Developmental Hip Dysplasia-MRI

A 9 month male baby has been felt to have clinically abnormal left hip with possible developmental dysplasia on the frontal radiograph with nondetectable femoral head. MR shows normal left femoral capital epiphysis, with possible delayed ossification ( not seen on the X-ray ) with dislocated position taking it to the upper and the outer quadrants of the intersection of hilgenreiner's line and perkin's lines with disturbed shenton's line with abnormal acetabular angle with normal capsule, labrum, ligamentum teres, iliopsoas tendon with mild free fluid and no AVN. Case submitted by Dr MGK Murthy, Mr Abdul Hamid, and Mr Sahadev Gupta.

Teaching points :

-        Developmental dysplasia of the hip is to be avoided with routine clinical examination at birth.

-        USG is a preferred modality till 6 months of age, when the femoral head shadowing may start interfering with acetabulum image ( femoral head starts ossification between 2 to 8 months ).

-        X-ray is the preferred modality after that with frontal projection and if needed frog leg positions ( Hip in flexion with external rotation )

-        MR is good for identified capsule, labrum, cartilage, presence of AVN and effusion, iliopsoas tendon compression, thick ligamentum teres and pulvinar hypertrophy.

-        Hilgenreiners (HG) line is the horizontal line between two triradiate cartilages.

-        Perkins line is perpendicular to HG and represents outer acetabular margin.

-        Shentons line is an extension of medial femoral metaphysis along the inferior edge of superior pubic ramus.

-        Acetabular angle is normally less than 28 degrees (decreases with age), and is measured as between HG and a line joining superolateral and inferomedial acetabular margins.