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F Graichen

Publications and source records attributed to F Graichen.

At least 37 records · Page 2Linked to original sources
PubMed1998

Placing a bone graft more posteriorly may reduce the risk of pedicle screw breakage: analysis of an unexpected case of pedicle screw breakage.

Telemeterized internal spinal fixation devices were implanted in a patient with degenerative instability and a narrow spinal canal in order to measure the fixator loads during daily activities. Anterior interbody fusion was performed three weeks later. During walking, the typical maximum flexion bending moments were 10 N m in the left and 5 N m in the right fixator. On removal of the implants three months later, a fatigue fracture was found not on the high loaded left side but in the upper right pedicle screw. The crack started on the caudal side of the cross-sectional area and progressed cranially. Upper vertebral tilting in the sagittal plane must have caused the screw breakage. This would probably have been prevented by a more posteriorly placed bone graft.

Activities of Daily Living↗
PubMed1997

Loads on an internal spinal fixation device during walking.

Only little knowledge exists concerning the loads on internal spinal fixation devices during walking. In this study, forces and moments were measured in two patients using telemeterized spinal fixators. Although implant loads differed strongly before and after anterior fusion as well as between the two patients, some results were consistent. In every test series, implant loads were higher in walking than in lying, sitting or standing. Walking speed had little influence on implant loads. Staircase walking put slightly higher loads on the implants than normal level walking. Normal use of two crutches reduced implant loads only slightly, whereas a wheeled invalid walker reduced them by about 25%.

Adult↗
PubMed1997

Comparison of loads on internal spinal fixation devices measured in vitro and in vivo.

The loads on internal spinal fixation devices were measured using modified, telemeterized AO-Dick internal fixators. The implants allow measurement of the three force components and the three moments acting on the implant. The modified fixators were mounted on cadaver spines, and the implant loads were measured in the intact and postcorpectomy spines for different loading modes, including axial compression force, flexion, extension, lateral bending, and torsion. The in vitro experiment did not consider muscle forces. Modified fixators were also implanted in three patients, and the implant loads were determined before and after anterior interbody fusion with autologous iliac-crest bone grafts. The results for different in vitro loading modes were compared with those in vivo in order to demonstrate the extent to which the in vitro loads represent the real situation in patients. In several cases, the implant loads in the in vitro experiment differed strongly from those measured in patients. For flexion and lateral bending, a tensile axial force occasionally was measured in the in vitro experiment, while in the patients the axial force was always compressive. Extension was predominantly associated with extension bending moments in the in vitro study but with flexion bending moments in the patients. When muscle forces are not considered in the in vitro experiment, the loads on the fixators may differ significantly from the situation found in patients.

Adult↗
PubMed1997

Hip joint forces during load carrying.

In some diseases affecting only 1 hip joint, it is necessary to keep the contact force between femoral head and acetabulum (hip joint force) permanently low at the affected side. Six subjects were examined while they were walking and carrying a load in 1 or 2 hands. It was determined how the forces in both hip joints are influenced by the magnitude of the load and the manner in which it is carried. A mathematical model was used to calculate the maximum forces in the frontal plane. One subject had instrumented endoprostheses implanted in both hips. For him the measured values were slightly higher than the calculated ones, but the overall results were similar. Carrying a load on 1 side keeps the force constant at the ipsilateral hip joint or even slightly lowers it. At the same time, there is a large increase on the opposite side. Carrying 25% of body weight with 1 hand causes about 2/3 higher forces in the contralateral joint than on the loaded side. If this load is evenly distributed between the 2 sides, both hip joint forces increase by 25%. In unilateral load carrying, additional relief of the ipsilateral joint can be achieved if the upper body is held upright and the loadcarrying arm is abducted, such as when using a large shopping basket.

Adult↗
PubMed1996

Patient monitoring system for load measurement with spinal fixation devices.

Fractures of the spine can be stabilized by different implants. Their stiffness varies widely and only little is known about the loads acting on these devices. In order to measure the forces and moments in the implant, the internal fixator after Dick was modified. An inductively powered telemetry unit is placed inside the fixator and is hermetically sealed against body fluids. An integrated eight channel telemetry chip was developed to measure the signals of six strain gauge sensors, the implant temperature and the power supply. Because two fixators are implanted together, two telemetry transmitters run at the same time. This paper describes the function of the instrumented implant and the external system components.

Biomechanical Phenomena↗
PubMed1996

In vitro load measurement using an instrumented spinal fixation device.

