MRI

MRI was performed bilaterally in all patients. A Siemens Magnetom Vision MRI machine was used between 2003 and June 2004 and a Siemens Magnetom Sonata Vision between July 2004 and December 2007 (Siemens, Erlangen, Germany). Both were 1.5 T machines. With both, MR images were taken with a bilateral TMJ surface coil. Images were taken in the closed and open mouth positions. In the closed mouth position, patients closed their mouth with their teeth in contact; sagittal and coronal images of the TMJ were taken. In the open mouth position, patients opened their mouths as much as possible without experiencing unbearable pain and the clinician placed a stepped plastic bite-block between the upper and lower incisors; sagittal images of the TMJ were taken. Sagittal sections were orientated perpendicular to the long axis of the condyle, and coronal sections were taken parallel to the long axis. Proton density and T2-weighted images were acquired using a double-echo turbo spin-echo sequence. Each sequence yielded 8–10 sections.

Two experienced oral radiologists interpreted the MR images blinded, with no knowledge of the patients’ clinical diagnoses. Observer calibration and subsequent image assessment occurred as follows. The observers interpreted the first 10 complete MRI examinations together. Each observer then interpreted the remaining 35 examinations separately. Observer assessments of these 35 examinations were compared, and if they differed, findings were re-evaluated and discussed until a consensus was reached. Anterior DDwoR was diagnosed if: in the intercuspal position, the posterior band of the disc was located clearly anterior to the 12:00 position, at least in the 11:30 position; and on opening, the posterior band remained clearly anterior to the 12:00 position.

Self-report measures

Average pain intensity with the jaw at rest and during movement of the jaw was rated on a 0–100 visual analogue scale (VAS) with end definitions of 0 = no pain and 100 = intolerable pain. Pain intensity was recorded in a pain dairy once a day for 7 days. An average mean was calculated for the week at baseline and at the follow-ups.

The characteristic pain index (CPI) describes the mean value of the present, the worst, and the average TMD-related pain during the last 6 months rated on a 0–10 NRS.

The primary outcome measure of the study was pain relief during jaw movement of at least 30% on the VAS.

The short-form jaw functional limitation scale (SF-JFLS) includes eight items: chew tough food, chew chicken, eat soft food, open wide enough to drink from a cup, swallow, yawn, talk, and smile. The patients rate the limitation on a 0–10-point scale where 0 corresponds to no limitation and 10 to maximal limitation. The average score for the eight items determines the global jaw function limitation of the JFLS scale.

The number of patients consuming any analgesics (e.g. non-steroidal anti-inflammatory drugs, paracetamol or opioids) for TMD pain was registered during 1 week before baseline and during 1 week before each follow-up.

The graded chronic pain scale (GCPS) is a self-report instrument that uses seven questions concerning pain intensity, interference in daily activities, and disability days to yield a 0–IV score. Grade 0 is defined as no TMD pain, grade I as TMD pain of low intensity, and grade II as high intensity pain. Grades III and IV reflect moderate to significant pain-related psychosocial disability regardless of pain level. The GCPS was found to be a reliable and valid instrument.

Depression was assessed using the 20 SCL-90R items that contribute to distress.

Nonspecific physical symptoms are measured by 12 items in the SCL-90R. A mean score was determined based on the items in the instrument.

Global improvement with treatment was assessed on a 0–6-point scale (completely well, much better, somewhat better, unchanged, somewhat worse, and much worse).

Treatment beliefs (credibility) were assessed on a VAS (0–100) with the endpoints ‘not at all’ and ‘very effective’. Patients registered their belief in treatment effect after the intervention.

Clinical examination

The clinical examination comprised assessing the vertical range of motion of the mandible: unassisted opening without pain, maximum unassisted opening, and maximum assisted opening. These were measured in mm according to the RDC/TMD protocol.

Treatment

One surgeon (LES) with 5 years of surgical experience performed all treatment procedures. This surgeon did not evaluate treatment outcome. The duration of each treatment was similar.

Premedication and anesthesia regimes were the same in both groups. 1 h before the injections, patients received 1000 mg paracetamol per os. Directly preceding surgery, patients were anesthetized. The TMJ region was scrubbed with 70% alcohol and covered with a sterile drape; 2.5 ml Xylocain-adrenalin (ASTRA Zeneca) 20 mg/ml was then injected for auriculotemporalis block.

In group A, saline was flushed into a cup that was hidden from the patient before the drape was removed to simulate lavage. In the AL group, a cannula was placed in the posterior part of the upper joint compartment. A second, wider cannula was inserted in the same compartment. Drainage was tested by carefully injecting a small amount of saline. The joint was flushed with 50 ml saline. Excess saline was evacuated by aspiration after the procedure. After surgery, all patients in both groups were advised to take paracetamol 1000 mg × 3 daily as needed.

Rescue treatment was given when necessary. Patients who reported increased pain and a desire to receive additional treatment at follow-up were withdrawn from the study and given individually adapted treatment. Patient data up to the time of withdrawal was used in the statistical analyses.

Statistical analysis

An independent samples t test was used to compare mean values of mouth opening capacity without pain, mouth opening capacity with assistance, and jaw functional limitation between the two patient groups. The χ ² -test and Fisher’s exact test were used to compare the distribution of categorical variables between the two patient groups for the variables TMD pain reduction, GCPS, and analgesic consumption. For ordinal variables such as pain intensity at rest and during jaw movements, CPI, JFLS, depression, and somatization the Mann–Whitney U -test was used. The Wilcoxon signed ranks test was used for within-group comparisons of ordinal variables and the sign test for within-group comparisons of categorical variables. All inferential statistical tests were two-tailed with a significance level of P ≤ 5%. Statistical analyses were done with the Statistical Package for the Social Sciences (SPSS, ver. 13.0 for Windows; SPSS Inc., Chicago, IL, USA).

Intention-to-treat (ITT) was analyzed for the outcome measures pain relief of at least 30% and 50% on the VAS.

Logistic regression with the likelihood ratio test was used when analyzing if the baseline difference between the groups in JFLS influenced treatment outcome at both follow-ups.

Sample size calculation was determined in a pilot study that compared arthrocentesis with no treatment. A mean ± SD difference of 3.3 ± 3.6 in pain intensity between the groups was found. A group size of 13 patients in each group would yield slightly more than 80% power, with a two-tailed test at the 5% level. The number of patients recruited was higher than the sample size originally planned to compensate for probable drop-outs ( Fig. 1 ).