Alloplastic Temporomandibular Total Joint Replacement

Abstract

Alloplastic temporomandibular total joint reconstruction provides an effective surgical treatment option for patients with end-stage temporomandibular joint disease. While temporomandibular disorders are often initially managed with non-surgical modalities, severe ankylosis, aberrant anatomic deformity, or loss of primary function necessitates surgical intervention in patients with late-stage disease. Modern advancements in the field of temporomandibular joint replacement, especially over the last three to four decades, have improved upon initial challenges of poor prosthetic design and improper material selection. Modern alloplastic prosthetic devices, including both stock and custom patient-fitted prostheses, have been shown to be both safe and effective in restoring temporomandibular form and function. Alloplastic temporomandibular total joint replacement now represents a successful surgical solution with advantages including improved accessibility, reduced operative time, earlier return to mobilization, and lower morbidity risks than autogenous methods. This chapter will provide an overview of the fundamental principles of temporomandibular joint replacement, indications for surgery, patient selection, stock versus custom prostheses, outcomes, and potential complications with reference to the current body of literature.

1. Introduction

Alloplastic total joint replacement (TJR) has become a safe, widely accepted, and accessible procedure in the treatment of end-stage temporomandibular joint (TMJ) disease [1]. As early as 1840, the fundamental idea of interposing artificial or exogenic materials between diseased joint surfaces was implemented by the American surgeon Dr. John Murray Carnochan, who placed wood between the articular surfaces of an ankylosed mandible after rudimentary gap arthroplasty [1]. Since that time, the field of temporomandibular total joint replacement (TMJ TJR) has had a colorful history filled with numerous attempts to successfully reconstruct the temporomandibular joint using various alloplastic materials. The intricate role of the TMJ in mastication, speech, and airway maintenance presented unique challenges in creating a viable joint replacement device [2]. Initially, TMJ reconstruction was performed only in severe cases of developmental maxillofacial deformity, inflammatory joint disease, ankylosis, or previous tumor resection [2]. As a result, early cases were rare and reporting of long-term complications was limited. Over the span of nearly a half-century, numerous synthetic materials including silicone elastomers, Teflon and Proplast, various acrylics, and other novel substances were utilized in search of the ideal alloplastic material [2]. As alloplastic total joint replacement became increasingly more common, various systems were developed and subsequently discontinued with a large variance in reported success rates, leading patients to require an increasing number of revisions of previous failed reconstructions, thus adding an additional layer of complexity [1, 2, 3].

The late 1990s brought about the advent of what is now considered the modern-day alloplastic temporomandibular joint replacement prosthesis. The global oral and maxillofacial surgery community has since made substantial progress in addressing the initial shortcomings that characterized historical alloplastic TMJ reconstruction [4]. Inappropriate prosthetic models, inadequate clinical trial design, and inattention to outcomes outlined in orthopedic literature have been amended with well-designed pre-market trials for both stock and patient-specific TMJ TJR devices [4]. As a result of these improvements, alloplastic total joint replacement now represents a highly effective surgical solution for advanced TMJ dysfunction or ankylosis, greatly benefitting the form and function of patients with late-stage disease.

2. Modern alloplastic TMJ reconstruction

The core principles of total TMJ reconstruction surgery include the resection of significantly degenerated articular structures due to inflammatory arthritic disease, the release of bony or fibrous ankylosis, the return of non-morbid occlusion, the re-establishment of vertical mandibular ramal height, the restoration of articular surfaces, and the creation of barriers to prevent further ankylosis and maintain jaw mobilization [1, 2]. Alloplastic TJR prostheses consist of two components that reconstruct the articulating surfaces of the temporomandibular joint: a mandibular ramal component and a glenoid fossa component. The mandibular component reconstructs the condylar process and a portion of the ramus of the mandible. It is typically fabricated out of titanium (Ti-6AL-4V) alloy and/or nickel-containing cobalt-chromium-molybdenum (Co-Cr-Mo) alloy due to the biocompatibility and strength of these materials. The glenoid fossa component is commonly fabricated out of an ultrahigh molecular weight polyethylene (UHMWPE), with or without an unalloyed titanium mesh backing. These alloplastic components are designed to withstand normal occlusal loads over the full range of motion while prosthetic components are stably fixated [2]. This combination of materials has been found to provide an optimal balance of flexibility, strength, wear and corrosion resistance, and biocompatibility to recreate the complex functions of the TMJ.

