Lateral Pelvis and Lumbar Motion in Seated and Standing Office Work and Their Association With Transient Low Back Pain.

OBJECTIVE: To assess frontal plane motion of the pelvis and lumbar spine during 2 h of seated and standing office work and evaluate associations with transient low back pain. BACKGROUND: Although bending and twisting motions are cited as risk factors for low back injuries in occupational tasks, few studies have assessed frontal plane motion during sedentary exposures. METHODS: Twenty-one participants completed 2 h of seated and standing office work while pelvic obliquity, lumbar lateral bending angles, and ratings of perceived low back pain were recorded. Mean absolute angles were compared across 15-min blocks, amplitude probability distribution functions were calculated, and associations between lateral postures and low back pain were evaluated. RESULTS: Mean pelvic obliquity (sit = 4.0 ± 2.8°, stand = 3.5 ± 1.7°) and lumbar lateral bending (sit = 4.5 ± 2.5°, stand = 4.1 ± 1.6°) were consistently asymmetrical. Pelvic obliquity range of motion was 4.7° larger in standing (13.6 ± 7.5°) than sitting (8.9 ± 8.7°). In sitting, 52% (pelvis) and 71% (lumbar) of participants, and in standing, 71% (pelvis and lumbar) of participants, were considered asymmetric for >90% of the protocol. Lateral postures displayed weak to low correlations with peak low back pain (R ≤ 0.388). CONCLUSION: The majority of participants displayed lateral asymmetries for the pelvis and lumbar spine within 5° of their upright standing posture. APPLICATION: In short-term sedentary exposures, associations between lateral postures and pain indicated that as the range in lateral postures increases there may be an increased possibility of pain.

A novel asymmetric horizontal splitting fracture of the lumbar spine: pediatric case report of a lateral bending, flexion and distraction fracture.

BACKGROUND: There are many lateral bending fracture cases presented in the literature that mostly involve facet dislocations or corpus collapse. In this report, we aim to describe a novel asymmetric lateral bending, flexion and distraction fracture, propose a mechanism, and delineate its clinical importance. CASE DESCRIPTION: A 13-year-old girl arrived at our trauma center 12 hours after a head-on truck collision. She had paraplegia, and her imaging revealed a spinal cord avulsion at the T10 level and a horizontal fracture at the L4 spinous process, left lamina, left pedicle, and left posterior-upper corner of the corpus, extending through the right lamina. Her posterior ligamentous complex, right facet joint, pedicle, and right side of the corpus were spared from the injury. The patient stated that she had been sitting on the right side of the back seat, turned toward her cousin in the middle. Her left leg was externally rotated and flexed on the seat while her right foot was on the floor at the time of the accident. The patient was managed conservatively with an orthosis. At follow-up, the patient was free of back pain and no lumbar kyphosis developed. CONCLUSION: The flexion-distraction injuries mostly require surgical stabilization according to TLICS classification, because of the instability. In this particular case, TLICS classification was not adequate for a treatment decision, and the conservative treatment came out to be a more than sufficient treatment option.

The biomechanical effect of single-level laminectomy and posterior instrumentation on spinal stability in degenerative lumbar scoliosis: a human cadaveric study.

