Femoroacetabular impingement

This is the clinical evidence summary written for health professionals. It is technical, and it lists the research this page was built from. You do not need to read it to understand your treatment or to make a decision about it.

Anatomy & Pathophysiology¶

Definitions and Classification¶

• Femoroacetabular impingement (FAI) is defined as a dynamic mechanical conflict between the proximal femur and the acetabulum [9].
• Intra-articular FAI occurs when the femoral head-neck junction abuts against the acetabular rim [9].
• Extra-articular FAI occurs due to conflicts between the lesser trochanter and ischium, greater trochanter and supra-acetabular region, or femoral neck and anterior-inferior iliac spine [9].
• Three types of FAI are recognized: cam, pincer, and combined cam/pincer [2].
• Combined cam/pincer deformities are common [2].
• Cam impingement is characterized by femoral-based abnormalities such as an aspherical femoral head, reduced head-neck offset, or femoral retroversion [2].
• Pincer impingement is characterized by acetabular-based disorders such as acetabular retroversion, global overcoverage, or acetabular protrusio [2].
• Cam impingement is most common in young males [5].
• Pincer impingement is most common in middle-aged females [5].

Cam Impingement Pathophysiology¶

• In cam impingement, the aspherical femoral head creates a shearing force along the acetabular cartilage during hip flexion [5].
• This shearing force results in articular cartilage delamination [5].
• Cam impingement may also result in avulsion of the labrum [5].
• The typical injury pattern with cam impingement is a tear at the base of the labrum at the labral-chondral junction [10].
• In cam impingement, the acetabular labrum is relatively spared compared to the adjacent articular cartilage [10].
• Cam deformity is typically located anterolateral on the femoral neck [5].

Pincer Impingement Pathophysiology¶

• Pincer impingement results from acetabular overcoverage causing abnormal contact between the acetabular rim and the femoral head-neck junction [5].
• Pincer impingement causes intrasubstance tears of the labrum, typically in the anterosuperior quadrant [5].
• In pincer impingement, the anterosuperior femoral head is levered against the acetabular rim [5].
• A contrecoup cartilage lesion may occur in the posteroinferior acetabulum due to levering of the femoral neck on the acetabular rim [5].
• In pincer impingement, the labrum suffers more damage than the adjacent articular cartilage, which is relatively spared [10].
• Pincer impingement may worsen over time due to reactive bone growth at the acetabular rim or calcification of the labrum [10].

Etiology and Development¶

• The origin of cam deformities is controversial and has been the focus of investigations [9].
• Cam deformity can be secondary to pediatric hip diseases including slipped capital femoral epiphysis (SCFE) and Legg-Calvé-Perthes disease (LCPD) [9].
• Idiopathic cam deformity is suggested to be the most common acquired hip deformity in adolescents [9].
• Intense physical activity during adolescence may cause mechanical overloading across the epiphyseal plate, leading to increased epiphyseal extension [9].
• Increased epiphyseal extension can broaden the head-neck junction, flattening the physiological convexity or creating a convex cam morphology [9].
• A 2.8 relative risk of cam deformity in the siblings of affected individuals suggests genetic contributions [18].
• Cam deformity is more prevalent in adolescents who practice impact physical activities such as basketball, hockey, and soccer [9].
• Studies of young athletes demonstrate a lack of cam deformity in skeletally immature individuals but a presence after physeal closure [18].
• A cross-sectional MRI study found that abnormal alpha angles were not present in any hips with open physes, but 14% of hips with closed physes had cam deformities [10].
• Daily activity levels for patients with cam deformities are significantly higher than for those without deformity [10].

Prevalence in Asymptomatic Populations¶

• The prevalence of FAIS deformity in asymptomatic adults is estimated at approximately 14%, with 24% in males and 5% in females [18].
• Males are three to five times more likely to have cam deformities than females [18].
• Cam deformity is more likely to be bilateral in males than in females [18].
• A review of 473 CT scans showed that 40% of asymptomatic hips had radiographic findings associated with FAI [16].
• In asymptomatic adolescents, the rate of cam deformity (α angle ≥55°) was 16.8%, pincer deformity (lateral center edge angle ≥40°) was 32.4%, and mixed-type deformity was 6.1% [16].
• Cam morphology is substantially more common in males, while pincer deformities are equally distributed among males and females [16].
• More than 90% of asymptomatic adolescents have at least one radiographic parameter suggesting FAI, and 50% have two [5].
• The prevalence of coxa profunda is the same in asymptomatic patients as in those with diagnosed FAI [5].

