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J Oral Maxillofac Surg70:2290-2298, 2012

Synovial Metaplasia Found in TissueEncapsulating a Silicone Spacer During

2-Staged Temporomandibular JointReplacement for Ankylosis

Florencio Monje, MD, PhD,* Louis Mercuri, DDS, MS,†

Laura Villanueva-Alcojol, MD,‡ and org

Jose Juan Fernandez de Mera, MD§ .

Synovial metaplasia has been reported to occurin tissue surrounding silicone breast implants1-6 and intissue adjacent to joint prostheses.7,8 It has also been

escribed in skin and soft tissues, most frequently inealing or healed traumatic or surgical wounds.9

Heterotopic bone formation (HBF) is defined as theformation of bone within the temporomandibularjoint (TMJ) that may cause partial or complete anky-losis of the joint, causing pain and limited range ofmotion.10 Multiple previous surgeries, a history oftrauma, and ineffective postsurgical physical therapyregimens have been postulated as possible contribut-ing factors to its development. Different therapeuticoptions have been proposed, each showing variablesuccess in preventing reankylosis.

We report the first case in which papillary syno-vial metaplasia occurred due to placement of atemporary silicone implant in a patient in whomHBF developed after total alloplastic TMJ replace-ment with a stock prosthesis and present a reviewof the literature.

*Department of Oral and Maxillofacial Surgery, University Hospi-

tal Infanta Cristina, Badajoz, Spain.

†Professor of Surgery, Division of Oral and Maxillofacial Surgery,

Department of Surgery, Stritch School of Medicine, Loyola Univer-

sity Medical Center, Maywood, IL, and Clinical Consultant, TMJ

Concepts, Ventura, CA.

‡Department of Oral and Maxillofacial Surgery, University Hos-

pital Infanta Cristina, Badajoz, Spain.

§Departments of Histopathology, University Hospital Infanta

Cristina, Badajoz, Spain.

Address correspondence and reprint requests to Dr Villanueva-

Alcojol: C/Juan de Badajoz, No. 14, 2 G, 06003, Badajoz, Spain;

e-mail: laurivillanueva@hotmail.com

© 2012 American Association of Oral and Maxillofacial Surgeons

278-2391/12/7010-0$36.00/0

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ttp://dx.doi.org/10.1016/j.joms.2012.06.177

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Report of Case

A 56-year-old woman was referred to the Department ofOral and Maxillofacial Surgery of the University Hospital In-fanta Cristina, Badajoz, Spain, after facial trauma occurredduring a road traffic accident, which resulted in a displaced leftmandibular condylar neck fracture (Fig 1). The patient wasinitially managed by placement of intermaxillary fixation for 3weeks. Postoperative physiotherapy was recommended, butshe was not cooperative. Six months later, she complained ofincreasing pain in the left TMJ and decreasing maximal inter-incisal opening (MIO). A computed tomography (CT) scanshowed heterotopic calcifications within the joint. The patientunderwent a left TMJ replacement with a total stock TMJprosthesis (Biomet Microfixation, Jacksonville, FL) (Fig 2A) tomanage the incipient ankylosis.

The surgery and initial post-replacement course wereuneventful; however, 2 years later, pain and limited range ofmandibular motion again developed. A new panoramic ra-diograph (Fig 2B) and CT scan (Fig 2C) showed the rede-velopment of heterotopic bone around the prosthesis espe-cially posterior to the articulation. The patient refused anyinvasive management at that time; however, she agreed toreturn for a re-evaluation every 6 months.

After 18 months, because the patient’s mandibular painand dysfunction symptoms were increasing, a panoramicradiograph and new CT scan were obtained; they exhibitedcomplete calcification around the prosthesis (Fig 3). Sheconsented to undergo further treatment, and a 2-staged leftTMJ replacement with a patient-fitted total TMJ prosthesiswas planned (TMJ Concepts, Ventura, CA).

At the first-stage surgery, the stock device componentswere removed and a gap resection of the heterotopic boneblock was performed (Fig 4). The gap between the remain-ing bony surfaces was maintained by implanting a sphericalsilicone spacer (Fig 5A) (Bausch & Lomb, Rochester, NY).

Once the patient-fitted device components had been de-signed and manufactured, the second-stage surgery wasplanned during which the spacer would be removed andthe left TMJ replaced with a patient-fitted TMJ Conceptsprosthesis. During the second-stage surgery, when the sili-cone spacer was removed, it was noted that a glistening,white, fibrous-looking encapsulating tissue had developedaround the spacer (Fig 5B). This tissue was only removedfrom areas that required bone-to-prosthesis contact and wasmaintained everywhere else that it had formed to poten-

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Samples of the tissue were taken and sent for histologicexamination. The TMJ Concepts device fossa and ramus/condyle components were implanted (Fig 6). An autoge-nous abdominal free fat graft was packed around the artic-ulation to prevent reankylosis.

