Femoroacetabular impingement (FAI) syndrome is a symptomatic, motion related clinical disorder caused by premature contact between the acetabulum and the femoral head or head-neck junction1 causing repetitive microtrauma, labral disruption, and degeneration of the femoroacetabular joint.
A triad of (1) symptoms, (2) clinical signs and (3) imaging findings might all be present to diagnose the FAI syndrome.1,2
The hip is susceptible to impingement at terminal range of motion3 but abnormal morphologies promote this premature contact. The most commonly described abnormal morphologies are: (1) abnormally shaped femoral head or head-neck junction, termed cam morphology, (2) excessive acetabular coverage of the femoral head, termed pincer morphology, or (3) both, co-existing cam and pincer morphologies.4,8
FAI is a syndrome. A syndrome is a recognizable complex of symptoms and physical findings which indicate a specific condition, but the underlying direct causes can differ. In the case of FAI, a number of risk factors have been identified, and it appears that they interact together to cause the specific constellation of symptoms of anterior groin pain. FAI has been proposed to be contributed to by activity related factors as well, which we will address below.
Epidemiology, risk factors and primary prevention
The incidence of FAI syndrome increased between 2000 to 2016 and is currently reported to be 54.4 per 100,000 person-years, with a high proportion of female compared to male patients. In this same time period, joint preserving operations such as hip arthroscopy, surgical hip dislocation, and anteverting periacetabular osteotomy, also increased.7 It is important also to recognize that radiographic signs of FAI are also seen in asymptomatic patients upon routine screening at a rate of 42.6-53%.9
Radiographic abnormalities associated with FAI have been noted in up to 35% of the general population, and up to 60.5% in patients who reported hip pain.7,8,10 Radiographic evidence of FAI was present in 36% of patients under the age 55 with hip replacement due to osteoarthritis (OA).11 Cam-type impingement is more typical in young active males, while pincer-type impingement is predominant in middle-aged athletic females.6,8,12 Isolated cam or pincer lesions present approximately 14% of the time, while approximately 86% are mixed lesions.4,8
Risk factors for FAI syndrome include the aforementioned etiologies but recent studies suggest that FAI is often related to participation in high impact sports during bone maturation or with activities that require a wide hip range of motion.13,14 Sports where FAI is commonly encountered involve kicking, cutting and sprinting, such as soccer, hockey, football, basketball and tennis.15 Sport-related cam deformities are most commonly seen in soccer and hockey in the male population, this may be due to the hip placed in vulnerable positions due to the unique cutting demands of the sport, this may lead to high physical stress and pathological contact between the proximal femoral physis and acetabulum during growth.15 It has been theorized that altering activity levels during adolescence could prevent cam morphologies, thereby eliminating this risk factor for OA, however there are no studies to support this theory.14
FAI syndrome caused by cam-type morphology leads to increased pressure at the acetabular margins with hip flexion and internal rotation.5,7,17 FAI syndrome caused by pincer-type morphology can result in acetabular cartilage and labrum damage.12,18,19
For pincer-related FAI, the predisposing intrinsic factors include protusio acetabuli, coxa profunda, acetabular retroversion, and a prominent acetabular rim. Pincer lesions can also be a consequence of pediatric hip disease including slipped capital femoral epiphysis, Legg-Calve-Perthes disease, and developmental hip dysplasia.
Regarding cam-related FAI, these again can be due to intrinsic factors, however, can also be post-surgical or post-traumatic in nature. These causes include prior femoral neck fracture with malunion, prior periacetabular or femoral osteotomy, femoral retrotorsion, and coxa vara.4,5,6,7
Clinical features and presentation over time
The majority of patients report an insidious, moderate to severe, aching or sharp pain. The most common location is the groin, followed by the lateral hip, thigh, buttock and lower back. Occasionally a specific trauma can be identified. Mechanical symptoms such as pop, snap, catch or locking and functional limitations such as limping during ambulation, limitation in walking distance, stair climbing and sitting tolerance have been described. The symptoms are exacerbated with activity and prolonged sitting and improve with rest and position changes.
