Updated: 11/17/2019

Femoroacetabular Impingement

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https://upload.orthobullets.com/topic/3130/images/cam.jpg
https://upload.orthobullets.com/topic/3130/images/pincer.jpg
https://upload.orthobullets.com/topic/3130/images/camanatomy.jpg
Introduction
  • Overview
    • abnormal contact between the femur and acetabulum which leads to labral damage and various degrees of chondral injury
  • Epidemiology
    • femoral and acetabular deformity common in general population and often asymptomatic
    • may become more apparent with participation in activities requiring extreme range of motion (ballet, gymnastics, martial arts)
  • Pathophysiology
    • mechanism of injury
      • proximal femur abuts acetabulum with range of motion, especially during flexion 
    • pathoanatomy
      • Cam impingement
        • refers to femoral based disorder usually in young athletic males
        • occurs if femoral head/neck bone is too broad, mostly on the anterolateral neck 
        • characterized by any of the following 
          • decreased head-to-neck ratio
          • aspherical femoral head
          • decreased femoral offset
          • femoral neck retroversion
        • this sphericity mismatch causes shearing at the chondro-labral junction, leading to cartilage delamination and labral separation
      • Pincer impingement
        • refers to acetabular based disorder usually in active middle-aged women
        • occurs if acetabular bone/labrum overhang is too broad, mostly at the anterosuperior quadrant 
          • anterosuperior acetabular rim overcoverage
          • acetabular retroversion
          • acetabular protrusio
          • coxa profunda
        • the femoral neck impinges and crushes the labrum creating intra-substance tearing
        • this levers the femoral head into the postero-inferior acetabulum leading to a contrecoup cartilaginous injury
      • combined Cam/Pincer impingement
      •  
        • can include both patient populations
        • refers to combinations of above (up to 80%)
        • SCFE deformity causes variable patterns of impingement
  • Associated injuries 
    • labral degeneration and tears
    • cartilage damage and flap tears
    • secondary hip osteoarthritis
  • Prognosis
    • natural history believed to lead to early onset hip dysfunction and arthritis
 