2.1 Advantages and disadvantages

The advantages of alloplastic TMJ replacement are numerous. Stock alloplastic systems are widely available and can be inventoried for immediate use as needed [5]. Unlike autogenous TMJ replacement options, alloplastic reconstruction also avoids the donor site morbidity risks associated with tissue harvest. For example, potential complications such as pneumothorax, increased anesthesia time, and post operative abductor weakness of the ipsilateral upper limb seen with costochondral graft harvest can be avoided [5]. The lack of donor site is also beneficial in decreasing surgical time, which is an important advantage where operating room resources are scarce. Patient-specific alloplastic options provide further benefit as they are custom manufactured to conform to each patient’s anatomy, decreasing the time needed for implant fitting and anatomic adaptation, as well as implantation. Unlike autogenous grafts, alloplastic implants are also not vulnerable to failure secondary to foreign body reaction from particulate matter from previous failed prostheses, which is a useful advantage in patients requiring revision of prior reconstructions [2]. Lastly, patients who undergo alloplastic TMJ replacement are not limited to delayed physical therapy and can often begin treatment in the immediate post-operative phase.

Although alloplastic TMJ replacement is an effective tool in temporomandibular joint replacement, it is not without disadvantages. There is a notable expense associated with both the computer-aided surgical simulation (CASS) and fabrication of the alloplastic components. Although surgical operating room and anesthesia fees may be less than with autogenous graft harvest and implantation, the fabrication cost of the alloplastic implants can be a significant barrier for many patients or health networks [5]. Another potential disadvantage associated with alloplastic TMJ replacement is longevity. Although the current expected lifespan of alloplastic TMJ TJR devices is not explicitly defined in the literature, recent studies have shown excellent durability of at least 10–20 years for modern TMJ TJR devices [3, 6, 7, 8, 9]. However, the need for revision surgery is presently unpredictable as long-term data regarding device longevity is still unknown. Although the biocompatibility of modern alloplastic joint components is well documented, material hypersensitivity remains a concern associated with any alloplastic joint replacement. The rate of aseptic failure due to alloplastic TMJ replacement, although infrequent, is not yet well defined [10]. The rare potential for wear debris and the subsequent biological response also represents a potential complication that cannot be overlooked [2]. Lastly, alloplastic TMJ joint replacement is currently only indicated in skeletally mature individuals which limits suitability in younger patients [2].

2.2 Indications, contraindications, and patient selection

The indications for alloplastic joint replacement are dictated by the fundamental goals and principles of total TMJ reconstruction. The principal objectives of any TMJ reconstructive surgery, be it autogenous or alloplastic, involve the cost-effective enhancement of mandibular form and function with concomitant pain reduction, while also preventing further morbidity [11]. One of the most common indications for alloplastic TMJ reconstruction is late-stage degenerative joint disease secondary to either non-inflammatory or inflammatory arthropathies [2]. Other indications include adolescent internal condylar resorption, recurrent ankylosis, revision of failed alloplastic or autogenous reconstruction, irreparable condylar fracture, avascular necrosis, congenital disorders such as orofacial or oromandibular dysostoses, and neoplasia requiring extensive resection [2, 8, 9]. Relative contraindications for alloplastic TMJ TJR include acute or chronic infection, skeletal immaturity, prosthetic material hypersensitivity, and patients with increased susceptibility to infection secondary to uncontrolled or poorly controlled systemic disease [3].

Patient selection is a critical component of successful total TMJ reconstruction. For skeletally immature patients, autogenous joint replacement or distraction osteogenesis have historically been referred to as the gold-standard methods of TMJ reconstruction [2]. Skeletally mature patients, on the other hand, may benefit from alloplastic joint reconstruction. As more experience is gained with alloplastic TMJ TJR devices, future advancements may allow for the inclusion of patients that have not yet reached skeletal maturity [2]. Mercuri and Swift reported that alloplastic TMJ TJR may also be beneficial in patients whose joints have no potential for continued growth due to severe ankylosis, mutilation, or multiple operations [12]. A stock prosthesis is safe and effective for reconstruction of a non-mutilated joint, however patients who have undergone multiple operations or have significant anatomic mutilation typically require a computer-assisted design/computer-assisted manufactured (CAD/CAM) custom joint prosthesis [2].

