|Year : 2013 | Volume
| Issue : 2 | Page : 63-69
Femoroacetabular impingement in athletes: A review of the current literature
Abdulrahman D Algarni
Department of Orthopedic Surgery, King Saud University, Riyadh - 11472, Saudi Arabia
|Date of Web Publication||20-Dec-2013|
Abdulrahman D Algarni
King Saud University, Riyadh 11472, P. O. Box: 7805 (49)
There are several well-recognized causes of hip and groin pain that commonly affect athletes. Femoroacetabular impingement (FAI), also known as hip impingement, is increasingly recognized as a common; and possibly often overlooked; etiology of hip pain in athletes. FAI is characterized by the abutment of the acetabular rim and the proximal femur, which may occur by two mechanisms known as "cam" or "pincer" impingement, although most commonly by a combination of the two. It affects athletes at a young age causing significant pain and disruption to athletic performance and activities of daily living. It injures the labrum and articular cartilage and can lead to early osteoarthritis of the hip if left untreated. Patients often report a groin pain, which is typically reproduced by the use of flexion, adduction and internal rotation of the supine hip. Early diagnosis is crucial in order to avoid the severe secondary damage that can occur. Although, FAI is significant for all patients, in athletic individuals they may bring about the end of their sporting careers. Both open and arthroscopic surgical methods are used, with recent reports in athletes showing excellent results for life-style improvement and frequency of returning to the sport. Whether treatment prevents or delays osteoarthritis of the hip is unknown. This article reviews the latest scientific literature in reference to FAI in athletes. It goes some way to explaining the principles, approach and guidelines for management of FAI in athletes.
هناك أسباب محددة للآلام الورك والمنطقة الإربية والتي تصيب الرياضيين. يعتبر الانحشار الحقي الفخذي أو ما يعرف أيضا باسم انحشار الورك من أهم أسباب الآلام الورك شيوعا عند الرياضيين. إن الانحشار الحقي الفخذي يتميز بحدوث انضغاط بين حافة الحق والنهاية الدانية للفخذ والتي قد تحدث من خلال إحدى آليتين وهما " الحدبة " والكماشة " وفي أكثر الأحيان تحدث كلتا الآليتين. يصيب الانحشار الرياضيين في سن مبكرة مما يسبب الآلام مبرحه وإعاقة لأداء الرياضيين مع التأثير على نشاط الحياة اليومي, وقد ينتج من ذلك أذى لشفة الحقي والغضروف المفصلي ويمكن أن يؤدي ذلك إلى فصال عظمي لمفصل الورك إذا تركت دون علاج. يشكو المرضى عادة من ألم في المنطقة الإربية يمكن إظهاره عن طريق الثني والتقريب والتدوير للداخل للورك في وضعية الاستلقاء. إن التشخيص المبكر ضروري لتفادي حدوث التغيرات الثانوية التي يمكن حدوثها. بالرغم من أن الانحشار الحقي الفخذي يعد أمراً هاماً عند جميع المرضى، إلا أن له أهمية خاصة لدى الرياضيين لأنة قد يؤدي إلى وضع نهاية لمستقبلهم الرياضي. يمكن استعمال كل من الجراحة المفتوحه أو جراحة المنظار للمعالجة وتكون النتائج ممتازة تسمح للرياضيين بالعودة إلى نمط حياتهم وحتى إلى ممارسة الرياضة، ولكن ليس هناك دليل ما إذا كان ذلك سيمنع أو يؤخرحدوث الفصال العظمي. يعرض هذا المقال أحدث المقالات العلمية التي تشير إلى الانحشار الحقي الفخذي عند الرياضيين، ويشرح المبادئ، وطريقة الوصول إلى التشخيص ومبادئ العلاج.
