Authors: Nicholas Wilken, Gary Warburton
Categories: Article, Degenerative joint disease, Reconstruction, TMJ replacement, Temporomandibular joint
Source: Journal of Oral Biology and Craniofacial Research
Degenerative joint disease (DJD), also known as osteoarthritis is the most common form of arthritis and can affect the temporomandibular joint (TMJ). TMJ DJD is characterized by degradation of the articular cartilage and synovial tissues resulting in characteristic morphologic changes in the underlying bone. DJD can occur at any age, but it is more common in older age groups. TMJ DJD may be unilateral or bilateral. The American Academy of Orofacial Pain categorizes TMJ DJD into primary and secondary types. Primary DJD is seen in the absence of any local or systemic factors and secondary DJD is associated with a prior traumatic event or disease process. Frequently, these patients present with pain and limited residual mandibular function resulting in significantly diminished quality of life. Classic radiographic features on orthopantogram and CT imaging include loss of joint space, osteophytes (bird-beak appearance of the condyle), subchondral cysts, erosions, flattening of the condylar head, bony resorption and/or heterotopic bone (Figure 1). Conservative and medical management is successful in the majority of patients until the active degenerative phase burns out, but some will progress to end stage joint disease and require reconstruction of the TMJ. Reconstruction of the mandibular condyle should be considered to restore mandibular function and form to patients who have lost it secondary to degenerative joint disease affecting the glenoid fossa/mandibular condyle unit.
Keywords: Temporomandibular joint, Reconstruction, Degenerative joint disease, TMJ replacement
Patients with end stage TMJ DJD who have failed non-surgical or conservative management may be candidates for surgical treatment and TMJ reconstruction. Many options for reconstructing the mandibular condyle/glenoid fossa exist; these range from autogenous options including vascularized free tissue transfer as well as non-vascularized tissue transfer. Alloplastic (prosthetic) materials can also be utilized; these exist in both patient specific/custom made devices and stock prostheses. Alloplastic options are most commonly utilized for patients undergoing reconstruction due to DJD.
Reconstruction of the mandibular condyle with autogenous tissue is a worthy consideration for multiple indications, however, infrequently in the setting of DJD. Following tumor ablation, reconstruction of both hard and soft tissue can be accomplished with vascularized free tissue transfer. Also, for patients whose infratemporal fossa or masticator space has been exposed to radiation therapy, a vascularized reconstruction may provide significant benefits. The fibula free flap is frequently used for to meet these reconstructive needs,^1^^,^^2^ however, the possibility of complications including ankylosis have been raised.^3^ In cases which require only osseous reconstruction costochondral (rib) grafts have been utilized^4^ and historically have been a reliable method of treating TMJ ankylosis and jaw growth deformities in children.^5^ Costochondral grafts however, carry the significant risk of overgrowth, resorption and ankylosis and so many authors now believe alloplastic reconstructions to be superior with better long term results.6, 7, 8
Many patients with end stage temporomandibular joint degenerative disease who undergo reconstruction of their joint(s) are treated with either a stock or custom-made alloplastic device or prosthesis (Fig. 1). In the USA there are only 2 FDA approved alloplastic devices for TMJ reconstruction (Fig. 2), however, many systems are available worldwide and the number is rapidly increasing. Elledge^9^ et al. completed a review of the current or developing TMJ replacement (TMJR) systems worldwide in 2019. A total of 27 TMJ replacement systems were identified from 15 different countries. Twenty-one of these systems utilize custom joint prosthesis designs, but only 4 have been granted regulatory approval. Long term data is only available for two established Stryker (TMJ Concepts) and Zimmer Biomet. All are designed to have both a glenoid fossa and ramal/condylar component. Ultra-high molecular weight polyethylene (UHMWPE) was found to be the most common fossa bearing surface and was used in 21 devices. A titanium alloy is used for the condyle in 10 systems. Nineteen systems utilize a titanium alloy for the condyle/ramus component. Seven systems utilized 3D printed metal components. Preclinical laboratory testing is reported for 12 systems; however, at the time of review no outcomes had been reported for 9 of the 27 systems. Ultimately, the review revealed that not all systems are equivalent with regards to design, material composition, preclinical laboratory testing, manufacturing methods, regulatory status, and reports of clinical outcomes. These elements vary widely among the systems that are currently emerging, and it is important that surgeons’ and patients understand this when deciding the best one to use. Just one year later the number of TMJ devices has increased even further and currently there are around 40 devices in 19 countries; 9 stock, 31 custom; 10 of which are 3D printed.
