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Biomedical subjects

M H Pope

Publications and source records attributed to M H Pope.

At least 37 records · Page 2Linked to original sources
PubMed1997

A dynamic approach to spinal instability. Part I: Sensitization of intersegmental motion profiles to motion direction and load condition by instability.

STUDY DESIGN: Human lumbar functional spinal units (FSUs) were moved throughout their range of motion in sagittal and lateral bending while the dynamics of this movement were computed in vitro. Functional spinal units were tested intact and after subsequent discectomy and unilateral facetectomy. OBJECTIVE: To establish "normal" velocity and acceleration curves during lumbar intersegmental bending in the intact FSU and then evaluate the changes of this dynamic behavior due to surgically induced component instability. SUMMARY OF BACKGROUND DATA: In preliminary clinical studies, researchers have provided evidence that dynamic motion measurements may be useful in the assessment of spinal impairment. METHODS: Human lumbar FSUs moved from extension to flexion, flexion to extension, left to right, and right to left a pure moment. Range of motion, as well as velocity and acceleration patterns of the main and coupled motions, were evaluated in six degrees of freedom by position changes of attached infrared light-emitting diodes recorded by cameras. Functional spinal units were tested in three surgical conditions (intact, discectomy, and unilateral facetectomy) under two preload conditions (no preload and 400 N preload). RESULTS: Motion of intact FSUs progressed with velocity and acceleration patterns that were relatively independent from motion direction and preload condition. After surgery, however, the dynamic motion became unequal between opposite motion directions (even if range of motion was equal between directions) and more sensitive to preload condition. CONCLUSION: The results suggest that equilibrium of dynamic motion parameters within a range of motion is an element of segmental stability. From this approach, segmental instability appears to change intersegmental acceleration and velocity patterns as a function of motion direction and load conditions. Whereas dynamic motion patterns in an intact FSU are relatively invariable between reversed motion directions, instability is characterized by a considerable diversity of dynamic motion parameters between reversed motion directions.

Acceleration↗
PubMed1997

A dynamic approach to spinal instability. Part II: Hesitation and giving-way during interspinal motion.

STUDY DESIGN: Human lumbar functional spinal units (FSUs) were moved throughout their range of motion in sagittal and lateral bending, while the dynamics of this movement were computed in vitro. Functional spinal units were tested intact and after subsequent discectomy and unilateral facetectomy. OBJECTIVE: To determine whether the patterns of small jerks observed during intersegmental motion are sensitive to spinal instability. SUMMARY OF BACKGROUND DATA: Small jerks have been observed as hesitation during increasing velocity and as giving way during decreasing velocity in the experiments described in Part I of this study. METHODS: Human lumbar functional spinal units were moved from extension to flexion, flexion to extension, left to right, and right to left, by a pure moment. Range of motion and velocity and acceleration patterns of the main and coupled motions were evaluated in six degrees of freedom by position changes of attached infrared light-emitting diodes recorded by cameras. Functional spinal units were tested in three surgical conditions (intact, discectomy, and unilateral facetectomy) under two preload conditions (no preload and 400-N preload). Discontinuous accelerations and decelerations (jerks) were computed in these motions and their location in relation to the main angular motion determined. RESULTS: Jerks were observed in almost all motions, in the intact functional spinal units and after surgery. The parameters describing the magnitude of the jerk decreased with increasing component instability. In the sagittal plane, there was a surgical condition by motion direction interaction (P < 0.014) regarding the location of the jerk. Independent from the motion direction, the jerk occurred around the neutral position (in relation to the primary angular motion) in the intact functional spinal units, whereas it shifted from the neutral position toward the beginning of the motion with increasing component instability. CONCLUSION: The results suggest that a small jerk is a normal component of fast intersegmental motion. The jerk has a certain magnitude and location in an intact functional spinal unit, whereas both of the parameters describing the jerk are sensitive to component instability.

Acceleration↗
PubMed1997

Classification of low back pain from dynamic motion characteristics using an artificial neural network.