Adequately treated patients usually improve and regain their usual activity level but untreated patients experience gradual deterioration. The long-term outlook for patients with FAI syndrome is still unknown.1
Associated conditions and complications
FAI is often found in association with labral tears, chondral injuries, and OA.20
Prospective cohort studies demonstrated association between cam morphologies and hip OA, but the same association has not been found in Pincer morphologies.14
Essentials of Assessment
A detailed history is necessary to suspect FAI syndrome. History of congenital malformations, pediatric hip pathology, femoral fractures, musculoskeletal disorders and systemic diseases should be explored. Participation in sports and recreational activities, including goals and expectations are important to develop a treatment plan that improves functionality.21
A comprehensive hip and groin examination is essential to diagnose FAI syndrome. Evaluation of the 5 components of the hip joint: (1) osseous, (2) capsulolabral, (3) musculotendinous, (4) neurovascular and (5) kinematic chain are important to develop an adequate differential diagnosis.1,21
A decrease in range of motion and muscle strength in hip adduction, flexion and internal rotation are the most described physical impairments.
The most common special tests to assess for FAI include the anterior impingement test known as FADDIR (sensitivity 80% and specificity 24%) and the posterior impingement test.21,22 The dynamic internal rotation (DIRI) and external rotation (DEXRIT) impingement tests (sensitivity 54-60 % and specificity 51-46%, respectively) and the FABER distance test (sensitivity 54%, specificity 38%) are also described in the literature.4,21,22
FAI syndrome limits activities involving hip flexion and internal rotation. Patients may report pain that affects their gait and mobility, especially squatting, rising from a seated position and walking up and down stairs.15 Abnormal movement pattern has also been described reflecting poor neuromuscular control during single leg standing or small knee bend motor control test. FAI should not interfere with self-care.
Radiographs are usually used for overall evaluation of the pelvis and hips, as well as exclusion of other causes of symptoms.23 Plain radiograph of the pelvis in anteroposterior view allows assessment of the acetabular morphology. Cross table, lateral or frog leg are needed to assess the femoral neck.3,24 A faux profile view is used to quantify acetabular over-coverage and to assess the posteroinferior hip joint. Radiographic angles used to assess FAI include the alpha angle, lateral center edge, offset edges, and cross-over sign. Cam morphology corresponds to an asphericity of the femoral head-neck junction and is usually assessed by measuring the alpha angle. Imaging signs of Pincer morphology include markers of increased acetabular coverage and of abnormal acetabular version.23
Magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRA) are useful to evaluate labral/chondral pathology. Computed tomography and MRI are better for characterizing abnormal joint morphologies.1
The sonographic examination as diagnostic technique for FAI syndrome still is of limited use.
Early predictions of outcomes
The available literature is insufficient to determine if patients with FAI syndrome have a greater risk of developing hip OA than patients with isolated cam morphologies, or to predict who will develop hip OA, chondral or labral damage. A recent study, however, suggested that there is an increased risk of hip OA of up to 10% in young patients with cam impingement morphology who were followed for at least 25 years.25
Negative predictors of return to high-level sport after surgery for FAI include presurgical chondral damage, mental health concerns in athletes, increased alpha angles, increased body mass index, duration greater than 2 years, and the presence of a limp.26
Social role and social support system
Taking into account that sports participation may be affected in patients with FAI syndrome, a support system should be considered for these patients. This system could be composed of the family members, therapist, treating physician, coach, or athletic trainer. It is also important to recognize the stressors created by increasing strenuous early athletics in the pediatric population and to increase awareness of the importance of healthy training at an early age to avoid development of FAI later in life.
