RemodelsReplaced by bone in6–18 months

Easy to use Granules, blocks, wedges, cylinders

Safe Synthetic origin provides unsurpassedsafety

Synthetic cancellous bone graft substitute (�-tricalcium phosphate)

�

Original Instruments and Implants of theAssociation for the Study of Internal Fixation –AO/ASIF

chronOS™

Remodels

ChronOS is replaced by host bone in 6–18 months. The remodellingprocess (simultaneous resorption and new bone formation) is possibledue to the specific chemical composition and the optimised scaffoldof ChronOS.

Easy to use

The off-the-shelf product is available in different shapes and sizes: granules, blocks, wedges and cylinders. ChronOS does not require preparation and is sterile packed.

Avoids bone harvesting

Autologous bone grafting is associated with several shortcomings andpotential complications. Studies have shown an incidence of up to 20.6%of minor complications and 8.6% of major complications associated withthe use of autograft material (Younger et al. 1989).

ChronOS is an advantageous alternative to bone harvesting. It shortensoperative time, solves the limitations in quantity and quality of availablebone graft and avoids donor site morbidity.

chronOS™

Synthetic cancellous bone graft substitute

Safe

The synthetic origin of ChronOS provides high biocompatibility and unsurpassed safety, preventing any risk of transmission of infectious disease.

chronOS™

Synthetic material characteristics

Strength of cancellous bone

The compressive strength of ChronOS is consistently 7.5 ± 1 MPa.The standardized manufacturing process guarantees constantquality and provides reliable mechanical stability. The compressivestrength of ChronOS is similar to that of cancellous bone which is typically between 2 and 10 MPa (Van Auderkercke, Martens 1984).

No adverse reactions

All investigations, according to ISO 10993-1, demonstrate the excellent biocompatibility of ChronOS. No adverse reactions have beenobserved in the 20 years of clinical applications (Steffen et al. 2001,Roesgen 1991, Gatti et al. 1990).

ChronOS

Right choice of chemical composition

Differences in chemical composition of biomaterials have profoundeffects on their in vivo behaviour. ChronOS consists of pure β-tricalciumphosphate which remodels completely. Hydroxyapatite, in contrast,resorbs very slowly, therefore remaining in the body for many years(Gazdag et al. 1995).

Other bone graftsubstitutes

β−tricalcium phosphate β-Ca3(PO4)2

Remodelling

Hydroxyapatite Ca10(PO4)6OH2

No remodelling

chronOS™

Engineered for osteoconductivity

Optimised scaffold

To induce the bone remodelling process osteoconductivity must occur.It is mainly influenced by three factors: the overall porosity, the inter-connected macropores and the micropores. ChronOS has been designedto optimise these features in order to mimic cancellous bone and providean ideal scaffold for bone tissue infiltration.

Interconnected macropores

The macropores of ChronOS are mainly distributed within a range from100–500 µm. This offers the optimal environment for vascularisationand migration of osteoclasts and osteoblasts (Gazdag et al. 1995). In ad-dition, the macropores are interconnected to allow bone formationthroughout the entire implant.

Micropores

ChronOS contains micropores, which are defined as the space withinthe material smaller than 10 µm. The microporosity accelerates the remod-elling process by increasing the surface area and allowing for circulationof body fluids.

Overall porosity

ChronOS has a total porosity of 60% for the granules and 70% for theblocks, wedges and cylinders. A high porosity enhances the osteocon-ductivity, although a porosity which is too high weakens the material’smechanical strength. ChronOS benefits from the highest possible degreeof porosity, without compromising the mechanical strength.

<100 >500

Distribution

160 240 320 400 500

0

10

20

30

40

%

Pore Sizeµm

Macropores of the required size

2 mm

30 µm

chronOS™

Remodelling is the key to success

Desired remodelling process

The key to success of ChronOS is the remodelling process. Resorptionand new bone formation happen simultaneously and are completed in6–18 months. This is the result of both the choice of the specific chemical composition and the optimised scaffold as described previ-ously.

Replaced in 6–18 months

Timing is the critical factor for a bone graft to remodel into naturalbone. If the resorption is too rapid, the osteoblasts lose the scaffoldneeded for the formation of new bone. If the resorption is too slow orincomplete, the graft will not be replaced by bone in an adequate timespan. ChronOS has been designed to remodel in an ideal time span,being replaced by host bone in 6–18 months.

Simultaneous resorption and new bone formation

As ChronOS is structurally and chemically similar to bone, osteoclastsresorb ChronOS like endogenous bone. During resorption, osteo-clasts attach to the matrix and create lacunae on the implant surface.As this resorption takes place, new bone is formed: osteoblasts fill thelacunae, thus synthesising extracellular matrix, which is subsequentlycalcified.

ChronOS

New bone

Osteoblasts

Osteoclast

Successful spinal interbody fusion

Cages filled with ChronOS granules were used to achieve inter-vertebral fusion in sheep. The following figures show non-decalcifiedsections stained with toluidine blue: grey represents ChronOS, blue represents bone, white represents medullary space (Steffen et al. 2001; histologies by R. K. Schenk, Berne).

chronOS™

Histology

8 weeks postoperative: Bone surrounds ChronOS granules and integrates in its pores.

16 weeks postoperative: Some of the granules are still surrounded by initially formed bonewith low mineral content, woven bone. Other parts of ChronOS arealready covered by dense oriented bone, lamellar bone.