An AO spinal fixateur interne was modified to study the effects of a corpectomy on implant performance. A hermetically sealed cartridge containing strain gauges and an inductively powered telemetry unit was integrated into the threaded portion of the original implant. Five cadaveric spines were instrumented with the modified implant spanning a single lumbar vertebra. The spines were tested in axial compression, torsion, flexion, extension and lateral bending. Measurements of the three forces and moments within the implant were performed in the intact spine and repeated following a corpectomy and corpectomy plus complete posterior ligamentous injury. The bending moment, increased following corpectomy in all testing modes. The largest increase was in the flexion bending moment, which increased from 155 Nmm to 3328 Nmm following corpectomy.

Aged↗
PubMed1995

Telemeterized load measurement using instrumented spinal internal fixators in a patient with degenerative instability.

STUDY DESIGN: In the present study, the loads in an internal spinal fixation device were measured in vivo. OBJECTIVES: To determine the implant loads for different activities before and after additional anterior stabilization of the spine. SUMMARY OF BACKGROUND DATA: Mathematical models exist for predicting spinal loads. The intradiscal pressure has been measured for many body positions and activities. The loads on internal spinal fixation devices have not been measured before in vivo. METHODS: Telemeterized AO spinal internal fixators were implanted in a patient with degenerative instability. The implants allow the in vivo measurement of three force components and three moments acting in the implant. RESULTS: When the patient was lying in relaxed positions, the implant loads were small. Before additional anterior stabilization, the loads were also small for sitting, standing, and walking. The bending moment in the sagittal plane was less than 3 Nm for these activities. The highest loads within the first 4 weeks after implantation were measured while the patient turned from a supine to a lateral position against the advice of the physiotherapist. After anterior stabilization, the maximum loads for the relaxed lying positions were altered only slightly. Much higher axial forces and bending moments were measured for sitting, standing, and walking. The maximum bending moment increased to 5-8 Nm for these activities. The implant loads for sitting were not higher than for standing. CONCLUSION: Flexion and lateral bending of the upper body and weight-carrying during sitting, standing, or walking should be avoided in the first few months after anterior stabilization.

Bone Screws↗
PubMed1995

In vivo measurement of implant loads in a patient with a fractured vertebral body.

It is not known what loads act on an internal spinal fixation device in patients with a fractured vertebral body. To measure the implant loads in vivo, telemeterized internal spinal fixators were implanted in a patient, and the implant loads measured for numerous body positions and activities before and after anterior fusion. The highest implant loads were found while the patient lifted both extended legs in a supine position. High implant loads were also measured for lateral bending during standing as well as for walking and carrying a load in one hand. The implant loads were small in recumbent positions. In contrast to findings in another patient, who was treated for degenerative instability, implant loads were smaller in the first months after anterior fusion than before. The indication for stabilization and surgical procedure strongly influence implant loads.

Adult↗
PubMed1995

Is staircase walking a risk for the fixation of hip implants?

Considerable forces and moments act at hip prostheses during most kinds of physical activities. High torque around the stem axis may contribute to implant loosening. With instrumented hip prostheses the joint force and its direction, the bending moment in the frontal plane and the torque were measured in two patients during upstairs, downstairs and level walking. The data give information on whether or not stairclimbing causes a more severe loading situation for the implants than walking. While going upstairs at normal speed the joint force is 10% higher than during walking at 3 km h-1. Downstairs it increases by 20%. The bending moments change by nearly the same amounts. Upstairs the torsional moment is about twice as high as during slow walking. But walking at 5 km h-1 or slow jogging causes forces and moments of similar magnitudes. Even higher loads were observed when the patients stumbled without falling. Although torque during staircase walking is high, extreme values exclusively during stairclimbing are not confirmed by our data. The torsional moments now observed in vivo are close to or even exceed the experimentally determined limits of the torsional strength of implant fixations, found in the literature. Obviously, torsional moments play an important role for the potential loosening of hip prostheses.

Aged↗
PubMed1995

Influence of shoes and heel strike on the loading of the hip joint.

The forces and moments acting at the hip joint influence the long-term stability of the fixation of endoprostheses and the course of coxarthrosis. These loads may depend on the kind of footwear and the walking or running style. These factors were investigated in a patient with instrumented hip implants. He wore different sports shoes, normal leather shoes, hiking boots and clogs and walked barefoot with soft, normal and hard heel strikes. The loads were lowest while walking and jogging without shoes. All shoes increased the joint force and the bending moment at the implant slightly but the torsional moment rose by up to 50%. No relation was found between the different type of shoes and the load increase, only shoes with very hard soles were clearly disadvantageous. Soft heels, soles or insoles did not offer advantages. Gait stability seems to play the most important role in increasing the joint loading and should be the criterion for the choice of footwear. Smooth gait patterns with soft heel strikes are the only means to reduce joint loading during slow jogging.

Aged↗
PubMed1994

A spinal fixation device for in vivo load measurement.

