Femoroacetabular Impingement Syndrome (FAIS) was described as early as 19361 and has been drastically increasing in popularity over the past two decades2. As this condition has become more respected amongst the medical community, the number of patients identified with FAIS was significantly increased3. With this increased recognition, there has also been a markedly rising number of hip arthroscopy surgeries being performed. Literature has demonstrated an 18-fold increase from 1999 to 20094 and a 25-fold increase between 2006 and 20135. With regards to indication for surgery, Peters and colleagues performed a scoping review to identify what factors surgeons use to make this decision6. This study found the below criteria used by surgeons for surgical intervention in the literature…

Criteria Studies reporting criteria
Alpha angle > 60°, CE angle > 40°, or presence of acetabular retroversion 72 (67%)
No clinical evidence of inflammatory arthritis changes 69 (64%)
Diagnostric injection or MRI indicating presence of intra-articular pathology or labral damage 66 (61%)
Acetabular retroversion (Crossover sign) 62 (57%)
Failed non-surgical treatment 47 (44%)
Anterior Impingement Test 39 (36%)
Positive FADDIR or Anterior Impingement Test 38 (35%)
Hip pain > 3 months 26 (24%)
Failed formal Physical Therapy-led program 19 (18%)
Lateral centre edge angle > 20° 18 (17%)
Flexion and IR decreased 12 (11%)
CE angle > 40° 8 (7%)
IR decreased 7 (6%)
Hip IR < 20° in 90° hip flexion 6 (6%)
Alpha angle > 60° 2 (2%)

As you can see from the data obtained from their study, the vast majority of the information used to determine surgery in this patient population is related to radiological findings and extent of morphological changes. Most surprisingly, failure of conservative management and especially failure of formal physical therapy was not included in the vast majority of published studies.

With this information, it appears we may be getting ahead of ourselves…

What is FAIS?

The femoroacetabular joint refers to the articulation between the proximal femur and the acetabulum of the pelvis. In FAIS, altered boney morphology of the femoral neck (Cam Morphology) or of the Acetabular rim (Pincer Morphology) leads to premature contact of the two osseous structures. Based on the orientation of the joint, this premature contact typically occurs during hip flexion and/or internal rotation7,8. This abnormal contact has also been blamed for additional pathological conditions such as acetabular labral tears, chondral lesions, and osteoarthritis.

Altered Morphology Does Not ALWAYS Matter

As with most morphological abnormalities, these factors do not always lead to pain and are fairly common in the general and athletic populations. A systematic review conducted by Frank and colleagues9 of 2,114 asymptomatic hips found a very high prevalence of altered morphology. They found that 67% of subjects had radiologically confirmed pincer morphology, whereas 37-55% of athletes and 23% of the general population demonstrated cam morphology. To further evaluate the association of morphology in symptomatic patients, athletes, and asymptomatic individuals, Mascarenhas and colleagues performed a systematic review of 60 studies10. This study found that cam morphology was significantly more common in athletes versus asymptomatic subjects but not compared to symptomatic patients, significantly more common in symptomatic versus asymptomatic cases. Whereas, no significant differences were found between pincer morphology prevalence when comparing athletes to symptomatic patients. However, mixed-type FAI was significantly more common in athletes versus asymptomatic subjects and in asymptomatic versus symptomatic subjects.

Additionally, when looking at those pathologies that are said to be caused by altered morphology, the prevalence is also very high among asymptomatic individuals. The presence of acetabular labral tears and chondral lesions were found in asymptomatic individuals with a prevalence of 44-69% and 20-24%, respectively11,12.

In fact, the level of morphological abnormality often does not coincide with severity of symptoms. A study of 616 adults with hip pain found no association between radiographic signs of FAIS or a positive Flexion Adduction Internal Rotation (FADDIR) test with degree of hip pain13. More recently, Jacobs and colleagues investigated the relationship of preoperative symptom severity and magnitude of boney morphology14. This study of 64 patients prior to arthroscopic hip surgery found no correlation between symptom severity and degree of acetabular labral tear or femoroacetabular boney morphology. There was however a significant influence of depressive symptoms (as determined by the Mental Component Score) and severity of hip-related symptoms, which gives further credence to the link between psychosocial factors and symptom severity irregardless of morphological or pathological changes.