It is important to note that dentofacial deformities which require surgical correction frequently exist together with temporomandibular joint disorders. Regardless of whether a patient’s TMJ pathology is a causative factor for subsequent dentofacial deformity, or it develops because of a pre-existing jaw deformity, patients with these concomitant conditions may benefit from surgical intervention which includes both alloplastic joint reconstruction and orthognathic surgery [2]. Orthognathic surgeons should realize that healthy and biologically stable temporomandibular joints are necessary for favorable surgical outcomes, with significant TMJ pathology often leading to unsatisfactory results in function, esthetics, pain, and skeletal/occlusal stability. Surgeons must recognize potential TMJ issues in patients with high occlusal plane angle progressively worsening class II morphologies, especially where an anterior open bite exists. Wolford outlines that major surgical advancements in the past 25 years have confirmed that combined temporomandibular joint and orthognathic surgery (C-TJR-OS) can be safely and predictably performed in a single operation with accurate diagnosis and planning (Figure 1) [2]. Wolford also notes that in his 25 year experience using patient-fitted TMJ TJR devices, “approximately two-thirds of patients requiring TMJ TJR can benefit from concomitant orthognathic surgery for improvement in function, airway and breathing capabilities, better aesthetic outcomes, and decreased or elimination of pain” [2]. Although an in-depth review of the intricacies of C-TJR-OS is outside the scope of this chapter, it is important to note that typically surgical sequencing involves condylectomy/coronoidectomy, mobilization of the mandible and placement of an intermediate splint, placement of the total joint prostheses, followed by maxillary osteotomy, and lastly adjunctive procedures such as genioplasty, rhinoplasty, uvulopalatopharyngoplasty, or other facial augmentation (Figure 2) [2].

Figure 1.

Patient with severe condylar degeneration secondary to rheumatoid arthritis. CASS was utilized to plan C-TJR-OS. Surgical movements included maxillary advancement and impaction, along with counterclockwise rotation of the maxillofacial complex, flattening of the occlusal plane angle, and concomitant bilateral TMJ TJR.

Figure 2.

Virtual surgical planning (VSP) workflow for a combined orthognathic and TMJ TJR surgery in a patient with condylar agenesis. Virtual surgical plan shows counter-clockwise rotation of the maxillomandibular complex, flattening of the occlusal plane angle, and pogonion advancement of 25 mm. Comparative pre-surgical and post-surgical AP and lateral cephalometric radiographs are shown.

2.3 Stock vs. custom prosthesis

There are currently two U.S. Food and Drug Administration (FDA) approved alloplastic temporomandibular total joint systems available for implantation. These include the TMJ Concepts (formerly Techmedica) custom patient-fitted device (TMJ Concepts, Ventura, California) and the Zimmer Biomet (formerly Biomet Lorenz) stock Total TMJ Replacement System (Zimmer Biomet, Jacksonville, Florida). Each of these systems gained approval by the FDA in 1999 and 2005 respectively. The stock Zimmer Biomet prosthesis was granted full FDA approval after completion of a 3-year follow up to an investigational device exemption study which included 442 joints [13]. In several other countries outside of the United States, the Biomet patient-matched, or “custom” Total TMJ Replacement System is available, with which several authors have reported statistically significant success [3, 14, 15]. At the authors’ institution (Toronto, Canada), the Zimmer Biomet patient-matched Total TMJ Replacement System receives approval on a case-by-case basis after special application to Health Canada.

Deciding between stock versus custom prostheses requires careful consideration of the advantages and disadvantages. The main advantages of stock prostheses are their immediate availability, fit flexibility, and lower cost than their custom counterparts [2]. Provided sufficient bone stock is available for the stabilization and fixation of stock components, these features make stock prostheses particularly useful in cases of irreparable trauma or tumor resection. However, stock prostheses have limited potential for anteroinferior movement of the mandible, therefore surgeon experience is an important factor in managing the variability of fit. Custom prosthetic joints, on the other hand, can address significantly distorted or anatomically unstable situations including excessive antero-inferior movement of the mandibular complex (Figure 3) [2]. Computer-assisted surgical simulation of patient-specific implants facilitates fabrication of prostheses which conform intimately to the patient’s existing anatomy, ensures optimal implant positioning and the avoidance of vital structures, and concomitant correction of facial contour (Figures 4–6) [3]. Unfortunately, these advantages come at a higher cost and a significant fabrication time of 8–12 weeks. Furthermore, there is limited flexibility in the surgical implantation of custom prostheses as surgeons must replicate model surgery exactly. In 2021, Brown et al. found 74% of cases in a study of 241 joints could be adapted to a stock prosthesis [16]. From their research, they concluded that custom TJR devices should be the gold standard in cases requiring a large mandibular advancement with counter-clockwise rotation of the mandibular plane angle, creating a gap of greater than 35 mm between the fossa and the ascending ramus [16]. Furthermore, custom prostheses should also be preferred in cases with severe mandibular dysplasia, syndromic patients, concurrent orthognathic surgery cases, and in the reconstruction of multiply operated joints [16, 17]. Regardless of the differences between stock and custom prostheses, appropriate perioperative planning to ensure intimate and stable adaptation of the alloplastic components is important in the long-term success of these prostheses.

