Femoroacetabular impingement syndrome

INTRODUCTION — Femoroacetabular impingement syndrome (FAIS) describes hip-related groin pain due to pathological contact between the femoral head-neck junction and the acetabular rim during a functional range of hip movement. It occurs secondary to predisposing cam or pincer hip morphology. FAIS is a strong risk factor for hip pain and osteoarthritis, and it is thought to be responsible for up to half of all hip osteoarthritis [1]. Considerable uncertainty exists with respect to the diagnosis and treatment of the condition.

The presentation, diagnosis, and management of FAIS is reviewed here. The approach to undifferentiated hip pain and other discrete causes of hip pain in adults and children are discussed separately:

●Hip pain in adults (see "Approach to the adult with unspecified hip pain" and "Approach to hip and groin pain in the athlete and active adult")

●Hip pain in children (see "Approach to hip pain in childhood" and "Evaluation of limp in children" and "Radiologic evaluation of the hip in infants, children, and adolescents")

●Selected injuries and hip conditions in adults (see "Greater trochanteric pain syndrome (formerly trochanteric bursitis)" and "Clinical manifestations and diagnosis of osteoarthritis", section on 'Hip' and "Overview of common hip fractures in adults")

●Selected injuries and hip conditions in children (see "Evaluation and management of slipped capital femoral epiphysis (SCFE)" and "Hip fractures in children")

TERMINOLOGY — Femoroacetabular impingement (FAI) describes abutment of the femoral head-neck junction against the acetabular rim due to an aspherical femoral head (cam morphology), over-coverage of the femoral head (pincer morphology) [2,3], or a combination of the two morphologies (figure 1). While all hips impinge at the extremes of movement [4], FAI describes contact between the femur and acetabulum within a functional range of motion. Importantly, only a small proportion of individuals with FAI morphology develop symptoms. In such cases, the condition is referred to as femoroacetabular impingement syndrome (FAIS) [5]. A consensus statement defines FAIS as a triad of symptoms, clinical signs, and imaging findings [5] as discussed below.

PATHOGENESIS — Cohort studies report a strong association and dose-response relationship between intense sporting activity (ie, sport requiring rapid change in direction ["cutting"], sprinting, and jumping) during adolescence in males and the development of cam morphology [6-10]. While the precise etiology is not understood, there is a strong relationship between the severity of cam morphology and epiphyseal extension along the femoral neck that results in convexity rather than concavity at the femoral head-neck junction [6]. The gradual increase in magnitude of the cam morphology with age in association with epiphyseal extension suggests a physiologic adaptation to loading rather than an acute slip of the proximal femoral epiphyseal region [6,8].

Researchers and an expert consensus panel agree that cam morphology that develops during skeletal maturation as a normal physiological response to load be referred to as primary cam morphology (as opposed to secondary cam morphology due to pre-existing hip disease or acute trauma, including Perthes disease, slipped capital femoral epiphysis, and healed proximal femoral fractures) [11,12]. This agreed taxonomy of types for cam morphology is important, not only in research when defining study populations, but also in the clinic, as each requires a different clinical approach. (See "Evaluation and management of slipped capital femoral epiphysis (SCFE)" and "Hip fractures in children".)

No adequate explanation has been provided as to why the prevalence of primary cam morphology is significantly lower in females or why there is no difference in primary cam morphology between dominant and non-dominant lower extremities [6,13]. It is proposed that modifying the intensity or pattern of hip loading during adolescent sporting activities may offer the potential to prevent the development of primary cam morphology and associated hip pathology.

The development of pincer morphology is less well understood than cam morphology and represents an area for future research (image 1).

NATURAL HISTORY — After skeletal maturity, no changes in hip morphology occur other than those associated with the development of acquired pathology, such as osteoarthritis with osteophytosis [6,8,14,15]. Cam morphology is causally associated with the development of osteoarthritis [14-16] and total hip replacement [17]. Patients with cam morphology represent approximately half of all those who develop hip osteoarthritis. Nevertheless, radiographic features of FAI morphology have limited value for identifying patients most likely to develop osteoarthritis [18]. The positive predictive value of cam morphology for subsequent development of osteoarthritis is reported to range from 6 to 25 percent, and the negative predictive value 98 to 99 percent [19]. (See "Management of hip osteoarthritis".)