When Does Altered Morphology Matter?

Previous diagnostic criteria for femoroacetabular impingement relied heavily upon the level of morphological changes. Ganz et al. and Sankar et al. determined that the diagnosis of FAIS was appropriate if (1) there was abnormal morphology of the femur and/or acetabulum, (2) if there was abnormal contact between these two structures, (3) if the patient participated in activities that resulted in supraphysiologic motion that results in such abnormal contact and collision, (4) repetitive motion resulting in the continuous insult, (5) presence of soft-tissue damage15,16. Once again, these criteria are not sufficient to accurately diagnose a patient with FAIS because there is no weight put on clinical signs or symptoms.

More recently, Griffin and colleagues attempted to better define appropriate terminology, diagnosis, treatment, and prognosis for FAIS17. At this consensus meeting, they agreed that accurate diagnosis depended upon clinical signs, symptoms, and diagnostic criteria. They therefore defined FAIS as:

“Femoroacetabular impingement syndrome is a motion-related clinical disorder of the hip with a triad of symptoms, clinical signs and imaging findings. It represents symptomatic premature contact between the proximal femur and the acetabulum.”

— 2016 Warwick Agreement on Femoroacetabular Impingement Syndrome (Griffin et al., 2016)

The key differentiating factors between this and previous descriptions are the additional criteria of ‘symptomatic’ and the emphasis on symptoms and clinical signs in addition to diagnostic criteria. This definition was met with a 9.8/10 agreement and allows for the entire patient presentation to be taken into consideration, not just the underlying morphological changes. To expand upon this agreement, Reiman and colleagues performed an international and multi-disciplinary Delphi survey to identify pertinent aspects of the subjective history, clinical examination, and radiological examination18. This survey found agreement on the following aspects in patients presenting with FAIS…

Subjective Examination
Descriptor Consensus Support
Deep anterior groin pain, especially worse with activities such as prolonged sitting, squatting, car transfers, and dressing 98.4%
Pain with hip flexion or rotational activities 96.7%
Pinching or aching in the hip/groin associated with activitity 96.7%
Deep groin pain with twisting or turning or pivoting 95.1%
Intermittent sharp deep groin pain 95.1%

Subjective self report should be the cornerstone of the examination of any injury and FAIS is no exception. Patients often present with reports of deep anterior groin pain that is exacerbated with activities involving deep flexion, rotational activities, and squatting. The subjective attributes agreed upon for individuals presenting with FAIS closely coincides with a diagnostic study performed by Clohisy and colleagues19 who looked at 51 patients with confirmed, symptomatic FAIS. This study showed that 88% of patients had pain localized to the groin region and aggravating factors included general activity-related (71%), running (69%), sitting (65%), and pivoting (63%).

Physical Examination
Descriptor Consensus Support
Limited IR with hip flexion with pain 96.7%
Limited IR with pain 91.8%
Limited and painful hip flexion 83.6%
Special Testing
Descriptor Consensus Support
Positive FADDIR/Anterior Impingement Test 91.8%
No special tests are diagnostic of FAIS; Only valuable as screening tool 82.0%

A systematic review of 16 studies related to physical impairments in individuals with FAIS demonstrates similar findings as the Delphi survey. This study agreed that the available literature currently demonstrates that individuals with FAIS have decreased hip ROM into impingement (flexion/internal rotation in 90° flexion), which is often limited by pain20.

