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Laboratory Sciences |

Design of a Magnetically Integrated Microporous Implant FREE

Timothy G. Murray, MD; Nicole L. Cicciarelli; Brandy H. Croft, BS; Scott Garonzik; Monika Voigt, MD; Eleut Hernandez
[+] Author Affiliations

From the Department of Ophthalmology, Bascom Palmer Eye Institute, University of Miami School of Medicine, Miami, Fla (Dr Murray, Mss Cicciarelli and Croft, and Mr Hernandez); SNG Prosthetic Eye Institute, Boca Raton, Fla (Mr Garonzik); and the Ophthalmic Clinic of Virchow/Charité Hospital, Humboldt University of Berlin, Berlin, Germany (Dr Voigt).


Arch Ophthalmol. 2000;118(9):1259-1262. doi:10.1001/archopht.118.9.1259.
Text Size: A A A
Published online

Objective  To determine the orbital tolerance of a microporous implant fitted with an integrated stainless steel post and the enhanced motility associated with magnetic coupling of the prosthetic and the implant in a rabbit model.

Methods  Six New Zealand white rabbits underwent primary enucleation with implantation of a 12-mm microporous polyethylene implant with a 2 × 3-mm stainless steel post embedded flush with the anterior surface. At 1 month, the rabbits were fitted with an external prosthesis containing two 1-mm circular rare earth dental magnets embedded at 0.5 mm off the midline (right and left of center at the horizon). Magnetic coupling forces were determined with a hanging block technique.

Results  No evidence of toxicity was observed in association with this integrated ocular implant. Magnetic coupling forces were noted maximally at 0.47 N. Clinical grading of motility documented enhancement in lateral excursion when compared with nonintegrated controls.

Conclusion  Magnetically integrated microporous implants achieve excellent enhancement of motility without evidence of complications in this rabbit model.

Clinical Relevance  This study establishes a framework for the clinical evaluation of a magnetically integrated implant that may enhance prosthetic motility without requiring direct mechanical coupling of the implant to the prosthesis.

Figures in this Article

BARTISCH FIRST described enucleation as a treatment of ocular disease in 1583.1 The current surgical approach was introduced in 1841 by Farrell and Bonnet, and in 1884, Mules placed the first orbital implant.2 In 1946, Ruedemann3 proposed the use of partially exposed, integrated implants with the attachment of the extraocular muscles to the implant to allow for better prosthetic motility. Complete tissue enclosure of the implant began in the 1950s, minimizing socket complications but limiting prosthetic motility. Troutman,4 in 1949, introduced a magnetic integrated implant. Magnetic implants were then evaluated by several investigators.58 Late complications associated with the magnetically integrated implants, including exposure and extrusion, led to the discontinuation of this reconstructive approach. The use of a microporous magnetic coupling system was postulated to eliminate the complications associated with prior magnetic implants.

The ideal orbital implant would offer excellent motility and cosmesis and few complications. To achieve this goal, various materials have been advocated, including cartilage, bone, fat, cork, rubber, gold, silver, silk, wool, aluminum, ivory, acrylics, silicone, quartz, glass, titanium, and, recently, porous materials, such as polyethylene and hydroxyapatite.2,913

Tissue-covered, quasi-integrated implants derived from acrylic irregularly shaped spheres include the Allen implant (in which extraocular muscles are passed through tunnels) and the Iowa and Universal implants (in which extraocular muscles are passed through grooves within the implant).911,1416

Porous spherical implants are most widely used at the Bascom Palmer Eye Institute, Miami, Fla, and other institutions.17,18 Porous polyethylene is made from synthetic, high-density polyethylene powder that is easily molded into virtually any shape. Hydroxyapatite, derived from reef-building coral of the genus Porites, was introduced in 1985 by Perry19,20 as a microporous implant material. Microporous implants allow for fibrovascular ingrowth and offer the theoretical, and real, advantage of lower extrusion or migration rates.

Decreased local complication rates have clearly been achieved with the nonintegrated microporous implants.1726 Unfortunately, attempts to increase motility through integration of the implant with the prosthesis have led to unacceptably high complication rates (approaching 28% of pegged implants).23,25,26

This study was designed to investigate the potential advantages of magnetically coupling a buried microporous implant with an ocular prosthesis for tissue tolerance and enhanced motility.