Fig. 1 Coronal and sagittal reformats of end stage TMJ DJD. Note the degenerative/resorptive process affecting the condylar head and glenoid fossa.
Fig. 2 FDA approved devices in the USAA) Stryker (TMJ Concepts) custom/patient specific device.B) Zimmer Biomet stock device.
Given the large emerging worldwide market of TMJR systems the characteristics of a device necessary for it to be successful should be kept in mind when choosing a system. Mercuri^10^ states four criteria which need to be met for a TMJR device to be successful; these include 1) the material from which the devices are made must be biocompatible, 2) the devices must be designed to withstand the loads delivered over the full range of function of the joint, 3) the devices must be stable in situ and 4) the surgery to implant the prosthesis must be performed for the proper indications and it must be performed aseptically.
The long-term outcomes of the stock Biomet and Techmedica/TMJ Concepts TMJ replacement devices have been evaluated by multiple studies. Rajkumar and Sidebottom performed a prospective analysis to assess the long-term benefits realized by patients who underwent TMJR with the TMJ Concepts joint replacement system. In this study, 43 patients, with 62 replaced joints, with at least 10 years of follow up were analyzed. The patient group consisted of all patients that had undergone TMJ between 2004 and 2011 and where operated by the senior author of the study (AJS). The patients included 39 females and 4 males with an average age of 45, and were treated for diagnoses including trauma, multiple previous operations, psoriatic and rheumatoid arthritis, degenerative disease and ankylosis. The study found that over the 10 year follow up period that a significant decrease in pain score from 7.4 pre-operatively to 1.7 at 10 years post-operatively (evaluated using 10 point VAS). Additionally, maximal mouth opening was found to improve from 21.0 mm pre-operatively to 34.7 mm at the 10-year post-operative date. Dietary score also significantly improved from 4.1 pre-operatively to 9.5 at the 10-year post-operative time point as evaluated on a 10-point VAS with 0 correlating to a liquid only diet and 10 correlating to no interference with a normal diet. Ultimately, the conclusion of the study reported that TMJR produces good long-term improvements by lessening pain and improving functions and is effective in managing irreparably damaged joints.^11^
Granquist et al. reported on the survivorship and need for subsequent surgical interventions in patients who underwent TMJR utilizing the Biomet TMJ replacement system. The study was designed as a prospective observational study in which patients that underwent device implantation between 1995 through 2010 were sent annual questionnaires from 2012 through 2015 to assess the occurrence of subsequent surgical site intervention (SSI) including device removal and re-operations. A total of 578 patients were invited to participate, however 259 did not participate in the study resulting in a participation rate of 55%. The enrolled group included 319 patients and 498 joints. The mean age of joint replacement was 46.6 year and 86.1% of patients were female. The mean length of follow up was found to 8.6 years. The rate of first SSI was found to be 11.2% (4.2% removal rate, 7% reoperation rate) with most common causes attributed to the SSI being adhesion removal (2.6%), heterotopic bone formation/ankylosis (2.0%) and infection (1.6%). Survivorship rates were found to be 96% at 3 years, 94% at 5 years and 86% at 10 years which is noted to be consistent other orthopedic devices 5-year survival rates (95.9% for total hip replacement and 97.2% for knee arthroplasty).^12^
Wolford et al. performed a prospective cohort study evaluating patients operated between 11/89 through 7/93 with implanted Techmedica/TMJ Concepts devices who were followed for a minimum of 19 years post-operatively. Fifty-six patients were able to be contacted and were found to have adequate records for review. Median follow up was 21 years and mean age at the time of surgery was 38.6 years. Subjective evaluations were made utilizing a Likert scale assessing TMJ pain, jaw function, diet, and quality of life. Statistically significant improvements in MIO, TMJ pain, jaw function and diet were all found. The study also indicated that increased number of previous surgeries resulted in lessened improvement of TMJ pain and MIO. At the latest follow up, 48 patients reported improved quality of life, while 6 patients reported no change and 2 reported worsened quality of life. With a median of 21 years of follow up the study found that the Techmedica/TMJ Concepts device continued to function well and that no devices need to be removed secondary to material wear.^13^
Stock devices come in a variety of sizes but for a stock prosthesis to have stability and be successful the surgeon must be able to make the patient's anatomy fit the prosthesis; this can be challenging in patients with anatomic anomalies. An inadequate fit or adaptation of the prosthesis can result in micromotion and ultimately lead to failure of the prosthesis requiring its removal. One major advantage is that since these prosthetic devices are not patient specific there is no delay necessary for fabrication of the device; the same cannot be said about custom prostheses.
