Impact of occlusal proprioception on static postural balance.

Conflicting results on the effects of occlusal proprioceptive information on standing sway have been reported in the literature, partly due to the heterogeneity of the occlusal criterion studied and the experimental protocol used. In this study, occlusal functions, different mandibular positions and visual conditions were used to investigate the involvement of occlusal proprioception information in static postural balance. Postural adjustments of 26 healthy young adults, divided into Class I malocclusion and Class I normocclusion groups, were studied in upright position, in five mandibular positions (1 free, 2 centric and 2 eccentric), with and without vision. Due to different reported test durations, postural parameters were examined for the first and last halves of the 51.2 s acquisition time. A permutation ANOVA with 4 factors was used: group, mandibular position, vision, time window. Mean length of CoP displacement was shorter with vision (ES = 0.30) and more affected by vision loss in the free than in the intercuspal mandibular position (ES = 0.76 vs. 0.39), which has more tooth contacts. The malocclusion group was more affected by vision loss (ES = 0.64). Unexpectedly, with vision, the mean length was smaller in one eccentric occlusion side compared to the other (ES = 0.51), but independent of the left or right side, and more affected by vision loss (ES = 1.04 vs. ES = 0.71). The first-time window of the acquisition time, i.e. 25.6 s, was sufficient to demonstrate the impact of dental occlusion, except for the sway area. Comparison of the two visual conditions was informative. With vision, the weight of occlusal proprioception was not strictly related to occlusal characteristics (number of teeth in contact; centered or eccentric mandibular position), and it was asymmetrical. Without vision, the lack of difference between groups and mandibular positions suggested a sensory reweighting, probably to limit postural disturbance.

Assessment of axial rotation movement in cervical dystonia using cone-beam computed tomography.

BACKGROUND: Cervical dystonia is a neurological disorder characterized by involuntary muscle contractions and abnormal postures of the head and neck. Botulinum neurotoxin injection is the first-line treatment. Imaging determination of the cervical segments involved (lower or upper according to the torticollis-torticaput [COL-CAP] Classification) is an aid in determining the muscles to be injected. We aimed to clarify the impact of dystonia on posture and rotational movement of cervical vertebrae in the transverse plane. METHODS: A comparative study was conducted in a movement disorders department. Ten people with cervical dystonia and 10 matched healthy subjects (without cervical dystonia) were recruited. 3-D images of posture and cervical range of motion in axial rotation in the sitting position were recorded by using a cone-beam CT scanner. Range of rotational motion of the upper cervical spine from the occipital bone to fourth cervical vertebra was measured and compared between the two groups. FINDINGS: The head posture analysis showed that the total cervical spine position was more significantly distant from the neutral position for people with dystonia than healthy subjects (p = 0.007). The rotational range of motion of the cervical spine was significantly lower in cervical dystonia participants than in healthy subjects for the total (p = 0.026) and for upper cervical spine (p = 0.004). INTERPRETATION: We demonstrated, by means of cone-beam CT, that the disorganization of movements due to cervical dystonia affected the upper cervical spine and mostly the atlantoaxial joint. The involvement of rotator muscles at this cervical level should be considered more in treatments.

Validity and reliability of center of pressure measures to quantify trunk control ability in individuals after stroke in subacute phase during unstable sitting test.