All experiments in this study were conducted under the auspices of the Animal Care and Use Committee of the University of Miami School of Medicine, Miami, Fla. Experiments adhered to the guidelines of the Association for Research in Vision and Ophthalmology Statement for the Use of Animals in Ophthalmic and Vision Research.

Microporous polyethylene implants (MEDPOR; Porex Corp, College Park, Ga) were custom modified to integrate a medical-grade 2 × 3-mm stainless steel post embedded flush with the microporous sphere (Figure 1). Custom-fitted rabbit ocular prosthetics were manufactured integrating two 1-mm circular medical-grade rare earth magnets (Figure 2). A spacing interval of 1 mm was maintained, and the magnets were embedded 0.5 mm lateral to the midline (right and left of center at the horizontal meridian) (Figure 2). The prosthetics were vaulted to achieve a 0.5-mm elevation from the central conjunctiva, thereby eliminating direct central apposition of the conjunctiva and prosthesis. An identically designed prosthesis without incorporation of the magnets was used as a control.

Place holder to copy figure label and caption
Figure 1.

Left, A medical-grade 2 × 3-mm stainless steel post integrated into a microporous implant. Right, A 2 × 3-mm stainless steel post.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 2.

The prosthesis, demonstrating placement of the medical-grade magnets (arrows). There is maintenance of horizontal midline orientation.

Graphic Jump Location

Magnetic field strength (force) was determined using a hanging ball technique.27 Briefly, the hanging ball technique measures the magnetic force by determining the amount of movement of a 0.32-cm steel ball as a test object placed at varying distances from the magnet test object. Field strength was determined in a single and combined magnet application at varying distances determined to approximate the clinical relation between the prosthetic and the implant.

Six animals underwent implantation of the custom-modified microporous implants (Figure 1). All animals were anesthetized with intramuscular injections of ketamine hydrochloride and xylazine hydrochloride, retrobulbar bupivacaine hydrochloride, and topical proparacaine hydrochloride. Under appropriate anesthesia and monitoring, primary enucleation of the right globe was performed using a previously reported technique.28 A custom 12-mm microporous implant with an integrated steel post was implanted to maintain the orientation of the post along the horizontal and vertical center of the socket (Figure 1). The recti muscles were reapproximated to the wrapped implant to maintain gross anatomic positioning. The deep and superficial Tenon tissues were closed with 5-0 polyglactin 910 sutures, and the conjunctiva was closed with a 7-0 polyglactin 910 suture. A small ophthalmic conformer was inserted, and an occlusive dressing was applied. The sockets were serially examined, and clinical photographs were obtained (Figure 3). At 6 weeks after enucleation, the magnetically integrated, custom-fitted prosthesis was placed in all animals (Figure 4). Animals were clinically evaluated for prosthetic motility using the eyes with a magnetically integrated prosthesis and the control eyes with a nonmagnetically integrated prosthesis. Control motility was determined by placement of the nonmagnetic prosthetic. Motility was graded, in a masked fashion, as good, fair, or poor, evaluating lateral prosthetic excursion during direct observation (poor indicates <1 mm; fair, 1-2 mm; and good, >2 mm).

Place holder to copy figure label and caption
Figure 3.

The implanted socket at 6 weeks after enucleation. There is no infection, inflammation, or evidence of extrusion.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 4.

The prosthesis placed within the integrated surgical socket. The overlying plica semilunaris conjunctiva is present.

Graphic Jump Location

Integration of the steel post within the microporous implant was accomplished without difficulty or compromise of the implant (Figure 1). Placement of the medical-grade magnets within the custom prosthesis did not impair the socket placement of the prosthesis (Figure 2 and Figure 4). Clinical and histopathologic evaluation of treated sockets, during a 20-month follow-up, disclosed no evidence of infection, inflammation, extrusion, or complication (Figure 3). Orbital histopathologic features at 6 and 12 weeks after placement of the prosthesis disclosed no evidence of conjunctival thinning or orbital complication. Magnetic movement forces achieved adequate field strengths to enable magnetic coupling of the buried implant and custom prosthesis (Table 1). All eyes with the magnetically integrated prosthesis were graded as having good motility, while all eyes with placement of the control, nonmagnetic prosthesis were graded as having poor motility.