32 weeks postoperative: Extensive substitution of ChronOS granules. Remodelling has re-placed mostly all tricalcium phosphate particles and simultaneously,the mean volume of bone matrix has increased constantly.

1 mm

1 mm

1 mm

Handling

ChronOS is preferably soaked with autogenous blood or sterile saline solu-tion. Soaking the blocks, wedges and cylinders fills the pores and drives outremaining air. This procedure enhances the rapid exchange of fluids insideChronOS and initiates the start of the remodelling process. For an easier per-fusion a syringe can be used. Soaking granules with autogenous bloodresults in a consistency that allows an easier placement into the surgical site.

In order to achieve its osteogenic and osteoinductive potential, ChronOScan be mixed with cancellous bone or bone marrow.

The blocks, wedges and cylinders can be easily formed to the desired shapewith a suitable instrument, e.g. a scalpel.

Indications

ChronOS can be used wherever cancellous bone graft would normallybe used. Depending on the size, voids of undefined geometric shapecan be filled with granules or combinations of granules and blocks. Voidswith defined geometric shape can be filled with blocks, wedges or cylinders.

Trauma and orthopaedicsFilling of voids caused by benign tumours, cysts and osteotomies,filling of defects arising from impacted fractures, refilling of cancellousbone harvesting sites, arthrodesis, non-unions and pseudoarthrosis.

Spine surgeryPostero-lateral fusion, interbody fusion (as cage filling material), verte-brectomies (as filling material of the vertebral implants).

Cranio-maxillofacial surgeryReconstruction of mandibular cyst defects and voids after tooth socketextractions, augmentation of the alveolar ridge and the maxillary sinus.

The use of ChronOS is restricted to applications with minor loading,unless supported with internal fixation devices.

chronOS™

Bibliography

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Manufacturer:Mathys Medizinaltechnik AGGüterstrasse 5CH-2544 Bettlach

EU authorized representative:Mathys Medical Belux N.V.-S.A.B-1000 Brussels

Distributed by:STRATEC MedicalEimattstrasse 3CH-4436 Oberdorf

SYNTHES GmbH & Co. KGIm Kirchenhürstle 4–6D-79224 Umkirch

Presented by:�

Twenty years of clinical experience

ChronOS has been used successfully in dental applications for twenty years.As early as 1988, P. S. Eggli et al. had suggested that ChronOS underwentosteoclastic resorption and in 1990 J.-P. Pochon wrote about ChronOS asan advantageous bone graft for bone defects in children (under thename Ceros-82). Since these publications, several studies have shown theexcellent behaviour of ChronOS as a bone graft in trauma, spinal and dental applications.

Clinical and animal studies

Muschik M, Ludwig R, Halbhübner S, Bursche K, Stoll T(2001) �-Tricalcium phosphate as a bone substitutefor dorsal spinal fusion in adolescent idiopathic scoliosis –preliminary results of a prospective clinical study. Eur Spine J 10: 178–184

Steffen T, Stoll T, Arvinte T, Schenk RK (2001) Porous tri-calcium phosphate and transforming growth factor usedfor anterior spine surgery. Eur Spine J 10: 132–140

Cross AR, Eschbach EJ, Lewis DD, Wheeler DL (2000)Surface contour analysis of tibial plateaus with subshon-dral bone defects supplemented with autograft or tri-calcium phosphate in a caprine model. Abstract, Transac-tions 645, Sixth World Biomaterial Congress 2000

Roesgen M (1991) Knöcherne Regeneration undCalciumphosphatkeramiken. Traumatologie aktuell,Band 4, Thieme, Stuttgart

Gatti AM, Zaffe D, Poli GP (1990) Behaviour of tricalciumphosphate and hydroxyapatite granules in sheep bonedefects. Biomaterials (England) 11: 513–517

Pochon J-P (1990) Knochenersatzplastiken mit Trikalzi-umphosphatkeramik im Kindesalter. Aktuelle Probl ChirOrthop (Switzerland) 36: 1–51

Eggli PS, Müller W, Schenk RK (1988) Porous hydroxy-apatite and tricalcium phosphate cylinders with differentpore size ranges implanted in the cancellous bone of rabbits – a comparative histomorphometric and histologicstudy of bony ingrowth and implant substitution. Clin Orthop 232 Jul: 127–38

Waisbrod H, Gerbershagen HU (1986) A pilot study of the value of ceramics for bone replacement. Arch OrthopTrauma Surg 105(5): 298–301

Other studies

Bohner M (2001) Physical and chemical aspects ofcalcium phosphates used in spinal surgery. Eur Spine J 10Suppl 2: S114–S21

Van Audekercke R, Martens M (1984) Mechanical pro-perties of cancellous bone. In: Hastings GW, Ducheyne P,Natural and living biomaterials. CRC Press, Boca Raton

Steffen T, Downer P, Steiner B, Hehli M, Aebi M (2000)Minimally invasive bone harvesting tools. Eur Spine J 9: 114–118

Gazdag AR, Lane JM, Glaser D, Forster RA (1995)Alternatives to autogenous bone graft: efficacy andindications. J Am Acad Orthop Surg 1995 3(1): 1–8

Younger EM, Chapman MW (1989) Morbidity at bonegraft donor site. J Orthop Trauma 3(3): 192–5