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Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

At least 109 records · Page 6Linked to original sources
PubMed1989

The biomechanics and biology of internal fixation using plates and nails.

In fracture healing, the mechanical environment and bone biology are closely related. Furthermore, the mechanics of the medullary nail fixation are, in many aspects, different from those of compression fixation using screws and plates. A few general items will be discussed to review the basic principles of the mechanics and biology involved and to clarify the terminology. This article outlines the basic ideas of mechanical and biological interaction.

Biomechanical Phenomena↗
PubMed1989

[High-speed motion picture analysis of bone fractures].

Torsional fractures of plastic and cadaver tibiae were investigated using high speed cinematography. The bones were fractured while immersed in water. With greater than 9000 frames/sec the fracture was displayed in about 5 frames showing the progression of the fracture lines. The immersion in water made a strong implosion visible which may result in considerable tissue damage in vivo.

Biomechanical Phenomena↗
PubMed1989

[Bone morphology following plate osteosynthesis as measured by axial tomography].

Previous examinations using computed tomography have shown that no geometrical changes in the cross-section was induced by the plate fixation; bone density was slightly reduced (10% in average) in the entire cross-section and not only next to the plate. A tomographic analysis is presented here about the quality and the amount of bone in the affected leg, compared to the contralateral one.

Adolescent↗
PubMed1989

[A new general orthopedic universal intramedullary nail for the tibia. Clinical development and experiences].

The new AO-Universal-Nail was developed through intensive cooperation between fundamental research, technicians and clinical application. We are now able to transfer the concept of a Universal-Nail (initially for the femur) to the tibia as well. The existing technique of the medullary nail was maintained as far as possible. Special features to be highlighted: The new AO-bend obtains better impact behavior and a more anatomical stabilization of the bone cavity. The tapered tip eases the gliding of the tip of the nail along the inner wall of the dorsal corticalis and past the fracture. Proximal locking is obtained through three transverse extending holes. They offer many choices for optimal placement of the locking bolts. Interlocking from anterior to posterior has been logically abandoned, due to danger for nerves and vessels. Distal looking offers a large selection for stabilization through one a.p.-hole and two transverse holes for the locking bolts. The design from anterior to posterior entables the protection of the soft tissue. The Universal-nail can either be inserted with or without interlocking. A free decision is possible during the operation. The new AO-Universal-Nail for the tibia (as for the femur) maintained reliable aspects and was consequently converted to meet new demands and findings. The basic fundamentals of the AO, namely the observance and application of biomechanical principles and safe operation procedure were attained through simple instrumentation and have been proved successful for clinical application.

Fracture Fixation, Intramedullary↗
PubMed1989

[Stress protection in plate osteosynthesis: myth or reality?].

It is generally admitted that plate fixation of fractures results in reduced stress (stress protection) and subsequent structural adaptation of bone (bone loss). The analysis of the stress pattern and the reduction of deformation work in plated bones is a prerequisite for the assertion that bone loss is stress related. The strain field within bones under eccentric axial load has been analyzed theoretically and verified experimentally. The difference between the reduction of stress obtained using the flexible plate materials is small. Reduction of plate stiffness does not result in proportional improvement of the bone strain.

Bone Plates↗
PubMed1989

A comparative study of the initial stability of cementless hip prostheses.

In the process of prosthetic loosening, the initial motion of the implant relative to the bone is a key element. In order to provide quantitative information, three straight and one curved cementless hip stems were submitted to in vitro tests in autopsy specimens of the femur under dynamic axial and torsional loads with the displacements measured in several directions. The results were compared to those of an additional group of cemented straight stem prostheses providing reference values. Subsidence of cementless implants on the average was significantly higher than the cemented reference, but single implants were comparable to the reference. Rotational motion was distinctly higher than the reference values, with considerable differences between designs. When comparing displacements perpendicular to the main load direction, the sagittal plane motion was found to be at least double the motion in the frontal plane. Micromotions at the prosthesis/bone interfaces under the load case selected were smallest for the curved and highest for one of the straight prostheses.

Biomechanical Phenomena↗
PubMed1988

Early temporary porosis of bone induced by internal fixation implants. A reaction to necrosis, not to stress protection?