The sampled tissue from around the silicone spacer wasfixed in 10% neutral phosphate-buffered formalin and em-bedded in paraffin for routine histologic analysis. Histo-pathologic examination showed a papillary surface consist-ing of a cellular interface lining overlying a relativelyacellular fibrous capsule. This lining consisted of large po-lygonal cells, some of which were multinucleated, oftenwith eccentric nuclei polarized away from the surface.These cells formed a layer 1 or 2 cells thick that lacked abasement membrane. The surface lining formed papillaryfolds. No collagen bundles, elastin fibers, or vascular chan-nels were associated with the luminal lining. Several spacesrepresenting particulated silicone surrounded by foreign-body giant cells could also be observed. An immunohisto-chemical study was performed, and it was strongly positivefor CD-68, PGP-9, S-100 protein, vimentin, and lysozyme.This membrane, rather than being a fibrous membrane,appeared consistent with the histologic and histochemicalfeatures of a synovial-like lining (Fig 7).

After 1 year, the patient remains asymptomatic and hashown a significant increase in post-replacement MIO thatas remained stable. Her MIO was 13 mm before TMJoncepts surgery and 32 mm 1 year after replacement.

Discussion

HBF or ossification was first described in 1883 byRiedel.11 HBF is defined as the abnormal formation of

ature lamellar bone in soft tissues.10 The overallncidence of HBF has been reported to be between% and 90%.12-17 HBF occurs in 70% to 75% of the

patients who have undergone total hip arthroplasty.12

However, the incidence of clinically significant HBFvaries from 3% to 7%.18 The incidence after total kneereplacement is less, 15%, but of these patients, only

FIGURE 1. Panoramic radiograph taken after road traffic acci-dent. The displaced left mandibular condylar neck fracture can beobserved (arrow).

Monje et al. Synovial Metaplasia. J Oral Maxillofac Surg 2012.

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1% complained of symptoms.19w

When HBF affects the TMJ, partial or complete

bony ankylosis will be the result, leading to com-plaints of pain and limited range of mandibular mo-tion. TMJ-related HBF has been reported in 52% ofcases after gap arthroplasty for ankylosis and rheuma-toid cases and reconstruction with a condylar pros-thesis without a fossa prosthesis.20 Topazian foundthat there was a 53% incidence of reankylosis withgap arthroplasty.21 Popescu22 noted a 100% rate ofecurrence of ankylosis when a simple arthroplastyas performed, even when a variety of mesenchymal

llografts were interposed. Wolford and Karras23

stated that 35% of the patients managed with totalalloplastic TMJ prostheses without fat grafting exhib-ited HBF and required reoperation.

HBF is believed to result from inappropriate differ-entiation of pluripotent mesenchymal stem cells. Adefinitive cause for this phenomenon is not yet clear,but it appears that there is an interaction betweenlocal and systemic factors. Growth factors and bonemorphogenetic protein have been identified as affect-ing the initiation, differentiation, and proliferation ofosteogenic cells.24 Although no definitive studies

ave been conducted to identify specific risk factorsor the development of heterotopic bone after TMJurgery, multiple previous surgeries, a history ofrauma (eg, fracture of the condyle), inadequate intra-perative hemorrhage control, and an ineffectiveostsurgical physical therapy regimen have all beenostulated as potential contributing factors.20

The size of the gap created during surgical manage-ment of TMJ ankylosis has been postulated as playingan important role in the prevention of HBF/reankylo-sis. A critical size defect is a bone-from-bone gap thatcannot be bridged by normal callus formation andsecondary healing. It has been recommended that thisdefect be 2.5 to 3.5 cm. Moreover, it has been sug-gested that the surgeon limit periosteal stripping ofadjacent bone, carefully debride all devitalized tissuein the area, irrigate copiously with normal saline so-lution to remove as many loose bony fragments aspossible, obtain good local hemostasis to minimizethe development of a hematoma, and promote aggres-sive and active postoperative physiotherapy.23,25

Patient-fitted TMJ Concepts device components aredesigned and manufactured for each specific clinicalsituation from a protocol CT scan–generated stereo-lithographic model with a reported mean dimensionalaccuracy of 97.9%.26 Therefore, in cases of ankylosisand/or reankylosis, the surgeon, during a first-stageprocedure, must remove the ankylotic bone and cre-ate an adequate gap and must place an anatomicspacer to prevent the reformation of tissue and/orbone27; placement of intermaxillary fixation is recom-

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mended to prevent movement of the spacer or

2292 SYNOVIAL METAPLASIA

FIGURE 2. Immediate postoperative panoramic radiograph (A) made after implantation of left total TMJ stock prosthesis and panoramicradiograph (B) and CT scan (C) taken 2 years later. HBF can be observed around the stock prosthesis, mainly in the posterior part of thearticulation (arrows).

