PubMed Health⌕ Search

Biomedical subjects

S M Perren

Publications and source records attributed to S M Perren.

At least 19 recordsLinked to original sources
PubMed2005

Aspects of internal fixation of fractures in porotic bone. Principles, technologies and procedures using locked plate screws.

Fractures of the bones of elderly people occur more often and have a more important effect because of a generally diminished ability to coordinate stance and walking. These fractures occur at a lower level of load because of lack of strength of the porotic bone. Prompt recovery of skeletal support function is essential to avoid respiratory and circulatory complications in the elderly. To prevent elderly people from the risks of being bedridden, demanding internal fixation of fractures is required. The weak porotic bone and the high level of uncontrolled loading after internal fixation pose complex problems. A combination of several technical elements of design, application and aftercare in internal fixation are proposed. Internal fixators with locked screws improve the biology and the mechanics of internal fixation. When such fixators are used as elevated splints they may stimulate early callus formation because of their flexibility, the limit of flexibility being set by the demands of resistance and function of the limb. Our own studies of triangulation of locked screws have demonstrated their beneficial effects and unexpected limitations.

Aged↗
PubMed2004

The influence of cyclic compression and distraction on the healing of experimental tibial fractures.

Interfragmentary displacement has a main effect on callus formation in fracture healing. To test whether compressive or distractive displacements have a more pronounced effect on new bone formation, a sheep osteotomy model was created whereby the gap tissue was subjected to constant bending displacement. A diaphyseal osteotomy with a gap of 2 mm was created in 18 sheep tibiae and stabilized with a special unilateral actuator-driven external fixator. Two experimental groups with six sheep each received either 10 or 1000 cycles evenly distributed over 24 h. The third group of six sheep served as a control group without actively induced displacement. The amount and direction of cyclic displacement was kept constant throughout the observation period, resulting in 50% compressive and 50% distractive displacement within the osteotomy gap. At sacrifice, six weeks after surgery, bending stiffness was measured and new bone formation was assessed radiologically and microradiographically. In all cycled groups, the amount of periosteal callus formation was up to 25 times greater on the compression compared to the distraction side (p < 0.001). The application of the higher number of daily cycles resulted in an up to 10-fold greater amount of periosteal new bone formation on the compression side (p < 0.012), while the difference on the distraction side was not significant. Ten cycles applied a day were sufficient to create an abundant periosteal callus on the compression side. In the 1000 cycle group, bending stiffness revealed slightly lower values but the difference was not significant. Solid periosteal bridging of the gap was observed in two sheep in the control group, whereas bridging in the cycled groups was observed exclusively at the medullary side. In conclusion, cyclic compressive displacements were found to be superior over distractive displacements. A higher number of enforced and maintained compressive displacements enhanced periosteal callus formation but did not allow bony bridging of the gap.

Animals↗
PubMed2003

[Are the terms "biology" and "osteosynthesis" contradictory?].

Biology and Osteosynthesis may, at first glance, appear to be contradictory. The disadvantages of the surgical procedure are offset by improved recovery of blood supply across a fracture zone and by stimulation of callus formation due to (controlled and slight) instability (elastically flexible fixation). Biological internal fixation is a principle in its own right; its technique is to some extent incompatible with conventional compression fixation. Locked screws provide better anchorage of the implant in both biological and compression internal fixation techniques. This generally offers improved potential in the treating fractures in osteoporotic bone. Because locked screws offer improved anchorage, the use of unicortical screws is made possible with the effect that the medullary circulation is damaged less. Locked unicortical screws, especially if they are self-drilling and self-cutting, offer important surgical advantages in minimally invasive percutaneous osteosynthesis (MIPO) whereas bicortical screws are required for epi- and metaphyseal anchorage.

Adolescent↗
PubMed2001

Biomechanical and biological considerations relating to the clinical use of the Point Contact-Fixator--evaluation of the device handling test in the treatment of diaphyseal fractures of the radius and/or ulna.

