Empty

Fig 1. A) Implant with proximal

gap packed with

B) Post-harvest radiograph.

Fig 2. Gap f

(grey) and

Calcium Based Fillers Promote1Lim, L Z; +1,2Bobyn

+Divisions of 1Experimental Medicine and 2Orthopaedics

Introduction:

Revision arthroplasty surgery often involves loss of bone stock and

cavitary defects that result in suboptimal implant fit, reduced initial

stability, and reduced potential for biologic fixation of porous implants.

Several types of biomaterials have been proposed for defect filling as

substitutes for autogenous bone graft; these include calcium

(CaP) and calcium sulfate (CaS) compounds. Medical grade

formulations of Ca-based biomaterials have been developed with

porosity and bio-degradation characteristics that encourage

cells, blood supply and osteoconduction, all of which are necessary

bone regeneration. The purpose of this study was to investigate the

healing potential of two different Ca-based materials in a canine implant

model using porous titanium implants.

Materials and Methods: Gap-type intramedullary implants were fabricated from commercially

pure titanium with a 5mm diameter central porous rod and 11mm

diameter solid end and central spacers to create two separate 3mm gap

regions between host bone and porous

metal implant (Fig 1). The titanium

foam core was 55% porous with an

average pore size of 400µm. One gap

filling material was a commercial

formulation of nanocrystalline apatitic

CaP (Etex Corp, MA). The CaS

material was in the form of small

granules ranging between 20-400 µm in

diameter. Adding sterile saline to the

materials at the time of surgery

produced compounds with handling

characteristics conducive to molding

and shaping into the implant gap regions. Prior to setting, t

compound was relatively soft and paste-like while the

was harder and more putty-like. The proximal 3mm implant gaps were

manually filled with either CaP or CaS, leaving the distal gaps empty as

controls. Six dogs underwent bilateral surgery, each dog receiving one

implant containing each material into the left or right proximal humerus

(institutionally approved protocol). After 12 weeks,

harvested to yield 6 sets of paired data from each animal

with CaS. The humeri were scanned with a high voltage, high resolution

microCT (µCT) scanner to obtain 18µm thick serial images of the

complete bone-implant construct. The resulting 1000 serial CT images

of each gap were used to quantify the extent of resorption of the

based materials and bone formation within the implant

as a volume percentage of the gap. Specimens were subsequently

embedded in acrylic and undecalcified transverse serial sections were

imaged with backscattered scanning electron microscopy

enable analysis of bone growth within the 3mm gaps a

the porous implant regions. Statistical comparisons were made using

paired and unpaired Student's t-tests and multiple two

models, with p≤0.05.

Results:

MicroCT quantified both native bone and residual CaS or CaP within

the gaps, without discriminating one material from the other.

with time zero, the total material within

CaP-filled gaps diminished by a mean

volume of 25%±13% (Fig 2). Compared

with time zero, the total material within

CaS-filled gaps diminished by a greater

mean volume of 49%±7% (p=0.001).

Compared with CaP at 12 wks, the CaS

material resorbed into a more porous

scaffold within and on which new,

interconnected trabeculae had formed in

continuity with surrounding host bone

(Figs 3, 4). Empty gaps were only 5% ±

1% filled at 12 wks (p=0.001).

Empty CaP CaS

mplant with proximal

gap packed with CaS material.

harvest radiograph.

Gap filling at time zero

and at 12 weeks (blue).

Promote Bone Defect Healing Around Porous Titanium Implants

Bobyn, J D; 2Okyere, M J; 3Barralet, J E; 2Bobyn, K M; 2Tanzer, M

Orthopaedics, Faculty of Medicine, 3Faculty of Dentistry, McGill University

john.bobyn@mcgill.ca

arthroplasty surgery often involves loss of bone stock and

defects that result in suboptimal implant fit, reduced initial

stability, and reduced potential for biologic fixation of porous implants.