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change in bony architecture and/or occlusion duringstage 1 surgery.

Because the components of the TMJ Concepts de-vice interface so closely with the host bone, allowingfor the screw fixation to be stable immediately afterimplantation, mandibular function and active physicaltherapy can begin immediately after implantation.This is essential in cases of ankylosis and reankylosisbecause muscle function has been compromised overtime in such cases. Salter,28 in his work on continuous

FIGURE 3. Panoramic radiograph (A) and CT scan (B) taken 18 mbe observed (arrows).

Monje et al. Synovial Metaplasia. J Oral Maxillofac Surg 2012.

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assive motion after orthopedic joint surgery, has fw

hown the importance of this concept to the long-erm functional results of any joint surgery.

Besides active and aggressive physical therapy, an-illary postoperative management options to preventeformation of heterotopic bone and reankylosis haveeen recommended. These include ionizing radiation,edications, and intraoperative placement of autoge-ous fat around the articulation of either autogenousr alloplastic total TMJ replacements. Ionizing radia-ion interferes with the processing of nuclear DNA

ater. The progression of the calcification around the prosthesis can

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2294 SYNOVIAL METAPLASIA

the differentiation of osteoprogenitor cells. Durr etal29 reported favorable outcomes in two-thirds oftheir patients with TMJ ankylosis who received post-surgical radiation. However, significant concerns ex-ist relative to the effects of this treatment on nearbystructures (brain, orbit, and parotid gland).24,29

Nonsteroidal anti-inflammatory drugs act by inhib-iting the production of prostaglandins, particularlyprostaglandin E2. Perioperative nonsteroidal anti-in-

ammatory drugs have also been reported to reducehe incidence of HBF by one-half to two-thirds. Thefficacy of indomethacin (25 mg 3 times a day for 5-6eeks) in preventing HBF has been shown.30

There are reports in the literature discussing theuse of bisphosphonates as prophylaxis against HBFafter total hip arthroplasty. However, despite the factthat bisphosphonates have the ability to inhibit min-eralization of osteoid, unfortunately, they have noinhibitory effect on the formation of osteoid. There-fore their use has been discontinued because it wasfound that these drugs only postpone ossification

FIGURE 4. A, Intraoperative view showing the bony ankylosis (ankylotic bone.

onje et al. Synovial Metaplasia. J Oral Maxillofac Surg 2012.

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until their use is stopped.31,32w

The transplantation of autogenous free fat graft intothe TMJ was reported as early as 1914.33 The use ofautologous fat transplantation has been reported byThomas34 as a way of preventing HBF after hip re-

lacement. The presence of dead space after exten-ive joint debridement leads to hematoma formation.ccording to Lexer, fat tissue has hemostatic proper-

ies, caused by the fast attachment of fat tissue to aleeding site, therefore stopping the bleeding. It haslso been postulated that fat may be a factor in pre-enting scar formation tissue.23 Mercuri et al,25 in a

study of 20 TMJ reankylosis patients managed by gaparthroplasty, total alloplastic patient-fitted TMJ pros-theses, and periarticular autogenous abdominal fatgrafts, reported significant improvement in reportedpain, jaw function, and diet consistency. Further-more, a significant number of these patients reportedimprovement in their quality of life after surgery.

Synovial metaplasia was first described by Brodyand White35 after their studies on implanted siliconejoints in chickens. The first human cases were de-

around the TMJ stock prosthesis. B, Same view after removal oficom

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scriptions of the formation of synovial-like mem-

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branes reported by investigators studying the reactionof the periarticular tissues to joint and tendon pros-theses.7,8 Later, Gonzalez et al9 reported the occur-rence of synovial metaplasia occurring in the skin inhealed surgical scars. There have also been numerous

FIGURE 5. A, Silicone orbital implant spacer (Bausch & Lomb) inplace before being removed. B, Glistening, white, fibrous connec-tive tissue capsule–like structure (arrow) found on removal of sili-cone orbital spacer.

Monje et al. Synovial Metaplasia. J Oral Maxillofac Surg 2012.ww.fed

reports of synovial metaplasia occurring adjacent tow

silicone breast implants and expanders1-6 or siliconeoice prostheses36 or produced experimentally afterepetitive subcutaneous injections of air after surgicalrocedures.37

The term “synovial metaplasia” is based on themorphologic resemblance of villous structures of thehyperplasic synovial membrane at histologic exami-nation. These histologic features include epithelioidcells with basally oriented nuclei overlying a fibrousmembrane; cytoplasmic processes, oriented perpen-dicular to the surface; occasional multinucleated giantcells; and a well-formed reticulin network. There is noevidence of elastin fibers or basement membrane (Fig7). Studies comparing the breast capsular membraneswith synovial membranes found in villonodular sy-novitis have shown similar histologic, histochemi-cal, and immunohistochemical features, in terms ofboth transmission appearance and scanning elec-tron microscopic appearance.1-4 Unfortunately, be-ause there are no unique and specific biomarkersor synovial cells, until one becomes available, itppears reasonable to assume that this membrane isynovial metaplasia.

