The effect of Providence night-time bracing on the sagittal profile in adolescent idiopathic scoliosis

PURPOSE

Adolescent idiopathic scoliosis (AIS) is characterized by coronal scoliosis and often a sagittal hypokyphosis. The effect of bracing on the sagittal profile is not well understood. The aim of this study is to assess the effect of night-time bracing on the sagittal profile in patients with AIS.

METHODS

We retrospectively included AIS patients with a main curve of 25-45° treated with a night-time brace in our institution between 2005 and 2018. Patients with estimated growth potential based on either Risser stage, hand X-rays, or menarchal status were included. Coronal and sagittal radiographic parameters were recorded at both brace- initiation and -termination. Patients were followed until surgery or one year after brace termination. Results were compared to a published cohort of full-time braced patients.

RESULTS

One hundred forty-six patients were included. Maximum thoracic kyphosis (TK) increased 2.5° (± 9.7) (p = 0.003), corresponding to a 3.5-fold relative risk increase post bracing in TK compared to a full-time brace cohort. Twenty-seven percent (n = 36) of the patients were hypokyphotic (T4/T12 < 20°) at brace initiation compared with 19% (n = 26) at brace termination (p = 0.134). All other sagittal parameters remained the same at follow-up. We found no association between progression in the coronal plane and change in sagittal parameters.

CONCLUSION

This is the first study to indicate that night-time bracing of AIS does not induce hypokyphosis. We found a small increase in TK, with a substantially lower risk of developing flat back deformity compared to full-time bracing. The coronal curve progression was not coupled to a change in TK.

Differences between men and women in coupled subtalar and tibiofemoral joint kinematics during gait revealed through dynamic biplane radiography

It has been suggested that subtalar and tibiofemoral kinematics are coupled, such that abnormal subtalar inversion during the impact and push-off portions of stance may affect tibial rotation, leading to abnormal compensatory knee motion. This study aimed to characterize tibiofemoral and subtalar coupled motion and to determine if sex-dependent differences exist in lower extremity coupled motion. Twenty young adults were imaged at 100 frames/s using dynamic biplane radiography while walking. Lower extremity CT scans were obtained and segmented into subject-specific 3D bone models. Digitally reconstructed radiographs generated from the models were matched to the biplane radiographs via a validated tracking process to obtain tibiofemoral and subtalar joint kinematics. Subtalar inversion/eversion was strongly associated with tibiofemoral internal/external rotation and tibiofemoral ab/adduction during impact and push-off (P < 0.001). Men reached neutral subtalar and tibiofemoral orientation at midstance, while women remained more inverted at the subtalar joint and more externally rotated at the tibiofemoral joint. The rate of tibiofemoral ab/adduction to subtalar eversion differed between sexes during push-off (P = 0.005). Women underwent subtalar inversion, as well as tibiofemoral internal rotation and adduction during push-off, while men underwent only subtalar inversion and tibiofemoral internal rotation, with effectively no tibiofemoral adduction. These results provide the first quantitative evidence characterizing subtalar and tibiofemoral coupled motion. Differences in coupled motion trajectories between men and women may be associated with the higher incidence of knee-related pathology in women. These novel findings may serve as a standard for comparison when evaluating patients with patellofemoral pain.

Toward a better understanding of direct vertebral rotation for AIS surgery: development of a multisegmental biomechanical model and factors affecting correction

BACKGROUND CONTEXT

The direct vertebral rotation (DVR) technique involves vertebral manipulation by the application of force in the transverse plane using a pedicle screw as the anchor point. The biomechanics of this technique has not been well studied, and the applied derotation force may affect cosmetic outcome and potential complications.

PURPOSE

The purpose of the study was to develop an in vitro biomechanical model replicating DVR and examine the effects of screw placement, derotation direction, and segmental versus en bloc rotation on correction.

STUDY DESIGN

This study is based on a cadaveric spine model examining the biomechanics of DVR.

METHODS

Short three vertebral segments were dissected from thoracolumbar cadaveric spines (T5-L4). Each pedicle of the central vertebra received a unicortical, bicortical, or in-out-in screw. Unconstrained biomechanical tests were performed in an axial rotation (medial and lateral directions) mimicking DVR surgery. Nondestructive tests were performed examining peak force and rotational stiffness with/without a contralateral rod. A destructive failure test was performed on each pedicle screw with a contralateral rod connecting via the contralateral pedicle screw. Repeated-measures analysis of variance and post hoc Student t tests were used to detect significance with screw placement and loading direction as main factors.

