J Oral Maxillalac Surg51:1217 -1220,1993

A Comparison of Microscrew and SutureFixation for Porous High-Density

Polyethylene Orbital Floor ImplantsRICHARD H. HAUG, DDS: DAVID KIMBERLY, BS,t

AND JON P. BRADRICK, DDS·

Twenty oral and maxillofacial surgeons compared the surgical features of a mi­croscrew fixation technique with a suture technique for fixation of porous high­density polyethylene orbital floor implants. One investlqator then compared ma­terial features of these two fixation techniques using recently procured bovineribs. The microscrew technique was found to be quicker (P > .01) and easier (P> .001), and it provided a higher quality of fixation (P > .001) than the suturetechnique. The mlcroscrew/implant system had a greater pullout strength (P >.001) and shear strength (P > .001) than the suture/implant system.

A vast array of autogenous and synthetic materialshave been used to reconstruct the orbital floor. Of thesynthetic materials, porous high-density polyethylene(PHDPE) seems to be best suited to this purpose. It isbiologically compatible, strong, moldable, has minimalmemory, and allows tissue ingrowth, which improvesfixation and provides greater stability.V Traditionalmethods of orbital implant fixation have includedwires, flanges, sutures, and craniofacial screws.' Withthe advent of microscrews in 1989, a new fixation mo­dality became available. The purpose of this investi­gation was to compare the surgical and material fea­tures ofa microscrew technique with a suture techniquefor PHDPE orbital floor implant fixation. Twenty oraland maxillofacial surgeons evaluated the surgical fea­tures, which included ease ofplacement, time requiredfor placement, and quality of fixation. One investigatorthen evaluated the material features, which includedpullout strength and shear strength, using recently pro­cured bovine ribs.

• Assistant Professor ofSurgery, Metrol lealth Medical Center, andthe Department ofSurgery, Case Western Reserve University, Schoolof Medicine, Cleveland, on.

t Extern , Case Western Reserve University, School of Denti stry,Cleveland, OH.

Supported in part by a grant from Synth es Maxillofacial, Paoli,PA.

Add ress correspondence and reprint requests to Dr Haug: Divisionof Oral and Maxillofacial Surgery, MctroH callh Medical Center, 2500MetroHcallh Dr, Cleveland, 011 44109-1998.

© 1993 American Association of Oral and Maxillofacial Surgeons

0278-2391/93/5111-0009$3.00/0

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Materials and Methods

SURGICAL EVALUATION

Twenty oral and maxillofacial surgeons evaluatedthe practical application of the suture and microscrewfixation techniques. They were asked to secure previ­ously fabricated, 1.5-mm-thick PHDPE orbital floorimplants with uniform contours and dimensions(Medpore, Porex Medical, Fairbur, GA) to standard­ized plastic skulls (Saw Bonz, Pacific Research Labo­ratories, Vashon Island, WA). For the suture technique,the surgeons were provided with a 3-0 Vicryl suture(Ethicon, Somerville, NJ), a needle holder, and a 1.1­mm-diameter wire-passing bur (Tava Surgical Instru­ments, Simi Valley, CA) attached to an electric drill.The surgeons were then instructed to secure the implantto the orbital floor with two interrupted sutures (FigI). Right and left orbital sites were randomized. Thetime required for placement by each surgeon was re­corded. The ease of placement was assessed by eachsurgeon on a scale of 1 to 10 (10 being the easiest and1 being the most difficult) and recorded, The qualityof the implant fixation was assessed by each surgeonon a scale of 1 to 10 (10 being the most secure and 1being the least secure) and recorded.

For the microscrew technique, the surgeons wereprovided with a .75-mm self-limiting bur (SynthesMaxillofacial, Paoli, PA) attached to an electric drill ,5.0-mm-long microscrews (Synthcs Maxillofacial)contained in an implant tray, and a Micro-Cruciform

1218 COMPARISON OF MICROSCREW AND SUTURE FIXATION

5econds

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 t9 20

Oral Surgeon

FIGURE 3. Time for placement of microscrew and suture fixation.-e-, Suture; -a-, bone screws.

FIGURE I. Implant fixation with sutures. Note that the implanthas been displaced from its original position and gaps exist betweenthe implant and the orbitailloor.

screwdriver (Synthes Maxillofacial). The surgeons wereasked to secure the implant with two microscrews (Fig2). Right and left orbital sites were randomized. Thetime of the procedure, ease of placement, and assess­ment of quality of fixation were recorded as for thesuture technique. The data were collected, means andstandard deviations were derived, significant differenceswere identified with a Student's t test, and the resultswere graphically illustrated.

tension loads were applied parallel to the implant sur­face until failure and the resistance in kilograms wasrecorded. Ten trials were performed with sutures and10 with microscrews. To evaluate pullout strength,tension loads were applied perpendicular to the implantsurface until failure and the resistance in kilogramswas recorded. Ten trials were performed with suturesand 10 with microscrews. The data were collected,means and standard deviations were derived and eval­uated for statistical significance with the Student's ttest, and the results were graphically illustrated.

