Mandibular condylar remodeling characteristics after simultaneous condylectomy and orthognathic surgery

Introduction

The objectives of this study were to evaluate postsurgical condylar remodeling using a radiographical interpretation, quantify condylar volumetric asymmetry, and assess soft tissue symmetry after simultaneous unilateral high condylectomy and bimaxillary osteotomies.

Methods

Sixteen patients diagnosed with unilateral condylar hyperplasia underwent unilateral high condylectomy and orthognathic surgery to correct skeletal and facial asymmetries. Cone-beam computed tomography scans were acquired before and 1-year after surgery. A radiographic consensus was evaluated for signs of reparative or degenerative changes. The condyles were mirrored and registered for assessment of volumetric and morphologic asymmetry. Soft tissue symmetry was evaluated by measurement of the distance of soft tissue pogonion from the skeletal midsagittal plane.

Results

Patients who undergo unilateral high condylectomy and orthognathic surgery present radiographic signs suggestive of degenerative changes, including sclerosis, osteophytes, flattening, and erosion in both the surgical and nonsurgical condyles ( P ≤0.01). There was an average volumetric improvement of 531.9 ± 662.3 mm 3 1-year postsurgery ( P = 0.006). Soft tissue symmetry improved in all patients, with an average improvement of 65.8% (4.0 mm ± 2.6 mm, P ≤ 0.01). There was no correlation between the change in condylar volumetric asymmetry and the stability of the soft tissue correction.

Conclusions

High condylectomy for the correction of a skeletal asymmetry in patients with condylar hyperplasia successfully reduces the volumetric asymmetry between the condyles. Postsurgical dysmorphic remodeling and degenerative changes were noted in both the surgical and nonsurgical condyles. Despite remarkable changes and remaining joint asymmetry, the soft tissue correction is stable 1-year postsurgery.

Highlights

  • High condylectomy with orthognathic surgery reduced volumetric asymmetry between condyles.

  • Significant radiographic signs of bone remodeling and degenerative changes were found.

  • Changes included sclerosis, bone cysts, osteophytes, flattening, erosion, and resorption.

  • If condylectomy is needed, follow protocols to minimize inflammation.

The mandibular condyles are unique in many ways, but possibly the most remarkable is the ability of the joints to remodel throughout life. The unique fibrocartilage layer covering the articular surface allows for adaptive remodeling in response to external stimuli during or after growth. , The health of the temporomandibular joint (TMJ) depends on the capacity of its components to adapt to normal and abnormal functions. Pathologies that result in alterations to the size, form, and spatial and functional relationships of the joint components can lead to progressive changes and compensations that may affect jaw and tooth positions.

Condylar hyperplasia (CH) is one of these pathologies. The condition was first described by Robert Adams in 1836. CH is a rare, idiopathic disorder characterized by the increased volume of the mandibular condyle, unilaterally or bilaterally. , , This pathologic process can lead to the development of debilitating functional and esthetic concerns, including asymmetric facial deformity, malocclusion, mandibular deviation, and TMJ and masticatory musculoskeletal dysfunction. , , ,

CH is most common during adolescence and is found equally in male and female patients. , The etiology and pathogenesis of CH remain uncertain. It is likely a complex and multifactorial process. Suggested theories include hypervascularity, trauma followed by excessive proliferation in repair, inflammation, infection, arthrosis, osteomyelitis, osteochondromas, , a possible genetic role, and changes in functional loading. ,

The diagnosis of CH is usually made by clinical and radiographic examinations. With the advent of 3-dimensional (3D) imaging, such as cone-beam computed tomography (CBCT) with voxel-based superimposition methods, clinicians are provided a better understanding of bilateral structures and greater accuracy than other 2D techniques.

Treatment of mandibular CH is primarily surgical and depends on the status of condylar growth, the degree of severity, and the age of the patient. , , , , High condylectomy is the most effective correction procedure and is indicated to arrest progression by removal of the growth site. , In this procedure, the bone is removed from the head of the condyle, with a recommended removal of 5-7 mm. , , After shaving of the condyle, the articular disc is repositioned over the condylar stump. Removal of the inflammatory and proliferative tissue from the condylar head allows for proper function, better esthetics, and prevention of postoperative relapse. , , Concomitant TMJ and orthognathic surgery is commonly indicated in patients who require correction of dentofacial deformities and have an existing pathology, such as CH.

