Mandibular condylar fractures can be treated with open or closed reduction, which has been controversial for decades. With closed reduction, positional changes and remodeling of the condyle are questionable compared with open reduction. In the fractured condyle, the proximal fragment is presumed to move under the action of the lateral pterygoid muscle. The displaced bone fragment moves anteromedially in the direction that is pulled toward the pterygoid plate, the origin of the lateral pterygoid. In terms of direction, one group of researchers reported that medial translation was statistically significant in closed treatment after overlapping the right and left condyles in 21 patients [5]. In this study, the extent of movement and direction of the fractured mandibular condyle were evaluated. We found that the fractured bone segments recovered the position, on average, after non-surgical treatment. Specifically, the fractured condyles moved medially on the x-axis, anteriorly on the y-axis, and inferiorly on the z-axis. The x-, y-, and z-axes were in the order of anterior > inferior > medial directions at T 0. This was the same after > 6 months of bone remodeling. The difference between the timepoints was statistically significant, which indicates that the position of the condyle head recovered.

Changes in condylar position and traumatic force can influence surrounding anatomical structures. Adjacent structures such as the articular disc and retrodiscal tissue can be damaged or moved together with a displaced segment. Certain studies that analyzed the soft tissue around the injured temporomandibular joint in 18 patients using Magnetic Resonance Imaging (MRI) revealed 15 anteriorly and inferiorly displaced discs, 9 torn capsules, 16 torn retrodiscal tissue events, and 19 cases of joint effusion [6]. Another study reported that retrodiscal tissue tearing was observed in 74.4% of the MRI of 129 patients with intracapsular condylar fractures [7]. In 20 pediatric patients with sagittal condylar fractures, researchers found that 77.4% of articular discs were displaced anteriorly. Anteriorly sustained 19.3% of discs after closed reduction resulted in unfavorable remodeling [8]. In the present study, we found that the condyle head that moved in the anterior direction recovered less in the posterior direction than in the lateral or superior directions. We also confirmed that the extent of posterior recovery on the y-axis did not significantly correlate with age. We speculated that, as the proximal fragment was moved forward by the lateral pterygoid, the retrodiscal tissue or capsule was torn or damaged histologically. This impairment could make it difficult to reduce the proximal segment posteriorly, which needs to be considered in the treatment of condylar fractures, even in pediatric patients.

There have been several arguments for non-surgical treatment, especially in pediatric patients, with few complications and favorable remodeling after closed reduction. Ghasemzadeh and colleagues [9] reviewed the medical records of 43 patients and reported that a closed reduction in pediatric patients resulted in few complications. In terms of bone remodeling after closed treatment, some studies or cases have indicated favorable outcomes [10,11,12,13]. Lindahl et al. [14] studied the radiographs of 76 patients, who were divided into four age groups: 3–11, 12–15, 16–19, and > 20 years. The condyles were completely remodeled to normal articulation in 20 of 27 children, recovered to a normal extent in teenagers, and only minor remodeling was observed in adults. They divided restitutional and functional remodeling into pediatric and adult patients, respectively. Ellis and Throckmorton [15] explained why the pattern of remodeling differs according to patient age, as condylar cartilage hypertrophy is possible at a younger age. In this study, we considered that various factors may be involved in the positional recovery of the fractured mandibular condyle. The independent variables included were sex, age, concomitant fracture, fracture site, IMF duration, and location of the fractured segment (inside or outside the glenoid fossa). Univariate and multivariate analyses of the aforementioned factors revealed that patient age had a statistically significant influence on lateral and superior recovery. Additionally, condylar positional change exhibited a negative correlation with age only in terms of lateral and superior recovery, but not in posterior movement. While a positive recovery in position was observed in the < 19-year-old group, there was little change in the ≥ 19-year-old group. This age-related recovery leads us to several speculations on the reasons including the attachment status of the lateral pterygoid muscle, occlusion, mandibular morphology, and possibility of compensatory growth of condyle, which could be clarified in further research.

In several studies regarding restitutional remodeling of condyles in pediatric patients, the relationship between the fractured condyle and the glenoid fossa at T 0 has been speculated on. A group of researchers elucidated that stress stimulation inside the glenoid fossa is a prerequisite for condylar remodeling after reviewing 27 children with extracapsular fractures [16]. In this study, we performed multivariate analysis and found that the functional force inside the glenoid fossa did not have a positive influence on the extent of recovery of fractured condyles. Further research involving larger sample sizes is recommended to confirm these results.

Functional prognosis is an important aspect in the evaluation of treatment results because favorable functional recovery without anatomical reduction after non-surgical treatment of condylar fractures is uncertain. Marker et al. [17] analyzed the results of conservative treatment in 348 patients with mandibular condylar fractures and reported that 13% of them had physical complaints such as mouth opening limitation and deviation on opening. TMD and malocclusion occurred in 3% and 2% of patients, respectively. The authors concluded that closed reduction is a safe and predictable method. Lee et al. [18] reported that the incidence of clinical complications was not significantly different between open and closed reductions in 198 patients. On the other hand, there was a study that unfavorable functional prognosis showed depending on the types of condylar fracture [19]. In the present study, functional prognosis was observed clinically after non-surgical treatment in patients with unilateral condylar fractures, and treatment results were favorable in most patients. We divided patients into two groups according to age, which was the only influential factor in positional recovery. There was a low percentage of functional complications of TMD and malocclusion only in the ≥ 19-year-old group and one case of facial asymmetry was observed in the < 19-year-old group. The only facial asymmetry occurred in the 9-year-old patient with a severely deviated extracapsular fracture outside the glenoid fossa. The amount of segment deviation was measured to be 11.24, 4.74, and 3.93 mm in x-, y-, and z-axes respectively. The asymmetry was corrected with orthognathic surgery at the age of 25. When non-surgical treatment is applied, different complications should be considered and informed to the patients depending on their age.

This study has certain limitations. First, it was designed retrospectively. Second, this study included patients with unilateral condylar fractures. It cannot be applied equally to patients with bilateral condylar fractures. Third, more significant results could be obtained with larger sample sizes.