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Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

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

[Mechanical properties of PDS-augmented patellar tendon transplants in reconstruction of the anterior cruciate ligament].

In 25 sheep the anterior cruciate ligament (ACL) was reconstructed after resection. Twelve modified "Jones procedures" were performed (transplantation of the central third of the patellar tendon with an initial load of 50 N) and 13 polydioxanone (PDS) augmentations. In 15 cases the ACL was resected from the right knee. Twenty-one sheep survived for 1 year and were then evaluated. Loss of the ACL leads to instable joints in this experiment. Within the first 6 months anterior translation occurs; after 1 year subluxations can be seen on the X-ray films. Macroscopical signs of extensive arthrosis were seen in the femorotibial and femoropatellar joints; the menisci were totally destroyed. Macroscopically strong ligaments were seen 1 year after PDS-augmented reconstruction as well as after transplantation of the patellar tendon with an initial load of 50 N. There was no difference between the two groups. The mechanical strength reached 54% of the maximum load of a control group in the Jones reconstructions and 61% after additional augmentation with a 2-mm biodegradable PDS cord. There was no statistically significant difference. Both methods are suitable for reconstruction of the ACL; the patellar tendon replaces the ACL very well.

Animals↗
PubMed1991

Role of interfragmentary strain in fracture healing: ovine model of a healing osteotomy.

It has been hypothesized that the histological pattern of fracture healing is controlled at least in part by the local mechanical strains in the interfragmentary region. To test this "interfragmentary strain hypothesis," we applied cyclic bending deformations to tibial osteotomies in 11 sheep. An instrumented flexible plate spanning a 1-mm osteotomy gap was deformed to create a gradient of tissue elongation from 10% under the plate to 100% at the opposite cortex. The cyclic deformations were applied three times per minute, 24 h per day, for 1-5 weeks. However, as a result of tissue differentiation, the bone-plate complex increased in stiffness with healing time, resulting in a marked reduction of the gap deformation at approximately 4 weeks. Fracture healing was evaluated using vascular injection of India ink and conventional histology. A nonlinear three-dimensional finite element model of the interfragmentary tissue at the initial stage of healing was used to predict the complex tissue strains. The ingrowth of vascularized soft tissue into the interfragmentary gap, as well as the subsequent differentiation of this tissue, occurred earlier and to a greater degree in regions of lower strain. In contrast, the proliferation of callus tissue was greatest at the periosteal and endosteal surfaces of the cortex opposite the plate. Direct comparison of the finite element predictions with the histology demonstrated that the spatial distribution of bone resorption at the fracture fragment ends directly corresponded to the locations of elevated tissue strain and stress. However, there was no consistent numerical relationship between the magnitude of these local peak strains and the corresponding volume of cortical bone resorption over the bone cross section.

Animals↗
PubMed1991

Deformation of the distal femur: a contribution towards the pathogenesis of osteochondrosis dissecans in the knee joint.

Osteochondrosis dissecans (OD) is a process of subchondral bone necrosis occurring predominantly in young individuals at specific sites. The aetiology of this disease remains controversial with mechanical processes due to trauma and/or ischaemic factors being proposed. This study aims at explaining the aetiology of OD in the knee joint as a result of the particular deformation of the condyles. A finite element analysis of the distal third of the femur was performed. A three-dimensional model was developed based on computed tomography scans of a normal femur, consisting of cortical bone, cancellous bone and articular cartilage. This model was subjected to physiological loads at 0, 30, 60 and 90 degrees of knee flexion. A complex deformation was found within each condyle as well as between the two condyles. Both medial and lateral condyles are deformed in the medio-lateral direction and at the same time compressed between the patella and the tibia in the antero-posterior direction. This effect is highest at 60 degrees of knee flexion. In both planes, the medial condyle is distorted more than the lateral one. Strain concentration in the subchondral bone facing the patella varies with flexion, especially for angles exceeding 60 degrees. The deformation of the femur in the predominant locus of OD in the medial condyle exceeds that of the lateral condyle considerably. The analysis shows that repeated vigorous exercise including extreme knee flexion may produce rapidly changing strains which in turn could ultimately be responsible for local subchondral bone collapse.

Biomechanical Phenomena↗
PubMed1991

Value of coining on the improvement of endurance in slotted intramedullary nails.

