Rigid Implants Research Articles

A flexible intramedullary nails for fractures in children.

©2004 British Editorial Society of Bone and Joint Surgery doi:10.1302/0301-620X.86B7. 15273 $2.00 J Bone Joint Surg [Br] 2004;86-B:947-53. Over the past few years there has been a marked increase in the use of intramedullary fixation in the management of fractures of long bones in children. To some extent this reflects a more interventionist attitude among paediatric orthopaedic surgeons but is also due to technical developments, notably that of the elastic stable intramedullary nail (ESIN). The use of intramedullary devices to stabilise fractures is not new. In the mid-19th century, ivory pins were used for this purpose and were then gradually supplanted by various metal devices.1 These were generally rigid implants, although more flexible ones were introduced in in the 1930s. The school of rigid intramedullary fixation was typified by the Kuntscher nail, which achieved great stability in all planes by occupying the entire medullary cross-sectional area of the bone.2 However, its use in growing children was limited by the difficulties encountered in trying to avoid the physes. The Rush nail was introduced at about the same time as the Kuntscher nail.3 It was the forerunner of modern elastic intramedullary fixation in that the objective was to achieve three-point fixation on the inner aspect of the cortex. Unlike the stiff Kuntscher nail, the Rush nail was slightly flexible and it was intended that it should be pre-bent to the appropriate configuration before insertion.3 Rotational stability was poor, however, and in most situations the flexibility was insufficient to allow insertion points in the metaphysis which were well away from the active physis in children. Others, such as Hackethal4 and Marchetti,5 used bundles of thinner wires which filled the medullary cavity but with stabilisation achieved by splaying the ends of the wires within the bone well beyond the fracture. Ender6 developed this further with his nails, which were the first to feature adaptations to both ends of the nail in order to improve both control of insertion and quality of fixation. These nails could be safely inserted into the metaphysis which made them suitable for consideration in paediatric fractures. In the early 1980s, surgeons in Nancy, France, developed an elastic stable intramedullary nail based on a theoretical concept by Firica.7 Previous experience had suggested that elasticity and stability were not easily combined in one construct. However, working from the concept of three-point fixation used with a single Rush nail, these surgeons were able to improve stability significantly by using two pre-tensioned nails inserted from opposite sides of the bone. Metazieau, Ligier and their colleagues7 were able to show that titanium nails which were accurately contoured and properly inserted could impart excellent axial and lateral stability to diaphyseal fractures in long bones. Rotational stability was also better than had previously been experienced, although this was to remain the weakest point of the technique. The use of titanium nails allowed greater elasticity than was available in the steel nails of the Ender system. Most contemporary work on flexible intramedullary nailing in children’s fractures is based on the Nancy experience, although there remain pockets of Ender and Marchetti enthusiasts. For the purposes of this review, flexible intramedullary nailing is taken to mean elastic stable intramedullary nailing using the concepts espoused by the Nancy group.

Implants digitaux

Joint replacements in the hand are indicated in the treatment of rheumatoid arthritis, degenerative and post traumatic arthritis. This surgery has to be very precise because of the delicate equilibrium between bones, fulcra, ligaments, complex connections between tendon structures and precise lever arms of these tendons. For the first carpo-metacarpal joint, total replacement provides a good solution in terms of pain, range of motion, grip, grasp and key pinch. The related possibility of replacing a failing prosthesis provides a solution for loosened implants and makes the procedure more secured. For metacarpal and interphalangeal joints, two-piece rigid implants and silicone implants are available.

Bioabsorbable composite implants for treatment of bone fractures and osteotomies

The advantages of bioabsorbable implants in bone surgery are significant: there is no need for removal operation, and osteoporosis associated with rigid metallic implants can be avoided or at least reduced and the bone itself heals better. The avoidance of removal procedures leads to financial benefits, psychological advantages, and it increases operative capacity.

A Tale of Two CAD Systems

Walter Lorenz Surgical Inc., Jacksonville, FL, specializes in the medical devices known as rigid fixation implants. Lorenz Surgical was purchased by Biomet Inc. of Warsaw, Indiana in the year 1992, which resulted in Lorenzo owning two computer-aided design (CAD) systems. In 1996, with the completion of Lorenz Surgical's new manufacturing facility in Jacksonville, all Lorenz operations were transferred back to Florida, including all the manufacturing equipment and its three seats of Unigraphics, which by then were running on Windows NT workstations. The company's management feels it could have stayed with Unigraphics and accomplished its goals, but that adding Solid Edge was a good move. It gave Lorenz flexibility in hiring, allowed it to buy more CAD seats than it could have if it had stayed with Unigraphics alone, and provided a very productive tool. Lorenz's surgical instruments are currently designed exclusively in Solid Edge. Instruments can be modeled in either CAD system, but the job goes faster in Solid Edge. The creators of Solid Edge put a lot of effort into usability, and this shows in how few mouse clicks are needed for common operations. Products that have many standard features, such as a screwdriver consisting of m any cylinders, are very quickly modeled in Solid Edge.

