Purpose: The purpose of this study was to investigate the three-dimensional morphological features of the proximal femur of developmental dysplasia of the hip (DDH).
Methods: From January 2012 to December 2014, 38 patients (47 hips) of DDH were admitted and 30 normal hips were selected as controls. All hips from both groups were examined by CT scan. CT data were imported into Mimics 17.0. Three-dimensional models of the proximal femur were then reconstructed, and the following parameters were measured: neck-shaft angle, neck length, offset, height of the centre of femoral head, level of isthmus, height of the tip of greater trochanter, the medullary canal diameter of isthmus(Di), the medullary canal diameter 10 mm above the apex of the lesser trochanter(DT + 10), the medullary canal diameter 20 mm below the apex of the lesser trochanter(DT-20), and then DT + 10/Di, DT-20/Di and DT + 10/DT-20 were calculated.
Results: There was no significant difference in neck-shaft angle between Crowe I, Crowe II-III DDH and the control group, while the neck-shaft angle was much smaller in Crowe IV DDH. The neck length of Crowe IV DDH was also much smaller than those of Crowe I and Crowe II-III DDH. Height of the tip greater trochanter in Crowe IV was greater than that in Crowe I, Crowe II-III DDH and the control group. The centre of femoral head in Crowe IV DDH was lower than those in Crowe I, Crowe II-III DDH and the control group. The level of isthmus in Crowe IV was much higher than those in Crowe I, Crowe II-III DDH and the control group. DT + 10, DT-20, DT + 10/Di and DT-20/Di were much smaller in Crowe IV DDH than those in Crowe I, Crowe II-III and the control group.
Conclusions: Neck-shaft angle in the DDH groups was not larger than that in the control group. Comparing to Crowe I, Crowe II-III DDH and the control group, Crowe IV DDH had a dramatic change in the intramedullary and extramedullary parameters, especially the dramatic narrowing of medullary canal around the level of the lesser trochanter. The on-shelf modular prosthesis may not be an ideal choice for the Chinese patients with Crowe IV hips.
Keywords: Crowe type IV; Developmental dysplasia of the hip; Femoral deformity; Total hip arthroplasty.