Table Graphic Jump LocationMagnetic Movement Forces (Coupling Attraction) Determined for the Magnetically Integrated Implant-Prosthetic Combination

Magnetic coupling of a buried, steel post–implanted, microporous implant appears to generate clinically effective force profiles for interaction with the modified magnetic prosthesis. No data are available to determine the ideal placement of the magnets within clinical practice. Data suggest that within the rabbit model, the spacing interval of 1 mm (0.5 mm lateral to the midline) for the 2 prosthetic magnets and a prosthetic vault of 0.5 mm will allow for enhanced movement of the prosthesis.

The design and production of these integrated devices are possible using medical-grade production items, including the microporous implant, steel post, and surgical-grade magnets. No intraoperative or postoperative complications were noted in any treated animal. Rapid socket healing and rehabilitation were associated with this surgical technique.

This technique appears to achieve the benefits of an invasively integrated implant-prosthetic combination without the associated concerns of socket-related complications, including epithelial breakdown, exposure, extrusion, or infection. Data suggest that these rates may be as high as 28% or greater for microporous implants undergoing "pegging" of the implant.23,25,26 These rates are concerning in light of the recently reported17,18 pediatric and adult complication rates in nonpegged microporous implants of less than 1.5%.

This study establishes the feasibility and efficacy of this magnetically coupled implant within this animal model. Advances in materials, surgical technique, and ocular prosthetic fitting allow for a reconsideration of a magnetically coupled implant.58,2432 True evaluation of enhanced cosmesis will require clinical study in humans undergoing enucleation and implant placement.

A caveat to the use of this implant will be the restriction of magnetic resonance imaging studies for these patients. Fortunately, computed tomographic scanning analysis continues to allow for adequate orbital and central nervous system imaging in most patients.

Accepted for publication February 24, 2000.

This study was supported by the American Cancer Society, Tampa, Fla (Dr Murray); and Fight for Sight/Prevent Blindness America, New York, NY (Dr Murray).

Reprints: Timothy G. Murray, MD, Bascom Palmer Eye Institute, University of Miami School of Medicine, PO Box 016880, Miami, FL 33101 (e-mail: tmurray@bpei.med.miami.edu).

