In vivo preclinical evaluation of the influence of osteoporosis on the anchorage of different pedicle screw designs

Abstract

We investigate the anchorage of pedicle screws with different surface treatments in osteoporotic bone. Eight ewes were divided into two groups of four animals each: four sheep underwent bilateral ovariectomy (OVX Group), whereas the operation was simulated in the remaining group (SHAM Group). Eighteen months after the first operation, the Dynesys(®) System was fitted to the sheep using pedicle screws with three different surface treatments: untreated, rough blasted (uncoated) and bioactive coated (bioactive). Uncoated screws showed a significantly higher bone ingrowth value compared with the untreated screws in the OVX group (9.3%, p < 0.005) and a significantly lower bone ingrowth value in the SHAM group (-11.0%, p < 0.05). Furthermore, the bioactive pedicle screws had a significant lower bone ingrowth value than the untreated screws in the SHAM group (-12.1%, p < 0.05). These results suggest that both tested surface treatments of pedicular screws may provide an advantage in terms of bone quality and osseointegration, when implanted in osteoporotic vertebrae.

Fig. 1

SEM microphotograph of the treated implant surface before (a) and after (b) soaking in SBF (30 days). Apatite crystals are observable. In the presence of body fluids, this treated surface induces apatite nucleation at the bone implant interface, resulting in a dense and homogenous calcium-phosphate layer at the surface and a graded structure down to the substrate metal with no distinct implant-coating interface

Fig. 2

Anteroposterior X-rays of lumbar spines of OVX_3 (a) and SHAM_1 (b) sheep. Asterisks indicate pedicle screw loosening

Fig. 3

Histologies of bioactive coated (a, b), rough blasted (c, d) and untreated (e, f) pedicle screws implanted in the vertebral pedicles (L2–L5) of OVX (a, c, e) and SHAM (b, d, f) sheep at a magnification of ×10 (Fuchsin acid and Fast green) (Scale bar 400 μm). All tested screws are in direct contact with peri-implant bone. Signs of bone rarefaction are evident in OVX sheep. The presence of coatings improves the screw–biomaterial interface even in the presence of osteopenia and no areas of biomaterial not in direct contact with bone are visible