The natural history of hip symptoms associated with FAI morphology is not well characterized, and studies demonstrate an inconsistent relationship between cam or pincer morphology and hip pain. Cam morphology is associated with worse patient-reported outcome scores (including pain and function limitations) in large population studies [20]. Pincer morphology is not reliably associated with pain or future osteoarthritis [21]. Limitations to these studies include differences in populations, definitions of abnormal morphology, and outcome measures.

Causal (ie, modifiable) risk factors for FAIS are contested, and most people with FAI morphology are asymptomatic, including some participants in high-level sport. Thus, there is no basis for individual screening. However, some population-wide interventions, such as training to increase hip muscle strength, are worth considering, especially among athletes competing in higher-risk sports (eg, football, ice hockey).

EPIDEMIOLOGY — Studies investigating hip morphology prevalence are clinically and methodologically diverse (heterogenous), limiting our understanding of its prevalence in the general population or in select subgroups, such as professional athletes [22]. Diverse study groups (eg, asymptomatic, symptomatic with hip pain, hip arthroscopy registrants, athletes, dancers), unspecified interventions or exposures (eg, no objective activity dose measurements), and unclear outcomes (no clear definition and diverse methods of measuring cam and pincer morphology) all contribute to clinical heterogeneity; variability in study design and high risk of bias contribute to methodologic heterogeneity.

Primary cam morphology — Primary cam morphology (image 2) is more prevalent in males, in symptomatic versus asymptomatic participants [23], and in maturing athletes participating in high-impact sports (eg, football [soccer], American football, ice hockey, rugby), track and field, and certain aquatic sports. The prevalence of cam morphology is 37 percent (range 7 to 100 percent) in asymptomatic hips; 54.8 percent in athletes versus 23.1 percent in the general population [24].

Pincer morphology — According to a systematic review of 60 studies of FAI, there is no significant difference in the prevalence of pincer morphology (image 3) among athletes compared with symptomatic patients [23]. Pincer morphology prevalence in asymptomatic hips is 67 percent (range 61 to 76 percent) and 49.5 percent in athletic populations [24]. However, the authors note that in many studies, pincer morphology was poorly defined and assessed using radiographs rather than computed tomography (CT) and thus, the findings should be interpreted with caution.

Mixed morphology — Mixed morphology (image 4) is significantly more common in athletes versus asymptomatic individuals and in asymptomatic versus symptomatic individuals [23]. This finding should be interpreted with caution due to study heterogeneity.

Femoroacetabular impingement syndrome — Evidence about the prevalence of FAIS (ie, symptomatic FAI) in the general population is extremely limited. General practitioners who participated in a prospective study to investigate the incidence of FAIS in the general population in the Netherlands between July 2013 and July 2014 saw 19,185 eligible patients between 15 and 60 years old. Of these, only 84 patients presented with groin pain (0.44 percent), and 14 of the 84 (17 percent) were diagnosed with FAI [25].

CLINICAL EVALUATION

History and presentation — The initial presentation of FAIS is insidious and often deceptive. Mild symptoms of groin pain may occur variably for a long time (years) before abruptly worsening and finally limiting or preventing participation in sport.

In the early stages, symptoms are often ignored by the patient and are sometimes dismissed as a groin or hip flexor strain. Typically, pain is most noticeable after sitting with the hips flexed to 90 degrees for a relatively long period (eg, working at a desk, taking a long automobile or plane ride) and diminishes when rising to the standing position. As symptoms progress, sporting activity is increasingly affected. In many cases, particularly if pain has persisted for more than 12 months, symptoms of osteoarthritis develop, with pain that increases in correlation with the distance walked and increasingly limited hip mobility, particularly external rotation and flexion.

The primary symptom of FAIS is movement- or position-related groin pain. Pain may radiate from deep within the hip region to the groin and, less frequently, the buttock in a C-shaped distribution. Patients, when asked to show the location of their pain, may grasp their hip region with their palm on the lateral hip, their thumb anterior, and their fingers over or pointing towards the buttock, thereby forming a "C." Some patients may develop additional pain at the back or thigh, and some may describe other sensations at the hip, such as clicking, catching, locking, stiffness, restricted motion, or giving way [5].

