Femoroacetabular Impingement

Other Names

• FAI
• Femoral Acetabular Impingement
• Originally described by Ganz
• Challenging to estimate prevalence, incidence
  • Radiographic and clinical findings do not always match up
• Frank et al estimates in asymptomatic individuals
  • Prevalence of cam deformity: general (23.1%), athletes (54.8%)
  • Prevalence of pincer deformity: general (67%)
• In symptomatic individuals
  • Nepple et al: FAI in 94% of NFL combine athletes
  • Mascarenhas et al: prevalence of cam impingement 49%

Pathophysiology

• The dynamic phenomenon of unclear etiology that leads to hip joint damage
  • Related to abnormal hip morphology, motion
  • The exact etiology remains unclear
• Cam-type lesions (femoral head-neck junction)
  • Refers to femoral head based pathology
  • Cause impingement to due to abnormal shaped femoral head rotates within the acetabulum
  • Particularly worse during forced flexion
  • Produces shearing forces of the Acetabular Labrum, most commonly anterior-superior
  • Worsened by increased α angle
  • Large cam lesions are associated with increased acetabular cartilage, labral damage
  • More common in young, mostly male athletes
• Pincer-type lesions (acetabular rim)
  • Characterized by acetabular over coverage
  • Can be described as local (acetabular retoversion) or global (coxa profunda or protrosio)
  • Impingement occurs due to abnormal contact of the acetabular rim, femoral head-neck junction
  • Leads to labral injuries initially, subsequent chondral injuries
  • More common inactive, middle-aged women
• Mixed pathology
  • A combination of cam- and pincer-type deformity is most common
  • Can occur individually, but less commonly so
• Radiographic studies
  • Murray et al: athletes participating in “aggressive athletic activities” at a younger age are more likely to have proximal femoral deformities
  • Sienbrock et al: increased alpha angle on MRI of elite basketball players with open physics compared to controls
  • Agricola et al: Among adolescent soccer players, the prevalence of cam lesion increased from 7.1% to 22.2%, and normal appearing head-neck junction decreased from 84.1% to 43.2% over 2.4 years of follow up
• Developmental
  • Sienbrock et al: physeal abnormalities could alter femoral head-neck relationship

Associated Injuries

• Hip Osteoarthritis
• Acetabular Labrum Tear
• Childhood history of:
  • Legg-Calve-Perthes Disease
  • Slipped Capital Femoral Epiphysis

• Hip Joint
  • Acetabulum formed by the confluence of ischium, ilium, pubic bones
  • Femoral Head sits on neck, anteverted 15° in relation to femoral condyles

• Genetic
  • Risk increases by 2.0-2.8 in sibling studies^[12]
• White race^[13]
• Sports
  • Hockey (10 fold)^[14]
  • Basketball (4 fold)
  • Soccer^[15]
  • Football^[16]

Differential Diagnosis

• Fractures And Dislocations
  • Pelvic Fracture
  • Hip Fracture
  • Acetabular Fracture
  • Femoral Neck Stress Fracture
  • Pelvic Stress Fracture
  • Hip Dislocation

• Arthropathies
  • Osteitis Pubis
  • Avascular Necrosis of the Hip
  • Hip Osteoarthritis
  • Femoroacetabular Impingement
  • Transient Osteoporosis of the Hip

• Muscle and Tendon Injuries
  • Hip Flexor Tendonitis
  • Piriformis Syndrome
  • Hamstring Strain
  • Proximal Hamstring Tendinopathy
  • Adductor Strain
  • Greater Trochanteric Pain Syndrome

• Bursopathies
  • Iliopsoas Bursitis
  • Ischial Bursitis

• Ligament Injuries
  • Acetabular Labrum Tear

• Neuropathies
  • Meralgia Paresthetica

• Other
  • Snapping Hip Syndrome
  • Septic Arthritis
  • Gout
  • Leg Length Discrepancy
• Pediatric Pathology
  • Transient Synovitis of the Hip
  • Developmental Dysplasia of the Hip (DDH)
  • Legg-Calve-Perthes Disease
  • Slipped Capital Femoral Epiphysis (SCFE)
  • Avulsion Fractures of the Ilium (Iliac Crest, ASIS, AIIS)
  • Ischial Tuberostiy Avulsion Fracture
  • Avulsion Fractures of the Trochanters (Greater, Lesser)
  • Apophysitis of the Ilium (Iliac Crest, ASIS, AIIS)

