Introduction

Internal derangement (ID) of the temporomandibular joint (TMJ) characterized by the disruption of the normal anatomical relationships among the condyle, articular disc, and articular tubercle, is the most prevalent form of temporomandibular joint disorders [1, 2]. Patients with IDs often exhibit symptoms such as joint pain, clinking, and limited mouth opening. Although ID is not a life-threatening disease, it significantly affects life quality and necessitates multidisciplinary treatment approaches, particularly in the presence of complex complications [2, 3]. Anterior disc displacement with reduction (ADDWR) and without reduction (ADDWoR) are the two most common types of ID. ADDWR can be treated by occlusal splints, manual repositioning, or intra-articular injections, and promising results have been obtained [4,5,6]. However, there is still no consensus on the best choice for the treatment of ADDWoR, although surgical intervention seems to be more promising [7].

There are two surgical approaches for repositioning of TMJ disc, and they are arthroscopic disc repositioning surgery and open disc repositioning surgery. The success rate of the former is reported to be between 80% and 98.1% [8,9,10,11]. However, this technique presents certain difficulties in repositioning patients with prolonged disc displacement and requires a high level of skill from the surgeon, which limits its application [9, 12, 13]. Open disc repositioning surgery (ODRS) was initially proposed by Annandale in 1887 [14]. Since then, significant improvements in both techniques and materials have been achieved by the scholars. Presently, pertinent evidence is accumulated for the stability and reliability of ODRS [12, 13, 15,16,17,18].

The TMJ is a unique joint in the human body as the joints on both sides are integrated together and move as a whole. Consequently, the functional state of the joint at one side can affect the clinical condition of the joint at the contralateral side. In patients with bilateral ID, ODRS is typically performed on one side only, usually due to severe symptoms in the operative joint and mild or no symptoms in the contralateral joint. Thus, an interesting question arises: when the ODRS is used to correct ID in the TMJ at one side and the internal structure of the joint is greatly improved, what influence may it impose on the contralateral joint with ID? Therefore, the objective of this prospective study was to explore the influence of unilateral ODRS on the internal derangement of the contralateral joint in patients with either ADDWR or ADDWoR.

Methods

Participants

Patients with bilateral internal derangement (ID) of the TMJ who received unilateral TMJ ODRS at the Department of Oral & Maxillofacial Surgery at Cangzhou Central Hospital from October 2021 to October 2022 were recruited. Before the ODRS, the patients were informed the possible treatment choices and any medical comorbidities involved, and obtained the written informed consents.

The inclusion criteria: (1) adults older than 20 years, (2) the TMJ joint at the surgical side presented a stage III disease according to the Wilkes–Bronstein staging system [19], (3) the contralateral join presented as either ADDWR or ADDWoR as confirmed by magnetic resonance imaging (MRI) examination and clinical evaluation, and (4) no requirements for surgical intervention or other treatment measures for the contralateral joint due to mild or no clinical symptoms. The exclusion criteria: (1) patients with incomplete data due to uncontrolled follow-up; (2) poor disc position after ODRS on the surgical side; (3) additional treatments were applied to the contralateral joint during the follow-up period; and (4) other clinical conditions affecting mandibular development, such as temporomandibular joint tumours and rheumatoid arthritis.

Sample size calculation

As the literature on prior sample size calculations is very limited [7, 20], sample size calculation in this research refers to Petersson’s study [21] and sample size in both groups were controlled to be not less than 45 to ensure adequate statistical power.

Surgical technique

The surgery was performed under general anaesthesia with nasotracheal intubation, and all patients underwent open surgery by a same senior oral surgeon using an improved internal approach to the tragus. Briefly, the superficial tissues were separated sequentially to expose the joint capsule (Fig. 1A), and an incision was made to get into the capsule (Fig. 1B). High-frequency electric knives and bipolar haemostatic forceps were used to thoroughly release the upper head of the lateral pterygoid muscle and the attached tissue, allowing the joint disc to freely cover the head of the condyle (Fig. 1C). Then, a gelatine sponge was used to fill the anterior capsule space to stop bleeding. A Mitek anchor nail was inserted into the posterior part of condyle approximately 10 mm below the condyle pole (Fig. 1D), and two unabsorbable polyester sutures were used to pull the joint disc in the direction of 12 − 1 o’clock in the condyle (Fig. 1E). The tissues were sutured in layers, and a drainage strip was placed (Fig. 1F). All patients underwent the same postoperative care procedure and were advised to wear preoperative prefabricated occlusal splints for 3 months.