Luce  CM A short history of enucleation. Int Ophthalmol Clin. 1970;10681- 687
Gougelmann  HP The evolution of the ocular motility implant. Int Ophthalmol Clin. 1970;10689- 711
Ruedemann  AD Plastic eye implant. Am J Ophthalmol. 1946;29947- 952
Troutman  RC Five-year survey on use of a magnetic implant for improving cosmetic result of enucleation. Arch Ophthalmol. 1954;5258- 62
Link to Article
Ellis  OHLevy  OR A new magnetic orbital implant. Arch Ophthalmol. 1956;56352- 360
Link to Article
Tomb  EHGearhart  DF A new magnetic implant. Arch Ophthalmol. 1954;52763- 768
Link to Article
Roper-Hall  MJ Magnetic orbital implant. Br J Ophthalmol. 1956;40575
Link to Article
Young  JH Magnetic intra-ocular implant: new surgery of the implant: the magnetic artificial eye. Br J Ophthalmol. 1954;38705- 718
Link to Article
Fan  JTRobertson  DM Long-term follow-up of the Allen implant (1967 to 1991). Ophthalmology. 1995;102510- 516
Link to Article
Hornblass  ABiesman  BSEviatar  JA Current techniques of enucleation: a survey of 5,439 intraorbital implants and a review of the literature. Ophthal Plast Reconstr Surg. 1995;1177- 88
Link to Article
Spivey  BEAllen  LBurns  CA The Iowa enucleation implant: a 10-year evaluation of technique and results. Am J Ophthalmol. 1969;67171- 188
Leatherbarrow  BKwartz  JSunderland  S  et al.  The "Baseball" orbital implant: a prospective study. Eye. 1994;8569- 576
Link to Article
Tyers  AGCollin  JR Baseball orbital implants: a review of 39 patients. Br J Ophthalmol. 1985;69438- 442
Link to Article
Anderson  RLThiese  SMNerad  JA  et al.  The Universal orbital implant: indications and methods. Adv Ophthalmic Plast Reconstr Surg. 1990;888- 99
Beard  C Remarks on historical and newer approaches to orbital implants. Ophthal Plast Reconstr Surg. 1995;1189- 90
Link to Article
Stone  W  Jr Symposium: orbital implants after enucleation: causes of complications and their solution. Trans Am Acad Ophthalmol Otolaryngol. 1952;5635- 42
Christmas  NJGordon  CDMurray  TG  et al.  Intraorbital implants after enucleation and their complications: a 10-year review. Arch Ophthalmol. 1998;1161199- 1203
Link to Article
Christmas  NJVan Quill  KMurray  TG  et al.  Evaluation of efficacy and complications: primary pediatric orbital implants after enucleation. Arch Ophthalmol. 2000;118503- 506
Link to Article
Perry  AC Integrated orbital implants. Adv Ophthalmic Plast Reconstr Surg. 1990;875- 81
Perry  AC Advances in enucleation. Ophthalmol Clin North Am. 1991;4173- 182
Dutton  JJ Coralline hydroxyapatite as an ocular implant. Ophthalmology. 1991;98370- 377
Link to Article
Shields  CLShields  JADe Potter  PSingh  AD Problems with the hydroxyapatite orbital implant: experience with 250 consecutive cases. Br J Ophthalmol. 1994;78702- 706
Link to Article
Karcioglu  ZAAl-Mesfer  SAMullaney  PB Porous polyethylene orbital implant in patients with retinoblastoma. Ophthalmology. 1998;1051311- 1316
Link to Article
De Potter  PShields  CLShields  JASingh  AD Use of hydroxyapatite ocular implant in the pediatric population. Arch Ophthalmol. 1994;112208- 212
Link to Article
Buettner  HBartley  GB Tissue breakdown and exposure associated with orbital hydroxyapatite implants. Am J Ophthalmol. 1992;113669- 673
Kaltreider  SANewman  SA Prevention and management of complications associated with the hydroxyapatite implants. Ophthal Plast Reconstr Surg. 1996;1218- 31
Link to Article
Joondeph  HCJoondeph  BCMulcahy  T Comparison of three permanent intraocular magnets. Retina. 1992;12270- 272
Link to Article
Buus  DRKronish  JWTse  DT Enucleation and techniques of orbital implant placement. Tse  DTedColor Atlas of Ophthalmic Surgery: Oculoplastic Surgery. Philadelphia, Pa JB Lippincott1992;348- 364
Chan  MFJohnston  CHowell  RACawood  JI Prosthetic management of the atrophic mandible using endosseous implants and overdentures: a six-year review. Br Dent J. 1995;179329- 337
Link to Article
Gillings  BRSamant  A Overdentures with magnetic attachments. Dent Clin North Am. 1990;34683- 709
Sandler  PJMeghji  SMurray  AM  et al.  Magnets and orthodontics. Br J Orthod. 1989;16243- 249
George  TMValiathan  AGeorge  AIPayapilly  DJ Magnets in orthodontics. J Pierre Fauchard Acad. 1992;645- 54

Figures

Place holder to copy figure label and caption
Figure 1.

Left, A medical-grade 2 × 3-mm stainless steel post integrated into a microporous implant. Right, A 2 × 3-mm stainless steel post.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 2.

The prosthesis, demonstrating placement of the medical-grade magnets (arrows). There is maintenance of horizontal midline orientation.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 3.

The implanted socket at 6 weeks after enucleation. There is no infection, inflammation, or evidence of extrusion.

Graphic Jump Location
Place holder to copy figure label and caption
Figure 4.

The prosthesis placed within the integrated surgical socket. The overlying plica semilunaris conjunctiva is present.

Graphic Jump Location

Tables

Table Graphic Jump LocationMagnetic Movement Forces (Coupling Attraction) Determined for the Magnetically Integrated Implant-Prosthetic Combination