Figure 3.

Preoperative CT images showing a right sided mandibular continuity defect and left sided condylar dislocation into the infratemporal fossa. Maxillary hardware from previous corrective orthognathic surgery is also seen. This aberrant anatomy shown in this image highlights the need for extended patient-matched prostheses for temporomandibular joint reconstruction.

Figure 4.

Computer-assisted surgical simulation (CASS) of the planned osteotomies to re-establish pre-morbid occlusion and placement of extended TJR prostheses. Utilization of virtual surgical planning is necessary for accurate prostheses placement, the avoidance of vital structures, and correction of facial contour.

Figure 5.

Intraoperative images of bilateral Zimmer Biomet patient-matched extended temporomandibular joint replacement prostheses.

Figure 6.

Comparative pre-surgical and post-surgical images showing improved facial balance and contour.

The Zimmer Biomet stock prosthesis fossa (Figure 7) is composed of Biomet’s ArCom^® ultrahigh molecular weight polyethylene (UHMWPE) fossa component, which is available in three different flange lengths. This UHMWPE is specifically designed to maintain a low coefficient of friction while being characterized by high tensile and shear strength properties, ideal for use in articulating orthopedic alloplastic joints [2]. The UHMWPE is gamma-radiated to increase cross-linking, which decreases wear properties [2]. The small, medium, and large-sized fossa components all share the same thickness, surface area, and geometric configuration of the articulating surface, while varying the anteroposterior length of the zygomatic flange. This variability allows for a differing number of screw fixation sites for the fossa component. Unlike patient-fitted or custom-made devices, which are specifically designed and manufactured for individual anatomy, the stabilization of the stock fossa component relies on appropriate surgical alteration of the articular eminence and lateral aspect of the zygomatic arch to achieve tripod stability. Typically, a diamond rasp is used to perform appropriate eminoplasty. The fossa component is fixated in place using 2.0 mm self-tapping screws.

Figure 7.

Zimmer Biomet microfixation stock total TMJ replacement system fossa (top row) and mandibular (bottom row) components.

The Zimmer Biomet stock prosthesis mandibular component (Figure 7) is composed of a Co-Cr-Mo alloy (ASTM type F799), which is plasma sprayed on the medial bone-contacting surface with a roughened titanium coating [2, 11]. Much like the stock fossa component, the ramal component is manufactured in three different lengths of 45 mm, 50 mm, and 55 mm. Of note, the 50 mm condylar component is also produced in an “offset” configuration, where the angulation of the condylar head is the opposite of the standard medially angulated head (Figure 8). This provides a laterally angulated condylar head for cases where the ramus is medially offset [2]. The ramal footplate also comes in two different designs, either “narrow” or the more commonly used “standard” with a broader ramal plate providing additional screw fixation options. The variability in screw placement is especially important in patients who may have altered anatomy secondary to previous chostochondral grafts or failed alloplastic implants. The mandibular component is fixated in place using 2.7 mm self-tapping bicortical screws.

Figure 8.

Zimmer Biomet microfixation stock total TMJ replacement system offset and standard mandibular configurations.

“Patient-fitted” or “custom-made” devices, such as the TMJ Concepts patient-fitted device (TMJ Concepts, Ventura, California), and the Zimmer Biomet (formerly, Biomet Lorenz) patient-matched Total TMJ Replacement Custom System (Zimmer Biomet, Jacksonville, Florida) are designed and manufactured for specific anatomical situations. They often require little to no bony surgical site alteration prior to implantation [2]. Furthermore, with the advent of CAD/CAM technology, extended TJR devices (eTJR) can be developed to replace segmental mandibular defects including skull base defects post-tumor resection or for craniofacial conditions such as hemifacial microsomia or Treacher Collins syndrome [3, 18, 19, 20, 21]. Aberrant anatomy, severe occlusal disharmony, and deficient recipient bone stock are surgical challenges that limit the application of stock TMJ TJR in patients needing extended patient-matched prostheses [3].

