Condylar Points Research Articles

A proposed novel digital condylar position adjustment technique to help restore a normal disc-condyle relationship

ObjectivesTo demonstrate a novel digital technique that enables real-time visualisation of occlusal transfer and adjustment of condyle position, to (1) improve the repeatability of occlusal transfer and the accuracy of condyle position adjustment and (2) be clinically effective in helping to restore the disc-condyle relationship. Materials and methodsThree participants were included in the study and underwent facebow transfers using two different methods. The digital method used patient-related three-dimensional imaging data matched with digital dental casts for occlusal transfer. The conventional method used anatomical facebows. The condylar position was adjusted based on occlusal transfer results. The results were evaluated and compared in three dimensions. In addition, clinical application data from 36 patients were analysed before and after condylar position adjustment. Statistical significance was set at p < 0.05. ResultsDifferences in the spatial positions of the three anatomical structures reproduced by both methods were statistically significant (p = 0.000). After adjusting the rotation of the condylar position, the positional deviation of the condylar point along the X- and Z-axes was significantly lower in the digital group (p < 0.05). After adjustment for translation (X and Z), the positional deviation showed no difference along the X- and Z-axes (p > 0.05) but a significant difference along the Y-axis (p < 0.001). ConclusionA novel digital technique for occlusal transfer and condylar position adjustment was presented. This technique simplifies clinical practice, improves the accuracy of results, and can help restore a normal disc-condyle relationship.

Evaluation of joint kinematics in patients with condylar reconstruction using mandibular motion simulation based on intraoral scanning registration.

To summarize the features of condylar kinematics in patients with condylar reconstruction using a mandibular motion simulation method based on intraoral scanning registration. Patients undergoing unilateral segmental mandibulectomy and autogenous bone reconstruction as well as healthy volunteers were enrolled in the study. Patients were grouped based on whether the condyles were reconstructed. Mandibular movements were recorded using a jaw tracking system, and kinematic models were simulated after registration. The path inclination of the condyle point, margin of border movement, deviation, and chewing cycle were analyzed. A t test and one-way analysis of variance (ANOVA) were carried out. A total of 20 patients, including 6 with condylar reconstruction and 14 with condylar preservation as well as 10 healthy volunteers were included. The patients with condylar reconstruction showed flatter movement paths of the condyle points. The mean inclination angle of the condylar movement paths of the patients with condylar reconstruction (0.57 ± 12.54 degrees) was significantly smaller than that of those with condylar preservation (24.70 ± 3.90 degrees, P = 0.014) during both maximum opening and protrusion (7.04 ± 12.21 degrees and 31.12 ± 6.79 degrees, respectively, P = 0.022). The inclination angle of the condylar movement paths of the healthy volunteers was 16.81 ± 3.97 degrees during maximum opening and 21.54 ± 2.80 degrees during protrusion; no significant difference compared with the patients. The condyles of the affected side tended to deviate laterally in all patients during mouth opening and protrusion. Patients with condylar reconstruction showed more severe symptoms of mouth opening limitation and mandibular movement deviation as well as shorter chewing cycles than patients with condylar preservation. Patients with condylar reconstruction showed flatter movement paths of the condyle points, greater lateral motion range, and shorter chewing cycles than those with condylar preservation. The method of mandibular motion simulation based on intraoral scanning registration was feasible to simulate condylar movement.

Automatic identification of posteroanterior cephalometric landmarks using a novel deep learning algorithm: a comparative study with human experts

This study aimed to propose a fully automatic posteroanterior (PA) cephalometric landmark identification model using deep learning algorithms and compare its accuracy and reliability with those of expert human examiners. In total, 1032 PA cephalometric images were used for model training and validation. Two human expert examiners independently and manually identified 19 landmarks on 82 test set images. Similarly, the constructed artificial intelligence (AI) algorithm automatically identified the landmarks on the images. The mean radial error (MRE) and successful detection rate (SDR) were calculated to evaluate the performance of the model. The performance of the model was comparable with that of the examiners. The MRE of the model was 1.87 ± 1.53 mm, and the SDR was 34.7%, 67.5%, and 91.5% within error ranges of < 1.0, < 2.0, and < 4.0 mm, respectively. The sphenoid points and mastoid processes had the lowest MRE and highest SDR in auto-identification; the condyle points had the highest MRE and lowest SDR. Comparable with human examiners, the fully automatic PA cephalometric landmark identification model showed promising accuracy and reliability and can help clinicians perform cephalometric analysis more efficiently while saving time and effort. Future advancements in AI could further improve the model accuracy and efficiency.