FIGURE 6. Intraoperative view of custom-made TMJ Conceptsprosthesis articulation.

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2296 SYNOVIAL METAPLASIA

The presence of a lining membrane with the histo-logic features of synovial tissue has important impli-cations for determining the origins and functionalsignificance of this tissue. A number of theories havebeen suggested to explain this phenomenon. Somestudies suggested that the tissue reaction can be cor-related with the implant surface or that the age of theimplant could be a significant factor.38,39 Raso et al1-3

attributed stimulation of synovial metaplasia forma-tion more to the silicone than to the surgical proce-dure. Another hypothesis suggests that mechanicalstress may influence the development of synovialmetaplasia.

There is now consensus that movement is impor-tant. Drachman and Sokoloff40 showed that synovialissue fails to develop in the embryo in the absence ofotion. They suggested that traction or motion pro-

FIGURE 7. Histologic appearance of papillary synovial metaplasby fibrovascular tissue. The nuclei of these cells are basally or(hematoxylin-eosin stain, original magnification �40). B, A numbgiant cells (arrows) (hematoxylin-eosin stain, original magnificationstrong staining of all cells within papillae (original magnification �

Monje et al. Synovial Metaplasia. J Oral Maxillofac Surg 2012.

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ides the biological signal that stimulates differentia- iw

ion and organization of individual cells into synovialissue. That is, mechanical forces (movement, shearorces, repeated surgery, trauma, and so on) are nec-ssary for the development of synovium. These au-hors also named other rarely cited factors necessaryor the formation of normal joint spaces: loose areolarissue that would develop spaces due to the move-ent and relatively smooth gliding surfaces thatould resist penetration by growing fibroblast pro-

esses.Edwards et al37 provided data supporting this con-

ept. They repeatedly injected air into subcutaneousissue. Analysis of the lining tissue of this cavity byight and electron microscopy and histochemicalechniques showed that after 5 to 30 days, the liningembrane was indistinguishable from synovial tissue.hese studies appear to show that mechanical forces,

single papillary fold, showing the synovial lining cells supportedand are polarized perpendicular to the cavity surface (arrow)aces representing dissolved silicone surrounded by foreign-bodyC, D, Immunohistochemical stain for CD-68 (C) and PGP-9 (D) with

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ia. A, Aienteder of sp�40).40).

n association with the natural developmental re-

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sponse of mesenchymal tissues surrounding an im-planted foreign body, and the chemical and physicalcomposition of the foreign body are most likely pri-marily involved with the formation of the synovialmetaplasia.37

Several manuscripts reported reactive tissue to tem-porary or permanent silicone spacers placed after discremoval decades earlier. Destructive lesions of thecondyle41 in conjunction with histopathologic find-ings of foreign-body reactions in articular tissues andregional lymph nodes42,43 were reported. Sanders etl44 affirmed that silicone elastomer became encapsu-ated by connective tissue in a reasonably short pe-iod, which worked as a reasonably smooth articularurface.

Westermark et al45 report histologic findings in softissue samples obtained from around 2 types of TMJrostheses (Biomet Microfixation and TMJ Concepts)fter up to 8 years of function. All joint capsule sam-les showed dense, fibrous connective tissue with no

nflammatory cells or foreign-body reactions. Theoint disc tissues showed even denser fibrous connec-ive tissue, free from inflammatory reactions. Someamples from the junction between capsule and dischowed synovial-like tissue.45

After a review of the literature, the case presentedappears to be the first reported case in which papil-lary synovial metaplasia occurred due to the use of asilicone temporary spacer implant during a 2-stagedalloplastic TMJ replacement in a patient in whom HBFdeveloped after reconstruction of the TMJ with astock prosthesis.

Although further investigation into this phenome-non in the TMJ is warranted, it seems reasonable tosuggest a 2-staged procedure to replace the TMJ inpatients who have had repeated failed surgical proce-dures or trauma and in whom ankylosis or reankylosisdeveloped because of HBF. In our opinion, such pa-tients could benefit from a 2-staged surgery, withplacement of a temporary silicone spacer implant atthe first-stage surgery; then, at the second-stage sur-gery after formation of the synovial lining, the clini-cian will implant the components of the prosthesisand place autogenous fat around the articulation, withactive physical therapy thereafter. This recommenda-tion is based on the assumption that this implantmaintains the gap and could induce the formation ofa synovial lining that prevents new heterotopic ossi-fication. However, further studies are necessary inthis area before a firm conclusion can be drawn.

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