Several types of biomaterials have been proposed for defect filling as

calcium phosphate

. Medical grade

based biomaterials have been developed with

courage invasion of

n, all of which are necessary for

to investigate the gap

based materials in a canine implant

implants were fabricated from commercially

pure titanium with a 5mm diameter central porous rod and 11mm

diameter solid end and central spacers to create two separate 3mm gap

Prior to setting, the CaS

like while the CaP compound

The proximal 3mm implant gaps were

, leaving the distal gaps empty as

Six dogs underwent bilateral surgery, each dog receiving one

left or right proximal humerus

the humeri were

paired data from each animal comparing CaP

The humeri were scanned with a high voltage, high resolution

scanner to obtain 18µm thick serial images of the

000 serial CT images

ent of resorption of the Ca-

implant gaps, expressed

. Specimens were subsequently

embedded in acrylic and undecalcified transverse serial sections were

imaged with backscattered scanning electron microscopy (BSEM) to

3mm gaps as well as within

porous implant regions. Statistical comparisons were made using

and multiple two-level hierarchical

MicroCT quantified both native bone and residual CaS or CaP within

from the other. Compared

Fig 3. Images from µCT scans of CaP-filled gap. A) Longitudinal image at zero. B) Longitudinal and C) transverse images

Fig 4. Images from µCT scans of CaS-filled gap. A) Longitudinal image at

zero. B) Longitudinal and C) transverse images

BSEM images more clearly showed that

predominantly filled by the material, with

and around the material pores (Fig 5). In contrast, BSEM revealed that

most of the CaS had resorbed by 12 weeks, with most of the gaps filled

with dense bony trabeculae connecting the porous implant c

surrounding host bone (Fig 5). CaP-filled implants

apposition at the porous implant perimeter

although the latter was associated with a greater mean extent of bone

ingrowth (p=0.04).

Discussion: Previous studies have shown that a 3mm gap around a porous implant

in the proximal humerus does not spontaneously heal with bone after 12

weeks. At time zero both Ca-based materials filled almost the entire gap.

By 12 weeks both materials resorbed and

the gap, on and within the porous implant and in continuity with

surrounding host bone. The CaS resorbed to a much greater extent,

facilitating more gap filling with new bone. It should be noted, however,

that the CaP compound is a more mechanic

property that could be advantageous in revision surgery where construct

strength is important. Longer implantation periods would likely result in

additional resorption of the CaP and replacement with new

Significance:

While possessing different properties and resorption characteristics,

both Ca-based materials demonstrated potential for use in gap healing

within a clinically relevant time frame.

Acknowledgments:

Canadian Institutes for Health Research, Na

Canada, Etex Corporation.

Fig 5. Transverse BSEM images of A) CaPimplant after 12 weeks (the darker grey is bone, lighter grey is residualarrows show bone in the implant pores.

round Porous Titanium Implants

McGill University, Montreal, Canada

ed gap. A) Longitudinal image at time at 12 weeks.

ed gap. A) Longitudinal image at time

s at 12 weeks.

that CaP-filled gaps remained

by the material, with some new bone formation in

In contrast, BSEM revealed that

had resorbed by 12 weeks, with most of the gaps filled

with dense bony trabeculae connecting the porous implant core with

filled implants showed more bone

apposition at the porous implant perimeter than the CaS group (p=0.06)

although the latter was associated with a greater mean extent of bone

that a 3mm gap around a porous implant

in the proximal humerus does not spontaneously heal with bone after 12

based materials filled almost the entire gap.

and new bone was evident within

the gap, on and within the porous implant and in continuity with

resorbed to a much greater extent,

facilitating more gap filling with new bone. It should be noted, however,

ompound is a more mechanically resistant material, a

property that could be advantageous in revision surgery where construct

Longer implantation periods would likely result in

and replacement with new bone.

While possessing different properties and resorption characteristics,

based materials demonstrated potential for use in gap healing

ealth Research, National Research Council

P-filled implant and B) CaS-filled (the darker grey is bone, lighter grey is residual CaS). Red

Poster No. 0979 • ORS 2012 Annual Meeting