Results

FIGURE 4. Ease of placement of microscrew and suture fixation.-e-, Suture; -.-, bone screws.

Eighty-five percent of the participating oral andmaxillofacial surgeons applied the microscrew fixationmore rapidly than the suture fixation. The mean timefor application of microscrews was 122 ± 36 seconds,and the mean time for suture fixation was 150 ± 30seconds (Fig 3). While this difference was statisticallysignificant (P> .01), it was not clinically significant.

Ninety percent of the participating surgeons foundthe microscrew fixation technique easier than the suturetechnique (Fig 4). The mean ease of placement ratingfor the microscrew fixation technique was very high(8.2 ± 1.0) while the rating for the suture fixation tech-

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Oral Surgeon

PIacement

Ratin9

MATERIAL EVALUATION

FIGURE 2. Implant fixation with microscrews. Note that the im­plant is held in intimate contact with the orbitailloor, with no voidsor irregularities.

One investigator evaluated the shear strength andpullout strength of the suture/implant, microscrew/implant fixation systems using recently procured bo­vine ribs. The ribs were stripped of soft tissues and a3.0 X 3.0-cm square of I.S-mm-thick PHDPE was se­cured with one suture or one screw using the equipmentdescribed in the previous section. The rib was securedwith a clamp and the PHDPE was attached to a self­recording spring balance. To evaluate shear strength,

HAUG, KIMBERLY. AND BRADRICK 1219

5

FIGURE 6. Shear strength for the microscrew and suture systems.••-. Screw; -.-. suture.

9 1084 5 6 7

Trial Number32

Ki 4

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.-------..

fluids and induces only a mild inflammatory responseafter placement. 1,5

While autogenous materials rapidly unite with thebody, the alIoplastic materials are never fully incor­porated, and thus some means of anchorage has beensuggested with their use.6

-8 This has traditionally been

accomplished with tongue or flange press-fit anchors,or by fixation with wires, sutures, or craniofacial screws(1.5- or 2.0-mm outer thread diameterj.' In 1989, mi­croscrews (less than 1.0 mm outer thread diameter)became available, thus providing an additional fixationmodality. The microscrews evaluated in this study werelow profile (less than 0.75 mm), self tapping, and fab­ricated from commercialIy pure titanium. Thus, theyare not palpable, rapidly placed, corrosion resistant,biocompatible, strong yet lightweight, and do not in­terfere with current imaging techniques such as mag­netic resonance imaging, or computed tomographyscanning." Although the problem of orbital floor re­construction has existed for more than a century, in­formation regarding orbital floor implant fixation hasbeen mostly anecdotal in technical notes, or observa­tional in retrospective clinical studies.

This investigation provided some very interestingfindings . Although microscrew fixation was a more re­cent development and less familiar to the participating

nique was moderate (5.7 ± 1.8). This difference wasboth statistically (P> .00 1) and clinically significant.

One hundred percent of the clinicians rated thequality of microscrew fixation superior to suture fixa­tion (Fig 5). Seven participants (35%) gave the mi­croscrew technique the highest possible rating, whilenine (45%) gave the second highest possible rating (Fig5). The quality rating for the microscrew technique(9.1 ± 0.9) was almost twice that ofthe suture technique(4.8 ± 1.2). This was both statistically (P > .001) andclinically significant.

The shear strength ofthe microscrew/implant system(4.4 ± 0.3 kg) was almost twice that of the suture/implant system (2.4 ± 0.1 kg) (Fig 6). This differencewas statistically significant (P> .001). Pullout strengthfor the microscrew fixation system (2.9 ± 0.2 kg) wasgreater than that for the suture fixation system (2.5 ±0.2 kg) (Fig 7). This difference was also statisticallysignificant (P > .001). All failures during this portionof the investigation occurred when the PHDPE implanttore. None of the microscrews or sutures pulled freefrom the bone.