Rehabilitation Management and Treatments
Available or current treatment guidelines
There is no definite treatment established for FAI syndrome. Treatment strategies include conservative care, physiotherapy-led rehabilitation, and surgery.1 Available literature has been unable to compare effectiveness of these strategies or to determine their effects. A multidisciplinary team is recommended to support the patient during informed decision-making process.1,27
Conservative care for FAI syndrome includes education, activity modifications to avoid hip impingement, oral analgesia, intra-articular steroid injection and watchful waiting. Injections with steroid and local anesthetic are typically employed for diagnostic, prognostic, and therapeutic purposes, as well as to provide relief while the hip pain takes its natural course.28 The published literature considers a conservative care trial as appropriate.28 Intra-articular steroid injection can be considered as conservative care, but this intervention is also a diagnostic instrument to confirm intra-articular hip pathology.1
The goals of physiotherapy-led rehabilitation are to reduce symptoms and physical impairments through improving range of motion, strength and restoring neuromuscular control.29 A staged approach of exercise-based programs focusing on the core hip musculature has been described in the literature.12,29 Almost half of available articles reviewing non-operative treatment of FAI support physiotherapy-led rehabilitation.2 The goals of rehabilitation program in the non-operative setting are to use joint mobilization, pain-free range of motion, and strengthening exercises to help restore the normal mobility of the hip joint.30
Physical therapy should also address pelvic tilt which has been shown to be significantly related to FAI. Increased anterior pelvic tilt may result loss of internal rotation and early occurrence of FAI.31 Anterior pelvic tilt maybe habitual in some patients or associated with poor spinopelvic biomechanics and lumbar mobility. Thus, reducing anterior pelvic tilt can be achieved through neuromuscular re-education. This, however, maybe challenging in patients with significant degenerative lumbar spine in which there might be limited room for improvement of lumbosacral motion.32 Another possible limiting factor to response to physical therapy is femoral version variation. Decreased femoral version is becoming increasingly recognized as contributing factor to the development of hip pain in patients with FAI and may explain poor response to treatment.33
Surgical management consists of open surgical dislocation with osteoplasty or arthroscopic techniques to correct the hip morphology and to repair the labral injury or chondral lesion if present.20 The available data is insufficient to determine benefits and safety due to the lack of randomized control trials. A recent systematic review found moderate-quality evidence that surgical treatment is not superior to conservative treatment for FAI syndrome in the short term, and there is low-quality evidence that it is not superior in the medium term.34
Pre-operative physical therapy should be individualized to best achieve positive post-operative outcomes. This can be accomplished through tailored assessment, advice, outcome measurements, education, exercises, and pain management interventions. The wide array of pre-operative pathologies, physical ability levels, and anatomy suggest that a single universal protocol may not be successful.30
Post-operative rehabilitation must take into account weight bearing and range of motion restriction and a step-wise progression to activity, which is the only universally accepted protocol. This, along with the lack of high-quality evidence due to aforementioned patient and study heterogeneity makes the agreement on evidence-based guidelines challenging.35 Despite this, post-surgical rehab should begin by focusing on segmental stability followed by more global muscular retraining, always functioning within the restrictions of the surgeon.30
At different disease stages
Early: The first line treatment for femoral acetabular syndrome is medical/rehabilitative.17 This includes activity modification, restriction of athletic activity, avoidance of hip motions that exacerbate symptoms, and NSAID medications. 3,17 The safety and efficacy of physical therapy warrant a trial before pursuing surgery. As such, physical therapy should be utilized, however, it is important to note that certain passive range of motion and stretching exercises may actually worsen symptoms, so therapy should be mainly focused on strengthening and patient education.3,7 The goal of treatment is to decrease the mechanical contact between the acetabulum and femoral neck.17
Middle: Intra-articular steroid injection is controversial due to cartilage toxicity from steroid use.36 However, imaging guided intraarticular steroid and local anesthetic injection can confirm intra-articular pathology and relieve symptoms if successful.6 Since femoral acetabular impingement occurs in an active population, activity modification and refraining from athletics can be difficult. Persistent symptoms require further physical therapy attempts. Intra-articular hyaluronic acid supplementation could potentially improve pain and function; however, this is only supported by low-quality evidence, and is not currently approved by the majority of insurance plans.37
Late: Surgical intervention can be considered if conservative treatments fail to improve symptoms. Surgical intervention typically consists of either open surgical dislocation with osteoplasty or arthroscopic techniques. Post-operatively, rehabilitation must take into account weight-bearing restrictions, range of motion restriction and a step-wise progression to activity. At a minimum, pain, loss of motion, muscle strength and proprioception around the hip should be addressed.29 Return to sport after surgical intervention varies greatly and depends on a number of factors. Expected timelines for return to sport are difficult to predict as no standard rehabilitation protocol has been published. In a recent meta-analysis return to sport after surgical intervention was between 3.1 and 14.5 months, with an average return of 7 months.38
Coordination of care
It is important to have clear and accurate communication with all members treating FAI syndrome. These include the patient, physical therapist, patient, treating physician, coach and trainer, if appropriate. If surgical options are explored, it is also important to communicate with the orthopedic surgeon for post-operative rehabilitation planning.