Diagnosis

• History
  • Inquire about prior trauma, previous hip pathology including Legg-Calve-Perthes Disease, Slipped Capital Femoral Epiphysis
  • Characterize type, intensity and frequency of athletic activity
  • Majority of patients endorse insidious onset related to activity^[17]
  • Groin pain is common in addition to hip pain
  • Pain often worse with hip flexion, difficulty sitting
• Physical Exam: Physical Exam Hip
  • Diminished internal rotation with the hip flexed to 90°, correlates to the severity of the lesion
• Special Tests
  • C Sign: patient cups hand over greater trochanter when asked to describe pain, suggesting deep, interior hip pain
  • FABER Test: flexion, abduction, external rotation
  • FADIR Test: flexion, adduction, internal rotation
  • Posterior Rim Impingement Test: Extend affected leg off the table, then abduct and externally rotate
  • Dynamic Internal Rotatory Impingement Test: flex the unaffected knee to 90°, then FADIR through an arc of motion
  • Dynamic External Rotatory Impingement Test: flex the unaffected knee to 90°, then FABER through an arc of motion

Radiographs

• Standard Radiographs Hip
  • Should include a PA, lateral view
  • Consider frog-leg, cross-table lateral
  • 45 degree Dunn lateral provides the most information for FAI^[19]
• Alpha angle (for cam deformity)
  • Most commonly used quantitative measurement for cam impingement
  • Determined by fitting a circle to the femoral head and connecting a line from the center of this circle to the center of the femoral neck^[20]
  • Second-line drew from the center of a circle to the superior head-neck junction outside the circle
  • No standardization of normal ranges from 42-63°
  • No agreement of the threshold for pathology ranges from 50-62°
  • The increasing threshold to 60° increased specificity to 74%, sensitivity to 76.5%^[21]
• Pincer deformity
  • Look for detection of retroversion, focal over coverage, and global overcoverage^[22]
  • Crossover sign: the anterior rim of the acetabulum crosses the line of the posterior aspect of the rim before reaching the lateral edge of the sourcil^[23]
  • Posterior wall sign: center of the femoral head is lateral to the posterior wall^[24]
  • Lateral center-edge angle: AP view, the angle is calculated by a line through the center of the femoral head, perpendicular to the transverse axis of the pelvis, and a line from the center of the head through the most superolateral point of the weight-bearing zone of the acetabulum^[25]

MRI

• Helpful to evaluate cartilage, labrum
• Degree of chondral injury predictive of patient outcomes and satisfaction^[26]

CT

• Helpful to better clarify osseous architecture
• Useful for surgical planning, especially with 3D surface rendering

Classification

• General
  • Head-neck junction (cam lesion)
  • Acetbular rim (pincer lesion)
  • Both or mixed

Treatment

Prognosis

• Palmer et al: Patients with symptomatic FAI referred to secondary or tertiary care achieve superior outcomes with arthroscopic hip surgery than with physiotherapy and activity modification.^[27]

Nonoperative

• Indications
  • Minimally symptomatic or no mechanical symptoms
• Activity modification
  • Individualized to patients athletic demands and symptoms
  • Exacerbating movements and activities should be avoided
• NSAIDS

Injections

• Khan et al systematic review^[28]
  • US guidance better tolerated than fluoroscopic guidance
  • Lack of response strong predictor of poor surgical outcome
  • Corticosteroid Injection: improvement in only 15% of patients at 6 weeks
  • Hyalouronic Acid provided relief at up to 12 months, superior to CSI

Operative

• Indications
  • Symptomatic
  • Failure of non-op
  • Non-arthritic joint
• Technique
  • Arthroscopic osteoplasty (preferred)
  • Open osteoplasty
  • Periacetabular osteotomy
  • Total hip arthroplasty