An anatomical study of plate-rod fixation in feline tibiae

Objective To investigate the feasibility of placing bi-cortical cortex (B-cort) or mono-cortical locking screws (M-lock) in a plate-rod construct applied to the feline tibia in combination with different intramedullary (IM) pins. Methods Twenty-four feline tibiae of cats were divided into 4 groups, corresponding to IM pin sizes filling approximately 30% (1.0 mm), 40% (1.4 mm), 45% (1.6 mm), and 50% (1.8 mm) of the medullary canal. Computed tomography (CT) was performed to trace potential screw trajectories in each group. A 12-hole, 2.4 mm locking compression plate was then applied on the medial aspect of the tibia. M-lock and B-cort screws were inserted subsequently in each plate hole. Success rates of screw insertion based on CT analysis and cadaveric simulation were compared with screw type, IM pin diameter, and anatomic location as variables. Results Screw insertion rates were underestimated on CT compared to cadaveric specimens. During cadaveric simulation, B-cort screws could be inserted in all specimens in the 3 most proximal plate holes and in at least 1 of the 3 distal plate holes. The smallest pin size (30%) allowed placement of a greater number of B-cort screws (P < .05) compared to other pins. Fewer B-cort screws could be inserted in the distal diaphyseal region (P < .05) compared to other regions. A total of 99.3% of M-lock screws could be inserted regardless of IMP size. Clinical significance Plate rod constructs can include bicortical screws in the proximal and distal metaphysis, and monocortical screws in the diaphysis, combined with an IM pin filling up to 50% of the medullary canal.