STUDY DESIGN: Data were collected from 183 subjects who were randomly assigned to the training and test groups. During testing of the classification system, knowledge of the low back pain condition or motion characteristics of the patients in the test group was not made available to the system. OBJECTIVES: To determine specific characteristics of trunk motion associated with different categories of spinal disorders and to determine whether a neural network analysis system can be effective in distinguishing patterns. SUMMARY OF BACKGROUND DATA: Numerous studies have established the difficulty of evaluating lower back pain. Imaging techniques are expensive and ineffective in many cases. A technique for evaluation of lower back pain was developed on the basis of analysis of such dynamic motion features as shape, velocity, and symmetry of movements, using a neural network classification system. METHODS: Dynamic motion data were collected from 183 subjects using a triaxial goniometer. Features of the movement were extracted and provided as input to a two-stage neural network classifier governed by a radial basis function architecture. After training, the output of the classifier was compared with Québec Task Force pain classifications obtained for the patients. Linear and nonlinear classification techniques were compared. RESULTS: The system could determine low back pain classification from motion characteristics. The neural network classifier produced the best results with up to 85% accuracy on novel "validation" data. CONCLUSIONS: A neural network based on kinematic data is an excellent predictive model for classification of lower back pain. Such a system could markedly improve the management of lower back pain in the individual patient.

Adult↗
PubMed1997

Effect of test environment on intervertebral disc hydration.

STUDY DESIGN: Water content of fresh human lumbar intervertebral discs (with adjacent endplates) was assessed in three studies: 1) after each of seven specimen preparation steps. 2) during exposure to either saline spray or a saline bath, and 3) during exposure to a saline bath and 445 N axial compression, either without or with previous exposure to the bath and no compression ("free swelling"). OBJECTIVE: To assess the effect on disc hydration of various aspects of specimen preparation and testing environments. SUMMARY OF BACKGROUND DATA: Water content is an important determinant of disc behavior. Specimen preparation method and testing environments may be important determinants of water content, yet no work appears to have been reported specifically on this topic. METHODS: Endplate-disc-endplate specimens were prepared from refrigerated cadavers within 24 hours of death by transverse sectioning of adjacent vertebral bodies. Water content change was determined by specimen weight change across each time interval of interest. RESULTS: Specimen preparation (including multiple freeze-thaw cycles) produced no water content change. Saline spray and plastic film wrap resulted in no change, but saline bath exposure resulted in a 24% increase over 7 hours, 44% of which occurred in the first 0.5 hour. A subsequent 7 hours of 445 N compression reduced the overall increase to 10%. This was not significantly different from the 8% increase that resulted from initial exposure to saline bath and compression. CONCLUSIONS: Specimen preparation as typically performed and specimen exposure to saline spray and plastic film wrap do not result in hydration change. Exposure to saline bath results in substantial swelling, which can either be reversed or prevented by axial compression in the physiologic range. Whether discs exposed to saline spray and wrap without compression and those exposed to saline bath with compression behave the same and which of these more closely mimics the in vivo condition are important issues for the experimentalist to test.

Adult↗
PubMed1997

Materials and design of spinal implants--a review.

Man-made devices have been implanted into the body to relieve pain, to restore function, and to facilitate healing. The subjects of this review are the materials, and to a lesser extent, the design aspects of the numerous implants that are available to the surgeon in dealing with the ailing spine. Often it is the material aspects of such devices that are responsible for their success or failure. It may be that osteoconductive properties are desired for implants to assist fusion, whereas as inert a material as possible would be preferred for interpositional barriers. The materials composing the instrumentation used to facilitate healing of spinal fractures would ideally have properties that optimize strength and biocompatibility, while at the same time minimizing imaging artifacts and allowing a gradual transfer of load from the instrumentation to the vertebral body (i.e., viscoelastic effects). The application of biomaterials and biomechanics to the design of spinal devices is obvious; what may be more subtle though is what the in vivo interactions of these will be. The study of such aspects must continue in order to better evolve the designs and subsequent results of implanted spinal devices.

Biocompatible Materials↗
PubMed1997

Laxity and flexibility of the ankle following reconstruction with the Chrisman-Snook procedure.