3. Surgical decision making and techniques

3.1 Pre-surgical planning and preparation

Appropriate pre-operative planning should include a lengthy discussion regarding potential post-operative complications. These include infection, sensory and/or motor nerve dysfunction, foreign body reaction or material hypersensitivity, heterotopic bone formation, dislocation, malocclusion, ongoing post-operative pain, and the possible need for revision [2]. Setting realistic patient expectations regarding surgical goals and outcomes is also an essential element of surgical preparation and informed patient consent. A detailed discussion of expected surgical outcomes, which is outlined later in this chapter, should also be reviewed with patients.

Consideration of comorbid medical conditions and overall patient health should also be included in the surgical planning phase. In patients with end-stage TMJ arthritis related to underlying rheumatologic disease, coordination with rheumatology may be required to arrange perioperative cessation of immunosuppressant medications such as anti-cytokine medication, disease-modifying biologics, or glucocorticoids [2]. Communication with patients’ primary care providers is also prudent to ensure chronic conditions such as diabetes or hypertension are stable and well managed prior to surgery.

3.2 Surgical techniques

After appropriate preparation of the surgical field(s), standard retromandibular and preauricular incisions are used to access the mandibular ramus and temporomandibular joint respectively. Regarding the retromandibular incision, a modified Risdon approach is used to expose the entire lateral aspect of the mandibular ramus, the coronoid process, the sigmoid notch, and the neck of the condylar process [4, 9]. Regarding the pre-auricular incision, a modified Al-Kyatt incision is made from the lobe to the top of the helix, with the superior aspect of this incision extending anteriorly and superiorly for about 3–4 cm at a 45° to the zygomatic process of the temporal bone [8]. In the pre-auricular approach, dissection is carried down to the level of the superficial layer of the temporalis fascia above the zygomatic arch and the parotidomasseteric fascia below the zygomatic arch. In close proximity to the tragal ligament, the auriculotemporal nerve and transverse facial artery are sacrificed during the approach [2, 4]. Further dissection is then commenced via incision through the superficial layer of the temporalis fascia superiorly. A fascial flap is then raised anteriorly, typically using periosteal elevators and dissecting scissors, along the zygomatic process of the temporal bone to expose the lateral aspect of the glenoid fossa and the articular tubercle of the temporal bone [2]. Care in preventing tearing or excessive retraction of this tissue should be used to prevent injury to branches of the facial nerve (CNVII) that run through this area. Next, the fossa is entered through the superior aspect of the capsule. Any remnants of the articular disc should be removed at this point, along with condylar resection.

Mandibular ramal osteotomy, and subsequently condylar resection, must be performed to ensure that a minimum of 15–20 mm between the mandibular ramal osteotomy and the height of the articular eminence exists to accommodate the fossa component of the alloplastic joint, depending on the specifications of the device being implanted [2]. At the authors’ institution, the mandibular ramus osteotomy including the condylar process, and potentially the coronoid process, is made through the retromandibular incision via reciprocating saw. After the osteotomy is performed, bleeding is controlled and the site is packed with moist gauze. The proximal condyloid process segment is removed through the preauricular incision, and if the coronoid process is being removed, it is removed through the retromandibular incision. To avoid excessive muscular oozing from the temporalis and lateral pterygoid muscular attachments, monopolar electrocautery is used to strip the muscle attachments prior to resection.

Once the condylar process is resected, the residual fossa must be thoroughly debrided before fossa prosthesis fixation. The fossa should be debrided posteriorly to the tympanic plate of the temporal bone, medially towards the medial capsular attachment to the temporal bone, and anteriorly to the anterior-most aspect of the articular eminence of the temporal fossa [2]. Typically, if improper or incomplete fossa preparation has been completed, the alloplastic fossa will not fully seat on the medial aspect, preventing appropriate condylar-fossa relationship upon implantation [2]. If a stock fossa system is used, fossa component stability requires tripod stability which is achieved by flattening the articular eminence with a reciprocating diamond rasp [4]. The fossa should be positioned parallel to the Frankfort horizontal plane, or slightly inferior anteriorly to prevent anterior dislocation. After appropriate fossa preparation, the mandibular ramus may need to be prepared for appropriate passive “flush fit” of the ramal prosthesis [2]. This can be accomplished via diamond reciprocating rasp to remove lateral ramal bony irregularities. Just prior to implantation, the fossa and mandibular prosthetic components should fit passively with appropriate articulating relationship at rest.

