The Relationship Between The Angle Of Femoral Varus And The Length Of Shortening After The Proximal Femur Osteotomy In Children

Objective:To investigate developmental dysplasia of hip?DDH?used locking compression pediatric hip plate?LCP-PHP?proximal femoral varus osteotomies the relationship between the varus angle and the femoral shortening length.Methods:Total of 55 patients?55 hips?with DDH used LCP-PHP proximal femoral varus osteotomies in our hospital from July 2013 to June2017 were enrolled in this study.All the preoperative and postoperative internal rotation hips x-ray film was collected.The hip joint X-ray,including12 males and 43 females;were from 2 years to 10 years old,an average of 5.6years old;left 30 cases,right 25 cases.The radiographs were brought into the Digimizer software to measure the proximal femoral shortening length??S?for each child by direct measurement.According to the geometrical relationship analysis of the operation procedure,the trigonometric function formula of proximal femur shortening length was derived as c?sin?₁-sin?₂?,c is the center of the femoral head to the most medial point of the proximal femur,?₁ is the angle between preoperative c and the osteotomy line,?₂ is the angle between c and the osteotomy line after varus osteotomy.The required parameters for the calculation were measured by the Digimizer software,and the results were taken into the derived calculation to obtain the proximal femur shortening length??S'?.Bland-Altman consistency analysis and Pearson correlation analysis between direct measurement method and calculation method are performed to verify the feasibility of the formula.Results:The 55 patients with DDH had direct measurement and calculation formula for the length of femoral shortening after varus osteotomy were:varus angle<10°,shortening length were?1.93±0.82?mm and?1.94±0.81?mm,respectively;varus angle of 10°to 20°were?6.11±2.12?mm and?6.16±2.11?mm,respectively;varus angle>20°were?9.97±2.49?mm and?9.96±2.37?mm,respectively.There was no significant difference between direct measurement method and calculation method c and proximal femur length?P>0.05?.The Bland-Altman analysis of these radiographs revealed that the 95%limits of agreement between femoral shortening length by the algorithm and direct measurement were between–0.80mm and+0.74 mm.The mean bias is–0.03mm.The results showed a high agreement between the two methods.Pearson correlation analysis the correlation coefficient of the two methods was 0.99?P<0.001?,and the results showed a significant correlation between the two methods.Conclusions:The trigonometric formula we deduced can accurately calculate the corresponding shortening length of the femur caused by different varus angles in DDH used locking compression pediatric hip plate?LCP-PHP?proximal femoral varus osteotomies,which is suitable for clinical application.