The Point Contact-Fixator (PC-Fix) was designed as part of the developmental evolution of more biological devices for internal fixations. It is a device characterized by minimal contact to the underlying periosteum and bone, hereby minimizing potential damage to perfusion. A multicentre handling test was conducted in 1993 and 1994 in six hospitals to assess its performance. A total of 83 fractured forearm bones (34 radii and 49 ulnae) in 52 patients were stabilized with a PC-Fix. The mean age of the patients was 37 years. There were 24 AO type A, 24 type B and 5 type C fractures. Nine fractures were open. Mean follow-up was 15.6 months; follow-up was 100%. All 21 surgeons involved considered the use of the PC-Fix self-explanatory and relatively easy. Handling difficulties were mainly related to insertion of the monocortical screws. In particular, the precision required for insertion, the inability to incline the screw and the inability to pull the plate to the bone using the screw were considered hard to deal with. Stripping of the hexagonal slot was a problem at removal of the implant, possibly related to overtightening of the screws at insertion. In 76 of 83 bones (49 of 53 forearms), the fractures united without additional surgery. The healing pattern typically showed early callus formation bridging the fracture, followed by progressive mineralization of the central radiolucent line. Complications included one infection, one late displacement and four delayed unions, all requiring revision surgery. In 8 forearms, plate removal was performed after a mean of 10.3 months. Two refractures occurred after removal of the implant 6 and 7 months postoperatively. In conclusion, the practical handling of the new implant was straightforward and easily learnt. The treatment failures observed were related to technical and strategic errors. We consider that, when using devices with a locking compression principle, a minimum number of three screws should be placed on each side of the fracture, that interfragmentary compression of simple fractures is desirable in order to increase stability and that, contrary to in vivo animal studies, early plate removal is not indicated. The trend in fracture fixation is to improve the biomechanical and biological properties of operating technique and the devices used. The PC-Fix has proven a useful step in the right direction in this evolutionary process.

Adolescent↗
PubMed2001

Methodology of clinical trials focusing on the PC-Fix clinical trials.

Once development and mechanical and biological laboratory testing have been completed, new technologies to be used in orthopaedic and trauma surgery must be investigated in humans before they can be used routinely. Prospective clinical investigations with or without randomization to standard treatments conducted according to the current standards and guidelines for Good Clinical Practice must be performed to prove the safety and efficacy of the new device. Furthermore, these tests serve to determine the specific indications, contraindications, tips and tricks as well as the pitfalls and how to avoid them. Last, but not least, the study must result in improved teaching of the use of the device and in improved follow-up of patients. The basis of every conclusion drawn from such a study is the complete documentation of each single use of the new device. We present the modalities and methodology for conducting a prospective clinical multicentre investigation in trauma surgery, focusing on the clinical trials carried out on the Point Contact Fixator (PC-Fix), a device for the internal fixation of long bone fractures developed as part of the scientific evolution towards the Less Invasive Stabilization Systems (LISS) now being introduced into clinical practice. Four prospective multicentre clinical investigations with an overall number of 1,229 PC-Fixators implanted from October 1993 to May 1998 were performed. To our knowledge this is the largest prospective series ever reported in orthopaedic trauma surgery to test a new device before market introduction. Due to a special documentation and implant replacement procedure, every PC-Fix implantation was documented. Very few patients were lost to long-term follow-up due to the personal commitment of the study monitors. Regular personal visits of the study monitor to the investigating hospitals and close communication between the surgeons, the engineers responsible for development, the study monitor, and the study sponsor meant that problems were identified and dealt with professionally without compromising the health of the patient. Case report forms were concise and had to be transmitted without delay. Handling of radiographs has become easier thanks to the transmission of digital images to the study centre via the internet. There are some aspects specific to trauma surgery which require special consideration and planning is essential, but clinical trials can be performed effectively.

Clinical Trials as Topic↗
PubMed2001

PC-Fix and local infection resistance--influence of implant design on postoperative infection development, clinical and experimental results.

