Absorbable Screw Fixation - The Podiatry Institute

CHAPTER 11 59threaded, whereas the SR-PLLA screw is availablefully- or partially-threaded. Current criteria for theuse of BIOFIX screws include humeral head fractures,olecranon fractures, condylar fractures of thehumerus, condylar fractures of the distal femur orproximal tibia, displaced ankle fractures, and anklearthrodesis.5 They have also been used successfullyin subtalar afihrodesis.The most significant difference between theSR-PGA and SR-PLLA screws is strength retention.The SR-PGA screw is stronger, but the SR-PLLAscrew persists longer.' The SR-PGA screw loses itsmechanical resistance in vivo between 30-60 days,and the SR-PLLA screw between 3-72 months.Biodegradation time, or time to complete absorption,is 5-10 months for the SR-PGA material, and variesfrom 15 to 60 months for SR-PLLA materiai. The actualtime depends on shape, size, molecular weight, andvariable tissue environments of implantation.The initial resistance to shear and flexion forcesof the screws is 20-30 times that of cancellousbone. Their modulus of elasticity is comparableto cortical bone, and roughly 2-3 times that ofcancellous bone. By comparison, the modulus ofelasticity of stainless steel is rnore than 20 times thatof cancellous bone. Clinically, the decrease inbending strength is more rapid than that of shearstrength.3'5 The screws require a dedicated screwdriver, tap, and countersink. A11 instrumentationpieces are compatible with the standard AO/ASIFquick release handles (Fig. 1).Screw InsertionInsertion of the screws requires attention to technique,and the following specifics are recommended by themanufacturers. Reduction of the osseous componentsis achieved and stabilized with clamps.Specific to ankle fracture repair, the screw is inserled75-85 degrees to the fracture line, as opposed to 90degrees. If the reduction is exact, the direction offixation is not the same as the rotational axis of thefragment, since rotation is not possible without anew fracture or failure of fixation.' The drill and/orover-drill hole is made with the corresponding sizedrills. Tapping is performed with care to ensurecrossing the entire length of the hole. The near cortexis then countersunk. The screw channel isflushed with saline and the screw insefied. The headof the screw is then cut so that only 1 mm remainsabove the cofiex.Since the torsional strength of the absorbablescrew is not as high as that of a metallic implant,care must be taken when inserting the screw. Thescrew must turn easily into the bone, otherwise itmay break. If a screw breaks, the exposed portionof screw is cut flush with the bone, rather thanattempting to remove it. A few reasons for screwbreakage are suggested by the Finnish surgeons:the drill hole may not be long enough; the tappingmay have been done improperly; or the drill holemay have been dry. Lastly, the longer the screw,the more chance for increasing the friction forceson the screw. Therefore, extra care should be takenduring insertion.5Figure 1. The tips of the screw driver, countersink, and tap requiredfor the BIOFIX absorbable screws. Note the size of the countersinkcompared to a standard AO/ASIF countersink.AdvantagesIn direct comparison with metallic screws, severalfeatures of absorbable screws are highlighted bythe manufacturers. Absorbable implants essentiallyeliminate the financial burden of secondary proceduresto remor,e internal fkation. This is oftenregarded as a psychological benefit as well, pafiicularlyin children. Magnetic resonance and computedtomography imaging are also possible without thescattering caused by metallic devices. The absorbablematerial is considered tissue equivalent. Absorbablescrews may also be left in sites of infection as theyare bacteriostatic. Growing bacteria do not affect theabsorption of the screws. The relationship betweenthese screws and the presence of stress protection orstress shielding has akeady been discussed.