Currently, the question remains as to the impact of high condylectomy on the health of the TMJ and overall correction stability. The present study uses CBCT scans to describe the morphologic changes that occur in the condylar stump after simultaneous unilateral high condylectomy and bimaxillary osteotomies in patients with unilateral CH. Specifically, this study investigated indicators of reparative and/or degenerative response using a consensus radiological interpretation, evaluated the changes in condylar morphology, quantified the changes in condylar volumetric asymmetry, and assessed the stability of the soft tissue correction. Our study is novel in that no previous research has been completed on the stability of this therapy in 3D.

Material and methods

This investigation is the secondary data analysis of deidentified CBCT scans for 16 patients diagnosed with unilateral CH who underwent simultaneous unilateral high condylectomy and bimaxillary orthognathic surgery by the same surgeon at the University of North Carolina (2010-2015). All patients signed an informed consent form for hospital admission, surgical procedures, and the release of deidentified information for research purposes. The study was granted Institutional Review Board exemption (HUM no. 00135357) from the University of Michigan. Patients received presurgical bone scans to assess the activity of the hyperplastic tissue. Every effort was made to acquire CBCT scans at the following time points: preoperative (T1), 4-6 weeks postoperative (T2), 1-year postoperative (T3), and 3-years postoperative (T4). Inclusion criteria were: a diagnosis of active unilateral CH, simultaneous unilateral high condylectomy and orthognathic surgery, postsurgical orthodontics, and presurgical and 1-year postsurgical imaging. Exclusion criteria included missing pre- or postsurgical imaging. For consistent imaging intervals, the final sample consisted of 16 patients, all of whom had T1 and T3 scans. The sample included 11 women and 5 men, ranging in age from 15-35 years, with 12 right and 4 left condyles affected. The average postsurgical follow-up was at 1 year 1 month.

CBCT scans were obtained with a NewTom 3G CBCT scanner (QR SL; AFP, Elmsford, NY). The scanning protocol involved 110 kVp, 15 mA, 17 × 23 cm extended field of view, during a 36-second scan, with 0.25 mm isotropic voxel size with the patient positioned in natural head position. The Digital Imaging and Communications in Medicine files were converted to Guy’s Image Processing Lab files for de-identification and use in open-source software ITK-SNAP ( www.itksnap.org ). Images were resampled to 0.42 mm isotropic voxel size (Downsize image, 3D Slicer Software, www.slicer.org ).

A multiplanar evaluation of the CBCT scans was completed by 2 expert observers from the Department of Radiology at the University of Michigan School of Dentistry (E.B. and F.N.S.). Multiplanar cross-sectional images were studied to assess presurgical and postsurgical condylar morphology in all 3 planes of space. The condyles were scored on the following categories, as defined and adapted from the Diagnostic Criteria for Temporomandibular Disorders (DC/TMD) : subcortical sclerosis, subcortical cyst, osteophyte, articular surface flattening, surface erosion, resorption, and proliferation. The presence/absence and severity of each category in a given condyle were scored on the basis of a 4-point scale ( Fig 1 ). Each CBCT scan was evaluated separately by the radiologists, followed by a consensus radiographic evaluation. The consensus data was used for interpretation.

Fig 1
Radiographic interpretation grading scale. Radiologists reviewed multiplanar slices to evaluate for the presence of sclerosis, bone cysts, osteophytes, flattening, erosion, resorption, and proliferation on the basis of the 4-point scale detailed above.

