Femoroacetabular Impingement Syndrome

Disease/Disorder

Definition

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 junction causing repetitive microtrauma, labral disruption, and degeneration of the femoroacetabular joint.

A triad of (1) symptoms, (2) clinical signs, and (3) imaging findings must be present to diagnose the FAI syndrome.¹

Etiology

The hip is susceptible to impingement at terminal range of motion,² but abnormal morphologies promote this premature contact. The most commonly described abnormal morphologies are: (1) abnormally shaped femoral head or head-neck junction where the femoral head has a non-spherical shape, termed cam morphology, (2) excessive acetabular coverage of the femoral head, termed pincer morphology, or (3) both, co-existing cam and pincer morphologies.^3,4

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 syndrome, 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 syndrome 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 is estimated to be 54.4 per 100,000 person-years, affecting a higher proportion of female compared to male patients (about 2:1, respectively).⁴ However, in a more elite cohort of NCAA Division 1 athletes, the incidence of FAI syndrome was 3.0% over a 3 year period, with no significant differences between males and females.⁵  Radiographic findings of FAI syndrome  (cam, pincer, mixed-deformities) are also seen in 31-53% of asymptomatic patients^6–8 and up to 60.5% in patients who reported hip pain.⁹ Radiographic evidence of FAI was present in 36% of patients under the age 55 with hip replacement due to osteoarthritis (OA).¹⁰ Cam-type impingement is more typical in young active males, while pincer-type impingement is predominant in middle-aged athletic females.^4,11,12 Isolated cam or pincer lesions present approximately 14% of the time, while approximately 86% are mixed lesions.^3,6 In those presenting with unilateral FAI syndrome, the rate of contralateral progression to symptomatic FAI ranges from 32.4% to 81%, with increased alpha angle and younger age being identified risk factors.¹³

FAI syndrome is often related to participation in high impact sports during bone maturation or with activities that require a wide hip range of motion,^14,15 with sporting exposure resulting in a dose-dependent increase in risk of cam deformities in males during adolescence.¹⁶ Sports where FAI is commonly encountered involve kicking, cutting and sprinting, such as soccer, hockey, football, basketball and tennis.¹⁷ Sport-related cam deformities are most commonly seen in soccer and hockey in the male population, which 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.¹⁷ 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.¹⁵

Patho-anatomy/physiology

FAI syndrome caused by cam-type morphology leads to increased pressure at the acetabular margins with hip flexion and internal rotation.^18–20 FAI syndrome caused by pincer-type morphology can result in acetabular cartilage and labrum damage.^12,21,22

For pincer-related FAI, the predisposing intrinsic factors include protrusio 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, this can be due to intrinsic factors; however, it 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 retroversion, and coxa vara.^3,11,18,19

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 syndrome is often found in association with labral tears, chondral injuries, and OA.²³

Prospective cohort studies demonstrated association between cam morphologies and hip OA, but the same association has not been found in Pincer morphologies.¹⁵

Essentials of Assessment

History

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.²⁴

Physical examination

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.^1,24

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 syndrome include the anterior impingement test (AIMT) and Flexion/Adduction/Internal Rotation (FADIR) test (sensitivity 80% and specificity 24-26%). The dynamic internal rotation test (DIRIT), dynamic external rotation impingement test (DEXRIT), and the Flexion/Abduction/External Rotation (FABER) test are also described in the literature (sensitivity 54%-60%, specificity 38%-51%).^3,24,25

Functional assessment

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.¹⁷ Abnormal movement pattern has also been described reflecting poor neuromuscular control during single leg standing or small knee bend motor control test. FAI syndrome usually does not interfere with self-care.

Imaging

Radiographs of the hip and pelvis are an essential part of the initial evaluation of FAI syndrome and the exclusion of other causes of symptoms.²⁶ Plain radiographs of the hip and pelvis in anteroposterior (AP) view allow assessment of the acetabular morphology, while lateral views including cross-table, frog leg, and Dunn 45°/90° are used to evaluate asphericity of the femoral head-neck junction.^26,27 The Dunn 45° view is most widely used lateral view in FAI screening due to its ability to visualize the anterosuperior aspect of head-neck junction, the most common site of cam-deformity.²⁷ 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, femoral head-neck offset, and cross-over sign (Table 1). Imaging signs of Pincer morphology include markers of increased acetabular coverage and of abnormal acetabular retroversion are also included in Table 1.²⁶

Table 1: Common radiographic findings used in the diagnosis of FAI syndrome^26-28 MRI – magnetic resonance imaging, CT – computerized tomography, AP – anteroposterior.