60 CHAPTER 11PrecautionsBIOFX screws are not recommended in patients over70 years of age. Caution is also advised in any patientwith advanced osteoporosis or a coruninuted fracture.In those patients with rheumatoid disease, andin cases of ankle afihrodesis, only the SR-PLIAimplants are advised. Lastly, the SR-PGA screws arespecifically recommended for transyndesmoticflxation when necessary in standard ankle fracturemaflagement. Furlher contraindications for their useinclude alcoholism or psychiatric disorders which limitthe patient's ability to cooperate.The most significant precaution regarding thebioabsorbable screws is the periodic developmentof a local fluid accumulation. This has beenobserved at 8-72 weeks after surgery utilizing SR-PGA screws and tB-36 months involving theSR-PLLA screws. The most recent literature reportsa complication rate of 0-40/0,This appears to be a nonspecific, foreign bodyreaction that is noninfectious and unique toabsorbable fixation. There are varying grades ofpresentation of this soft tissue response. If the reactionis clinically noticeable, but sma1l and painless,it may only be obserued. If it is red and inflamed,painful, and larger than 1.5 centimeters in diameteqit should be aspirated. On occasion, a sinus tract orfistula will form that should be incised and drained.The fluid is viscous, yellow to clear, and aseptic.The wound will completely resolve within 10weeks. This reaction has no effect on the final outcomeof the osseous surgery or functional recovery.are available. Howeveq the authors offer somegeneral obseruations regarding the feasible uses inpodiatric surgery.The currently avarlable screw sizes are applicableto selected forefoot, midfoot, rearfoot andankle surgical procedures. The thread geometry ofthe screws is unique. The profile most closelyresembles a 3.5-mm AO/ASIF cortical screw withthe pitch a 4.0-mm cancellous AOIASIF screw,however, they are not identical (Fig. 2). The screwhead is rectangular-shaped and slightly larger thanan AOIASIF screw of the same size (Figs. lA, 3B).The screw head does not contain a hexagonalFigure 2. The thread pitch of a BIOFIX screw is 1.75-mm, the same as a,1.0-mm cancellous AO/ASIF screw. The thread profile is shallower andcoarser in comparison to standard metallic screws. Left, AO/ASIF 4.0-mmcancellous, Center. SR-PLLA 3.5-mm, Right, AO,/ASIF 3.5-mm cortical.EARLY CLINICAL IMPRESSIONS ANID APODIAIRIC PERSPECTTVEThe research and clinical experience regardingabsorbable materials such as rods, screws, membranes,and tacks, is vast. More than 15 doctoraltheses and over 600 scientific studies have beenpublished entailing animal studies and humantrials.6 However, clinical and scientific investigationin North American literature is in its infancy in respectto absorbable screws. Our clinical use of these screwsat this time is limited to first metatarsophalangealarthrodesis, hallux interphalangeal arthrodesis, andproximal first metatarsal osteotomies. Any impressionwith regard to long-term efficacy in these applicationsis premature. Since this is the first report of suchclinical use in the world literature, no comparisonsFigure JA. A comparison of screw head sizes and shapes. left, SR-PLLA 4.5-mm, Center, AO/ASIF 3.5-mm, Right, SR-PLLA 3.5-mm.

CHAPTER 116IFigure 38. Heacl profiles of same scres,-s as shown in Figure 3A.recipient for the screw driver as do AO/ASIFscrews. Therefore, the screw driver is designed togrip the screw head circumferentially. The screwalso possesses a small fissure at its tip, whichreportedly opens when the fixation is firm enough.This screw driver tip-screw head design significantlyincreases the torque forces along the shaft ofthe screw and at the screw head-shaft junction duringinserlion. Excessive tightening of the screw canbreak the head or cause the screw to splinter alongits shaft (Figs. 4A-4C). These torque forces are similarlyincreased if the screw hole has not beentapped completely and the screw is attempting tocut its own threads.Figure 48, Tightening of the screw past the point of resistance causesf':Ltigue failure of the screrv along its shaft. The linear strand configurationof the screu' has disrupted (color change) as compared toFigure 5. The screw does not tolerate high torque fbrces rvell.Figure 4C. This SR-PGA screw has splintered along its slraft due toercessive torque forces applied experimentally.Figure 4A. Insertion of a SR-PLLA screw in a bone model to the pointof resistance.Figure 5. Reduction of the head of a SR-PLLA 3.5-mm screw with anoscillating saw.