The effect of reconstruction of the anterior talofibular ligament with the Chrisman-Snook procedure on neutral zone laxity (anterior-posterior displacement at low loads) and flexibility (a measure of the nonlinear load-displacement response) of the ankle was investigated in vitro during the anterior drawer test. Neutral zone laxity was defined as the magnitude of anterior-posterior displacement of the ankle joint at +/- 2.5 N of applied load. The flexibility parameter was defined as the slope of a line between the natural logarithm of the anterior load applied to the ankle and the resulting displacement. After reconstruction with the Chrisman-Snook procedure, the values for neutral zone laxity of the ankle were significantly less than normal at 0 degree of plantar flexion, whereas the flexibility values were significantly greater than normal. This study revealed that, after the Chrisman-Snook procedure, values for ankle flexibility are not restored to normal even if those for neutral zone laxity are reduced to less than normal. The findings suggest that this nonanatomical reconstruction procedure does not reproduce normal kinematics of the ankle joint. This may help explain some of the adverse clinical reports associated with the Chrisman-Snook reconstruction procedure.

Adolescent↗
PubMed1997

The upper extremity attenuates intermediate frequency vibrations.

Vibration is related to reports of low back pain; however the biomechanics of vibration transmission through the hand-arm system has not been previously studied. Vibration was recorded on an accelerometer mounted to a pin percutaneously imbedded in the spinous process of L4 of five human subjects. The energy was applied through an impact via a pendulum. The subjects adopted an erect, relaxed or bent knee posture. The first resonance was 4-6 Hz and the second at 9-14 Hz. With the knee bent, the signal was almost completely attenuated. If the impact was applied through a handle and the hand-arm system there was complete attenuation.

Acceleration↗
PubMed1997

Correlation of bone equivalent mineral density to pull-out resistance of triangulated pedicle screw construct.

Thirty single-pedicle and triangulated pedicle screws were subjected to pull-out tests until complete dislodgment was achieved. Peak load, displacement curves, angle of triangulation, and equivalent mineral density were recorded. Dual pedicle screw triangulation produced a 154.4% increase in peak pull-out strength compared with that of the single pedicle screw. Salvage triangulation (replacing failed screws with a triangulation construct) produced a 127.4% increase in peak strength over that of the single screw. Positive correlation was found between individual screw peak strength, bone mineral density, and displacement at peak load. Primary and salvage triangulation produced higher resistance to pull-out than a single pedicle screw, which reflects the potential, beneficial effect of using this technique. Triangulation, therefore, can be used as primary (prophylactic) technique to enhance pedicular screw pull-out during forceful vertebral manipulation.

Aged↗
PubMed1996

Muscular response to sudden load. A tool to evaluate fatigue and rehabilitation.

STUDY DESIGN: Subjects were exposed to fatiguing and restorative interventions to assess their response to sudden loads. OBJECTIVES: To investigate the erector spinae and rectus abdominis response characteristics to "sudden load" and the effect of fatigue and rehabilitation. SUMMARY OF BACKGROUND DATA: Unexpected loads which people often experience, can lead to high forces in the spine and may be a cause of low back injury. METHODS: Muscle responses to sudden load were mediated by fatigue, walking, expectation, method of load application, exposure to vibration, and cognitive-behavioral rehabilitation in patients with chronic low back pain. A novel technique, perfected in this work, called wavelet analysis, was used to analyze these data. RESULTS: Reaction time was affected by fatigue and expectation. Vibration exposure significantly increased the muscle response time. Walking was able to ameliorate that effect. Back muscles responded differently, depending on whether loads were applied to the back through the hands or through the trunk. Electromyographic reaction time and magnitude decreased in patients after a 2-week rehabilitation program. CONCLUSIONS: Sudden loads can exacerbate fatigue effects. Walking after driving reduces the risk to the back caused by handling unpredictable loads. Vibration exposure guidelines should be more conservative. Patients have longer response times than healthy subjects, but patients can improve their response to sudden loads via rehabilitation. Patients exhibit a flexion-extension oscillation at 5 Hz in response to a sudden load, suggesting that the 5-Hz, seated, natural frequency observed during whole-body vibration may result from neurophysiologic control limits.