When looking at the included criteria for special testing in FAIS, the two agreed upon findings seem contradictory. On one end, a positive FADDIR test is beneficial, however on the other end, it is also noted that no special tests are diagnostic for FAIS. According to the literature in reference to special testing for FAIS, there has been no test that can be seen as confirmatory of the diagnosis due to very low positive likelihood ratios and specificity values21-23. That being said, the use of the FADDIR test does offer benefit due to the very high sensitivity and low negative likelihood ratios reported in the literature (Sn= 0.94-0.99, -LR= 0.14-0.45)22, however its capacity as a screening method has recently come into question24. A cross-sectional study of 74 ice hockey players (average age of 16 years old) contradicted the current literature with regards to the FADDIR test’s screening capacity. This unique study questions its capacity to screen for pure cam, pincer, or combined morphology (Sn= 0.41, -LR= 1.24) and pure cam or combined morphology (Sn= 0.60, -LR= 0.78). As we continue to evaluate the capacity to screen for FAIS, there will be more consensus, but as of now the FADDIR can be used as a screening tool with caution and with taking into consideration the patient’s additional clinical signs and subjective complaints.

Understanding that FAIS is far more than morphological changes to the proximal femur or acetabulum will allow us as clinicians and researchers to move forward in the evaluation, treatment, and return to sport of this patient population. By evaluating the ability of conservative management to return athletes to their prior level of function, this drastic spike in surgical procedures may start to stabilize. Boney morphology is a well-known contributor to FAIS, but it only tells one portion of the story, we need to dig deeper in order to successfully manage this patient population.