62 CHAPTER 11The instnrmentation and screws were initiallydeveloped for use in the tibia and fibula for anklefracture repair. The countersink is quite large, andremoves excessive bone from a smaller structuresuch as a first metatarcal. The authors have foundit safer to create the countersink in a first metatarsalwith a rotary burr. Generally, the screw headremains prominent, and the manufacturer's recommendationsare to reduce the head to 1 millimeterabove the coftex or cut it flush with a small saw(Fig. 5). This not only reduces the prominence butpresumably diminishes the chance of an adversesoft tissue reaction postoperatively.The most publicized benefits of absorbablefixation are a lack of need for removal, and reductionof stress shielding. The most commonly referred-todisadvantages of metallic fixation are stress shielding,corrosion, sensitization dermatitis (rare) and the needfor removal.T However, metallic fixation has generallybeen used quite successfully with minimal complicationsin foot and ankle surgery. For absorbable screwsto be clearly advarrtageous, they must offset thesedisadvantages, possess minimal detriments of theirown, and provide adequate stability for bone union.In the authors' opinion, three reasonablequestions may be entefiained regarding the use ofthese screws in podiatric surgery. Is the avoidanceof removal of metallic fixation a benefit that will beconsistently realized? Is the presence of stressshielding clinically significant? Vhat is the clinicalsignificance of the occasional soft tissue reactionsto the implants?The elimination of secondary procedures forretrieval of internal fixation is attractive in patientc re, both economically and psychologically.However, this is an economic savings only if thepracticing surgeon routinely removes hardware.Although the AO/ASIF school has recommendedeventual removal of fixation to restore normal biomechanicalforces on bone, the current range ofpractice likely exists between routine removal androutine retention. Although the possibility of softtissue reaction to a long-standing foreign body(such as corrosion) exists, by far the usual reasonfor removal of metallic fkation is discomfort due toprominence beneath the skin.Absorbable screws have this clear advantageregarding ankle fracture repair and the use of internalfixation in areas of limited soft tissue coverage.Articles exist showing favorabte comparisonsbetween metallic and absorbable fixation in thisapplication.',' Either SR-PGA or SR-PLLA screwshave demonstrated clinical success in stabilizing allcomponents of an ankle fracture: the fibula, medialmalleolus, and posterior malleolus. In thosepodiatric procedures where removal of fkationmay be performed under local anesthesia in theoffice, any economic or psychological savings fromthe absorbable screws are less well-defined.Savings may be further diminished in light of theadditional initial expense of the absorbable screws.The clinical significance of stress shieldingdepends laryely on the anatomic region of thelower extremity. The stress protection created by adynamic compression plate with screws in afemoral fracture is understandably more significantthan that of a K-wire in a digital fusion. Thepremise exists that the stiffness of metallic screwsmay contribute to nonunions in ankle afthrodesis,'particularly if the screws are insefied in such a waythat they prevent stress transfer to the uniting bonesurfaces. An example of this is when a fibular onlaygraft is stabilized with screws perpendicular to theaxis of the tibiotalar surfaces. SR-PLLA absorbablescrews inserted obliquely from the tibia and fibula,toward the uniting talotibial joint, have demonstratedan excellent fusion rate in conjunction withfull-weight bearing in a short leg cast from thesecond postoperative day.'Immediate weight bearing was also allowed ina series of subtalar extra-articular arthrodeses inchildren with spastic neuromuscular deformity. Infive out of seven cases, those fixated with SR-PLLAabsorbable screws demonstrated better radiographicunion than their counterparts that werestabilized with metallic fixation. The remaining twocases were equal at one year.eIn such uses of absorbable screws peftinent topodiatric surgery, the common denominatorappears to be minimally- to non-weight-bearingstructures (fibula, medial malleolus), or axiallyloaded fusion sites (ankle, subtalar joints). Theliterature suggests better and faster radiographicunion and less porosity with the absorbablescrews. This is attributable to the modulus of elasticityof the implant which is near equal to boneinitially, and graduaily weakens as the bone gainsstrength. This reduction of stress shielding and theresultant benefits appear to be very real advantagesof absorbable screws in these indications. The successfulallowance of immediate weight bearing is indistinction to standard podiatric ankle or subtalar