OBJECTIVEDegenerative lumbar scoliosis, or de novo degenerative lumbar scoliosis, can result in spinal canal stenosis, which is often accompanied by disabling symptoms. When surgically treated, a single-level laminectomy is performed and short-segment posterior instrumentation is placed to restore stability. However, the effects of laminectomy on spinal stability and the necessity of placing posterior instrumentation are unknown. Therefore, the aim of this study was to assess the stability of lumbar spines with degenerative scoliosis, characterized by the range of motion (ROM) and neutral zone (NZ) stiffness, after laminectomy and placement of posterior instrumentation.METHODSTen lumbar cadaveric spines (T12-L5) with a Cobb angle ≥ 10° and an apex on L3 were included. Three loading cycles were applied per direction, from -4 Nm to 4 Nm in flexion/extension (FE), lateral bending (LB), and axial rotation (AR). Biomechanical evaluation was performed on the native spines and after subsequent L3 laminectomy and the placement of posterior L2-4 titanium rods and pedicle screws. Nonparametric and parametric tests were used to analyze the effects of laminectomy and posterior instrumentation on NZ stiffness and ROM, respectively, both on an individual segment's motion and on the entire spine section. Spearman's rank correlation coefficient was used to study the correlation between disc degeneration and spinal stability.RESULTSThe laminectomy increased ROM by 9.5% in FE (p = 0.04) and 4.6% in LB (p = 0.01). For NZ stiffness, the laminectomy produced no significant effects. Posterior instrumentation resulted in a decrease in ROM in all loading directions (-22.2%, -24.4%, and -17.6% for FE, LB, and AR, respectively; all p < 0.05) and an increase in NZ stiffness (+44.7%, +51.7%, and +35.2% for FE, LB, and AR, respectively; all p < 0.05). The same changes were seen in the individual segments around the apex, while the adjacent, untreated segments were mostly unaffected. Intervertebral disc degeneration was found to be positively correlated to decreased ROM and increased NZ stiffness.CONCLUSIONSLaminectomy in lumbar spines with degenerative scoliosis did not result in severe spinal instability, whereas posterior instrumentation resulted in a rigid construct. Also, prior to surgery, the spines already had lower ROM and higher NZ stiffness in comparison to values shown in earlier studies on nonscoliotic spines of the same age. Hence, the authors question the clinical need for posterior instrumentation to avoid instability.

Three-dimensional motion analysis of lumbopelvic rhythm during lateral trunk bending.

[Purpose] To examine the variations in the lumbopelvic rhythm and lumbar-hip ratio in the frontal plane. [Subjects and Methods] Markers were placed on the T10 and T12 spinous processes, bilateral paravertebral muscles at the T11 level, the pelvis, and the femur. Lumbar spine and hip angles were measured during lateral trunk bending using three-dimensional motion analysis. Data from the trunk lateral bending movement were categorized into descending (start of hip movement to when the hip angle reached its maximum value) and ascending (from the maximum hip angle to the end of movement) phases. The lumbar-hip ratio was calculated as the ratio of the lumbar spine angle to the hip angle. [Results] The lumbar-hip ratio decreased from 5.9 to 3.6 in the descending phase, indicating lumbar spinal movement was less than hip movement. In the ascending phase, the lumbar-hip ratio was reversed. The lumbopelvic rhythm was better expressed by a cubic or quadratic function rather than a linear function. These functions indicate that when the hip inclines by 1° that the lumbar spine bends laterally by 2.4°. [Conclusion] The lumbopelvic rhythm and lumbar-hip ratio indicate lumbar lateral bending instead of a limitation of hip inclination.

Coupled rotation patterns in cervical spine axial rotation can change when the head is kept level.

The biomechanical literature describes axial rotation occurring coupled with lateral bending and flexion in the cervical spine. Since the head is kept level during some activities of daily living, we set out to investigate the changes in total and segmental motion that occur when a level gaze constraint is applied to cadaveric cervical spine specimens during axial rotation. 1.5Nm of left and right axial rotation moment was applied to sixteen C2-T1 cadaveric specimens with C2 unconstrained and C2 constrained to simulate level gaze. Overall and segmental motions were determined using optoelectronic motion measurement and specimen-specific kinematic modeling. Without a kinematic constraint on C2, motions were as described in the literature; namely, flexion and lateral bending to the same side as axial rotation. Keeping C2 level reduced that total axial rotation range of motion of the specimens. Changes were also produced in segmental coupled rotation in all specimens. The observed changes included completely opposite coupled motion than in the uncoupled specimens, and traditional coupled behavior at one load extreme and the opposite at the other extreme. Constraining C2 during axial rotation to simulate level gaze can produce coupled motion that differs from the classically described flexion and lateral bending to the same side as axial rotation. Statement of Clinical Significance: Activities of daily living that require the head to be kept level during axial rotation of the cervical spine may produce segmental motions that are quite different from the classically described motions with implications for biomechanical experiments and implant designers.

Reference values of lumbar spine range of motion by sex and age based on the assessment of supine trunk lateral bending-A preliminary study.

