Insufficient Evidence for Load as the Primary Cause of Nonspecific (Chronic) Low Back Pain. A Scoping Review

OBJECTIVE: To assess the causal role of the relationship between loading and the onset of nonspecific low back pain (NSLBP) and persistence of NSLBP (chronic low back pain [CLBP]). DESIGN: Scoping review. LITERATURE SEARCH: We searched the literature from 2010 until May 2021 using a combination of terms related to (spinal) load and the Bradford-Hill (BH) criteria. STUDY SELECTION CRITERIA: Operational definitions were developed for every criterion of the BH framework for causality. Study selection was based on the causal role of load in the onset of NSLBP and persistence of chronic low back pain. DATA SYNTHESIS: The BH criteria were operationalized, and causation was considered established when evidence supported the BH criteria strength, temporality, biological gradient, experiment, and biological plausibility. RESULTS: Twenty-two studies were included. There was no consistent support for an association between load and the incidence of NSLBP, or that more load increased the risk of NSLBP/CLBP. Half of the studies did not support specific load exposures to increase incidence of or increase pain in NSLBP/CLBP. Half of studies did not support load preceding NSLBP. No study supported plausible biological explanations to influence the relationship between load and NSLBP/CLBP, or that similar causes have similar effects on NSLBP. Nine of 10 experimental studies did not support that load results in NSLBP or that relieving load reduces NSLBP/CLBP. CONCLUSION: There was insufficient evidence to support a causal relationship between loading and the onset and persistence of NSLBP/CLBP based on the BH criteria. These results question the role of load management as the only/primary strategy to prevent onset and persistence of NSLBP/CLBP. J Orthop Sports Phys Ther 2024;54(3):1-15. Epub 25 January 2024. doi:10.2519/jospt.2024.11314.

Towards space-deployable laser stabilization systems based on vibration-insensitive cubic cavities with crystalline coatings

We present the development of a transportable laser frequency stabilization system with application to both optical clocks and a next-generation gravity mission (NGGM) in space. This effort leverages a 5-cm long cubic cavity with crystalline coatings operating at room temperature and with a center wavelength of 1064 nm. The cavity is integrated in a custom vacuum chamber with dedicated low-noise locking electronics. Our vacuum-mounted cavity and control system are well suited for space applications, exhibiting state-of-the-art noise performance while being resilient to radiation exposure, vibration, shock, and temperature variations. Furthermore, we demonstrate a robust means of automatically (re)locking the laser to the cavity when resonance is lost. We show that the mounted cavity is capable of reaching technology readiness level (TRL) 6, paving the way for high-performance ultrastable laser systems and eventually optical atomic clocks amenable to future satellite platforms.

Functional popliteal angle tests improve identification of short hamstring muscle-tendon length in patients with a central neurological lesion

This study introduces a functional exercise protocol to improve the identification for short hamstring muscle-tendon length (HMTL), a common contributor to crouch gait in patients with central neurological lesions (CNL). The functional exercise protocol incorporates a knee extension movement with hip in a flexed position, while standing on one leg (functional popliteal angle test) and walking with large steps to the current standard protocol (walking at comfortable speed and as fast as possible). The main aim was to establish whether the new protocol allows better determination of maximum HMTLs and diagnostics of short HMTL in patients with a CNL. Lower limb 3D marker position data from 39 patient limbs and 10 healthy limbs performing the exercises were processed in OpenSim to extract HMTLs. The new protocol provoked significantly larger HMTLs compared to the current standard protocol. The total number of limbs classified as having too short HMTLs reduced from 16 to 4 out of a total of 30 limbs walking in crouch. The new protocol improves determination of maximum HMTL, thereby improving short HMTL diagnostics and identification of patients in need of lengthening treatment. Inter-individual variability observed among patients, indicating the need to include all exercises for comprehensive diagnosis.