Objective: The objective of this study was to assess, for individuals with hemiparesis after a stroke in subacute phase, the validity and reliability of center of pressure (CoP) parameters measured during sitting balance on an unstable support. Materials and methods: Thirty-two individuals after stroke were included in this observational study for validity and reliability (mean age: 64.34 ± 9.30y, 23 men, mean post-stroke duration: 55.64 ± 27days). Intra-Class Correlation (ICC) and Bland Altman plot assessed intra-rater reliability and inter-rater reliability of CoP parameters during unstable sitting balance test (anteroposterior or mediolateral imbalance). Validity was established by correlating CoP parameters with the Modified Functional Reach Test, trunk strength, Balance Assessment in Sitting and Standing and Timed Up and Go tests. Results: The findings highlighted significant correlations between CoP parameters and trunk strength for anteroposterior seated destabilization. Good to excellent intra and inter-rater reliability (0.87 ≤ ICC ≤ 0.95) was observed for all CoP length parameters and CoP mean velocity in both mediolateral and anteroposterior imbalance conditions. CoP parameters for mediolateral unstable sitting condition were more reliable than for anteroposterior instability. Conclusion: Trunk control assessment during unstable sitting position on a seesaw is a reliable test for assessing trunk control ability in individuals after a stroke. CoP length and mean velocity are found to be the best parameters.

Phantom Sensations Influenced by Global and Local Modifications of the Prosthetic Socket as a Potential Solution for Natural Somatosensory Feedback During Walking: A Preliminary Study of a Single Case.

Following lower limb amputation, amputees are trained to walk with a prosthesis. The loss of a lower limb deprives them of essential somatosensory information, which is one of the causes of the difficulties of walking with a prosthesis. We here explored whether a solution to this lack of somatosensory feedback could come from natural sensations of the phantom limb, present in most amputees, instead of from substitutive technologies. Indeed, it is known that phantom sensations can be modulated by (i) global mechanical characteristics of the prosthesis socket, and (ii) locally applying a stimulus on an area of the residual limb. The purpose of this pilot study was to verify the feasibility of influencing phantom sensations via such socket modifications in a participant with transfemoral amputation. Four prosthetic interface conditions were studied: a rigid and a semi-rigid socket, each one with and without a focal pressure increase on a specific area of the residual limb. The results show that phantom sensations during walking were different according to the 4 interface conditions. The participant had more vivid phantom sensations in his foot and calf of which some varied as a function of the gait phases. Preliminary gait analysis with wearable sensors shows that these modifications were accompanied by changes in some gait spatiotemporal parameters. This preliminary study of single case demonstrates that phantom sensations can be modulated by the prosthetic interface and can provide natural somatosensory information dynamically varying with gait phases. Although this needs to be confirmed for a larger population of lower limb amputees, it already encourages non-painful phantom sensations to be considered early during the rehabilitation of lower limb amputees.

Influence of car seat firmness on seat pressure profiles and perceived discomfort during prolonged simulated driving.

During a driving task, the seat-driver interface is particularly influenced by the external environment and seat features. This study compares the effect of two different seats (S1 - soft & S2 - firm) and the effect of visual simulation of different road types (city, highway, mountain, country), on pressure distribution and perceived discomfort during prolonged driving. Twenty participants drove two 3-h sessions (one per seat) on a static simulator. Contact Pressure (CP), Contact Surface (CS), and Seat Pressure Distribution Percentage (SPD%) were analyzed throughout, using two pressure mats positioned on seat cushion and backrest. Whole-body and local discomfort for each body part were rated every 20 min. The softer seat, S1, induced a greater contact surface on cushion and backrest and a lower SPD%, reflecting better pressure distribution. Pressure profiles were asymmetrical for both S1 and S2, with higher CP under left buttock (LBu) and right lower back (RLb) and greater CS under thighs and RLb. Pressure distribution was less homogeneous on mountain and city roads than on monotonous roads (highway and country). Despite the pressure differences between the seats, however, both led to similar increases in perceived whole-body discomfort throughout the driving session. Moreover, the highest discomfort scores were in the neck and the lower back areas, whatever the seat. These findings on pressure variables may have implications for the design of backrests and cushions to ensure more homogeneous pressure distribution, even though this is not shown to minimize perceived driver discomfort.

Influence of chemotherapy on postural control and quality of life in women with gynaecological cancer: a protocol of a prospective observational study.