Fig. 1
figure 1

Open disc repositioning surgery of temporomandibular join (TMJ). A, separate the superficial tissue; B, separation of articular capsule to expose internal structure (black arrow); C, disc repositioning (blue arrow); D, anchor nail insertion (green arrow); E, suturing in layers and F, post-operation appearance

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Study design

All patients underwent clinical and MRI evaluation preoperatively (T0) and at 1 (T1), 6 (T6) and 12 (T12) months postoperatively. Clinical evaluation and MRI examination were performed to evaluate the changes of clinical symptoms and internal structures of the joints on both sides of TMJ. In addition, the change of the clinical types of ID on the contralateral joint with either ADDWR or ADDWoR were also recorded.

Clinical evaluation criteria

(1) Unilateral intermaxillary distance (UID): It is the maximum distance between the upper and lower first molars, and it was recorded using a Vernier calliper. (2) The visual analogue scale (VAS): This scale ranges from 0 to 100 points and represents pain intensity levels from none to excruciating. The UID and VAS of both sides were evaluated independently.

MRI measurements

MRI was performed using a 1.5-Tesla imager (Singa; General Electric, Milwaukee, WI, USA) equipped with a dedicated 3-inch diameter temporomandibular joint coil. Imaging data were acquired with a slice thickness of 2 mm and no spacing, focusing on the 5th to 6th layers for measurements. Images were analysed using Adobe Photoshop 2023 (Adobe Systems, San Jose, CA), and measurements were performed with MB Ruler software (Markus Bader, Berlin, Germany), achieving an accuracy of 0.01 mm.

To precisely outline the structure of the TMJ, including the condyle and joint disc, a three-circle method was used according to published methods (Fig. 2) [15, 22, 23]. The three circles were defined as O1, O2, and O3, corresponding to the condyle head, the junction of the condyle head and neck, and the narrowest segment of the condyle neck, respectively. A straight line passing through O1O2 was drawn and denoted y′, while the line passing through O2O3 was denoted y, which represents the long axis of the condyle. The intersection points y′ on the upper surface of the condyle was defined as D. A line passing through the mandibular notch perpendicular to y was defined as x, and the line perpendicular to y and tangent to O1 was defined as x′. Thus, the contour and position of the condyle were well recorded. In addition, the shape of the joint disc was also outlined, and three important points (A, B and C) were determined. Point A is the location on the anterior part of the joint disc with the maximum distance to the condyle, point B is the narrowest point in the middle zone of the joint disc, and point C is the location at the posterior end of the disc closest to the condyle.

Evaluation variables. (1) Disc length (DL) was defined as the distance from A to B and B to C; (2) condylar height (CH) was defined as the distance between line x and x′; and (3) disc-condyle angle (DCA) was defined as the angle formed by lines C-O1 and O1-D (∠CO1D). If point C is at front of point D, ∠CO1D is a positive value, otherwise it is negative.

MRI variables were independently measured by two skilled oral surgeons. Each variable was measured thrice, and the average value was recorded. Any discrepancies exceeding 2% between the two surgeons prompted review by a third specialist, and the final measurement results were determined by the third expert.

Fig. 2
figure 2

Magnetic resonance imaging (MRI) measurements ① and a schematic diagram ②

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Statistical analysis

Data from clinical and MRI evaluations are expressed as the mean ± standard deviation (SD), and statistical analysis was performed using SPSS 29.0 (IBM Corp., Armonk, NY, USA). Paired t tests were used to compare the differences in UID, VAS, DL, CH and DCA between different time points. P < 0.05 was considered to indicate statistical significance.

