Conc

osit

cCaS., Joazzoc

anchoscopigraft/

attach replacement ligaments in tunnels drilled for anterior and posterior cruciate ligament recon-struction. Suture anchors are used in surgical procedures wherein it is necessary for a surgeon toattach (tie) tissue to the surface of the bone, for example, during joint reconstruction and ligamentrepair or replacement. The composition of these implants ranges from metals to polymers and

Iiciscranim

FCo

RA

Mavering

PAss

0dcomposites. Typically, because of the relatively large amount of torque that must be applied duringinsertion, these screws are constructed from metal. However, interference screws and suture anchorshave also been constructed from bioabsorbable polymers and composites. The ideal material would(1) provide adequate mechanical fixation, (2) completely degrade once no longer needed, and (3) becompletely replaced by bone. Because no material has been shown to be superior for all applications,the surgeon must weigh the advantages and disadvantages of each to evaluate the optimum materialfor a given application and patient. The purpose of this article is to present a comprehensive reviewof the commercially available interference screws and suture anchors, with an emphasis on implantcomposition, interaction, and design. This article provides the orthopaedic surgeon with a back-ground on biomaterials, specifically those used in interference screws and suture anchors. Becausethere is no material that is perfect for all surgical situations, this review can be used to make educateddecisions on a case-by-case basis.

nterference screws and suture anchors are com-monly used in arthroscopic surgery and sports med-ne for fixation of soft tissue to bone. Interferenceews provide a press fit between bone, graft/tendon,d screw, whereas suture anchors tie soft tissue to anplant embedded in bone. These implants are made

from metals, polymers, and composites. Osseointegra-tion, or the ability of a material to form direct bone-implant contact, allows for effective transmission ofloading forces and enhances stability essential forlong-term stabilization. The literature on biomaterialsis vast but has confusing language because it is mostlywritten for the materials scientist. The purpose of thisarticle is to present a comprehensive review of thecommercially available interference screws and sutureanchors, with an emphasis on implant composition,interaction, and design. A review of the bone-implantinteraction for each material type is also conducted,with emphasis on biocomposites.

Bioabsorbable materials have received considerableattention because of the advantages of less compli-cated revision surgeries, better postsurgical imaging,

rom the Department of Orthopaedic Surgery, University ofnnecticut Health Center, Farmington, Connecticut, U.S.A.eceived November 30, 2009; accepted December 21, 2009.ddress correspondence and reprint requests to Augustus D.zzocca, M.S., M.D., Department of Orthopaedic Surgery, Uni-sity of Connecticut Health Center, 263 Farmington Ave, Farm-ton, CT 06030, U.S.A. E-mail: mazzocca@uchc.eduublished by Elsevier Inc. on behalf of the Arthroscopyociation of North America749-8063/9711/$00.00Current

Material Properties and Comp

Maureen Suchenski, M.D., Mary Beth MDerek Hansen, B.S., William McKinnon, B.

and Augustus D. M

Abstract: Surgical interference screws and sutureand tendons, to bone are routinely used in arthroscrew fixation provides a press fit between bone,gooi:10.1016/j.arthro.2009.12.026

Arthroscopy: The Journal of Arthroscopic and Related Surepts

ion of Soft-Tissue Fixation

rthy, B.S., David Chowaniec, B.S.,hn Apostolakos, Robert Arciero, M.D.,ca, M.S., M.D.

rs for attaching soft tissue, such as ligamentsc surgery and sports medicine. Interferencetendon, and screw and is frequently used tood biocompatibility, and lack of need for removal

821gery, Vol 26, No 6 (June), 2010: pp 821-831

operations. The ideal material provides adequate me-chnebio

usmelemtioanbodutroveresmeleneleMatocoleaou

othligbinStamito

tiointcescrricsudirlayoxphbinmatiamaodmastace

ings, osseointegration is not always complete. In ananscrtiss

hadisendiforopingpuofgra

inNJuspocaibidifmePoanplaareproanerttypplamoromtogicaligothmedimalspaanpliclolat

the

822 M. SUCHENSKI ET AL.anical fixation, completely degrades once no longereded, and is replaced by bone. The hope is thatcomposites will be able to meet these criteria.