INTRODUCTION: Chemotherapy-induced peripheral neuropathy is a frequent side effect of some chemotherapies that can cause postural control disorders and has a serious impact on quality of life (QoL). An enhanced understanding of postural control dysfunction could help build a systematic and accurate assessment as well as specific exercises to limit the impact on QoL. This study aims to assess the influence of chemotherapy on postural control and the QoL for women with gynaecological cancer. METHODS AND ANALYSIS: This prospective observational study will include 37 participants with cancer treated using neurotoxic chemotherapy. Their postural control in various conditions (rigid and foam surfaces, eyes open and closed, with and without tendon vibration, and dual tasks), limits of stability, QoL and modified Total Neuropathy Score will be assessed. A linear mixed model will compare postural control pre-chemotherapy and post-chemotherapy. ETHICS AND DISSEMINATION: This study was approved by an ethical review board in Geneva (CCER-2020-01639). The study findings will be disseminated through conference presentations and publications in peer-reviewed journals. TRIAL REGISTRATION NUMBER: NCT04692168.

Car seat impact on driver's sitting behavior and perceived discomfort during prolonged real driving on varied road types.

Prolonged driving under real conditions can entail discomfort linked to driving posture, seat design features, and road properties like whole-body vibrations (WBV). This study evaluated the effect of three different seats (S1 = soft; S2 = firm; S3 = soft with suspension system) on driver's sitting behavior and perceived discomfort on different road types in real driving conditions. Twenty-one participants drove the same 195 km itinerary alternating highway, city, country, and mountain segments. Throughout the driving sessions, Contact Pressure (CP), Contact Surface (CS), Seat Pressure Distribution Percentage (SPD%) and Repositioning Movements (RM) were recorded via two pressure mats installed on seat cushion and backrest. Moreover every 20 minutes, participants rated their whole-body and local discomfort. While the same increase in whole-body discomfort with driving time was observed for all three seats, S3 limited local perceived discomfort, especially in buttocks, thighs, neck, and upper back. The pressure profiles of the three seats were similar for CP, CS and RM on the backrest but differed on the seat cushion. The soft seats (S1 & S3) showed better pressure distribution, with lower SPD% than the firm seat (S2). All three showed highest CP and CS under the thighs. Road type also affected both CP and CS of all three seats, with significant differences appearing between early city, highway and country segments. In the light of these results, automotive manufacturers could enhance seat design for reduced driver discomfort by combining a soft seat cushion to reduce pressure peaks, a firm backrest to support the trunk, and a suspension system to minimize vibrations.

Eccentric training effects for patients with post-stroke hemiparesis on strength and speed gait: A randomized controlled trial.

BACKGROUND: In hemiparetic patients, the skeletal muscle is mainly affected with a combination of abnormalities (denervation, remodeling, spasticity, and eventually muscular atrophy). OBJECTIVE: This study examined the role of eccentric exercise in strengthening muscles of the lower extremity and ultimately improving autonomy in patients with post-stroke hemiparesis during gait. METHODS: Thirty-seven patients hemiparetic adults were recruited, randomized into a control group (n = 19) and an intervention group receiving eccentric muscle strengthening (n = 18). The protocol consisted of three sets of five repetitions of eccentric contraction of the paretic limb after determining the maximum repetition (1 MRI). Evaluation of the 1RM, 10 meters and 6WMT was performed before and after the exercise for each group. Manova test was used to compare the differences between the control and intervention groups. RESULTS: The paretic limb showed significant increase in one-repetition maximum (1RM) between before and after rehabilitation (p≤0.00003). The two groups of Patients increased their walking speed (p≤0.0005), but we observed a significant difference between groups only for the 6MWT and not on the 10 meters Test. CONCLUSIONS: Eccentric training can be useful in strengthening the muscles of the lower limbs, and promoting gait performance. Eccentric training could complement other methods of managing patients with post-stroke hemiparesis.

Influence of foot position and vision on dynamic postural strategies during the "grand plié" ballet movement (squatting) in young and adult ballet dancers.