Cracking of intramedullary nails, starting at the proximal end of the partial slot and propagating in a circumferential direction, has been observed. These partial cracks are relatively frequent, although full failures are very rare and do not disturb fracture healing. Coining is a cold-working process used to improve the endurance of structures with residual compressive stresses generated by plastic deformation. The influence of coining was investigated to evaluate its practical value in controlling these fatigue cracks. Bending and torsional tests were performed on high frequency machines. Coined zones of different shapes and depths were examined, comparing the elapsed number of load cycles with crack initiation. The results showed that the endurance of coined nails was improved by factors of approximately 10 and 5 in bending and torsion, respectively. This increase in fatigue life corresponds to a more than 50% larger dynamic load after a million cycles. Variations in coining shape and depth did not yield any significant differences.

Bone Nails↗
PubMed1991

Internal fixation with a self-compressing plate and lag screw: improvements of the plate hole and screw design. 1. Mechanical investigation.

For a number of years, self-compressing plates, with oval holes and using special drill guides, have been in use. Recently, the advantages offered by lag screw interfragmentary compression inserted through the plate have gained prominence. Often such screws are inserted in an inclined position toward the fracture plane for better efficiency. It has also become evident that inclined screws placed into oval holes undergo a displacement toward the fracture. Efforts to improve the effect of this technique have led to a new plate and screw interaction that is described herein. The result is versatility and efficiency of the fracture fixation.

Biomechanical Phenomena↗
PubMed1991

Internal fixation with a self-compressing plate and lag screw: improvements of the plate hole and screw design. 2. In vivo investigations.

A mechanically improved design of bone plate and screw was compared in vivo with conventional plate fixation. This method was investigated biologically in a standardized osteotomy model on sheep tibiae. It was found that maintenance of reduction of an osteotomy was facilitated and there was no adverse effect of this fracture fixation system on bone remodeling. The modified implant permits the reduced surgical approach to the bone through one plane and optimal fixation of the fracture or osteotomy.

Animals↗
PubMed1991

Induction and prevention of pin loosening in external fixation: an in vivo study on sheep tibiae.

In external fixation of fractures, pin loosening is a major concern. Preloading the pins is generally done to ensure their stability within the bone cortex. The effect of radial preload and bending preload in reducing resorption at the pin/bone interface was tested. Schanz screws were fixed to live sheep tibiae using a pneumatically operated external fixator frame. Evaluation was based on radiological observation and fluorochrome histology using sequential labels. Though not completely absent, bone resorption was minimal in the radial preload group, compared with the two other groups. More important, the bone-to-pin contact surface in the radial preload group was found to be almost intact after 5 weeks. In this study, radial preload appears to be superior to bending preload in terms of minimizing the problems of pin loosening.

Animals↗
PubMed1991

A paradigm of delayed union and nonunion in the lumbosacral joint. A study of motion and bone grafting of the lumbosacral spine in sheep.

In a group of nine sheep (Group A), it was noted that when small, interlocking cancellous and cortical cancellous bone grafts are placed posteriorly on the lumbosacral spine, union always occurred in the interlumbar motion segments and almost never occurred at the lumbosacral joint. One of the main differences in these two areas is the amount of motion that occurs at each level with flexion and extension. Because nonunion following bone grafting for arthrodesis of the spine is a serious clinical problem, we have studied the amount of motion seen at the interlumbar and lumbosacral joints in sheep to ascertain how much motion is compatible with union and how much is associated with nonunion. In vivo studies were carried out in eight sheep (Group B), and five normal spine segments were studied in vitro to determine normal motion in this species. To simplify the complex in vivo motion that occurs at the lumbar motion segments, the simple linear displacement and strain of the fusion mass (consisting of fibrous tissue and bone grafts placed on and between the laminas posteriorly) was measured with the spine in flexion and extension. When the displacement and strain at the interlaminar level of the L6-S1 joint was measured, the linear displacement was found to be 5.2 mm and the associated linear strain 36%. The displacement at the L5-L6 interspace was 1.2 mm, and the strain 10%. The stiffness of the L5-L6 joint (which always fused) and the L6-S1 joint (which did not fuse, with one exception) were also studied. In a third group of four animals (Group C), internal fixation of the lumbosacral joint was attempted in addition to bone grafting.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Induction of monocyte chemotaxis in devascularized rabbit bone.