METALS

Most bone anchors currently approved for clinicale are made of metal.1 The 2 most commonly usedtals are stainless steel and titanium. Potential prob-s associated with metallic implants include migra-

n and magnetic resonance imaging artifact. Metalchors also remain permanently embedded in thene, thereby limiting options for anchor placementring subsequent surgery. Metals are shiny or lus-us solid materials that are malleable and ductile yetry durable. The shiny and lustrous property is ault of the tightly packed atomic structure found intals that prevents the transmission of visible wave-gths of light through the material. Metals have lowctronegativities and therefore easily lose electrons.

etals undergo metallic bonding, which means thatms are held together by a sea of electrons not

nfined to 1 nucleus. This allows metals to be mal-ble and ductile, because atoms can be moved with-t breaking the metallic bond.A metal can be used alone or can be combined wither metals to form an alloy. Titanium is a strong,htweight material by itself, but it can also be com-ed with other metals, such as iron or aluminum.inless steel is an alloy of iron, carbon, and chro-um. It is stronger than pure iron and more resistantcorrosion than regular steel.Titanium is widely used for orthopaedic applica-ns. Unlike most metals, which do not integrate wello surrounding bone, titanium behaves more like aramic at the bone-implant interface. Stainless steelews become encapsulated by a fibrous membraneh in inflammatory cells,2 whereas titanium forms arface layer of calcium and phosphate, which bondsectly to bone3 without evidence of this fibrouser4 and with minimal inflammatory response.5 Anide layer spontaneously forms, and calcium andosphate precipitate on this layer. Osteoblasts thend to the surface and actively secrete osteoidtrix.5 Although this affords titanium some poten-l for osseointegration, it is less than that of otherterials. To increase this potential, various meth-s of surface modification have been used withrked success,6 including calcium phosphate sub-nces7 and the induction of a titanium dioxideramic-metal transition layer.8 Despite these coat-imal study, although titanium-coated and uncoatedews had direct bone-implant contact in areas, softueimplant contact was present in both.7

Metallic screws provide rigid, reliable fixation andve been used successfully for decades. However,advantages are associated with their use. The pres-ce of metal screws makes revision surgery moreficult, because the screws must either be removedbe avoided. When one is evaluating a patient post-eratively, it is sometimes necessary to obtain imag-, and both magnetic resonance imaging9 and com-

ted tomography scan are distorted by the presencea metal screw. In addition, metal screws can causeft laceration, particularly with soft-tissue grafts.10

POLYMERS

Polymer-based absorbable implants were first usedthe early 1960s when American Cyanamid (Wayne,) developed Dexon, a polyglycol material that wased as a resorbable suturing material.11 In the 1970slymers for use as biomaterials in orthopaedics be-me popular because of the demand for biocompat-lity and nontoxicity. Furthermore, because of theficulties in imaging and revision surgery thattal implants posed, polymers were investigated.lymers do not interfere with postoperative imaging,d they facilitate revision surgery because the im-nt either resorbs or can be drilled through. Plasticsfound all around us with a variety of material

perties ranging from soft to hard, pliable to robust,d transparent to opaque. This array of material prop-ies allows for the fabrication of plastics for variouses of applications. Polymers are solid, nonmetallicstics composed of a small repeating unit, ornomer, covalently bonded together to form a mac-olecule chain. Although rigid covalent bonds hold

ether monomers, chains are held together by phys-l interaction, similar to entangled Christmas treehts. Polymer chains can move relative to one an-er without breaking covalent bonds, allowing poly-rs to deform without fracturing. However, this alsoinishes strength compared with ceramics and met-

. Inhibiting the ability of polymer chains to slidest each other results in more entanglement of chainsd increased polymer strength. This can be accom-shed by use of larger monomers, longer chains, orser packing (e.g., crystalline regions, as discusseder).Polymers are named for the monomer from whichy are synthesized (e.g., polyethylene from ethyl-

ene) and can be either copolymers or homopolymers.A(pomoD-theicagiolowocchtalthelintalammodecoset

higstrcredifdeingiothe

papoD,theabcutheofdifenPLye

Bi

joifixthaingtioim

sion operations. Bioabsorbable polymer screws haveshwi(Areslinanpoofav

anIfmethecaostiosyfortiobyforenvatiodritio

beantoyeissteInfibAttra

Bi

toomesamthea schPomoPE

823SOFT-TISSUE FIXATIONhomopolymer is derived from a single monomerlyethylene), and a copolymer is derived from 1 orre monomers (poly-D,L-lactide from L-lactide andlactide). These terms are important for determining

degree of crystallinity, which influences mechan-l and degradation characteristics. Crystalline re-ns occur where an ordered, repeating structure al-s for tight packing of chains. Amorphous regions