[Purpose] The purpose of this study was to clarify the preliminary reference values for the lumbar spine range of motion associated with lateral bending exercises by gender and age group. [Methods] Subjects were 82 volunteers without low back pain, including five males and five females in each age group from 16-19 to 80-89 years. All subjects underwent radiographs of the lumbar spine with lateral flexion; the range of lateral flexion of the vertebrae from T12 to the sacrum (ROLB) was measured twice by three observers. [Results] The ROLB of the entire T12-S1 of all subjects showed a significant negative correlation with age in both sexes (p < 0.01). The ROLB of the lumbar spine tended to be greater in females, with a statistically significant difference between those aged 16-19 and 70-79 (p < 0.05). Lateral flexion angles for each intervertebral segment were largest at L3-L4 and smallest at L5-S1 (0.7°). [Conclusion] Lumbar ROLB reference values were examined by gender and age group; ROLB was greatest in L3-L4, and ROLB tended to be lower in older age groups.

Are owls technically capable of making a full head turn?

The three-dimensional configuration of the neck that produces extreme head turn in owls was studied using the Joint Coordinate System. The limits of planar axial rotation (AR), lateral, and sagittal bending in each vertebral joint were measured. They are not extraordinary among birds, except probably for the extended ability for AR. The vertebral joint angles involved in the 360° head turn do not generally exceed the limits of planar mobility. Rotation in one plane does not expand the range of motion in the other, with one probable exception being extended dorsal bending in the middle of the neck. Therefore, the extreme 360° head turn can be presented as a simple combination of the three planar motions in the neck joints. Surprisingly, certain joints are always laterally bent or axially rotated to the opposite side than the head was turned. This allows keeping the anterior part of the neck parallel to the thoracic spine, which probably helps preserve the ability for peering head motions throughout the full head turn. The potential ability of one-joint muscles of the owl neck, the mm. intertransversarii, to ensure the 360° head turn was addressed. It was shown that the 360° head turn does not require these muscles to shorten beyond the known contraction limit of striated vertebrate muscles. Shortening by 50% or less is enough for the mm. intertransversarii in the middle neck region for the 360° head turn. This study has broad implications for further research on vertebral mobility and function in a variety of tetrapods, providing a new method for CT scan-based measurement of intervertebral angles.

Lateral Bending of Ag Nanowires toward Controllable Manipulation.

Nanowires (NWs) provide opportunities for building high-performance sensors and devices at micro-/nanoscales. Directional movement and assembly of NWs have attracted extensive attention; however, controllable manipulation remains challenging partly due to the lack of understanding on interfacial interactions between NWs and substrates (or contacting probes). In the present study, lateral bending of Ag NWs was investigated under various bending angles and pushing velocities, and the mechanical performance corresponding to microstructures was clarified based on high-resolution transmission electron microscope (HRTRM) detections. The bending-angle-dependent fractures of Ag NWs were detected by an atomic force microscope (AFM) and a scanning electron microscope (SEM), and the fractures occurred when the bending angle was larger than 80°. Compared with an Ag substrate, Ag NWs exhibited a lower system stiffness according to the nanoindentation with an AFM probe. HRTRM observations indicated that there were grain boundaries inside Ag NWs, which would be contributors to the generation of fractures and cracks on Ag NWs during lateral bending and nanoindentation. This study provides a guide to controllably manipulate NWs and fabricate high-performance micro-/nanodevices.

Société de Biomécanique Young Investigator Award 2019: Upper body behaviour of seated humans in vivo under controlled lateral accelerations.

BACKGROUND: A deep understanding of human reactions and stabilization strategies is required to predict their kinematics under external dynamic loadings, such as those that occur in vehicle passengers. Low-level frontal accelerations have been thoroughly investigated; however, the human response to different lateral accelerations is not well understood. The objective of this study is to gain insight regarding the responses of seated humans to lateral perturbations from volunteer experiments in different configurations. METHODS: Five volunteers anthropometrically comparable to the 50th-percentile American male, were seated on a sled and submitted to 21 lateral pulses. Seven configurations, each repeated three times, were investigated in this study: a relaxed muscular condition with four pulses, namely, sine and plateau pulses of 0.1 and 0.3 g in a straight spinal posture; a relaxed muscular condition with a plateau pulse of 0.3 g in a sagging spinal posture; and a braced condition with both plateau pulses in a straight spinal posture. Upper body segment kinematics were assessed using inertial measurement units. FINDINGS: The maximum lateral bending of the head was found to differ significantly among the four acceleration pulses (p < 0.001). Braced muscles significantly reduced lateral bending compared to relaxed muscles (p < 0.001). However, no significant difference was found in lateral bending between straight and sagging spinal postures (p = 0.23). INTERPRETATION: The study shows that not only pulse amplitude but also pulse shape influences human responses to low accelerations, while spinal posture does not influence lateral head bending. These data can be used to evaluate numerical active human body models.

