The goal of this clinical trial is to evaluate the long-term outcome of surgical intervention (arthroscopy or discectomy) due to the diagnoses temporomandibular joint disc displacement with or without displacement. The main questions it aims to answer are:

• Does the surgical outcome recorded at the earlier 6-month follow up persist at the long-term follow up approximately 10 years postoperatively?
• How does the radiologically determined degree of joint degeneration change with time in patients that have had joint surgery? Researchers will compare the six-month surgical outcome to the ten-year outcome to see if temporomandibular joint surgery results are stable over time.

Participants with an earlier performed joint surgery will:

• Have a clinical examination approximately ten years postoperatively.
• Have a temporomandibular joint x-ray scan performed (cone-beam computed tomography).

1. BACKGROUND Disc displacement (DD) of the temporomandibular joint (TMJ) is a common condition, reported to affect up to 20-30% of the population. Fortunately, only a minority of the affected experience pain and restricted mandibular movements, which are common reported signs of DD when symptomatic. Primary treatment for TMJ DD is non-surgical interventions such as orthotic splint, physiotherapy, pharmacological therapy, etc., all showing good outcome. If non-surgical management fails, surgical interventions might be considered. There are several reports on arthrocentesis, arthroscopy, and open joint surgery showing good results when treating TMJ DD. Most surgical reports have a follow-up period between 3-24 months and therefore little is known about the long-term outcome. Studies on arthroscopic treatment of the TMJ with the longest follow-up was found to be between 4.4 to 5 years. All these studies were retrospective. One study reporting on the outcome after arthroscopy was performed with a survey sent to 37 patients 10 year postoperative. The situation is almost the same regarding discectomy, with few clinical reports on long-term follow-up (10 years) of the surgical outcome. A 30-year follow-up survey was made on a Swedish patient material in the 1980´s, showing a good outcome.

   Since there is a shortage of clinical studies exploring long-term outcome of arthroscopic and open joint surgery, the aim of this study is to do a clinical investigation of a patient cohort earlier prospectively followed for a period of six months postoperative. The plan is to do follow-ups at approximately 10 and 15 years postoperatively.

2. HYPOTHESIS/RESEARCH QUESTIONS Our hypothesis is that the six-month postoperative outcome is a predictive marker for long-term outcome regarding surgical intervention due to TMJ DD. The outcome will be longitudinally evaluated by maximum mouth opening capacity, patient reported TMJ pain and TMJ disability. This was the original outcome parameters used for this patient cohort earlier investigated. The ethical permit for the earlier studies is (EPN 2014/764-31/2 and 2014/622-31/1) and the patients had their surgery between 2014 and 2017.

   The primary research question is whether the long-term outcome of surgery in patients with TMJ DD (DDwR and DDwoR) might be correlated to the six-month outcome.

   A secondary question is to investigate the long-term outcome of TMJ surgery due to DD.

   Tertiary questions:

   • Do any of the registered pre-operative variables serve as prognostic markers when correlated to the long-term outcome?
   • is the clinical long- or short-term outcome correlated to the radiological outcome?
   • Is the preoperative radiological examination predictive for the surgical outcome in long- or short-term?
   • Can naturally occurring deterioration of the TMJ surfaces be distinguished from earlier or present symptoms?

3. METHODS 3.1. Study design A prospective longitudinal cohort study.

   3.2. Data source/study population

   Please, see eligability below.

   3.3. Exposure/Intervention The exposure was arthroscopy or discectomy performed between the years 2014 and 2017. A follow up visit/control will be performed to assess the subjective and objective outcome of the exposure.

   3.4. Outcome

   Please, see "outcome measures" below,

   3.5. Sample size

   The trial aims at including all patients that had TMJ surgery (arthroscopy or discectomy) participating in two different studies between the years 2014-2017. Power analysis in section 4.

   3.6. Inclusion criteria

   Please, see "eligibility" below.

   3.7. Exclusion criteria

   Please, see "eligibility" below.

   3.8. Data collection

   All eligible patients will receive a letter with information about the project alongside an appointment for investigation of their TMJ status. At the appointment different variables will be collected according to a case record form, see attachment.

   The assessor/-s will be calibrated in accordance with the DC/TMD criteria. The surgeon originally responsible for the surgical treatment of the patients will not be involved in the assessment of the patients, minimizing any potential interviewer's bias.

   Anamnestic data: age, sex, operated joint (left, right), present health issues, present medication, later operation of TMJ (Y/N), use of orthotic splint (Y/N), TMJ exercise (Y/N), painkillers due to TMJ disorder (Y/N), continuous controls at specialist in gnathology (Y/N), continuous controls at physiotherapist (Y/N), patient-reported TMJ disability (VAS 0-10), patient-reported TMJ pain (VAS 0-10), patient-reported psycho-social impairment because of TMJ disorder (VAS 0-10), patient-reported global pain (VAS 0-10).

   Objective data: MIO (mm), lateral excursive movement right and left(mm), protrusion (mm), pain upon palpating masticatory muscles (Y/N), pain upon lateral joint palpation (Y/N).