Adult↗
PubMed1996

Hyperextension and spine height changes.

STUDY DESIGN: The effect on spine height changes from different combinations of time and angle of static prone hyperextension, and one intervention of dynamic hyperextension was explored. OBJECTIVES: To explore whether controlled hyperextension would cause an height increase with greater duration than previously shown, and to find an optimal combination of hyperextension angle and duration of the intervention. SUMMARY OF BACKGROUND DATA: Hyperextension is a METHODS: Ten subjects were exposed to hyperextension in the prone position for different time periods and with different amounts of hyperextension. The effect was measured using the stadiometer for measurement of spine height changes. RESULTS: The study showed that time was the most important variable, and also that for a given time, there was an increased recovery with increased angle. CONCLUSIONS: The results indicate that hyperextension can be a beneficial maneuver to unload temporarily the spine after loading and to rehydrate the discs, providing enough time is given for the procedure. The optimal time and angle combination was 20 degrees for 20 minutes because this intervention resulted in the largest recovery that lasted for a relatively long period of time.

Adult↗
PubMed1996

Are occupational drivers at an increased risk for developing musculoskeletal disorders?

STUDY DESIGN: This study analyzed the role of exposure to driving and other covariates in reports of back, neck, and shoulder pain and resultant disability. Cohorts in Sweden and the United States were compared. OBJECTIVES: To establish the effect of mechanical and psychosocial factors in reporting back, neck, and shoulder pain and work loss. SUMMARY OF BACKGROUND DATA: There are numerous reports of a positive relationship between back pain and driving. However, exposure data are minimal. The influence of job satisfaction has not been assessed. METHODS: The physical factors affecting reports of back, neck, and shoulder pain were investigated in a two-country cohort study of bus and truck drivers and sedentary workers. Vibration exposure was obtained by directly measuring the vibration imposed on the driver during a typical work day. Lifting exposure was attained by questionnaire. Cumulative exposure was computed based on work history. Musculoskeletal health information was based on a modified nordic questionnaire, and other questionnaires recorded the physical and psychosocial aspects of the work environment. RESULTS: Of the sample, 50% reported low back pain, with no difference between countries. The highest risk factors (odds ratios) for back and neck pain were long-term vibration exposure, heavy lifting, and frequent lifting. A combination of long-term vibration exposure and frequent lifting carried the highest risk of low back pain. Work loss from low back pain was influenced by perceived job stress. CONCLUSIONS: Vibration (resulting from driving) and lifting cause back, neck, and shoulder pain, whereas inability to work seems affected by stress at work.

Adult↗
PubMed1996

European Spine Society--the AcroMed Prize for Spinal Research 1995. Unexpected load and asymmetric posture as etiologic factors in low back pain.

Unexpected loads, which often occur in the working environment, can lead to high forces in the spine and, thus, may be a cause of low back injury. This paper discusses the effect of "sudden load" on the erector spine reaction and amplitude. Muscle responses were mediated by several factors, including fatigue, posture, expectation and rehabilitation, in chronic low back pain patients. The subjects were fatigued by holding a 20% maximum voluntary contraction for 1 min. A functional restoration program was tested for its efficacy in reducing reaction time and EMG amplitude in chronic low back pain patients. Reaction time was longer and EMG amplitude lower in patients than in their matched controls. EMG reaction time and magnitude decreased in patients after a 2-week rehabilitation program, including specific training of coordination and posture control. The results of the modelling showed higher spinal compressive load and lower shear forces when the load was expected than when the load was unexpected. The effect of sudden loads can be exacerbated if a worker is not standing on a flat surface or is fatigued. Chronic low back pain patients have less ability to protect themselves from sudden loads, but they can be trained to improve their response by means of an appropriate rehabilitation program.

Adult↗
PubMed1996

Does a back support have a positive biomechanical effect?

Back supports, or lifting belts, are widely used. Subjects, free of low back pain, lifted in a simulated task, meeting the 1993 NIOSH guidelines. The back support reduced the electromyographic signal in the dorsal muscles. The back support also reduced the height loss as measured by a stadiometer. In most subjects the support also gave a subjective impression of increased support and increased lifting capacity.

