The document describes a new radiographic classification system called IHDI for classifying the severity of hip dysplasia. IHDI uses four grades based on the location of the femoral head center relative to the acetabulum. A study found IHDI had excellent reliability between raters, both experts and trainees, and was more reliable than the existing Tonnis method. IHDI could classify all hips, unlike Tonnis which could not classify 25% of hips that lacked ossification centers. The conclusion is IHDI provides a reliable new method for classifying hip dysplasia severity.

1. IHDI Classification of Hip
Dysplasia
Unni G. Narayanan, Kishore Mulpuri,
Charles T. Price, Pablo Castaneda, Nick
M.P. Clarke, Peter Cundy, Jose HerreraSoto, James R. Kasser, John H. Wedge
J Child Orthop (2011) 5 (Suppl1):S10

2. RADIOGRAPHIC CLASSIFICATION (IHDI)
• Based on lateral & proximal migration of hip adapted
from Tönnis method
• Hilgenreiner’s horizontal line (level of tri-radiate) instead
of superolateral margin of the acetabulum
• Perkins’ vertical line
• Diagonal line (45° line from junction of H & P lines)
• H-Point: center of the superior margin of metaphysis is
the center of the femoral head arc of rotation
• Supine AP x-ray of pelvis with the hips at rest while the
lower limbs are held gently in the neutral position
without traction and the patellae forward.

3. RADIOGRAPHIC CLASSIFICATION (IHDI)

4. H-Point at or medial
to Perkins’ line
H-Point lateral to D-Line
& at or inferior to H-line
H-Point lateral to P-Line
& at or medial to D-line
H-Point superior to H-line

5. RADIOGRAPHIC CLASSIFICATION (IHDI)
P LINE
H LINE
D LINE
IHDI GRADE III
IHDI GRADE I
H
POINT

6. AIM OF THE STUDY
• Test the reliability of the IHDI method of
radiographic classification of the severity of
hip displacement in DDH.
– Experts
– Trainees
• Compare the reliability of the IHDI method
with that of Tönnis classification

7. METHODS
• 20 standardized AP x-ray of the pelvis of children with
untreated DDH (n = 40 hips)
• Purposeful sample
– Age: New born to 24 months at presentation
– Full spectrum of severity
• Classified by Tönnis method & IHDI method
• 6 experienced pediatric orthopaedic surgeons from
– USA, Canada, United Kingdom, Australia, Mexico
– 2 (trained) senior Orthopaedic Residents
• Analysis: Inter-rater reliability was tested
– Intra Class Correlation coefficient (ICC) to measure
concordance between raters.

8. RESULTS
• All 40 hips were classifiable by the IHDI method
by all raters.
• 10 /40 (25%) of hips could not be classified by
the Tönnis method because of the absence of the
ossific nucleus.

9. RESULTS: RELIABILITY
• Inter-rater reliability: All raters
RELIABILITY
IHDI
TÖNNIS
RIGHT HIP
ICC (95% CI)
0.90
(0.83-0.95)
0.63
(0.46-0.80)
LEFT HIP
ICC (95% CI)
0.95
(0.91-0.98)
0.60
(0.43-0.78)
• There was no significant difference between the
ICCs of the 6 experts and two trainees.

10. CONCLUSIONS
• IHDI method is a new radiographic classification of
the severity of hip displacement in DDH
– Four grades
– Based on location of the center of the femoral head arc
of rotation (H-Point) relative to the acetabulum.
• IHDI method of classification has excellent interrater reliability both among experts and novices
• Reliability is superior to that of Tönnis method
• IHDI method can be applied reliably even when
the ossification centre is absent
– In conjunction with the ultrasound