Biomechanical Load of Neck and Lumbar Joints in Open-Surgery Training

The prevalence of musculoskeletal symptoms (MSS) like neck and back pain is high among open-surgery surgeons. Prolonged working in the same posture and unfavourable postures are biomechanical risk factors for developing MSS. Ergonomic devices such as exoskeletons are possible solutions that can reduce muscle and joint load. To design effective exoskeletons for surgeons, one needs to quantify which neck and trunk postures are seen and how much support during actual surgery is required. Hence, this study aimed to establish the biomechanical profile of neck and trunk postures and neck and lumbar joint loads during open surgery (training). Eight surgical trainees volunteered to participate in this research. Neck and trunk segment orientations were recorded using an inertial measurement unit (IMU) system during open surgery (training). Neck and lumbar joint kinematics, joint moments and compression forces were computed using OpenSim modelling software and a musculoskeletal model. Histograms were used to illustrate the joint angle and load distribution of the neck and lumbar joints over time. During open surgery, the neck flexion angle was 71.6% of the total duration in the range of 10~40 degrees, and lumbar flexion was 68.9% of the duration in the range of 10~30 degrees. The normalized neck and lumbar flexion moments were 53.8% and 35.5% of the time in the range of 0.04~0.06 Nm/kg and 0.4~0.6 Nm/kg, respectively. Furthermore, the neck and lumbar compression forces were 32.9% and 38.2% of the time in the range of 2.0~2.5 N/kg and 15~20 N/kg, respectively. In contrast to exoskeletons used for heavy lifting tasks, exoskeletons designed for surgeons exhibit lower support torque requirements while additional degrees of freedom (DOF) are needed to accommodate combinations of neck and trunk postures.

Side-effects and adverse events of a shoulder- and back-support exoskeleton in workers: A systematic review

INTRODUCTION

While the biomechanical effects of exoskeletons are well studied, research about potential side-effects and adverse events are limited. The aim of this systematic review was to provide an overview of the side-effects and adverse events on shoulder- and back-support exoskeletons during work tasks.

METHODS

Four in-field studies and 32 laboratory studies were included in this review, reporting on n = 18 shoulder exoskeletons, n = 9 back exoskeletons, n = 1 full body with a supernumerary arm, and n = 1 combination of shoulder and back exoskeleton.

RESULTS

The most frequent side-effect reported is discomfort (n = 30), followed by a limited usability of the exoskeleton (n = 16). Other identified side-effects and adverse events were changes in muscle activity, mobility, task performance, balance and posture, neurovascular supply, gait parameters and precision. An incorrect fit of the exoskeleton and the decreased degrees of freedom are most often reported as causes of these side-effects. Two studies did not find any side-effects. This review also showed that there are differences in the occurrence of side-effects in gender, age, and physical fitness. Most studies (89%) were conducted in a laboratory setting. Most studies (97%) measured short-term effects only. Psychological and social side-effects or adverse events were not reported. Side-effects and adverse events for active exoskeletons were understudied (n = 4).

CONCLUSION

It was concluded that the evidence for side-effects and adverse events is limited. If available, it mainly consists of reports of mild discomfort and limited usability. Generalisation is limited because studies were conducted in lab settings and measured short term only, and most participants were young male workers.

Pilot Validation Study of Inertial Measurement Units and Markerless Methods for 3D Neck and Trunk Kinematics during a Simulated Surgery Task

Surgeons are at high risk for developing musculoskeletal symptoms (MSS), like neck and back pain. Quantitative analysis of 3D neck and trunk movements during surgery can help to develop preventive devices such as exoskeletons. Inertial Measurement Units (IMU) and markerless motion capture methods are allowed in the operating room (OR) and are a good alternative for bulky optoelectronic systems. We aim to validate IMU and markerless methods against an optoelectronic system during a simulated surgery task. Intraclass correlation coefficient (ICC (2,1)), root mean square error (RMSE), range of motion (ROM) difference and Bland-Altman plots were used for evaluating both methods. The IMU-based motion analysis showed good-to-excellent (ICC 0.80-0.97) agreement with the gold standard within 2.3 to 3.9 degrees RMSE accuracy during simulated surgery tasks. The markerless method shows 5.5 to 8.7 degrees RMSE accuracy (ICC 0.31-0.70). Therefore, the IMU method is recommended over the markerless motion capture.