Progression to Osteoarthritis¶

• FAI is recognized as a common cause of hip dysfunction and secondary osteoarthritis [2].
• In patients under 50 years of age undergoing total hip replacement for osteoarthritis, 97% had radiographic signs of cam, pincer, or mixed type impingement after excluding developmental dysplasia, SCFE, and Perthes disease [10].
• A cam deformity with an alpha angle of more than 60 degrees had an adjusted odds ratio of 3.67 for development of end-stage osteoarthritis [10].
• An alpha angle of more than 83 degrees had an adjusted odds ratio of 9.66 for development of end-stage osteoarthritis [10].
• In a 20-year longitudinal study of 1003 women, each degree increase in the alpha angle over 65 degrees was associated with a 5% increase in the risk of developing osteoarthritis [10].
• In a comparison of hips undergoing total hip arthroplasty for osteoarthritis to nonarthritic hips, 20% of arthritic hips had evidence of acetabular retroversion, compared to 5% of asymptomatic hips [10].
• Deep acetabular sockets had an adjusted risk ratio of 2.4 for the development of osteoarthritis in the Copenhagen Osteoarthritis Study [10].
• Chondrolabral damage occurs in asymptomatic patients with FAI and progresses within five years in those younger than 20 years [22].
• Chondrolabral damage develops within five years in patients treated with in situ pinning for SCFE, as the acquired deformity causes cam-type impingement [22].

Extra-Articular Impingement¶

• Subspine impingement is an extra-articular form of impingement occurring between the femoral head-neck junction and a prominent anterior-inferior iliac spine (AIIS) [17].
• The prevalence of subspine impingement is reported to be 23.7% [17].
• Three variants of AIIS morphology are described: type I (smooth ilium wall), type II (AIIS prominence extends to or above acetabular rim), and type III (AIIS extends distally to acetabular rim) [17].
• Pathologic AIIS morphology can be developmental (types I and II) or arise following pelvic osteotomy or prior rectus femoris injury/avulsion (type III) [17].
• Ischiofemoral impingement occurs between the lesser trochanter and the ischium [17].
• Trochanteric-pelvic impingement occurs between the greater trochanter and the ilium [17].
• Intra-articular steroid injection typically provides no relief or only partial relief of symptomatic extra-articular impingement [17].

Classification¶

• Three types of femoroacetabular impingement (FAI) are recognized: cam, pincer, and combined cam/pincer [2].
• Cam impingement is characterized by femoral-based abnormalities, including an aspherical femoral head, reduced head-neck offset, and femoral retroversion or relative retroversion [2].
• Cam impingement results in repetitive abutment of the acetabular rim and the femoral head-neck junction [2].
• Pincer impingement is characterized by acetabular-based disorders, including acetabular retroversion, global overcoverage, and acetabular protrusio [2].
• Pincer impingement creates abnormal abutment of the acetabular rim and the femoral head-neck junction [2].
• Combined cam/pincer deformities are common in patients with FAI [2].
• Subspinal impingement morphology is a frequent finding in patients with symptomatic FAI evaluated by computed tomography [24].
• A decrease in femoral anteversion is considered a useful criterion to suspect subspinal impingement morphology [24].

Clinical Presentation¶

History and Symptoms¶

• Patients with symptomatic femoroacetabular impingement (FAI) frequently present with activity-related groin pain that is exacerbated by hip flexion activities [2].
• Patients may report difficulty with prolonged sitting, walking, running, or pivoting [2].
• The onset of symptoms is often insidious or follows minor trauma [2].
• Patients may complain of pain with sitting, driving, or putting on socks and shoes [7].
• Mechanical symptoms secondary to labral and articular cartilage disease are common in symptomatic FAI [2].
• Most patients with symptomatic impingement present with activity-related groin pain [4].
• Active adolescents and young adults who report hip and/or groin pain should be assessed for FAI syndrome (FAIS) [4].