Keywords: Athletes, cam, femoroacetabular impingement, hip arthroscopy, pincer, surgical hip dislocation
|How to cite this article:|
Algarni AD. Femoroacetabular impingement in athletes: A review of the current literature. Saudi J Sports Med 2013;13:63-9
| Introduction|| |
The differential diagnosis of hip and groin pain in athletes is broad and includes conditions of the hip, lower back and pelvis. It is estimated that hip and groin injuries accounted for 5-6% of all adult athletic injuries and are a significant cause of morbidity in athletes.  Conditions such as athletic pubalgia (or sports hernia), Piriformis Syndrome, stress fractures, strains and snapping hip are established and well-reported causes of such athletic injuries. In recent years, notable progress has been made in the diagnosis and treatment of non-arthritic hip injuries. Femoroacetabular impingement (FAI) - related labral tears and early cartilage damage are now recognized as common sources of hip pain.  The concept of FAI as a cause of osteoarthritis is credited to Professor Reinhold Ganz from Bern, Switzerland.  Early-age onset osteoarthritis among adults in their fourth and fifth decades is often attributed to this process. It is now recognized that FAI can cause serious joint damage among young athletes, even in their second and third decades. 
In the past, this pathological process simply went undiagnosed. Athletes often experienced poorly-explained groin pain that eventually ended their competitive careers with an ill-defined, unsolved problem. With growing recognition and treatment, many athletes have been able to resume competitive activities and thus created more awareness of the disorder. It is unclear, which portion of asymptomatic athletes will eventually develop progressive secondary joint damage. However, many athletes have significant grade III and grade IV articular lesions at the time of surgical intervention, suggesting that secondary damage occurs by the time the clinical circumstances are sufficient to recommend surgery. Thus, a cautious watchful approach is important, even with the mildest symptoms associated with FAI.
Cam and pincer mechanisms have been suggested, which may occur together or in isolation [Figure 1]. Cam-type impingement is primarily an abnormality of the femoral head-neck junction, whereas the pincer type is principally an abnormality of the acetabulum causing impingement against the femoral neck. Both these subtypes vary slightly in their pathological consequences, but both have been shown to cause cartilage delamination, labral tears and have been linked to early osteoarthritis of the hip. ,, Thus, this article focuses on the underlying pathology, clinical assessment and diagnostic imaging findings with special emphasis on the importance of early detection on athletic individuals.
| Pathology|| |
Cam-type impingement has an approximately 3:1 predilection for men and often presents with problems in young adulthood.  It refers to a cam effect caused by a non-spherical femoral head rotating inside the acetabulum.  This has long been recognized as a sequela of a slipped capital femoral epiphysis (SCFE) where posterior displacement of the head leaves a prominence of the anterior neck, resulting in severely limited internal rotation of the hip.  Operations performed to excise this bony prominence have been referred to as a cheilectomy.  However, more subtle or subclinical forms of an aspherical femoral head are much more common and only more recently recognized as a cause of impingement. With flexion, the non-spherical portion of the head rotates into the acetabulum, creating a shear force on the anterolateral edge of the acetabular articular surface. With repetitive motion, this eventually results in articular delamination and failure of the acetabular articular cartilage. In this condition, there is a preferential articular pathology and relative labral preservation. Over time, the labrum will eventually start to fail but only after the process is advanced on the articular surface.
Pincer-type impingement occurs about equally in men and women and often starts to cause symptoms in middle age.  It is caused by an excessive prominence of the anterolateral rim of the acetabulum.  This can occur simply from overgrowth of the anterior acetabular edge or due to acetabular retroversion, which is a condition where the face of the acetabulum tilts slightly backward instead of its normal, forward position. Sometimes there is a separate piece of bone along the anterolateral rim; an os acetabulum.  With hip flexion, the prominent rim of the acetabulum crushes the labrum against the femoral neck. This cyclical submaximal repetitive microtrauma leads to breakdown and failure of the acetabular labrum. Secondarily, over time, a variable amount of articular failure within the adjacent acetabulum will occur.
| Etiology and Epidemiology|| |
The etiology of the condition is still unclear, however, certain types of sports such as hockey, tennis, soccer and horse riding have been suggested to induce femoral neck abnormality through the osteophyte-type formation or simply exaggerate a problem by utilizing specific ranges of motion, especially that of internal rotation in flexion.  The pain exhibited on internal rotation in flexion in patients with FAI is due to the abutment and impingement of the femoral neck against the acetabular labrum and it could be postulated that sports in which this mechanism is utilized would be in those in which FAI is most common.
There are very few published data demonstrating the prevalence of FAI in the general population. Murray  reported a 24% prevalence of cam-type FAI in high-activity athletes, which is higher than the estimated 10-15% prevalence in the general population.  It is also known that conditions such as malunion of femoral neck fractures can be related to sport  and lead to a cam-type impingement. , These figures lend support to the assertion that certain sports increase the risk of developing the condition, not simply of becoming symptomatic and also may explain why young men are most at risk for this condition.