1. Smith-Petersen M. Treatment of malum coxae senilis, old slipped upper femoral epiphysis, intrapelvic protrusion of the acetabulum, and coxa plana by means of acetabuloplasty. J Bone Joint Surg Am. 1936; 18: 869–80.
2. Khan M, Oduwole KO, Razdan P, et al. Sources and quality of literature addressing femoroacetabular impingement: a scoping review 2011-2015. Curr Rev Musculoskelet Med. 2016. doi:10.1007/s12178-016-9364-5.
3. Montgomery SR, Ngo SS, Hobson T, et al. Trends and demographics in hip arthroscopy in the United States. Arthroscopy. 2013; 29: 661–5.
4. Colvin AC, Harrast J, Harner C. Trends in hip arthroscopy. J Bone Joint Surg Am. 2012; 94: e23. dos:10.2106/JBJS.J.01886
5. Cvetanovich GL, Chalmers PN, Levy DM, et al. Hip arthroscopy surgical volume trends and 30-day postoperative complications. Arthroscopy. 2016; 32: 1286–92.
6. Peters S, Laing A, Emerson C, et al. Surgical criteria for femoroacetabular impingement syndrome: a scoping review. British Journal of Sports Medicine. February 2017. doi:10.1136/bjsports-2016-096936.
7. Fernquest S, Arnold C, Palmer A, et al. Osseous impingement occurs early in flexion in cam-type femoroacetabular impingement: a 4D CT model. The Bone & Joint Journal. 2017;99-B(4 Supple B):41-48. doi:10.1302/0301-620X.99B4.BJJ-2016-1274.R1.
8. Kobayashi N, Inaba Y, Kubota S, et al. The Distribution of Impingement Region in Cam-Type Femoroacetabular Impingement and Borderline Dysplasia of the Hip With or Without Cam Deformity: A Computer Simulation Study. Arthroscopy. November 2016. doi:10.1016/j.arthro.2016.08.018.
9. Frank JM, et al. Prevalence of Femoroacetabular Impingement Imaging Findings in Asymptomatic Volunteers: A Systematic Review. Arthroscopy. 2015 Jun;31(6):1199-204. doi: 10.1016/j.arthro.2014.11.042.
10. Mascarenhas VV, Rego P, Dantas P, et al. Imaging prevalence of femoroacetabular impingement in symptomatic patients, athletes, and asymptomatic individuals: A systematic review. European Journal of Radiology. 2016;85(1):73-95. doi:10.1016/j.ejrad.2015.10.016.
11. Register B, et al. Prevalence of abnormal hip findings in asymptomatic participants: a prospective, blinded study. Am J Sports Med. 2012 Dec;40(12):2720-4. doi: 10.1177/0363546512462124.
12. Tresch F, Dietrich TJ, Pfirrmann CWA, Sutter R. Hip MRI: Prevalence of articular cartilage defects and labral tears in asymptomatic volunteers. A comparison with a matched population of patients with femoroacetabular impingement. J Magn Reson Imaging. December 2016:1-12. doi:10.1002/jmri.25565.
13. Yamauchi R, Inoue R, Chiba D, et al. Association of clinical and radiographic signs of femoroacetabular impingement in the general population. J Orthop Sci. November 2016. doi:10.1016/j.jos.2016.09.014.
14. Jacobs CA, Burnham JM, Jochimsen KN, Molina D, Hamilton DA, Duncan ST. Preoperative Symptoms in Femoroacetabular Impingement Patients Are More Related to Mental Health Scores Than the Severity of Labral Tear or Magnitude of Bony Deformity. The Journal of Arthroplasty. July 2017. doi:10.1016/j.arth.2017.06.053.
15. Ganz R, Parvizi J, Beck M, et al. Femoroacetabular impingement: a cause for osteoarthritis of the hip. Clin Orthop Relat Res 2003; 417: 112–20.
16. Sankar WN, Nevitt M, Parvizi J, et al. Femoroacetabular impingement: defining the condition and its role in the pathophysiology of osteoarthritis. J Am Acad Ortho Surg. 2013; 21(Suppl 1) :S7–S15.
17. Griffin DR, Dickenson EJ, O’Donnell J, et al. The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome): an international consensus statement. British Journal of Sports Medicine. 2016; 50(19): 1169-1176. doi:10.1136/bjsports-2016-096743.
18. Reiman MP, Thorborg K, Covington K, Cook CE, Holmich P. Important clinical descriptors to include in the examination and assessment of patients with femoroacetabular impingement syndrome: an international and multi-disciplinary Delphi survey. Knee Surg Sports Traumatol Arthrosc. 2017;22(4):806. doi:10.1007/s00167-017-4484-z.
19. Clohisy JC, Knaus ER, Hunt DM, Lesher JM, Harris-Hayes M, Prather H. Clinical Presentation of Patients with Symptomatic Anterior Hip Impingement. Clinical Orthopaedics and Related Research. 2009;467(3):638-644. doi:10.1007/s11999-008-0680-y.
20. Diamond LE, Dobson FL, Bennell KL, Wrigley TV, Hodges PW, Hinman RS. Physical impairments and activity limitations in people with femoroacetabular impingement: a systematic review. British Journal of Sports Medicine. 2015;49(4):230-242. doi:10.1136/bjsports-2013-093340.
21. Pacheco-Carrillo A, Medina-Porqueres I. Physical examination tests for the diagnosis of femoroacetabular impingement. A systematic review. Phys Ther Sport. 2016;21:87-93. doi:10.1016/j.ptsp.2016.01.002.
22. Reiman MP, Goode AP, Cook CE, Holmich P, Thorborg K. Diagnostic accuracy of clinical tests for the diagnosis of hip femoroacetabular impingement/labral tear: a systematic review with meta-analysis. British Journal of Sports Medicine. 2015;49(12):811-811. doi:10.1136/bjsports-2014-094302.
23. Reiman MP, Goode AP, Hegedus EJ, Cook CE, Wright AA. Diagnostic accuracy of clinical tests of the hip: a systematic review with meta-analysis. British Journal of Sports Medicine. 2013;47(14):893-902. doi:10.1136/bjsports-2012-091035.
24. Casartelli NC, Brunner R, Maffiuletti NA, et al. The FADIR test accuracy for screening cam and pincer morphology in youth ice hockey players. J Sci Med Sport. June 2017. doi:10.1016/j.jsams.2017.06.011.

About the Author John Snyder, PT, DPT, OCS, CSCS

I am a Physical Therapist, a Board Certified Orthopaedic Specialist, a Strength & Conditioning Specialist, an Educator, and a Research Junkie. My goal is to provide resources for orthopedic and sports medicine clinicians to keep up to date with the current literature and allow them to translate it to their practice.

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