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Femoroacetabular impingement and snapping hip

Femoroacetabular impingement and causes of audible snapping on hip flexion.

14 questions 2 source pages 1 fact-check flags

Images appear with the first question taken from each source page — tap a question to open it.

14 questions
Q1What are the X-ray findings in femoroacetabular impingement?▸
  • Cam lesion at the femoral neck: pistol grip appearance, decreased neck offset, aspherical head (SCFE, Perthes, fracture malunion)
  • Pincer lesion: anterosuperior acetabular rim overhanging
  • Retroversion: cross cover sign, posterior wall medial to femoral head centre, prominent ischial spine
  • Coxa profunda vs protrusio (head medial to ilioischial line); excessive CEA
Q2What are the symptoms and signs of FAI?▸
  • Previous injury or childhood hip problems
  • Mechanical hip pain, difficulty sitting, pain in flexion and internal rotation
  • PE: limited flexion and IR; positive anterior impingement test (FADDIR)
Q3Describe the alpha angle and its normal and abnormal values.▸
  • Angle between the central axis of the femoral neck and the line from femoral head centre to where the head loses sphericity
  • Normal <42 degrees; >42 degrees suggestive of head-neck offset deformity
  • >50-55 degrees indicates cam deformity
Q4What other radiographic measurements are used in FAI?▸
  • Head-neck offset ratio: draw 2 lines parallel to neck central axis, one touching anterior head and one touching anterior neck, difference of the 2 lines divided by head diameter; >0.17 normal
  • CEA >40; anterior CEA >20; herniation pit
  • False profile view (pelvis 65 degrees from film) for anterior CEA
  • Dunn view (hip flexion 90, abduction 20, neutral rotation) for CAM
Q5What is the role of CT and MRI/MR arthrogram in FAI?▸
  • CT: bony architecture, measure alpha angle
  • MRI/MR arthrogram: labral injury (more in pincer lesion), cartilage injury (more in cam lesion)
  • Countercoup lesion (unfavorable as difficult to attach posterior pathology)
Q6What are the treatment options and what does hip arthroscopy involve?▸
  • Conservative: NSAIDs, physiotherapy
  • Operative: arthroscopic cam trim +/- labral debridement/repair; Ganz surgical dislocation; periacetabular osteotomy; THR
  • Hip arthroscopy: GA/SA on traction table, ~50 lb traction (pudendal nerve risk), X-ray guidance, 70 degree scope
  • Risks: direct cartilage injury, HO, instability from iatrogenic capsular deficiency (prevented by meticulous capsulotomy and closure/plication)
  • Nerve risks: pudendal (traction), superior gluteal (anterolateral portal), lateral cutaneous nerve of thigh/femoral vessels (anterior portal), sciatic (posterolateral portal), LFCA ascending branch
Q7What are the indications for hip arthroscopy?▸
  • Intra-articular: FAI/labral lesion, chondral lesion, loose bodies, synovial disease
  • Extra-articular: AIIS impingement, capsular tear, iliopsoas pathology
Q8What are the compartments examined in hip arthroscopy and which require traction?▸
  • Central (intra-articular): acetabular rim and fossa, femoral head, AIIS, capsule - requires traction
  • Peripheral (lateral to labrum): HN junction, iliopsoas, zona orbicularis, medial synovial fold - no traction needed
  • Lateral (peritrochanteric): ITB, trochanteric bursa - no traction
  • Deep gluteal: piriformis, ischial tuberosity (hamstring origin) - no traction
Q9What are the portals used in hip arthroscopy?▸
  • Anterolateral portal first (primary viewing portal): 2cm anterior and superior to anterosuperior corner of GT
  • Anterior portal (central viewing): intersection of vertical line from ASIS and superior ridge of GT
  • Distal anterolateral (peripheral viewing): 3-5cm distal to anterolateral portal
  • Posterolateral (posterior viewing): 1cm posterior and superior to GT
Q10What is coxa saltans and who is affected?▸
  • Snapping sound on hip flexion
  • Common in athletes and dancers in their teens/20s
  • Usually the patient can reproduce the symptoms; +/- pain
Q11What are the causes of external, internal and intracapsular snapping hip?▸
  • External: posterior IT band sliding over greater trochanter; glut max (gluteus maximus; repeated gluteus injections -> contracture/fibrosis); fibrotic bursa; exostosis
  • Internal: iliopsoas (prominent iliopectineal ridge, page over femoral head, iliopsoas bursa, lesser trochanter exostosis)
  • Intracapsular: loose body, synovial chondromatosis, labral tear
Q12How do you examine a snapping hip?▸
  • External: visible snap; pressing on the greater trochanter abolishes it; Ober’s +ve (limited adduction when hip placed in extension)
  • Internal: audible snap when hip moves from flexed + ER to extended + IR
Q13What investigations are used for snapping hip?▸
  • X-ray (looking for chondromatosis)
  • USG (dynamic assessment)
  • MR arthrogram (rule out loose body/labral tear)
  • Iliopsoas bursography
Q14What is the management of snapping hip?▸
  • Nonoperative: activity modification, physiotherapy, steroid injection
  • USG-guided injection (GT bursa, iliopsoas sheath, intra-articular)
  • Operative: excision of GT bursa with Z-plasty of ITB; release of iliopsoas tendon; resect lesser trochanter (distal part only); removal of loose body or labral repair

Fact check

Alpha angle normal <42 degrees; >42 degrees is suggestive of a head-neck offset deformity — Misleading threshold: 42 degrees is the mean in normal controls, not a diagnostic cutoff — The usual diagnostic cutoff for cam morphology is >55 degrees (50 widely used); recent syntheses suggest 57-60 degrees and many normal hips exceed 42 degrees — source
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