It is important to note the severe impact that this condition may have on athletes. Reports describe significant impairment in activities of daily living,  together with severe limitations in sporting activities, particularly high-demand sports involving cutting or sprinting. In these activities, 88% of athletes reported moderate to total inability to perform. Bizzini et al. reported that the loss of range of motion in hip rotation, especially internal rotation, was the main performance-limiting factor in their study.
| Assessment|| |
The examining physician must distinguish whether symptoms are originating from the hip joint or are due to extra-articular causes. Athletic pubalgia (or sports hernia) may coexist with FAI.  Hammoud et al. recently reported a high incidence of symptoms of athletic pubalgia in professional athletes with FAI and the authors urge caution in diagnosing athletic pubalgia in a patient with FAI. Likewise; a snapping iliopsoas tendon might coincidentally be present in athletes with a hip impingement. With care, these conditions can usually be distinguished from FAI.
Athletes with FAI typically presents with an insidious onset groin pain that may radiate to the medial thigh.  They often cup the anterolateral hip with fingers in the shape of a "C" (C-sign).  Symptoms may be preceded by minor trauma; although, many patients will report no history of any specific precipitating factor.
During the early stages, the pain is intermittent and may be exacerbated by physical activities and exercise and hence a misdiagnosis of hip or groin pain of soft-tissue origin may occur. The pain experienced may also be aggravated by prolonged sitting, turning, twisting or pivoting movement. An incorrect diagnosis at this stage may then lead to several weeks or months of inappropriate management.
Poor hip flexibility is compensated by the increased pelvic and lumbosacral motion, which may create other problems that commonly coexist with FAI.  It is therefore important that FAI becomes a more widely appreciated cause of hip pain, especially in sports involving internal rotation in flexion and should be considered as a cause of groin pain in these athletes.
Patients with FAI have a restricted range of motion, particularly flexion and internal rotation; , although, there is much variation in the normative data on hip range of motion. Furthermore, although only one hip may be symptomatic, the altered morphology is usually present in both hips and there may not be much asymmetry in motion when the symptomatic side is compared with asymptomatic side. The flexion, adduction and internal rotation constitute the impingement test  [Figure 2] and is the most sensitive physical examination test for FAI.  Hip impingement tests in patients with FAI have been shown to be almost always positive and are therefore of paramount importance for the evaluation. , However, virtually any irritable hip, regardless of the cause, will be uncomfortable with this maneuver. Thus, although the test is quite sensitive, it is not necessarily specific for impingement. Most important is whether it re-creates the characteristic pain that the athlete experiences with activities.
These conditions often have a chronic component, even at the initial evaluation. Thus, secondary findings may be present because of compensatory mechanisms. Lateral pain may be present from trochanteric bursitis and posterior tenderness within the gluteal muscles may be present protecting the hip joint. These secondary features may be more apparent on examination and can obscure the underlying primary joint pathology.
Philippon et al.  reported the amount of loss of range of motion in cam-type (anterosuperior lesion) FAI. The authors showed that hip flexion on the affected side was 9° less than the opposite limb, together with mean reductions of adduction (3° less) and internal rotation (4° less). They also showed that the impingement test was positive in 99% of athletes and the (flexion abduction and external rotation) test was positive in 97%. Although anterior impingement is common, pincer-type impingement (posteroinferior lesions) is also often found; however, the most common pathology is often reported to be a combination of the two  as previously outlined.
To test for posteroinferior impingement, the patient lies supine and extends their leg over the edge of the examination couch. The examining physician then provides external rotation of the hip in full extension, which will reproduce their symptoms of groin pain should a posteroinferior lesion be present.