Cervical Disc Arthroplasties Fail to Maintain Physiological Kinematics Under Lateral Eccentric Loads.

STUDY DESIGN: In vitro human cadaveric biomechanical analysis. OBJECTIVES: Optimization of prostheses for cervical disc arthroplasties (CDA) reduces the risk of complications. The instantaneous helical axis (IHA) is a superior parameter for examining the kinematics of functional spinal units. There is no comprehensive study about the IHA after CDA considering all 3 motion dimensions. METHODS: Ten human functional spinal units C4-5 (83.2 ± 7.9 yrs.) were examined with an established measuring apparatus in intact conditions (IC), and after CDA, with 2 different types of prostheses during axial rotation, lateral bending, and flexion/extension. Eccentric preloads simulated strains. The IHA orientation and its position at the point of rest (IHA0-position) were analyzed. RESULTS: The results confirmed the existing data for IHA in IC. Lateral preloads showed structural alterations of kinematics after CDA: During axial rotation and lateral bending, the shift of the IHA0-position was corresponding with the lateral preloads' applied site in IC, while after CDAs, it was vice versa. During lateral bending, the lateral IHA orientation was inclined, corresponding with the lateral preloads' applied site in the IC and oppositely after the CDAs. During flexion/extension, the lateral IHA orientation was nearly vertical in the IC, while after CDA, it inclined, corresponding with the lateral preloads' applied site. The axial IHA orientation rotated to the lateral preloads' corresponding site in the IC; after CDA, it was vice versa. CONCLUSION: Both CDAs failed to maintain physiological IHA characteristics under lateral preloads, revealing a new aspect for improving prostheses' design and optimizing their kinematics.

In vitro coupled motions of the whole human thoracic and lumbar spine with rib cage.

Study design: In vitro biomechanical study investigating the coupled motions of the whole normative human thoracic spine (TS) and lumbar spine (LS) with rib cage. Objective: To quantify the region-specific coupled motion patterns and magnitudes of the TS, thoracolumbar junction (TLJ), and LS simultaneously. Background: Studying spinal coupled motions is important in understanding the development of complex spinal deformities and providing data for validating computational models. However, coupled motion patterns reported in vitro are controversial, and no quantitative data on region-specific coupled motions of the whole human TS and LS are available. Methods: Pure, unconstrained bending moments of 8 Nm were applied to seven fresh-frozen human cadaveric TS and LS specimens (mean age: 70.3 ± 11.3 years) with rib cages to elicit flexion-extension (FE), lateral bending (LB), and axial rotation (AR). During each primary motion, region-specific rotational range of motion (ROM) data were captured. Results: No statistically significant, consistent coupled motion patterns were observed during primary FE. During primary LB, there was significant (p < 0.05) ipsilateral AR in the TS and a general pattern of contralateral coupled AR in the TLJ and LS. There was also a tendency for the TS to extend and the LS to flex. During primary AR, significant coupled LB was ipsilateral in the TS and contralateral in both the TLJ and LS. Significant coupled flexion in the LS was also observed. Coupled LB and AR ROMs were not significantly different between the TS and LS or from one another. Conclusions: The findings support evidence of consistent coupled motion patterns of the TS and LS during LB and AR. These novel data may serve as reference for computational model validations and future in vitro studies investigating spinal deformities and implants.

Kinematics of the Cervical Spine Under Healthy and Degenerative Conditions: A Systematic Review.