Results

General information

According to inclusion criteria, a total of 141 patients who underwent unilateral open disc repositioning surgery (ODRS) were initially recruited for this study. However, 45 patients were excluded due to incomplete clinical data (30 patients), poor postoperative disc position (3 patients) or additional treatment of the contralateral joint (12 patients) during follow-up. Ultimately, 96 patients were enrolled in the study, including 47 patients in ADDWR group and 49 patients in ADDWoR group.

The ADDWR group included 13 males, 34 females with a mean age of 27.42 ± 7.87 years (21–35 years) and a medical history of 109.94 ± 132.13 days (1-540 days), while the ADDWoR group included 7 males, 42 females with a mean age of 31.65 ± 11.38 years (22–62 years) and a medical history of 93.08 ± 129.56 days (5-720 days). According to the medical records of the included patients, 30 patients had received conservative treatments such as physiotherapy, intra-articular injections, non-steroidal anti-inflammatory drugs (NSAIDs) and occlusal splint at the surgical side prior to ODRS. Eighteen patients in the ADDWR group had a preoperative clinking sound in the contralateral TMJ, among which 11 patients showed a gradual improvement of their symptoms during the follow-up period.

Evaluation of TMJ on the surgical side

Unilateral TMJ ODRS significantly increased the unilateral intermaxillary distance (UID), disc length (DL), and condylar height (CH) of the operative TMJ (P < 0.05), but significantly decreased the visual analogue scale (VAS) (P < 0.05) (Fig. 3). UID increased from 19.37 ± 4.13 mm at T0 to 21.19 ± 3.65 mm, 22.37 ± 3.77 mm, and 24.00 ± 3.26 mm at T1, T6, and T12, respectively. A total of 4.63 ± 5.36 mm increase was obtained after 1-year follow-up (P < 0.05). In terms of pain assessment, the preoperative VAS was 32.60 ± 8.61, which decreased to 26.67 ± 7.21, 4.79 ± 5.23 and 3.64 ± 5.05 at T1, T6, and T12, respectively, with a total decrease of 28.96 ± 10.21 during one-year follow-up (P < 0.05).

The preoperative DL was 7.89 ± 1.40 mm, which increased to 11.25 ± 2.33 mm, 11.58 ± 2.43 mm, and 12.18 ± 2.15 mm at T1, T6, and T12, respectively. The gain of DL was 3.36 ± 2.41 mm at T1 and 4.29 ± 2.73 mm at T12 (P < 0.05), respectively. The CH measurements at T0, T1 and T6 were 24.10 ± 3.38 mm, 24.03 ± 3.18 mm, and 24.42 ± 2.92 mm, respectively. No significant difference was observed between these values (P > 0.05). However, it increased to 25.08 ± 2.93 mm at T12, which was significantly higher than that at T0 (P < 0.05). DCA was 21.86 ± 3.14 degrees at T0. it decreased to -2.35 ± 3.51 degrees one month after operation (T1)(P < 0.05), indicating an overcorrection of the disc after the surgery. At T12, DCA was − 0.83 ± 2.64 degrees, showing a 1.51 ± 4.09 degree anterior displacement of disc compared to that at T1 (P < 0.05).

Taken together, these results suggest the efficacy of unilateral open disc repositioning surgery (ODRS) to alleviates articular pain, increase mouth opening and restore normal structure of temporomandibular joint (TMJ).

Fig. 3
figure 3

Evaluation of the unilateral intermaxillary distance (UID)(a), visual analogue scale (VAS)(b), disc length (DL)(c), condylar height (CH)(d) and disc-condyle angle (DCA)(e) of the operative TMJ at T0, T1, T6 and T12. ns, P>0.05

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Evaluation of contralateral joint with ADDWR

The evaluation results were presented in Fig. 4. Clinical assessment revealed that unilateral TMJ ODRS significantly alleviated clinical symptoms of contralateral joint with ADDWR and both UID and VAS were significantly changed(P < 0.05). UID measurements at T0, T1, T6, and T12 were 21.40 ± 3.07 mm, 21.24 ± 2.89 mm, 22.36 ± 2.56 mm, and 23.03 ± 2.31 mm(P < 0.05), respectively, showing an overall increase of 1.63 ± 3.65 mm during 1-year follow-up. Whereas VAS decreased from 15.96 ± 10.77 at T0 to 10.21 ± 8.21, 7.23 ± 6.49, and 3.83 ± 5.73 at T1, T6, and T12 (P < 0.05), respectively, showing a significant decrease of 12.13 ± 13.01.