Once appropriate occlusion has been set intraorally, with the utmost care being taken not to contaminate the implantation sites, alloplastic component fixation can commence. At this point, the fossa and mandible implants may be seated into position to confirm passive positioning of the implant components. A fossa seating tool or ramus component clamp can be used to assist in orientation and stabilization of the implant components if preferred [2]. Once the components are deemed to be in the appropriate articulating relationship, with the condylar head of the mandibular ramus component centered in fossa in the lateromedial direction and seating against the posterior aspect of the load bearing surface of the fossa, the components are fixated into position using a slow speed guided drill with copious irrigation.

Lastly, after implantation, maxillomandibular fixation is released and the mandible functioned while maintaining the sterility of the implantation sites. When appropriate occlusion and range of motion is noted, training elastics are placed. Imaging confirmation of component alignment, position, and fixation may be undertaken intraoperatively at the discretion of the surgeon, using A-P skull radiographs [2].

3.3 Post-operative management

Post-operative management after alloplastic total temporomandibular joint reconstruction is extremely important and cannot be overlooked. Immediately post-operatively, an auditory canal examination should be undertaken to ensure the integrity of the external auditory canal and tympanic membrane. A Barton-type pressure dressing should be placed, typically to be removed the following morning. Regarding mandibular range of motion, in the immediate and early post-operative periods, limitation of mouth opening may be considered to avoid dislocation, particularly in patients who have undergone coronoidectomies or extensive soft tissue dissection to regain pre-morbid mouth opening or to reposition the mandible [2]. Typically, the risk of dislocation is only a concern for the first week post-operatively. The use of training elastics can reduce the propensity for dislocation [2]. When the risk for dislocation is deemed low, and no immediate component dislocation is noted when the mandible is functioned on the operating table, some clinicians may release guiding elastics as early as 8–12 hours after surgery [2]. Functioning the alloplastic joint as quickly as possible post-operatively will enhance healing and decrease peri-articular scar tissue formation which can limit post-operative mouth opening [22]. A significant advantage of alloplastic joint replacement is that patients are typically able to start active physical therapy immediately post-operatively utilizing commercially available jaw exercise devices, such as the Therabite® (Atos Medical, Milwaukee, WI) [1]. Physiotherapy referral to increase and maintain mandibular range of motion may be necessary in the months following alloplastic joint replacement.

4. Outcomes and survivorship

In appropriately selected patients, alloplastic TMJ TJR is a safe, predictable, efficient, and cost-effective treatment option for end-stage temporomandibular joint disease. In 2018, Zhou et al. completed a meta-analysis of the alloplastic TMJ TJR literature that showed both custom and stock devices deliver similar outcomes for decreased pain, improvements in function and diet, and maximum interincisal opening [23]. Like any surgery, reasonable patient expectations are essential for successful joint reconstruction [4]. With careful pre-operative planning and proper placement of alloplastic TMJ TJR devices, patients can be counseled that a post-operative interincisal mouth opening of 30-35 mm is achievable with a total joint prosthesis. Furthermore, a 60–70% reduction in preoperative pain levels and a functional diet 75% of normal are attainable goals with TMJ TJR devices [2]. In an FDA approved Investigational Device Exception (IDE) study published in 2005 on data from 224 cases, Zimmer Biomet noted that patients had significant improvement in pain after 3 years, with pain scores decreasing from 8.5/10 to 2.8/10 [1, 13]. Furthermore, maximum interincisal opening (MIO) improved from 20.1 mm to 29.3 mm at the 3-year mark [1, 13]. Lastly, patient satisfaction scores were high, with 99% of patients stating that they would choose to undergo the surgery again. Wolford et al. published a prospective cohort study in 2015 that reported similarly positive subjective and objective outcomes, as well as improved quality of life in patients with severely degenerated and functionless temporomandibular joints treated with custom TMJR devices at a median of 21 years after surgery [6, 17]. In 2017, Johnson et al. published a systematic review and bias-adjusted meta-analysis of total temporomandibular joint prostheses, including TMJ Concepts prostheses, Biomet prostheses, and Nexus prostheses [24]. The authors concluded that there were no real differences between pain, diet, and MIO scores among the prostheses, although there was more data available for the TMJ Concepts prosthesis [24]. In 2020, a prospective observational study by Granquist et al. noted the Kaplan-Meier survivorship rate of Biomet stock TMJR devices was 96% at 3 years, 94% at 5 years, and 86% at 10 years [25].

5. Complications

As with every surgical procedure, complications may occur that require further management. The most common complications associated with alloplastic temporomandibular joint replacement include, but are not limited to, periprosthetic infection, heterotopic bone formation, dislocation, increasing neuropathic pain, material hypersensitivity, sensory and motor nerve dysfunction, and massive hemorrhage [2]. This section of the chapter will introduce a broad overview of some of the common complications that are seen in TMJ TJR surgery and their management.