Flexible Machine Learning Algorithms for Clinical Gait Assessment Tools

The current gold standard of gait diagnostics is dependent on large, expensive motion-capture laboratories and highly trained clinical and technical staff. Wearable sensor systems combined with machine learning may help to improve the accessibility of objective gait assessments in a broad clinical context. However, current algorithms lack flexibility and require large training datasets with tedious manual labelling of data. The current study tests the validity of a novel machine learning algorithm for automated gait partitioning of laboratory-based and sensor-based gait data. The developed artificial intelligence tool was used in patients with a central neurological lesion and severe gait impairments. To build the novel algorithm, 2% and 3% of the entire dataset (567 and 368 steps in total, respectively) were required for assessments with laboratory equipment and inertial measurement units. The mean errors of machine learning-based gait partitions were 0.021 s for the laboratory-based datasets and 0.034 s for the sensor-based datasets. Combining reinforcement learning with a deep neural network allows significant reduction in the size of the training datasets to <5%. The low number of required training data provides end-users with a high degree of flexibility. Non-experts can easily adjust the developed algorithm and modify the training library depending on the measurement system and clinical population.

Conservative interventions to improve foot progression angle and clinical measures in orthopedic and neurological patients - A systematic review and meta-analysis

To establish the comparative effects of conservative interventions on modifying foot progression angle (FPA) in children and adults with orthopaedic and neurological disease was the main aim of the literature review. Pubmed, Embase, Cinahl, and Web of Science were systematically searched for studies evaluating the effects of conservative interventions on correcting the FPA. The study protocol was registered with PROSPERO (CRD42020143512). Two reviewers independently assessed studies for inclusion and quality. Studies that assessed conservative interventions that could have affected the FPA and objectively measured the FPA were included. Within group Mean Differences (MD) and Standardized Mean Differences (SMDs) of the interventions were calculated for the change in FPA and gait performance (walking speed, stride/step length) and clinical condition (pain). Intervention effects on FPA were synthesized via meta-analysis or qualitatively. 41 studies were identified. For patients with knee osteoarthritis gait training interventions (MD = 6.69° and MD = 16.06°) were significantly more effective than mechanical interventions (MD = 0.44°) in modifying the FPA towards in-toeing (p < 0.00001). Increasing or decreasing the FPA significantly improved pain in patients with medial knee OA. Results were inconclusive for the effectiveness of gait training and mechanical devices in patients with neurological diseases. Gait feedback training is more effective than external devices to produce lasting improvements in FPA, reduce pain, and maintain gait performance in patients with medial knee OA. However, in neurological patients, the effects of external devices on improvements in FPA depends on the interaction between patient-specific impairments and the technical properties of the external device.

Effects of rocker radii with two longitudinal bending stiffnesses on plantar pressure distribution in the forefoot

INTRODUCTION

Outsole parameters of the shoe can be adapted to offload regions of pain or region of high pressures. Previous studies already showed reduced plantar pressures in the forefoot due to a proximally placed apex position and higher longitudinal bending stiffness (LBS). The aim of this study was to determine the effect of changes in rocker radii and high LBS on the plantar pressure profile during gait.

METHOD

10 participants walked in seven shoe conditions of which one control shoe and six rocker shoes with small, medium and large rocker radii and low and high longitudinal bending stiffness. Pedar in-shoe plantar pressure measuring system was used to quantify plantar pressures while walking on a treadmill at self-selected walking speed. Peak plantar pressure, maximum mean pressure and force-time integral were analyzed with Generalized Estimated Equation (GEE) and Tukey post hoc correction (α = .05).

RESULTS

Significantly lower plantar pressures were found in the first toe, toes 2-5, distal and proximal forefoot in all rocker shoe conditions as compared to the control shoe. Plantar pressures in the first toe and toes 2-5 were significantly lower in the small radius compared to medium and large radii. For the distal forefoot both small and medium radii significantly reduced plantar pressure compared to large radii. Low LBS reduced plantar pressure at the first toe significantly compared to high LBS independent of the rocker radius. Plantar pressures in the distal forefoot and toes 2-5 were lower in high LBS compared to low LBS.

CONCLUSION

Manipulation of the rocker radius and LBS can effectively reduce peak plantar pressures in the forefoot region during gait. In line with previous studies, we showed that depending on the exact target location for offloading, different combinations of rocker radius and LBS need to be adopted to maximize treatment effects.