cur where there is disorder or malalignment ofains. Polymers are either semicrystalline (both crys-line and amorphous regions) or amorphous because

large chains do not allow for completely crystal-e structures. Homopolymers are typically semicrys-line, whereas copolymers typically have a singleorphous phase because the presence of multiplenomers interferes with ordered arrangement.12 The

gree of crystallinity also depends on the rate ofolingslower cooling allows polymer chains totle into an ordered configuration before solidifying.Because order allows for closer packing and aher density, semicrystalline polymers are typically

onger and more resistant to degradation. The de-ased density of amorphous regions allows for fasterfusion into the polymer, leading to more rapidgradation. In semicrystalline polymers this resultsa 2-phase degradation process: the amorphous re-n degrades first, followed by slower degradation ofcrystalline region.

To illustrate the importance of these concepts, com-re PLLA and PLDLA. PLLA is a homopolymer ofly-L-lactide, and PLDLA is a copolymer of poly-L-lactide. Whereas D-lactide and L-lactide contain

same functional groups, they are non-superimpos-le mirror images and are therefore different mole-les (like right and left hands). The combination ofse monomers interferes with ordered arrangementthe polymer chains, because each bonds with aferent 3-dimensional geometry. This small differ-ce has large implications for the degradation ofDLA: the loss of mass time for PLLA occurs overars, compared with 12 to 16 months for PLDLA.13

oabsorbable Polymers

The total number of shoulder reconstructions, smallnt fixations, meniscal repairs, and cruciate ligamentations in the United States is estimated to be moren 250,000 each year. Therefore there is an increas-demand for biodegradable or bioabsorbable fixa-

n implants. These polymers do not interfere withaging and do not need to be removed during revi-own similar or superior fixation strength comparedth metal,10,14-17 and anterior cruciate ligamentCL) reconstructions have shown acceptable clinicalults.16-19 Commercially available implants are out-ed in Table 1. PLLA is used both as a homopolymerd part of a copolymer with polyglycolide (PLGA) orly-D-lactide (PLDLA). Polyglyconate, a copolymerglycolic acid and trimethylene carbonate, is also

ailable.Each polymer has a different degradation profile,d the optimum time frame is yet to be determined.degraded too quickly, the rapid release of the mono-r overwhelms the bodys ability to clear it, and

accumulation of the degradation products canuse adverse reactions. Foreign-body reactions,20-22teolysis,22 synovitis,22,23 intraosseous cyst forma-n,19,24-26 intra-articular inflammatory reactions,27stemic allergic response,28 and loose intra-articulareign bodies29-32 are sometimes seen. These reac-ns are thought to be due to the acidic nature of theproducts.33,34 This may also interfere with bonemation, because hydroxyapatite (HA) is the prefer-tial form of calcium phosphate only at higher pHlues.35 Another disadvantage is failure during inser-n36,37; however, alterations in screw design andve mechanisms have led to less breakage on inser-n.36Degradation times determined in vitro have noten consistent with in vivo degradation. Both PLLAd PLGA have been shown to persist in vivo for up5 years19,26,35,38 and completely resorb at 7 and 10ars, respectively.26,39 When complete reabsorptionseen, screws were not replaced with bone but in-ad consisted of a partially calcified fibrous tissue.39addition, the bone-implant interface consists of arous layer that may interfere with bony ingrowth.12 weeks in PLLA implants, no host tissue pene-

tion was seen at the implant-bone interface.40

ostable Polymers

Because some bioabsorbable polymers can degraderapidly, causing adverse reactions, biostable poly-

rs were investigated. These materials offer thee advantages of bioabsorbable polymers without

se complications. Polyetheretherketone (PEEK) istable, highly unreactive structure that is resistant toemical, thermal, and radiation-induced degradation.lyethylene and polyacetal are also biostable ther-plastic polymers used in orthopaedic implants.EK is a rigid, semicrystalline thermoplastic poly-

TABLE 1. Commercially Available Bioabsorbable and Biostable Polymer Implants and Their Compositions

Art

Art

Bio

Ca(

Co(

Co(

Mi

824 M. SUCHENSKI ET AL.Manufacturer

Suture Anchors Interference Screws

Name BA/BS Composition Name BA/BS Composition

hrex (Naples, FL) Bio-PushLock BA PLLA Bio-Cortical BA PLLABio-PushLock SP BA PLLA/titanium tip Bio-Interference BA PLLA