Many patients with FAIS have an associated labral tear, which typically presents with sharp pain and catching sensation at the groin. These sensations often occur with flexion and abduction of the hip but may happen during activities such as sprinting, rapid change of direction during sport ("cutting"), or kicking. However, exacerbation of these symptoms can be unpredictable and may occur while sitting or traveling in a vehicle. As dysfunction progresses, many patients develop secondary greater trochanteric pain syndrome or lower back pain. (See "Greater trochanteric pain syndrome (formerly trochanteric bursitis)" and "Approach to hip and groin pain in the athlete and active adult", section on 'Acetabular labrum injury'.)

Physical examination

General examination — As the presentation of FAIS is often insidious and the differential diagnosis broad, it is important to perform a careful examination of the hip and groin region. This examination is discussed separately, as is the approach to undifferentiated hip and groin pain. (See "Musculoskeletal examination of the hip and groin" and "Approach to the adult with unspecified hip pain" and "Approach to hip and groin pain in the athlete and active adult".)

In addition, clinicians should examine carefully the lower back and abdomen. Note the presence of any signs associated with lumbar spine pathology, such as pain with straight leg raise and lower extremity weakness or radiculopathy radiating from the lumbar spine. Note any generalized joint mobility restrictions or laxity. Inspect and palpate the abdomen and inguinal region for tenderness, swelling, or other abnormality.

The examination of the pelvis, hip, and lower extremities, should include the following:

●Gait assessment (see "Clinical assessment of walking and running gait")

●Single-leg balance and strength assessment

●Palpation of soft tissues around the hip (see "Musculoskeletal examination of the hip and groin", section on 'Physical examination')

●Hip range of motion testing (see "Musculoskeletal examination of the hip and groin", section on 'Tests for acetabular pathology')

Provocative maneuvers — There is no single diagnostic sign for FAIS. Several clinical tests are commonly used to assist in the diagnosis of FAI. The most common is the hip flexion, adduction, and internal rotation (FADIR), or anterior impingement test. The FADIR test classically produces restriction (reduced internal rotation) and pain at 90 degrees of hip flexion and 10 degrees of adduction (picture 1). It is often performed in conjunction with the hip flexion, abduction, and external rotation (FABER) test (picture 2), which is used to help diagnose labral tear. The sensitivity of these tests is generally good (0.7 to 1.0); however, a number of studies report poor specificity (0.1 to 1.0) [26,27].

The location of pain should be noted during either test. In patients with FAIS, pain location typically mirrors symptoms, being either groin focused or present in a C-shaped distribution radiating from within the hip to the groin, and possibly the buttock. The FADIR test sometimes reproduces pain from sacroiliac and occasionally trochanteric conditions. Therefore, when performing the test, the clinician should ask the patient the location of any pain that is elicited.

Of note, examination maneuvers should be used in conjunction with the history and imaging studies. Many authors regard FAIS as a syndrome that can only be confirmed with a positive history, clinical test, and an associated morphology on imaging [5].

In a systematic review of 25 studies investigating the diagnostic accuracy of clinical tests for the diagnosis of FAIS or hip labral tear, only the hip flexion, adduction, and internal rotation (FADIR) and hip flexion-internal rotation tests were of value; both were sensitive (ie, accurate for ruling out FAIS when negative) but not specific (ie, not diagnostic of FAI when positive) [28]. According to another systematic review of 29 studies reporting on 23 clinical tests, the absence of pain during the FADIR test and the presence of unrestricted hip motion during the FABER test compared with the unaffected side were best for ruling out FAIS [29]. However, no tests were found to be diagnostic, and the overall quality of the included studies was assessed to be low.

