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Selective Posterior Epiphysiodesis of the Triradiate Cartilage of the Acetabulum: Preliminary Results of an Experimental Study in Rabbits

Background: Residual acetabular dysplasia is one of the main complications of developmental dysplasia of the hip (DDH). Without treatment, over time degenerative osteoarthritis of the joint will develop, inexorably leading to the need for joint replacement. Acetabular and/or femoral osteotomies do not avoid the appearance of osteoarthritis in a significant number of patients. The purpose of this study was to assess the possibility of provoking changes in the morphology of the acetabulum through selective epiphysiodesis of the extra-articular portion of the ilioischial arm of the triradiate cartilage, using a percutaneous cannulated screw with the guidance of an imaging intensifier in an experimental model in rabbits. Methods: In a pilot study, 3-week-old New Zealand rabbits (n = 20) were submitted to unilateral surgery of the hip while the contralateral hip of the same group was used as a control. Posterior epiphysiodesis to the triradiate cartilage of the acetabulum was performed by placement of a cannulated screw. The rabbits were followed-up until 18 weeks of life. Radiographic measurements of the hips were performed immediately postoperatively and at 12 weeks of life and before the rabbits were sacrificed at week 18. Three-dimensional computed tomography (3D-CT) scans were performed. Non-parametric tests for paired samples and the Wilcoxon test were used to compare the differences between group 1 and group 2. A p < 0.05 was considered significant. Results: The non-intervened hips showed that, when the rabbit matured, the acetabulum lost concavity and depth. When comparing the median differences of the angles evaluated at 12 weeks between groups, a statistically significant difference was found in all radiographic measurements: an increase in Wiberg’s angle but a decrease in acetabular index, acetabular angle of Sharp, acetabular depth index, and acetabular anteversion. Evaluating the operated hips at 12 and 18 weeks (three months after having removed the screw) using 3D-CT, we observed a rebound effect in the correction confirming that the effect obtained through selective epiphysiodesis did not cause the definitive closure of the cartilage. Conclusions: Selective growth arrest of the ilioischial arm of the triradiate cartilage (posterior epiphysiodesis) can alter growth and change the shape of the acetabulum in rabbits. A rebound effect was observed when the screw was removed, confirming that the technique did not provoke definitive closure of the physis. Level of evidence: Level-2, therapeutic study.