The objective of this study was to determine whether the effectiveness of viscosupplementation with hyaluronic acid (HA) in patients with temporomandibular joint (TMJ) degenerative disorders depends on the presence of intra-articular effusion. In this study of case–control design, two groups of 25 patients were recruited: patients with a clinical diagnosis of painful chronic TMJ osteoarthritis and magnetic resonance imaging (MRI) signs of TMJ degeneration, with (effusion group) or without (no effusion group) MRI evidence of TMJ effusion. All patients underwent five weekly single-needle arthrocenteses plus medium molecular weight HA and 6 months of follow-up. Several clinical outcome parameters were assessed. For all variables, analysis of variance (ANOVA) for repeated measures was performed to assess the existence of significant within-group and between-group treatment effects. Over time, both groups showed significant improvements in all outcome parameters, which were maintained at the 6-month follow-up ( P < 0.05). Between-group comparisons showed that the treatment effects did not differ significantly for either the primary outcome variable (pain levels: F = 0.849, P = 0.548) or secondary outcome variables (chewing efficiency: F = 0.854, P = 0.544; functional limitation: F = 1.35, P = 0.226; mouth opening: F = 0.658, P = 0.707). The null hypothesis that there are no differences in treatment effectiveness between patients with and without effusion could not be rejected.
Degenerative disorders of the temporomandibular joint (TMJ) are a common cause of pain and treatment-seeking behaviour in the field of orofacial pain, and require careful diagnostic assessment and therapeutic planning. Among the various strategies that have been proposed over the years to manage pain and improve function, viscosupplementation with hyaluronic acid (HA) injections has been gaining widespread attention. The introduction of this approach within the practice of TMJ disorders has resulted from the progressive evolution and modification of the first works on TMJ arthrocentesis, as well as to a parallel increase in knowledge about the potential application of HA to manage osteoarthritis (OA) of the larger joints.
The potential role of impairment in joint lubrication as a risk factor for TMJ internal derangements and subsequent inflammatory–degenerative disorders has provided a rationale for TMJ viscosupplementation, and several clinical studies have shown that it may be an effective treatment modality. Nevertheless, a recent review pointed out that, despite seemingly encouraging findings at the study population level, much information is yet to be gathered on the most suitable protocol and indications at the individual level. Since then, several clinical trials have been conducted by our research group to collect data on the most effective number of injections, the ideal HA molecular weight, and, more in general, on the predictive factors for clinical symptom improvement.
An issue that is worthy of exploration is the effect of joint effusion on the effectiveness of viscosupplementation treatment, based on reports from studies on the larger joints (i.e. knee, hip) indicating that protocols of HA injections may not be of benefit in the presence of intra-articular effusion. This issue has not been addressed so far in the TMJ literature; hence exploratory trials on this subject may provide additional useful information to tailor the treatment of TMJ degenerative disorders.
Based on these premises, the aim of the present investigation was to answer the clinical research question: in patients with TMJ degenerative disorders, does the effectiveness of viscosupplementation with hyaluronic acid depend on the presence of intra-articular effusion? The null hypothesis was that there are no differences in treatment effectiveness between patients with and without effusion. To test the hypothesis, the investigators assessed treatment-related changes in certain clinical outcome variables in two groups of patients with painful TMJ degenerative disorders, those with and without magnetic resonance imaging (MRI) signs of TMJ effusion.
Materials and methods
To address the research purpose, the investigators designed a clinical trial by recruiting patients seeking treatment at the temporomandibular disorders clinic of the study institution. The study population was composed of patients aged between 40 and 60 years with a clinical diagnosis of OA (Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) version 1.0–axis I group IIIb) and with joint pain lasting for more than 6 months. All patients had to have MRI signs of TMJ degeneration. Based on recent findings showing the influence of psychosocial factors on treatment effectiveness, patients with RDC/TMD axis II high levels of pain-related impairment were excluded from the study.
The sample size required for the investigation was ascertained. The primary outcome variable was treatment effectiveness based on the assessment of pain levels on a 10-point visual analogue scale (VAS) with 0 being the absence of pain and 10 being the worst pain ever. Previous calculations in the literature based on investigations with similar study populations, assuming a mean VAS value of 6/10 ± 3/10 for the main outcome variable (i.e. pain levels), have shown that 40 subjects are needed to detect an approximate 40% between-groups difference in mean pain for chewing VAS values, with a statistical power of 5% for type I error (i.e. false-positive results) and 20% for type II error (i.e. false-negative results). Thus, to further increase the statistical power, 50 patients were recruited for the present investigation.
Using a case–control study design, patients were split into two groups, one with MRI signs of effusion and one without effusion ( Figs. 1 and 2 ). Joint effusion was identified in T2- or DP-weighted images as a large area of high signal intensity inside the joint space. More specifically, in accordance with the hypothesis that a mild to moderate amount of fluid can be detected in normal joints as well, the presence of effusion was defined as the presence of areas of high signal intensity greater than 2 mm in superior–inferior height or anterior–posterior length inside the articular space. To avoid interpretation bias related to the assessment of images by different radiologists, the MRI were interpreted by the expert clinicians of this investigation (DM and LGN), who recorded the presence/absence of effusion and disc position abnormalities by consensus.