Bacterial infection is still one of the main complications after internal fixation of fractures. The design of implants influences local infection resistance. To reduce the development of infections around implants after internal fixation, the vitality of the bone should be preserved to optimize cellular and humoral host defence mechanisms. For extramedullary fracture fixation, two implant designs are currently in routine use: the Dynamic Compression Plate (DCP) and the Limited Contact Dynamic Compression Plate (LC-DCP). The Point-Contact-Fixator (PC-Fix) is a new design concept based on the philosophy of the LC-DCP and the external fixator. Its function relies on splinting the fragments of a fracture internally with locking bolts rather than with screws that compress the plate to the bone. In this way, the blood supply is not compromised by compression of the periosteum. We investigated the effect of this new design on the incidence of postoperative infection rates in a clinical and an experimental setting. In a prospective multicentre study 1,229 PC-Fixators were used in 896 patients. Of these, 1,172 were available for assessment of infection development. The overall infection rate was 1.1% (13/1,172). The infection rate after open fractures was 1.6% (4/256) and after closed procedures (including closed fractures, osteotomies and non-unions) 1.0% (9/916). These rates are low in comparison to published rates using DCP and LC-DCP. In an experimental study, we compared the infection rates across two groups of rabbits four weeks after fixing either a bacterially contaminated DCP or a PC-Fix to the tibia. Infection rates in the DCP group were significantly higher than in the PC-Fix group: Of the 38 evaluated animals, 12 with a DCP and 5 with a PC-Fix developed local infection (p=0.022). The new PC-Fix design shows low postoperative infection rates in the clinical setting and lower infection rates than the DCP in the experimental setting. The design is an important step in the process of reducing postoperative infection rates.

Adolescent↗
PubMed2001

Treatment of diaphyseal fractures of the forearm using the Point Contact Fixator (PC-Fix): results of 387 fractures of a prospective multicentric study (PC-Fix II).

Fractures of the forearm are considered to be a very good indication for plating. Conventional plating is still technically demanding. Extensive animal studies show that there is potential for improvement. The method consists of using an internal fixator that minimizes implant contact to the bone to reduce biological damage. Furthermore, foregoing the need for precise reduction and interfragmental compression makes it easier to use and, therefore, it should be safer. The goal of the study was to observe handling qualities, healing, and complications. For this purpose the study was designed to yield a very high follow-up in clinics with adequate experience and with a number of different surgeons performing the internal fixation. The study was designed as a prospective multicentre investigation in 16 trauma centres worldwide. To test the new approach to internal fixation, diaphyseal fractures of the forearm were stabilized surgically with the PC-Fix (Point-Contact Fixator) system, namely, 387 fractured bones involving 277 forearms in 272 patients. Internal fixation was performed using 387 PC-Fixators. 21% of the fractures were open and 25% occurred in polytraumatized patients. The rate of follow-up was 97%. 355 fractured bones healed uneventfully within four months. Overall, there were 32 complications before bone union occurred; 27 of these bones required re-operation (27 of 387, 7%). All of them subsequently healed without further complications. There were 15 delayed or non-unions and seven implant loosenings, two of which were associated with infection. Two superficial (0.6%) and two deep infections (0.6%) occurred in 306 closed fractures. Deep infection developed in one of 81 osteosyntheses of open fractures (1.2%). Other complications included one synostosis, fractures with the implant in situ with adequate trauma involving three bones, and two secondary correction procedures for postoperative malalignment. There were seven refractures occurring at a mean of three weeks after the removal of 150 PC-Fixators (4.7%). This study demonstrated that the technique of using an internal fixator is a simple one for the fixation of forearm fractures, resulting in shorter duration of surgery with a low rate of complications compared with the data reported in the literature on conventional techniques for forearm fracture stabilization.

Adolescent↗
PubMed2001

Loads acting in an intramedullary nail during fracture healing in the human femur.

The form and function of the musculo-skeletal system is closely related to the forces acting in its components. Significant forces are present in the long bones, but their magnitudes have so far only been estimated from mathematical models. Fracture fixation by means of metal implants provides an opportunity to measure the implant-born forces and to estimate the long bone forces before healing occurs. The load changes during fracture healing may provide additional information. Therefore, a telemetrized, interlocking femoral nail for wireless transmission of forces and moments acting across the fracture site was developed. The design was based on the geometry and material of a 16 mm AO nail with a circular, closed cross-section allowing full protection of the electronic circuits from the body fluids. After careful testing, it was implanted in a 33-year-old patient who had sustained a multifragmentary fracture of the left femur. Measurements at a rate of approx. 0.4 Hz were performed in different patient postures between the 2nd and 26th postoperative week. Significant axial forces and bending moments were measured during several activities such as sitting, unsupported leg elevation and partial weight bearing in a standing position. Forces orthogonal to the nail axis remained small. The reductions of the implant loads due to fracture consolidation were in the order of 50%. Dynamization of the nail did not change the forces. Even though the telemetry system did not allow for dynamic measurements and the results presented here provide data from one subject only, the new information will be useful with respect to implant design, biomechanics of fracture fixation and evaluation of healing progression.