Subsequent 3D image analysis was performed by a single, blinded examiner (A.L.G.) using a combination of the open-source software programs 3DSlicer and ITK-SNAP, as shown in Figure 2 . Three-dimensional segmentation of the T1 Guy’s Image Processing Lab files was constructed. A labeled map of the bone is created by adjusting the range file or density of tissue that is selected (Intensity Segmenter, 3D Slicer Software). The segmentations were cleaned and cropped to improve visualization and decrease the file size. Segmentations were converted into models composed of triangular meshes. Directional change is strongly influenced by head orientation; therefore, all models must be oriented in the same way. Ruellas et al validated the reproducibility of head orientation on the basis of a standardized coordinate system.

Fig 2
Image analysis methodology. ( A ) Deidentified CBCTs were received from the University of North Carolina. A radiographic evaluation was completed by 2 expert radiologists. ( B ) 3D image analysis was carried out using ITK-Snap and 3DSlicer to mirror and register the right and left condyles for evaluation of morphologic changes and calculation of volumetric asymmetry. ( C ) The Q3DC tool in 3DSlicer allowed measurement of the soft tissue chin position relative to the skeletal midsagittal plane.

To further ensure consistent orientation, the T3 and T4 scans were manually approximated relative to the T1 scans on the basis of the stable structures of the maxilla and cranial base. Subsequently, cranial base segmentations were isolated and used in conjunction with the CMF Registration tool in 3DSlicer to carry out a fully automated voxel-based registration. This process registers the T3 and T4 scans and segmentations relative to T1 on the basis of correspondence of over 300,000 voxels to achieve consistent registration. This registration method has been previously validated and avoids observer-dependent techniques on the basis of overlap of anatomic landmarks.

To evaluate preoperative and postoperative changes in condylar volume and morphology, 3D surface models of the condyles were generated. Detailed manual segmentations were completed with the Image Edges tool. This program allows the operator to view slice-by-slice the effectiveness of the segmentation procedure and perform manual editing in all planes of space. The condyles were mirrored in the sagittal plane to assess right-to-left condylar asymmetry. The CMF Registration tool applies this transformed matrix to the scan and segmentation. A manual approximation of the right and left condylar surface models were performed for all patients and all time points. In ITK-SNAP, a model was isolated, indicating the specific region for superimposition, referred to as the mask. The mask included the proximal portion of the ramus superior to any surgical cuts or bone plates and inferior to the sigmoid notch. Changes occurring postsurgically in the condyle and coronoid process precluded their inclusion in the mask. Three-dimensional regional voxel-based registration was executed for each time point. This registration was run with 7 degrees of freedom on the basis of the correspondence of thousands of voxels to achieve a reliable and reproducible 3D regional condylar superimposition.

To analyze changes in condylar volumetric asymmetry, the superimposed models were simultaneously cropped to include the portion of the condylar neck at a level tangent to the most inferior point of the sigmoid notch (Easy Clip tool, 3DSlicer). The 3DSlicer extension Mesh to Label Map was used to compute a label map from a 3D model. The difference in volume between the surgical and nonsurgical condyles was measured and recorded in cubic millimeters. Overlays of the mirrored and registered condyles were used to assess changes in condylar morphology.

Anatomic landmarks of interest were prelabeled in ITK-SNAP on the registered T1, T3, and T4 scans. This previously validated method allows for increased consistency and reproducibility of landmark placement. Sagittal, axial, and coronal slices of the gray scale images and the 3D segmentation were used to determine accurate landmark placement. Sella, Basion, and soft tissue pogonion were prelabeled on the oriented scans. Surface models were generated for the full-face segmentations and prelabeled landmarks for each time point. In 3DSlicer 3D landmarks were plotted on the prelabeled surface models. The Q3DC tool was used to calculate the medial-lateral displacement of soft tissue pogonion from the skeletal midsagittal plane, as defined by Sella, Crista Galli, and Basion. Linear distances were reported in millimeters.

