Introduction
The temporomandibular joint (TMJ) is frequently affected in children with juvenile idiopathic arthritis (JIA), with occurrence varying widely depending on factors such as JIA subtype, diagnostic approaches, and study population. Inflammation of the TMJ can result in joint deformity, dysfunction, and substantial morbidity in the pediatric arthritis population. Management of TMJ arthritis is difficult due to the uniqueness of the joint, confusion over terminology, and need for multidisciplinary care in diagnosis, interception, and management. Between 17–87% of JIA patients have TMJ arthritis, depending on the method used to determine TMJ arthritis, and all JIA subtypes can be affected. Most patients are asymptomatic, and by the time symptoms or clinical findings are present, associated damage has likely already occurred.
TMJ uniqueness
The TMJ is a unique joint for a number of reasons:
- the mechanical loading of the TMJ is higher than any other joint in the body;
- in contrast to other joints, the growth center lies directly under the surface of the condylar head, close to the inflamed synovium, with a suspected higher vulnerability of joint growth being affected by ongoing inflammation; and
- the mandibular condyle is the key growth center for most of the elongation but also angulation growth of the mandible.
For years it was thought the condylar damage from JIA-associated TMJ arthritis was permanent, however condylar regeneration has been described.
TMJ in JIA terminology
With TMJ arthritis research expanding, terminology has become increasingly more confusing. To improve research comparisons and communication among the multidisciplinary team of providers who care for those with TMJ arthritis, standardized definitions are necessary. The TMJaw group (formerly known as euroTMjoint) recently defined seven standardized operational terms to provide a framework for communication, which are:
- TMJ arthritis;
- TMJ involvement;
- TMJ arthritis management;
- dentofacial deformity;
- TMJ deformity;
- TMJ symptoms; and
- TMJ dysfunction.
These terms are to be used solely in the context of patients with JIA and can be used as a reference standard in research and clinical care to optimize both research and management.
Imaging methods in TMJ diagnosis
Numerous imaging modalities can be used in TMJ arthritis diagnosis. Methods such as cephalograms, orthopantomograms, and cone beam computed tomography can detect chronic bony changes and disease progression; however these cannot detect acute inflammation and are not useful in early disease. Ultrasound images are helpful in that they show acute inflammation, chronic bony changes, and disease progression; but are not sensitive for early disease and the quality of the image is dependent on the examiner. Magnetic resonance imaging (MRI) with contrast is currently considered the “gold standard” of imaging methods in TMJ diagnosis and management because it shows acute inflammation, chronic bony changes, and disease progression, with disadvantages limited to cost, exam length, and the potential need to sedate young children. However, even MRI imaging is dependent on the familiarity of the radiologist with normal appearance of the TMJ, and the ability to follow changes over time by using TMJ arthritis scoring methods. Diagnosing TMJ arthritis by MRI remains a difficult task, implicating TMJ prevalence, diagnosis, interception, and management.
Clinical examination
TMJ arthritis usually develops without many symptoms and is not apparent until damage is present and TMJ dysfunction has developed. Examination of the TMJ is essential to identify minimal abnormalities that might indicate new TMJ arthritis activity. The TMJaw group has developed five clinical examination recommendations, which are listed below.
- Assessment of relevant medical history.
- Assessment of patient reported orofacial symptoms.
- Palpation of the TMJ and masticatory muscles, assessment of pain on mandibular movement, and assessment of TMJ sounds.
- Assessment of TMJ function (maximal mouth opening, mouth opening deviation, protrusion, laterotrusion, and condylar translation).
- Assessment of facial morphology and symmetry.
These recommendations are for monitoring the TMJ, and are not specific for the diagnosis of TMJ arthritis.
Treatment options
Local therapy options include corticosteroid injections, and lavage with or without corticosteroids. The benefits of corticosteroid injections include pain relief, the settling of acute inflammation, and improved maximal interincisal mouth opening. However, corticosteroid injections often have short-lived results, do not stop the progression of chronic changes, and interference with growth and deformities of the mandible have been shown in studies with mice, rabbits, and humans, and are therefore not recommended in skeletally-immature patients. Experimental infliximab injections have been shown to be well tolerated with no adverse events, and resulted in resolution of arthritis in some TMJs, but allowed for the progression of acute and chronic changes in other patients. Systemic options include disease-modifying antirheumatic drugs and biologics. Aggressive treatment of TMJ arthritis is felt to be necessary and it should be treated as sacroillitis with immediate initiation of systemic biologic treatment.
Mechanical interventions include splinting, physiotherapy, and orthognathic surgery. Stabilization splinting for 8 weeks can result in a reduction in orofacial pain frequency and intensity, as well as significant improvement in TMJ function. Orthopedic splint treatment used for an average of 57 months can also reduce mandibular asymmetries like ramus height and total vertical mandibular height. Orthodontic and orthopedic appliances may provide symptom relief and can minimize or correct developing deformity, and joint reconstruction can correct dentofacial deformity and improve function where necessary.
Conclusion
JIA-associated TMJ arthritis has long been under-recognized, but the TMJaw group has initiated multiple multidisciplinary research efforts. Due to the uniqueness of the TMJ, a team effort is crucial in identifying patients, and a multidisciplinary approach, including medical treatment, orthopedic splints, physiotherapy, and behavioral therapy is recommended. Intra-articular TMJ injections generally result in symptom relief but may negatively influence TMJ growth and cause heterotopic bone formation, and should be used with caution in skeletally immature JIA patients. Orthopedic therapy options like stabilization splints can be a safe, reversible, and low-cost treatment that is familiar to most dental practitioners, while oral maxillofacial surgery is an option for patients with severe TMJ dysfunction. Awareness of JIA-associated TMJ arthritis needs to increase so that early diagnosis, monitoring, and treatment can potentially reduce the morbidity associated with this disease.