Every custom prosthesis is fabricated for a specific patient. Accurate fabrication requires a high-resolution, artifact-free CT scan from which an anatomic model can be created and the custom joint fabricated. This process varies from manufacturer to manufacturer and ranges from 3 to 8 weeks during which time a plan should be developed to continue management of the patient's symptoms. Custom prostheses are designed to achieve perfect adaptation to the osseous architecture of the patient. Furthermore, they can be designed to overcome significant anatomic anomalies in more complex cases. The surgeon is required to ensure the prosthesis is properly positioned without soft tissue lying between the prosthesis and bone. It is important that the surgeon remove all soft tissue and disk remnants to allow the fossa component to fully seat against the skull base during implantation and installation of the screws. An osteotomy to remove the residual condyle is frequently required; care should be taken to place this osteotomy in the same way it was planned during the virtual surgery. This ensures the remaining condylar neck will not interfere with the ramal component and that there will be bone present to secure the screw which bears the highest load; the screw nearest the condyle as detailed by Kashi et al.^14^ Having cutting guides and the model present at the time of surgery affords the surgeon the ability to make appropriate measurements to ensure the osteotomy is accurate and that the removed residual condyle is identical to what was planned.
The majority of TMJ DJD cases are amenable to a single stage TJR which is accomplished via an endaural or preauricular incision and a retromandibular incision (Fig. 3). However, some cases of DJD result in hyperplastic bone formation in and around the glenoid fossa (Fig. 4). This may be an indication to perform a 2-stage procedure with resection in the first stage and then fabrication of the custom device from a post resection CT scan and placement at a 2nd stage surgery. This 2-stage approach ensures the appropriate fit of the fossa component. However, cutting guides can help achieve an accurate fossa ostectomy and the appropriate fit of a custom device in a single stage.
Fig. 3 Standard endaural and retromandibular access1. First osteotomy to allow removal of the condyle2. With the condyle removed, the remaining condylar neck can be mobilized further superiorly and the residual condylar needing to be removed can be accessed.
Fig. 4 CT scan showing hyperplastic bone formation.
Due to the anatomical nature of the glenoid fossa and mandibular ramus stable screw fixation is necessary as press fits and/or cementing the components of the prosthesis are not viable options but are techniques which have been employed for fixating other orthopedic prosthetic devices. The work of Hsu et al. highlighted the importance the number and position of screws used during fixation of TMJ prostheses. Micromotion and strain within the implant and bone was decreased when at least 3 staggered screws are utilized for fixation; the position of the screws was found to be more meaningful than the number of screws used. Increasing the number of screws beyond three was found to enhance stability and reduce stress in the implant, though only slightly.^15^
Ultra-high-molecular weight polyethylene (UHMWPE) is frequently used as the load bearing surface on the stable component of hip and knee replacement devices and well as in the glenoid fossa component in a majority of the TMJR systems. The benefits of this material for this application are a low coefficient of friction, high impact strength and its ability to undergo cold flow or creep rather than particulation. However, polyethylene wear debris induced periprosthetic osteolysis remains a major cause for failure of hip arthroplasty in orthopedics.
