摘要目的:探讨股骨转子间骨折术后内固定失效特点并根据"杠杆-平衡-重建"理论分析可能原因。方法:采用回顾性病例对照研究分析1999年1月至2019年12月北京大学人民医院收治的40例股骨转子间骨折内固定失效患者临床资料，其中男20例，女20例；年龄43～92岁[(74.1±11.5)岁]。髓外固定17例(髓外固定组)，髓内固定23例(髓内固定组)。记录内固定并发症类型(内固定切出、髋内翻畸形、内固定退出、股骨颈短缩和内固定断裂等)。基于"杠杆-平衡-重建"理论，固定术前、术后的力臂变化和支点外移，测量术前、术后和内固定失效后股骨近端的动力臂和阻力臂长度。结果:40例患者中，发生内固定切出18例，髋内翻畸形37例，内固定退出29例，股骨颈短缩37例，内固定断裂3例。髓外固定组：正常股骨近端动力臂长度为(8.0±1.0)mm，阻力臂长度为(59.4±10.9)mm；内固定后动力臂长度为(72.7±21.7)mm，阻力臂长度为(8.9±7.4)mm；内固定失效后动力臂长度为(50.3±14.9)mm，阻力臂长度为(33.6±17.6)mm。髓内固定组：正常股骨近端动力臂长度为(6.7±0.6)mm，阻力臂长度为(49.8±9.9)mm；内固定后动力臂长度为(51.5±7.0)mm，阻力臂长度为(19.8±5.9)mm；内固定失效后动力臂长度为(41.6±9.6)mm，阻力臂长度为(32.4±7.7)mm。各组内正常股骨近端与内固定后的动力臂、阻力臂长度变化差异均有统计学意义( P<0.05)，内固定及其失效后股骨近端的动力臂、阻力臂变化差异均有统计学意义( P<0.05)。内固定后髓外固定组动力臂长度显著大于髓内固定组( P<0.05)，内固定失效后髓外固定组动力臂短缩大于髓内固定组( P<0.05)。 结论:股骨转子间骨折髓外、髓内固定术后重建支点发生外移，内固定失效后动力臂均发生短缩。"杠杆-平衡-重建"理论有助于分析并发症原因。髓外固定后力臂比髓内固定更长，因此也更容易发生内固定失效。

abstractsObjective:To investigate the characteristics of postoperative internal fixation failures of femoral intertrochanteric fractures and analyze the related reasons using the leverage-balance-reconstruction theory.Methods:A retrospective case series study was performed for 40 patients suffering from implant failure after internal fixation of femoral intertrochanteric fractures admitted to Peking University People's Hospital from January 1999 to December 2019. There were 20 males and 20 females, aged from 43 to 92 years [(74.1±11.5)years]. The patients were assigned to extramedullary fixation (extramedullary fixation group, 17 patients) and intramedullary fixation (intramedullary fixation group, 23 patients). Complications associated with internal fixation were recorded, including internal fixation cutout, coxa vara deformity of hip joint, internal fixation withdrawal, femoral heck shortening and internal fixation breakage. Based on the lever-balance-reconstruction theory, the failure reasons of internal fixation were analyzed in combination with the change of arm length and outward shift of fulcrum measured before operation, after internal fixation and after fixation failure.Results:Among 40 patients, internal fixation cutout occurred in 18 patients, coxa vara deformity of hip joint in 37, internal fixation withdrawal in 29, femoral neck shortening in 37 and internal fixation breakage in 3. In extramedullary fixation group, the lengths of primary power arm and resistance arm were (8.0±1.0)mm and (59.4±10.9)mm, the lengths of power arm and resistance arm after fixation were (72.7±21.7)mm and (8.9±7.4)mm, the lengths of power arm and resistance arm after fixation failure were (50.3±14.9)mm and (33.6±17.6)mm. In intramedullary fixation group, the lengths of primary power arm and resistance arm were (6.7±0.6)mm and (49.8±9.9)mm, the lengths of power arm and resistance arm after fixation were (51.5±7.0)mm and (19.8±5.9)mm, the lengths of power arm and resistance arm after fixation failure were (41.6±9.6)mm and (32.4±7.7)mm. In each group, the lengths of power arm and resistance arm after internal fixation showed significant differences from that of normal ones and from that after fixation failure ( P<0.05). The length of power arm in extramedullary fixation group was larger than that in intramedullary fixation group ( P<0.05). The shortening of power arm in extramedullary fixation group was larger than that in intramedullary fixation group after fixation failure ( P<0.05). Conclusions:The extramedullary and intramedullary fixation of femoral intertrochanteric fractures result in the displacement of reconstruction fulcrum. The shortening of power arm is observed after fixation failure. The leverage-balance-reconstruction theory is helpful to analyze the cause of complications. The power arm after extramedullary fixation is longer than that after intramedullary fixation and is therefore more prone to fixation failure. The primary cause of postoperative internal fixation complications is to achieve a new balance of leverage.