Static mandibular condyle positions studied by MRI and condylar position indicator

We compared mandibular condyle positions as determined by magnetic resonance imaging (MRI) and a mechanical device, the condylar position indicator (CPI). Both methods assessed 3 mandibular positions in 10 asymptomatic males and 10 asymptomatic females, aged 23 to 37 years, free from temporomandibular disorders: maximum intercuspation, bimanually manipulated centric relation, and the unguided neuromuscular position. Bite registrations were obtained for bimanual operator guidance and neuromuscular position. 3 T MRI scans of both temporomandibular joints produced 3D data of the most superior condylar points in all 3 mandibular positions. Using mounted plaster casts and the same bite registrations, an electronic CPI displayed 3D data of its condylar spheres in these positions. The results showed interclass correlation coefficients ranging from 0.03 to 0.66 (95% confidence intervals from 0 to 0.8) and significantly different condyle positions between both methods (p = 0.0012, p < 0.001). The implications of the study emphasize that condyle position is unpredictable and variable. Its exact knowledge requires radiological imaging and should not rely on CPI assessments.

Condylar morphology and position changes after miniscrew-assisted rapid palatal expansion in skeletal Class III malocclusion adult patients with mandibular deviation and unilateral posterior crossbite

BackgroundTo evaluate the morphological and positional changes of mandibular condyle after miniscrew-assisted rapid palatal expansion (MARPE) in skeletal Class III malocclusion adult patients with horizontal mandibular deviation (MD).MethodsThe sample consisted of 15 patients with MD (6 males and 9 females, mean age 21.58 ± 3.12 years). The CBCT scans were taken before and after MARPE immediately. The pre- and post-registered images of the cranial base and mandible were measured, respectively, by Mimics.ResultsAfter expansion, the distance between superior condylar point and the Frankfort horizontal plane on the deviated side and the non-deviated side increased by 0.96 ± 0.60 mm (P = 0.011) and 0.70 ± 0.65 mm (P = 0.046); coronal condylar angle of the deviated side increased by 0.39° ± 0.34 (P = 0.028) and 0.06° ± 0.49 (P = 0.917) on the non-deviated side. No statistically significant differences were found when comparing the condylar position on both sides before and after treatment. The degree of mandibular deviation decreased 0.43 mm (P = 0.270).ConclusionsThis study suggested that for skeletal Class III malocclusion adult patients with horizontal MD, the condyle on the deviated side rotated toward the non-deviated side in the coronal direction; the condylar remodeling occurred mainly on the deviated side after MARPE in the vertical direction.

Comparison of the Post-Surgical Position of the Temporomandibular Joint after Orthognathic Surgery in Skeletal Class III Patients and Patients with Cleft Lip and Palate.