Anatomy 
  • Osteology  
    • highly congruous joint formed by
      • Acetabulum  
        • formed by confluence of ischium, ilium and pubic bones
      • Femur
        • spherical head on neck, anteverted 15 degrees in relation to femoral condyles
  • Muscles
    • 5 major muscle groups acting across hip
    • hip flexors, extensors, abductors, adductors, and external rotators
  • Capsule and Ligaments
    • 3 ligaments of the form joint capsule
      • iliofemoral ligament (Y ligament of Bigelow)
      • ischiofemoral ligament
      • pubofemoral ligament
    • labrum
      • horseshoe-shaped fibrocartilaginous tissue extending around periphery of acetabulum
      • connected by transverse acetabular ligament at inferior acetabulum
      • increases acetabular volume and provides suction seal
    • ligamentum teres
      • extends from cotyloid fossa to femoral head
      • negligible contribution to vascular supply of femoral head in adult
Presentation
  • Symptoms
    • common symptoms
      • activity related groin or hip pain, exacerbated by hip flexion
      • difficulty sitting
      • mechanical hip symptoms of clicking or popping
      • can present with gluteal or trochanteric pain
        • due to aberrant gait mechanics
  • Exam
    • motion
      • limited hip flexion (<90 degrees), especially with internal rotation (<5 degrees)
      • anterior impingement test (flexion, adduction, internal rotation) elicits pain 
    • inspection
      • externally rotated extremity
        • can be due to post-SCFE deformity
Imaging
  • Radiographs 
    • recommended views
      • AP with true lateral view (hip placed in 15 degrees of internal rotation)
    • optional views
      • Dunn or modified Dunn view
      • false profile view 
        • to assess anterior coverage of the femoral head
        • standing position at an angle of 65° between the pelvis and the film 
    • findings
      • asphericity and contour of femoral head and neck
        • pistol grip deformity 
          • indicates Cam impingement
      • examine for acetabular protrusio, retroversion, and coxa profunda
        • crossover sign
          • indicates acetabular retroversion in Pincer impingement 
        • posterior wall sign
    • measurements
      • alpha angle  
        • method
          • measured frog-leg lateral radiograph
          • first line is drawn connecting the center of the femoral head and the center of the femoral neck.
          • second line is drawn from the center of the femoral head to the point on the anterolateral head-neck junction where prominence begins
          • the intersection of these two lines forms the alpha angle
        • normal values
          • values of >42° are suggestive of a head-neck offset deformity, >50-55° indicates Cam deformity
      • head-neck offset ratio  
        • method
          • measured from lateral radiographs
          • a
            line #1 is drawn through the center of the long axis of the femoral neck
          • line #2 is drawn parallel to line 1 through the anteriormost aspect of the femoral neck
          • line #3 is drawn parallel to line 2 through the anteriormost aspect of the femoral head
          • the head-neck offset ratio is calculated by measuring the distance between lines 2 and 3, and dividing by the diameter of the femoral head
        • normal values
          • If the ratio is <0.17, a cam deformity is likely present
      • lateral center-edge angle (angle of Wiberg) 
        • normal value under 40 degrees
      • anterior center-edge angle 
        • normal value over 20 degrees 
      • acetabular index or Tonnis roof angle 
        • normal value above 0 degrees
  • CT
    • can be used as adjunct to assess for structural abnormalities
  • MRI and/or MR arthrogram 
    • best modality to evaluate for articular cartilage and labral damage
    • can assess anatomy of femoral head/neck junction abnormalities
Differential 
  • Various pathologies will refer pain to the hip region
    • hip instability
    • iliopsoas pathology
    • adductor strains
    • lumbar radiculopathy
Treatment
  • Nonoperative
    • activity modification, PT, NSAIDs
      • indications
        • minimally symptomatic patient
        • no mechanical symptoms
      • modalities
        • period of rest or activity modification followed by physical therapy to address kinetic chain abnormalities
        • NSAIDs
  • Operative 
    • arthroscopic osteoplasty 
      • indications
        • symptomatic patient with mechanical symptoms
        • failure of non-operative measures
        • non-arthritic
      • outcomes
        • recent literature supports arthroscopy shows equivalent results to open hip surgery
    • open surgical hip dislocation and osteoplasty
      • indications
        • previous gold standard for patients with clinical signs and structural evidence of impingement
        • preserved articular cartilage, correctable deformity, reasonable expectations
        • significant femoral deformity (residual SCFE or Perthes)
    • periacetabular osteotomy 
      • indications
        • structural deformity of acetabulum with significant retroversion
    • hip arthroplasty 
      • indications
        • arthritic and end-stage hip degeneration
        • controversial regarding hip resurfacing versus total hip arthroplasty
Techniques
  • Arthroscopic osteoplasty
    • approach
      • arthroscopic approach to the hip 
    • soft tissue
      • capsulotomy required to access peripheral component to address CAM
      • labral repair/refixation required following acetabuloplasty if labrum is destabilized
    • bony work
      • trim femoral head/neck in Cam impingement 
      • acetabular rim trimming followed by labral debridement vs repair/reconstruction 
        • isolated labral debridement of labral tears will not provide long-term benefit without treatment of underlying bony pathology 
    • outcomes
      • equivalent success compared to open procedure
    • complications
      • neurapraxias associated with hip arthroscopy
  • Ganz open surgical hip dislocation and osteoplasty 
    • approach
      • Kocher-Langenbeck incision while in lateral decubitus position, gluteus maximus split
      • digastric "trochanteric flip" performed and fragment mobilized anteriorly
      • capsulotomy performed, hip dislocated anteriorly, ligamentum teres likely transected
      • allows safe access to proximal femur and acetabulum
      • alternatively, a direct anterior approach may be utilized but grants limited visualization to posterior acetabulum
    • bony work
      • same as arthroscopic osteoplasty
    • soft tissue
      • labral repair/refixation/reconstruction required following acetabuloplasty if labrum is destabilized
    • outcomes
      • provides wide exposure of femoral head and acetabulum while preserving all external rotators and blood supply to femoral head (medial circumflex femoral artery)
      • no increase in AVN risk
      • median expected time to return to sports is 7 months in adolescent athletes
    • complications
      • trochanteric hip pain
  • Combined arthroscopic and limited open approach
    • combines aspects of both procedures to gain access to entire femur and acetabulum
    • early results promising
Complications
  • Femoral neck fracture
    • at risk during femoroplasty
    • risk is minimized by limiting depth of femoral head-neck osteoplasty to <30% of femoral neck diameter, using multiple fluoroscopy views of femoral neck during procedure
  • Heterotopic ossification
  • Residual deformity following arthroscopic treatment 
    • use of multiple fluoroscopy views
 

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(OBQ11.259) In the radiographic evaluation of femoroacetabular impingment (FAI), which of the following views is obtained with a standing radiograph and an angle of 65 degrees between the pelvis and the film? Review Topic

QID: 3682
1

AP pelvis

2%

(89/5289)

2

Inlet

5%

(266/5289)

3

Outlet

3%

(157/5289)

4

Frog lateral

5%

(285/5289)

5

False profile

85%

(4475/5289)

L 1

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(SAE07HK.44) Figure 24 shows the radiograph of a 36-year-old volleyball player with right hip pain. What is the cause of the pain? Review Topic

QID: 6004
FIGURES:
1

Osteonecrosis

1%

(2/218)

2

Rheumatoid arthritis

0%

(1/218)

3

Developmental dysplasia of the acetabulum

3%

(7/218)

4

Femoral neck fracture

0%

(1/218)

5

Femoral acetabular impingement

94%

(205/218)

L 1

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(SAE07HK.35) A patient reports pain in the hip with functional positioning. With the patient supine, pain in which of the following positions would be typical for femoral acetabular impingement? Review Topic

QID: 5995
1

Hip is internally rotated, passively flexed to 90 degrees, and adducted

75%

(156/209)

2

Hip is internally rotated, passively flexed to 90 degrees, and abducted

10%

(20/209)

3

Hip is externally rotated, maximally flexed to 90 degrees, and adducted

2%

(5/209)

4

Hip is externally rotated, passively flexed to 90 degrees, and abducted

11%

(23/209)

5

Hip is externally rotated, maximally flexed, and abducted

1%

(3/209)

L 2

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