Biomedical subjects

Manohar M Panjabi

Publications and source records attributed to Manohar M Panjabi.

At least 19 recordsLinked to original sources

PubMed2006

Hybrid multidirectional test method to evaluate spinal adjacent-level effects.

BACKGROUND: Several clinical studies have documented long-term adjacent-level effects of spinal fusion, due to stress concentration and motion loss at the fused segment. Non-fusion motion preservation devices are designed to eliminate or slow down such adverse effects. Therefore, appropriate biomechanical evaluation of the adjacent-level effects in spine is important and timely. Although many biomechanical studies are available and have provided some understanding of the adjacent-level effects, results have large variation and are conflicting, mostly due to the use of inappropriate and ill-defined methods. A new test method especially designed to study spinal adjacent-level effects is needed. METHODS: The proposed Hybrid method uses unconstrained pure moment to provide rotation-input for multi-directional testing. The new method has four steps: (1) Intact spine specimen with entire mobile region is used. The specimen is prepared to measure various biomechanical parameters, e.g., disc pressures, ligament strains, and facet loads. (2) Appropriate unconstrained pure moment is applied to the intact specimen and total range of motion is determined. (3) Unconstrained pure moment is applied to the spinal construct (specimen with an implant) until the total range of motion of the construct equals that of the intact. (4) Statistical comparison of the biomechanical parameters between the construct and intact quantifies the adjacent-level effects. FINDINGS: The uniqueness of the proposed method, to study the adjacent level effects due to fusion and non-fusion devices, is that it applies the needed rotation-input to the spine specimen, using available methodology with minimal modification. INTERPRETATION: Previous studies have lacked appropriate and well-defined methodologies to evaluate spinal adjacent-level effects. The proposed method uses well-known methodology and yields high quality, and laboratory-independent results for the fusion and non-fusion devices.

Biomechanical Phenomena↗

PubMed2006

Neck ligament strength is decreased following whiplash trauma.

BACKGROUND: Previous clinical studies have documented successful neck pain relief in whiplash patients using nerve block and radiofrequency ablation of facet joint afferents, including capsular ligament nerves. No previous study has documented injuries to the neck ligaments as determined by altered dynamic mechanical properties due to whiplash. The goal of the present study was to determine the dynamic mechanical properties of whiplash-exposed human cervical spine ligaments. Additionally, the present data were compared to previously reported control data. The ligaments included the anterior and posterior longitudinal, capsular, and interspinous and supraspinous ligaments, middle-third disc, and ligamentum flavum. METHODS: A total of 98 bone-ligament-bone specimens (C2-C3 to C7-T1) were prepared from six cervical spines following 3.5, 5, 6.5, and 8 g rear impacts and pre- and post-impact flexibility testing. The specimens were elongated to failure at a peak rate of 725 (SD 95) mm/s. Failure force, elongation, and energy absorbed, as well as stiffness were determined. The mechanical properties were statistically compared among ligaments, and to the control data (significance level: P < 0.05; trend: P < 0.1). The average physiological ligament elongation was determined using a mathematical model. RESULTS: For all whiplash-exposed ligaments, the average failure elongation exceeded the average physiological elongation. The highest average failure force of 204.6 N was observed in the ligamentum flavum, significantly greater than in middle-third disc and interspinous and supraspinous ligaments. The highest average failure elongation of 4.9 mm was observed in the interspinous and supraspinous ligaments, significantly greater than in the anterior longitudinal ligament, middle-third disc, and ligamentum flavum. The average energy absorbed ranged from 0.04 J by the middle-third disc to 0.44 J by the capsular ligament. The ligamentum flavum was the stiffest ligament, while the interspinous and supraspinous ligaments were most flexible. The whiplash-exposed ligaments had significantly lower (P = 0.036) failure force, 149.4 vs. 186.0 N, and a trend (P = 0.078) towards less energy absorption capacity, 308.6 vs. 397.0 J, as compared to the control data. CONCLUSION: The present decreases in neck ligament strength due to whiplash provide support for the ligament-injury hypothesis of whiplash syndrome.

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PubMed2006

Dynamic sagittal flexibility coefficients of the human cervical spine.