CFIAPTER 11 63fusion techniques with metallic fixation that requireprolonged periods of non-weight bearing.However, the pertinence of stress-shielding orstress-protection osteopenia in forefoot surgery islikely more procedure specific. For example, in thetechnique of hallux interphalangeal joint fusion,the absorbable screw does not seem advantageous.Stress shielding at this site is minimal, and if screwremoval is necessary, it is easily performed underlocal anesthesia. Metallic flxation also subjectivelyoffers firmer purchase and compression in theproximal phalanx than the absorbable screws.However, the forces acting upon a first metatarsalproximal osteotomy or a midfoot fusion are signiticantlylarger due to the unique biomechanics of thefoot in gait. The reduction of stress shieldingafforded by the less rigid absorbable screws mayencourage more rapid and solid osseous consolidationin these applications, similar to the successnoted in ankle fusions.Absorbable screws do contribute a potentialsoft tissue complication that must be clearly understood.This transient soft tissue reaction has beenextensively studied since it was first noted with theearly development of polyglycolide rods.3 Theexact reason for the reaction is unknown, butappears to be a unique foreign body reaction to theraw materials, alpha-hydroxy polyesters. Currently,there is no evidence that the reaction is immunologicallymediated or infectious in nature. A lowerincidence has been reported since the removal ofthe aromatic quinone (green) dye from the firstgeneration polyglycolide rods and screws, but thisis also clearly not the only factor. Since the adventof the colorless raw materials used to make thescrews, the reported incidence of tissue reactions isless than 4ol0.'The development of a clinically manifestedreaction seems to be associated with the phase ofliquefaction of the degrading polymer.'O The clearanceof liquid debris from the implant depends onlocal tissue tolerance and clearing capacity.,, Therelatively compact nature of cancellous bone maybe a factor. Surgical technique may also play a role,such as when a large amount of screw head is leftabove the cortex in an area where soft tissuecoverage is thin.In general, reactions to the PLLA implants arereported less often. However, reactions have beenseen with PLLA implants approximately 4 yearsafter surgery." The longer degradation time andassociation befween clinical reaction and liquefactionphase of the implant may be a factor.Interestingly, the follow-up review of most articlesrarely approaches four years, which theoreticallymight affect the number of reported reactions.Lastly, PLLA raw material from varying sources candiffer considerably in thermal history, molecularweight, and crystallinity, resulting in differentdegradation patterns and tissue responses.The actual tissue reaction may vary from localerythema that resolves in a few days to a sinus tractformation which requires surgical debridement.The incidence of sinus tract formation may bedecreased or prevented by aspirating or incisinglocal fluid accumulations. The reactions are apparently manageable without difficulty, and do notinfluence the functional recovery in any way. Theauthors have not had any experience with thesereactions to date. It should be emphasized thatreports in the podiatric literature of reactions toBIOFIX material were with the use of PGA pins,and prior to the removal of the green dye.","Final observations are that the screws areradiolucent, and thal the amount of interfragmentarycompression seems less than that which isattainable with metallic fixation. Both factors maybe disconcerting to surgeons accustomed to standardAO/ASIF techniques and materials (Figs. 6A,Figure 6A. Preoperative x-ray of a moderateseverehallux valgus deformity.