Patient & family education
Special emphasis should be placed on patient and primary care provider education since FAI is an uncommon condition.
Patients should be educated as part of the treatment plan, including avoiding exacerbating/impingement positions, home exercises, and return to play.
Few specific outcome measures for FAI have been developed, however there has been a continuous increase in the number of published studies regarding FAI syndrome with the majority evaluating arthroscopic surgery. The modified Harris Hip Score (mHHS) remains being the most commonly used.39
Ideally pain and function should be followed during treatment. Validated questionnaires for patients with hip or groin pain and for assessment of perceived quality of life and general health status, such as the international Hip Outcome Tool (iHOT), Hip and Groin Outcome Score (HAGOS) and Hip Outcome Score (HOS) are recommended for evaluation of patients with FAI syndrome.1
Regenerative medicine for symptomatic relief and to delay surgical management has been considered in the literature, but scientific data to support their use in FAI syndrome is insufficient.
There is insufficient literature addressing the treatment of FAI syndrome with orthobiologics. Low-quality evidence demonstrates improved pain and function with intra-articular hip hyaluronic acid.40 Otherwise, there is insufficient evidence to support the use of injection therapies for the treatment of FAI syndrome at this time.35,37,40
In one recent study, patients that failed conservative management for labral tears, including intra-articular steroid injection, were treated with leukocyte-rich platelet rich plasma using ultrasound guidance into the labrum. Although this was a small pilot study (n=8), it did show a statistically reduced pain level at two, four, and six weeks on the mHHS, with improved function.41
Translation into practice: practice “pearls”/changes in clinical practice behaviors and skills
Adequate recognition of the symptomatology, clinical signs and imaging findings for FAI syndrome is key in differentiating FAI syndrome from other pain syndromes. Delayed diagnosis may cause functional impairments, degenerative changes of the hip joint and leads to unnecessary imaging studies and interventions.
Some of the key clinical practice pearls are as follows:
- Males are more likely to present with cam morphology, Females are more likely to present with pincer morphology.
- Plain radiographs can be obtained to define cam and pincer deformity
- This hip morphology is frequent in asymptomatic individuals and presence of a cam or pincer morphology is not equal to FAI.
- Repetitive physical activity during growth with poor spine/pelvic biomechanics may cause this anatomical morphology.
- Early recognition is important as addressing underlying biomechanical or anatomical abnormalities can help prevent worsening of cam or pincer anatomy.
- Delayed treatment may lead to early osteoarthritis in a proportion of patients.
Cutting Edge/ Emerging and Unique Concepts and Practice
It is necessary to know the proper nomenclature to diagnose FAI syndrome. The triad of symptoms, clinical signs and imaging findings must be fulfilled. Understanding the pathophysiology of hip impingement could help in diagnosing FAI and screening people at risk. Future research is necessary to help guide clinical practice and better recognize the condition.
Gaps in the Evidence-Based Knowledge
Additional investigation to understand the following key factors is needed:
- Morphologic development.
- Effect of sporting activities in childhood on FAI syndrome.
- Possible triggers for FAI development.
- Utility of diagnostic criteria in FAI.
- Long-term natural history of the disorder.
Prospective randomized controlled trials are needed to assess whether physical therapy or surgery are superior in long term outcomes.
- Griffin DR, Dickenson EJ, O’Donnell JM, et al. Infographic. The Warwick Agreement on femoroacetabular impingement syndrome (FAI syndrome): an international consensus statement. Br J Sports Med 2016;50:1169–76.
- Parvizi J, Leunig M, Ganz R. Femoroacetabular impingement. JAAOS. 2007;15:561-570.
- Mauro CSV, James E, Kelly BT. Femoroacetabular impingement surgical techniques. Operative Techniques in Othropaedics. 2010;20:223-230.