The goal of the present study was to determine the dynamic sagittal flexibility coefficients, including coupling coefficients, throughout the human cervical spine using rear impacts. A biofidelic whole cervical spine model (n=6) with muscle force replication and surrogate head was rear impacted at 5 g peak horizontal accelerations of the T1 vertebra within a bench-top mini-sled. The dynamic main and coupling sagittal flexibility coefficients were calculated at each spinal level, head/C1 to C7/T1. The average flexibility coefficients were statistically compared (p<0.05) throughout the cervical spine. To validate the coefficients, the average computed displacement peaks, obtained using the average flexibility matrices and the measured load vectors, were statistically compared to the measured displacement peaks. The computed and measured displacement peaks showed good overall agreement, thus validating the computed flexibility coefficients. These peaks could not be statistically differentiated, with the exception of extension rotation at head/C1 and posterior shear translation at C7/T1. Head/C1 was significantly more flexible than all other spinal levels. The cervical spine was generally more flexible in posterior shear, as compared to axial compression. The coupling coefficients indicated that extension moment caused coupled posterior shear translation while posterior shear force caused coupled extension rotation. The present results may be used towards the designs of anthropometric test dummies and mathematical models that better simulate the cervical spine response during dynamic loading.

Accidents, Traffic↗

PubMed2006

Alar, transverse, and apical ligament strain due to head-turned rear impact.

STUDY DESIGN: Determination of alar, transverse, and apical ligament strains during simulated head-turned rear impact. OBJECTIVES: To quantify the alar, transverse, and apical ligament strains during head-turned rear impacts of increasing severity, to compare peak strains with baseline values, and to investigate injury mechanisms. SUMMARY OF BACKGROUND DATA: Clinical and epidemiologic studies have documented upper cervical spine ligament injury due to severe whiplash trauma. There are no previous biomechanical studies investigating injury mechanisms during head-turned rear impacts. METHODS: Whole cervical spine specimens (C0-T1) with surrogate head and muscle force replication were used to simulate head-turned rear impacts of 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. The peak ligament strains during impact were compared (P < 0.05) to baseline values, obtained during a noninjurious 2 g acceleration. RESULTS: The highest right and left alar ligament average peak strains were 41.1% and 40.8%, respectively. The highest transverse and apical ligament average strain peaks were 17% and 21.3%, respectively. There were no significant increases in the average peak ligament strains at any impact acceleration compared with baseline. CONCLUSIONS: The alar, transverse, and apical ligaments are not at risk for injury due to head-turned rear impacts up to 8 g. The upper cervical spine symptomatology reported by whiplash patients may, therefore, be explained by other factors, including severe whiplash trauma in excess of 8 g peak acceleration and/or other impact types, e.g., offset, rollover, and multiple collisions.

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PubMed2006

Dynamic intervertebral foramen narrowing during simulated rear impact.

STUDY DESIGN: A biomechanical study of intervertebral foraminal narrowing during simulated automotive rear impacts. OBJECTIVES: To quantify foraminal width, height, and area narrowing during simulated rear impact, and evaluate the potential for nerve root and ganglion impingement in individuals with and without foraminal spondylosis. SUMMARY OF BACKGROUND DATA: Muscle weakness and paresthesias, documented in whiplash patients, have been associated with neural compression within the cervical intervertebral foramen. To our knowledge, no studies have comprehensively examined dynamic changes in foramen dimensions. METHODS: There were 6 whole cervical spine specimens (average age 70.8 years) with muscle force replication and surrogate head that underwent simulated rear impact at 3.5, 5, 6.5, and 8 g, following noninjurious baseline 2 g acceleration. Peak dynamic narrowing of foraminal width, height, and area were determined during each impact and statistically compared to baseline narrowing. RESULTS: Significant increases (P < 0.05) in average peak foraminal width narrowing above baseline were observed at C5-C6 beginning with 3.5 g impact. No significant increases in average peak foraminal height narrowing were observed, while average peak foraminal areas were significantly narrower than baseline at C4-C5 at 3.5, 5, and 6.5 g. CONCLUSIONS: Extrapolation of the present results indicated that the highest potential for ganglia compression injury was at the lower cervical spine, C5-C6 and C6-C7. Acute ganglia compression may produce a sensitized neural response to repeat compression, leading to chronic radiculopathy following rear impact.

