4.1. Advanced TMJ Arthroscopy
TMJ arthroscopy is a treatment modality with a rich history (
Figure 2), and there are several areas within arthroscopy that have seen advancement recently. One of the most notable developments in advanced TMJ arthroscopy in the last 10-15 years has been the development of discopexy for repositioning and fixation of an anteriorly displaced TMJ disc[
72,
73]. First reported by Israel in 1989[
74], important variations soon followed[
75,
76,
77,
78,
79]. The technique documented in 1992 by McCain et al[
80] involving 11 temporomandibular joints (8 patients was subsequently modified by Yang et al in 2012[
81]. The technique described by McCain et al. involves release of the anterior portion of the disc from its attachment to the synovium. Once the disc is reduced, it is sutured posterolaterally. With this technique, the suture is passed through the posterior margin of the disc using a spinal needle, while the Meniscus Mender II uses a lasso-type suture retriever. McCain’s technique involved a small incision within the preauricular crease adjacent to the suture exit point to facilitate tying the suture within the extracapsular fatty tissue.
Yang and colleagues’ main modifications to this suture discopexy technique is in the suturing technique and instruments used[
81]. Most notably, a horizontal mattress pattern is used with two sutures and the sutures are tied such that the knots are beneath the cartilage of the external auditory canal (EAC). This method of suturing not only prevents dimpling of the skin, but also minimizes risk of entrapment of the frontal branch of the facial nerve and allows for a vector of traction on the disc that is directed along the anterior-posterior long axis of the disc, as opposed to the posterolateral traction of prior techniques. Yang’s technique also involves an exchangeable, custom-designed lasso-type and hook-type gripper.
A follow-up study by Yang et al that used MRI to evaluate the efficacy of their arthroscopic suture discopexy technique to reposition anteriorly displaced discs in 764 joints found a success rate of 98.56%. However, the post-operative MRI was obtained only between 1 to 7 days post-operatively[
82]. More recently, Jerez et al describe a modification to Yang’s suture discopexy technique that utilizes more commonly available suture equipment consisting of 2 patented lasso grippers, and 2 Meniscus Mender II curved and straight spinal needles. However, this technique requires 5 to 6 puncture sites compared to 3 puncture sites with Yang’s technique[
83].
Alternative techniques for discopexy have also arisen. Martinez-Gimeno have described a single portal discopexy technique, fixing the the dixc to the tragal cartilage without an anterior release[
84]. 1-year follow up seemed favorable on a limited number of subjects, most with anterior disc displacement with reduction. Alternatively, arthroscopic discopexy using resorbable pins in lieu of sutures has also recently received more long-term appraisal showing efficacy[
85]. Using the technique initially published in 2016[
86], and similar to Goizueta-Adame in 2014[
87], resorbable pin use appears to offer at least five years of benefit, in terms of range of motion and pain reduction. Although the sample is 33 subjects and only 23 made it to 5 year follow up, the findings are encouraging, and larger case numbers will further solidify this technique as viable for the Wilkes III patient. Lastly, a separate study reported arthroscopic use of a titanium anchor for disc repositioning and 6 months of follow up with patient benefit in a Wilkes II-III population[
88].
Multiple studies have assessed the effectiveness of disc repositioning and suturing in arthroscopic vs open techniques. A study by Abdelrehem et al. evaluated the outcomes of TMJ arthroscopic versus open disc repositioning for management of anterior disc displacement in 277 joints (177 patients)[
89]. This study found that while there was improvement in pain score, clicking, diet, and MIO in both the arthroscopic and open groups, the clinical improvements occurred earlier in the arthroscopic group (1 month) versus the open group (6 months.) Additionally, the success rate in the arthroscopic group was slightly higher than the open group, 98.1% versus 97.3%. Condylar remodeling occurred in 70.2% of patients in the arthroscopy group versus 30.1% of patients in the open group. Recent systematic reviews by Askar et al., and Santos et al, have found that arthroscopic and open disc repositioning reduced pain and improved MIO. However, both studies indicate that the number of studies and evidence is limited, with Askar et al noting that the heterogeneous nature of the study designs and data reporting was such that the studies could not be directly compared, and quantitative analysis could not be performed[
90,
91].
The Wilkes classification of TMJ internal derangement has been shown to predict the likelihood of a successful arthroscopic discopexy. McCain et al. found that Wilkes stage II and III had a successful primary outcome (absence of joint pain at 12 months postoperatively) of 86.7% compared to 25% for Wilkes stage IV and V[
92]. This contrasts an older study by Murakami et al. that reported a 92% and 93% success rate for Wilkes stage IV and V, respectively[
93]. However, this study utilized arthroscopic lysis and lavage for Wilkes stage IV and advanced arthroscopic procedures (synovectomy, discoplasty, and debridement) for Wilkes stage V as opposed to discopexy.