Magnetic resonance imaging (MRI) and magnetic resonance arthrography (MRA) are useful to evaluate labral/chondral pathology. Computed tomography (CT) 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 symptomatic hip OA than patients with isolated cam morphologies, or to predict who will develop symptomatic 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.²⁹

Negative predictors of outcomes and 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, the presence of a limp, and use of hip corticosteroid injections.^30–32

Positive predictors of meeting minimally clinically important difference (MCID) or patient acceptable symptom state (PASS) following arthroscopic FAI surgery include younger age and normal joint space, while lower Hip Outcome Score (HOS) were more likely to reach MCID versus higher HOS were more likely to achieve PASS.³³

Social role and social support system

Taking into account that ability to be active and participate in sports may be affected in patients with FAI syndrome, a support system should be considered for these patients. This system could be composed of 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 combined with physiotherapy-led rehabilitation versus surgery.¹ Improvement in pain and function can be obtained through both conservative and surgical management, however, more recent evidence suggests possible surgical superiority in short and medium-term outcomes.^34–37 Trial of conservative management is reasonable, particularly in athletes who wish to avoid loss of time from sport.⁵ Ultimately, an individualized approach is warranted. A multidisciplinary team is recommended to support the patient during informed decision-making process.¹

Conservative care for FAI syndrome includes education, activity modifications to avoid hip impingement, oral analgesia, intra-articular steroid injection, watchful waiting, and physical therapy. 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.³⁸ However, a recent systematic review suggests its diagnostic utility in FAI syndrome is not well supported, citing heterogeneity, bias, and mixed conclusions from the limited number of studies available.³⁹

The goals of physiotherapy-led rehabilitation are to reduce symptoms and physical impairments through improving range of motion, strength, and restoring neuromuscular control. Non-operative treatment protocols for FAI syndrome have been established such as personalized hip therapy (PHT), with evidence supporting supervised, core-focused, and active strengthening physical therapy protocols.^40,41 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 and function of the hip joint.⁴²

Physical therapy should also address pelvic tilt which has been shown to be significantly related to FAI. Increased anterior pelvic tilt may result in loss of internal rotation and early occurrence of FAI.⁴³ Anterior pelvic tilt may be 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, may be challenging in patients with degenerative lumbar spine pathology in which there might be limited room for improvement of lumbosacral motion.⁴⁴ 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.⁴⁵

Surgical management consists of both open and arthroscopic techniques.  Open techniques include surgical hip dislocations, periacetabular osteotomy, and femoral derotation osteotomy,⁴⁶ often performed in the setting of concomitant hip dysplasia and pincer morphology.  Arthroscopic techniques offer a minimally invasive approach to correct the cam hip morphology and to repair a labral injury or chondral lesion if present.  Arthroscopy offer faster recovery, return to sport, and fewer complications compared to open techniques.^28,46 Prior systematic review found moderate-quality evidence that surgical treatment is not superior to conservative treatment for FAI syndrome in the short term and low-quality evidence that it is not superior in the medium term.⁴⁷ However, a more recent systematic review and meta-analysis with additional RCTs suggests greater functional outcomes at 6 months and 12 months following arthroscopic treatment compared to conservative treatment.³⁵ Arthroscopy is most beneficial when performed early in patients with Tönnis grade of 1 or less, and proper labral repair and capsular closure are key to successful outcomes. Delays of surgical intervention are associated with poorer outcomes and increased risk of OA progression.⁴⁸

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.⁴²

Post-operative rehabilitation must take into account the specific surgical procedure performed, weight bearing and range of motion restrictions, and the resulting step-wise progression to activity. Though no robust literature exists supporting an ideal post-operative rehabilitation program, various therapy protocols have been described and usually align with non-operative rehabilitation goals including core-stabilization, neuromotor control and strengthening, and improved range of motion. Typically divided in into 4 to 5 phases, post-operative rehabilitation timelines can range from 12-28 weeks.^42,49  Advancement through each phase will vary depending on the individual’s specific surgical intervention, tissue healing, tolerance of exercises, range of motion goals, and strength progression. Future research is needed to understand the impact of various rehabilitation protocols on pain and functional outcomes.