Accidents, Traffic↗

PubMed2006

Multiplanar cervical spine injury due to head-turned rear impact.

STUDY DESIGN: Head-turned whole cervical spine model was stabilized with muscle force replication and subjected to simulated rear impacts of increasing severity. Multiplanar flexibility testing evaluated any resulting injury. OBJECTIVES: To identify and quantify cervical spine soft tissue injury and injury threshold acceleration for head-turned rear impact, and to compare these data with previously published head-forward rear and frontal impact results. SUMMARY OF BACKGROUND DATA: Epidemiologically and clinically, head-turned rear impact is associated with increased injury severity and symptom duration, as compared to forward facing. To our knowledge, no biomechanical data exist to explain this finding. METHODS: Six human cervical spine specimens (C0-T1) with head-turned and muscle force replication were rear impacted at 3.5, 5, 6.5, and 8 g, and flexibility tests were performed before and after each impact. Soft tissue injury was defined as a significant increase (P < 0.05) in intervertebral flexibility above baseline. Injury threshold was the lowest T1 horizontal peak acceleration that caused the injury. RESULTS: The injury threshold acceleration was 5 g with injury occurring in extension or axial rotation at C3-C4 through C7-T1, excluding C6-C7. Following 8 g, 3-plane injury occurred in extension and axial rotation at C5-C6, while 2-plane injury occurred at C7-T1. CONCLUSIONS: Head-turned rear impact caused significantly greater injury at C0-C1 and C5-C6, as compared to head-forward rear and frontal impacts, and resulted in multiplanar injuries at C5-C6 and C7-T1.

Accidents, Traffic↗

PubMed2006

Screw fixation of scaphoid fractures: a biomechanical assessment of screw length and screw augmentation.

PURPOSE: To assess the biomechanical stability relative to screw length and K-wire augmentation in scaphoid fracture fixation using a flexibility testing protocol and cadaver scaphoids whose soft tissue attachments remained undisturbed. Our hypothesis was 2-fold: increasing screw length and augmenting fixation with a K-wire would improve fracture fragment stability, individually and in combination. METHODS: Flexion and extension loading applied through wrist tendons was performed on 10 cadaveric wrists after volar wedge scaphoid osteotomy and internal fixation. Each wrist participated in 3 experimental groups: short screw, long screw, and long screw augmented with a K-wire transfixing the distal pole to the capitate. Interfragmentary displacements were measured. RESULTS: Analysis of variance showed significantly less fracture fragment motion with longer screws than with short screws in 4 of the 6 displacement axes. The flexion/extension axis rotations for the short, long, and augmented long-screw groups were 8.2 degrees +/- 4.8 degrees, 3.9 degrees +/- 1.6 degrees, and 1.8 degrees +/- 1.3 degrees, respectively. Although K-wire augmentation reduced displacement of the fracture fragments it did not decrease interfragmentary motion significantly when compared with the long-screw group. CONCLUSIONS: Under physiologically applied loading of cadaveric wrists with unstable scaphoid waist fractures the long screw provided significantly greater stability than the short screw. Although K-wire augmentation in the long-screw group did improve stability the improvements were not significant. Based in part on the biomechanical data from this study it is our recommendation that the optimally placed screw for scaphoid fracture fixation stability is a long screw positioned down the central axis of the scaphoid deep into subchondral bone.

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PubMed2006

Calculation of dynamic spinal ligament deformation.

OBJECTIVE: Previous methods to determine spinal ligament deformation have included either custom-designed transducers or computational methods using rigid body transformation of kinematic data. Goals of the present study were to describe a computational methodology to determine dynamic deformations of an arbitrarily oriented ligament in a spine specimen and its associated errors. METHODS: Calculation of ligament deformation in a spinal segment with vertebral motion tracking flags utilized digital stereophotography, lateral neutral posture radiograph, and detailed quantitative anatomy to develop geometrical relationships between flag markers and ligament attachment points. A custom jig, consisting of two flags each with four markers, was constructed to quantify errors associated with computed ligament deformation, flag marker translation, and flag rotation. RESULTS: Average error in ligament deformation was dependent upon motion direction and ranged between 0.03 mm (SD 0.45 mm) and 0.28 mm (SD 0.18 mm). Average error for flag marker translation ranged between 0.02 mm (SD 0.14 mm) and 0.11 mm (SD 0.39 mm), and for flag rotation ranged between -0.06 degrees (SD 0.17 degrees ) and 0.07 degrees (SD 0.12 degrees ). CONCLUSIONS: Accuracy of the present technique was equivalent to or greater than that of previous methods. The present technique utilized relatively cost-effective digital stereophotography, and may be used to calculate strain in ligaments not readily accessible for transducer application. The methodology has wide-spread applicability for analyses of dynamic or static spinal or other ligament strains, and may be used to determine spinal canal and intervertebral foramen narrowing and area reduction.