Conventional radiographic evaluation for FAI includes two radiographs: An anteroposterior pelvic (AP) view and an axial cross-table view of the proximal femur.  For the AP view, the patient lies supine with the legs 15° internally rotated to compensate for femoral anteversion and to provide better imaging of the lateral femoral head-neck junction.  An alternative to the axial view, a Dunn/Rippstein view in 45° of flexion can be obtained to reveal abnormalities of the anterior femoral head-neck junction.  A faux profile view  [Figure 3] is rarely indicated and is used to assess the posteroinferior part of the joint to detect the so-called contre-coup lesions in pincer-type impingement.
|Figure 3: Faux profile view showing pincer‑type impingement with posteroinferior joint space narrowing (arrow) as a result of recurrent subluxations|
Click here to view
The radiographs may show bony abnormalities suggestive of cam impingement including coxa vara, pistol grip deformity, , subclinical SCFE  or an os acetabulum. The cause of an os acetabulum is variable, ranging from an unfused apophysis to a traction phenomenon (from the pull of the rectus femoris origin) to a rim fracture secondary to cam impingement. Over coverage of the anterior acetabulum, characteristic of pincer impingement is suggested by a crossover sign or figure-of-configuration, which can be due to an acetabular retroversion indicated by the posterior wall sign. Coxa profunda, acetabular protrusion and herniation pits are other pathomorphologic features for potential pincer impingement. A herniation pit may be present at the anterolateral femoral head-neck junction, which can obscure the extent of a cam lesion. This has been reported in 30% of pathological cases of FAI, but can be present in asymptomatic individuals. 
Computed tomography (CT) is much better at showing bone architecture and structure. Three-dimensional CT with reconstructions provides a better image of the bony contour of the cam lesion and its morphology and is especially helpful in the pre-operative planning for arthroscopic treatment. ,,
Magnetic resonance imaging is also now commonly used in the evaluation of painful FAI. ,, It allows assessment of the head-neck morphology, cartilage and labral abnormalities.  Sutter et al. showed that increasing the alpha-angle threshold value for FAI from 55° to 60° maintains a reasonable sensitivity and reduces false-positive results. Assessment of labral and cartilage damage is enhanced with magnetic resonance arthrography (MRA) demonstrates greater sensitivity in detecting intra-articular pathology,  including labral lesions. A concomitant injection of long-acting anesthetic with the contrast during MRA is advantageous; however, it eliminates the opportunity to assess for an effusion. An optimal protocol includes a select series of both pre- and post-contrast images. Aprato et al.  recently reported that MRA correlate well with the intra-operative findings of labral tears, cam-type impingement lesions and os acetabula; however, it was less efficacious in the diagnosis of cartilage abnormalities of both femoral and acetabular parts.
| Management|| |
An initial period of conservative management; with an emphasis on early recognition; is recommended, recognizing that many patients may subsequently need surgical intervention. This entitles activity modification with a reduction of excessive end-range movements together with appropriate anti-inflammatory medications and analgesics.
Surgical intervention is indicated in symptomatic cases with imaging evidence of impingement and secondary joint damage. The goal of surgery is to alleviate the abutment between the femoral head and the acetabulum, to repair or remove injured tissue and to halt or delay the process of chondral and labral damage. Both open , and arthroscopic techniques ,, have been developed to achieve this goal.
Although hip arthroscopy has lagged behind that of the other joints, it is now becoming increasingly adopted and is regarded as an accepted or "gold standard" of care. 
In addition to diagnostic capability, , different arthroscopic techniques for treating FAI have been described, ,, depending upon the type and extent of the impingement, the details of which are beyond the scope of this article.
Hip arthroscopy is not without risks and both avascular necrosis of the femoral head and femoral neck fracture have been reported after therapeutic arthroscopic treatment.  Fabricant et al. reported short-term improvements in hip scores without complications after arthroscopic treatment of FAI in athletic patients. Similarly, Byrd and Jones  reported successful outcomes of the arthroscopic management of FAI with few complications and that most athletes in their series were able to resume activities.
Surgical hip dislocation have long been recommended to provide a full, unobstructed view of the femoral head and acetabulum.  For cam-type impingement with a non-spherical femoral head, surgical hip dislocation  allows excision osteoplasty of the anterolateral portion of the femoral head-neck junction necessary to relieve the impingement. It is recommended to keep excision to the minimal amount required to alleviate the abutment as removing more than 30% of the head-neck junction may result in an increased rate of fracture in response to axial loading and is therefore to be avoided. 
For pincer-type impingement due to an acetabular overhang, a resection osteoplasty of the excessive acetabular rim may be undertaken. Likewise, a periacetabular osteotomy may be performed to re-orient the acetabulum in cases of pincer-type impingement due to acetabular retroversion.  The shortcomings of the open surgical treatment include post-operative stiffness, heterotrophic ossification and sciatic nerve neuropraxis.  Alradwan et al. reported in a recent systematic review that surgical treatment for FAI resulted in a high return to pre-injury activity levels of sports in athletic patients.