Since the early 2000's gamma or electron radiation (50-100jGy) has been used to produce highly cross-linked ultrahigh molecular weight polyethylene (UHMWPE), which has superior wear resistance and reduces wear debris and osteolysis. However, during the cross-linking process, free radicals are formed, making this highly cross-linked polyethylene vulnerable to oxidative degradation. In order to reduce this process, antioxidant vitamin E has been incorporated into the polyethylene. A recent orthopedic study of vitamin E blended highly crosslinked polyethylene showed 95% lower wear rates compared to conventional polyethylene in a hip wear simulator. However, to our knowledge there are no TMJ devices currently utilizing these types of polyethylene.^16^
Titanium alloys possess better properties compared to pure Titanium and are the most common material used in orthopedic and dental replacement devices due to their biocompatibility and biointegration characteristics. The most widely used Titanium alloy is Ti6Al4V (ASTM F136). Titanium alloys are further classified into α, α+β and β types based on the phase type present in the alloy. The β phase is more ductile while the α-phase is stronger.^17^ However, titanium alloys exhibit low wear resistance and may not be optimal for articular bearing surfaces. Cobalt chrome (CoCr) provides better wear resistance and has therefore been used in the condylar head and performs well when articulating against UHMWPE. The cobalt chrome alloy as used in orthopedic and TMJR implants contains cobalt alloyed with 27–30% chromium, 5–7% molybdenum, with manganese and silicon <1%, iron <0.75%, nickel <0.5%, and with traces of carbon, nitrogen, tungsten, phosphorus, sulfur, and boron.^18^
As previously noted, 10 of the TMJR systems currently available worldwide utilize 3D printed metal components.^9^ 3D printing has potential advantages including less material waste compared to traditional milling and subtraction manufacture methods where a large block of wrought metal is required to fabricate a small device. In a review of 3D printing and its applications within surgical practice Tack et al. reported several advantages of this process including reduced surgical time, improved medical outcomes and decreased radiation exposures; however questions regarding the cost-effectiveness of the process are also raised.^19^ It is important for the surgeon to realize that while all these Titanium alloys are Ti6Al4V and classified as ASTM F136, they may have very different biomechanical properties depending on several variables. The different additive manufacturing processes for fusing powder into metal constructs in 3D printing include selective laser melting (laser sintering), electron beam melting and laser melting deposition. The method used may have significant impact on the final properties of the printed metal. Concerns regarding the biomechanical properties of 3D printed material exist (Table 1) and include increased porosity or decreased density of the material making it more likely to fracture or crack under functional load and cyclical stress, the presence of residual stress within the material secondary to temperature changes encountered during the fabrication process leading to deformation, warping or cracking as the metal cools, and the need for post-fabrication polishing which may result in exposure of deeper and larger pores which may provide areas in which contaminant organisms can take hold.
Metals used in alloplastic joint replacements are subject to both mechanical wear and corrosion; collectively known as tribocorrosion resulting in the release of metal particles into the surrounding tissues and even systemically. These particles may cause adverse local tissue reactions and also, systemic organ damage and type IV hypersensitivity. When these products trigger cells of the immune system, CD4^+^ T cells, inflammatory responses may result.^20^ Warshaw et al. found nickel, via patch testing, to the be the most common allergen and affects 17.5% of the population.^21^ The first correlation between a CoCr alloy containing orthopedic prosthesis and eczematous dermatitis was reported by Fossereau and Laugier.^22^ Currently, routine allergy testing is not indicated prior to placement of a metal implant however it could be helpful if the patient reports a previous allergic reaction to a metal implant or jewelry intolerance.^20^ When considering allergy testing, two options exist including a skin patch test (SPT) and lymphocyte transformation test (LTT). Luque et al.^23^ and Nyfeler and Pichler^24^ report that LTT may be of better diagnostic value compared to SPT. This is because macrophages and dendritic cells are the major antigen presenting cells in the peri-prosthesis environment where the immunologic insult caused by the degraded metal debris occurs as discussed by Hallab et al.^25^ and Everness et al.^26^ The utility of the SPT is debatable as it tests the reactivity of the Langerhans cell, the antigen presenting cell (APC) of the skin, not the macrophages or dendritic cells which are the APC of the peri-prosthesis environment and thought to mediate resulting hypersensitivity reactions. Recent studies have shown no correlation between SPT and alloplastic joint replacement outcomes.
No surgical procedure is free of complications; replacement of the temporomandibular joint is no different. The two most frequently encountered complications of great significance are infection and heterotopic ossification.