DIAGNOSTIC IMAGING

Approach to imaging — Initial imaging for suspected FAIS (figure 1) consists of an anteroposterior pelvis radiograph and lateral radiograph of the symptomatic hip, such as a cross-table lateral or Dunn 45 degree view [5,30-33]:

●Normal hip and pelvis (image 5 and image 6)

●Cam morphology (image 2 and image 7)

●Pincer morphology (image 3)

●Mixed cam-pincer morphology (image 4)

Population cohort studies investigating the pathogenesis of osteoarthritis frequently use only anteroposterior radiographs due to the availability of this projection. A single anteroposterior radiograph may fail to identify up to half of all cam morphology [34,35]. Cam morphology is maximal at the anterosuperior femoral neck [6,34-36], meaning that even when both an anteroposterior and lateral radiographic projection is acquired, up to one-third of cam morphology is not identified [34,35]. Therefore, hip imaging should not be interpreted in isolation but always in the context of the patient's history, symptoms, and examination findings.

Conversely, in a patient whose history and examination findings are consistent with FAIS, plain radiographs that reveal a cam and/or pincer morphology of the affected hip are sufficient for diagnosis. Advanced imaging is not necessary in such cases and only obtained subsequently if the patient fails to improve with physical therapy and surgery is planned.  

Three-dimensional imaging is essential to exclude FAI morphology when clinical suspicion persists after plain radiographs are found not to be definitive. Magnetic resonance imaging (MRI) is the preferred study in this setting, although published studies of both MRI and computed tomography (CT) for FAIS are limited methodologically, in part due to the high pre-test probability of FAIS in the study populations [28].

MRI allows for evaluation of hip morphology in three dimensions and of the surrounding soft tissues for signs of associated pathology, such as labral tears or chondropathy [28]. MRI must include radial slices around the femoral neck to evaluate anterosuperior femoral neck morphology (figure 2) [34,35,37]. Oblique axial MRI alone is no more sensitive than radiography at identifying cam morphology [34,37]. Arthrography is not required for evaluating internal derangement of the hip when using 3 Tesla MRI, which is at least as sensitive as MRI arthrography at 1.5 Tesla [38].

Several MRI-based software systems are available to help assess bony morphology and hip biomechanics. While these systems are accurate for measuring morphology, they model hip biomechanics using static images, and so these results must be interpreted with great caution.

CT provides three-dimensional assessment of the hip with excellent visualization of bone morphology, but it requires ionizing radiation and does not allow simultaneous visualization of soft tissues without arthrography. Real-time, dynamic imaging is available with many newer CT scanners. This technique enables the hip to be placed in the impingement position during the scan, allowing accurate assessment of the impingement angle. This may help guide activity modification and pre-operative planning. Therefore, CT should be limited to patients being considered for hip surgery.  

In a systematic review and meta-analysis of imaging strategies for the diagnosis of FAI, none of the studies met the requirements for meta-analysis. Salient limitations of research in this field include different imaging protocols and the absence of agreed diagnostic criteria for FAI morphology (figure 2) [28,30,34-38].

Measurement of FAI morphology — Typically, a standard anteroposterior (AP) plain radiograph of the pelvis is used to make the basic measurements for assessing FAI morphology [39].

Cam morphology — The most widely adopted measure to quantify cam morphology is the alpha angle [40]. To determine this angle, a line is drawn from the center of a best-fit circle surrounding the femoral head to the midpoint of a line transecting the narrowest portion of the femoral neck. Another line is then drawn from the center of the best-fit circle to where the contour of the femoral head first exits the best-fit circle. The angle between the two lines is denoted the alpha angle and increases as the severity of asphericity increases (image 8).

An alpha angle of 60 degrees or more has been proposed as diagnostic for cam morphology [41,42], but this is not adopted in routine clinical practice where typically symptoms, examination findings, and qualitative imaging assessment are used to make the diagnosis. Increased cam morphology size (as reflected by a larger alpha angle) is associated with cartilage defects and labral tears in young adult football players with and without pain, and with labral injury [43-45].

Other appearances used to characterize cam morphology include Gosvig's index [46] and femoral head-neck offset [47].