PURPOSE: To analyse dynamic postural strategies during the "grand plié" in two different foot positions (parallel or turned out), with and without vision, and as a function of age in ballet dancers. METHOD: Twenty young dancers (YD) aged from 8 to 16 years, and 20 adult dancers (AD) aged from 17 to 30 years were recruited. Center of pressure (CoP) and ground reaction forces (GRF) were recorded (500 Hz) during the grand plié (lowering, squatting and rising). This movement was tested with the feet parallel and with both lower limbs turned out (foot angle >140°), with eyes open (EO) and eyes closed (EC). Groups were compared using Student t-tests. Repeated analysis of variance was used to examine the effects of eyes and foot conditions, with a significance level of p < 0.05. RESULTS: The results of this study showed that dynamic postural strategies during the "grand plié" ballet movement are influenced by age, foot position and visual condition. CoP displacement length (p < 0.003) and CoP speed (p < 0.003) were higher in YD compared with AD. CoP surface (p < 0.05), mediolateral CoP speed (p < 0.048) and GRF parameters, particularly the mediolateral (p < 0.049), were higher than in the parallel than the turned out position. In both groups all CoP (p < 0.042) and GRF parameters (p < 0.049), except the vertical component, were higher with EC than EO. CONCLUSION: The effect of foot position was greatest with EO. The parallel position was less stable. The YD were more unstable in the parallel position, particularly with EC. For both groups, the lack of vision increased instability. These results show the importance of integrating balance training in a variety of foot positions and visual conditions, particularly during the initial stages of training to prevent injury.

Beliefs of rehabilitation professionals towards guided self-rehabilitation contracts for post stroke hemiparesis.

Purpose To investigate the beliefs of physiotherapy students (ST), professionals (PT) and physicians (MD) about engaging patients with post-stroke hemiparesis into Guided Self-Rehabilitation Contracts (GSC), to increase their exercise intensity and responsibility level. Method A survey examining beliefs about post-stroke rehabilitation was completed by first (n = 95), second (n = 105), and third (n = 48) year STs; PTs (n = 129) and MDs (n = 65) in France. Results The belief about whether a patient may exercise alone varied between the professional groups with more STs and MDs finding it acceptable: 62% of PTs vs. 74% of STs (p = 0.005) and 79% of MDs (p = 0.02). For 93% of therapists (STs and PTs together), the caregiver may take part in physical therapy sessions. The appropriate weekly duration of exercises in chronic hemiparesis should be over 5 h for 19% of PTs, 37% of STs, and 51% of MDs (MDs vs. PTs, p < 0.005). After stroke, functional progress through rehabilitation is possible all lifelong for 11% of STs, 19% of PTs (p < 0.05, STs vs. PTs), and 29% of MDs (MD vs. PT, NS). Conclusions The strategy of asking patients to perform exercises alone, in the practice or at home, is still not accepted by a large proportion of physical therapy professionals as compared with students or with physicians. Most therapists still see a <5-h weekly duration of exercise as sufficient after stroke. Few therapists are ready to utilize the persistence of behavior-induced brain plasticity regardless of age or delay after the lesion.

Does dystonic muscle activity affect sense of effort in cervical dystonia?

BACKGROUND: Focal dystonia has been associated with deficient processing of sense of effort cues. However, corresponding studies are lacking in cervical dystonia (CD). We hypothesized that dystonic muscle activity would perturb neck force control based on sense of effort cues. METHODS: Neck extension force control was investigated in 18 CD patients with different clinical features (7 with and 11 without retrocollis) and in 19 control subjects. Subjects performed force-matching and force-maintaining tasks at 5% and 20% of maximum voluntary contraction (MVC). Three task conditions were tested: i) with visual force feedback, ii) without visual feedback (requiring use of sense of effort), iii) without visual feedback, but with neck extensor muscle vibration (modifying muscle afferent cues). Trapezius muscle activity was recorded using electromyography (EMG). RESULTS: CD patients did not differ in task performance from healthy subjects when using visual feedback (ANOVA, p>0.7). In contrast, when relying on sense of effort cues (without visual feedback, 5% MVC), force control was impaired in patients without retrocollis (p = 0.006), but not in patients with retrocollis (p>0.2). Compared to controls, muscle vibration without visual feedback significantly affected performance in patients with retrocollis (p<0.001), but not in patients without retrocollis. Extensor EMG during rest, included as covariate in ANOVA, explained these group differences. CONCLUSION: This study shows that muscle afferent feedback biases sense of effort cues when controlling neck forces in patients with CD. The bias acts on peripheral or central sense of effort cues depending on whether the task involves dystonic muscles. This may explain why patients with retrocollis more accurately matched isometric neck extension forces. This highlights the need to consider clinical features (pattern of dystonic muscles) when evaluating sensorimotor integration in CD.