Objective: The purpose of our research is to compare the post-surgical position of the temporomandibular joint in skeletal Class III patients and patients with cleft lip and palate treated with two-jaw orthognathic surgery using a three-dimensional computer tomography image. Materials and Methods: Twenty-three skeletal Class III patients with mandibular prognathism associated with maxillary retrognathism in group 1 and twenty cleft mid-face retrusion skeletal Class III patients in group 2 were enrolled in this study. All subjects were treated with two-jaw orthognathic surgery. Computed tomography scans were taken in all subjects at 3 weeks preoperatively and 6 months postoperatively. Three-dimensional craniofacial skeletal structures were build-up, and assessed the temporomandibular joint position changes before and after surgery. Results: Forty-three selected patients were separated into two groups. The mean age of patients was 22.39 ± 4.8 years in group 1 and 20.25 ± 3.8 years in group 2. The range of mean three-dimensional discrepancy of the selected condylar points was 0.95–1.23 mm in group 1 and 2.37–2.86 mm in group 2. The mean alteration of intercondylar angle was 2.33 ± 1.34° in group 1 and 6.30 ± 2.22° in group 2. The significant differences in the discrepancy of TMJ and changes in intercondylar angle were confirmed within the intra-group and between the two groups. Conclusions: Significant changes in postoperative TMJ position were present in both groups. Furthermore, the cleft group presented significantly more postoperative discrepancy of TMJ and more changes in intercondylar angle after surgery. This finding may be a reason leading to greater postoperative instability in cleft patients compared with skeletal Class III non-cleft patients. Clinical Trial Registration Number: IRB No: 202201108B0.

Visualization of mandibular movement relative to the maxilla during mastication in mice: integration of kinematic analysis and reconstruction of a three-dimensional model of the maxillofacial structure

BackgroundMastication is one of the most fundamental functions for the conservation of human life. To clarify the pathogenetic mechanism of various oral dysfunctions, the demand for devices for evaluating stomatognathic function has been increasing. The aim of the present study was to develop a system to reconstruct and visualize 3-dimensional (3D) mandibular movements relative to the maxilla, including dynamic transition of occlusal contacts between the upper and lower dentitions during mastication in mice.MethodsFirst, mandibular movements with six degrees of freedom were measured using a motion capture system comprising two high-speed cameras and four reflective markers. Second, 3D models of maxillofacial structure were reconstructed from micro-computed tomography images. Movement trajectories of anatomical landmark points on the mandible were then reproduced by integrating the kinematic data of mandibular movements with the anatomical data of maxillofacial structures. Lastly, 3D surface images of the upper dentition with the surrounding maxillofacial structures were transferred to each of the motion capture images to reproduce mandibular movements relative to the maxilla. We also performed electromyography (EMG) of masticatory muscles associated with mandibular movements.ResultsThe developed system could reproduce the 3D movement trajectories of arbitrary points on the mandible, such as incisor, molars and condylar points with high accuracy and could visualize dynamic transitions of occlusal contacts between upper and lower teeth associated with mandibular movements.ConclusionsThe proposed system has potential to elucidate the mechanisms underlying motor coordination of masticatory muscles and to clarify their roles during mastication by taking advantage of the capability to record EMG data synchronously with mandibular movements. Such insights will enhance our understanding of the pathogenesis and diagnosis of oral motor disorders by allowing comparisons between normal mice and genetically modified mice with oral behavioral dysfunctions.

Postsurgical Stability of Temporomandibular Joint of Skeletal Class III Patients Treated with 2-Jaw Orthognathic Surgery via Computer-Aided Three-Dimensional Simulation and Navigation in Orthognathic Surgery (CASNOS).

Objective The aim of this study is to clarify the postsurgical stability of temporomandibular joints in skeletal class III patients treated with 2-jaw orthognathic surgery which was performed utilizing computer-aided three-dimensional simulation and navigation in orthognathic surgery (CASNOS) protocol. Materials and Methods 23 consecutive nongrowing skeletal class III patients with mandibular prognathism associated with maxillary retrognathism treated with 2-jaw orthognathic surgery between 2018 and 2019 were enrolled in this study. The surgery was planned according to the standardized protocol of CASNOS (computer-aided three-dimensional simulation and navigation in orthognathic surgery). Computed tomography (CT) scans were performed in all patients 3 weeks presurgically and 6 months postsurgically. ITKSNAP and 3D Slicer software were used to reconstruct three-dimensional facial skeletal images, to carry out image segmentation, and to superimpose and quantify the TMJ position changes before and after surgery. Amount of displacement of the most medial and lateral points of the condyles and the change of intercondylar angles were measured to evaluate the postsurgical stability of TMJ. Results A total amount of 23 skeletal class III patients (female : male = 12 : 11) with age ranged from 20.3 to 33.5 years (mean: 24.39 ± 4.8 years old) underwent Le Fort I maxillary advancement and BSSO setback of the mandible. The surgical outcome revealed the satisfactory correction of their skeletal deformities. The mean displacement of the right most lateral condylar point (RL-RL′) was 1.04 ± 0.42 mm and the mean displacement of the left most lateral condylar point (LL-LL′) was 1.19 ± 0.41 mm. The mean displacement of the right most medial condylar point (RM-RM′) was 1.03 ± 0.39 mm and the left most medial condylar point (LM-LM′) was 0.96 ± 0.39 mm. The mean intercondylar angle was 161.61 ± 5.08° presurgically and 159.28 ± 4.92° postsurgically. Conclusion The postsurgical position of TM joint condyles in our study only presented a mild change with all the landmark displacement within a range of 1.2 mm. This indicates the bimaxillary orthognathic surgery via 3D CASNOS protocol can achieve a desired and stable result of TMJ position in treating skeletal class III adult patients with retrognathic maxilla and prognathic mandible.