   3.9. Radiological evaluation

   At the timepoint of examination, a radiological evaluation of the TMJ status will be made with a cone beam computed tomography (CBCT). The patients were evaluated preoperatively with a CBCT scan, which makes it possible to evaluate eventual time dependent deterioration of the joints. The CBCT will be taken according to a strict protocol (the departments usual CBCT examination protocol regarding TMJ will be used): FOV 15cm x 6cm, 90kV, 125mAs, voxel size 0,3cm3. Based on the dose area product (DAP) the resulting/effective radiation dose is 0.2 mSv/examination.

   The preoperative CBCTs and the CBCTs taken at the planned follow-ups will be qualitatively and quantitatively examined regarding hard- and soft-tissue changes in the TMJ area. If there is a sufficient postoperative radiological examination already exposed during the last year, this will be used instead of taking a new CBCT.

4. STATISTICAL ANALYSIS With a power of 90% (β) and α equal to 0.05, 44 patients need to be enrolled to detect a VAS difference of 1 unit (standard deviation: 2). The DDwoR cohort who had arthroscopy consists of 67 patients and should be sufficient for the purpose.

   Preoperative data and surgical outcome will be analysed with ordinal regression to evaluate possible outcome predictors. Repeated measurements as MIO, TMJ pain and TMJ disability will be analysed with mixed effects model. If linear relations between pre- and post-operative values exists, multiplicative linear regression might be used.

   All statistical analyses will be made with STATA/SE 16.1, Statacorp, Texas.

5. TIME PLAN

   The study includes one post-operative control for patients (n=91) who earlier had their TMJs operated. The control will take approximately 30 minutes. The control will be scheduled in 2025. The gathered information will be analysed 2026 and a manuscript produced and submitted during 2027.

6. ETHICS

   The are some ethical considerations regarding this study. The patients are already operated, and the planned clinical examination/control poses no risks for the individual patient. The examination is although an extra examination, not a part of any scheduled post-operative check-ups. The examination will take approximately 30 minutes and the patients will not have any obvious advantages by undergoing the examination. During the examination findings might reveal ongoing pathology in some patients. This will be handled accordingly. The examination is also on voluntary basis and all patients included in the original studies were 18 years and older and where able to verify informed consent independently. If a situation will arise where there are doubts regarding a patient's ability to make independent decisions, the patient will not be included in this study.

   If any of the patients eligible for this study still regularly has appointments at the Oral and Maxillofacial unit at Karolinska University Hospital of any kind, they should be ensured that they have the right (as any of the other patients) to not participate in this study, and that this decision will not affect the care given to them in any way.

   Regarding the voluntary radiology examination planned, the patient will be exposed to ionizing radiation with a dose equivalent of 0.2 mSv. Although, there is no radiation dose that is considered as totally harmless, the dose of the planned radiological examination is equivalent with approximately 2,5 month of natural radiation. The average radiation dose in Sweden is approximately 3 mSv/year, and this examination contributes to the patient's total radiation burden. The choice of CBCT and the applied examination protocol is a standard protocol optimized for examination TMJ according to ALARA principle (as low as reasonably achievable). Some patients in the cohort might have an indication for a CBCT because of their symptoms and clinical findings. However, within this project, all the included patients with given consent will be radiologically examined. The examination in itself will possibly not contribute to the well-being of the patient or pose any advantages. On the other hand, unexpected findings might appear that in a wide patient-oriented perspective might be beneficial to detect. The reason that we believe this project justifies performing this radiological examination is the fact that no earlier long-term follow-ups have been presented and that radiological findings, together with the clinical examination, will give a detailed insight into the patient-group´s outcome. This might hypothetically lead to revised follow-up protocols. By identifying potential risk factors, the radiological examinations might be more individualized according to the risk factors of the individual patient. The risk of missing important findings in the CBCT examinations exposed for the study will be low. All the CBCT scans will be examined by a specialist in radiology according to the normal review & referral procedure.

7. RELEVANCE

There are no long-term, prospective, follow-up studies on DD surgery made, as known of. This is why this study will fill a knowledge gap and will lead to new insights in the natural post-operative course of this patient group. This might change how patients are selected for surgery, and perhaps how postoperative follow-ups are scheduled with a more individualized follow up programme.

Inclusion Criteria:

• Patients participating in the studies with ethical approval numbers EPN 2014/764-31/2 and 2014/622-31/1.
• Initial diagnosis DDwR or DDwoR.

Exclusion Criteria:

• Patient unable to verify informed consent.

The cohort has already been operated (arthroscopy or discectomy) due to temporomandibular joint disc displacement during the years 2014-2017, then participating in a prospective cohort study mainly focusing on surgical outcome predictors (ethical approval: 2014/622-31/1 and 2014/764-31/2). These patients will now be offered a clinical and radiological examination approximately 10 years postoperative.

IPD used in the result published will be shared.

Study protocol and SAP is available through ClinicalTrials.