Some of the findings regarding Wilkes staging and success in arthroscopic discopexy was further assessed in a very recent study by Sah et al[
94]. This retrospective study assessed whether certain prognostic factors impacted the success of Yang’s arthroscopic suture discopexy technique in the treatment of TMJ closed lock. It was found that age, duration of illness, Wilkes classification, and prior orthodontic treatment all impacted surgical outcomes. Specifically, younger age, Wilkes stage III, shorter duration of illness, and current orthodontic treatment were all associated with positive surgical outcomes. On the contrary, older age, Wilkes stage IV, longer duration of illness, and previous orthodontic treatment were associated with poor surgical outcomes.
When considering the efficacy of TMJ disc repositioning in cases of anterior disc displacement, it is also important to consider the ability of disc repositioning to prevent complications that could arise secondary to lack of treatment of disc displacement. In the adolescent population, untreated unilateral TMJ anterior disc displacement may result in mandibular asymmetry, while bilateral anterior disc displacement may result in mandibular retrusion. Prior to recently, there were very few studies that evaluated condylar bone remodeling following arthroscopic TMJ surgery. Condylar bone remodeling following treatment of disc displacement would be beneficial in preventing complications regarding mandibular symmetry and thus occlusion in patients with disc displacement. Dong and colleagues recently performed a study to evaluate condylar remodeling following Yang’s arthroscopic surgery in patients with anterior disc displacement both with and without reduction[
95]. While the specifics of the arthroscopic surgery patients underwent was not discussed in detail, they found that 70.3% of the 229 patients had new condylar bone formation when evaluated with MRI 1 year following their arthroscopic surgery. The youngest age group (10-15 years-old) had the greatest percentage of patients with new condylar bone formation (94.33%) while the oldest age group (above 30 years-old) had the lowest percentage (25%). The percentage of new condylar bone formation was found to decrease as patient age increased[
95]. More than half of patients (53.53%) had bone formation on the posterior slope of the condyle. Meanwhile, the area of the condyle with the smallest amount of bone formation was the anterior slope of the condyle with only 10.37% of patients having new bone formation in this area. This study is important in showing that the condyle still has the propensity to form new bone, especially in younger patients, after repositioning of the TMJ disc. This may ultimately represent a protective factor in preventing against mandibular asymmetry and retrusion in cases of anterior disc displacement.
Outside of arthroscopic discopexy, arthroscopic management of a painful or problematic alloplastic TMJ prosthesis has been recently reported[
96]. This is an important advancement in technique as TMJ prostheses are gaining traction and becoming more widely used. The method described involves altered access points and the opportunity to examine the prosthesis and potentially remove areas of synovial impingement or fibrosis. It represents an opportunity for less-invasive diagnosis and treatment of symptomatic prostheses, but also is in its infancy as a technique, with a higher risk for damaging the prosthesis or neighboring structures due to different access and the instruments required.
4.2. Treatment of TMJ Subluxation and Dislocation
TMJ subluxation, or forward displacement of the mandibular condyle past the articular eminence which reduces spontaneously or can be self-reduced, can have multiple different etiologies[
97]. It is most commonly an acute event that may be spontaneous or secondary to trauma, a congenital condition, prior dental or otorhinolaryngological procedure, or an underlying psychiatric condition. Rarely, it may become a recurrent or habitual event. It is important to distinguish TMJ subluxation from dislocation, where the condyle is displaced out of the glenoid fossa and usually must be reduced by someone else[
97]. Over the years, less invasive procedures have been added to the arsenal of oral and maxillofacial surgeons for recurrent subluxation and dislocation[
98].
Botulinum toxin type A, which traditionally has been used to treat focal dystonia or other conditions involving involuntary muscle activity, has recently been shown to be an option for the treatment of recurrent TMJ dislocation. A study by Fu et al, explored the long-term efficacy of botulinum toxin type A for recurrent TMJ dislocation[
99]. They found that injections of 25-50 units of BTX-A into the lateral pterygoid muscle was successful in preventing any additional TMJ dislocations during a follow-up spanning 3 months to 2 years, without needing additional injections. However, the sample size of this study was small (N = 5) and CTs were obtained to determine the position of the lateral pterygoid muscles. This can be performed with EMG guidance[
100] or alternatively could be combined with another procedure with direct or arthroscopic visualization.