In 2011, Mercuri and Psutka published a retrospective survey of 2476 alloplastic temporomandibular joint replacement cases, with 3368 total joints, where 51 periprosthetic joint infections (PJI) occurred, totaling a 1.51% incidence of infection over a mean of 6 months post-operatively [26]. Although the incidence of periprosthetic joint infection is rare, the consequences of this complication can be detrimental. The Musculoskeletal Infection Society (MSIS) workgroup proposed a universal definition for periprosthetic joint infection in 2011 [27]. This definition includes the presence of a sinus tract communicating with the prosthesis, a pathogen isolated by culture from two or more samples obtained from the affected prosthetic joint, and four of the six following criteria:

• elevated serum ESR/serum CRP concentrations

• elevated synovial WBC count

• elevated synovial PMN percentage

• presence of purulence in the affected joint

• isolation of microorganisms in one culture of periprosthetic tissue/fluid

• >5 neutrophils per high-power field in 5 high-power fields observed in a sample for histological analysis of periprosthetic tissue at 400x magnification

Although the detailed management of periprosthetic joint infection (PJI) is outside the scope of this chapter, diagnostic and management algorithms have been outlined based on the existing body of TMJ TJR PJI literature [26, 28, 29, 30, 31, 32], as well as the American Academy of Orthopedic Surgeons’ (AAOS) Clinical Practice Guidelines for diagnosis of PJI [33]. Practically speaking, periprosthetic joint infections can be dichotomized into either early (within days to <3 weeks) or delayed (>3 weeks) infections, which helps to guide subsequent management decisions. Early PJI are characterized by pain, swelling, redness, and drainage at the surgical site(s), serology showing elevations in ESR and CRP, positive synovial fluid culture with the presence of WBC, and stable components on imaging. The management of early PJI infections typically includes incision and drainage, surgical debridement of the prosthetic components with implant retention, and long-term antibiotics [31]. Late PJI on the other hand, are characterized by pain, swelling, redness, and potentially fistula formation at the surgical site(s). ESR and CRP values may or may not be elevated in these patients. Like early PJI, positive synovial fluid cultures are seen with the presence of WBC, but components typically appear unstable on imaging. The management of late PJI infections typically includes 2-stage prosthetic implant removal, placement of an antibiotic impregnated spacer, and later replacement [31].

Temporomandibular joint heterotopic bone is loosely defined as the abnormal presence of bone in the soft tissue surrounding a total joint reconstruction. Heterotopic bone formation within the joint space decreases interincisal opening and can be a significant cause of pain, joint dysfunction, and eventual progression to ankylosis. Various pharmacologic agents have been used in the management and prophylaxis of heterotopic bone formation, however limited data exists on their effectiveness. Non-steroidal anti-inflammatories such as indomethacin and diphosphonates such as etidronate have been used in the orthopedic literature with varying success [33, 34, 35]. Localized low dose (10Gy) ionizing radiation in the initial 4–7 days post-operatively has also been recommended in the management of heterotopic bone formation with success [36]. Concerns have been raised, however, about potential adverse effects on adjacent structures from local radiation. Furthermore, postoperative radiation following autogenous reconstruction with costochondral grafts, gap arthroplasty, or debridement of heterotopic bone has been shown to fail in preventing heterotopic bone formation in 33–50% of cases [37, 38]. Along with surgical excision of heterotopic bone to preserve joint mobility, numerous authors have recommended autogenous fat grafts to be packed around the articulation of the prosthesis to decrease potential recurrences [39, 40]. This obliterates the dead space and prevents the formation of a blood clot. Studies have shown fat grafting around prostheses to be favorable to lack of fat grafting when evaluating heterotopic bone formation, subsequent ankylosis, and maximum interincisal opening [39, 40, 41, 42, 43].

As mentioned previously, anterior condylar component dislocation is an immediate and early post-operative concern after alloplastic total temporomandibular joint reconstruction. Typically, dislocation occurs secondary to either concomitant unilateral or bilateral coronoidectomy or due to significant stripping of the mandibular masticatory musculature during the procedure. Immediate post TMJ TJR dislocation is managed with bimanual reduction and placement of light intermaxillary elastics and Barton style pressure bandage for 1 week [2]. Late post TMJ TJR dislocation may require a combination of either general or intravenous sedation along with bimanual reduction. Occasionally, repeat surgical intervention is required to achieve reduction. Posterior dislocation is a rare phenomenon that typically only occurs in patients where a stock TMJ TJR prosthesis without a posterior flange has been placed for concomitant orthognathic surgery [2].

