Do Long-Segment Blocking Screws Increase the Stability of Intramedullary Nail Fixation in Proximal Tibia Fractures, Eliminating the "Bell-Clapper Effect?".

Abstract

To determine change in stiffness and horizontal translation of a geriatric extra-articular proximal tibia fracture model after intramedullary nailing with distal (long)-segment blocking screws versus proximal (short)-segment blocking screws. Unstable extra-articular proximal tibia fractures (OTA/AO 41-A3) were created in 12 geriatric cadaveric tibias. Intramedullary nails were locked with a standard construct (4 proximal screws and 2 distal screws). Specimens were then divided into 2 groups (6 matched pairs per group). Group 1 had a blocking screw placed lateral to the nail in the proximal segment (short segment). Group 2 had a blocking screw placed 1 cm distal to the fracture and medial to the nail (long segment). Specimens were then axially loaded and cycled to failure or cycle completion (50,000 cycles). Long-segment blocking screws significantly decreased the amount of horizontal translation at the fracture site compared with short-segment screws (0.77 vs. 2.0 mm, P = 0.039). They also resulted in a greater trend towards greater baseline stiffness, (807.32 ± 216.95 N/mm vs. 583.12 ± 130.1 N/mm, P = 0.072). There was no difference in stiffness after cyclic loading or survival through 50,000 cycles between the long-segment and short-segment groups. Long-segment blocking screws added to an intramedullary nail construct resulted in decreased horizontal translation at the fracture site compared with short-segment screws in this model of a geriatric proximal tibia fracture. Blocking screws are commonly used to aid in fracture alignment during intramedullary nailing of proximal tibia fractures. Even when not required to attain or maintain alignment, the addition of a blocking screw in either the proximal or the distal (long) segment may help mitigate the "Bell-Clapper Effect" in geriatric patients.