Temporary impairment of blood supply has been suggested to cause bone remodeling. The degradation of cells and matrix and the attraction of resorbing cells were examined in this study. Bone specimens of rabbits were stored in vitro for 2-20 days. At the end of this aging process the probes were tested for their chemotactic activity toward autologous leukocytes in a diffusion chamber. Both supernatant from the aged bone specimens and ground bone particles exhibited significant chemotactic activity that was specifically attracting monocytes. It is suggested that soluble bone matrix proteins or degeneration products liberated during ischemic damage to cortical bone initiate the resorptive process.

Animals↗
PubMed1990

Biomechanics of the interlocking nail. A study of the proximal interlock.

Conventional interlocking nails for the femur use an inclined proximal interlocking screw; the AO/ASIF universal interlocking nail utilizes a transverse interlocking screw which is anchored in cortical bone. The transverse position of the screw allows one to employ the nail for either the right or left side. The yield strength of the thinner diameter transverse screw, (thread 4.5 mm. core 3.0 mm) was compared with that of the Grosse-Kempf nail oblique screw (thread 6.3 mm, core 4.5 mm) by testing in cadaver femora to evaluate the risk of fatigue failure. The test, performed using slow loading rates (50 N/s), simulated either a diaphyseal or a subtrochanteric fracture situation. The test rig applied a load corresponding to body weight and pull at the trochanter. Taking the highest load without plastic deformation as a criterion, the mechanical strength of the two screws was evaluated for each fracture situation. The thinner but shorter transverse interlocking screw demonstrated higher strength (4500 N vs. 3000 N; P less than or equal to 0.02) than the thicker inclined screw in the diaphyseal and the subtrochanteric fracture situation (2300 N vs. 1100 N; P less than or equal to 0.06). The biomechanical test showed the transverse screw to have sufficient and superior strength.

Biomechanical Phenomena↗
PubMed1990

The limited contact dynamic compression plate (LC-DCP).

To realize the new concept of biological internal fixation the limited contact dynamic compression plate was developed. It minimizes vascular damage to the plated bone segment. It should lead to a more versatile and efficient application of internal fixation using plates.

Bone Plates↗
PubMed1990

Reaming versus non-reaming in medullary nailing: interference with cortical circulation of the canine tibia.

Medullary nails have only been used with reluctance in the treatment of open fractures since reaming interferes with the cortical circulation. The technique of interlocking offers the interesting possibility of inserting a relatively stiff nail which does not necessarily require reaming. The effects of reaming prior to nail insertion upon the cortical circulation was investigated in the canine tibia. Intravital staining with procion red was used to trace areas of disturbed circulation. Nail insertion without reaming provided clear advantages for the bone's blood supply, while reaming disturbed perfusion in two-thirds of the cortical area and regionally extended through the entire thickness of the cortex. The disturbance without reaming was limited to the inner layer of the cortex and involved only one-third of the cortical cross-section.

Animals↗
PubMed1990

Limb lengthening and three-dimensional deformity corrections. A retrospective clinical study.

Different methods of limb lengthening as used at the Orthopedic Surgery Clinic of the Medical School, University of Zagreb, are compared. The results of operations performed between 1979 and 1989 on 111 patients are presented. These patients were subjected to surgery aimed at length equalization of limbs and/or correction of three-dimensional deformities. Lengthening was performed in 104 patients at one level, and in 7 patients at two levels of the same limb for a total of 118 procedures. In order to compare limb lengthening techniques the patients were divided into four groups: group I, original Wagner technique (45 patients); group II, Wagner technique using corticotomy (33 patients); group III, original Ilizarov technique (35 patients); group IV, continuous lengthening (2 patients). The evaluation covered radiological aspects of regenerated bone, complications and basic lengthening parameters. The results indicate that corticotomy has considerable advantages over osteotomy, provided bone circulation is maintained. These advantages manifest themselves in a reduced number of operations, lower incidence of infection and improved bone regeneration. It is preferable to perform corticotomy at the metaphysis site because of its optimum blood supply and its higher potential for osteogenesis. With corticotomy performed at the diaphysis site, satisfactory results were observed in only one-third of the cases.

Adolescent↗
PubMed1990

Histology of the alar and transverse ligaments.