Bio-SutureTak BA PLDLAFully threaded Bio-

Interference BA PLLABio-Corkscrew BA PLDLA Sheathed Bio-Interference BA PLLABio-Corkscrew FT BA PLLA RetroScrew BA PLLABio-FASTak BA PLDLA Bio-Tenodesis screw BA PLLABio-SwiveLock BA PLLA/PEEK eyelet Delta-Tapered BA PLLABio-SwiveLock SP BA PLLA/titanium tip PEEK Tenodesis Screw BS PEEKPEEK PushLock BS PEEKPEEK PushLock SP BS PEEK/titanium tipPEEK Corkscrew FT BS PEEKPEEK SwiveLock BS PEEKPEEK SutureTak BS PEEK

hroCare (Austin, TX) ParaSorb BA PLLA Graftlok Tapered BA PLLALabraLock P BS PEEKMagnum PI BS PEEKSpeedScrew BS PEEK

met (Warsaw, IN) LactoScrew BA 85% PLLA/15% PGA Gentle Threads BA 82% PLLA/18% PGA

LactoScrew BA 82% PLLA/18% PGA Rattler BA 82% PLLA/18% PGA

ALLThread LactoSorbL15

BA 85% PLLA/15% PGA Bio-Core BA 82% PLLA/18% PGA

MicroMAX BA 85% PLLA/15% PGAArthroRivet RC Tack BA 82% PLLA/18% PGAArthroRivet Cannulated

TackBA 82% PLLA/18% PGA

Hitch LactoSorb L15 BA 85% PLLA/15% PGAALLthread PEEK BS PEEKHitch PEEK BS PEEK

yenne MedicalScottsdale, AZ)

iFix BS PEEK

vidienMansfield, MA)

Polysorb BA PLLA/PGA

nMed LinvatecLargo, FL)

Duet suture anchor BA SR PLDLA(96% L/4% D)

The Wedge BA SR PLDLA(96% L/4% D)

IMPACT suture anchor BA SR PLDLA(96% L/4% D)

SmartScrew ACL BA SR PLDLA(96% L/4% D)

BioCuff and BioCuff C BA SR PLDLA(96% L/4% D)

BioScrew BA PLLA

Paladin BA SR PLDLA(96% L/4% D)

Bio Mini-Revo BA SR PLDLA(96% L/4% D)

Bio-Anchor BA PLLABioTwist RC BA PLLAUltraSorb RC BA PLLA

tek (Raynham, MA) QuickAnchor Minilok BA PLLA Absolute BA PLLAQuickAnchor Microfix BA PLLA Intrafix BS PolyethyleneBioknotless SA BA PLLABioROC EZ anchor BA PLLALupine BA PLLASpiraLok BS PLLAPanaLok BS PLLAHealix PEEK SA BS PEEK

meplarelponodenoinflhaplacarcreneproHAflutio

merev

TABLE 1. Continued

positi

lenend Tita

Sm( onate

onate

alStr

(

Zim

N t in botfol GA forbio rs (22

A ed.

825SOFT-TISSUE FIXATIONr with excellent mechanical properties.41 Thermo-stic polymers harden on cooling and tend to beatively soft.42 PEEK offers the advantages of goodstoperative imaging43-46 and stable fixation whilet having the complications associated with polymergradation. PEEK implants in animals have shownacute inflammatory response and only mild chronicammation.47 Similar to metals, the major problem

s been poor osseointegration. In animals PEEK im-nts showed direct bone contact in some areas buttilage and fibrous interfaces as well.47 This de-ased bone-implant interaction is because the inert-

ss and hydrophobicity of PEEKs surface hindertein and cell adhesion.46,48,49 PEEK fails to form

on its surface when exposed to simulated bodyid.50 As with metals, methods of surface modifica-n have been used with PEEK.46,48,51

BIOCOMPOSITES

Biocomposites have the same advantages of poly-rs, such as ease of postoperative imaging16,52 andision surgery, with the added benefit of bone for-

Manufacturer

Suture Anchors

Name BA/BS Com

ROC EZ anchor BS Polyethy

Versalok BSPEEK a

eyeletith & NephewMemphis, TN)

TwinFix AB BA PLLASuretac BA PolyglycBioRaptor 2.9 BA PLLARaptormite BA PLLATAG BA PolyglycKINSA BS PEEKBioRaptor PK BS PEEKTwinFix PK BS PEEKFootprint PK BS PEEKSpyromite BS PEEKDynomite BS PEEKRaptormite PK BS PEEKNonabsorbable TAG BS Polyacet

ykerHopkinton, MA)