MRI examination also revealed some change of both DL and CH. At T0, T1, T6, and T12, the DL were 9.54 ± 1.42 mm, 9.69 ± 1.47 mm, 9.74 ± 1.25 mm, and 10.23 ± 1.37 mm respectively and CH were 27.18 ± 3.19 mm, 27.38 ± 2.86 mm, 27.33 ± 2.69 mm, and 28.28 ± 2.82 mm respectively. There was no significant change for both DL and CH between the first three time points (P > 0.05). However, DL and CH got a final respective increase of 0.68 ± 2.01 mm and 1.10 ± 3.38 mm at T12 when compared to T0 (P < 0.05). Meanwhile, the disc-condyle angle (DCA) only slightly increased during the follow-up period, but the change was not statistically significant (P > 0.05). These findings indicate that unilateral ODRS may also improve internal structure of the contralateral joint with ADDWR.

After 1-year follow-up, the change of clinical types of ID on the contralateral joint with ADDWR were shown in Table 1. Based on clinical and MRI evaluation, 2 discs restored to normal position, 23 discs kept unchanged, and 13 discs changed to either medial or lateral disc displacement, whereas only 9 discs progressed to ADDWoR. This means that ODRS may benefit restoration of normal articular structure and slow down disease progression in most of ADDWR patients, but it cannot stop disease development in all patients.

Fig. 4
figure 4

Evaluation of the unilateral intermaxillary distance (UID)(a), visual analogue scale (VAS) (b), disc length (DL)(c), condylar height (CH)(d) and disc-condyle angle (DCA)(e) of the contralateral joint with ADDWR at T0, T1, T6 and T12. ns, P>0.05

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Table 1 Change in the displacement type of the articular disc in the ADDWR group
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Evaluation of contralateral joint with ADDWoR

The evaluation results were presented in Fig. 5. The UID at T0, T1, T6, and T12 were 19.37 ± 2.21 mm, 19.16 ± 2.33 mm,18.87 ± 2.11 mm, and 18.50 ± 2.43 mm, respectively. The UID decreased slowly during the follow-up, but no significant difference was observed between the time points (P > 0.05). The VAS at T0, T1, T6, and T12 were 9.80 ± 9.24, 8.16 ± 7.55, 14.29 ± 10.21, and 18.37 ± 13.59, respectively. Although a slight decrease was observed at one month after operation (T1), the VAS at T6 and T12 were significantly higher than that at T0 (P < 0.05) and a final increase of 8.57 ± 17.68 were obtained. These findings suggest that ODRS cannot stop development of disease and eliminate clinical symptoms of the contralateral joints with ADDWoR.

MRI revealed significant changes of the DL, CH, and DCA (Fig. 5). At T0, T1, T6, and T12, the DL were 7.78 ± 2.04 mm, 7.74 ± 1.98 mm, 7.47 ± 1.67 mm and 7.23 ± 1.69 mm, respectively, and the CH were 24.36 ± 3.18 mm, 24.63 ± 3.37 mm, 24.24 ± 3.25 mm and 23.94 ± 3.03 mm, respectively. Both variables showed a steady decrease during the follow-up and got a final decrease of 0.55 ± 2.36 mm for DL and 0.41 ± 4.28 mm for CH, but no significant difference were observed (p > 0.05). Conversely, DCA demonstrated a significant increase from 20.23 ± 2.89 degree at T0 to 29.24 ± 6.08 degree at T12 (P < 0.05), with a final increase of 9.01 ± 5.77 degree. These results indicate that the ODRS cannot stop the progression of disease and improve the articular structure of the contralateral joint with ADDWoR. In addition, the ADDWoR type of internal derangement kept no changed in all patients.

