Biomechanical evaluation of subcortical versus bicortical screw purchase in anterior cervical plating.

The purpose of this in vitro study is to compare the stabilities provided by anterior cervical H-plating with screws purchased either subcortically or bicortically on porcine cervical spines. Nine porcine cervical spines (C3-C4) were challenged by 12 Nm in extension followed by 6 Nm in flexion in 6 consecutive steps, i.e., (1) when disc was intact, (2) after discectomy. Subsequently, a tricortical bone graft was inserted to simulate interbody fusion. Each specimen was tested again (3) when plated with 16 mm screws to purchase subcortically and (4) after cyclic loading (f = 0.5 Hz, n = 1000), (5) when plated with 30 mm screws to purchase bicortically and (6) after cyclic loading. Neutral zone and range of motion were parameters normalized for comparison. The results showed comparable stability in constructs plated with screws purchased either subcortically or bicortically before cyclic loading. Cyclic loading deteriorated construct-bone relation in both groups, yet bicortically purchased screws rendered additional stability in anterior cervical plating.