Old adults preserve motor flexibility during rapid reaching

Purpose

Our ability to flexibly coordinate the available degrees of freedom allows us to perform activities of daily living under various task constraints. Healthy old adults exhibit subclinical peripheral and central nervous system dysfunctions, possibly compromising the flexibility in inter-joint coordination during voluntary movements and the ability to adapt to varying task constraints.

Method

We examined how healthy old (75.4 ± 5.2 years, n = 14) compared with young adults (24.3 ± 2 years, n = 15) make use of the available motor flexibility to adapt to physical and dexterity constraints during a rapid goal-directed reaching task. We manipulated physical and dexterity demands by changing, respectively, external resistance and target size. Motor flexibility was quantified by an uncontrolled manifold (UCM) analysis.

Results

We found that healthy young and old adults employ similar motor flexibility as quantified by the ratio between goal equivalent and non-goal equivalent variability (V_Ratio) and were similarly able to adapt to increases in physical and dexterity demands during goal-directed rapid reaching (V_Ratio: p = .092; young: 0.548 ± 0.113; old: 0.264 ± 0.117). Age affected end-effector kinematics. Motor flexibility and end-effector kinematics did not correlate.

Conclusion

The data challenge the prevailing view that old age affects movement capabilities in general and provide specific evidence that healthy old adults preserve motor flexibility during a reaching task. Future studies applying UCM analysis should examine if experimental set-ups limit movement exploration, leaving possible age differences undetected.

Ultrafast two-dimensional infrared spectroscopy of guanine-cytosine base pairs in DNA oligomers

NH and OH stretching excitations of hydrated double-stranded DNA oligomers containing guanine-cytosine (GC) base pairs in a Watson-Crick geometry are studied by two-dimensional (2D) infrared spectroscopy. The 2D spectra measured at a low hydration level (∼4 water molecules/base pair) are dominated by NH stretch contributions from the NH2 groups of G and C and the NH group of G. Partially hydrated NH2 groups display red-shifted NH stretch frequencies and a mixing of the wave functions of the two local NH oscillators via the mechanical vibrational coupling. The NH stretch lifetimes are of the order of 200-300 fs. Weak couplings exist between NH stretch oscillators within a base pair, while interactions between neighboring GC pairs in the double helix are negligible. The absence of spectral diffusion on a 1 ps time scale suggests a relatively rigid structure of the hydrogen bonds between DNA and residual water molecules. 2D spectra recorded with fully hydrated DNA oligomers exhibit NH and OH stretch contributions with a weak influence of water fluctuations on the NH stretch lineshapes. The femtosecond spectral diffusion of OH stretch excitations is slower than that in bulk H2O and originates from structural fluctuations of the water shell and the formation of a vibrationally hot ground state by vibrational relaxation. We compare our findings with measurements on hydrated adenine-thymine DNA oligomers and anhydrous GC base pairs in solution.

Not all is lost: old adults retain flexibility in motor behaviour during sit-to-stand

Sit-to-stand is a fundamental activity of daily living, which becomes increasingly difficult with advancing age. Due to severe loss of leg strength old adults are required to change the way they rise from a chair and maintain stability. Here we examine whether old compared to young adults differently prioritize task-important performance variables and whether there are age-related differences in the use of available motor flexibility. We applied the uncontrolled manifold analysis to decompose trial-to-trial variability in joint kinematics into variability that stabilizes and destabilizes task-important performance variables. Comparing the amount of variability stabilizing and destabilizing task-important variables enabled us to identify the variable of primary importance for the task. We measured maximal isometric voluntary force of three muscle groups in the right leg. Independent of age and muscle strength, old and young adults similarly prioritized stability of the ground reaction force vector during sit-to-stand. Old compared to young adults employed greater motor flexibility, stabilizing ground reaction forces during sit-to-sand. We concluded that freeing those degrees of freedom that stabilize task-important variables is a strategy used by the aging neuromuscular system to compensate for strength deficits.