Physical Examination¶

• A mild, intermittent limp is common in patients with FAI, occurring in up to 75% of patients [23].
• Abductor weakness on the affected side is often seen with a positive Trendelenburg sign [23].
• Restricted hip motion is a defining feature of symptomatic FAIS [4].
• Affected individuals often have less than 100° of straight flexion and less than 10° of internal rotation with the hip at 90° of flexion [23].
• Bilateral disease is seen in approximately 75% of patients, but is symptomatic in fewer than 25% [23].
• Patients with FAI will exhibit restricted hip internal rotation in 90° of flexion [2].
• The anterior impingement test (flexion, adduction, internal rotation) elicits pain in the anterior groin and is present in most patients (88%) with symptomatic FAIS [23].
• The anterior impingement test is not specific for FAI and may be positive in any patient with a labral or chondral injury [23].
• The subspine impingement test involves maximal anterior groin pain with direct hip flexion beyond 90° while maintaining neutral rotation and abduction [23].
• Intra-articular anesthetic injection can be used to diagnose FAI; substantial or complete relief signifies an intra-articular source of pathology [23].
• Little to no pain relief following intra-articular injection warrants assessment for extra-articular sources of impingement or other pelvic or lumbar pathology [23].

Imaging and Diagnostic Findings¶

• The AP pelvis view is used to assess acetabular anatomy, including version, acetabular coverage, and femoral head sphericity [2].
• Lateral views, most commonly the 45° Dunn view and frog-leg lateral, are used to assess femoral head sphericity and head-neck offset [2].
• MRI or magnetic resonance arthrography provides information regarding the integrity of the acetabular labrum and articular cartilage [2].
• Low-dose CT with three-dimensional reformats is particularly useful in surgical planning of complex or borderline deformities [2].
• A "pistol-grip deformity," demonstrating a nonspherical femoral head, is seen in cam impingement [5].
• A crossover sign, where the anterior wall crosses lateral to the posterior wall, is classically seen with acetabular retroversion that causes pincer impingement [5].
• An alpha angle of more than 50 degrees is typical in hips with loss of sphericity [7].
• The prevalence of coxa profunda has been demonstrated to be the same in asymptomatic patients as in those with diagnosed FAI [5].
• There is a high rate of false-positive radiographic findings for FAI [5].

Investigations¶

Clinical Presentation and History¶

• Most patients with symptomatic femoroacetabular impingement (FAI) present with activity-related groin pain that is exacerbated by hip flexion activities [2].
• Patients with symptomatic FAI frequently report difficulty with prolonged sitting, walking, running, or pivoting [2].
• The onset of symptoms in FAI is typically insidious or follows minor trauma [2].
• Approximately 80% of patients with symptomatic impingement present with pain in the anterior groin or lateral hip [12].
• Approximately 25% of patients with symptomatic impingement report pain in the lumbar spine, buttock, or referred pain to the knee [12].
• Patients with symptomatic impingement often display the classic "C" sign when describing the location of pain [12].
• Pain in FAI is often worse with activity such as running, cutting, and pivoting, and is exacerbated in positions of hip flexion such as prolonged sitting or squatting [12].

Physical Examination¶

• Patients with FAI exhibit restricted hip internal rotation in 90° of flexion [2].
• The impingement test, performed by flexion, adduction, and internal rotation of the hip, elicits pain but is not specific for FAI [2].
• A positive anterior impingement test is defined as reproduction of symptoms with passive flexion, adduction, and internal rotation [5].
• Patients with FAI generally have more passive external rotation than internal rotation [5].
• A FABER (flexion, abduction, external rotation) test may show an increased knee-to-table distance on the affected side in patients with FAI [7].
• Palpation of the hip typically does not reproduce tenderness in patients with FAI [7].
• Asymmetrical range of motion between the hips is a characteristic finding in FAI [7].

Plain Radiography¶

• Standard preoperative radiographs for FAI include a standing AP pelvis, false-profile, Dunn views, and frog-lateral views [14].
• For an accurate standing AP pelvis view, the coccyx should be centered in the midline with its tip within 1 to 3 cm of the pubic symphysis [14].
• A crossover sign, where the anterior wall crosses lateral to the posterior wall, is classically seen with acetabular retroversion causing pincer impingement [5].
• The alpha angle is determined on lateral radiographs, and values greater than 50° indicate cam deformity [14].
• The 45° Dunn view has been shown to be more sensitive in detecting the presence and severity of cam deformity than the 90° Dunn view [14].
• The frog-lateral view has improved specificity for cam morphology compared with the Dunn view [14].
• On the AP pelvis view, a lateral center edge angle (LCEA) greater than 40° indicates pincer morphology [14].
• A crossover sign combined with an ischial spine sign and a posterior wall sign is indicative of true acetabular retroversion [14].
• The false-profile view is obtained with the patient rotated at an angle of 65° between the pelvis and x-ray source to profile the anterior acetabulum [14].
• An anterior center edge angle greater than 40° on the false-profile view indicates excessive anterior overcoverage [14].
• Radiographic findings concerning for acetabular undercoverage include an LCEA less than 20° and a Tönnis angle greater than 10° [14].
• An anterior center edge angle less than 20° on the false-profile view is indicative of acetabular undercoverage [14].

