A new radiographic classification of 'three lines & one point’ for developmental dysplasia of the hip

Abstract

Objective To explore the clinical significance and inter-observer agreement of a new radiographic classification of three lines & one point for developmental dysplasia of the hip (DDH). Methods From January to June 2016, 69 DDH cases (90 hips) were hospitalized, including 17 boys and 52 girls with a mean age of 21(5-75) months. The involved sides were left (n=46) and right (n=44). All preoperative pelvic radiographs were collected. Three pediatric orthopedists were selected to classify all cases according to Ji SJ classification, three lines & one point' method, Tonnis classification and International Hip Dysplasia Institute classification. Inter-observer agreement was determined by the Kappa method. Three lines & one point' denotes Hilgenreiner (H) line, Perkin (P) line, superior lateral (S) line and Hilgenreiner (H) point. H-line is drawn bilaterally through the top of tri-radiate cartilages. And P-line lies perpendicularly to H-line at superolateral margin of acetabulum. Then S-line is parallel to H-line at superolateral margin of acetabulum. H-point is defined as the midpoint of superior margin of ossified metaphysis. To classify DDH in acetabula dysplasia, H-point is located at or medially to P-line; in hip subluxation, H-point is lateral to P-line and medial point of superior margin of ossified metaphysis (M-point) lies at or medially to P-line; in hip dislocation, M-point is lateral to P-line. For grading hip dislocation in grade I, H-point lies at or inferiorly to H-line; for grade Ⅱ, H-point between H- and S-lines or at S-line; for grade Ⅲ, H-point superior to S-line. Results Ninety hips in this cohort had total dislocations. Nucleus of femoral head was not ossified in 17 hips so that Tonnis classification remained invalid. The Kappa values for the above-mentioned four methods was 0.523±0.173, 0.786±0.223, 0.674±0.164 and 0.727±0.296 respectively (P=0.000 each). Conclusions The new radiographic classification of three line of one point method for DDH is readily comprehensible with some reference significance for its precise and individualized treatments. Key words: Developmental dysplasia of the hip; Femoral head; X-ray computed tomography