A Statistical Shape Model-Based Analysis of Periacetabular Osteotomies: Technical Considerations to Achieve the...

Classic and reverse Bernese periacetabular osteotomy (PAO) have been shown to be effective for the treatment of developmental dysplasia of the hip (by classic PAO), severe acetabular retroversion (by reverse PAO), and some protrusio acetabuli (by reverse PAO). Especially in severe cases with higher degrees of correction, a relevant overlap between the osteotomized fragment and the pelvis might occur, leading to necessary fragment translation. The aim of the present study was to analyze the necessary translation as a function of the degree of correction using a statistical mean model of the pelvis according to the technique (classic PAO or reverse PAO).

A mean statistical shape model of the pelvis and 2 extreme models were used to simulate rotation of the osteotomized fragment during a classic or reverse PAO and to calculate rotations from -20° to 20° in the frontal, sagittal, and transverse planes and a combination thereof. The depth and volume of the intersection between the mobilized fragment and the pelvis were calculated, and the minimum translation of the fragment necessary to avoid segment overlap was determined.

The maximum intersection distances between the pelvis and the 20° rotated fragment were 6.7 and 15.3 mm for adduction and abduction (frontal plane), 6.4 and 4.5 mm for internal and external rotation (transverse plane), and 27.8 and 9.2 mm for extension and flexion (sagittal plane). The necessary translations for 20° of fragment rotation were 7.0 and 12.8 mm for adduction and abduction (frontal plane), 4.8 and 5.0 mm for internal and external rotation (transverse plane), and 18.5 mm and 8.8 mm for extension and flexion (sagittal plane).

Acetabular reorientation with the classic or reverse PAO results in translation of the fragment and in a consequent change in the rotational center. This finding is more pronounced with higher degrees of fragment reorientation in abduction and extension; it becomes especially pronounced in reverse PAO for acetabular retroversion or protrusio acetabuli, and might limit the ability to achieve the intended improvement in overall hip biomechanics.