Background:
Proximal humeral fractures are common injuries, and numerous surgical
methods have been described for their treatment. The biomechanical
characteristics of various internal fixation devices that are used
to treat these fractures have not been extensively studied, nor
has the potential beneficial effect of calcium phosphate cement
supplementation.
Methods:
We used a cadaveric three-part proximal humeral osteotomy model
to perform a biomechanical evaluation of three types of internal
fixation devices: a cloverleaf plate, an angled blade-plate, and
Kirschner wires. The effect of supplementing the fixation with SRS
(Skeletal Repair System) calcium phosphate cement was evaluated
as well. Eighteen pairs of fresh-frozen humeri were obtained, and
the bone-mineral density of each specimen was measured. In each
pair, one specimen was secured with internal fixation alone and
the contralateral specimen was secured with internal fixation combined
with calcium phosphate cement. The specimens were tested cyclically in
abduction and in external rotation for 250 cycles to evaluate interfragmentary
motion. The specimens were then loaded to failure in external rotation
to measure torsional load to failure and torsional stiffness.
Results:
Overall, there were no significant differences between the specimens
treated with the blade and cloverleaf plates, whereas the specimens
treated with Kirschner wires demonstrated more interfragmentary
motion, less stiffness, and lower torque to failure. In general,
supplementation with calcium phosphate cement led to significant
improvements in the mechanical performance of all three forms of
internal fixation as demonstrated by a significant decrease in interfragmentary motion,
a significant increase in torque to failure, and a significant increase
in torsional stiffness. The addition of calcium phosphate cement
increased the stiffness of even the most osteoporotic specimens
to levels that were higher than those of the most osteodense specimens
that had been treated with internal fixation alone.
Conclusion:
The initial biomechanical properties of internal fixation as measured
with use of a proximal humeral osteotomy model and three methods
of fixation were significantly improved by the addition of calcium
phosphate cement.
Clinical Relevance:
The addition of calcium phosphate cement may augment the mechanical
characteristics of internal fixation of difficult, three-part proximal
humeral fractures. The ability to stabilize the interface between
the implant and cancellous bone, particularly in the presence of
osteopenia, may make calcium phosphate cement a valuable clinical
tool in the treatment of these difficult fractures.