64 CHAPTER 1168). The radiolucency is a drawback in those procedureswhere confirmation of position of fixationis desirable. More reliance on the position of temporaryflxation and the technical execution of theprocedure may be necessary. The obtainable interfragmentarycompression is a product of screwdesign and the operative technique recommendedby the manufacturers. Howevel the more pefiinentissue is whether the compression is adequate.Clinical studies clearly indicate that the difference inbiomechanics of these implants, as compared withmetallic screws, does not affect the radiographic orclinical outcome in the recommended uses.Figure 68. Immediate postoperative x-ray of halluxvalgus correction via a transpositionalproximal osteotomy. The SR PLI.A 3.5-mm screwused for flration is completely radiolucent.The only absorbable screw available for clinicaluse in the United States at this time is the SR-PGA4.5-mm fully-threaded screw. The literature supportsits immediate use in ankle fracture repair. It is particularlywell-suited to trans-syndesmotic fkationdue to its relatively shofi strength duration and theelimination of a second procedure for fixationremoval. The indications and uses of absorbablescrews will expand in the ensuing years as othersizes and the SR-PLLA screws are released. Theyrepresent an exciting option in the selection of internaltixation devices currently avallable. Appropriateindications in podiatric surgery will require objectiveevaluation of matters such as those discussed here,and other factors elucidated by present and futurescientific research.6789101112.L3.74REFERENCESPartio EK: Absorbable screws in the firation of cancellous bonefractures and arthrodesis. A clinical study of 318 patients.Academic dissefiation, from the Depafiment of Othopaedics andTraumatology, Helsinki University Central Hospital, Helsinki, 1992.Pafiio EK, Bostman O, Hirvensalo E, et al.: Self-reinforcedAbsorbable Screws in the Fixation of Displaced Ankle Fractures.A Prospective Clinical Study of 152 Patients J Ortbop Trauma5:209-215,1992.Biofix-Tissue Management Systems, Implantes reabsorbiblesauto-reforzados de acidos poliglicolido (SR-PGA) y polilactido(SR-PLIA), para la fijacion de fracturas. (product information)Bioscience Limited, Tampere, Finland.Tormrilzi P. Vasenius J, Vainionptii S et a1.: Ultra-high-strengthabsorbable self'-reinforced polyglycolide (SR-PGA) compositerods for internal fkation of bone fractures: In vitro and in vivoswdy. J Biomed Mater Res 25:1.-22, 791)7.Biofix, Absorbable Self-Reinforced Tissue Management Implants,lYorksbop Trdining Manual, Part III, Full Tlcreacl Screus JbrOrthopaedics and Traumatology. Bioscience Limited, Tampere,Finland, 1992.Manuscript for the Bioflr sales aid, Bioscience Limited, Tampere,Finland. 1994.Bostman O, Pafiio EK, Hirwensalo E, Rokkanen P: Foreign bodyreactions to polyglycolide screws. Observations io 24/2L6 malleolarfracture cases. Acta Orlhop Scand 63173-176,1992.Pafiio EK, Hirvensalo E, Pafiio E, et al.; Talocn:ral Arthodesiswith Absorbable Screws. Acta Ofihop Scand.53:170-172, 1992.Pafiio EK, Merikanto J, Heikkia JT, et a1.: Totally absorbablescrews in the firation of subtalar extra-articular arthrodesis inchildren with spastic neuromuscular disease. J Pediatr Ortbop \21646-6i0, 1992.Pihlajamziki H, Bostman O, Hirvensalo E, et a1.: Biodegradablepolylactide pins in the fl\ation of fractures and osteotomies.XXWI World Congress of the Intemational College of Surgeons,Bologna, Italy, Monduzzi Editore, 1992, pp 617-621,1992.Suuronen R, Laine P, Sarkial E, et a1.: Sagittal split osteotomyfixed with biodegradable, self-reinforced poly-L-lactide screws. Apilot study in sheep. Int J Orul M.lxillcfac Surg 21,:303-308, 7992.Rozema FR, Bos RRM, Boering G: Late tissue response to bonepaltes and screws of poly (LJactide) used for firation of zygomaticfractures: report of 4 cases. Proc 9tb Europe.4n Conferenceon Bionxaterials Chester, 1991, p 151.Parks RM, Nelson G: Complications with the use of bioabsorbablepins in the fctc;t. J Am Podiatr Med Assoc 32(2):153-167,1.993.Johnson JD: Adverse reaction to absorbable rods.(letter to theeditoi) J Am Podidtr Med Assoc 83(]):427-128, 1993.