BioZip BA PLLAXCEL anchor BA PLLAPEEK IntraLine BS PEEKPEEK BioZip BS PEEKPEEK TwinLoop BS PEEK

mer (Warsaw, IN) Bio-Statak BA PLLAOTE. Pure PLLA was the most common bioabsorbable componen

lowed by PLGA for interference screws (3 [16%]). PLDLA and PLstable polymer in interference screws (2 [67%]) and suture anchobbreviations: BA, bioabsorbable; BS, biostable; SR, self-reinforction within the screw. A composite consists of 2ferent materials, and those used in interferenceews and suture anchors (Table 2) consist of aamic and polymer. All available implants consist ofioabsorbable polymer and bioactive ceramic, butEK-ceramic composites are currently being inves-ated.50 Studies have shown good clinical resultsth biocomposite interference screws,53,54 as well asisfactory biomechanical testing.10,55A ceramic is a compound composed of metallic andnmetallic elements with predominantly ionic bond-. The metallic cation (positively charged ion) andnonmetallic anion (negatively charged ion) are

n held together by an electrostatic force becauseposite charges attract. Although this force is strong,ing ceramics an inherit strength and toughness, it is

t rigid and can be disrupted by movement of thems relative to one another, particularly with tensilesheer forces. This gives ceramics their characteris-brittleness. Bioactive ceramics (those that enhance

ne formation) include HA [Ca10(PO4)6(OH)2],tricalcium phosphate (-TCP [Ca3(PO4)2]), bipha-calcium phosphate (HA and -TCP), calcium car-

Interference Screws

on Name BA/BS Composition

nium

BioRCI BA PLLAEndo-FIX L BA PLLA

Bioabsorbable wedge BA PLLA

h interference screws (14 [74%]) and suture anchors (22 [55%])suture anchors (8 [20%]) were equal. The most commonly used[92%]) is PEEK.madifscrcera bPEtigwisat

noingthetheopgivnoatoorticbo-sic

bonate, and calcium sulfate. Because HA and -TCPareinomiwi

forsobioapthewihaleawhfolocbosloabpoblatisca

erapromalowgeimbomeacinttiosiotitaforexentioingmoex

podeforsoan10

TABLE 2. Commercially Available Composite Implantsand Their Compositions

ArtS

I

ArtS

I

BioI

CoI

MiS

I

SmS

I

StrI

Nscr-Tinte

826 M. SUCHENSKI ET AL.composed of calcium and phosphate, the primaryrganic component of bone, they closely mimic itsneral phase.56,57 Essentially, bone mineral is HAth the addition of impurities.56Bioactive ceramics have been studied extensively

use as bone-graft substitutes.58-60 Whereas bioab-rbable polymers are surrounded by a fibrous layer,61active ceramics spontaneously form a bone-like

atite layer from amorphous calcium phosphate onir surface,62 which bonds directly to and integratesth the bone matrix.27,56,58,62 Both HA and -TCPve excellent osteoconductivity because of the re-se of calcium and phosphate when degraded,60ich encourages mineralization and provides a scaf-d for bone growth.63,64 This degradation is oste-last mediated and similar to that of normalne.57,65 However, the degradation of HA is muchwer, and it is sometimes classified as nonresorb-le.66 The increased calcium levels with degradationtentiate chemotaxis and differentiation of osteo-sts. Several proteins associated with connective

sue regeneration increase expression with increasedlcium concentration.67,68The similarity of this apatite-like layer to the min-l phase of bone allows osteoblasts to preferentiallyliferate and differentiate, forming an extracellulartrix of biological apatite and collagen.62 This al-s new cells to migrate into the implant69 and

nerate bone from within58,60,70 at the same time asplant resorption.60,71 Biocomposites show increasedne formation and contact area compared with poly-rs.61 The mineral matrix may also mimic the inter-

tions of osteoblasts with normal bone and regulateracellular signal transduction and gene transcrip-n, enhancing bone production. Serum protein adhe-n to HA is almost 60 times greater than adhesion tonium,56 and many of these proteins are importantdirecting the differentiation of osteoblasts. For

ample, fibronectin and vitronectin, known to influ-ce cellular response to growth factors, differentia-n, and proliferation of osteoblasts, mediate spread-