Advanced Imaging¶

• The sensitivity of MRI to acetabular rim chondral lesions is limited [2].
• CT can provide additional information about femur-acetabulum mismatch [5].
• Magnetic resonance arthrogram can be used to provide information about cartilaginous and labral injuries [5].
• In asymptomatic adolescents, the rate of cam deformity (defined as an α angle ≥55°) was 16.8%, pincer deformity (defined as a lateral center edge angle ≥40°) was 32.4%, and mixed-type deformity was 6.1% [16].
• In a study of 96 asymptomatic hips with radiographic findings consistent with FAI, 82.3% of patients remained free of radiographic arthritic changes at a mean follow-up of 18.5 years [16].
• Subspinal impingement morphology was a frequent finding in patients with symptomatic FAI evaluated by computed tomography using a three-dimensional dynamic study [24].
• A decrease in femoral anteversion was considered a useful criterion to suspect subspinal impingement morphology [24].

Diagnostic Injections¶

• Anesthetic intra-articular and extra-articular injections can aid in the diagnosis of combined FAI and athletic pubalgia [13].
• Initial management of FAI is typically conservative, including diagnostic or therapeutic injections [5].

Treatment¶

Non-Operative Management¶

• The 2016 Warwick Agreement defined FAI syndrome as a diagnosis related to the triad of symptoms, clinical signs, and imaging findings [8].
• Evidence supports the use of formal physical therapy interventions postoperatively versus self-directed rehabilitation [8].
• Nonsurgical rehabilitation for FAI syndrome should focus on activity modification, treatment of physical impairments, and optimization of joint function [8].
• Activities that place the hip in a position of impingement should be minimized as an initial recommendation when treating FAI syndrome [8].
• Combined positions of flexion, adduction, and internal rotation are commonly associated with increased symptoms in FAI [8].
• Deep squatting, lunging, cycling, and hurdling are examples of activities that may require modification during rehabilitation for FAI [8].
• Individuals with FAI syndrome have been noted to have particular deficits of the abductors, external rotators, flexors, and extensors of the hip compared with a control group [8].
• Uncontrolled pelvic motion in the frontal and transverse planes can contribute to the pain associated with FAI [8].
• Individuals with FAI syndrome have been found to have reduced posterior pelvis excursion and altered pelvifemoral coordination in both weight-bearing and non-weight-bearing tasks [8].
• Strengthening exercises for FAI should be advanced to include weight-bearing activities that challenge the patient to control excessive adduction and internal rotation of the hip [8].
• Exercises that maximize gluteal recruitment and minimize use of the tensor fascia lata should be emphasized in FAI rehabilitation [8].
• Resisted clam shell, resisted sidestep, unilateral bridge, and quadruped hip extension exercises are examples of exercises used to maximize gluteal recruitment in FAI rehabilitation [8].
• Exercises to strengthen the lumbopelvic muscles should be considered for patients with FAI [8].
• Appropriate lumbopelvic control can help decrease the occurrence of excessive anterior pelvic tilt associated with impingement secondary to altered acetabular orientation [8].
• Patients with FAI syndrome may demonstrate impaired hip and pelvic musculature flexibility [8].
• Treating hip flexor tightness should be a priority in flexibility activities for FAI because excessive tightness can be associated with anterior pelvic tilt [8].
• Anterior pelvic tilt has been correlated with the occurrence of FAI earlier in hip range of motion [8].
• Clinicians must be cautious to avoid placing patients in positions associated with symptomatic impingement when prescribing stretching activities for FAI [8].
• Joint mobilization may be indicated for patients with FAI when examination suggests a loss of capsular mobility [8].
• Examination findings suggesting a loss of capsular mobility in FAI include loss of passive range of motion, a capsular end-feel with passive range of motion assessment, and a decrease in symptoms with manual distraction of the hip joint [8].
• Soft-tissue mobilization can be useful for patients with FAI when tissue restricts joint mobility [8].
• A loss of motion associated with an elastic end-feel coupled with an immediate response to manual treatment of the target tissue indicates soft-tissue mobilization as a potentially useful intervention for FAI [8].

