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

Abstract

Objective To compare the biomechanical stabilities among different combinations of anterior and medial cortical supports after intramedullary nailing for unstable intertrochanteric fractures. Methods Twenty-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. Results For 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. Conclusions The 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. Key words: Hip fractures; Fracture fixation, internal; Biomechanics; Positive cortical; Reduction