An instrumented spinal fixation device has been developed that allows in vivo measurement of the forces and moments acting on the implant. The telemetry is inductively powered, hermetically sealed by electron beam welding and is active only during the measurements. The instrumented fixateur interne is similar in size to the original Dick internal fixator implant and has the strength of the original implant. Laboratory tests with paired implants mounted in plastic vertebrae show that small changes in the position of the implants have a strong influence on the distribution of the loads on the implants.

Activities of Daily Living↗
PubMed1994

[Telemetric transmission system for in vivo measurement of the stress load of an internal spinal fixator].

For stabilizing fractures of the spine, a number of implantable devices are available. However, not much is known about the loads acting on these devices. In order to measure the forces and moments within the implant, the Dick internal fixation device was modified and fitted out with a hermetically sealed inductively powered telemetry unit. An integrated 8-channel telemetry chip was specially developed to measure the signals of six strain gauge sensors, the temperature of the implant and the supply voltage. Since the internal fixation devices are always implanted in pairs, two telemetry units are operated at the same time. This article details the function of the implanted electronic circuit and the external system components.

Adult↗
PubMed1993

Hip joint loading during walking and running, measured in two patients.

The resultant hip joint force, its orientation and the moments were measured in two patients during walking and running using telemetering total hip prostheses. One patient underwent bilateral joint replacement and a second patient, additionally suffering from a neuropathic disease and atactic gait patterns, received one instrumented hip implant. The joint loading was observed over the first 30 and 18 months, respectively, following implantation. In the first patient the median peak forces increased with the walking speed from about 280% of the patient's body weight (BW) at 1 km h-1 to approximately 480% BW at 5 km h-1. Jogging and very fast walking both raised the forces to about 550% BW; stumbling on one occasion caused magnitudes of 720% BW. In the second patient median forces at 3 km h-1 were about 410% BW and a force of 870% BW was observed during stumbling. During all types of activities, the direction of the peak force in the frontal plane changed only slightly when the force magnitude was high. Perpendicular to the long femoral axis, the peak force acted predominantly from medial to lateral. The component from ventral to dorsal increased at higher force magnitudes. In one hip in the first patient and in the second patient the direction of large forces approximated the average anteversion of the natural femur. The torsional moments around the stem of the implant were 40.3 N m in the first patient and 24 N m in the second.

Aged↗
PubMed1993

[Stress measurements with an instrumented internal spinal fixator].

Little is known about the loads acting on internal spinal fixation devices. The effective forces and moments associated with different external loads have now been measured using instrumented implants. Measurements were obtained in intact cadaver spines and following vertebrectomy. The influence of the implant itself on the distribution of the loads was also investigated. It was found that the implants are not loaded symmetrically. Following vertebrectomy, the forces acting on the fixation device are significantly higher than in the case of an intact spine.

Biomechanical Phenomena↗
PubMed1991

Four-channel telemetry system for in vivo measurement of hip joint forces.

The long-term loosening of artificial hip joints remains a serious clinical problem. Optimization of implant design and material will improve the fixation, but it requires a detailed knowledge of the forces which act on the implant. A four-channel telemetric transmitter was developed and arranged completely inside a hermetically closed artificial hip joint. This permits long term in vivo measurements of the three-dimensional forces without endangering the patient. The external telemetry system consists of an inductive power supply, an RF receiver, a microcomputer with hardware extension and a VHS video system. The personal computer offers real-time data processing of three orthogonal force components as well as slow motion analysis of recorded measurements. After several years of animal tests, two instrumented prostheses were implanted in the first patient (male) in May and August of 1988. In March 1990 a third prosthesis was implanted in a second patient (female). Joint force measurements have regularly been performed from the first post-operative day until now for several kinds of activity.

Biomechanical Phenomena↗
PubMed1988

Multichannel strain gauge telemetry for orthopaedic implants.

In vivo measurements of the loads and deformations occurring in orthopaedic implants will allow future improvements to be made. This paper describes an extremely small telemetry for long term measurements with three strain gauges and methods for an absolutely safe implant design. Developed for measuring the load at hip prostheses, the telemetry can also be used for other implants. Its size makes feasible instrumentation of devices with only slight mechanical modifications. In addition to the description of our own measuring system, the paper gives a survey on the problems of telemetrized implants, on methods for measuring spatial loads, and on the investigations of other authors. Future publications will present in vivo measurements with this telemetry, among others on hip endoprostheses.

Equipment Design↗
PubMedDate not supplied

[In-vitro measurement of loading using an instrumented vertebral internal fixator].

Only little is known about the loads acting on internal spinal fixation devices. The forces and moments for different external loads were now measured using instrumented implants. Measurements were performed on intact cadaver spines and after a corpectomy. Additionally the influence of the mounting accuracy on the distribution of the loads in the fixators was investigated. It could be shown that the implants are not loaded symmetrically. After a corpectomy the loads on the implants are significantly higher than for an intact spine.

Aged↗