Statistical analysis

SPSS statistics software (version 16.0; SPSS Inc, Chicago, Ill) was used for all statistical computations. Both paired-samples t tests and Wilcoxon signed rank tests were used to evaluate the T1 to T3 surgical and T1 to T3 nonsurgical condyles. The paired-samples t tests assume a normal distribution and continuous variables, whereas this analysis used a finite 4-point scoring system ( Fig 1 ). Therefore, Wilcoxon signed rank tests were also used to support the determination of significance. Parametric and nonparametric tests found the same results. An independent t test was calculated to assess any relationship between surgical and nonsurgical condyles presurgically and between surgical and nonsurgical condyles postsurgically. The only statistically significant difference between the surgical and nonsurgical condyles at the same time point was in the evaluation of flattening at T3 ( P = 0.024, power = 65%). A repeated measures Student t test was calculated to compare the change in condylar volumetric asymmetry. For all volumetric analyses, given a sample size of 16 patients and α of 0.05 for a 2-tailed t test, the effect size was determined to be 0.803 and power of 85%. A repeated measures Student t test was used to evaluate the change in the asymmetry of soft tissue pogonion in relation to the skeletal midsagittal plane from T1 to T3. For all soft tissue analyses, given a sample size of 16 patients and α of 0.05 for a 2-tailed t test, the effect size was determined to be 1.498 and power of 99%. The Pearson correlation coefficient was used to evaluate the relationship between the change in condylar volumetric asymmetry and the asymmetry of soft tissue pogonion from T1 to T3. No correlation was found.

Results

Overall interreviewer reliability was good, with 95.30% exact or within 1 category agreement. Figure 3 and Table I show the results of the subsequently completed consensus radiographic evaluation. There was an increase in the presence or severity of sclerosis in 14 of the 16 surgical condyles, with 12 of these found to be moderate to severe. There was also an increase in the presence or severity of sclerosis in 11 of the 16 nonsurgical condyles. No condyles, surgical or nonsurgical, improved in the presence or severity of sclerosis. Bone cysts were not as prevalent in this sample. Only 1 surgical and one nonsurgical condyle showed any greater than 2 cysts before or after surgery. There was an increase in the presence or severity of osteophytes in all except one surgical condyle. Not a single condyle, surgical or nonsurgical, improved in the presence or severity of osteophytes 1-year postsurgery. Scoring for the flattening of the surgical condyle is not reliable as these joints underwent intentional flattening via the high condylectomy procedure. However, 7 of the 16 nonsurgical condyles showed increased flattening, and none improved the degree of flattening postsurgically. Twelve of the surgical condyles experienced a progression of erosion, with 9 of these being diagnosed as moderate to severe. Twelve of the nonsurgical condyles also experienced a progression of erosion, with 8 of these being diagnosed as moderate to severe. No condyles, surgical or nonsurgical, improved in the presence or severity of erosion 1-year postsurgically. Overall resorption and proliferation were measured relative to presurgical (T1) height and width of the condyles. A majority of the surgical (15 of 16) and nonsurgical (10 of 16) condyles showed resorption at T3. Twelve surgical condyles were viewed to have severe (>50%) resorption. Most condyles showed no change or only mild proliferations.

Fig 3
Confusion matrix of the consensus radiographic evaluation scoring from T1 to T3.

Table I
Statistical analysis of the radiographic evaluation
T1 to T3 Mean SD SE Paired-samples t test sig (2-tailed) Wilcoxon signed rank test sig (2-tailed)
Sclerosis, non-Sx −1.07 0.85 0.23 0.00 0.00
Sclerosis, Sx −1.56 -0.89 0.22 0.00 0.00
Bone Cysts, non-Sx −0.38 0.62 0.16 0.03 0.03
Bone Cysts, Sx −0.13 1.03 0.26 0.63 0.76
Osteophytes, non-Sx −0.44 0.63 0.16 0.01 0.02
Osteophytes, Sx −1.31 0.70 0.18 0.00 0.00
Flattening, non-Sx −0.56 0.73 0.18 0.06 0.01
Flattening, Sx −1.75 0.93 0.23 0.00 0.00
Erosion, non-Sx −1.19 0.91 0.23 0.00 0.00
Erosion, Sx −1.25 1.00 0.25 0.00 0.00
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Oct 30, 2021 | Posted by in Orthodontics | Comments Off on Mandibular condylar remodeling characteristics after simultaneous condylectomy and orthognathic surgery
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