Hemispheric specificity for proprioception: Postural control of standing following right or left hemisphere damage during ankle tendon vibration.

Right brain damage (RBD) following stroke often causes significant postural instability. In standing (without vision), patients with RBD are more unstable than those with left brain damage (LBD). We hypothesised that this postural instability would relate to the cortical integration of proprioceptive afferents. The aim of this study was to use tendon vibration to investigate whether these changes were specific to the paretic or non-paretic limbs. 14 LBD, 12 RBD patients and 20 healthy subjects were included. Displacement of the Centre of Pressure (CoP) was recorded during quiet standing, then during 3 vibration conditions (80 Hz - 20s): paretic limb, non-paretic limb (left and right limbs for control subjects) and bilateral. Vibration was applied separately to the peroneal and Achilles tendons. Mean antero-posterior position of the CoP, variability and velocity were calculated before (4s), during and after (24s) vibration. For all parameters, the strongest perturbation was during Achilles vibrations. The Achilles non-paretic condition induced a larger backward displacement than the Achilles paretic condition. This condition caused specific behaviour on the velocity: the LBD group was perturbed at the onset of the vibrations, but gradually recovered their stability; the RBD group was significantly perturbed thereafter. After bilateral Achilles vibration, RBD patients required the most time to restore initial posture. The reduction in use of information from the paretic limb may be a central strategy to deal with risk-of-fall situations such as during Achilles vibration. The postural behaviour is profoundly altered by lesions of the right hemisphere when proprioception is perturbed.

Baseline Features Influencing the Effectiveness of Retraining Therapy for Writer's Cramp.

Background: The effectiveness of retraining therapy (RT) for writer's cramp is difficult to predict and its determinants are unknown. Methods: We examined factors potentially predicting improved legibility after RT in patients with writer's cramp (WC). We reviewed the files of 693 WC patients treated with RT from 1995 to 2009. Standardized assessments were made both at baseline and after 2 months of RT in 305 patients. The effect of RT on legibility was evaluated by using the handwriting subscore of the Burke-Fahn-Marsden (BFM) disability scale. Initial and final handwriting samples were blindly scored in random order. Associations between WC patterns and changes in legibility were identified by uni- and multivariable analyses. Results: Legibility improved by ≥1 point in the BFM handwriting subscore in 93 patients (31%). WC patients who improved were more likely to have synergic dystonic patterns involving the wrist and forearm (60% vs. 40%; P = 0.03) and less likely to have flexion of fingers F3 to F5 (19% vs. 81%; P = 0.017). Outcome was not related to gender, age, or dystonia duration. Our results confirm that retraining therapy could improve legibility in patients with writer's cramp. Conclusions: The pattern of writer's cramp can help to identify patients who are most likely to benefit from retraining therapy, regardless of age, gender, and disease duration.

Neglect following stroke: the role of sensory sensitivity in visuo-spatial performance.

