Femoroacetabular Impingement

Original Editor - Douglas Wix

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Clinically Relevant Anatomy

File:Interactive hip - hip - L5F1.jpg

© Primal Pictures

The hip (acetabulofemoral joint) is a synovial joint formed by articulation between the femur and acetabulum of the pelvis. The head of the femur is cover by type II collagen (Hyaline cartilage) and proteoglycan. The acetabulum is the concaved portion of the ball and socket joint. The acetabulum has a ring of fibrocartilage called the labrum that deepens the acetabulum and improves stability of the hip joint. The hip joint is very stable because of the congruence of the femoral head and acetabular labrum as well as the five ligaments that surround the joint. The three extracapsular ligaments are the iliofemoral, ischiofemoral, and pubofemoral ligament attached to the bones of the pelvis. The ligamentum teres (intracapsular ligament) is attached to the acetabular notch and the femoral head.
There are a variety of pathoanatomical lesions that may be the cause of hip and groin pain in athletes. Recently femoroacetabular impingement has been recognizes as a possible cause of hip pain. Femoroacetabular impingement can be subdivided into a CAM or pincer impingement, although both typically occur together. CAM impingement is characterized by morphological abnormality of the superior-anterior aspect of the femoral head-neck junction. This increase in bone results in impingement of the superior-anterior aspect of the femur with the superior-anterior aspect of the acetabulum. Pincher impingement is characterized by excessive bone growth of the superior-anterior aspect of the acetabulum which results in impingement in the same area as the CAM lesion. Both CAM and pincher impingement typically result in cartilage delamination and labral lesions. Either Cam or pincher impingement can cause significant disability with athletic activities and/or ADL’s.

Mechanism of Injury / Pathological Process

Pathological Process CAM Type FAI

• Abnormal morphology of the anterior femoral head–neck junction.
• Prominence of the femoral head-neck junction in the anterior/anterosuperior portion of the proximal femur is known as the “pistol grip deformity"
• Younger males. 
• Prominence femoral head-neck junctions produces intermittent and consistent stress (the cam effect) on the associated articular cartilage.
• The shear forces cause damage to both the acetabular labrum and the articular cartilage of the femoral head and acetabulum.

Pathological Process PINCER Type FAI

• Abnormal acetabulum contacting a normal femur.
• Usually presents in elderly women.
• This can be due to increased acetabular anteversion or coxa profunda.
• Acquired causes can be acetabular protrusio or postsurgical prominent anterosuperior acetabulum.
• Acetabular retroversion: may be seen as a result of trauma or as part of acetabular dysplasia (either in isolation or part of a complex). 
• The acetabular labrum is the first structure to be effected.
• The repetitive impact results in degeneration of the labrum with intrasubstance ganglion formation or ossification of the acetabular rim.
• Ossification can lead to further deepening of the acetabulum and therefore more overcoverage of the femoral head by the acetabulum.
• When cartilage lesions do occur with pincer impingement they are typically focal and involve small areas of the acetabular rim

Clinical Presentation

Clinical Findings:

• Estimated prevalence: 10-15%
• Onset of hip pain usually in the young 20-40 y/o, usually unilateral
• CAM type: Male:Female 14:1 (avg age: 32).
• Pincer type: Male:Female 1:3 and usually middle age women (avg age: 40)
• Present with groin pain with hip rotation, in sitting position, or during/after sports
• Typically aware of limited hip mobility long before sx.
  

Clinical exam:

• Loss of internal rotation out of proportion to the loss of range of movement at other positional extremes.
• Osteoarthosis will usually produce a universal limited range of motion.
• A grinding and popping sensation can be felt when the femur is externally rotated when the hip is maximally abducted
• Restricted range of motion, particularly flexion and internal rotation
• Positive impingement test: for anterior femoroacetabular impingement if forced internal
• rotation/adduction in 90 degreea of flexion reproduces pain.
• For posterior impingement: painful forced external rotation in full extension with legs hanging off the end of table and uninvolved leg flexed.
• Drehmann’s sign: unavoidable passive external rotation while performing hip flexion.
  

Diagnostic Procedures

The contour of the femoral head-neck junction as a predictor for the risk of anterior impingement.  Using standardised MRI, the symptomatic hips of patients who have impingement have significantly less concavity at the femoral head-neck junction than do normal hips. This test may be of value in patients with loss of internal rotation for which a cause is not found. 

Outcome Measures

Harris Hip Score (HHS) 

Non-arthritic Hip Score 

Management / Interventions

Surgical management for Femoroacetabular Impingment. 

Differential Diagnosis

Acute hip pain due to tumore, infection, septic arthritis, osteomyelitis, or an inflammatory condition, fracture, and avascular necrosis are all "red flag" conditions that should be ruled out. 

Resources

http://blog.evidenceinmotion.com/evidence/files/Tanzer-ClinOrthopRelRes-2004-HipPainLabralTearOA.pdf

http://www.hss.edu/conditions_Hip-Mobility-Arthroscopy-Patient's-Guide-Femoro-Acetabular-Impingement.asp

Presentations

Evidence Based Treatment of the Hip: FAI This presentation, created by Bridgit Finley as part of the Evidence In Motion OMPT Fellowship in 2012, discusses the evidence based treatment for the hip and specifically for femoral-acetabular impingement. View the presentation