Knowledge of spinal kinematics is essential for the diagnosis and management of spinal diseases. Distinguishing between physiological and pathological motion patterns can help diagnose these diseases, plan surgical interventions and improve relevant tools and software. During the last decades, numerous studies based on diverse methodologies attempted to elucidate spinal mobility in different planes of motion. The authors aimed to summarize and compare the evidence about cervical spine kinematics under healthy and degenerative conditions. This includes an illustrated description of the spectrum of physiological cervical spine kinematics, followed by a comparable presentation of kinematics of the degenerative cervical spine. Data was obtained through a systematic MEDLINE search including studies on angular/translational segmental motion contribution, range of motion, coupling and center of rotation. As far as the degenerative conditions are concerned, kinematic data regarding disc degeneration and spondylolisthesis were available. Although the majority of the studies identified repeating motion patterns for most motion planes, discrepancies associated with limited sample sizes and different imaging techniques and/or spine configurations, were noted. Among healthy/asymptomatic individuals, flexion extension (FE) and lateral bending (LB) are mainly facilitated by the subaxial cervical spine. C4-C5 and C5-C6 were the major FE contributors in the reported studies, exceeding the motion contribution of sub-adjacent segments. Axial rotation (AR) greatly depends on C1-C2. FE range of motion (ROM) is distributed between the atlantoaxial and subaxial segments, while AR ROM stems mainly from the former and LB ROM from the latter. In coupled motion rotation is quantitatively predominant over translation. Motion migrates caudally from C1-C2 and the center of rotation (COR) translocates anteriorly and superiorly for each successive subaxial segment. In degenerative settings, concurrent or subsequent lesions render the association between diseases and mobility alterations challenging. The affected segments seem to maintain translational and angular motion in early and moderate degeneration. However, the progression of degeneration restrains mobility, which seems to be maintained or compensated by adjacent non-affected segments. While the kinematics of the healthy cervical spine have been addressed by multiple studies, the entire nosological and kinematic spectrum of cervical spine degeneration is partially addressed. Large-scale in vivo studies can complement the existing evidence, cover the gaps and pave the way to technological and clinical breakthroughs.

The effect of end condition on spine segment biomechanics in compression with lateral eccentricity.

During axial impact compression of the cervical spine, injury outcome is highly dependent on initial posture of the spine and the orientation, frictional properties and stiffness of the impact surface. These properties influence the "end condition" the spine experiences in real-world impacts. The effect of end condition on compression and sagittal plane bending in laboratory experiments is well-documented. The spine is able to escape injury in an unconstrained flexion-inducing end condition (e.g. against an angled, low friction surface), but when the end condition is constrained (e.g. head pocketing into a deformable surface) the following torso can compress the aligned spine causing injury. The aim of this study was to determine whether this effect exists under combined axial compression and lateral bending. Over two experimental studies, twenty-four human three vertebra functional spinal units were subjected to controlled dynamic axial compression at two levels of laterally eccentric force and in two end conditions. One end condition allowed the superior spine to laterally rotate and translate (T-Free) and the other end condition allowed only lateral rotation (T-Fixed). Spine kinetics, kinematics, injuries and occlusion of the spinal canal were measured during impact and pre- and post-impact flexibility. In contrast to typical spine responses in flexion-compression loading, the cervical spine specimens in this study did not escape injury in lateral bending when allowed to translate laterally. The specimen group that allowed lateral translation during compression had more injuries at high laterally eccentric force, saw greater peak canal occlusions and post-impact flexibility than constrained specimens.

Lateral bending and buckling aids biological and robotic earthworm anchoring and locomotion.

Earthworms (Lumbricus terrestris) are characterized by soft, highly flexible and extensible bodies, and are capable of locomoting in most terrestrial environments. Previous studies of earthworm movement focused on the use of retrograde peristaltic gaits in which controlled contraction of longitudinal and circular muscles results in waves of shortening/thickening and thinning/lengthening of the hydrostatic skeleton. These waves can propel the animal across ground as well as into soil. However, worms benefit from axial body bends during locomotion. Such lateral bending and buckling dynamics can aid locomotor function via hooking/anchoring (to provide propulsion), modify travel orientation (to avoid obstacles and generate turns) and even generate snake-like undulatory locomotion in environments where peristaltic locomotion results in poor performance. To the best of our knowledge, lateral bending and buckling of an earthworm's body has not yet been systematically investigated. In this study, we observed that within confined environments, worms use lateral bending and buckling to anchor their body to the walls of their burrows and tip (anterior end) bending to search the environment. This locomotion strategy improved the performance of our soft-bodied robophysical model of the earthworm both in a confined (in an acrylic tube) and above-ground heterogeneous environment (rigid pegs), where present peristaltic robots are relatively limited in terradynamic capabilities. In summary, lateral bending and buckling facilitates the mobility of earthworm locomotion in diverse terrain and can play an important role in the creation of low cost soft robotic devices capable of traversing a variety of environments.