Both proprioceptive and visual manipulations have led to some improvement of the spatial neglect syndrome. Until now, their effects on visuo-spatial behaviour have never been compared simultaneously. The objective of this study was to determine their influence, as a function of the presence of neglect and the side of the brain damage. 19 stroke patients with right and 14 with left brain damage, without or with neglect; realized the Bells test in 5 conditions: a reference condition and 4 sensory conditions, defined according to the side of application (contralesional vs ipsilesional) and the type of perturbation (visual vs proprioceptive). The visuo-spatial behaviour was analyzed for global and spatial aspects and for individual extreme performances. For the neglect group, the restriction of the visual field to the ipsilesional hemi-field significantly diverted the centre of exploration towards the ipsilesional side compared to all other conditions. The weighting of visual cues from the ipsilesional hemi-field seems to be increased in sensory-motor integration processes in neglect patients. In all the groups, although some improvements in performance did occur with sensory manipulation, they were dependent on the individual, particularly for neglect patients. A same performance can be achieved through the use of different sensory-motor strategies, which are individual-related. It is thus important to consider the sensory sensitivity and the responsiveness of each patient before beginning any sensory therapies.

Postural stabilization during bilateral and unilateral vibration of ankle muscles in the sagittal and frontal planes.

BACKGROUND: The purpose was to investigate the postural consequences of proprioceptive perturbation of the Triceps Surae and Peroneus Longus muscles. These muscles are known to control posture respectively in the sagittal and frontal planes during standing. METHODS: Standard parameters and the time course of center of pressure (CoP) displacements were recorded in 21 young adults, instructed to maintain their balance during tendon vibration. Following 4 s of baseline recording, three types of vibration (80 Hz) were applied for 20 s each on the Peroneus or Achilles tendons, either unilaterally or bilaterally (with eyes shut). The recording continued for a further 24 s after the end of the vibration during the re-stabilization phase. To evaluate the time course of the CoP displacement, each phase of the trial was divided into periods of 4 seconds. Differences between the type of tendon vibration, phases and periods were analyzed using ANOVA. RESULTS: During all tendon vibrations, the speed of the CoP increased and a posterior displacement occurred. These changes were greater during Achilles than during Peroneus vibration for each type of vibration and also during bilateral compared with unilateral vibration. All maximal posterior positions occurred at a similar instant (between 12.7 and 14 s of vibration). Only unilateral Achilles vibration led to a significant medio-lateral displacement compared to the initial state. CONCLUSIONS: The effect of the proprioceptive perturbation seems to be influenced by the position of the vibrated muscle according to the planes of the musculoskeletal postural organization. The amplitude of the destabilization may be related to the importance of the muscle for postural control. The medial CoP displacement which occurred during unilateral Achilles vibration is not a general reaction to a single-limb perturbation. Proprioceptive input from the non-perturbed leg was not sufficient for the antero-posterior displacement to be avoided; however, it helped to gain stability over time. The non-perturbed limb clearly plays an important role in the restoration of the postural referential, both during and immediately following the end of the vibration. The results demonstrated that at least 16 s of vibration are necessary to induce most postural effects in young adults.

Impaired force control in writer's cramp showing a bilateral deficit in sensorimotor integration.

BACKGROUND: Abnormal cortical processing of sensory inputs has been found bilaterally in writer's cramp (WC). This study tested the hypothesis that patients with WC have an impaired ability to adjust grip forces according to visual and somatosensory cues in both hands. METHODS: A unimanual visuomotor force-tracking task and a bimanual sense of effort force-matching task were performed by WC patients and healthy controls. RESULTS: In visuomotor tracking, WC patients showed increased error, greater variability, and longer release duration than controls. In the force-matching task, patients underestimated, whereas controls overestimated, the force applied in the other hand. Visuomotor tracking and force matching were equally impaired in both the symptomatic and nonsymptomatic hand in WC patients. CONCLUSIONS: This study provides evidence of bilaterally impaired grip-force control in WC, when using visual or sense of effort cues. This suggests a generalized subclinical deficit in sensorimotor integration in WC.

Effects of aging in postural strategies during a seated auto-stabilization task.