Pincer morphology — Pincer impingement may be localized in acetabular retroversion or global in coxa profunda (deep, medial-lying acetabulum) or protrusio acetabuli (medial intrapelvic displacement of acetabulum and femoral head) [48]. As a result, there are number of radiographic appearances and measurements to quantify pincer morphology [47]. The most frequently adopted measurement is the lateral center edge angle, which represents the angle between the vertical axis and a line connecting the bony acetabular rim to the center of the femoral head (image 8) [49]. A lateral center edge above 40 degrees is frequently considered diagnostic for pincer morphology [50]. Other appearances used to characterize pincer morphology describe acetabular depth, acetabular inclination, and acetabular version [47].

DIAGNOSIS — The diagnosis of FAIS is made based on diagnostic imaging studies in the setting of an appropriate history and consistent examination findings. Of note, many patients with femoral neck or acetabular morphology consistent with the diagnosis of FAIS are asymptomatic. FAIS is generally insidious in onset and presents initially with intermittent groin pain exacerbated by particular postures (generally involving prolonged hip flexion) or movements. Symptoms progress and come to interfere with activities. The flexion, adduction, and internal rotation (FADIR; anterior hip impingement) test (picture 1) typically reproduces the patient's symptoms.

DIFFERENTIAL DIAGNOSIS — The hip and groin-related symptoms and signs of FAIS are nonspecific and potentially confusing when interpreted in isolation. Therefore, it is important to work through the potential causes of the patient's hip or groin pain systematically. The differential diagnosis for such pain is reviewed in detail separately. (See "Approach to hip and groin pain in the athlete and active adult" and "Approach to the adult with unspecified hip pain".)

FAIS may mimic or coexist with other hip and groin or remote disease entities, including diseases causing secondary cam morphology (eg, slipped capital femoral epiphysis, Perthes disease, osteonecrosis of the femoral head), labral tears, femoral-acetabular cartilage disease, hip osteoarthritis, hip dysplasia, hip and groin tumors, and pelvic/spinal disease. A table listing important alternative diagnoses and some findings that distinguish them from FAIS is provided (table 1). The patient's history, clinical signs, and imaging findings must all be considered when making the diagnosis of FAIS [5,51].

Conditions to consider in the differential diagnosis include the following:

●Other hip joint pathology

•Dysplasia/hip instability (see "Developmental dysplasia of the hip: Clinical features and diagnosis" and "Overview of the causes of limp in children")

•Labral disease

•Chondral disease

•Osteoarthritis (see "Clinical manifestations and diagnosis of osteoarthritis")

•Avascular necrosis of the hip (see "Clinical manifestations and diagnosis of osteonecrosis (avascular necrosis of bone)")

•Legg-Calve-Perthes disease

•Slipped capital femoral epiphysis (see "Evaluation and management of slipped capital femoral epiphysis (SCFE)")

●Muscle and tendon conditions of the hip and groin

•Adductor-related groin pain (eg, adductor tendinopathy/enthesopathy, adductor muscle strain) (see "Adductor muscle and tendon injury")

•Iliopsoas-related groin pain (eg, iliopsoas muscle strain, iliopsoas tendinopathy, bursitis)

•Inguinal-related groin pain

•Pubic-related groin pain (eg, osteoarthritis of the symphysis pubis joint)

●Bone conditions

•Stress fracture of the hip and pelvis (see "Overview of stress fractures" and "Femoral stress fractures in adults")

•Apophysitis

●Nerve injury

•Ilioinguinal nerve entrapment (see "Overview of lower extremity peripheral nerve syndromes")

•Obturator nerve entrapment

•Genitofemoral

•Iliohypogastric

●Tumors (eg, testicular tumors, prostate cancer, urinary tract cancer, bone and soft tissue tumors, digestive tract cancer)

●Rheumatologic disease (eg, spondyloarthropathy, rheumatoid arthritis)

●Intra-abdominal and genitourinary conditions (eg, prostatitis, urinary tract infection, kidney stone, appendicitis, diverticulitis)

●Gynecologic conditions (eg, ovarian cyst)

●Lumbar spine and sacroiliac joint conditions, including radicular pain

INDICATIONS FOR ORTHOPEDIC REFERRAL — Orthopedic referral is typically made for patients with FAIS whose symptoms and function fail to improve despite compliance with a well-designed, incremental exercise rehabilitation program for three to six months. Patients who do not respond to nonoperative measures and who wait longer than 12 months for surgery are at increased risk of developing osteoarthritis and less likely to have a good operative outcome.

