小儿股骨近端内翻截骨术后股骨内翻角度与短缩长度之间的关系

Relationship between angle of femoral varus and length of shortening after proximal femoral osteotomy in children

目的探讨发育性髋关节发育不良(developmental dysplasia of the hip,DDH)应用小儿髋部锁定加压接骨板(locking compression pediatric hip plate,LCP-PHP)行股骨内翻截骨术,其内翻角度与股骨近端短缩长度间的关系,并验证推导出计算股骨近端短缩长度计算式的可行性。方法回顾性收集2013年7月至2017年6月收治的55例DDH患儿(55髋)股骨内翻截骨术前和术后即刻髋关节X线片,其中男12例,女43例;年龄2~10岁(平均5.6岁);左侧30例,右侧25例。对手术操作过程进行几何关系分析,推导出股骨近端短缩长度的三角函数计算式为c(sinθ1-sinθ2),c为股骨头中心至股骨截骨近端最内侧点的距离,θ1为术前c与截骨线的夹角,θ2为内翻截骨术后c与截骨线夹角。将X线片导入Digimizer软件采用直接测量法量出每例患儿的术后股骨近端短缩长度值(ΔS)。通过Digimizer软件测量计算式所需参数,得出股骨近端短缩长度计算式值(ΔS′)。采用配对t检验比较两种方法计算所得结果,进行一致性和相关性分析,验证推导出计算式的可行性。结果对55例DDH患儿运用直接测量法和计算式计算法计算得出内翻截骨术后股骨短缩长度分别为:内翻角度<10°,短缩长度分别为(1.93±0.82)mm和(1.94±0.81)mm;内翻角度为10°~20°,短缩长度分别为(6.11±2.12)mm和(6.16±2.11)mm;内翻角度>20°,短缩长度分别为(9.97±2.49)mm和(9.96±2.37)mm。55例DDH患儿的术前、术后X线片直接测量法和计算式计算法的c和股骨近端短缩长度差异均无统计学意义(P>0.05)。运用Bland-Altman分析直接测量法和计算式计算法所得值,两者的一致性界限(95%)位于-0.80 mm到+0.74 mm之间,差值均数为-0.03 mm,说明两者具有较高的一致性。Pearson相关性分析两种方法的相关系数r=0.99(P<0.001),结果显示两种方法为显著相关。结论推导出的三角函数计算式能准确计算出DDH患儿股骨近端行内翻截骨术后不同内翻角度所致的相应股骨近端短缩长度,适合临床应用。

Objective To explore the relationship between varus angle and length of proximal femoral shortening in patients with developmental dysplasia of hip (DDH) using a locking compression pediatric hip plate (LCP-PHP) during pediatric femoral varus osteotomy and to verify the feasibility of our calculation formula for proximal femoral shortening. Methods A total of 55 DDH patients (55 hips) undergoing LCP-PHP proximal femoral varus osteotomy from July 2013 to June 2017 were enrolled. All preoperative and postoperative internal rotation hip radiographic films were collected. There were 12 boys and 43 girls with an average age of 5.6(2-10) years. The involved side was left (n=30) and right (n=25). According to the geometrical relationship of operative procedure, the trigonometric function formula of proximal femoral shortening length was derived as c (sinθ1-sinθ2), c was the center of femoral head to the most medial point of proximal femur,θ1 the angle between preoperative c and osteotomic line,θ2 the angle between c and osteotomic line after varus osteotomy. The radiographs were imported into the Digimizer software for directly measuring the value of proximal femoral shortening length (ΔS) for each child. And Digimizer software was employed for measuring the parameters required for the calculation formula and the value of proximal femoral shortening length (S') was obtained. Paired t-test was used for comparing the results of two methods, and consistency/correlation analysis performed for verifying the feasibility of deducing the calculation formula. ResultsFifty-five DDH children had direct measurements and formula calculations. The femoral shortening lengths after varus osteotomy were calculated as follows: varus angle <10°, shortening length were (1.93±0.82) and (1.94±0.81) mm;varus angle of 10°~20°(6.11±2.12) and (6.16±2.11) mm;varus angle >20°(9.97±2.49) and (9.96±2.37) mm respectively. No significant difference existed between direct measuring and calculation methods of c and proximal femoral length (P>0.05). The Bland-Altman analysis of these radiographs revealed that 95% limits of agreement between femoral shortening length by algorithm and direct measuring were between -0.80mm and + 0.74 mm. The mean bias was -0.03 mm. The results indicated a high agreement between two methods. Pearson’s correlation analysis revealed that the correlation coefficient of two methods was 0.99 (P<0.001) and the results showed a significant correlation between two methods. Conclusions The above trigonometric formula can accurately calculate the corresponding femoral shortening length caused by different varus angles during proximal femoral varus osteotomy in DDH children. Wider clinical application is recommended.