At different disease stages

Disease stages in FAI syndrome are not well-defined. Key factors such as patient age, function, goals, duration and severity of disease, and labral and cartilage integrity all contribute to treatment management decisions and the timing of those interventions.²⁸

As previously discussed, both conservative and surgical management can result in improved outcomes, with recent data leaning towards surgical superiority.^34–37 Despite this, conservative care offers a minimal risk and low-cost intervention compared to surgery and is often pursued initially.^5,41

In this early period, conservative care includes activity modification, NSAIDs, and physical therapy focused on core and hip strength, ROM, posture, and neuromotor control. This approach also offers the benefit of little to no missed time from sport.⁵

Intra-articular hip steroids injections can be considered if symptoms persist despite other conservative management (some suggesting at least 10 weeks),⁵ but this remains controversial due to concern for cartilage toxicity, OA progression, and osteonecrosis.⁵⁰ Additionally, hip corticosteroid injections have also been indicated to negatively affect outcomes after hip arthroplasty.³² Other intra-articular injections such as hyaluronic acid and PRP may improve pain and function in FAI syndrome. However, the literature is sparse, and overall evidence quality is low.⁵¹

Conversion to surgical management has been reported up to 50-70% following initial conservative care.^5,52  Indicators for surgery in FAI are not standardized but often include persistent symptoms despite conversative care (duration of symptoms ranging from <3 months to >1 year), limited ROM, positive exam findings, and radiographic evidence of impingement, and labral tearing.^31,46,53,54 Return to sport after surgical intervention varies greatly and depends on a number of factors, including surgical technique (open versus arthroscopic, labral repair or microfracture versus labral debridement), weight-bearing restrictions, rehab protocol, and tolerance of post-operative therapy.^46,49 A meta-analysis evaluating return to sport after surgical intervention revealed a range of 3.1 to 14.5 months, with an average return of 7 months.⁵⁵

Symptom duration of greater than 2 years is associated with worse outcomes and higher rates of reoperation following arthroscopic surgery.⁵⁶ Operative interventions directed at FAI syndrome should be avoided in arthritic hips (joint space ≤2 mm), advanced age (>45 years old), and large acetabular chondral defects. In these scenarios, total hip arthroplasty is a reasonable alternative.⁴⁶

Coordination of care

It is important to have clear and accurate communication with all members treating FAI syndrome. These include the patient and family, physical therapist, treating physician, and coach and athletic 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 the education of the patient and primary care provider to develop a stepwise and comprehensive treatment and rehabilitation plan.

Patients should be educated as part of the treatment plan, including avoiding exacerbating/impingement positions, home exercises, and return to play.

Outcome measures

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) is the most commonly used.⁵⁷

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

Emerging interventions

Orthobiologics for symptomatic relief and to delay surgical management have been considered in the literature, but scientific data to support their use in FAI syndrome is insufficient.

Low-quality evidence demonstrates improved pain and function with intra-articular hip hyaluronic acid.⁵⁸ Otherwise, there is insufficient evidence to support the use of injection therapies for the treatment of FAI syndrome at this time.^51,58,59

In one 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.⁶⁰

Perioperative orthobiologics including platelet-rich plasma and cell-based therapies used alongside hip arthroscopy for FAI syndrome with associated pathologies (labral tears and acetabular chondral defects) have also been studied. A recent systematic review evaluating these treatments suggests improved patient-reported outcomes when treated with cell-based therapies (specifically bone marrow aspirate concentrate (BMAC) and microfragmented autologous adipose tissue transplantation (MATT)) compared to control, though the studies are of low-level evidence with variable indications and treatment heterogeneity.⁶¹

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 lead 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 deformities.
• Radiographic findings of FAI are frequent in asymptomatic individuals and presence of a cam or pincer morphology is not equal to FAI syndrome.
• Repetitive physical activity during growth with poor spine/pelvic biomechanics may cause these anatomical morphologies.
• 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

• Morphological 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.
• Specific rehabilitation protocols for both nonoperative and operative management.

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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, Benjamin Miller, DO. Femoroacetabular Impingement Syndrome. 1/13/2022

Author Disclosure

Ryan L. Russell, DO
Nothing to Disclose

Allison N. Schroeder, MD
Nothing to Disclose