Assessment of paradoxical anterior translation in a CR total knee prosthesis coupling dynamic RSA and FE techniques

PurposeThe study aims were to assess the kinematic data, Internal-External (IE) rotation, and Antero-Posterior (AP) translation of the contact points between the femoral condyles and polyethylene insert and to develop a combined dynamic RSA-FE (Radiostereometric – Finite Element) model that gives results congruent with the literature.MethodsA cohort of 15 patients who underwent cemented cruciate-retaining highly congruent mobile-bearing total knee arthroplasty were analyzed during a sit-to-stand motor task. The kinematical data from Dynamic RSA were used as input for a patient-specific FE model to calculate condylar contact points between the femoral component and polyethylene insert.ResultsThe femoral component showed an overall range about 4 mm of AP translation during the whole motor task, and the majority of the movement was after 40° of flexion. Concerning the IE rotation, the femoral component started from an externally rotate position (− 6.7 ± 10°) at 80° of flexion and performed an internal rotation during the entire motor task. The overall range of the IE rotation was 8.2°.ConclusionsDuring the sit to stand, a slight anterior translation from 40° to 0° of flexion of the femoral component with respect to polyethylene insert, which could represent a paradoxical anterior translation. Despite a paradoxical anterior femoral translation was detected, the implants were found to be stable. Dynamic RSA and FE combined technique could provide information about prosthetic component’s stress and strain distribution and the influence of the different designs during the movement.

Evaluation of condylar cortical bone thickness in patient groups with different vertical facial dimensions using cone-beam computed tomography.

The aim of this study is to evaluate through computed tomography differences in cortical plate thickness of condyle in patients with a different facial vertical skeletal pattern. The final sample of this retrospective study included CBCT exams of 60 adult subjects (mean age 33.2 ± 5.6), selected from the digital archive of a private practice. The subjects were assigned to 3 different groups according to the values of the Frankfurt-mandibular plane angle: hyper-, normo-, and hypodivergent groups. The volume rendering of the mandible was obtained and three condylar points were marked on it: median pole, lateral pole and the most cranial point. For each considered reference point, the minimum distance between external and internal cortical surface was measured, obtaining three different outcomes: condylar cortical bone thickness of median pole (CCBToMP), lateral pole (CCBToLP) and cranial pole (CCBToCP). The measurements were executed by means of Mimics software by the same expert operator in specific scan views. The cortical bone thickness of hyperdivergent patients was found to be statistically thicker than normodivergent patients and hypodivergent patients. Cortical bone thickness of normodivergent patients was found thicker than hypodivergent patients. All the differences were statistically significant (p < 0.05). The Pearson correlation coefficient showed a statistically significant correlation (p < 0.001) between the Frankfurt-mandibular plane angle and the evaluated cortical bone thickness outcomes. Facial biotype characteristics that define vertical facial skeletal pattern affect the cortical bone thickness of mandibular condyle.

