Interlocking screw configuration influences distal tibial fracture stability in torsional loading after intramedullary nailing.

Purpose: This study evaluated the influence of fracture obliquity and locking screw configuration on interfragmentary motion during torsional loading of distal metaphyseal tibial fractures fixed by intramedullary (IM) nailing.

Methods: The stability of six IM nail locking screw configurations used to fix distal metaphyseal tibial fractures of various obliquities was evaluated. A coronal osteotomy from proximal lateral to distal medial was made in sawbone tibiae at different obliquities from 0° to 60°. After fixation, motion at the fracture was assessed during internal and external rotation tests to 7 Nm under two compressive loading conditions: 20 N and 500 N.

Results: With results organized by interlocking configuration, significant differences in interfragmentary rotation between fracture obliquities are observed when the number of interlocking screws is decreased to one distal static and one proximal dynamic during internal rotation. During external rotation testing, significant rotational differences between fracture obliquities are encountered with two distal static screws and one proximal dynamic. No significant differences were seen between different distal interlocking screw orientations (two parallel versus perpendicular distal screws) for all fracture obliquity patterns tested.

Conclusion: Fracture obliquity influences rotational stability which can be mitigated by interlocking screw configurations when nailing distal tibia fractures. At least two distal and one proximal interlocking screw in a static mode is recommended to resist torsional loading of distal tibia fractures undergoing intramedullary nailing. The addition of more interlocking screws than this did not significantly alter control of torsional displacement with load.