Seven sets of human transverse and alar ligaments, after tensile testing, and eight corresponding ligaments without testing, were examined histologically with respect to their fiber composition and fiber orientation. Various staining techniques were supplemented by polarized light microscopy. Both the transverse and the alar ligaments consist of collagen fibers, with very few elastic fibers in the peripheral layer. In the central portion of the transverse ligament, the collagen fibers cross each other at an angle of approximately 30 degrees. Close to the dens, the transverse ligaments show on their ventral side a transition into fibrocartilage. Except for the immediate site of failure, no differences became evident between tested specimens and controls. The collagen, as the almost exclusive constituent, together with the fiber orientation determine the mechanical properties of these ligaments. This supports the hypothesis that the ligaments could be irreversibly overstretched or even ruptured when the head is rotated and, in addition, flexed by impact trauma, especially in unexpected rear-end collisions.

Aged↗
PubMed1990

[Treatment of defects of the long bones using distraction osteogenesis (Ilizarov) and intramedullary nailing. Theoretic principles, animal experiments, clinical relevance].

For large shaft defects of tibia and femur, distraction-compression osteosynthesis (Ilizarov) provides an ideal autologous bone graft. Combination of this with an intramedullary interlocking nail instead of an external fixator could improve patient comfort, because transport with a small external device takes only one-third of the total fixation period. Using 21 adult female sheep we created standardized tibia shaft defects 20 mm (medium size) and 45 mm (large size) in length. The tibiae were stabilized with non-reamed intramedullary interlocking nails. Following corticotomy by chisel, segments were transported using subcutaneous traction wires with a screw as a fulcrum to maintain stationary skin exit points without soft tissue problems. The external traction devices were removed after 12 or 16 weeks. Animals were sacrificed after 12 or 24 weeks with medium-size defects, and after 16 or 32 weeks with large defects. We evaluated the results clinically, by standardized weekly X-rays and, after sacrifice, by quantitative computed tomography (QCT). No animals had to be excluded from the study. Despite primary destruction of the intramedullary circulation all distraction gaps were spanned with bone. X-Rays showed typical signs of good quality of distraction bone regeneration (narrow radiolucent zone in the middle of the regenerate, longitudinal structure), continuous calcification, and cortex formation. QCT cross sections showed completely circular bone regeneration with small and large defects. Bone regeneration was faster on the dorsal side, where more bone was formed than ventrally. Small defects can remain ventrally in the regenerate; these close secondarily.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1989

Experimental method for the in vitro testing of the initial stability of cementless hip prostheses.

Micromotions at the interface between bone and prosthesis are believed to induce bone resorption and ultimately lead to loosening of the implant. Thus the initial stability achieved by a hip prosthesis is an important factor for the long-term function of the implant. Knowing the biological consequences of the mechanical conditions, it appears to be mandatory to measure the extent of these three-dimensional movements. An in vitro dynamic method for measurement of the micromotion of the femoral component of hip prostheses has been developed. Tests in cemented prostheses have confirmed that the use of cement reduces sinkage and rotation manyfold and have yielded reference values for stability. Comparison with two types of cementless prostheses has shown that certain cementless implants may achieve stability comparable to cemented ones in some load directions.

Bone Cements↗
PubMed1989

The effect of radial preload on the implant-bone interface: a cadaveric study.

The most common complication of external fixation is pin loosening. Preloading the implant-bone interface is believed to retard this process. Radial preload, in particular, may be useful, as it allows loading in more than one direction. To investigate the effect of varying degrees of radial preload on the pin-bone interface, 30 freshly thawed human cadaveric tibiae were sectioned into 4-cm segments. Uniform drill holes were produced in the anterior tibial ridge of all segments and custom experimental bolts, oversized in diameter by as much as 1 mm, were pressed into each specimen. Macroscopic surface fractures were noted at the time of bolt insertion for misfits greater than 0.2 mm. Following histologic preparation, the implant-bone interface was evaluated microscopically based on the appearance of osteonal compression, lamellar distortion, and microfractures. Insertion of external fixator pins with misfits of greater than 0.4 mm resulted in significant microscopic structural damage to the bone surrounding the pin. High degrees of radial preload, exceeding the elastic limit of cortical bone, may be produced around pin holes by a small misfit. The use of oversized pins or screws must therefore be questioned.

Biomechanical Phenomena↗