N-H stretching excitations in adenosine-thymidine base pairs in solution: pair geometries, infrared line shapes, and ultrafast vibrational dynamics

We explore the N-H stretching vibrations of adenosine-thymidine base pairs in chloroform solution with linear and nonlinear infrared spectroscopy. Based on estimates from NMR measurements and ab initio calculations, we conclude that adenosine and thymidine form hydrogen bonded base pairs in Watson-Crick, reverse Watson-Crick, Hoogsteen, and reverse Hoogsteen configurations with similar probability. Steady-state concentration and temperature dependent linear FT-IR studies, including H/D exchange experiments, reveal that these hydrogen-bonded base pairs have complex N-H/N-D stretching spectra with a multitude of spectral components. Nonlinear 2D-IR spectroscopic results, together with IR-pump-IR-probe measurements, as also corroborated by ab initio calculations, reveal that the number of N-H stretching transitions is larger than the total number of N-H stretching modes. This is explained by couplings to other modes, such as an underdamped low-frequency hydrogen-bond mode, and a Fermi resonance with NH(2) bending overtone levels of the adenosine amino-group. Our results demonstrate that modeling based on local N-H stretching vibrations only is not sufficient and call for further refinement of the description of the N-H stretching manifolds of nucleic acid base pairs of adenosine and thymidine, incorporating a multitude of couplings with fingerprint and low-frequency modes.

Ultrafast Energy Redistribution in Local Hydration Shells of Phospholipids: A Two-Dimensional Infrared Study

Structural and functional properties of phospholipids are strongly influenced by dynamics of their hydration shells. Here, we show that local water pools as small as three water molecules around the polar headgroups in phospholipid reverse micelles (dioleoylphosphatidylcholine, DOPC) serve as efficient sinks of excess energy released during vibrational relaxation. Transient two-dimensional (2D) infrared spectra of OH stretching excitations of H2O shells demonstrate a subpicosecond buildup of a hot water ground state, in which excess energy is randomized in low-frequency modes. An analysis of center line slopes of the 2D spectra reveals kinetics of energy dissipation that are significantly faster than structural fluctuations of the water pool and remain unchanged at intermediate hydration levels between three and eight water molecules per polar headgroup. Our results suggest that confined small water pools in biomolecular systems are sufficient to dissipate excess energy originating from the decay of electronic or vibrational excitations.

N-H stretching modes of adenosine monomer in solution studied by ultrafast nonlinear infrared spectroscopy and ab initio calculations

The N-H stretching vibrations of adenine, one of the building blocks of DNA, are studied by combining infrared absorption and nonlinear two-dimensional infrared spectroscopy with ab initio calculations. We determine diagonal and off-diagonal anharmonicities of N-H stretching vibrations in chemically modified adenosine monomer dissolved in chloroform. For the single-quantum excitation manifold, the normal mode picture with symmetric and asymmetric NH(2) stretching vibrations is fully appropriate. For the two-quantum excitation manifold, however, the interplay between intermode coupling and frequency shifts due to a large diagonal anharmonicity leads to a situation where strong mixing does not occur. We compare our findings with previously reported values obtained on overtone spectroscopy of coupled hydrogen stretching oscillators.

Effects of glutamine supplementation of an amino acid-based purified diet on intestinal mucosal integrity in cats with methotrexate-induced enteritis

OBJECTIVE

To determine effects of glutamine-supplemented and glutamine-free amino acid-based purified diets, compared with a dry expanded diet, on intestinal structure and function in a model that used cats with methotrexate-induced enteritis.

ANIMALS

18 adult specific-pathogen-free cats.

PROCEDURE

12 cats were given intragastric feedings of an amino acid-based purified diet supplemented with glutamine (7% [wt:wt]) or an isonitrogenous amount of glycine and alanine; 6 cats consumed a dry expanded diet. After 21 days, cats received methotrexate (MTX; 11 mg/kg of body weight, IV). Intestinal permeability testing was performed immediately before and 66 hours after MTX administration. Celiotomy was performed 72 hours after MTX administration for aseptic removal of mesenteric lymph nodes, collection of full-thickness intestinal biopsy specimens, determination of intestinal cellular proliferation, and collection of aortic and portal venous blood samples for determination of arteriovenous amino acid concentrations across the intestine.

RESULTS

Administration of MTX was associated with severe enterotoxicosis manifested as diarrhea (8/12 cats), vomiting (12/12), and positive results for bacterial culture of mesenteric lymph nodes (12/12) in cats receiving the purified diets, independent of glutamine supplementation. Diet did not affect villus tip length and villus surface area in the small intestine or cellular proliferation. Administration of MTX was associated with significantly increased intestinal permeability, which was not attenuated by glutamine supplementation.