of human osteoblast-like cells on HA.56 Theselecules are absent on titanium,56 which may help

plain its inferior osseointegration.The combination of ceramics with biodegradablelymers creates a macroporous structure on polymergradation. Porosity is an important factor in themation of bone,60 because it allows for faster re-

rption of the calcium phosphate (Ca-P) componentsd better bony ingrowth.60 A minimum pore size of0 nm is required, but microstructure is also impor-Manufacturer Polymer Ceramic

hrexuture anchorsBiocomposite

Corkscrew FT85% PLA 15% -TCP

BiocompositeSutureTak

85% PLA 15% -TCP

BiocompositePushLock

85% PLA 15% -TCP

nterference screwsBiocomposite

Interference70% PLDLA 30% Biphasic

Ca-PhroCareuture anchorsDoubleplay 30% PLLA TCP

nterference screwsBilok Parallel Sided 70% PLLA 30% -TCPBilok Tapered PLLA TCP

metnterference screws

ComposiTCP 40% PLDLA 60% -TCPnMed Linvatecnterference screws

Matryx 75% SR PLDLA(96% L/4% D)

25% -TCP

tekuture anchorsHealix BR 70% PLGA

(85% PLLA/15% PGA)

30% -TCP

Lupine BR 70% PLGA(85% PLLA/15% PGA)

30% -TCP

BioKnotless BR 70% PLGA(85% PLLA/15% PGA)

30% -TCP

Gryphon BR 70% PLGA(85% PLLA/15% PGA)

30% -TCP

nterference screwsBio-Intrafix 70% PLLA 30% -TCPMilagro BR 70% PLGA

(85% PLLA/15% PGA)

30% -TCP

ith & Nephewuture anchorsOsteoRaptor 75% PLLA 25% HA

nterference screwsBioRCI-HA 75% PLLA 25% HABioSure HA 75% PLLA 25% HA

ykernterference screws

Biosteon Wedge 75% PLLA 25% HA

OTE. Pure PLLA comprised the majority of interferenceews (7 [64%]) and suture anchors (5 [56%]) for polymers.CP was used as the ceramic component most often in bothrference screws (6 [55%]) and suture anchors (7 [89%]).

tant because increased pore roughness correlates withbecoofocboanityresphforingmean

apatite layer in simulated body fluid unless modified,

Art

Art

Bio

Co

Co

aniumanium

Mi aniumaniumaniumaniumanium

Sm aniumanium

Str aniumanium

Wr(

anium

Zim anium

N etal scom suture

827SOFT-TISSUE FIXATIONtter bone-forming ability. In animals PLGA/Ca-Pmposites formed a porous material on degradationPLGA and showed bony ingrowth in the previouslycupied spaces, whereas Ca-P alone only showedne formation within small fractures of the cementd minimal implant reabsorption.60 Increased poros-by changing the polymer percentage from 15 to 30ulted in more bone formation.60 Biphasic calciumosphate shows good integration between newlymed bone within the degrading material and exist-

bone.59 -TCP bonds directly to bone, but itschanism appears to be different from that of HA

d other bioactive ceramics.66 -TCP fails to form an

TABLE 3. Commercially Available M

Manufacturer

Suture Ancho

Name

hrex FASTak TitFASTak II TitCorkscrew TitCorkscrew FT TitCorkscrew FT II Tit

hroCare Magnum X StaMagnum2 StaMini-Magnum StaParafix Tit

met ALLThread Titanium TitTitanium TitHarpoon StaMini-harpoon Sta

vidien Ogden TitHerculon Tit

nMed Linvatec Ultrafix RC StaUltrafix Knotless Minimite StaUltrafix Minimite StaUltrafix Micromite StaRevo TitMini-Revo TitSuper Revo Tit

tek Knotless TitMini anchor/micro anchor TitGII anchor TitEasy anchor/Quick anchor TitFastin Tit

ith & Nephew TwinFix Titanium TitMiniTac Tit

yker Titanium wedge anchor TitIntraLine Tit

ight Medical TechnologyArlington, TN)