References

Luce  CM A short history of enucleation. Int Ophthalmol Clin. 1970;10681- 687
Gougelmann  HP The evolution of the ocular motility implant. Int Ophthalmol Clin. 1970;10689- 711
Ruedemann  AD Plastic eye implant. Am J Ophthalmol. 1946;29947- 952
Troutman  RC Five-year survey on use of a magnetic implant for improving cosmetic result of enucleation. Arch Ophthalmol. 1954;5258- 62
Link to Article
Ellis  OHLevy  OR A new magnetic orbital implant. Arch Ophthalmol. 1956;56352- 360
Link to Article
Tomb  EHGearhart  DF A new magnetic implant. Arch Ophthalmol. 1954;52763- 768
Link to Article
Roper-Hall  MJ Magnetic orbital implant. Br J Ophthalmol. 1956;40575
Link to Article
Young  JH Magnetic intra-ocular implant: new surgery of the implant: the magnetic artificial eye. Br J Ophthalmol. 1954;38705- 718
Link to Article
Fan  JTRobertson  DM Long-term follow-up of the Allen implant (1967 to 1991). Ophthalmology. 1995;102510- 516
Link to Article
Hornblass  ABiesman  BSEviatar  JA Current techniques of enucleation: a survey of 5,439 intraorbital implants and a review of the literature. Ophthal Plast Reconstr Surg. 1995;1177- 88
Link to Article
Spivey  BEAllen  LBurns  CA The Iowa enucleation implant: a 10-year evaluation of technique and results. Am J Ophthalmol. 1969;67171- 188
Leatherbarrow  BKwartz  JSunderland  S  et al.  The "Baseball" orbital implant: a prospective study. Eye. 1994;8569- 576
Link to Article
Tyers  AGCollin  JR Baseball orbital implants: a review of 39 patients. Br J Ophthalmol. 1985;69438- 442
Link to Article
Anderson  RLThiese  SMNerad  JA  et al.  The Universal orbital implant: indications and methods. Adv Ophthalmic Plast Reconstr Surg. 1990;888- 99
Beard  C Remarks on historical and newer approaches to orbital implants. Ophthal Plast Reconstr Surg. 1995;1189- 90
Link to Article
Stone  W  Jr Symposium: orbital implants after enucleation: causes of complications and their solution. Trans Am Acad Ophthalmol Otolaryngol. 1952;5635- 42
Christmas  NJGordon  CDMurray  TG  et al.  Intraorbital implants after enucleation and their complications: a 10-year review. Arch Ophthalmol. 1998;1161199- 1203
Link to Article
Christmas  NJVan Quill  KMurray  TG  et al.  Evaluation of efficacy and complications: primary pediatric orbital implants after enucleation. Arch Ophthalmol. 2000;118503- 506
Link to Article
Perry  AC Integrated orbital implants. Adv Ophthalmic Plast Reconstr Surg. 1990;875- 81
Perry  AC Advances in enucleation. Ophthalmol Clin North Am. 1991;4173- 182
Dutton  JJ Coralline hydroxyapatite as an ocular implant. Ophthalmology. 1991;98370- 377
Link to Article
Shields  CLShields  JADe Potter  PSingh  AD Problems with the hydroxyapatite orbital implant: experience with 250 consecutive cases. Br J Ophthalmol. 1994;78702- 706
Link to Article
Karcioglu  ZAAl-Mesfer  SAMullaney  PB Porous polyethylene orbital implant in patients with retinoblastoma. Ophthalmology. 1998;1051311- 1316
Link to Article
De Potter  PShields  CLShields  JASingh  AD Use of hydroxyapatite ocular implant in the pediatric population. Arch Ophthalmol. 1994;112208- 212
Link to Article
Buettner  HBartley  GB Tissue breakdown and exposure associated with orbital hydroxyapatite implants. Am J Ophthalmol. 1992;113669- 673
Kaltreider  SANewman  SA Prevention and management of complications associated with the hydroxyapatite implants. Ophthal Plast Reconstr Surg. 1996;1218- 31
Link to Article
Joondeph  HCJoondeph  BCMulcahy  T Comparison of three permanent intraocular magnets. Retina. 1992;12270- 272
Link to Article
Buus  DRKronish  JWTse  DT Enucleation and techniques of orbital implant placement. Tse  DTedColor Atlas of Ophthalmic Surgery: Oculoplastic Surgery. Philadelphia, Pa JB Lippincott1992;348- 364
Chan  MFJohnston  CHowell  RACawood  JI Prosthetic management of the atrophic mandible using endosseous implants and overdentures: a six-year review. Br Dent J. 1995;179329- 337
Link to Article
Gillings  BRSamant  A Overdentures with magnetic attachments. Dent Clin North Am. 1990;34683- 709
Sandler  PJMeghji  SMurray  AM  et al.  Magnets and orthodontics. Br J Orthod. 1989;16243- 249
George  TMValiathan  AGeorge  AIPayapilly  DJ Magnets in orthodontics. J Pierre Fauchard Acad. 1992;645- 54

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