The rate of peri-prosthetic infection following TMJR reported by Mercuri is low, 1.5–2.7%; however the results of it can be devastating.^27^ Many steps should be taken to decrease the risk of infection including reducing the patient's bacterial burden,^28^ routine administration of pre-operative prophylactic antibiotics 1 h prior to surgery,^29^ and coating or soaking the TMJR components with antimicrobial drugs or bactericidal nano-crystals.^30^^,^^31^ Acute suppurative infections are easy to diagnose but diagnosis becomes much more challenging when the infection is low grade due to a biofilm. There is no single test that has 100% sensitivity in diagnosing periprosthetic joint infections (PJI). Therefore, differentiating between peri-prosthetic infection, material hypersensitivity, aseptic joint failure, adverse local tissue reaction and potentially unrelated local skin processes can be very challenging. Acute early infections (within 3–4 weeks of device placement) can be treated and often salvaged with thorough debridement and antibiotic protocols. According to the orthopedic literature, cases of PJI resulting from a biofilm should be treated with explanation of the prosthesis, placement of antimicrobial spacer and long-term IV antibiotics (6–8 weeks) prior to consideration of reimplantation of a prosthetic device. The most common organisms causing PJI include staphylococcus aureus, staphylococcus epidermidis and cutibacterium acnes (previously known as propioibacterium acnes).^32^^,^^33^ Cultures taken at the time of surgery will guide the IV antibiotic choice. C. Acnes is a gram-positive skin commensal that prefers anaerobic growth conditions, and it requires a prolonged incubation of 2 weeks in order to identify its presence in cultures.
Heterotopic ossification following TMJR is also a common complication and found to occur in approximately 1.24% of cases. While continuing research occurs regrading this topic the use of NSAIDs, radiation therapy and autogenous fat grafting are considered acceptable prophylactic and management options until better alternatives are discovered.^34^ Ongoing research regarding a naturally occurring glycoprotein, Alpha 2-Heremans-Schmid glycoprotein/fetuin-A (Ahsg fetuin-A) as an inhibitor of unwanted mineralization is underway and may result in the utilization of fetuin-A as a therapy to limit heterotopic ossification.35, 36, 37, 38
Obtaining surgical exposure of the mandibular ramus, condylar head and glenoid fossa as is necessary for the installation temporomandibular joint replacement devices places branches of the facial nerve at risk. Hohman et al. performed a chart review of patients seen between 2002 and 2012 at the Massachusetts Eye and Ear Infirmary Facial Nerve Center. Of the patients reviewed, 102 were found to have suffered iatrogenic facial nerve injuries; 27% of the injuries reviewed were the result of temporomandibular joint replacement surgeries. Fifty percent of these TMJ procedures however were revision surgeries. The frontal branch was most commonly involved.^39^ Care should be taken while raising and retracting the soft tissue off of the zygomatic arch as to not transect or stretch the frontal branch resulting in post-operative palsies.
The design of the fossa component significantly influences the chance of component dislocation posteriorly. The design of a small flange in the posterior fossa greatly reduces the chance of posterior dislocation (Fig. 5). This is of great importance when TJR is used to perform a mandibular advancement when posterior dislocation is much more likely.
Fig. 5 A) posterior dislocation. B) Posterior flange/lip design to minimize posterior dislocation.
Many TMJ DJD cases are unilateral which raises the concern regarding what impact the altered biomechanics of an alloplastic joint has on the natural joint on the opposite side. In a finite element analysis Bekcioglu^40^ et al. concluded that in the TMJ model with the unilateral total TMJ prosthesis, increased stress values were observed at the disc and condyle of the contralateral natural TMJ. However, this amount of increased stress could be well tolerated by the disc and condyle. The increase in stress found in this model may not create a clinical consequence for the patients. This is supported in a clinical study where Perez^41^ et al. concluded that patients requiring unilateral TMJR with a patient-fitted total joint prosthesis have a strong probability of improving their clinical condition and do not require bilateral reconstruction if the contralateral TMJ is healthy. Patients with previous or concomitant contralateral TMJ surgery have an approximately 30% chance of requiring a TMJR in the future. In a prospective cohort study by Teschke^42^ that included 39 patients who underwent unilateral TJR, only 2 (5.1%) required subsequent contralateral TJR after a mean follow-up of 4.3 years.
In summary alloplastic TMJ replacement remains the gold standard for reconstruction of end stage degenerative disease of the joint. This surgery should utilize established joint replacement systems which have been adequately tested and should be performed by surgeons with adequate experience of this technique.
Nicholas Wilken, Email: NWilken@umaryland.edu.
Gary Warburton, Email: GWarburton@umaryland.edu.