Biomechanical Phenomena↗

PubMed2006

Predicting multiplanar cervical spine injury due to head-turned rear impacts using IV-NIC.

OBJECTIVE: Intervertebral Neck Injury Criterion (IV-NIC) hypothesizes that dynamic three-dimensional intervertebral motion beyond physiological limit may cause multiplanar soft-tissue injury. Present goals, using biofidelic whole human cervical spine model with muscle force replication and surrogate head in head-turned rear impacts, were to: (1) correlate IV-NIC with multiplanar injury, (2) determine IV-NIC injury threshold at each intervertebral level, and (3) determine time and mode of dynamic intervertebral motion that caused injury. METHODS: Impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of T1 vertebra (n = 6; average age: 80.2 years; four male, two female donors). IV-NIC was defined at each intervertebral level and in each motion plane as dynamic intervertebral rotation divided by physiological limit. Three-plane pre- and post-impact flexibility testing measured soft-tissue injury; that is significant increase in neutral zone (NZ) or range of motion (RoM) at any intervertebral level, above baseline. IV-NIC injury threshold was average IV-NIC peak at injury onset. RESULTS: IV-NIC extension peaks correlated best with multiplanar injuries (P < 0.001): extension RoM (R = 0.55) and NZ (R = 0.42), total axial rotation RoM (R = 0.42) and NZ (R = 0.41), and total lateral bending NZ (R = 0.39). IV-NIC injury thresholds ranged between 1.1 at C0-C1 and C3-C4 to 2.9 at C7-T1. IV-NIC injury threshold times were attained between 83.4 and 150.1 ms following impact. CONCLUSIONS: Correlation between IV-NIC and multiplanar injuries demonstrated that three-plane intervertebral instability was primarily caused by dynamic extension beyond the physiological limit during head-turned rear impacts.

Acceleration↗

PubMed2006

Cervical spine loads and intervertebral motions during whiplash.

OBJECTIVE: To quantify the dynamic loads and intervertebral motions throughout the cervical spine during simulated rear impacts. METHODS: Using a biofidelic whole cervical spine model with muscle force replication and surrogate head and bench-top mini-sled, impacts were simulated at 3.5, 5, 6.5, and 8 g horizontal accelerations of the T1 vertebra. Inverse dynamics was used to calculate the dynamic cervical spine loads at the centers of mass of the head and vertebrae (C1-T1). The average peak loads and intervertebral motions were statistically compared (P < 0.05) throughout the cervical spine. RESULTS: Load and motion peaks generally increased with increasing impact acceleration. The average extension moment peaks at the lower cervical spine, reaching 40.7 Nm at C7-T1, significantly exceeded the moment peaks at the upper and middle cervical spine. The highest average axial tension peak of 276.9 N was observed at the head, significantly greater than at C4 through T1. The average axial compression peaks, reaching 223.2 N at C5, were significantly greater at C4 through T1, as compared to head-C1. The highest average posterior shear force peak of 269.5 N was observed at T1. CONCLUSION: During whiplash, the cervical spine is subjected to not only bending moments, but also axial and shear forces. These combined loads caused both intervertebral rotations and translations.

Acceleration↗

PubMed2006

Test protocols for evaluation of spinal implants.