The post-operative rehabilitation protocol involves a protected weight-bearing ambulation for approximately 6 weeks, with avoidance of extremes of hip flexion and rotation.  The speed of rehabilitation is variable; however, athletes generally take 4-6 months to return to sports following surgical treatment. Nho et al. found that 78% of athletes were able to return to play at 1 year and that 73% of athletes were able to play at 2-year follow-up.
| Conclusion|| |
FAI is a common cause of joint damage among athletes, especially in those participating in sports that involve internal rotation and loading in hip flexion. The emphasis should remain on early recognition of this entity so as to avoid secondary joint damage. The key to recognizing FAI lies in maintaining a high index of suspicion. History and careful physical examination, incorporating hip impingement tests will aid to establish the diagnosis in many patients. Emerging methods of imaging are becoming of paramount importance in determining the effects and degree of impingement. When indicated, both open and arthroscopic surgical procedures can address the underlying impingement and successful results with a return to sports can often be expected.
| References|| |
|1.||Keogh MJ, Batt ME. A review of femoroacetabular impingement in athletes. Sports Med 2008;38:863-78. |
|2.||Byrd JW. Hip morphology and related pathology. In: Johnson D, Pedowitz RA, editors. Practical orthopaedic sports medicine and arthroscopy. Philadelphia, PA: Lippincott Williams and Wilkins; 2007. p. 491-503. |
|3.||Ganz R, Parvizi J, Beck M, Leunig M, Nötzli H, Siebenrock KA. Femoroacetabular impingement: A cause for osteoarthritis of the hip. Clin Orthop Relat Res 2003;417:112-20. |
|4.||Byrd JW, Jones KS. Arthroscopic femoroplasty in the management of cam-type femoroacetabular impingement. Clin Orthop Relat Res 2009;467:739-46. |
|5.||McCarthy JC, Noble PC, Schuck MR, Wright J, Lee J. The Otto E. Aufranc award: The role of labral lesions to development of early degenerative hip disease. Clin Orthop Relat Res 2001;393:25-37. |
|6.||Ito K, Minka MA 2 nd , Leunig M, Werlen S, Ganz R. Femoroacetabular impingement and the cam-effect. A MRI-based quantitative anatomical study of the femoral head-neck offset. J Bone Joint Surg Br 2001;83:171-6. |
|7.||Leunig M, Beck M, Woo A, Dora C, Kerboull M, Ganz R. Acetabular rim degeneration: A constant finding in the aged hip. Clin Orthop Relat Res 2003;413:201-7. |
|8.||Erard MC, Drvaric DM. Cheilectomy of the hip in children. J Surg Orthop Adv 2004;13:20-3. |
|9.||Byrd JW, Jones KS. Arthroscopic management of femoroacetabular impingement. Instr Course Lect 2009;58:231-9. |
|10.||Martinez AE, Li SM, Ganz R, Beck M. Os acetabuli in femoro-acetabular impingement: Stress fracture or unfused secondary ossification centre of the acetabular rim? Hip Int 2006;16:281-6. |
|11.||Murray RO. The aetiology of primary osteoarthritis of the hip. Br J Radiol 1965;38:810-24. |
|12.||Beck M, Kalhor M, Leunig M, Ganz R. Hip morphology influences the pattern of damage to the acetabular cartilage: Femoroacetabular impingement as a cause of early osteoarthritis of the hip. J Bone Joint Surg Br 2005;87:1012-8. |
|13.||Kang L, Belcher D, Hulstyn MJ. Stress fractures of the femoral shaft in women′s college lacrosse: A report of seven cases and a review of the literature. Br J Sports Med 2005;39:902-6. |
|14.||Eijer H, Myers SR, Ganz R. Anterior femoroacetabular impingement after femoral neck fractures. J Orthop Trauma 2001;15:475-81. |
|15.||Bettin D, Pankalla T, Böhm H, Fuchs S. Hip pain related to femoral neck stress fracture in a 12-year-old boy performing intensive soccer playing activities: A case report. Int J Sports Med 2003;24:593-6. |
