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Biomedical subjects

M H Pope

Publications and source records attributed to M H Pope.

At least 91 records · Page 5Linked to original sources
PubMed1992

External fixator pin design.

The integrity of the bone-pin interface is the critical link in the stability of external fixation systems. External fixation pins placed in cancellous metaphyseal bone frequently loosen over time, resulting in fixation failure and an increased risk of infection. To design an external fixation pin with optimal bone-metal interface strength in cancellous bone, a systematic study of various thread design features was performed. Combinations of pitch, tooth profile, and minor diameter in 5 mm self-tapping half pins were evaluated in coaxial pullout testing using a fresh bovine cancellous bone. A significant increase in pullout strength was found with a decrease in minor diameter. No statistical differences were found in pullout strength attributable to thread profile and pitch. There were no significant interactions between minor diameter and tooth profile or minor diameter and pitch. The data obtained suggest significantly greater holding power in cancellous bone can be achieved by using an external fixation pin with a smaller minor diameter or a larger interference. Additional pullout testing of five commercially available external fixator pins was performed. Of these, the two pins with the largest interference demonstrated greater pullout strength. Therefore, within a range of acceptable major diameters and adequate minor diameters for the torsional strength requirements, an optimal interference for cancellous pin application may exist and it may well be larger than that present in currently available external fixation pins.

Animals↗
PubMed1992

Diagnosing instability.

The various definitions of instability are reviewed and preference is given to the definition of instability as a loss of stiffness. This definition fits with current laboratory observations. Roentgenographic changes, particularly those associated with degeneration, have no relationship to instability. Multiple roentgenographic images can be of use, but accuracy is limited, and often valuable information at midmotion range or in other planes is missing. Stereoroentgenography appears to offer some promise, but implanted metallic markers are necessary to attain adequate accuracy. Ionizing radiation dose levels are of concern in these techniques. External fixation techniques appear to be of use in some patients. Kinematic linkages and frames containing infrared light emitting diodes are extremely promising, because they give kinematic information in detail.

Humans↗
PubMed1991

The impact response of the seated subject.

An impact method for establishing the dynamic response of the seated subject is introduced. The method employs a pendulum to apply the impact to the suspended seat. Pins are placed in the spinous process at L3. Highly reproducible results are obtained. The results were not affected by the amplitude of impact, implying a linear system. A marked peak of transmissibility is found in the 4-5 Hz range and an attenuation peak is found close to 8 Hz. Both muscle contraction and postural changes affect the dynamic response. A relaxed posture shows greater gain and attenuation peaks. A valsalva stiffens the system and reduces the effective damping. The vertical response of the body probably shows in the 5-6 Hz peak, while the rotational response is probably encompassed in the 8 Hz attenuation peak.

Adult↗
PubMed1991

Intervertebral motion during vibration.

Vibration exposure is widely recognized as a risk factor for low back pain. An experimental protocol was designed to quantify the intervertebral motion response in human subjects to sinusoidal vertical vibration at 5 and 8 Hz, and at a variety of acceleration levels. Intervertebral motion in the mid-sagittal plane was measured using a transducer linkage system attached to pins placed directly into the spinous processes of adjacent vertebrae. The postures of the subjects were carefully controlled. The effects of forward flexion, arm support, gravitational load, and sitting on a cushion were evaluated. The rigid body motion of the superior vertebra with respect to the inferior vertebra was expressed in terms of relative sagittal plane rotation, axial translation, and anterior-posterior shear translation. It was found that the lumbar motion segments exhibited coupled periodic behaviour in response to sinusoidal vertical vibration, with up to 1 mm peak-to-peak displacement in the axial direction. The greatest intervertebral motion occurred when the subject was exposed to 5 Hz vibration as compared to 8 Hz. For a constant frequency of 5 Hz excitation, the peak-to-peak amplitudes of the computed motions tended to increase as the acceleration level increased. In the flexed posture, with no arm support, the active trunk musculature helped reduce the intervertebral motion. Additional gravitational load on the shoulders caused increased relative axial displacement. A polyethylene foam cushion placed on the seat reduced vibration transmission at 5 Hz excitation and consequently decreased the intervertebral motion.

