Reducing Fracture Risk Adjacent to a Plate With an Angulated Locked End Screw.

OBJECTIVES: Locking screws often are used in the treatment of osteoporotic fractures. Studies show that locking screws can increase bone stresses at the plate end, which increases the possibility of peri-implant fracture. This study evaluates whether the technique used to insert the end screw is related to the fracture tolerance adjacent to the plate. METHODS: Twelve groups of plate constructs were evaluated using a fibular diaphyseal surrogate with mechanical properties similar to osteoporotic bone. All inboard screws were nonlocked with only the end screw fixation differing among groups. The end screws were inserted either perpendicularly to the plate or at an angle of 30 degrees for 6- and 12-hole plates. For both orientations, the end screws were inserted nonlocked, locked, or by a locked overdrilling technique, resulting in 6 groups per plate length. The perpendicular nonlocked screws represented a control group. The constructs were tested to failure in 4-point bending to determine peak load, failure energy, and stiffness. RESULTS: All constructs failed by peri-implant fracture along a plane through the 2 cortical holes of the end screw. Compared with the control group, an angulated locked screw at the plate end significantly increased the peak bending moment and energy required to produce a fracture for both plate lengths (6-hole, P = 0.008, P < 0.001; 12-hole, P = 0.006, P < 0.001). CONCLUSIONS: The use of an angulated locked end screw may enhance the resistance of osteoporotic bone to peri-implant fractures caused by bending forces.

Reverse oblique end screws in nonlocking plates decrease construct strength in synthetic osteoporotic bone medium.

Fracture stability can be challenging for osteoporotic individuals. The end screw of nonlocked plates is subjected to the greatest loading and is typically the site of construct failure. To enhance fixation, the end screw can be angled away from the fracture. The current study biomechanically evaluated screws angled the other direction: toward the fracture using 3.5-mm dynamic compression plates in an osteoporotic bone model. Three different plate lengths (6-, 8-, 12-hole) were tested in three-point bending with an oblique, perpendicular, or reverse oblique end screw. The peak load for loss of screw fixation for the reverse oblique end screw constructs was significantly less than the other screw orientations for all plate lengths. The 12-hole peak load, energy, and displacement magnitudes for all three screw orientations were significantly greater than all 6- and 8-hole constructs. The use of a reverse oblique end screw is inferior to both perpendicular and oblique end screws.