Continued or increasing pain after TMJ TJR can have both extrinsic and intrinsic causes [2]. In the orthopedic literature, post total joint replacement pain can be a significant problem, both clinically and economically, and can vary from between 10 and 50% in the surgical literature [44]. In TMJ TJR, surgeons must be able to systematically rule out and/or manage these intrinsic and extrinsic causes appropriately. Intrinsic causes include, but are not limited to, infection, heterotopic bone formation, dislocation, material sensitivity, aseptic component fracture or failure, osteolysis, neuroma formation, and synovial entrapment syndrome [2]. Extrinsic etiology of post-surgical pain includes chronic centrally mediated pain, neurologic injury, prior misdiagnosis, persistent myofascial pain, complex regional pain syndrome, temporalis tendonitis, Frey’s neuralgia, integrin formation, and coronoid impingement [2].

6. Future directions in TMJ reconstruction

The practice of modern oral and maxillofacial surgery, specifically in the treatment of end-stage temporomandibular joint disease, is becoming increasingly impossible without the use of a clinically successful and predictable alloplastic total joint replacement prosthesis. Despite the pitfalls and shortcomings of previous total joint replacement techniques, modern advances in biochemical engineering, material sciences, and our understanding of joint mechanics have made present-day alloplastic TJR devices a safe and effective option for the treatment of end-stage temporomandibular joint disease. In 2016, Onoriobe et al. reported that from 2005 to 2014, there was a 38% increase in TMJ replacement cases performed in the United States. Furthermore, the authors projected that there would be an increased demand (58%) for TMJ TJR devices in the United States by 2030 [45]. As a consequence of increased need, the continued development and improvement of alloplastic temporomandibular joint replacement prostheses is of utmost importance. Undoubtedly, as the demand for TMJ TJR continues to increase, research regarding anatomic and biologic considerations, alloplastic materials, biomedical engineering, design and manufacturing, and the consequences of long-term wear will continue to be necessary [17].

As knowledge in materials science continues to advance, the residual (<1%) nickel in current TJR Co-Cr-Mo alloys is often considered the offending factor in material hypersensitivity. The adverse effects of nickel ions have prompted research and development of high-nitrogen nickel-free austenitic stainless-steel alternatives to currently used Co-Cr-Mo alloys [46, 47, 48]. Although Ti6AlV4 alloys have been used with great success in implantable medical devices, there are notable reports of aluminum and/or vanadium hypersensitivity, which have led to the investigation of titanium alloys containing non-toxic elements such as niobium, molybdenum, tantalum, zirconium, and tin [49]. UHMWPE is currently the most used articulating surface material in alloplastic joint replacement devices (including acetabular cups, tibial plateau, and TMJR fossa, etc.) [17]. UHMWPE boasts superior wear performance, durability, and biological inertness [17]. Research into alternate load bearing surfaces include ceramics, which are used in total hip prostheses, and diamond-like coating (DLC), although the appropriateness of these materials has not yet been fully assessed [17].

Other research initiatives focused on advancing TMJ TJR devices for addressing post-implantation complications include the use of human monoclonal antibody component coating to deter biofilm formation and subsequent infection. Another example involves employing acoustic emission detection to monitor micromotion in device components, providing a means to detect potential issues, leading to revision and prevention of premature device failure [50, 51].

7. Conclusion

In conclusion, this chapter was designed to provide a brief overview of the management of severe end-stage temporomandibular joint disease via alloplastic temporomandibular total joint replacement. While conservative management with non-surgical therapies is appropriate first-line treatment for temporomandibular joint disorders, severe anatomic deformity, ankylosis, or loss of function often requires surgical reconstruction to restore form and function. Advances in the field of temporomandibular joint replacement have produced stock and custom patient-fitted alloplastic prosthetic devices that are safe, effective, and reliable. Alloplastic temporomandibular total joint replacement now represents a successful surgical solution with advantages including improved accessibility, reduced operative time, earlier return to mobilization, and lower morbidity risks than past methods. Although research on long-term outcomes is ongoing, a strong body of literature supports the positive outcomes of modern TMJ TJR surgery in patients with late-stage TMJ disease.

Conflict of interest

Dr. David J. Psutka is an occasional consultant and teacher for Zimmer Biomet.

Dr. Ryan J. McCoy has no conflicts of interest to report.