Loose Screw or No Screw? A Biomechanical Study to Answer a Common Intraoperative Dilemma.

BACKGROUND: Insertion of cortical screws with poor purchase during metacarpal plate fixation may occur, yet the biomechanical tradeoff of retaining versus removing a loose screw remains difficult to quantify. Removing a loose screw avoids risking screw migration but may decrease fixation strength or create a stress riser at the empty hole. Our study evaluated bending and torsional properties in plate fixation for comminuted metacarpal diaphyseal fractures with or without a single loose screw.

METHODS: Sixty-four cadaveric fractures were fixed in bridge mode using nonlocking screws. A single screw was overtightened and stripped to simulate screw loosening and then either retained or removed. Testing groups were assigned based on loading configuration (cantilever bending or torsion) and the presence of a loose screw. Multivariable linear regression models evaluated relationships between screw presence and biomechanical outcome measures. Failure modes were analyzed using Fisher exact test.

RESULTS: Cantilever bending load at 2 mm displacement was 7.6 N (SD = 1.9 N) with loose screw retained versus 8.0 N (SD = 2.6 N) with screw removed (P = .796). Torque at 10° rotational displacement showed no difference between retained (0.363 N m, SD = 0.054 N m) and removed screw groups (0.370 N m, SD = 0.139 N m; P = .858). No differences were identified in stress or stiffness. Cantilever bending clinical failure occurred with all specimens bending through the plate. During torsional testing, 6 of 16 with retained loose screw secondarily failed, with the loose screw hole fracturing after rotating past the clinical endpoint.

CONCLUSION: Removing a single loose screw in bridge plate fixation for comminuted metacarpal diaphyseal fractures safely avoids screw migration without imparting a stress riser or compromising biomechanical strength.