Adult↗
PubMed1991

ACL reconstruction: in vivo measurement of patellar tendon graft elongation.

The implantation of a free autogenous patellar tendon graft is the surgical technique that currently offers the best results in anterior cruciate ligament reconstruction. However, numerous aspects regarding both technique and postoperative rehabilitation can still be improved. The aim of this study was to measure the elongation of the patellar tendon in vivo in the operating room after reconstructive surgery, subjecting the knee to normal strain such as passive mobilization or anterior displacement of the tibia. Three volunteers were studied. Our results were different from those reported in a previous study conducted in vivo on a normal anterior cruciate ligament (ACL). In spite of the isometric position of the tendon, passive mobilization provoked a progressive increase in the elongation of the graft within each cycle of flexion-extension and between one cycle and the next. This also occurred during the Lachman test. These findings suggest that the graft undergoes a process of tensile adjustment when it is first put under strain. Continued elongation once this process appears stabilized raises doubts as to the reliability of isometric measuring devices.

Adult↗
PubMed1991

Whole-body vibration exposure in subway cars and review of adverse health effects.

New York City Transit Authority subway operators have a high prevalence of back problems. To evaluate a possible dose-response relationship for whole-body vibration, we studied subway car vibrations measured and analyzed according to the International Standard Organization 2631 and Verein Deutscher Ingenieure 2057 standards. Vibration transducers in triaxial orientation were mounted in a disc pad directly on the subway operator's seat. The relatively high lateral and vertical accelerations, primarily the combined effects, may all contribute to the high rate of musculoskeletal complaints, especially of the lower back. Other factors aggravating whole-body vibrations include primitive ergonomic cab and seat design, forced body posture, high noise levels, and organizational work stress.

Back Pain↗
PubMed1991

Dynamic lifting capacity: the relationship between peak force and weight as an indicator of effort.

Quantification of lifting capacity has become a major component in clinical and occupational evaluations of people with or at risk for low back pain. The ideal test of maximum acceptable lifting would include an index of subject effort. Heart rate response appears to have significant limitations as an indicator of effort. In this study a device that records vertical lifting force measured peak force/weight ratios (PF/W) and differences (PF-W) for individual lifts. Seventeen men without low back pain lifted the device with progressively heavier loads. The PF/W, PF-W, and heart rate responses were compared at half-maximum and maximum effort levels. The PF/Ws were higher, while the PF-Ws and heart rate responses were lower during half-maximum efforts. As an indicator of subject effort, the relationship between peak force and weight may play a key role in isoinertial lifting evaluations.

Adult↗
PubMed1991

Epidemiology and prevention of skiing injuries.

Between 1972 and 1987, the authors prospectively evaluated all 5701 injuries which were reported to the injury clinic operating in the base lodge of a ski area in northern Vermont, USA. During that time approximately 1,690,000 skier visits were estimated to have occurred at the ski area. The total injury population was divided into 28 groups and sub-groups and examined by regression analysis for long term trends. Among upper body injuries, only lacerations showed a positive improvement. Among lower extremity injuries, virtually all injuries below the knee improved dramatically, some groups by more than 80%. Knee injuries, although improved as a group, showed a marked 2.7-fold increase in serious (third degree) sprains usually involving the anterior cruciate ligament. Clavicular fractures were the only upper extremity injury which increased significantly in incidence.

Athletic Injuries↗
PubMed1990

Arthroscopic strain gauge measurement of the normal anterior cruciate ligament.

This article describes a new arthroscopic technique to study the anterior cruciate ligament (ACL) in vivo. A Hall effect strain transducer (HEST) is inserted arthroscopically into the anterior medial band (AMB) of the ACL. The strain is calculated from HEST displacement data. This method determines a reference length of the AMB when it becomes taut and load bearing. Data from HEST implantation in five patients with normal ACLs are reported. The HEST was implanted in the AMB with patients under local anesthesia. Strain was calculated during anterior-posterior shear testing and isometric quadriceps contractions at 30 and 90 degrees of knee flexion. The results demonstrate that this technique is safe and reliable. Lachman testing (anterior shear testing at 30 degrees) caused significantly higher strain in comparison to the drawer tests (anterior shear testing at 90 degrees). A significant increase in strain occurred during isometric quadriceps contraction when the knee was flexed at 30 degrees. No significant change in strain was measured, however, during isometric quadriceps contraction at 90 degrees of flexion. These results confirm previous studies showing that the Lachman test is a more sensitive clinical method for evaluating the AMB. They suggest that isometric quadriceps activity at 90 degrees of knee flexion can be prescribed for rehabilitation without risk of increased strain of the AMB.

