Stability of Locking and Non-Locking Plates in an Osteoporotic Calcaneal Fracture Model

Till Illert, MD; Stefan Rammelt, MD, PhD; Tim Drewes, MD; Rene Grass, MD

Foot & Ankle International: March 2011 (Vol.32 #3)

Background: The aim of this biomechanical cadaver study of calcaneal

fractures was to investigate whether a locking calcaneal plate provides

more stiffness in osteoporotic bone compared to a non-locking plate.

Materials and Methods: Sixteen fresh frozen bone mineral density

(BMD)-matched cadaver feet were tested in a four-part model of a

Sanders Type IIB calcaneal fracture. The fractures were fixed either

with a non-locking AO (Sanders) plate or an interlocking AO plate

(Synthes, Paoli, PA) to the lateral calcaneal wall with six screws.

Specimens were subjected to cyclic loading which was increased stepwise

to full body weight. Displacement of the posterior facet fragment was

measured with an optical tracking system in the sagittal and transverse

planes. Results: No statistically significant differences were observed

between the non-locking and the locking plates with respect to number

of cycles to failure or 1-mm displacement of the posterior facet. The

initial stiffness was significantly higher for non-locking plates.

Conclusion: In osteoporotic bone, the greater stiffness of the

screw-locking plate construct was offset by the smaller diameter of the

screw threads and the lower friction between the plate and bone when a

locking plate was used. In clinical practice, the plate should first be

compressed to osteoporotic bone with cancellous screws and at least two

screws should be placed in the anterior process and in the tuberosity

of the calcaneus.

Key Words: Calcaneus; Fracture; Locking Plate; Non-Locking Plate;

Biomechanical Properties