Fig. 5
figure 5

Evaluation of the unilateral intermaxillary distance (UID)(a), visual analogue scale (VAS)(b), disc length (DL)(c), condylar height (CH)(d) and disc-condyle angle (DCA)(e) of the contralateral joint with ADDWoR at T0, T1, T6 and T12. ns, P>0.05

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Discussion

Bilateral internal derangement of TMJ with either anterior disc displacement with reduction (ADDWR), anterior disc displacement without reduction (ADDWoR) or other disorders, is a common clinical condition in young population, especially in young women [24, 25]. The disease needs systemic treatment procedures to correct the disorders. Due to different clinical status, unilateral open disc repositioning surgery (ODRS) is often performed in one joint and the contralateral joint left intact. As TMJ functions and moves bilaterally as a whole, the change of joint at one side may affect the joint at the other side. As a result, improvement of internal structure of TMJ by ODRS may bring some positive change to the contralateral joint. A recent research exploring the stability of the contralateral joint disk position after ODRS on one side did provide some useful information [26]. However, the exact influence of ODRS on clinical symptom and MRI-evidenced structure change of contralateral joint with ADDWR or ADDWoR remains unclear. Therefore, this study is aimed to answer the question.

ADDWR is the most common type of internal derangement of TMJ. Our results demonstrate that ODRS can increase mouth opening (unilateral intermaxillary distance, UID) and decrease pain sensation (visual analogue scale, VAS) of the contralateral joint with ADDWR. In addition, disc length (DL) and condylar height also gradually increased during 1-year follow-up and a final gain of 0.68 ± 2.01 mm and 1.10 ± 3.38 mm was achieved, respectively. These means ODRS can improve both clinical symptom and internal structure of contralateral joint. Regarding the reasons for the above changes, the following should be considered: (1) ODRS effectively corrected improper disc-condylar relationship on the surgical side and restored its joint function, which then decrease the function dependence and mastication loading on the contralateral joint. As a result, clinical symptom and structure of contralateral joint are improved. (2) correction of joint structure at surgical side and subsequent mandible movement improvement may correct musculature dysfunction, which then reduce the abnormal force from lateral pterygoid muscle on contralateral disc and improve its shape and position; (3) improvement of mandible movement, musculature contraction and mastication loading, will eventually decrease the stress exerted by the condyle on the contralateral disc and facilitate its shape and function restoration. Despite the above reasons, patients’ psychology changes may also play an important role. Alleviation of clinical symptoms may improve the patient psychological state and thus decrease negative nervous stimulus on musculature and TMJ system, leading to a change from dysfunction to normal. Relief of psychological stress can also significantly enhance the quality of patient’s life.

What should be pointed out is that 19.15% of ADDWR (9 out of 47 patients) had progressed into ADDWoR and only 4.26% (2 out of 47 patients) exhibited a return to normal disc-condyle position after 1-year follow-up in our study. The result is consistent with the study by Chuan Lu et al [26], in which 23.5% of ADDWR progressed to ADDWoR and 3.9% restored to normal. This may be due to the fact that similar surgical procedure was applied. The above results suggest that recovery of normal disc position by ODRS cannot completely stop the development of internal derangement of TMJ at the other side. It is necessary to evaluate the change of internal derangement of contralateral joint during follow-up and take useful measurements to control disease development.