Prior to implantation, medical devices are subjected to rigorous testing to ensure safety and efficacy. A full battery of testing protocols for implantable spinal devices may include many steps. Testing for biocompatibility is a necessary first step. On selection of the material, evaluation protocols should address both the biomechanical and clinical performance of the device. Before and during mechanical testing, finite element modeling can be used to optimize the design, predict performance, and, to some extent, predict durability and efficacy of the device. Following bench-type evaluations, the biomechanical characteristics of the device (e.g., motion, load-sharing, and intradiscal pressure) can be evaluated with use of fresh human cadaveric spines. The information gained from cadaveric testing may be supplemented by the finite element model-based analyses. Upon the successful completion of these tests, studies that make use of an animal model are performed to assess the structure, function, histology, and biomechanics of the device in situ and as a final step before clinical investigations are initiated. The protocols that are presently being used for the testing of spinal devices reflect the basic and applied research experience of the last three decades in the field of orthopaedic biomechanics in general and the spine in particular. The innovation within the spinal implant industry (e.g., fusion devices in the past versus motion-preservation devices at present) suggests that test protocols represent a dynamic process that must keep pace with changing expectations. Apart from randomized clinical trials, no single test can fully evaluate all of the characteristics of a device. Due to the inherent limitations of each test, data must be viewed in a proper context. Finally, a case is made for the medical community to converge toward standardized test protocols that will enable us to compare the vast number of currently available devices, whether on the market or still under development, in a systematic, laboratory-independent manner.

Animals↗

PubMed2006

Head-turned rear impact causing dynamic cervical intervertebral foramen narrowing: implications for ganglion and nerve root injury.

OBJECT: A rotated head posture at the time of vehicular rear impact has been correlated with a higher incidence and greater severity of chronic radicular symptoms than accidents occurring with the occupant facing forward. No studies have been conducted to quantify the dynamic changes in foramen dimensions during head-turned rear-impact collisions. The objectives of this study were to quantify the changes in foraminal width, height, and area during head-turned rear-impact collisions and to determine if dynamic narrowing causes potential cervical nerve root or ganglion impingement. METHODS: The authors subjected a whole cervical spine model with muscle force replication and a surrogate head to simulated head-turned rear impacts of 3.5, 5, 6.5, and 8 G following a noninjurious 2-G baseline acceleration. Continuous dynamic foraminal width, height, and area narrowing were recorded, and peaks were determined during each impact; these data were then statistically compared with those obtained at baseline. The authors observed significant increases (p < 0.05) in mean peak foraminal width narrowing values greater than baseline values, of up to 1.8 mm in the left C5-6 foramen at 8 G. At the right C2-3 foramen, the mean peak dynamic foraminal height was significantly narrower than baseline when subjected to rear-impacts of 5 and 6.5 G, but no significant increases in foraminal area were observed. Analysis of the results indicated that the greatest potential for cervical ganglion compression injury existed at C5-6 and C6-7. Greater potential for ganglion compression injury existed at C3-4 and C4-5 during head-turned rear impact than during head-forward rear impact. CONCLUSIONS: Extrapolation of present results indicated potential ganglion compression in patients with a non-stenotic foramen at C5-6 and C6-7; in patients with a stenotic foramen the injury risk greatly increases and spreads to include the C3-4 through C6-7 as well as C4-5 through C6-7 nerve roots.

Acceleration↗

PubMed2005

Effect of rotated head posture on dynamic vertebral artery elongation during simulated rear impact.

BACKGROUND: Elongation-induced vertebral artery injury has been hypothesized to occur during non-physiological coupled axial rotation and extension of head. No studies have quantified dynamic vertebral artery elongation during head-turned rear impacts. Therefore, we evaluated effect of rotated head posture vs. forward head posture at the time of impact on dynamic vertebral artery elongation during simulated rear impacts. METHODS: A whole cervical spine model with surrogate head and muscle force replication underwent either simulated head-turned (n = 6) or head-forward (n = 6) rear impacts of 3.5, 5, 6.5 and 8 g. Continuous dynamic vertebral artery elongation was recorded using custom transducer and compared to physiological values obtained during intact flexibility testing. FINDINGS: Average (SD) peak dynamic vertebral artery elongation of up to 30.5 (2.6) mm during head-turned rear-impact significantly exceeded (P < 0.05) the physiological beginning at 5 g. Highest peak elongation of 5.8 (2.1) mm during head-forward rear impact did not exceed physiological limit. Head-turned rear impact caused earlier occurrence of average peak vertebral artery elongation, 84.5 (4.2) ms vs. 161.0 (43.8) ms, and higher average peak vertebral artery elongation rate, 1336.7 (74.5) mm/s vs. 211.5 (97.4) mm/s, as compared to head-forward rear impact. INTERPRETATION: Elongation-induced vertebral artery injury is more likely to occur in those with rotated head posture at the time of rear impact, as compared to head-forward.