Stabilization of the fracture using implants requires contact surfaces between implant and bone. Such contact has been observed to induce bone porosis first seen at one month after surgery. Bone loss in the vicinity of implants has hitherto been explained as being induced by mechanical unloading of the bone (stress protection). Experiments in sheep, dogs, and rabbits combining intravital staining of blood circulation and polychrome fluorescent labeling of bone remodeling leads to the conclusion that early bone porosis in the vicinity of the implants is the result of internal remodeling of cortical bone and is induced by necrosis rather than by unloading. This theory is favored by the evidence that (1) the bone porosis is of a temporary nature, an intermediate stage in internal bone remodeling; (2) the pattern of the remodeling zone is closely related to that of the disturbed circulation, and not to that of unloading; (3) plastic plates may produce more porosis than steel plates; and (4) improved blood circulation using modified plates resulted in reduced porosis. The clinical relevance of these findings is related first to the temporary weakening of the bone, and second to the possibility of sequestration. Sequestration may be the result of intensified remodeling activity in the presence of inflammation or infection.

Animals↗
PubMed1987

Laser Doppler flowmetry for clinical evaluation of femoral head osteonecrosis. Preliminary experience.

Most theories concerning osteonecrosis of the femoral head have as their central focus ischemia of bone. This has been difficult to prove because of lack of a method for direct measurement of bone blood flow. The authors evaluated femoral head blood flow in five patients with established femoral head osteonecrosis using laser Doppler flowmetry. Blood flow within the "avascular" segment was lower than that of the normal cancellous bone of the intertrochanteric region. A surrounding zone of hyperemia was noted in four of the five patients. Laser Doppler flowmetry was easy to use and is a reproducible method for direct estimation of bone-blood flow.

Femur Head↗
PubMed1986

Laser Doppler flowmetry for bone blood flow measurement: correlation with microsphere estimates and evaluation of the effect of intracapsular pressure on femoral head blood flow.

Laser Doppler flowmetry (LDF) was used to measure bone blood flow in the rabbit femoral head and femoral condyles. To correlate the LDF output signal blood cell flux to in vivo blood flow, simultaneous measurements using LDF and 85Sr-labeled microspheres were made in an adult rabbit model. There was no correlation between the two methods for blood flow in the femoral condyles and the correlation between the two methods for blood flow in the femoral head does not achieve statistical significance. An LDF signal of 0.4 V was approximately equal to a microsphere measured flow rate of 0.4 ml blood/g bone/min. The strength of the correlation in the latter case may have been affected by (a) large arteriovenous shunts, (b) inadequate mixing of the microspheres with a left ventricular injection, and (c) insufficient numbers of microspheres present in the bone samples with which to satisfy the mathematical requirements of the microsphere method. When LDF was used to evaluate the effect of elevated intracapsular pressure on femoral head blood flow in skeletally mature rabbits, femoral head subchondral bone blood flow declined with increasing intracapsular pressure from a baseline value of 0.343 +/- 0.036 to a value of 0.127 +/- 0.27 at 120 cm of water pressure. The decline in femoral head blood flow was statistically significant at pressures of 40 cm of water or higher (p less than 0.001), and evaluation of sections of the proximal femora made from preterminal disulphine blue injections confirmed these findings. Intracapsular tamponade has an adverse effect on femoral head blood flow beginning well below central venous pressure and should be considered in the pathophysiology of posttraumatic and nontraumatic necrosis of the femoral head. Laser Doppler flowmetry was easy to use and appears to be a reproducible technique for evaluating femoral head blood flow, offering distinct advantages over the microsphere technique for measuring bone blood flow. Further studies of the in vivo calibration of the LDF method for bone blood flow are necessary for the method to have potential for clinical application.

Animals↗
PubMed1986

The effects of reaming and intramedullary nailing on fracture healing.

Most closed fractures of the shaft of the femur and tibia can be treated successfully with internal fixation with medullary or interlocking nails. Unlike plate fixation, intramedullary nailing does not provide absolutely rigid fixation, so that some motion at the fracture site exists. The process of reaming causes circulatory disturbances in the inner two-thirds of the diaphyseal cortex. However, this does not impede the formation of external callus. The parts of bone that have sustained vascular damage by trauma or surgery are revascularized. Delay in the healing process due to disruption of the blood supply to fracture fragments is not known. The majority of patients are able to weight-bear a few days after surgery.

Animals↗
PubMed1985

Stress analysis of compression plate fixation and its effects on long bone remodeling.

A three-dimensional finite element model is generated for an intact plexiglass tube with an attached six-hole stainless steel compression plate. The results for a wide range of loads, including cyclic external loads and static tensile preloads in the plate and screws, are examined as specifically related to plate-induced osteopenia. The model demonstrates that disuse osteopenia, resulting from a reduction in magnitude of cyclic axial stress, should be limited to the central region between the inner screws. Also, the addition of a static preload negates any reduced axial stress levels in this region, thus raising questions on the relative importance of static and cyclic stresses for the internal remodeling of bone.

Animals↗