Do Long-Segment Blocking Screws Increase the Stability of Intramedullary Nail Fixation in Proximal Tibia Fractures, eliminating the “Bell-clapper Effect?”

Abstract

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 twelve geriatric 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 1cm 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 to short segment screws (0.77 mm vs. 2.0 mm (p=.039). They also resulted in greater baseline stiffness, although this difference was not significant (807.32± 216.95N/mm vs 583.12 ± 130.1 N/mm, p=.072). There was no difference in stiffness after cyclic loading or survival through 50,000 cycles between the long- 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 to 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 the distal (long) segment may help mitigate the “Bell-clapper Effect” in geriatric patients.