A Research On Evaluation Of The Outcomes Of Pelvic And Proximal Femoral Osteotomies For Treatment Of Perthes Disease By Using Computer Assisted Design Model

BACKGROUNDS: Pelvic and femoral osteotomies can be used in the treatment of Legg-Calvé-Perthes disease(LCPD),which were designed to improve the containment of femoral head and to restore the biomechanical environment of the affected hip joint.However,satisfactory containment could,in some cases,not be achieved while the over containment could lead to femoral acetabular impingement.The current study aimed to conduct a quantitative dynamic analysis of hip morphology using computer assisted design(CAD)model in order to evaluate the outcome of the surgeries and provide data for precise operative planning.METHODS: Data of patients with unilateral Perthes disease treated by pelvic and proximal femoral osteotomies were collected.CAD models of both affected and contralateral hip were established based on the data of CT scan on which morphological parameters were measured.Shape difference analysis of asymptomatic hips was adopted to locate the most apparent displacement and the main stream on the surface of proximal femur.RESULTS: Fifteen patients were included whose average age at initial consultations was 5.67 years old(range,3.5 to 8.5 years old).Thirteen of these patients are boys,while 10 left hips of all 15 cases were involved.The mean age of receiving operation was 6.63 years old(range,4.5 to 9 years old).There were 10 hips rated as Herring type C,and the rest were type B.The implantations were removed after an average duration of 9.3 months(range,6 to 17 months).Preoperative and postoperative CAD models of bilateral hips were established.As for ‘center to center' distance between femoral sphere and acetabular sphere,the measured values of the affected side were longer than the one of asymptomatic side(3.35±0.81 mm and 1.05±0.56 mm for preoperative and postoperative,respectively.).The difference of coverage area of femoral head surface between affected and asymptomatic side was bigger in preoperative model(511.12±97.28mm2 and 196.35±71.40mm2 for preoperative and postoperative,respectively.).Similarly,the difference of femoral head volume between affected and asymptomatic side was more evident in preoperative model(3266.14 ± 625.74mm3 and 1462.19±541.99mm3 for preoperative and postoperative,respectively.).Acetabular radius and the area of surface was not significant different between preoperative and postoperative models.The displacement happened mainly on superior and lateral superior femoral head where the stresses are concentrated.CONCLUSION: By the application of CAD model,it proved that the displacement happened mainly on superior and lateral superior femoral head where the stresses are concentrated.Pelvic and femoral osteotomies could effectively improve the superior and superoposterior area of acetabulum containment with increased femoral head volume.The short-term effect of the surgeries was satisfactory with Herring Type B and C cases.CAD model and shape difference analysis can provide better understanding of deformations of Perthes disease and more information for surgical planning and evaluation of treatment effects.