Adult↗
PubMed2001

Kinematics of the wrist with a new dynamic external fixation device.

The kinematic properties of a new dynamic external fixator device for treatment of distal radial fractures are described. Using a combination of data obtained from computed tomography scans and high-speed video images, a three-dimensional reconstruction of carpal motion was made. To describe carpal motion, the radiolunate, capitolunate, and scapholunate angles were measured during flexion and extension and during radioulnar deviation. During these types of motion, the device changed normal carpal kinematics to a limited extent although the differences in kinematic pattern with and without the device were small. The results for flexion and extension correspond with data from previously published studies with other dynamic external fixators. However, because the new device (Flexafix) allows flexion and extension and radioulnar deviation, in contrast to other dynamic external fixation devices, with its use normal carpal kinematics can be approached more closely.

Adult↗
PubMed2001

Treating forearm fractures using an internal fixator: a prospective study.

Some major complications of internal fixation with plates, such as infections and disturbance of healing, have been shown to be related to necrosis of bone and to the soft tissues immediately deep to the plate. This is attributable to plate contact. To deal with this phenomenon, an internal fixator, the Point Contact Fixator, was developed according to a new concept. The Point Contact Fixator resembles a plate but functions like a fixator, that is, the fracture is stabilized using a splint fixed to the bone by monocortical, angularly locked screws that are designed not to exert pressure between the splint and the bone, thereby minimizing implant-to-bone contact. Vascular damage to the osseous blood supply consequently is avoided. The new internal fixator is the first of a new family of implants in addition to nails, plates, and external fixators. To study the potential of the Point Contact Fixator in a prospective study, 79 forearm fractures in 55 patients were treated in a consecutive series by one surgeon using the same technique throughout. Followup to union is reported for 100% of the patients. Handling the fixator was simple; healing was uneventful; and the rate of complication was low.

Adult↗
PubMed2000

Development and testing of a new self-locking intramedullary nail system: testing of handling aspects and mechanical properties.

A distal interlocking system has been developed which is easy to use, carries out an aligning effect on the distal fracture fragment, reduces the exposure to radiation for the surgeon and the patient, and allows for a decrease in operating time. The goal of this study was to develop and test the handling and mechanical properties of two prototype nails in comparison to a conventional interlocking nail concept (Unreamed Femoral Nail system). It was shown that the prototype designs represent an improvement over this system. Both designs were easy to use. The prototype with the asymmetrically offset interlocking bolts exhibited an exemplary aligning effect on the distal fracture fragment. Both designs showed mechanical stability comparable or superior to that of the standard contralateral control in four-point-bending and axial compression. Given the handling advantages afforded by the new self-locking intramedullary implant system, it would be expected that use of this system would reduce exposure to radiation for the surgeon as well as the patient and allow for a decrease in operating time. This new development may be of particular interest for clinics without access to fluoroscopes in the operating theatre (e.g. in the Third World).

Aged↗
PubMed2000

Stress protection due to plates: myth or reality? A parametric analysis made using the composite beam theory.

A generally accepted idea has been that plate fixation of fractures may result in the structural adaptation of bone (bone loss) to reduced stress (stress protection) with the subsequent danger of refracture after implant removal. This was the negative aspect of stress protection. For this reason, it was proposed that plates made from more deformable materials be used (titanium, polymers or carbon fibres). A theoretical analysis using composite beam theory, with different loading conditions (axial load and bending), demonstrates that stress protection, i.e. early temporary porosis, is a myth. Mechanics of materials shows that when an over-large plate is fixed to small bones (as in small animals, e.g. rabbits), the reduction of bone strain is exaggerated; in contrast, using plates of varying flexibility (steel, titanium or carbon fibre) on large bones leads to strain reduction with an astonishingly similar amplitude.

Animals↗