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PubMed2005

Effects of charité artificial disc on the implanted and adjacent spinal segments mechanics using a hybrid testing protocol.

STUDY DESIGN: Finite element model of L3-S1 segment and confirmatory cadaveric testing were used to investigate the biomechanical effects of a mobile core type artificial disc (Charité artificial disc; DePuy Spine, Raynham, MA) on the lumbar spine. OBJECTIVE: To determine the effects of the Charité artificial disc across the implanted and adjacent segments. SUMMARY OF BACKGROUND DATA: Biomechanical studies of artificial discs that quantify parameters, like the load sharing and stresses, are sparse in the literature, especially for mobile-type core artificial disc designs. In addition, there is no standard protocol for studying the adjacent segmental effects of such implants. METHODS: Human osteo-ligamentous spines (L1-S1) were tested before and after L5-S1 Charité artificial disc placement. The data were used to validate further an intact 3-dimensional (3-D) nonlinear L3-S1 finite element model. The model was subjected to 400-N axial compression and 10.6 Nm of flexion/extension pure moments (load control) or pure moments that produced the overall rotation of the L3-S1 Charité model equal to the intact case (hybrid approach). Resultant motion, load, and stress parameters were analyzed at the experimental and adjacent levels. RESULTS: Finite element model validation was achieved only with the load-controlled experiments. The hybrid approach, believed to be more clinically relevant, revealed that Charité artificial disc leads to motion increases in flexion (19%) and extension (44%) at the L5-S1 level. At the instrumented level, the decrease in the facet loads was less than at the adjacent levels; the corresponding decrease being 26% at L3-L4, 25% at L4-L5, and 13.4% at L5-S1 when compared to the intact. Intradiscal pressure changes in the L4-L5 and L3-L4 segments were minimal. Shear stresses at the Charité artificial disc-L5 endplate interface were higher than those at S1 interface. However, in the load control mode, the increase in facet loads in extension was approximately 14%, as compared to the intact case. CONCLUSIONS: The hybrid testing protocol is advocated because it better reproduces clinical observations in terms of motion following surgery, using pure moments. Using this approach, we found that the Charité artificial disc placement slightly increases motion at the implanted level, with a resultant increase in facet loading when compared to the adjacent segments, while the motions and loads decrease at the adjacent levels. However, in the load control mode that we believe is not that clinically relevant, there was a large increase in motion and a corresponding increase in facet loads, as compared to the intact.

Biomechanical Phenomena↗

PubMed2005

Spinal canal narrowing during simulated frontal impact.

Between 23 and 70% of occupants involved in frontal impacts sustain cervical spine injuries, many with neurological involvement. It has been hypothesized that cervical spinal cord compression and injury may explain the variable neurological profile described by frontal impact victims. The goals of the present study, using a biofidelic whole cervical spine model with muscle force replication, were to quantify canal pinch diameter (CPD) narrowing during frontal impact and to evaluate the potential for cord compression. The biofidelic model and a sled apparatus were used to simulate frontal impacts at 4, 6, 8, and 10 g horizontal accelerations of the T1 vertebra. The CPD was measured in the intact specimen in the neutral posture (neutral posture CPD), under static sagittal pure moments of 1.5 Nm (pre-impact CPD), during dynamic frontal impact (dynamic impact CPD), and again under static pure moments following each impact (post-impact CPD). Frontal impact caused significant (P<0.05) dynamic CPD narrowing at C0-dens, C2-C3, and C6-C7. The narrowest dynamic CPD was observed at C0-dens during the 10 g impact and was 25.9% narrower than the corresponding neutral posture CPD. Interpretation of the present results indicate that the neurological symptomatology reported by frontal impact victims is most likely not due to cervical spinal cord compression. Cord compression due to residual spinal instability is also not likely.