CHAPTER 11 65ADDITIONAL REFERENCESAxelson PB: Fkation of cancellous bone and physeal fractures in dogsand cats. A comparison of the use of self-reinforced biodegradabledevices to the use of metallic devices and extemal fixaiion.Acta Vet Scand 30:259-65, 1989.Barfod G, Svendsen RN: Synovitis of the knee after intra-afiicularfracture fixation with Biofix. Report of two cases. Acta OltbopScand 63(.6) ;680-681, 1992.Beiser IH, Kanat IO: Biodegradable internal fixation. A literarurereview. J Am Podiatr Med Assoc 80(.2):72-75, 1,990.Dijkema AR, van der Elst M, Breederweld RS, Verspui G, patka p,Haarman HJ: Surgical treatment of fracture-dislocations of theankle joint with biodegradable implants: A prospective randomizedstudy. / Trauma 34(1):82-84, 1,993.Eitenmiiller J, David A, Muhr G: Treatment of ankle fractures withcomplete biodegradable plates and screws of high molecularweight polylactide. Proc p2ru1 Congres Francais de Cbirurgie,Paris 1990.Frid6n T, Rydholm U: Severe aseptic synovitis of the knee afterbiodegradable internal fixation. A case repofi. Acttl Otthop Scdnd63(.L):94-97, 1.992.Frokjaer J, Moller B: Biodegradable fixation of ankle fracrures.Complications in a prospective study of 25 cases. Acta Or"thopS c an d 63(.4) : 43 4-436, 1992.Gerbert J: Effectiveness of absorbable fixation devices in Austinbunionectomies. J Am Podi.ttr Med Assoc 82(4):189-195. 1992.Lavery LA, Higgins KR, Ashry HR, Athanasiou KA: Mechanical characteristicsof poly-L-lactic acid absorbable screws and stainless steelscfews in basilar osteotomies of the first metatarsal. .l Foot AnkleSurg 33(3):249-254, 1991.Niskanen RO, Lehtimaki MY, Hzimzilziinen MM, Tormilzi p, RokkanenP U: Arthrodesis of the first metatarsophalangeal joint in rheumatoidafihdtis. Biodegradable rods and Kirschner-wires in J! cases.Acta Ofihop Scand 61(1'):100-1.02, 1993.Pafiio EK, Hiruensalo E, Bostman O, Patiala H, Vainionpzizi S, VihtonenK, Helevirta P, Tormdli P, Rokkanen P: Broches et vis bioresorbables:Une nouvelle methode de flxation des fractures del'olecrane. Etude clinique prospective sur ,11 malades. Int Ofibop(SICOD 76:250-254. 1992.Pihlajamiki H, Bostman O, Hirvensalo E, Tomala P, RokkanenP:Absorbable pins of self reinforced polyJJactide acid forflration of fractures and osteotomies. J Bone Joint Surg (.Br).74(8):853-857 , 1992.Rokkanen P: Biofix symposiums in Italy. Question and Answersession. Bioscience Limitecl Tar;lpere, Finland, 1993.Yen RG, Giacopelli JA, Granoff DP, Steinbroner RJ: The Biofkabsorbable rod. A preliminary repoft. ./ Am podiatr Med Assoc81(2);62-67 , 7997.