- Kaplan KM, Shah M, Youm T. Femoroacetabular impingement: diagnosis and treatment. Bulletin of the NYU Hosp for Joint Diseases. 2010;68:70-75.
- Martin DE, Tashman S. The biomechanics of femoroacetabular impingement. Operative Techniques in Orthopaedics. 2010;20(4):248â€“254.
- Field RE, Rajakulendran K. The labro-acetabular complex. Bone Jt. Surg. (Am). 2011;93 Suppl 2:22-27.
- Tannast M, Siebenrock KA, Anderson SE. Femoroacetabular impingement: radiographic diagnosis—what the radiologist should know. AJR Am J Roentgenol 2007;188:1540–52.
- Hale RF, Melugin HP, Zhou J, et al. Incidence of Femoroacetabular Impingement and Surgical Management Trends Over Time. The American Journal of Sports Medicine. 2021;49(1):35-41.
- Thier S, Gerisch D, Weiss C, Fickert S, Brunner A. Prevalence of Cam and Pincer Deformities in the X-Rays of Asymptomatic Individuals. Biomed Res Int. 2017;2017:8562329.
- Zhou, J, Melugin, HP, Hale, RF, et al. The prevalence of radiographic findings of structural hip deformities for femoroacetabular impingement in patients with hip pain. Am J Sports Med. 2020;48(3):647-653.
- FAI, S, Khanduja V. Current concepts in the diagnosis and management of femoroacetabular impingement. International Orthopaedics. 2011;35:1427-1435.
- Macfarlane RJ, Haddad F. The diagnosis and management of femoro-acetabular impingement. Annals of RCS England. 2010;92:363-367.
- Nepple JJ, Vigdorchik JM, Clohisy JC. What is the association between sports participation and the development of proximal femoral cam deformity? A systematic review and meta-analysis. Am. J. Sports Med. 2015; 43:2833–40.
- Philippon MJ, Maxwell R, Johnston T, Schenker M, Briggs K. Clinical presentation of femoroacetabular impingement. Knee Surgery, Sports Traumatology, Arthroscopy. 2007;15:1041-1047.
- Agricola R, Waarsing JH, Arden NK, et al. Cam impingement of the hip: a risk factor for hip osteoarthritis. Nat Rev Rheumatol 2013;9:630–4.
- Knapik DM, Gaudiani MA, Camilleri BE, et al. Reported Prevalence of Radiographic Cam Deformity Based on Sport: A Systematic Review of the Current Literature. Orthop J Sports Med. 2019 Mar 19;7(3):2325967119830873.
- Emara K, Samir W, Motasem el H, Ghafar K. Conservative treatment for mild femoroacetabular impingement. J Orthop Surg (Hong Kong) 2011;19:41-45.
- Ejnisman L, Philippon M, Lertwanich P. Femoroacetabular impingement: the femoral side. Clinics in Sports Medicine. 2011;30:369-377.
- 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. Bone Jt. Surg. (Brit). 2005;87:1012-1018.
- 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.
- Manaster BJ, Zakel S. Imaging of femoral acetabular impingement syndrome. Clinics in Sports Medicine. 2006;25:635-657.
- Pålsson A, Kostogiannis I, Ageberg E. Combining results from hip impingement and range of motion tests can increase diagnostic accuracy in patients with FAI syndrome. Knee Surg Sports Traumatol Arthrosc. 2020;28(10):3382-3392. doi:10.1007/s00167-020-06005-5.
- Mascarenhas VV, Castro MO, Rego PA, et al. The Lisbon Agreement on Femoroacetabular Impingement Imaging-part 1: overview. Eur Radiol. 2020 Oct;30(10):5281-5297.
- Martin HD, Palmer IJ. History and physical examination of the hip: the basics. Curr Rev Musculoskelet Med 2013;6:219–25.
- Hoch A, Schenk P, Jentzsch T, Rahm S, Zingg PO. FAI morphology increases the risk for osteoarthritis in young people with a minimum follow-up of 25 years. Arch Orthop Trauma Surg. 2021 Jul;141(7):1175-1181.
- Stone AV, Beck EC, Malloy P, et al. Preoperative predictors of achieving clinically significant athletic functional status after hip arthroscopy for femoroacetabular impingement at minimum 2-year follow-up. Art Ther. 2019; 35:3049–56.)