Discussion

Since the first description ofan orbital floor fractureby Lang in 1889, materials and techniques for orbitalfloor reconstruction have been debated." Virtually ev­ery type ofimplantable material has been used to repairorbital floor defects. While autogenous bone has near­ideal qualities, difficult three-dimensional shaping, un­predictable resorption with resultant enophthalmus,and second surgical site morbidity remain shortcom­ings.' Of the synthetic materials, PHDPE seems to bewell suited for orbital floor repair. It is a sintered syn­thetic of pure polyethylene that has a high tensilestrength and resists fatigue.P The material is flexible,yet possesses minimal memory, and thus is easilyshaped and contoured. The porosity of the materialalIows both bone and soft tissue ingrowth, which en­hances fixation and stability.P It is insoluble in tissue

1098456 7

Trial Number32

3 .5

K 3 • • ----iI

2.50

9r 2ams 1.5

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20

Oral Surgeon

QuaIitY

Ratin9

FIGURE 5. Quality of microscrew and suture fixation. -." Suture;'.-. bone screws.

FIGURE 7. Pullout strength for the microscrew and suture systems.-.-. Screw; •••• suture.

1220

surgeons (approximately 50% used this system for thefirst time during the study), 17 of 20 participants ap­plied this modality more rapidly than the traditionalsuture technique (Fig 3). The surgeons found the del­icate microscrew instrumentation to be more efficientthan the cumbersome suture instrumentation. This wasverifieddramatically by the 18 of 20 surgeons who ratedthe microscrews easier to place than the sutures(Fig 4).

The most impressive finding during the investigationwas that a unanimous opinion was reached by the par­ticipating surgeons regarding the quality of fixation.One hundred percent of the participants found thatthe quality of fixation with microscrews was higher byalmost a factor of two than fixation with sutures (Fig5). Sixteen of the 20 surgeons gave the microscrewtechnique their highest or second highest rating. Themicroscrew fixation was found to be firm and stable,with the PHDPE implant well adapted to the orbitalfloor (Fig 2). The suture fixation was found to be lessstable, with implant mobility easily induced. Also,poorer adaptation of the PHDPE implant to the orbitalfloor was observed with suture fixation (Fig I). Themicroscrew fixation was able to compensate for theseminor implant contouring imperfections.

Infection and rejection are the most common com­plications ofsynthetic orbital floor placement.v" Theseare considered to be host responses and are not signif­icantly affected by fixation techniques. Migration anddisplacement of the implant, however, are directly re­lated to the fixation modality.v" Anterior displacementwith extrusion of the implant through the skin or mi­gration of the implant with encroachment on vitalstructures are the more common of the mechanicalcauses for clinical failure. These are best representedby the tests for shear strength and pullout strength in

COMPARISON OF MICROSCREW ANO SUTURE FIXATION

our benchtop evaluation. The microscrew/implantsystem was found to have almost twice the shearstrength of the suture/implant system (Fig 6). Addi­tionally, the microscrew/implant system had a greaterpullout strength than the suture/implant system(Fig 7).

During all of the trials in this portion of the inves­tigation, failure resulted from tearing of the PHDPEsheets. In no instance did the microscrews or suturespull out of or shear free from the bone. Thus, the lim­iting factors during this portion of the investigationwere the material properties of the implant and theirinteraction with the fixation device, and not the fixationdevice alone.

References

I. RomanoJJ, WelIiszT, Manson PN, et al: Experience with poroushigh density polyethylene in.plants in 97 patients with facialfractures. Presented at the 1990 International Symposium onPlastic Surgery, held in Queensland, Australia, September 2­6,1990

2. Rubin LR: Polyethylene as a bone and cartilage substitute: A32-year retrospective, in Rubin LR (ed): Biomaterials in Re­constructive Surgery. St Louis, MO, Mosby, 1983, Chapter30, pp 474-493

3. Ellis E: Fractures ofthe zygomatic complex and arch, in FonsecaRJ, Walker RV (eds): Oral and Maxillofacial Trauma. Phil­adelphia, PA, Saunders, 1991, Chapter 18, pp 484-485

4. Lang W:Traumatic enophthalmus with retention of perfectacuityof vision. Trans Ophthalmol Soc UK 9:43, 1889

5. BerghausA: Porous polyethylene in reconstructive head and necksurgery. Arch Otol Rhinol Laryngol 111:154, 1985·

6. Browning CW: Alloplast materials in orbitall1oor repair. Am JOphthalmol 63:955, 1967

7. Aronowitz JA, Freeman BS,Spira M: Long-term stabilityofTef­Ion orbital implants. Plast Reconstr Surg 78:166, 1986

8. Rankow RM, Mignogna FV: Surgical treatment of orbitall1oorfractures. Arch Otol Rhinol LaryngollOl:19, 1975

9. Williams OF: Titanium and titanium alloys, in Williams OF(ed): Biocompatibility of Clinical Implant Materials, vol I.Boca Raton, FL, CRC, Chapter 2, pp 9-44