CONCLUSIONS

Feeding of a glutamine-supplemented amino acid-based purified diet was unable to preserve intestinal function in cats with MTX-induced enteritis.

CLINICAL RELEVANCE

Intestinal morphologic alterations correlate poorly with intestinal function as measured by means of bacterial translocation and intestinal permeability.

Cell turgor changes associated with ripening in tomato pericarp tissue

The pressure microprobe was used to determine whether the turgor pressure in tomato (Lycopersicon esculentum Mill., variety "Castelmart") pericarp cells changed during fruit ripening. The turgor pressure of cells located 200 to 500 micrometers below the fruit epidermis was uniform within the same tissue (typically +/- 0.02 megapascals), and the highest turgors observed (<0.2 megapascals) were much less than expected, based on tissue osmotic potential (-0.6 to -0.7 megapascals). These low turgor values may indicate the presence of apoplastic solutes. In both intact fruit and cultured discs of pericarp tissue, a small increase in turgor preceded the onset of ripening, and a decrease in turgor occurred during ripening. Differences in the turgor of individual intact fruit occurred 2 to 4 days before parallel differences in their ripening behavior were apparent, indicating that changes in turgor may reflect physiological changes at the cell level that precede expression of ripening at the tissue level.

Collagen crosslinking and cartilage glycosaminoglycan composition in normal and scoliotic chickens

The amounts of lysine-derived crosslinks in collagens from tendon, cartilage, intervertebral disc, and bone and changes in the composition of sternal cartilage glycosaminoglycans were estimated in two lines of chickens, a control-isogenic line and a line that develops scoliosis. In the scoliotic line, scoliosis first appears at 3-4 weeks and progressively increases in severity and incidence so that 90% of the birds express the lesion by week 10. We have reported previously that cartilage, tendon, and bone collagens from scoliotic birds are more soluble than corresponding collagens from normal birds. Herein, collagen crosslinking and altered proteoglycan metabolism are examined as possible mechanisms for the differences in collagen solubility. At 1 week of age there were fewer reducible crosslinking amino acids (hydroxylysinonorleucine, dihydroxylysinonorleucine, and lysinonorleucine) in collagens from sternal cartilage and tendon in the scoliotic line than in the isogenic line. However, by week 3 and at weeks 5 or 7 values were similar in both groups. The amounts of hydroxypyridinium in vertebral bone and intervertebral disc collagen were also similar in both groups of birds. Consequently, differences in collagen crosslinking do not appear to be a persistent developmental defect underlying the expression of scoliosis in the model. However, differences were observed in cartilage proteoglycans and glycosaminoglycans from the scoliotic line that were not present in cartilage from the isogenic line. The average molecular weight of the uronide-containing glycosaminoglycans was 30% less in the scoliotic line than in the isogenic line, i.e., 12,000 compared to 18,000. The size distribution of cartilage proteoglycans from the scoliotic line also differed from that of proteoglycans from the isogenic line.(ABSTRACT TRUNCATED AT 250 WORDS)

Diet as an external factor in the expression of scoliosis in a line of susceptible chickens

An inbred line of chickens that develops severe scoliosis, an isogenic line and a line of birds derived from crossing the isogenic and inbred lines were used to study factors that influence the expression of scoliosis. Using the line of birds derived from the cross, the incidence of the lesion, defined as a spinal curve greater than 20 degrees, was influenced by deficiencies of copper, manganese or vitamin B-6. In the cross, scoliosis was expressed in 40-50% of birds. Vitamin B-6, manganese or copper deficiency, however, caused an increase in expression to 60-75% of birds. In contrast, protein deficiency, mild vitamin A deprivation, pantothenic deficiency, food restriction or calcium deficiency did not influence expression. Also, the addition of zinc (400 micrograms/g) or cadmium (5 micrograms/g) to a commercial nonpurified diet did not influence expression. That vitamin B-6, manganese and copper are dietary factors important to the expression of scoliosis may be related to their roles in the formation of connective tissue components, such as matrix glycoproteins, collagen or proteoglycans. For example, alterations and abnormalities in connective tissue may partly underlie progression of scoliosis and its potential for expression.

Scoliosis in chickens. A model for the inherited form of adolescent scoliosis

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