Other indications for expediting referral to an orthopaedic surgeon include an uncertain diagnosis and evidence of hip osteoarthritis.

Persistent loss of hip internal rotation and positive impingement tests after treatment are not of concern in otherwise asymptomatic patients, but these patients warrant orthopedic referral if symptoms return due to the risk of progressive degenerative joint damage.

MANAGEMENT

General approach — There is low-quality evidence that patients with FAIS who are not treated experience a worsening of symptoms [5]. Treatment options consist of conservative care, rehabilitation, or surgery:

●Conservative care (education, watchful waiting, lifestyle and activity modification)

●Exercise rehabilitation to improve hip stability, neuromuscular control, strength, range of motion, and movement patterns) [52,53]. (See 'Exercise rehabilitation and other nonoperative interventions' below.)

●Surgery (open or arthroscopic to improve hip morphology and repair damaged tissue) followed by a structured, physiotherapist-led incremental exercise rehabilitation program (see 'Surgical management' below)

For young, active patients, we suggest that initial treatment consist of a combination of conservative care and clinician-led, incremental exercise rehabilitation, as described above. Should rehabilitation prove ineffective, patients are referred to an orthopedic surgeon.

The results of observational studies with short-term follow-up suggest that this approach reduces symptoms and improves function. As an example, in a prospective cohort study, 82 percent of symptomatic hips among adolescent and young adult patients with FAIS managed nonoperatively made significant improvements in functional outcome scores at a mean follow-up of two years [54]. The study included 76 patients (93 symptomatic hips) with a mean age of 15.3 years (range 10.4 to 21.4). Sixty-five hips (70 percent) were managed with physical therapy, rest, and activity modification alone; eleven hips (12 percent) received a glucocorticoid injection without subsequent surgery; and 17 hips (18 percent) required arthroscopic surgery.

Exercise rehabilitation and other nonoperative interventions — Clinician-led, incremental, exercise-based rehabilitation is widely recommended as the initial treatment for FAIS. Thus, it is concerning that referral to physical therapy is not consistent practice. In an observational study of 1870 patients with FAIS, 59 percent did not see a physical therapist prior to surgery, and only 12 percent had six or more documented visits for physical therapy [55].

Should symptoms fail to improve with rehabilitation, referral to a sports medicine physician or orthopedic surgeon is indicated to review the diagnosis and consider whether surgery is warranted. The period to trial nonoperative treatment is decided by the patient and treating clinician but is typically three to six months. (See 'Indications for orthopedic referral' above.)

The optimal rehabilitation protocol for treating FAIS is not known. Consensus groups propose a progressive, individualized, exercise-based program that includes interventions to optimize core strength and movement control [52,56-58]. According to a systematic review of five randomized trials involving 128 patients, supervised physical therapy using dynamic exercises and focusing on core strength development resulted in statistically significant improvements in functional outcomes compared with programs lacking these characteristics [59]. An effective physical therapy program should address any weakness of the hip musculature, particularly the external rotators [60,61].

Nonoperative strategies also include analgesia with nonsteroidal anti-inflammatory drugs (NSAIDs) and acetaminophen, potentially supplemented by an intra-articular glucocorticoid injection, and avoiding or minimizing activities that provoke symptoms.

Surgical management — Surgical treatment of FAIS consists of procedures to excise the impinging bone and address damage to the adjacent labrum and articular cartilage. With cam morphology, impinging bone is ground away to restore the concavity at the femoral head-neck junction (osteochondroplasty). The treatment of pincer impingement depends on morphology, but localized over-coverage of the femoral head can be treated by removing impinging bone. Surgery can be performed open or arthroscopically, although most cases are now performed arthroscopically due to lower complication rates and improved outcomes [62]. As an example, the number of arthroscopic hip procedures performed in England between 2002 and 2013 increased by 727 percent [63].

Given the high prevalence of FAI morphology in the general population, the majority of whom are asymptomatic, combined with the absence of evidence that intervention has disease-modifying potential, there is no role for treating asymptomatic individuals with surgery. In the presence of established osteoarthritis, hip arthroplasty is indicated rather than joint-preservation surgery.

