基于杠杆平衡重建理论分析动力髋螺钉固定股骨转子间骨折的失效原因

Reason for failed fixation with dynamic hip screws for intertrochanteric fracture:analysis based on the lever-balance-reconstruction theory

目的基于杠杆平衡重建理论探讨动力髋螺钉(DHS)固定治疗股骨转子间骨折的失效原因及DHS的适应证。方法回顾性分析1999年1月至2019年12月期间北京大学人民医院创伤骨科采用DHS固定治疗的32例股骨转子间骨折患者资料。男22例,女10例;年龄为34~91岁,平均67.7岁;骨折AO分型:31-A1型15例,31-A2型13例,31-A3型4例。根据杠杆平衡重建理论,从骨折线与内固定的关系确定术后支点的位置,并测量骨折内固定术后的内侧力臂和外侧力臂。将32例患者根据内固定术后支点位置的不同分为两组:A组13例,支点在髓腔中心及以内,B组19例,支点在髓腔中心外。比较两组患者的内固定失效情况。结果32例患者中15例患者发生内固定失效:头颈螺钉切割但均未穿透2例,退钉8例,髋内翻畸形10例,股骨颈短缩畸形15例。两组患者除骨折AO分型外其余术前一般资料及内固定类型比较差异均无统计学意义(P>0.05),具有可比性。A组患者的内侧力臂(动力臂)长度平均为51.12 mm(39.4~57.9 mm),外侧力臂(阻力臂)长度平均为23.37 mm(15.1~31.0 mm),3例患者术后发生内固定失效;而B组患者的内侧力臂(动力臂)长度平均为63.71 mm(52.3~74.5 mm),外侧力臂(阻力臂)长度平均为9.94 mm(3.1~18.3 mm),12例患者发生内固定失效,两组患者内固定失效情况比较差异有统计学意义(P=0.036)。结论股骨转子间骨折DHS内固定术后发生失效与术后重建的支点位置有关。DHS仅适用于骨折线(重建后支点)靠近髓腔中心及其内侧的股骨转子间骨折,而不适合应用于骨折线(重建后支点)靠近髓腔外的骨折类型。

Objective To study the reason for failed fixation with dynamic hip screws(DHS)and the indications for DHS fixation in the treatment of intertrochanteric fracture based on the lever-balance-reconstruction theory.Methods A retrospective analysis was performed of the data of 32 patients with intertrochanteric fracture who had been treated by DHS fixation at Department of Orthopaedic Trauma,Peking University People's Hospital from January 1999 to December 2019.There were 22 males and 10 females,aged from 34 to 91 years(average,67.7 years).By the AO classification,15 fractures were type 31-A1,13 ones type 31-A2,and 4 ones type 31-A3.According to the lever-balance-reconstruction theory,after the position of postoperative fulcrum was determined depending on the relationship between fracture line and internal fixation,the medial and lateral force arms were measured after internal fixation.The 32 patients were divided into 2 groups according to the position of fulcrum after internal fixation.In group A of 13 patients,the fulcrum was located in or within the center of the medullary cavity;in group B of 19 patients,the fulcrum was located outside the center of the medullary cavity.The incidence of internal fixation failure was compared between the 2 groups.Results Internal fixation failure occurred in 15 of the 32 patients:cutting out of the head and neck screws without penetration in 2 cases,screw withdrawal in 8 cases,hip varus deformity in 10 cases,and femoral neck shortening in 15 cases.The 2 groups were comparable because there were no statistically significant differences in their preoperative general data or types of internal fixation between them except AO classification(P>0.05).The length of medial force arm(power arm)averaged 51.12 mm(from 39.4 to 57.9 mm)and the length of lateral force arm(resistance arm)23.37 mm(from 15.1 to 31.0 mm)in group A where 3 patients experienced internal fixation failure after operation;the length of medial force arm(power arm)averaged 63.71 mm(from 52.3 to 74.5 mm)and the length of lateral force arm(resistance arm)9.94 mm(from 3.1 to 18.3 mm)in group B where 12 patients experienced internal fixation failure after operation.There was a significant difference between the 2 groups in internal fixation failure(P=0.036).Conclusions In the DHS fixation of intertrochanteric fracture,the postoperative fixation failure is associated with the fulcrum position after reconstruction.DHS is only indicated for intertrochanteric fractures whose fracture line(post-reconstruction fulcrum)is near and inside the center of the medullary cavity,but not for those whose fracture line(post-reconstruction fulcrum)is outside the medullary cavity.