Adjacent-segment effects of lumbar cortical screw-rod fixation versus pedicle screw-rod fixation with and without interbody support.

OBJECTIVE: Cortical screw-rod (CSR) fixation has emerged as an alternative to the traditional pedicle screw-rod (PSR) fixation for posterior lumbar fixation. Previous studies have concluded that CSR provides the same stability in cadaveric specimens as PSR and is comparable in clinical outcomes. However, recent clinical studies reported a lower incidence of radiographic and symptomatic adjacent-segment degeneration with CSR. No biomechanical study to date has focused on how the adjacent-segment mobility of these two constructs compares. This study aimed to investigate adjacent-segment mobility of CSR and PSR fixation, with and without interbody support (lateral lumbar interbody fusion [LLIF] or transforaminal lumbar interbody fusion [TLIF]). METHODS: A retroactive analysis was done using normalized range of motion (ROM) data at levels adjacent to single-level (L3-4) bilateral screw-rod fixation using pedicle or cortical screws, with and without LLIF or TLIF. Intact and instrumented specimens (n = 28, all L2-5) were tested using pure moment loads (7.5 Nm) in flexion, extension, lateral bending, and axial rotation. Adjacent-segment ROM data were normalized to intact ROM data. Statistical comparisons of adjacent-segment normalized ROM between two of the groups (PSR followed by PSR+TLIF [n = 7] and CSR followed by CSR+TLIF [n = 7]) were performed using 2-way ANOVA with replication. Statistical comparisons among four of the groups (PSR+TLIF [n = 7], PSR+LLIF [n = 7], CSR+TLIF [n = 7], and CSR+LLIF [n = 7]) were made using 2-way ANOVA without replication. Statistical significance was set at p < 0.05. RESULTS: Proximal adjacent-segment normalized ROM was significantly larger with PSR than CSR during flexion-extension regardless of TLIF (p = 0.02), or with either TLIF or LLIF (p = 0.04). During lateral bending with TLIF, the distal adjacent-segment normalized ROM was significantly larger with PSR than CSR (p < 0.001). Moreover, regardless of the types of screw-rod fixations (CSR or PSR), TLIF had a significantly larger normalized ROM than LLIF in all directions at both proximal and distal adjacent segments (p ≤ 0.04). CONCLUSIONS: The use of PSR versus CSR during single-level lumbar fusion can significantly affect mobility at the adjacent segment, regardless of the presence of TLIF or with either TLIF or LLIF. Moreover, the type of interbody support also had a significant effect on adjacent-segment mobility.

Total disc arthroplasties change the kinematics of functional spinal units during lateral bending.

BACKGROUND: Information about kinematics in different functional spinal units before and after total disc arthroplasties is necessary to improve prostheses and determine indications. There is little information about the nonstationary instantaneous helical axis of rotation under lateral bending in the cervical spine before and after total disc arthroplasty. METHODS: Kinematic analyses were performed with an established measuring apparatus on 8 human functional spinal units (C3/C4, C5/C6) under intact conditions and after total disc arthroplasty with two different types of prostheses: Bryan and Prestige. The instantaneous helical axis, migration, and stiffness of the segments were calculated. FINDINGS: The instantaneous helical axis direction was always inclined ventrally. Ventral inclination was significantly higher in segment C3/C4 than in segment C5/C6 under all conditions (p < 0.001). Both types of arthroplasties significantly increased ventral inclination compared to intact conditions. In both segments, the path length of the instantaneous helical axis' migration was significantly longer after total disc arthroplasty with Bryan (p = 0.001) and shorter after Prestige (p < 0.001) prostheses than under intact conditions. After both types of arthroplasties, the migration path length was significantly longer and the stiffness was significantly lower in segment C3/C4 than in segment C5/C6. INTERPRETATION: Both types of arthroplasties changed the kinematics of both segments during lateral bending. Altered instantaneous helical axis migration, greater ventral inclination and less stiffness after both arthroplasties indicate unphysiological motion. Both arthroplasties had greater impact on segment C3/C4 than on segment C5/C6 in terms of hypermobility. Increased translational motion after total disc arthroplasty with a Bryan prosthesis might be caused by the prosthetic design.