Condylar changes in patients with idiopathic condylar resorption: retrospective 2-year follow-up CBCT-based case-control study.

To compare condylar development and changes in condylar radiological appearance in patients with idiopathic condylar resorption (ICR) to a healthy, age- and gender matched, control group. This case-control study included 16 ICR patients [mean age: 15years, 9 months; standard deviation (SD): 4 years) and 16 controls (mean age: 16 years, 8 months; SD: 4 years, 7 months), with diagnostic (T0) and 2-year follow-up (T1) CBCT examinations. Condylar changes were evaluated through changes in condylar neck angle (CNA), and the transversal, vertical and anteroposterior displacement of five condylar points between T0 and T1. The magnitude and direction of condylar changes were evaluated using vector analyses. A qualitative radiological evaluation of the TMJ was performed based on healthy, erosive and repaired morphological appearance. Linear and angular measurements were assessed using ANOVA and a Tukey post-hoc test, and vectors were tested using an independent-sample 2-tailed t-test. Fisher's exact test was used for the qualitative evaluation. At T0, ICR patients exhibited decreased condylar height, smaller condylar width and posteriorly inclined CNA compared with the control group (P < 0.05). During observation, condylar vertical growth was smaller in the ICR group than in the control group (P < 0.05). Vector analysis showed an upward direction of vertical displacement for all condylar points in the control group; the ICR group showed a downward direction (P < 0.003). The radiological appearance of 75% of the ICR condyles and 94% of the control condyles did not change during the 2-year follow-up period. ICR condyles displayed reduced vertical development compared with control condyles. The radiological appearance remained unchanged for most joints. Observed changes in radiological appearance did not always follow a progressive model of degenerative joint disease.

Influence of body and head posture on the deviation of the condylar point during dental treatment

Influence of body and head posture on the deviation of the condylar point during dental treatment

Estimated functional space of centric condyle positions in temporomandibular joints of asymptomatic individuals using MRI

Magnetic resonance imaging (MRI) studies on centric condyle positions lack 3D comparisons of guided and unguided methods, which are used for accomplishing centric relation reference positions. The purpose of this study was to describe the space, in which mandibular condyles are placed in vivo by dental intercuspation, Dawson’s bimanual manipulation, and neuromuscular position. Twenty asymptomatic individuals aged 23 to 37 years underwent separate bite registrations using bimanual manipulation and the unguided neuromuscular technique. Subsequent 3-Tesla MRI scans of both temporomandibular joints yielded 3D data of the most superior condylar points at maximum intercuspation and both centric relation positions. We found concentric condyle positions in maximum intercuspation but considerable variation of condyle position after bimanual manipulation and neuromuscular technique. Their 95% predictive confidence ellipses overlapped substantially and created a space of reference positions. Its smallest volume averaged 2 mm3 for a minimal convex hull (95% confidence interval 1.1–3.2) and 3.5 mm3 for a minimal ellipsoid hull (95% confidence interval 1.8–5.4). Visualized in vivo by MRI, condyle positions at bimanual manipulation and neuromuscular position were not predictable and showed substantial variation in asymptomatic subjects. Clinicians should be aware of the functional space and its effect on dental intercuspation.

Development and evaluation of a jaw-tracking system for mice: reconstruction of three-dimensional movement trajectories on an arbitrary point on the mandible

BackgroundMastication is one of the most fundamental functions for the conservation of life. The demand for devices for evaluating stomatognathic function, for instance, recording mandibular movements or masticatory muscle activities using animal models, has been increasing in recent years to elucidate neuromuscular control mechanisms of mastication and to investigate the etiology of oral motor disorders. To identify the fundamental characteristics of the jaw movements of mice, we developed a new device that reconstructs the three-dimensional (3D) movement trajectories on an arbitrary point on the mandible during mastication.MethodsFirst, jaw movements with six degrees of freedom were measured using a motion capture system comprising two high-speed cameras and four reflective markers. Second, a 3D model of the mandible including the markers was created from micro-computed tomography images. Then, the jaw movement trajectory on the certain anatomical point was reproduced by integrating the kinematic data of the jaw movements with the geometric data of the mandible.ResultsThe 3D movements at any points on the mandible, such as the condyle, molar, and incisor during mastication, could be calculated and visualized with an accuracy > 0.041 mm in 3D space. The masticatory cycle was found to be clearly divided into three phases, namely, the opening, closing, and occlusal phases in mice.ConclusionsThe proposed system can reproduce and visualize the movements of internal anatomical points such as condylar points precisely by combining kinematic data with geometric data. The findings obtained from this system could facilitate our understanding of the pathogenesis of eating disorders or other oral motor disorders when we could compare the parameters of stomatognathic function of normal mice and those of genetically modified mice with oral behavioral dysfunctions.