RESULTS

Without the contralateral rod, the rotation direction was significant (p=.004, medial stiffness more than lateral). With the contralateral rod, in-out-in placement demonstrated lower stiffness than unicortical or bicortical screws (p=.009), and the rotation direction was significant (p=.003, medial stiffness more than lateral). There was no interaction effect between main factors. Peak force with and without a contralateral rod resulted in a similar pattern of significance as stiffness. Destructive failure tests showed that the placement was significant (p<.02) with in-out-in resulting in lower stiffness than unicortical- and bicortical-placed screws. In-out-in (25±6 N) and unicortical (35±16 N) placements resulted in lower peak load (p<.001) than bicortical (48±17 N) screws.

CONCLUSIONS

The biomechanical characteristics of DVR are dependent on the derotation direction and screw placement. Correction for adolescent idiopathic scoliosis can be attempted irrespective of the type of pedicle screw placement, more efficiently if performing derotation maneuvers en bloc on bicortical screws in the medial direction.

In vivo three-dimensional intervertebral kinematics of the subaxial cervical spine during seated axial rotation and lateral bending via a fluoroscopy-to-CT registration approach

Accurate measurement of the coupled intervertebral motions is helpful for understanding the etiology and diagnosis of relevant diseases, and for assessing the subsequent treatment. No study has reported the in vivo, dynamic and three-dimensional (3D) intervertebral motion of the cervical spine during active axial rotation (AR) and lateral bending (LB) in the sitting position. The current study fills the gap by measuring the coupled intervertebral motions of the subaxial cervical spine in ten asymptomatic young adults in an upright sitting position during active head LB and AR using a volumetric model-based 2D-to-3D registration method via biplane fluoroscopy. Subject-specific models of the individual vertebrae were derived from each subject's CT data and were registered to the fluoroscopic images for determining the 3D poses of the subaxial vertebrae that were used to obtain the intervertebral kinematics. The averaged ranges of motion to one side (ROM) during AR at C3/C4, C4/C5, C5/C6, and C6/C7 were 4.2°, 4.6°, 3.0° and 1.3°, respectively. The corresponding values were 6.4°, 5.2°, 6.1° and 6.1° during LB. Intervertebral LB (ILB) played an important role in both AR and LB tasks of the cervical spine, experiencing greater ROM than intervertebral AR (IAR) (ratio of coupled motion (IAR/ILB): 0.23-0.75 in LB, 0.34-0.95 in AR). Compared to the AR task, the ranges of ILB during the LB task were significantly greater at C5/6 (p=0.008) and C6/7 (p=0.001) but the range of IAR was significantly smaller at C4/5 (p=0.02), leading to significantly smaller ratios of coupled motions at C4/5 (p=0.0013), C5/6 (p<0.001) and C6/7 (p=0.0037). The observed coupling characteristics of the intervertebral kinematics were different from those in previous studies under discrete static conditions in a supine position without weight-bearing, suggesting that the testing conditions likely affect the kinematics of the subaxial cervical spine. While C1 and C2 were not included owing to technical limitations, the current results nonetheless provide baseline data of the intervertebral motion of the subaxial cervical spine in asymptomatic young subjects under physiological conditions, which may be helpful for further investigations into spine biomechanics.

Kinematics of the thoracic spine in trunk lateral bending: in vivo three-dimensional analysis

BACKGROUND CONTEXT

In vivo three-dimensional kinematics of the thoracic spine in trunk lateral bending with an intact rib cage and soft tissues has not been well documented. There is no quantitative data in the literature for lateral bending in consecutive thoracic spinal segments, and there has not been consensus on the patterns of coupled motion with lateral bending.

PURPOSE

To demonstrate segmental ranges of motion (ROMs) in lateral bending and coupled motions of the thoracic spine.

STUDY DESIGN

In vivo three-dimensional biomechanics study of the thoracic spine.

PATIENT SAMPLE

Fifteen healthy male volunteers.

OUTCOME MEASURES

Computed analysis by using voxel-based registration.

