Enhancement of pedicle screw stability using calcium phosphatecement in osteoporotic vertebrae: in vivo biomechanical study

Abstract

We conducted an experimental study using femalebeagles with and without ovariectomy-induced osteoporosisto determine the effect of calcium phosphate cement (CPC)on the mechanical stability of inserted pedicle screws. A drillhole was created from the base of the transverse process to thevertebral body; CPC was injected into the hole, and then ascrew was inserted into the same hole. In the presence ofosteoporosis evidenced by dual X-ray absorptiometry, the stabilityof the inserted screw augmented by CPC against pulloutand cephalocaudal forces were significantly greater by28% and 54% at 1 week after operation, 48% and 71% at 2weeks, and 56% and 68% at 4 weeks compared with thosewithout CPC. The pull-out strength increased progressivelywith time after surgery, probably reflecting new-bone growthfrom the surrounding cancellous bone, which was in directcontact with the CPC, as shown in the histologic study. Ateach time point the cephalocaudal rigidity was similar and thepull-out strength greater than that for the screws insertedwithout CPC in nonporotic dogs. These findings suggest thatCPC augments the stability of the inserted pedicle screws andincreases the stiffness of fixed osteoporotic motion segmentsusing instrumentation.