Femoroacetabular Impingement - Knee & Sports

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
- indications
  - can be used as adjunct to assess for structural abnormalities
- views
  - 3D reconstructions aid in pre-operative assessment
MRI and/or MR arthrogram
- indications
  - best modality to evaluate for articular cartilage and labral damage
  - can assess anatomy of femoral head/neck junction abnormalities
- views
  - ensure MRI is formatted to be in-line with femoral neck
- findings
  - labral fraying or frank tears, chondral damage, subchondral cyst formation

Differential

Various pathologies will refer pain to the hip region
- hip instability
- iliopsoas pathology
- Ischiofemoral impingment
- adductor strains and athletic pubalgia
- 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
    - decreased functional and symptomatic outcomes in patients with evidence of hip osteoarthritis (Tonnis grade 1 or greater)
- 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