Femoroacetabular Impingement - Knee & Sports (2024)

• 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)

• 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

• labral degeneration and tears

• cartilage damage and flap tears

• secondary hip osteoarthritis

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

• 5 major muscle groups acting across hip

• hip flexors, extensors, abductors, adductors, and external rotators

• 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

• 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

• 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

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

      • < 42° considered normal

        • 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

      • > 0.17 considered normal

        See Also

        Femoroacetabular Impingement - OrthoInfo - AAOS

        • 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

• 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

Ischiofemoral impingment

adductor strains and athletic pubalgia

• 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 with quicker return to activity after arthroscopic surgery

    • decreased functional and symptomatic outcomes in patients with evidence of hip osteoarthritis (Tonnis grade 1 or greater) or subchondral edema on MRI

• 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

• 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

  • professional athletes without osteoarthritis are expected to return-to-play at the same level at a rate of >85-90%

• complications

  • trochanteric hip pain

• combines aspects of both procedures to gain access to entire femur and acetabulum

• early results promising

• 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

Residual deformity following arthroscopic treatment

• use of multiple fluoroscopy views

• symptoms

  • pain different than preoperative symptoms

  • pain or apprehension with hip extension and ER

  • loss of recoil with log roll

  • gross instability

• risk factor

  • no capsular closure

  • trauma

  • overaggressive rehab

  • failure to comply with ROM restrictions

• treatment

  • capsular repair

  • capsular reconstruction with graft

    • large, unrepairable defects