Acceleration↗

PubMed2005

Injured rabbit ACL treated by radiofrequency. Effects of cyclic loading.

BACKGROUND: Radiofrequency treatment is increasingly used to treat shoulder instability. Patients are asked to restrain their physical activities after this treatment but there is no precise information concerning the necessity for the restrain. METHODS: There were two groups of ten specimens each. Treatment group specimens were stretched to subfailure injury, treated by a radiofrequency probe, and then cyclically loaded. Control group specimens were stretched to the same subfailure injury, Sham treated, and then cyclically loaded. Between each step of the experiment in both groups there was a relaxation test to examine the ligament viscoelastic properties. At the end, each ligament was stretched to failure and the load-elongation curve obtained. FINDINGS: Relaxation forces decreased after the subfailure injury in both groups (average 76% and 81% of intact state, in treatment and control groups, respectively). In the treatment group, the relaxation forces first increased after the radiofrequency treatment (average 99% of intact state), and then decreased after the cyclic loading (average 50% of intact state). The treated ligaments failed at lower loads and smaller deformations than the controls. INTERPRETATION: The radiofrequency treatment restored viscoelastic properties of the injured ligaments, but cyclic loading degraded these. Protection of the treated ligament is advised during the immediate post-operative period.

Animals↗

PubMed2005

Frontal impact causes ligamentous cervical spine injury.

STUDY DESIGN: Whole cervical spine model with muscle force replication was subjected to simulated frontal impacts of increasing severity, and resulting injuries were evaluated via flexibility testing. OBJECTIVES: To identify and quantify cervical spine soft tissue injury and the injury threshold acceleration due to frontal impact. SUMMARY OF BACKGROUND DATA: Cervical spine instability may result from automotive collisions. No previous studies have quantified soft tissue injuries due to frontal impact. METHODS: Six human cervical specimens (occiput-T1) with muscle force replication were subjected to frontal impacts of 4, 6, 8, and 10 g. Before frontal impact, baseline flexibility data were collected following a 2 g simulation. Flexibility parameters of total (flexion plus extension) neutral zone (NZ), flexion NZ, total range of motion (ROM), and flexion ROM were obtained following each impact and compared with baseline flexibility. Injury was a significant increase (P < 0.05) in intervertebral flexibility due to frontal impact over baseline. Injury threshold was the lowest T1 peak acceleration that caused injury. RESULTS: The injury threshold acceleration was 8 g, as determined by significant increases of 12.6 to 51.4% over the baseline flexibility, in the C4-C5 total NZ, and the C6-C7 total NZ, flexion NZ, total ROM, and flexion ROM. Following 10 g, significant increases in flexibility parameters were observed at C2-C3, C3-C4, C4-C5, C6-C7, and C7-T1. CONCLUSIONS: Middle (C2-C3 to C4-C5) and lower (C6-C7 and C7-T1) cervical spine were at risk for injury during frontal impacts, for the experimental conditions studied.

Acceleration↗

PubMed2005

A hypothesis of chronic back pain: ligament subfailure injuries lead to muscle control dysfunction.

Clinical reports and research studies have documented the behavior of chronic low back and neck pain patients. A few hypotheses have attempted to explain these varied clinical and research findings. A new hypothesis, based upon the concept that subfailure injuries of ligaments (spinal ligaments, disc annulus and facet capsules) may cause chronic back pain due to muscle control dysfunction, is presented. The hypothesis has the following sequential steps. Single trauma or cumulative microtrauma causes subfailure injuries of the ligaments and embedded mechanoreceptors. The injured mechanoreceptors generate corrupted transducer signals, which lead to corrupted muscle response pattern produced by the neuromuscular control unit. Muscle coordination and individual muscle force characteristics, i.e. onset, magnitude, and shut-off, are disrupted. This results in abnormal stresses and strains in the ligaments, mechanoreceptors and muscles, and excessive loading of the facet joints. Due to inherently poor healing of spinal ligaments, accelerated degeneration of disc and facet joints may occur. The abnormal conditions may persist, and, over time, may lead to chronic back pain via inflammation of neural tissues. The hypothesis explains many of the clinical observations and research findings about the back pain patients. The hypothesis may help in a better understanding of chronic low back and neck pain patients, and in improved clinical management.

Animals↗