METHODS

Participants underwent computed tomography of the thoracic spine in three supine positions: neutral, right maximum lateral bending, and left maximum lateral bending. The relative motions of vertebrae were calculated by automatically superimposing an image of vertebrae in a neutral position over images in bending positions, using voxel-based registration. Mean values of lateral bending were compared among the upper (T1-T2 to T3-T4), the middle-upper (T4-T5 to T6-T7), the middle-lower (T7-T8 to T9-T10), and the lower (T10-T11 to T12-L1) parts of the spine.

RESULTS

At lateral bending, the mean ROM (±standard deviation) of T1 with respect to L1 was 15.6°±6.3° for lateral bending and 6.2°±4.8° for coupled axial rotation in the same direction as lateral bending. The mean lateral bending of each spinal segment with respect to the inferior adjacent vertebra was 1.4°±1.3° at T1-T2, 1.3°±1.2° at T2-T3, 1.4°±1.3° at T3-T4, 0.9°±0.9° at T4-T5, 0.8°±1.0° at T5-T6, 1.1°±1.1° at T6-T7, 1.7°±1.2° at T7-T8, 1.3°±1.2° at T8-T9, 1.6°±0.7° at T9-T10, 1.8°±0.8° at T10-T11, 2.3°±1.0° at T11-T12, and 2.2°±0.8° at T12-L1. The smallest and the largest amounts of lateral bending were observed in the middle-upper and the lower parts, respectively. There was no significant difference in lateral bending between the upper and the middle-lower parts. Coupled axial rotation of each segment was generally observed in the same direction as lateral bending. However, high variability was found at the T2-T3 to T5-T6 segments. Coupled flexion was observed at the upper and middle parts, and coupled extension was observed at the lower part.

CONCLUSIONS

This study revealed in vivo three-dimensional motions of consecutive thoracic spinal segments in trunk lateral bending. The thoracolumbar segments significantly contributed to lateral bending. Coupled axial rotation generally occurred in the same direction with lateral bending. However, more variability was observed in the direction of coupled axial rotation at T2-T3 to T5-T6 segments in the supine position. These results are useful for understanding normal kinematics of the thoracic spine.

Thoracic coupled motions of korean men in good health in their 20s

[Purpose] The purpose of this study was to investigate thoracic coupled motions of 20 Korean young individuals. [Methods] Thoracic motion of twenty healthy male college students aged 23.2±3.1 was examined. The coupled motions of the thoracic regions T1-4, T4-8, T8-12 were measured using a three dimensional motion capture system. [Results] Coupled axial rotation in the same direction as lateral bending was observed in T1-T4 and T4-T8 in the neutral, flexed, and extended postures of the thoracic spine. In T8-T12, coupled axial rotation in the same direction as lateral bending were observed in the neutral and flexed postures, while coupled axial rotation in the opposite direction was observed in an extended posture. [Conclusion] The patterns of coupled motions in the thoracic spine demonstrated some variability between postures and regions in vivo. However, coupled motions in the same direction were predominantly lateral flexion or axial rotation in the three postures.

Estimation of tibiofemoral static zero position during dynamic drop landing

OBJECTIVE

The objective is to assess the in vivo knee secondary motions intrinsic to flexion in isolation from actual displacements during a landing activity. For this purpose a "static zero position", which denotes the normal tibiofemoral position to the static flexion angle, was introduced to describe the intrinsic secondary motion.

METHODS

The three-dimensional motion data of the healthy knee were collected from 13 male and 13 female young adults by using an auto motion analysis system and point cluster technique. First, the relationship between flexion and secondary motion in the static state was determined during a single-leg quasistatic squat. The static zero position during a single-leg drop landing was then calculated by substituting the flexion angle into the flexion-secondary relational expression obtained.

RESULTS

After the foot-ground contact, the estimated static zero positions shifted monotonically in valgus, internal rotation, and anterior translation in the case of both the male and female groups. For the time-course change, noticeable differences between the actual displacement and estimated static zero position were found from the foot-ground contact up to 25ms after the contact for the valgus/varus and external/internal rotation, and between 20 and 35ms after the contact for the anterior/posterior translation.

SUMMARY

The static zero position demonstrated relatively modest but not negligible shift in comparison with the actual displacement. The intrinsic tibiofemoral motion, or baseline shift, would be worth taking into account when examining the fundamental function and injury mechanics of the knee during an impulsive activity.