Operative Management¶

• Hip arthroscopy is an effective treatment modality for FAI syndrome [4].
• Both arthroscopic and open techniques are effective in the surgical management of FAI syndrome [4].
• Failure to address all the components of osseous impingement is a prime reason for continued pain and dysfunction following hip arthroscopy [4].
• Residual deformity is a leading cause of continued pain after the surgical management of FAI syndrome [4].
• In the absence of preexisting chondral disease, residual impingement is the leading cause of continued postoperative pain and revision surgery [21].
• A recent randomized clinical trial reported that hip arthroscopy led to a greater improvement than physical therapy [21].
• The current literature does not support prophylactic cam or pincer decompression in asymptomatic patients [21].

Outcomes and Prognostic Factors¶

• Reduced pain and improved function are reported in 68% to 96% of patients following surgical treatment of FAI syndrome [21].
• Approximately 75% of athletes are able to return to competition at the same level or better following surgical treatment of FAI syndrome [21].
• The long-term effect of hip arthroscopy and its potential to alter the natural history of FAI syndrome and prevent early degenerative joint disease remain to be determined [21].
• Ten-year outcomes on 145 patients reported a 76% survivorship following surgical treatment of FAI syndrome [21].
• The presence of preoperative osteoarthritis (Tönnis grade ≥ 2 or Outerbridge grade ≥ 3) is the strongest predictor of poor outcome following hip arthroscopy for FAI syndrome [21].
• Older age, a longer duration of symptoms, more severe preoperative pain, and poorer functional scores are factors associated with a poorer outcome following surgical intervention for FAI syndrome [21].
• Older age, preexisting osteoarthritis, and a longer duration of symptoms are risk factors for poor outcomes following surgical intervention for FAI syndrome [4].

References¶

[2] Aaos Comprehensive Orthopaedic Review 3. Nonarthroplasty Surgical Treatment of the Hip > I. Femoroacetabular Impingement.

[4] Orthopaedic Knowledge Update Sports Medicine 6. Femoroacetabular Impingement > Summary.

[5] Miller S Review Of Orthopaedics. SECTION 16 PATELLAR TRACKING IN TOTAL KNEE ARTHROPLASTY > FEMOROACETABULAR IMPINGEMENT > 2. Types (Fig. 4.33).

[7] Campbell S Operative Orthopaedics 4 Volume Set. ANTERIOR CRUCIATE AND ANTROLATERAL LIGAMENT RECONSTRUCTION (BOX 51.8) > FEMOROACETABULAR IMPINGEMENT.

[8] Orthopaedic Knowledge Update Sports Medicine 6. Hip Rehabilitation > Femoroacetabular Impingement Syndrome.

[9] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Pediatric Hip Disorders > Femoroacetabular Impingement.

[10] Campbell S Operative Orthopaedics 4 Volume Set. HIP PAIN IN THE YOUNG ADULT AND HIP PRESERVATION SURGERY > FEMOROACETABULAR IMPINGEMENT.

[12] Orthopaedic Knowledge Update Sports Medicine 6. Femoroacetabular Impingement > History.

[13] Orthopaedic Knowledge Update Sports Medicine 6. Core Muscle Injury/Athletic Pubalgia and Groin Pathology > Combined Athletic Pubalgia and Femoroacetabular Impingement.

[14] Orthopaedic Knowledge Update Sports Medicine 6. Femoroacetabular Impingement > Imaging > Plain Radiographs.

[16] Orthopaedic Knowledge Update. Slipped Capital Femoral Epiphysis and Femoroacetabular Impingement > Femoroacetabular Impingement > Epidemiology.

[17] Orthopaedic Knowledge Update Sports Medicine 6. Femoroacetabular Impingement > Types of Impingement > Extra-­articular Impingement.

[18] Orthopaedic Knowledge Update Sports Medicine 6. Femoroacetabular Impingement > Etiology.

[21] Orthopaedic Knowledge Update Sports Medicine 6. Femoroacetabular Impingement > Outcomes.

[22] Orthopaedic Knowledge Update 13 Ebook Without Multimedia. Early Degenerative Changes of the Hip > Femoroacetabular Impingement.

[23] Orthopaedic Knowledge Update Sports Medicine 6. Femoroacetabular Impingement > Physical Examination.