Other conservative treatments for habitual TMJ subluxation that has been a focus of research is autologous blood injection (ABI) and dextrose prolotherapy[
101]. Studies on ABI indicate that it is effective, although will occasionally require multiple injections[
102,
103,
104], but has good long-term success[
105]. It appears to be more effective when injected in the pericapsular tissues and not just the superior joint space alone[
106,
107], and the technique may be combined successfully with arthrocentesis or arthroscopy[
108,
109]. The European of Society of TMJ Surgeons (ESTMJS) have recently published a consensus on the treatment of condylar dislocation finding the best level of evidence for the use of autologous blood as a minimally invasive technique[
97]. Following autologous blood prolotherapy, there may be a benefit in limiting the MIO of the jaws. However, intermaxillary fixation alone is currently not recommended[
97]. It does appear that combination of a course of IMF and ABI is more effective at reducing recurrence than ABI alone.[
104]
Dextrose prolotherapy may have similar effectiveness in long-term management of symptoms associated with TMJ subluxation. A study by Refai, in which 10% dextrose prolotherapy was administered to 61 patients with symptomatic TMJ subluxation found significant reduction and pain, clicking, and frequency of locking in those with symptomatic TMJ subluxation[
110]. It is important to note that only 3 patients in this study had recurrent TMJ dislocation, but they all reported improvement after one treatment. A few systematic reviews evaluating dextrose prolotherapy versus placebo have been performed in recent years. These reviews have found that dextrose prolotherapy significantly reduced pain. However, there was differing findings regarding a significant reduction in MMO and functional scores[
111,
112]. Additionally, the systematic review by Nagori et al., found that there was no significant difference in the frequency of TMJ subluxation or dislocation[
111]. It is important to note that the literature regarding the efficacy of dextrose prolotherapy is not very robust currently, with each systematic review comprising only 3 and 10 randomized controlled trials, respectively[
111,
112]. Thus, it appears further studies using dextrose prolotherapy would be beneficial in determining its efficacy. A more recent study by Pandey et al, compared autologous blood and 25% dextrose prolotherapy for treatment of recurrent TMJ dislocation[
113]. This retrospective study found that autologous blood prolotherapy was more effective in reducing MMO and improving lateral and protrusive mandibular movements, while dextrose prolotherapy was more effective in reducing pain intensity.
4.3. Extended Total Temporomandibular Joint Reconstruction Prostheses (eTMJR)
The first total temporomandibular joint reconstruction procedure was first described in the 1970s. By the early 2000s, multiple companies had developed a total temporomandibular joint prosthesis that consisted of a titanium mandibular condyle and a polyethylene mandibular fossa implant[
114]. Although there have been advances in the workflow of the conventional total temporomandibular joint reconstruction (TJR) prosthesis over the last 20 years, the overall design of the prosthesis replacing the glenoid fossa and the mandibular condyle has largely remained the same. Generally, the mandibular component of the TJR prosthesis does not extend beyond the area of the angle of the mandible. However, in patients with extensive pathologies or deformities involving the TMJ, the conventional prosthesis design cannot be used. For these purposes, extended TJR (eTMJR) prostheses have been designed and used in situations in which defects in the mandible or base of skull must be reconstructed in addition to the TMJ complex[
115,
116].
A classification system for the eTMJR prosthesis has recently been described to aid in communication and clinical decision-making. There is a separate classification for both the fossa component and the condyle/mandible component. The fossa component classification ranges from F0 (the standard fossa component), up to F5 (fossa prosthesis covering a temporal defect that extends to the jugular foramen). Similarly, the condyle/mandible classification ranges from M0 (standard condyle-ramus component), up to M4 (total alloplastic mandible prosthesis that includes both condyles). This initial classification was based on a review of 19 patients/prostheses from the manufacturer TMJ Concepts (Ventura, California, USA)[
117]. This classification system was recently validated by the same authors by sending a survey to 64 high volume alloplastic TJR surgeons. It was found that the mandibular component of the classification system had good inter-rater agreement. This was not the case with the fossa classification[
118]. This study proposed a revision of the original classification for the fossa component to a simpler 3-tier classification system. This classification system ranged from F0 (standard fossa component) to FA (extended fossa component confined to zygomatic arch) to FT (extended fossa component that includes a temporal bone defect). Unfortunately, there were multiple limitations in this study including respondent size (N = 17) and survey protocol that made it difficult to view and score the fossa components. The modified fossa component classification was again validated by the same group of authors[
119]. This study found better inter-rater agreement with the 3-tier fossa component classification system. Again, the study was limited by a small number of respondents (N = 24).
Overall, data regarding the efficacy of the various eTMJR prostheses has been limited to primarily case reports and case series[
120]. A recent review by Khattak et al., looked to evaluate the effectiveness of eTMJRs based on functional and esthetic variables, and the postoperative complications associated with these protheses[
115]. The variables reported and analyzed included maximum incisal opening, occlusion, symmetry, pain, and diet. The authors found that overall there was an improvement across these variables with the use of eTMJR prostheses. Yet, this study also revealed the significant gaps in information regarding eTMJR prostheses such as prevalence of post-operative complications (nerve palsy, infection, etc.). Lastly, it was noted that only one of the studies analyzed utilized the eTMJR prosthesis classification system making it difficult to perform comparative analyses. This highlights the importance of utilizing a classification system and more comprehensive data reporting in future studies on eTMJR prostheses.