The management of skeletally immature patients with FAIS is challenging, and evidence is limited. When nonoperative management fails, surgery may be beneficial. As an example, in an observational study, hip arthroscopy using a physeal-sparing approach in growing adolescents (n = 157) was safe and effective when compared with a matched adult surgical group [64].

Overall, evidence suggests that arthroscopic surgery is superior to physiotherapy at improving short-term patient-reported outcomes in patients referred for FAIS. Three randomized, controlled trials have compared arthroscopic hip surgery with physiotherapy [56,57,65]. The two largest found that arthroscopic treatment was superior to physiotherapy for improving patient-reported outcomes with a clinically important difference between groups at 8- to 12-month but not at 24-month follow-up [56,57]. A further study did not demonstrate a difference between treatment groups, but there was a 70 percent crossover from physiotherapy to surgery [65].

A systematic review of 14 studies (two prospective) involving 753 adolescents (832 hips) treated with hip arthroscopy for FAIS reported a high rate of return to sport, good functional outcomes, and low complication rates [66]. However, many studies were retrospective, methodology varied among studies, and risk of bias was significant, making it difficult to interpret these results.

Available studies have limitations. As an example, it is not known whether symptom improvement is sustained and osteoarthritis averted with surgery; studies with longer-term follow-up are needed. Furthermore, up to half of patients do not gain a clinically important improvement with either treatment, suggesting that more accurate patient selection is required. The randomized controlled studies performed to date have not been sufficiently powered to explore differences among subgroups, but cohort studies report that increasing patient age, worse preoperative patient-reported symptom and function scores, and the presence of osteoarthritis have negative effects on surgical outcomes [67-70].

RETURN TO PLAY — Patients typically have three questions when considering treatment options for FAIS:

●"Will I be able to return to the same level of sport or physical activity if I follow this treatment option?"

●"If not, can I do any other sport or activity?"

●"Will I suffer from chronic pain, hip osteoarthritis, or one day need hip replacement surgery?"

These questions are all highly contextual, and answers necessarily vary depending on patient factors (eg, age, type and level of sports participation, comorbidities, values, perceptions, circumstances), hip disease-related factors (eg, severity, duration), and clinician factors (eg, experience, resources, biases). Given this broad range of considerations, clear answers are impossible. It is important for clinicians to quantify patient expectations regarding their return to physical activity (including level of sport competition, sport performance, and occupation performance) [71]. Nevertheless, when discussing treatment options, clinicians must consider what evidence should be used to help patients make informed decisions.

The size and position of cam morphology determines the severity and location of progressive hip cartilage damage; alpha angles exceeding 89 degrees predict the development of clinically relevant osteoarthritis progression with a sensitivity of 77.8 percent and a specificity of 75 percent [72]. Thus, clinicians should take the size and position of cam morphology into account when deliberating treatment options. However, we do not know if surgery to reduce the size of the cam morphology will influence the risk of early osteoarthritis.

As noted above, return to play following treatment for FAIS varies depending on a number of factors, but some general data are available [71,73-75]. In a 2022 systematic review of 81 studies that provided data about return to play, the overall rate was 85.4 percent (3638/4261) over a mean of 6.6 months, while the rate of return to play to a preinjury level of performance, reported in 49 studies, was 72.6 percent (1673/2303) [76]. Return to play among professional athletes was reported in 23 studies and was 92.4 percent (571/618), while return to full duty among military personnel was 67.6 percent (631/934). Most studies were small cases series, and the overall quality of evidence was noted to be low.

Rates of successful return to play following surgery vary by sport. National Hockey League players experience a decline in performance after surgery with shortened careers and are able to play fewer games per season [74]. This is not the case for players in the National Football League, Major League Baseball, or the National Basketball Association. According to small observational studies, a high percentage of football (soccer) players successfully return to full play [77-79].

There is much less evidence available about return to play after nonoperative management of FAIS. In all cases, the decision should be guided by symptoms and the return performed gradually. An alternative approach is to participate in only low-impact sport that avoids the impingement position, such as swimming or cycling.