Anchorlok Tit

mer Statak Tit

OTE. The current commercially available implants comprise 33 mprised all of the available metal interference screws and 73% ofcause the formation appears to be more pH depen-nt and forms only at higher pH values.Compared with the well-documented inflammatoryponse seen with bioabsorbable polymers, severaldies have failed to observe adverse clinical reac-ns with biocomposites54,60,72 or have shown only ald reaction.52,61 Histologically, less inflammatoryponse was seen in HA/PLLA composites than withLA alone.61 The release of basic salts by the deg-ation of the bioceramic may buffer the acidicakdown products of the polymers. -TCP has been

own to buffer the pH near poly(lactic acid)-polyycolic acid) implants undergoing degradation,33

mplants and Their Compositions

Interference Screws

mposition Name Composition

alloy Fully threaded Titanium alloyalloy RetroScrew Titanium alloyalloy Softscrew Titanium alloyalloy Sheathed cannulated Titanium alloyalloy Tenodesis screw Titanium alloysteel Graft fixation screw Titaniumsteelsteel

TunneLoc Titaniumalloysteelsteelalloyalloysteel Guardsman Titanium alloysteel Propel Titanium alloysteelsteelalloyalloyalloyalloy/nitinol arcs Profile Titanium alloyalloy/nitinol arcs Advantage Titanium alloyalloy/nitinol arcs Big Advantage Titanium alloyalloy/nitinol arcs

Cannuflex silk TitaniumRCI TitaniumSoftsilk TitaniumWedge Titanium

alloyalloy

alloy

uture anchors and 16 metal interference screws. Titanium alloyanchors (24).bede

resstutiomiresPLradbresh(gl

etal I

rs

Co

aniumaniumaniumaniumaniuminlessinlessinlessaniumaniumaniuminlessinlessaniumaniuminlessinlessinlessinlessanium

and pH buffering causes less toxicity.34 HA has alsoTABLE 4. Summary of Interference Screw and SutureAnchor Compositions

TyTis

Me

Bio

Bio

BioC

P

Ty

Me

Bio

Nonobstructive in imaging Nonobstructive in subsequent

surgeries Wide range of material properties Metal-like mechanical properties are

Bios

EK)Bio

N sorptioins

A acid); T

828 M. SUCHENSKI ET AL.en shown to buffer the acidic breakdown productsPLLA (pH 7.3 for HA/PLLA v 3.0 for PLLA).73ilar to polymers, screw breakage during insertion

an issue for biocomposites.36The bioabsorbable polymer in biocomposites can beed as a vehicle for the release of molecules tohance bone formation. BMP is well known to en-nce bone formation.6,70 Biodegradable polymers re-se BMP slowly,70 which studies have shown to best effective.6 Several studies have proven the effi-

cy of biocomposites as vehicles for growth factorlivery.59,74,75

SCREW GEOMETRY

Although attention must be given to material compo-on and biomechanical suitability, it is important tonsider the screw geometry. This is especially impor-t when comparing different studies, because some

s Materials Used for Soft-Tissue FixationDisadvantages Examples

Migration Magnetic resonance imaging artifact Artifact in subsequent surgeries Can result in graft laceration Incomplete osseointegration

Titanium Aluminum Stainless steel Alloys

Byproducts of degradation are acidic May interfere with bone and soft-

tissue healing Possibility of foreign-body reactions Failure during insertion

PLLA PLGA PLDLA

Poor osseointegration because ofinertness and hydrophobicity

PEEK PET

Failure during insertion HA/PLA PLA/-TCP PEEK-ceramic PLGA/Ca-P PLA/PLGA/TMC PLC

n, osseointegration, and compatibility; however, failure during

MC, trimethylenecarbonate.achievable Positive clinical results Various degradation profiles

stable polymers Same advantages of bioabsorbablepolymers with fewer complication

Polymer that does not degrade Little to no inflammatory response Very similar modulus to bone (PE

composites Advantages of polymers Consists of ceramic and polymer

making the screw bioactive Positive clinical results Creates macroporous structure on

polymer degradation to improveosseointegration

Able to carry growth factors Little to no inflammatory response

OTE. Many of the new materials have shown an increase in abertion still remains problematic.bbreviations: PET, polyethylene terephthalate; PLA, poly(lacticbeofSimis

usenhaleamocade

siticotan

pe of Soft-sue Fixation Suture Anchors Interference Screws

tal 24 Titanium (73%) 16 Titanium (100%)9 Stainless steel (27%)

absorbablepolymer

22 PLLA (55%) 14 PLLA (74%)8 PLDLA (20%) 3 PLGA (16%)8 PLGA (20%) 2 PLDLA (11%)2 Polyglyconate (5%)

stablepolymer

22 PEEK (92%) 2 PEEK (67%)1 Polyethylene (4%) 1 Polyacetal (33%)1 Polyacetal (4%)

compositeeramic 8 -TCP (89%) 6 -TCP (55%)