- Wall PD, Brown JS, Parsons N, et al. Surgery for treating hip impingement (femoroacetabular impingement). The Cochrane Library, 2014.
- Kuroda Y., Rai A., Matsumoto K., Khanduja V. (2021) Current Concepts in the Management of Femoroacetabular Impingement. In: Drescher W.R., Koo KH., Windsor R.E. (eds) Advances in Specialist Hip Surgery. Springer, Cham.
- Wall PD, Fernandez M, Griffin DR, et al. Nonoperative treatment for femoroacetabular impingement: a systematic review of the literature. PM R 2013;5:418–26.
- Takla A, O’Donnell J, Voight M, et al. The 2019 International Society of Hip Preservation (ISHA) physiotherapy agreement on assessment and treatment of femoroacetabular impingement syndrome (FAIS): an international consensus statement. J Hip Preserv Surg. 2021 Mar 19;7(4):631-642. Erratum in: J Hip Preserv Surg. 2021 May 31;7(4):643.
- McCrum, CL. Editorial Commentary: Lumbosacral Anatomy and Mechanics Influence Femoroacetabular Impingement Syndrome and Surgical Outcomes: The Hip Bone Is Connected to the Back Bone. Arthroscopy. 2021 Jan;37(1):156-158.
- Fader RR, Tao MA, Gaudiani MA, et al. The role of lumbar lordosis and pelvic sagittal balance in femoroacetabular impingement. Bone Joint J. 2018 Oct;100-B(10):1275-1279.
- Lerch TD, Boschung A, Todorski IAS, et al. Femoroacetabular Impingement Patients With Decreased Femoral Version Have Different Impingement Locations and Intra- and Extraarticular Anterior Subspine FAI on 3D-CT–Based Impingement Simulation: Implications for Hip Arthroscopy. The American Journal of Sports Medicine. 2019;47(13):3120-3132.
- Bastos RM, de Carvalho Júnior JG, da Silva SAM, et al. Surgery is no more effective than conservative treatment for Femoroacetabular impingement syndrome: Systematic review and meta-analysis of randomized controlled trials. Clin Rehabil. 2021 Mar;35(3):332-341.
- Grzybowski JS, Malloy P, Stegemann C, Bush-Joseph C, Harris JD, Nho SJ. Rehabilitation Following Hip Arthroscopy – A Systematic Review. Front Surg. 2015 May 26;2:21.
- Kompel AJ, Roemer FW, Murakami AM, et al. Intra-articular Corticosteroid Injections in the Hip and Knee: Perhaps Not as Safe as We Thought? Radiology. 2019 Dec;293(3):656-663.
- Trigg SD, Schroeder JD, Hulsopple C. Femoroacetabular Impingement Syndrome. Curr Sports Med Rep. 2020 Sep;19(9):360-366.
- Parvaresh KC, Wichman D, Rasio J, Nho SJ. Return to Sport After Femoroacetabular Impingement Surgery and Sport-Specific Considerations: a Comprehensive Review. Curr Rev Musculoskelet Med. 2020;13(3):213-219
- Lindman et al. Evaluation of outcome reporting trends for femoroacetabular impingement syndrome- a systematic review J EXP ORTOP (2021) 8:33
- Abate M, Scuccimarra T, Vanni D, et al. Femoroacetabular impingement: is hyaluronic acid effective? Knee Surg. Sports Traumatol. Arthrosc. 2014; 22:889–92.
- De Luigi AJ, Blatz D, Karam C, et al. Use of Platelet-Rich Plasma for the Treatment of Acetabular Labral Tear of the Hip: A Pilot Study. Am J Phys Med Rehabil. 2019 Nov;98(11):1010-1017.
Original Version of the Topic
Mark L. Miedema, MD, Ryan O. Stephenson, DO. Femoral acetabular syndrome. 12/28/2012.
Previous Revision(s) of the Topic
Fernando Sepulveda, MD, Belmarie Rodriguez, DO. Femoral acetabular syndrome. 7/31/2017.
Mohammed Emam, MD
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Benjamin Miller, DO
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