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Hip and groin pain".)

SUMMARY AND RECOMMENDATIONS

●Definitions – A small proportion of individuals with FAI morphology develop hip pain and associated symptoms. In such cases, the condition is referred to as femoroacetabular impingement syndrome (FAIS). FAIS describes hip-related groin pain due to pathological contact between the femoral head-neck junction and the acetabular rim within a functional range of hip movement. It occurs secondary to predisposing cam or pincer hip morphology (figure 1). FAIS is a risk factor for osteoarthritis. (See 'Terminology' above and 'Natural history' above.)

●Clinical presentation – The initial presentation of FAIS is insidious and often deceptive. Mild groin pain may occur variably for a long time (years) before abruptly worsening. Typically, pain is most noticeable after sitting with the hips flexed to 90 degrees for a relatively long period and diminishes when standing. As symptoms progress, sporting activity is increasingly affected.

The primary symptom of FAIS is movement- or position-related groin pain. Pain may radiate from deep within the hip region to the groin and, less frequently, the buttock. Some patients may develop additional pain at the back or thigh, and some may describe other sensations at the hip, such as catching, stiffness, or restricted motion. Many patients have an associated labral tear, which typically presents with sharp pain and catching sensation at the groin. These sensations often occur with flexion and abduction of the hip but may happen during activities such as sprinting, rapid change of direction during sport ("cutting"), or kicking. (See 'History and presentation' above.)

●Physical examination – There is no single diagnostic sign for FAIS. The hip flexion, adduction, and internal rotation (FADIR) and hip flexion-internal rotation tests are both sensitive (ie, accurate for ruling out FAIS when negative) but not specific (ie, not diagnostic of FAI when positive). The FADIR test classically produces restriction (reduced internal rotation) and pain at 90 degrees of hip flexion and 10 degrees of adduction (picture 1). (See 'Physical examination' above.)

●Differential diagnosis – Given the often insidious onset and absence of definitive examination findings in patients with FAIS, the differential diagnosis is broad and includes other pathologies of the hip joint (eg, Legg-Calve-Perthes, osteoarthritis), muscle and tendon injuries and conditions (eg, adductor injury), bone conditions (eg, stress fracture, lumbosacral injury), nerve entrapment syndromes (eg, ilioinguinal, obturator), tumors, rheumatologic diseases, and gynecologic conditions (eg, ovarian cyst) (table 1). (See 'Differential diagnosis' above.)

●Imaging – Initial imaging for suspected FAI consists of an anteroposterior (AP) pelvis radiograph and lateral view of the symptomatic hip (image 7 and image 4 and image 9). An AP plain radiograph of the pelvis is used to make the basic initial measurements for assessing FAI morphology. These consist of the alpha angle for cam morphology and the lateral center edge angle for pincer morphology (image 8). Three-dimensional imaging is essential to exclude FAI morphology when clinical suspicion persists after plain radiographs are found not to be definitive. Magnetic resonance imaging (MRI) is the preferred study in this setting. (See 'Diagnostic imaging' above.)

●Diagnosis – FAIS is diagnosed based on the presence of cam and/or pincer morphology on imaging studies in the setting of an appropriate history and consistent examination findings. (See 'Diagnosis' above.)

●Treatment and indications for orthopedic referral – Exercise-based rehabilitation is the initial treatment for FAIS. Orthopedic or sports medicine referral is indicated for patients whose symptoms and function fail to improve despite compliance with a well-designed rehabilitation program for three to six months. Other reasons for referral include an uncertain diagnosis and evidence of hip osteoarthritis. (See 'Management' above and 'Indications for orthopedic referral' above.)

Given the high prevalence of FAI morphology in the general population, the majority of whom are asymptomatic, combined with the absence of evidence that intervention has disease-modifying potential, there is no role for treating asymptomatic individuals.

●Return to activity – Successful return to activity depends on patient factors (eg, age, type and level of sports participation, comorbidities, values, perceptions, circumstances), disease-related factors (eg, severity, duration), and clinician factors (eg, experience, resources, biases). (See 'Return to play' above.)