Lateral condylar retrograde humeral nail for management of high-energy distal humeral fractures.

Distal metaphyseo-diaphyseal humeral fractures are challenging particularly if open, comminuted, or associated with nerve injury. In cases of open distal complex metaphyseo-diaphyseal humeral fractures inamenable for traditional methods of fixation, retrograde intramedullary locked humeral nail with a new lateral condylar point of entry has been proposed. Two phases of study were conducted; phase I comprised computerized tomography evaluation of right humeri of 120 adult subjects, while phase II entailed prospective analysis of 18 patients who sustained firearm injuries resulting in open distal metaphyseo-diaphyseal humeral fractures associated with radial nerve injuries. All patients were surgically managed using lateral condylar retrograde humeral nailing with primary radial nerve exploration. Distal sagittal medullary diameter of the humeral medulla was the narrowest in comparison to axial and coronal medullary diameters in phase II, which matched the results of phase I. The mean postoperative disability of the arm, shoulder, and hand score was 11.2 ± 6.4. Only five patients underwent subsequent successful tendon transfer. Lateral condylar retrograde humeral nail with early radial nerve exploration in cases of high-energy distal metaphyseo-diaphyseal humeral fractures yielded good results regarding union and spontaneous radial nerve recovery or later on reconstruction.

Rotation tendency of the posteriorly displaced proximal segment after vertical ramus osteotomy

Intraoral Vertical Ramus Osteotomy (IVRO) is one of the operative techniques used for orthognathic surgery. The aim of this study was to assess the posterior displacement of the proximal segment in patients undergoing IVRO at 1-year follow-up.In total, 52 hemimandibles from 26 patients who underwent IVRO in whom the proximal segment was posteriorly displaced without overlap with the distal segment at immediate post-operation (Imm) (30 cases, experimental group), and 26 patients in whom the proximal segment was not posteriorly displaced with overlap with the distal segment (Imm) (22 cases, control group) under three-dimensional computed tomography (3D CT) were included in the study. To analyze the movement of segments, the positions of the mid condyle point (MCP) and angle of condyle line (Con) were determined and the movement of the ramus angle (posterior edge of proximal segments) was measured at the proximal segment.Regression of the proximal segment in sagittal direction of the MCP was observed in both groups and all directions of the ramus angle in the experimental group, and only sagittal direction in the control group.In conclusion, posterior displacement of the proximal segment after IVRO showed tendency to regress its original position.

Radiographic cephalometry analysis of condylar position after bimaxillary osteotomy in patients with mandibular prognathism.

Postoperative condylar position is a substantial concern in surgical correction of mandibular prognathism. Orthognathic surgery may change condylar position and this is considered a contributing factor for early skeletal relapse and the induction of temporomandibular disorders. The purpose of this study was to evaluate changes in condylar position, and to correlate angular skeletal measurements following bimaxillary surgery. On profile teleradiographs of 21 patients with mandibular angular and linear parametres, the changes in condylar position, were measured during preoperative orthodontic treatment and 6 months after the surgical treatment. A statistically significant difference in values between the groups was found. The most distal point on the head of condyle point (DI) moved backward for 1.38 mm (p = 0.02), and the point of center of collum mandibulae point (DC) moved backward for 1.52 mm (p = 0.007). The amount of upward movement of the point DI was 1.62 mm (p = 0.04). In the patients with mandibular prognathism, the condyles tend to migrate upward and forward six months after bimaxillary surgery.

