Patients and selection
This study was designed as a technical advance article. It was approved by the Local Ethics Committee at Leipzig University Hospital following the Declaration of Helsinki on medical protocols and ethics (Eth-30/17, 12/06/2017). Three patients of a tertiary care center who needed MITMS were included in the study from March to August 2020. The patients were diagnosed with an internal derangement (ID) of the TMJ, which was classified according to the Wilkes classification system . All patients underwent TMJ surgery using the guided endaural template. None of the patients needed additional open surgical procedures. Follow-up time was three months. Outcome variables were categorical. We noted fitting of the templates, which was judged by the surgeon in terms of position and rotational stability. Furthermore, surgical side effects and complications were recorded for each patient. Patients with effect modifiers or a potential confounder, which would require an additional open approach, were excluded from the study because the template would no longer fit.
The surgical procedure was conducted under sedation or general anesthesia. The template was positioned in the ear, and the skin was marked through the pilot channel for the desired incision after insertion of the trocar. The template was temporarily removed, and the subcutaneous tissue was spread with fine
-point scissors. After the guide had been repositioned, while the mandible was distracted downward and forward, the anterior wall of the external auditory canal was perforated with the sharp trocar up to the capsule (endaural access). Next, the endoscope was inserted through the other pilot channel after marking and incising the skin (Figure 6). The authors preferred a 0° arthroscopic cannula for the procedures.
The production of an endaural template was conducted according to the following four steps:
1. A 3D data set of the patient’s skull was created. This was done by computed tomography (CT), cone beam computed tomography (CBCT), or magnetic resonance imaging (MRI). In our cohort, CBCT data sets were used for all patients (Kodak 9500 3D; Carestream Health, Toulouse, France).
2. The surface imprint of the end- and preauricular region was assessed. A precise acquisition was necessary for the template’s position and rotational stability (Figure 1). The external acoustic meatus was used as a “key lock structure”, and an impression had to be taken using silicone material (Omnisil; Omnident Dental, Rodgau, Germany). The transfer of the imprint to a digital model was performed with CBCT from the plaster model (Figure 2) due to the availability of the device and ease of image fusion (Figure 3).
3. The data sets were fused in planning software (Facial Analysis Tool (FAT)). It was then possible to create the template with two pilot channels for the endoscope and the manipulation instruments from the superior-posterolateral and endaural approaches. The alignment was directed to the upper joint space (Figure 4).
4. Finally, the template was manufactured using a 3D printer (Formlab 2; Formlabs Inc., Somerville, USA) and a CE-certified biocompatible photopolymer resin (Dental SG Resin; Formlabs, Somerville, USA) (figure 5). Due to the small number of patients, no statistical analysis was performed.