ADDWoR is regarded as an advanced stage of ADDWR, but it should not be construed as a terminal pathology. The strategy for managing ADDWoR should pivot towards timely surgical intervention [22, 27]. However, 49 joints with ADDWoR in this study did not resort to surgical intervention or undergo bilateral joint surgery simultaneously, mainly due to being asymptom or bearing mild symptoms of the joints. In these ADDWoR patients, ODRS brought no change on mouth opening (UID), but pain sensation (VAS) and MRI variables including disc length (DL), condylar height (CH) and disc-condyle angle (DCA) were all significantly changed. DL showed a 0.31 ± 2.49 mm and 0.55 ± 2.36 mm decrease at 6 and 12 month after surgery, respectively. Although DL was shortened and the state of disc was deteriorated, the change was less than natural shrinkage of the disc without surgical intervention [28], which is 0.63 ± 1.42 mm. In addition, CH also demonstrated a decrease of 0.12 ± 3.50 mm and 0.41 ± 4.28 mm at 6- and 12-month follow-up respectively, indicating gradual deterioration of condyle surface. The change is also less than those in previous reports. Hu reported a 0.29 mm decrease of CH over an average 7.96-month follow-up in 125 cases of naturally developed ADDWoR. Cai [23] also reported that during an average 10.9-month follow-up, 44 joints showed an average of 0.56 mm decrease in CH. Above results suggest that although ODRS cannot stop progress of ADDWoR in contralateral joint, it does slow down disease development and alleviate the deterioration of the joint. Another important variable, DCA (∠CO1D), also showed an increase of 9.01 ± 5.77 after 12-month follow-up, indicating continuous anterior displacement of the disc.

As continuous development of ADDWoR, it is advisable to take some conservative treatments after unilateral open disc repositioning surgery. Even if these patients exhibit no symptoms, close and frequent follow-ups are necessary. The interval between check-ups should be shortened to 3 months for these patients. Additionally, if surgical intervention is an indication, immediate surgical treatment should be taken to maximize the therapeutic effects of the surgery.

The primary objective of TMJ ODRS is to ensure sufficient mouth opening, relieve articular pain, establish functional stability, and maintain the long-term position of the disc [16, 29,30,31]. In our study, the unilateral intermaxillary distance (UID) showed an increase of 4.63 ± 5.36 mm, and the visual analogue scale (VAS) decreased by 28.96 ± 10.21 at one year postoperatively compared to preoperative values. These findings are consistent with the results of Liu [18] and Lee [29], indicating that unilateral TMJ ODRS significant improved joint function and patients’ quality of life. Disc length and condylar height are key indicators of the severity of ADDWoR and are also important parameters in the assessment of surgical outcomes [27]. One month postoperatively, the disc length increased by 2.32 ± 2.20 mm, suggesting that the disc shortening observed on preoperative MRI scans may not reflect actual disc state, but a result of disc folding or internal and external rotation from a two-dimensional perspective [15]. Recent studies [22] have shown higher recurrence rates in patients younger than 15 years who underwent ODRS. Therefore, this study focused on patients over the age of 20 to avoid the risk of recurrence associated with rapid condylar growth. One year after surgery, the condyle height increased by 1.51 ± 3.85 mm, indicating adaptive condyle remodelling and new bone deposition due to disc reduction. The research also shows that even when patients are past the growth phase of the mandible, the condyle cartilage behind the repositioned disc still has the potential to regenerate.

Drawing upon the surgical techniques detailed by Zhang [32] and He [33], over corrective repositioning of the disc was undertaken in all cases. However, one year postoperatively, some patients exhibited mild anterior displacement of the disc once more. This suggests a significant anterior traction force on the disc, highlighting the need for comprehensive loosening of its anterior attachment structures.

Although valuable data have been obtained on the changes of contralateral joint with ADDWR and ADDWoR after ODRS on one side, this study still have some limitations. The first is the patients excluded from the study. A total of 45 patients were excluded due to various reasons and this may lose some valuable information helpful to understand all of the outcomes. It is particularly important for the 12 patients excluded due to additional treatment of the contralateral joint during follow-up. The additional treatment is always associated with deteriorated disease, and it may decrease our expect on the beneficial effect of ODRS on the contralateral joint. Other limits include the small sample size, lack of occlusion evaluation and a short follow-up period. Future studies with a larger sample, a longer follow-up period, evaluation of occlusion change, and a complete consideration of valuable information form excluded patients, are needed to make these questions clearer.

Conclusion

Unilateral open disc repositioning surgery is a promising method to correct the internal derangement and maintain the structure stability of the operated joint, and it may also improve clinical condition of disc displacement with reduction and slow down the progress of disc displacement without reduction at the contralateral joint. In patients with bilateral internal derangement, proper postoperative evaluation of TMJ on both sides during follow-up are necessary to monitor and take useful treatment measures to control the disease progression.