Impaired sensory, motor and central processing systems combining with biomechanical changes are risk of fall factors in the elderly population. The aim of this study was to assess the auto-adaptation and the regulation of the dynamic control of equilibrium in age-related adaptive strategies, by using a seated position on a seesaw. 15 young adults and 12 healthy middle-aged adults were asked to actively maintain a sitting posture as stable as possible during 12.8s, on a 1-degree of freedom seesaw (auto-stabilization paradigm), with and without vision. The seesaw was placed in order to allow roll or pitch oscillations. We determine length and surfaces CoP shifts, mean positions and variability, a Postural Performance Index (PI) and a Strategy Organization Ratio (SOR). Our results shows that adopted strategies are plane-dependant during auto-stabilization (parallel and perpendicular axes control is impacted) and age-dependant. PIx during roll seated auto-stabilization tasks appears as the most relevant parameter of aged-related instability. The visual effect, during pitch auto-stabilization, characterizes the postural sensory-motor human behavior. The quantitative and qualitative postural assessment, thanks to seated auto-stabilization task, need to be promoted for long-term health care and probably for the rehabilitation of various disorders.

Learning effect on the dynamical strategies in sitting position on seesaw motion for idiopathic scoliosis patients.

Our study meant to determine, for idiopathic scoliosis patients, the biomechanical processes involved in postural regulation when self-imposed disturbances occur in seated position in both directions during successive trials. 12 female adolescents with right thoracic scoliosis (SG) and 15 control adolescents (CG) were included in this study. Ground reaction forces were studied using a force platform while the subjects were maintaining their balance in sitting position on a seesaw. Every test is recorded with eyes opened, arms on shoulders and legs free. The force platform data (AP and ML forces data) obtained were processed to determine the following normalized force parameters: delta value (difference between maxima and minima), maximal and minimal force values (peak and occurrence), and the variability of AP and ML forces. We used a variance analysis (ANOVA test) to analyze and compare 3 trials and groups. Our results show that, whatever the directions of destabilization (AP versus ML), SG was always in a learning situation. Indeed, the first test is always less stable than the second and third trials. However, for CG, adaptability between the tests is only highlighted during ML imbalance. Significant differences of strategies between the groups are only visible for the AP force component. For all conditions imposed, scoliotic patients perform specific trunk balance strategies. Clinical tests and rehabilitation methods should include the learning effect within the spatio-temporal adaptation to ground reaction forces.

Beyond the classic correction system: a numerical nonrigid approach to the scoliosis brace.

BACKGROUND CONTEXT: Adolescent idiopathic scoliosis (AIS) causes a spine and rib cage three-dimensional (3D) deformity previously treated by bracing. Whatever the manufacturing process, this rigid system acts biomechanically on the patient through the "three-point bending" mechanical principle. It applies corrective forces to a limited area and acts especially in the frontal plane. It seemed to us that a nonrigid system, called "Cbrace," with 3D action allowing distribution of forces could increase compliance and provide better long-term correction prospects. PURPOSE: The aim of this study was to design a nonrigid brace by numerically testing in a finite-element model developed here. STUDY DESIGN: A finite-element model has been developed to simulate brace effect on AIS right thoracic deformation of a 10-year-old patient. METHODS: A two-step method was needed; first, the reliability of our model is evaluated, and then, the ability to use distributed forces to correct scoliosis deformation is tested. To obtain a 3D correction, several treatments are experimented, leading to a comparison test between the best combination to the "three-point bending" principle. RESULTS: The numerical model developed here shows good qualitative answers for the treatment of brace forces. The first results demonstrate numerically that distributed forces may be of interest in brace treatment design. Overall force of 40 N above cartilage of the last nonfloating ribs associated to two posterior asymmetrical areas appears to be the best way to correct scoliosis deformation with nonrigid action. CONCLUSION: The results show numerical efficacy of distributed forces to correct spinal deformities and raises the prospect that a new numerical brace, called "Cbrace," could be a starting point in the search for a nonrigid system.