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- Static vs. Dynamic Exam
- Dynamic exam reveals subluxation during ROM
- Applications
- visual confirmation/quantification of disease in children with abnormal physical exams
- monitoring efficacy of Pavlik harness treatment (every 7-10 days)
- routine screening
- used commonly in Europe
- not cost effective
- Morphological assessment
- alpha angle - quantifies slope of superior aspect of acetabulum
- 0-12 wks: >50 degrees is normal
- 6-12 wks: > 60 degrees is normal
- beta angle - quantifies cartilaginous aspect of acetabulum; not extremely useful
- normal coverage: ~50%
- alpha angle - quantifies slope of superior aspect of acetabulum
Radiography:
- Plain radiographs should be used to confirm diagnosis at 4-6 weeks of age
- proximal femoral ossific center appears at 4-7 months
- radiographic lines
- Hilgenreiner's line
- Perkin's line
- medial metaphyseal beak and secondary ossification center should be located in inferior, medial quadrant of intersection of Perkin's line and Hilgenreiner's line
- Acetabular Index
- Useful in children 8 y/o or younger
- Acetabular angle of Sharp
- used after triradiate cartilage is closed
- Shentons line - should be intact on all views in patients older than 3-4 years of age
- Lateral center edge angle (of Wiberg)
- useful in children 5 y/o and older
- Anterior center edge angle (of Lequesne)
- For adult radiographic measurements, see the Hip Dysplasia page
- Other radiographic findings:
- absence of teardrop
- delayed appearance of femoral head ossification center or small ossification center
- Look for accessory centers of ossification in the acetabulum as the patient ages. Present in as many as 60% of DDH hips. They are likely stimulated by abnormal forces between the femoral head and acetabulum and contribure to the development of a more normal, deeper acetabulum.
MRI - Need for anesthesia limits utility
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- PavliK harness fails to reduce the hip in as many as 8% of cases
- AVN occurs in as many as 2.4% of cases splinted in the safe zone
- AVN incidence increases in open procedures with an incidence of
- 8% for antero-lateral approaches
- 10% for inguinal approaches
- 17% for the Ludloff (medial) approach
- 5% when shortening femoral osteotomy was combined with open reduction
- Salter indicators of AVN
- Failure of appearance of the ossific nucleus 1 year after reduction
- Failure of growth of an existing nucleus 1 year after reduction
- Broadening of femoral neck 1 year after reduction
- Increased radiographic density of the femoral head followed by radiographic appearance of fragmentation
- Residual deformity of head and neck when re-ossification is complete
- Coxa vara
- Coxa magna
- Coxa plana
- Coxa breva (short broad femoral neck)
- Pre-reduction traction and adductor tenotomy did not decrease the incidence of AVN
- Abduction into the frog position was the incriminating factor, causing compression of vessels of the trochanteric anastomosis and retinacular vessels
- Long term growth defect occurred in 0.7%
References
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