Adult↗
PubMed1990

Body height change during upright and recumbent posture.

Body height changes are known to occur in response to changes in loads acting along the spine, such as those produced by movement from a recumbent to an upright posture. Lack of previously available data is addressed here by body height measurements closely spaced in time of ten normal subjects during 8 hours upright and 4 hours recumbent, with particular attention paid to the initial changes. Experimental errors are carefully defined and determined. A Kelvin-unit model is fitted to the mean data for each phase and confidence limits provided for the model equation parameters. Rapid height changes are shown to occur: 26% of the 8-hour loss occurred in the first hour upright, and 41% of the 4-hour recovery occurred in the first hour recumbent.

Adult↗
PubMed1990

Factors affecting the dynamic response of the seated subject.

An impact method, combined with pins placed into the spinous process at L3, has been used to establish the dynamic response of the spine of the seated subject. The resonant frequency is at 4-5 Hz, due primarily to a vertical response of the buttocks-pelvis system. A maximum attenuation at 8 Hz occurs because of a second resonance due to pelvic rotation. The attenuation is also affected by additional load and by the addition of a helmet. Neck braces have no dynamic effect.

Adult↗
PubMed1989

Internal deformations of intact and denucleated human lumbar discs subjected to compression, flexion, and extension loads.

Three rows of six evenly spaced 0.5 mm metal beads were implanted midsagittally into the discs of ten L4-5 human lumbar motion segments. The intradiscal bead displacements in response to compression, flexion, and extension loads were obtained by digitizing the bead positions from sagittal plane radiographs taken before and during the load application. Each disc was denucleated and the loading process was repeated. For the intact discs, in compression, the intradiscal bead displacements were predominantly anterior. In flexion, the beads in the center of the disc moved posteriorly whereas the beads closer to the periphery of the disc moved anteriorly. In extension, the central beads moved anteriorly and the beads closer to the periphery of the disc moved posteriorly. After denucleation, the bead displacements for compression and flexion implied an inward bulging of the inner wall of the annulus, despite outward bulging of the disc surface. We hypothesize that the inward bulging causes radial tensile stresses within the disc, leading to disruption of adjacent layers of annulus.

Biomechanical Phenomena↗
PubMed1989

Trunk muscle electromyography and whole body vibration.

By measuring the electromyographic (EMG) activity of the paraspinal muscles, we have estimated the average and peak-to-peak torque imposed on the spine during whole body vibration. Six subjects had surface electrodes placed on their erector spinae muscles at the L3 level. The EMG-torque relationship was estimated by having each subject perform isometric horizontal pulls in an upright seated posture. The subject was then vibrated vertically and sinusoidally in a controlled, flexed, slightly lordotic seated posture, in 1 Hz increments from 3 to 10 Hz at a 0.1 g RMS seat acceleration level. Between vibration readings taken at each frequency, a static reading was also taken with the subject maintaining the same posture. The entire vibration-static 3-10 Hz test was repeated for reliability purposes. Specialized digital signal processing techniques were developed for the EMG signals to enhance the measured cyclic muscle activity and to allow automatic measurement of the time relationship between the mechanical displacement and the estimated torque. We found significantly more average and peak-to-peak estimated torque at almost all frequencies for vibration vs static sitting.

Acceleration↗
PubMed1989

The dynamic response of a subject seated on various cushions.

An impact pendulum was used to examine the dynamic response of the seated subject. The dynamic response is of interest in establishing the relationship between driving and low-back pain. Accelerometers were placed on the seat and in vivo at the L3 vertebra. The transmissibility and phase angle were obtained in the frequency domain for a variety of cushions. Soft cushions were found to increase the gain at the first natural frequency.

Acceleration↗