|16.||Philippon M, Schenker M, Briggs K, Kuppersmith D. Femoroacetabular impingement in 45 professional athletes: Associated pathologies and return to sport following arthroscopic decompression. Knee Surg Sports Traumatol Arthrosc 2007;15:908-14. |
|17.||Bizzini M, Notzli HP, Maffiuletti NA. Femoroacetabular impingement in professional ice hockey players: A case series of 5 athletes after open surgical decompression of the hip. Am J Sports Med 2007;35:1955-9. |
|18.||Meyers WC, McKechnie A, Philippon MJ, Horner MA, Zoga AC, Devon ON. Experience with "sports hernia" spanning two decades. Ann Surg 2008;248:656-65. |
|19.||Hammoud S, Bedi A, Magennis E, Meyers WC, Kelly BT. High incidence of athletic pubalgia symptoms in professional athletes with symptomatic femoroacetabular impingement. Arthroscopy 2012;28:1388-95. |
|20.||Byrd JW. Physical examination. In: Byrd JW, editor. Operative Hip Arthroscopy. 2 nd ed. New York, NY: Springer; 2005. p. 36-50. |
|21.||Meyers WC, Foley DP, Garrett WE, Lohnes JH, Mandlebaum BR. Management of severe lower abdominal or inguinal pain in high-performance athletes. PAIN (performing athletes with abdominal or inguinal neuromuscular pain study group). Am J Sports Med 2000;28:2-8. |
|22.||Ito K, Leunig M, Ganz R. Histopathologic features of the acetabular labrum in femoroacetabular impingement. Clin Orthop Relat Res 2004;429:262-71. |
|23.||Philippon MJ, Maxwell RB, Johnston TL, Schenker M, Briggs KK. Clinical presentation of femoroacetabular impingement. Knee Surg Sports Traumatol Arthrosc 2007;15:1041-7. |
|24.||Tannast M, Murphy SB, Langlotz F, Anderson SE, Siebenrock KA. Estimation of pelvic tilt on anteroposterior X-rays: A comparison of six parameters. Skeletal Radiol 2006;35:149-55. |
|25.||Meyer DC, Beck M, Ellis T, Ganz R, Leunig M. Comparison of six radiographic projections to assess femoral head/neck asphericity. Clin Orthop Relat Res 2006;445:181-5. |
|26.||Lequesne M, de Seze. False profile of the pelvis. A new radiographic incidence for the study of the hip. Its use in dysplasias and different coxopathies. Rev Rhum Mal Osteoartic 1961;28:643-52. |
|27.||Stulberg SD. Unrecognized childhood hip disease: A major cause of idiopathic osteoarthritis of the hip. In: Cordell LD, Harris WH, Ramsey PL, MacEwen GD, editors. Proceedings of the Third Open Scientific Meeting of the Hip Society. St. Louis (MO): Mosby; 1975. p. 212-28. |
|28.||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;79:1489-97. |
|29.||Leunig M, Beck M, Kalhor M, Kim YJ, Werlen S, Ganz R. Fibrocystic changes at anterosuperior femoral neck: Prevalence in hips with femoroacetabular impingement. Radiology 2005;236:237-46. |
|30.||Gelberman RH, Cohen MS, Desai SS, Griffin PP, Salamon PB, O′Brien TM. Femoral anteversion. A clinical assessment of idiopathic intoeing gait in children. J Bone Joint Surg Br 1987;69:75-9. |
|31.||Reikerås O, Bjerkreim I, Kolbenstvedt A. Anteversion of the acetabulum and femoral neck in normals and in patients with osteoarthritis of the hip. Acta Orthop Scand 1983;54:18-23. |
|32.||Reikerås O, Høiseth A. Femoral neck angles in osteoarthritis of the hip. Acta Orthop Scand 1982;53:781-4. |
|33.||Nötzli 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;84:556-60. |
|34.||Siebenrock KA, Wahab KH, Werlen S, Kalhor M, Leunig M, Ganz R. Abnormal extension of the femoral head epiphysis as a cause of cam impingement. Clin Orthop Relat Res 2004;418:54-60. |
|35.||Kassarjian A, Yoon LS, Belzile E, Connolly SA, Millis MB, Palmer WE. Triad of MR arthrographic findings in patients with cam-type femoroacetabular impingement. Radiology 2005;236:588-92. |