Temporomandibular joint articulations on working side during chewing in adult females with cross-bite and mandibular asymmetry.

Influence of mandibular asymmetry and cross-bite on temporomandibular joint (TMJ) articulation remained unknown. This study aimed to investigate whether/how the working-side condylar movement irregularity and articular spaces during chewing differ between patients with mandibular asymmetry/cross-bite and control subjects. The cross-bite group and the control group consisted of 10 adult female patients and 10 adult female subjects, respectively. They performed unilateral gum-chewing. The mandibular movements were recorded using a video-based opto-electronic system. The 3D articular surface of the TMJ for each individual was reconstructed using CT/MRI data. For local condylar points, the normalised jerk cost (NJC) towards normal direction to the condylar surface, the angle between tangential velocity vector and condylar long axis and intra-articular space were measured. Three rotatory angles at centre of the condyle were also measured. During closing and intercuspation, (i) movements of posterior portion of the deviated side condyle showed significantly less smoothness as compared with those for the non-deviated side and control subjects, (ii) the rotations of the condyle on the deviated side induced greater intra-articular space at posterior and lateral portions. These findings suggest that chewing on the side of mandibular deviation/cross-bite may cause irregular movement and enlarged intra-articular space at posterior portion of the deviated side condyle.

Influence of balancing-side occlusal interference on smoothness of working-side condylar movement and intra-articular space in chewing efforts.

Response of temporomandibular joint (TMJ) articulation adapting to occlusal alteration has been sparsely known. For 10 healthy adults with acceptably good occlusion, an artificial occlusal interference (OI) was introduced to the lower molar on the balancing side of unilateral chewing. Subjects were asked to chew a gum on their preferred side. The chewing jaw movements with/without the OI were recorded using a video-based optoelectronic system. The mandibular movements were generated in each individual's TMJ model reconstructed by magnetic resonance images. The smoothness of local condylar point movements towards the normal direction of the condylar surface and interarticular space on the working side was measured. Overall, the smoothness of condylar point movements in the closing phase was impaired immediately after introduction of the OI. In the intercuspal phase, the OI increased the joint space. After about 60 chewing cycles, the movement smoothness and joint space began to recover. These findings suggest that OI on the balancing side induced irregular stress field translation on the working-side condylar surface followed by acute recovery process.

How precise is computer-navigated gap assessment in TKA?

Methods to improve gap balancing in total knee arthroplasty (TKA) include the development of calibrated distractors and various devices to determine the distances of the gaps. However, few studies have validated the accuracy or precision of computer navigation to determine these measurements, especially gaps created after bone cuts have been made; doing so would be important, because optimal surgical technique relies on appropriate gap spacing. We investigated the ability of a new image-free computer navigation surface registration protocol to measure gap distances in TKA. Eight embalmed cadaveric specimens of the lower extremity were used. A surface registration software protocol defined the most distal and posterior surface points of the femoral condyles and the navigation system measured the distance of the most distal femoral condyle point to the surface of the tibia after tibial resection. The tibial resection was perpendicular to the mechanical axis and was cut with a 7° posterior slope. The navigation system measured gaps spaced by modular spacing blocks at 5° intervals from full extension to 120° of flexion. Repeatability assessed repeated measures by one surgeon. Reproducibility was assessed by performing the same measurements after complete reregistration of the computer protocol to the cadaver bones. The gaps measured by the computer were statistically the same as those assessed with the use of blocks with a maximum measurement error of 1mm. Reregistration did introduce error into the measurement. The gaps changed with position of knee flexion, and there was gradual and significant stretching of the gaps with repeated measurements. Preliminary testing shows that computer navigation can reproduce static measurements reliably and with equal accuracy as spacer blocks. We have not demonstrated that this could be applied in a dynamic setting. This computer navigation system has sufficient precision to warrant investigation in the clinical setting for measuring gaps created during the surgical procedure.