanter back onto the femur.2, 5 The arthroscopic technique involves traction on the leg to distract the joint followed by the insertion of instrumentation through 2 or 3 portals and the subsequent correction of the anatomic impingement and any damaged structures (eg, labrum), similar to that done in an open procedure. Although less invasive, there are currently limitations on what can be done arthroscopically, and there are less published data on these procedures.5, 6

Both procedures have their potential problems. Complications can include peripheral nerve injuries, trochanteric nonunion, osteonecrosis of the femoral head, and femoral neck fracture. In a study15 of 34 patients undergoing the open procedure as described earlier, 10 subsequently underwent further surgery for complications related to the procedure itself by 3-year follow-up, 9 of these for screw removal from the trochanteric fixation.

Is Treatment Effective? 

There are several small, prospective, nonrandomized studies on the surgical treatment of FAI that describe postsurgical outcomes as “encouraging.”5, 15, 16 There are no published controlled trials of surgical treatment of patients with FAI. There are no level 1 data published of which we are aware. In the study by Beaule et al15 of 34 patients undergoing an open procedure for FAI, there was an increase in overall quality of life at the 3-year follow-up, but 11 patients underwent further surgery on the same hip and 6 were dissatisfied with their outcome. Beck et al17 reported on 19 patients followed for 4.7 years after an open procedure for FAI. Beck graded 13 as having good to excellent results, but 5 had gone on to have THA within that time. Peters and Erickson18 reported on the results of open surgery in 30 hips at a mean of 32 months. Although overall improvement was noted for the group, 8 patients had progression of degenerative changes and 4 had undergone or were expected to shortly undergo THA. In general, interventions seem less effective in the setting of more advanced arthritic changes.

Unfortunately, there are no long-term data on the effects of treatment for FAI. Because one of the primary reasons for considering surgical intervention in these patients is the prevention of progressive OA, the lack of any data on long-term postsurgical outcomes is a substantial problem. It is possible that short-term benefits in pain reduction and functional improvement noted in some patients undergoing surgery for FAI are related to labral débridement rather than extensive bony removal, the latter presumably being performed to maintain the viability of the hip over time. The true extent of benefit, or lack thereof, from surgery in terms of preserving the joint is not currently documented.

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Conclusions 

The idea of a procedure with low morbidity that could prevent the progression of degenerative arthritis in young people with abnormal hip morphology is attractive. This is the basic premise behind intervention for FAI. There may be a population with prior hip pathology, such as a slipped capital epiphysis, who have significant abnormalities of the femoral head and may benefit from some type of intervention to prevent or retard the development of OA. However, this population is small. Extrapolating this concept to more subtle morphologic abnormalities in the hip may be rational, but there are very limited data on which to base a decision on who to treat, what that treatment should be, and if the treatment is helpful or harmful in the long-term. Patients need this information to make educated decisions about their health care. Consideration has to be given to the lack of conclusive data on the long-term efficacy and safety of extensive interventions. Longer-term, randomized controlled trials seem justified based on the available data and should be pursued so that we can understand the diagnosis itself better and provide recommendations for effective treatment.

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References 

  1. Bredella M, Stoller D. MR imaging of femoroacetabular impingement. Magn Reson Imaging Clin N Am. 2005;13:653–664
  2. Ganz R, Parvizi J, Beck M, Leunig M, Notzli H, Siebenrock KA. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Dec Clin Orthop Relat Res. 2003;417:112–120
  3. Jaberi F, Parvizi J. Hip pain in young adults: femoroacetabular impingement. J Arthoplasty. 2007;22(7 Suppl 3):37–42
  4. Kassarjian A, Brisson M, Palmer WE. Femoroacetabular impingement. Eur J Radiol. 2007;63:29–35
  5. Parvizi J, Leunig M, Ganz R. Femoroacetabular impingement. J Am Acad Orthop Surg. 2007;15:561–570
  6. Zebala LP, Schoenecker PL, Clohisy JC. Anterior femoroacetabular impingement: a diverse disease with evolving treatment options. Iowa Orthop J. 2007;27:71–81
  7. Goodman DA, Feighan JE, Smith AD, Latimer B, Buly RL, Cooperman DR. Subclinical slipped capital femoral epiphysis (Relationship to osteoarthrosis of the hip). J Bone Joint Surg Am. 1997;79:1489–1497
  8. Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular impingement: radiographic diagnosis—what the radiologist should know. AJR Am J Roentgenol. 2007;188:1540–1552
  9. Notzli HP, Wyss TF, Stoecklin CH, Schmid MR, Treiber K, Hodler J. The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement. J Bone Joint Surg Br. 2002;84:556–560
  10. Pfirrmann CW, Mengiardi B, Dora C, Kalberer F, Zanetti M, Hodler J. Cam and pincer femoroacetabular impingement; characteristic MR arthrographic findings in 50 patients. [published erratum in: Radiology 2007;244:626] Radiology. 2006;240:778–785
  11. Keeney JA, Peelle MW, Jackson J, Rubin D, Maloney WJ, Clohisy JC. Magnetic resonance arthrography versus arthroscopy in the evaluation of articular hip pathology. Clin Orthop Rel Res. 2004;429:163–169(Dec)
  12. Solomon L. Patterns of osteoarthritis of the hip. J Bone Joint Surg Br. 1976;58:176–183
  13. Tanzer M, Noiseux N. Osseous abnormalities and early osteoarthritis (The role of hip impingement). Dec Clin Orthop Rel Res. 2004;429:170–177
  14. Giori NJ, Trousdale RT. Acetabular retroversion is associated with osteoarthritis of the hip. Dec Clin Orthop Relat Res. 2003;417:263–269
  15. Beaule PE, LeDuff MJ, Zaragoza E. Quality of life following femoral head-neck osteochondroplasty for femoroacetabular impingement. J Bone Joint Surg Am. 2007;89:773–779
  16. Khanduja V, Villar RN. The arthroscopic management of femoroacetabular impingement. Knee Surg Sports Traumatol Arthrosc. 2007;15:1035–1040
  17. Beck M, Leunig M, Parvizi J, Boutier V, Wyss D, Ganz R. Anterior femoroacetabular impingement: part II (Midterm results of surgical treatment). Jan Clin Orthop Relat Res. 2004;418:67–73
  18. Peters CL, Erickson JA. Treatment of femoro-acetabular impingement with surgical dislocation and débridement in young adults. J Bone Joint Surg Am. 2006;88:1735–1741

 No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors or upon any organization with which the authors are associated.

PII: S0003-9993(08)00137-8

doi:10.1016/j.apmr.2008.02.013

Archives of Physical Medicine and Rehabilitation
Volume 89, Issue 5 , Pages 890-893, May 2008

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