不同组合前内侧皮质支撑复位对股骨转子间骨折髓内钉术后稳定性影响的生物力学研究

Effects of reduction with different anterior and medial cortical supports on stability after in- tramedullary nailing for unstable intertrochanteric fractures:a biomechanical comparison

目的比较不同组合的前内侧皮质支撑复位在股骨转子间骨折髓内钉固定中的力学稳定性。方法采用27个Synbone人造股骨,先按照AO/OTA分类制作成不稳定型(31-A2.1型)股骨转子间骨折模型。再在正、侧位X线片上,按照前内侧皮质对位的正性、中性和负性进行两两组合,分为9组(n=3):正-正组、正-中组、正-负组、中-正组、中-中组、中-负组、负-正组、负-中组、负-负组,共27个标本。然后采用头髓钉固定。在生物力学测试机上进行静态加载、疲劳测试和极限加载,检测头颈骨块的相对位移和屈服载荷。结果正-正组、正-中组、正-负组、中-正组、中-中组、中-负组、负-正组、负-中组、负-负组标本疲劳试验后头颈骨块的垂直位移分别为(5.33±0.58)、(7.83±0.29)、(7.73±0.15)、(8.17±0.29)、(8.33±1.15)、(8.83±0.29)、(9.33±0.58)、(9.67±1.15)、(12.00±1.00)mm,差异有统计学意义(P<0.05),正-正组标本垂直位移最小,与其他各组比较差异均有统计学意义(P<0.05);屈服载荷分别为(4967±153)、(4467±58)、(3717±76)、(2767±58)、(2533±58)、(2267±58)、(1833±58)、(1667±58)、(1333±58)N,各组之间两两比较差异均有统计学意义(P<0.05)。在极限加载后,失败表现为股骨头-颈界面松动2例,转子间区域界面松动15例,远端交锁螺钉处劈裂骨折2例,股骨远端与固定的夹具界面松动断裂8例。结论头颈骨块与股骨干的内侧皮质支撑对股骨转子间骨折术后稳定性起主要作用,前侧皮质支撑起次要作用,术中要尽量避免内侧皮质的负性对位。

Objective To compare the biomechanical stabilities among different combinations of anterior and medial cortical supports after intramedullary nailing for unstable intertrochanteric fractures.MethodsTwenty-seven synthesized femur specimens were used to create models of unstable intertrochanteric fracture of type 31A2.1 according to AO/ASIF classification. They were divided into 9 groups (n=3) ac-cording to 9 combinations of anterior and medial cortical supports on the anteroposterior and lateral X-ray films: positive-positive, positive-neutral, positive-negative, neutral-positive, neutral-neutral, neu-tral-negative, negative-positive, negative-neutral, negative-negative groups. After all the fractures were fixated with the newly adapted femoral intertrochanteric nails (FITN), static loadings were applied for tests of fatigue and destruction to investigate the relative displacements and yield loads of the head-neck fragments.ResultsFor the positive-positive, positive-neutral, positive-negative, neutral-positive, neutral-neutral, neutral-negative, negative-positive, negative-neutral, negative-negative groups, the vertical displacements of the head-neck frag-ments under fatigue loading were respectively 5.33±0.58 mm, 7.83±0.29mm, 7.73±0.15 mm, 8.17±0.29 mm, 8.33±1.15 mm, 8.83±0.29 mm, 9.33±0.58 mm, 9.67±1.15 mm and 12.0±1.0 mm, showing significant differences (P<0.05). The smallest displacement was observed in the positive-positive group, significantly smaller than that in any other groups (P<0.05). For the above 9 groups, the yield loads were respectively 4,967±153 N, 4,467±58 N, 3,717±76 N, 2,767±58 N, 2,533±58 N, 2,267±58 N, 1,833±58 N, 1,667±58 N and 1, 333±58 N, showing significant differences between any 2 groups (P<0.05). In the destruction test, bone interface loosening in the femoral head happened in 2 cases, bone interface loosening in the intertrochanteric zone in 15 cases, split fracture at the zone of distal locking nail in 2 cases, and loosening and breakage of the internal fixator in the distal femur in 8 cases.ConclusionsThe medial cortical support plays a major role and the anterior cortical support plays a secondary role in the stability of unstable intertrochanteric fracture. In the surgical procedure, surgeons should avoid the medial cortical negative support as much as possible.