Journal Article↗
PubMed1996

Epidemiological and aetiological aspects of low back pain in vibration environments - an update.

The article reviews the substantial body of epidemiological evidence linking vibration exposure and low back pain. Drivers appear to be at particular risk if exposures exceed those recommended by the ISO exposure limit. Various aetiological factors associated with vehicular vibration, flattening of the lumbar lordosis, increased motion segment flexibility, disc pressure and mechanical softening are discussed. Vibration studies of functional spinal units are also discussed, as are in vivo whole-body vibration experiments. Animal models have shown that vibration leads to compromised nutrition, higher disc pressures, release of neuropeptides, increased creep and histological changes.

Journal Article↗
PubMed1996

Mechanical stress reduction during seated jolt/vibration exposure.

The risk of experiencing low back pain is associated with mechanical factors. Anatomic factors, such as advancing pregnancy, can also place extra mechanical stress on the lower back. Mechanical factors, such as those related to the workplace, can be minimized by ergonomic interventions. A constrained, seated posture, in combination with exposure to whole-body, jolt/vibration can impose significant stresses on the posterior intervertebral disc and can lead to back muscle fatigue. Interventions that reduce the jolt/vibration magnitude and duration of exposure will decrease the mechanical work performed on the intervertebral disc. Such interventions range from jolt/vibration isolating seats and vehicle cabs, to decreasing exposure time and maintaining simple supported postures during ingress and egress. Improvements in seat configuration can reduce the intervertebral disc pressure and the strain on the posterior disc.

Biomechanical Phenomena↗
PubMed1996

A sagittal plane model of the knee and cruciate ligaments with application of a sensitivity analysis.

In this investigation the complex multi-bundle structure of the cruciate ligaments and their interaction with the tibiofemoral joint was modeled analytically by representing the different regions of the cruciates with ligament elements. A sensitivity analysis was then performed to describe the effect that variations of the model input parameters had on the model variables (outputs). The effect that the cruciate ligament bundles had in controlling joint kinematics was dependent on knee flexion angle, and the load applied to the tibiofemoral joint. For passive range of knee motion with the thigh in the horizontal plane (a common rehabilitation activity), all cruciate ligament bundles were strained with the joint positioned between 0 and 10 deg of knee flexion, between 10 and 50 deg only the anterior bundle of the posterior cruciate ligament A-PCL was strained, and from 50 to 90 deg both the anteromedial portion of the anterior cruciate ligament A-ACL and the A-PCL were strained. This finding indicates that a strain distribution about a transverse cross section of the cruciates exists, and demonstrates the importance of differentiating between the strained and unstrained (unloaded) states of these ligaments. The strain value of a cruciate ligament bundle was an indication of how the bundle controls joint kinematics, while the unstrained values describe how much the ligament bundle must deform before it becomes strained and a restraint to tibiofemoral joint motion. In response to anterior and posterior directed loads, applied parallel to the tibial plateau, the respective, ACL and PCL load values were larger in magnitude. The sensitivity of the model outputs to the input parameters was highly dependent on knee flexion angle. The geometrical input parameters of the model (including the ligament insertion site locations and articular surface geometry) had the most pronounced effect on the model output quantities, while the stiffness and initial strain conditions of the ligament bundles had less of an effect on the model outputs. When loaded, the strain values of the ligament bundles were sensitive to the ligament insertion site position. The greatest sensitivity of the model outputs was the femoral insertion of the ACL; supporting clinical impressions and previous experimental findings. Changes in the anterior-posterior dimension of the femoral articular surface did not produce a substantial effect on the model outputs, while changes in the proximal-distal dimension created a large effect; similar results were found for the tibial surface dimensions. These findings indicate that rigid body contact between the articular surfaces may not be a realistic assumption particularly with application to the prediction of tibiofemoral compressive loading and the force/strain values of the cruciate ligament elements. This also has important implications for the design and clinical application of total knee replacements (that function as rigid bodies), particularly those that spare the PCL.

Anterior Cruciate Ligament↗