Objectives: 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.
Methods: 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).
Results: 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.
Conclusion: 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.
Clinical relevance: 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.
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