1 HA (11%) 4 HA (36%)1 Biphasic Ca-P (9%)

olymer 5 PLLA (56%) 7 PLLA (64%)4 PLGA (44%) 3 PLDLA (27%)

1 PLGA (9%)

TABLE 5. Advantages and Disadvantages of Varioupe of Soft-Tissue Fixation Advantages

tals Malleable Ductile Durable Formation of alloys Reliable fixation

absorbable polymers Biocompatible Bioabsorbable

have suggested that screw geometry is a more impor-tanmatanthrgaanare

C

turingartobAmmetacobrep

fouenintare

bioPLscrsecferanPLscrwibioantersu

plapofer[56mosu

an

CONCLUSIONS

moartscrscrtisarenethetenscrtertenosoftraWredformacatdisria

Asea&Arlite

1.

2.

3.

4.

5.

6.

7.

829SOFT-TISSUE FIXATIONt determinant of pullout strength than the type ofterial. Several studies have stressed the impor-ce of various aspects of screw geometry, such asead diameter,15,76 core diameter, screw length,77p size,77,78 buttress geometry,79,80 and drive mech-ism.76 In general, increased thread-bone surfacea results in increased fixation strength.77,80

OMMERCIALLY AVAILABLE PRODUCTS

Companies producing interference screws and su-e anchors were identified by contacting the operat-

room coordinators at local hospitals, checkingicles for references to orthopaedic companies, andtaining product pamphlets from exhibitors at theerican Academy of Orthopaedic Surgeons annual

eting in February 2009. Each company was con-ted, and information on available products wastained from each companys Web site and salesresentatives.

IMPLANT REVIEW

The review of commercially available implantsnd 33 metal suture anchors and 16 metal interfer-

ce screws (Table 3). All of the available metalerference screws and 73% of suture anchors (24)made of titanium alloys.

Table 1 outlines the available bioabsorbable andstable polymers. For bioabsorbable polymers, pureLA was the most common in both interferenceews (14 [74%]) and suture anchors (22 [55%]). Theond most common material was PLGA for inter-ence screws (3 [16%]), with a tie between PLDLAd PLGA for suture anchors (8 [20%]). Seven of theDLA implants (5 suture anchors and 2 interferenceews) are self-reinforced, containing PLDLA fibersthin the implant. PEEK is the most commonly usedstable polymer in interference screws (2 [67%])

d suture anchors (22 [92%]). Only 3 biostable in-ference screws are available, compared with 24ture anchors.The compositions of available biocomposite im-nts are outlined in Table 2. For the polymer com-nent, pure PLLA comprised the majority of inter-ence screws (7 [64%]) and suture anchors (5%]). For the ceramic component, -TCP was usedst often in both interference screws (6 [55%]) and

ture anchors (7 [89%]).Table 4 summarizes the available interference screwsd suture anchors by material category.Interference screws and suture anchors are com-nly used for fixation of soft tissue to bone inhroscopic surgery and sports medicine. Interferenceews tightly sandwich the graft/tendon between theew and the bone, whereas suture anchors attach softsue to an implant embedded in bone. Many implants

made from metals; however, the advancement ofw polymers and composites has made the use ofse materials more common (Table 5). In bicepsodesis and ACL reconstruction, bioabsorbableews provide mechanical stabilization in the shortm, allowing for early range of motion while bone-don healing occurs. Biological fixation, through

seointegration, provides the long-term stabilizationthe tenodesis or ACL graft by allowing for effectivensmission of loading forces and enhancing stability.hen this stability is achieved, the screw becomesundant. Attention has turned to options that allowbone formation within the implant. Because no

terial has been shown to be superior for all appli-ions, the surgeon must weigh the advantages andadvantages of each to evaluate the optimum mate-l for a given application and patient.

cknowledgment: The authors thank Arthrex for re-rch support. They also thank the Arthrex, Stryker, Smith

Nephew, Biomet, ConMed Linvatec, Mitek, Zimmer, andthroCare sales representatives for assistance with productrature.

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Material Properties and Composition of Soft-Tissue FixationMETALSPOLYMERSBioabsorbable PolymersBiostable Polymers

BIOCOMPOSITESSCREW GEOMETRYCOMMERCIALLY AVAILABLE PRODUCTSIMPLANT REVIEWCONCLUSIONSAcknowledgmentREFERENCES