Head forward flexion, lateral bending and viewing distance in smartphone users: A comparison between sitting and standing postures.

BACKGROUND: Smartphones (SPs) are widely used by people of all age groups and genders. Users spend many hours per day on the SPs for different purposes, which imposes significant stress on their musculoskeletal system. OBJECTIVES: This study explored head forward flexion, lateral bending angle, and viewing distance while working with a SP in sitting/standing postures and one-handed/two-handed grips. The users' performance as well as pain development were also investigated. METHODS: Participants answered a questionnaire on pain experience before and after SP usage. Neck kinematics of 20 SP users were monitored by a motion analysis system while doing three tasks (typing, video watching, and reading) in sitting and standing postures. Performance was evaluated by number of typed words, amount of errors in typing, and total read words. RESULTS: The results indicated a significant increase in pain complaints in neck and upper limbs after test completion. Working with SPs in sitting and standing postures were, respectively, associated with greater head forward flexion for watching and viewing distance for two-handed typing tasks. Higher left lateral bending values were measured for one-handed watching and reading tasks in standing posture. The performance measures were superior for two-handed grips in all conditions. CONCLUSIONS: Overall, using SPs in sitting posture creates greater head forward flexion and lower lateral bending angles in all tasks and grip types. The findings of this study can be used to provide recommendations for SP users.

Biomechanical evaluation of two alternative techniques to the Goel-Harms technique for atlantoaxial fixation: C1 lateral mass-C2 bicortical translaminar screw fixation and C1 lateral mass-C2/3 transarticular screw fixation.

OBJECTIVE: The authors conducted a study to investigate the biomechanical feasibility and stability of C1 lateral mass-C2 bicortical translaminar screw (C1LM-C2TL) fixation, C1 lateral mass-C2/3 transarticular screw (C1LM-C2/3TA) fixation, and C1LM-C2/3TA fixation with transverse cross-links (C1LM-C2/3TACL) as alternative techniques to the Goel-Harms technique (C1 lateral mass-C2 pedicle screw [C1LM-C2PS] fixation) for atlantoaxial fixation. METHODS: Eight human cadaveric cervical spines (occiput-C7) were tested using an industrial robot. Pure moments that were a maximum of 1.5 Nm were applied in flexion-extension (FE), lateral bending (LB), and axial rotation (AR). The specimens were first tested in the intact state and followed by destabilization (a type II odontoid fracture) and fixation as follows: C1LM-C2PS, C1LM-C2TL, C1LM-C2/3TA, and C1LM-C2/3TACL. For each condition, the authors evaluated the range of motion and neutral zone across C1 and C2 in all directions. RESULTS: Compared with the intact spine, each instrumented spine significantly increased in stability at the C1-2 segment. C1LM-C2TL fixation demonstrated similar stability in FE and LB and greater stability in AR than C1LM-C2PS fixation. C1LM-C2/3TA fixation was equivalent in LB and superior in FE to those of C1LM-C2PS and C1LM-C2TL fixation. During AR, the C1LM-C2/3TA-instrumented spine failed to maintain segmental stability. After adding a cross-link, the rotational stability was significantly increased in the C1LM-C2/3TACL-instrumented spine compared with the C1LM-C2/3TA-instrumented spine. Although inferior to C1LM-C2TL fixation, the C1LM-C2/3TACL-instrumented spine showed equivalent rotational stability to the C1LM-C2PS-instrumented spine. CONCLUSIONS: On the basis of our biomechanical study, C1LM-C2TL and C1LM-C2/3TACL fixation resulted in satisfactory atlantoaxial stabilization compared with C1LM-C2PS. Therefore, the authors believe that the C1LM-C2TL and C1LM-C2/3TACL fixation may serve as alternative procedures when the Goel-Harms technique (C1LM-C2PS) is not feasible due to anatomical constraints.