|36.||Sutter R, Dietrich TJ, Zingg PO, Pfirrmann CW. How useful is the alpha angle for discriminating between symptomatic patients with cam-type femoroacetabular impingement and asymptomatic volunteers? Radiology 2012;264:514-21. |
|37.||Byrd JW, Jones KS. Diagnostic accuracy of clinical assessment, magnetic resonance imaging, magnetic resonance arthrography, and intra-articular injection in hip arthroscopy patients. Am J Sports Med 2004;32:1668-74. |
|38.||Aprato A, Massè A, Faletti C, Valente A, Atzori F, Stratta M, et al. Magnetic resonance arthrography for femoroacetabular impingement surgery: Is it reliable? J Orthop Traumatol 2013 [Epub ahead of print]. |
|39.||Beck M, Leunig M, Parvizi J, Boutier V, Wyss D, Ganz R. Anterior femoroacetabular impingement: Part II. Midterm results of surgical treatment. Clin Orthop Relat Res 2004;418;67-73. |
|40.||Murphy S, Tannast M, Kim YJ, Buly R, Millis MB. Debridement of the adult hip for femoroacetabular impingement: Indications and preliminary clinical results. Clin Orthop Relat Res 2004;429:178-81. |
|41.||Sampson TG. Arthroscopic treatment of femoroacetabular impingement. Tech Orthop 2005;20:56-62. |
|42.||Weiland D, Philippon M. Arthroscopic technique of femoroacetabular impingement. Oper Tech Orthop 2005;15:256-60. |
|43.||Philippon MJ, Schenker ML. Arthroscopy for the treatment of femoroacetabular impingement in the athlete. Clin Sports Med 2006;25:299-308. |
|44.||Glick JM, Sampson TG, Gordon RB, Behr JT, Schmidt E. Hip arthroscopy by the lateral approach. Arthroscopy 1987;3:4-12. |
|45.||Lage LA, Patel JV, Villar RN. The acetabular labral tear: An arthroscopic classification. Arthroscopy 1996;12:269-72. |
|46.||McCarthy JC, Busconi B. The role of hip arthroscopy in the diagnosis and treatment of hip disease. Orthopedics 1995;18:753-6. |
|47.||Sampson TG. Arthroscopic treatment of femoroacetabular impingement. Am J Orthop (Belle Mead NJ) 2008;37:608-12. |
|48.||Fabricant PD, Heyworth BE, Kelly BT. Hip arthroscopy improves symptoms associated with FAI in selected adolescent athletes. Clin Orthop Relat Res 2012;470:261-9. |
|49.||Byrd JW, Jones KS. Arthroscopic management of femoroacetabular impingement in athletes. Am J Sports Med 2011;39 Suppl: 7S-13S. |
|50.||Lavigne M, Parvizi J, Beck M, Siebenrock KA, Ganz R, Leunig M. Anterior femoroacetabular impingement: Part I. Techniques of joint preserving surgery. Clin Orthop Relat Res 2004;418:61-6. |
|51.||Ganz R, Gill TJ, Gautier E, Ganz K, Krügel N, Berlemann U. Surgical dislocation of the adult hip a technique with full access to the femoral head and acetabulum without the risk of avascular necrosis. J Bone Joint Surg Br 2001;83:1119-24. |
|52.||Mardones RM, Gonzalez C, Chen Q, Zobitz M, Kaufman KR, Trousdale RT. Surgical treatment of femoroacetabular impingement: Evaluation of the effect of the size of the resection. J Bone Joint Surg Am 2005;87:273-9. |
|53.||Siebenrock KA, Schoeniger R, Ganz R. Anterior femoro-acetabular impingement due to acetabular retroversion. Treatment with periacetabular osteotomy. J Bone Joint Surg Am 2003;85-A:278-86. |
|54.||Alradwan H, Philippon MJ, Farrokhyar F, Chu R, Whelan D, Bhandari M, et al. Return to preinjury activity levels after surgical management of femoroacetabular impingement in athletes. Arthroscopy 2012;28:1567-76. |
|55.||Nho SJ, Magennis EM, Singh CK, Kelly BT. Outcomes after the arthroscopic treatment of femoroacetabular impingement in a mixed group of high-level athletes. Am J Sports Med 2011;39 Suppl:14S-9S. |
[Figure 1], [Figure 2], [Figure 3]