With a subjective improvement of the main complaint in 62% of cases at short-term follow-up and 53% at medium-term follow-up, our success rates are rather low if compared to previous studies.7,9,18,19,22 Ulmner and colleagues found in their short-term prospective study that 89% of patients with DJD, 80% of patients with ADDwoR and 64% of patients with chronic inflammatory arthritis benefited from an arthroscopy.19 Haeffs et al. on the other hand only had a successful surgical outcome in 62.3% of patients with TMJ arthralgia or internal derangement.7 Other reports describe successful outcomes in 67% of patients with arthralgia with or without OA, rheumatic disease or chronic closed lock, in 80% of patients with ADDwoR and 86,7% in patients with internal derangement.9,18,22 It is hard to have a direct comparison of all these results considering heterogeneity in disease classification, presentation, and follow-up. Although more recently, diagnostic criteria for temporomandibular disorders, known as the DC/TMD, are available they are not universally used in clinical practice.23,24 Secondly, the duration of the symptoms before the arthroscopic intervention might play an important role in the success of arthroscopic lysis and lavage.9,25 The average time between the first consult and the arthroscopy was 18.9 months. Israel et al. found a negative correlation between duration of the symptoms and success of an arthroscopy in patients with inflammatory or degenerative TMJ diseases.25 Thirdly, it is important to note that only 36 out of the 47 patients attended a MT appointment which leads to a possible incomplete representation of MT success rates.
Our main aim was to identify different variables observed during MRI and/or arthroscopy that are significantly correlated with success of the arthroscopic lysis and lavage. On MRI, an irregular, crumpled or rounded disc is mostly seen in later stages of internal derangement. In the early stages, the disc retains its normal shape.26 The fact that the absolute or probable absence of a crumpled disc and the absolute absence of a rounded disc deformation, i.e. absence of clear signs of advanced internal derangement, correlated with better outcomes suggests that early intervention in internal derangement might be beneficial for patients; although care should be taken not to overtreat patients. Some authors also believe that increased thickness of the attachment of the lateral pterygoid muscle can be seen as an indirect sign of progression in TMJ dysfunction and that flattening of the articular eminence can be interpreted as a secondary result of internal derangement.13,26,27 The absolute and probable absence of lateral pterygoid muscle deformations and absolute absence of articular eminence deformations correlated significantly with improvement in pain at the ST, again suggesting the positive effect of the lysis and lavage before signs of the advanced disease become visible on MRI. Other studies support these findings that arthroscopic interventions might be more beneficial in early stages of TMD.9,25,28 For example, in a recent network meta-analysis comparing different treatments for arthrogenous TMDs, Al-Moraissi et al. stated that there was “a clear superiority of the minimally invasive procedures (intra-articular injections, arthroscopy and arthrocentesis, each in combination with platelet-rich plasma, hyaluronic acid or corticosteroids) over non-invasive procedures both in short and intermediate-term periods for reducing pain and increasing MIO in patients with osteoarthritis and/or internal derangement” and that “minimally invasive procedures should be considered rather early, i.e. as soon as patients do not show clear benefit from an initial conservative treatment”.28 Generally, non-invasive treatment strategies should be tried for at least 3–6 months prior to more invasive treatment modalities.2
By combining the variables scored on MRI and during diagnostic arthroscopy, we attempted to make a combined prediction model. The absolute or probable absence of discal reduction evaluated on arthroscopic video was the only new significant variable in predicting improvement in main complaint in the short-term follow-up. Absence of discal reduction is mostly seen in patients suffering from ADDwoR. Patients with ADDwoR also tend to respond well on arthroscopy in other studies with success rates of up to 80%.19 Part of the aetiology of ADDwoR is the presence of adhesions in the upper joint compartment. These adhesions are removed during a lysis and lavage procedure which can explain the success of arthroscopy in ADDwoR.9,19
Our study had some limitations. The retrospective design increased the risk of bias and inaccurate data when reviewing patient records for the extraction of clinical parameters. Furthermore, because all arthroscopic videos were reviewed retrospectively, not being able to manipulate the scope during the assessment made the interpretation of the videos more difficult. In addition, while a stepwise regression model is a valuable tool for approaching considerable numbers of potential variables, it also has some drawbacks. If for example two variables are correlated strongly and both have a good relationship with the outcome, only one of those two variables is included in the model. This has the consequence that included variables can represent a group of variables that correlate strongly between themselves. Besides, a model selection is only successful for those patients where all variables are measured. This explains why results of the combined analysis differ from the separate analyses. Finally, a study population of 50 joints poses a statistical challenge and care should be taken to transfer these results to the general population.