Significance of recumbent curvature in prediction of in-orthosis correction for adolescent idiopathic scoliosis.

BACKGROUND:: Prediction of in-orthosis curvature at pre-orthosis stage is valuable for the treatment planning for adolescent idiopathic scoliosis, while the position of spinal curvature assessment that is effective for this prediction is still unknown. OBJECTIVES:: To compare the spinal curvatures in different body positions for predicting the spinal curvature rendered by orthosis. STUDY DESIGN:: A prospective cohort study. METHODS:: Twenty-two patients with adolescent idiopathic scoliosis (mean Cobb angle: 28.1°± 7.3°) underwent ultrasound assessment of spinal curvature in five positions (standing, supine, prone, sitting bending, prone bending positions) and that within orthosis. Differences and correlations were analyzed between the spinal curvatures in the five positions and that within orthosis. RESULTS:: The mean in-orthosis curvature was 11.2° while the mean curvatures in five studied positions were 18.7° (standing), 10.7° (supine), 10.7° (prone), -3.5° (prone bending), and -6.5° (sitting bending). The correlation coefficients of the in-orthosis curvature and that in five studied positions were r = 0.65 (standing), r = 0.76 (supine), r = 0.87 (prone), r = 0.41 (prone bending), and r = 0.36 (sitting bending). CONCLUSION:: The curvature in recumbent positions (supine and prone) is highly correlated to the initial in-orthosis curvature without significant difference. Thus, the initial effect of spinal orthosis could be predicted by the curvature in the recumbent positions (especially prone position) at the pre-orthosis stage. CLINICAL RELEVANCE: Prediction of in-orthosis correction at pre-orthosis stage is valuable for spinal orthosis design. This study suggests assessing the spinal curvature in recumbent position (especially prone position) to predict the initial in-orthosis correction for optimizing the orthosis design.

Supplemental rods are needed to maximally reduce rod strain across the lumbosacral junction with TLIF but not ALIF in long constructs.

BACKGROUND CONTEXT: Rod fracture at the lumbosacral (LS) junction remains challenging in long segment fusions and likely stems from increased LS strain. Reduction of LS instrumentation strain may help reduce fracture rates. PURPOSE: The goal of this investigation was to assess the effect of supplemental posterior 4-rod (4R) construction on LS stability and rod strain compared with standard 2-rod (2R) construction in a long segment fusion model. STUDY DESIGN/SETTING: Cadaveric biomechanical study. OUTCOME MEASURES: Range of motion (ROM), rod strain, and sacral screw (SS) bending moments during flexion, extension, compression, lateral bending, and axial rotation. METHODS: Standard nondestructive flexibility tests (7.5 Nm) were performed on 14 cadaveric specimens (L1-ilium) to assess ROM stability, rod strain, and SS bending moment of a supplemental 4R construction versus standard 2R construction. Specimens were equally divided into L5-S1 anterior lumbar interbody fusion (ALIF) or L5-S1 transforaminal lumbar interbody fusion (TLIF) groups. Three conditions were tested in each group: (1) no lumbar interbody fusion (No LIF)+2R, (2) ALIF or TLIF+2R, and (3) ALIF or TLIF+4R. Data were analyzed using repeated measures analysis of variance (ANOVA) or ANOVA. RESULTS: No differences were observed between groups 1 and 2 for age, sex, bone mineral density, or baseline ROM (p>.09). Overall, TLIF+2R demonstrated greater ROM than ALIF+4R in extension (p=003), with greater rod strain in flexion, extension, and compression (p<.001), and greater SS in compression and AR (p<.04). Compared with TLIF+2R, TLIF+4R resulted in reduced rod strain in flexion, extension, compression, and LB (p<.04), as well as SS in AR (p<.001). The TLIF+4R yielded biomechanics comparable to ALIF+2R in ROM and rod strain but SS inflexion, extension, compression, and AR remained elevated (p<001). The ALIF+4R did not significantly improve ROM, rod strain, or SS (p>.11). CONCLUSIONS: The use of ALIF and adding accessory rods with TLIF significantly reduced LS rod strain in a long segment cadaveric model with iliac fixation. CLINICAL SIGNIFICANCE: Reducing strain could decrease the risk of failure associated with long segment fixation.