Clinical outcome after spinal fusion with a rigid versus a semi-rigid pedicle screw system

Several biomechanical studies have evaluated the quality of fusion obtained with a rigid versus a semi-rigid pedicle screw implant. Some studies indicate that increased rigidity of the implant system results in an increased strength of the fusion mass. Other reports have underlined the risk of stress shielding due to rigid implant systems. Based on these findings some authors have recommended the use of a semi-rigid system. There are, however, few studies focusing on any possible difference in clinical outcome between the two different types of implant systems. Questionnaires were sent to 89 patients who had undergone primary spinal fusion with either a rigid or a semi-rigid pedicle-screw-based implant system. In every case the diagnosis was spondylolisthesis or degenerative lumbar disease. The questionnaires were analysed using forward stepwise logistic regression analysis. Eighty (90%) of the questionnaires were returned. There was a mean follow-up of 4 years (range 2-8 years). It was not possible to demonstrate any difference in clinical outcome between patients undergoing lumbar fusion with a rigid implant system and those given a semi-rigid system. The overall patient satisfaction rate was 69%, with no difference between the two types of implant. No difference in clinical outcome between the two types of implant was found. Considering the fact that the primary goal of spinal fusion procedure is to obtain a solid fusion mass, biomechanical tests favour the used of a rigid pedicle screw system. This fact combined with the fact that early mobilisation is possible with rigid implants justifies the use of rigid implant systems, although no difference in clinical outcome could be demonstrated in this study.

Flexible (Polyactive ®) versus rigid (hydroxyapatite) dental implants

In a beagle dog study, the peri-implant bone changes around flexible (Polyactive ®) and rigid hydroxyapatite (HA) implants were investigated radiographically by quantitative digital subtraction analysis and by assessment of marginal bone height, with the aid of a computerized method. A loss of approximately 1 mm of marginal bone height was observed for both the dense Polyactive and the HA implants, after 6 months of loading. This value appeared to be stable from 12 weeks of loading onward. Along the total length of the implant during the first 6 weeks of loading, both the flexible (dense Polyactive) and the rigid (HA) implants showed a decrease in density. However, after this 6-week period, the bone density around the implants increased, and after 18 weeks the original bone density was reached. The flexible Polyactive implants provoked less decrease in density than the rigid HA implants, although not to a statistically significant level. This finding sustains the hypothesis that flexible implant materials may transfer stresses to the surrounding bone more favorably.

A comparative study of flexible (Polyactive®) versus rigid (hydroxylapatite) permucosal dental implants. II. Histological aspects

summary Of the many materials that are applied in dental implantology, most have a high Young's modulus. In the concept of osseointegration, which is generally preferred, chewing forces are therefore directly transmitted from rigid implant materials to the relatively flexible surrounding bone. Polyactive® is an elastomeric polyethylene‐oxide polybutylene‐terephthalate (PEO:PBT) copolymer, with a low modulus of elasticity, that exhibits bone‐bonding characteristics. Previous finite‐element analysis emphasized the benefit of the application of flexible implant materials. To assess the validity of this finite element model, one dense and two porous types of flexible Polyactive® permucosal dental implants and one rigid hydroxylapatite (HA) implant were clinically tested in a beagle dog study and were compared during 30 weeks of loading. In an earlier report, it was concluded that dense Polyactive® implants function clinically adequately and resemble the mobility of natural teeth. In the current study, the amount of bone contact was quantitatively assessed. Polyactive® implants showed a statistically significantly higher bone contact, as compared to the HA implants, probably due to a significant water uptake and a subsequent increase in the volume of the denser Polyactive®. Morphological analysis, based on back‐scatter electron microscopy and light microscopy, revealed little remodelling activity of the bone surrounding the Polyactive® implants. Few remodelling lacunae were seen and de novo bone formation was rarely observed. At some locations, a continuity between calcification zones with the polymer surface and the surrounding interfacial bone was observed, indicating the occurrence of bone‐bonding. Also, the bone surrounding the HA implants showed little remodelling activity, although large resorption lacunae were observed, in which HA particles were present. Based on the observations of this study, flexible bone bonding implants might be more capable of transferring stresses to the surrounding bone and are therefore promising alternatives to ‘routine’ rigid implants.

The effect of pulsed electromagnetic fields on instrumented posterolateral spinal fusion and device-related stress shielding.

This study was designed to examine stress-shielding effects on the spine caused by rigid implants and to investigate the effects of pulsed electromagnetic fields on the instrumented spine. To investigate the effects of pulsed electromagnetic fields on posterolateral spinal fusion, and to determine if osteopenia induced by rigid instrumentation can be diminished by pulsed electromagnetic fields. Although device-related osteopenia on vertebral bodies is of a great clinical importance, no method for preventing bone mineral loss in vertebrae by stiff spinal implants has been effective. Twenty-eight adult beagles underwent L5-L6 destabilization followed by posterolateral spinal fusion. The study was divided into four groups: 1) Group CNTL: without instrumentation, without pulsed electromagnetic fields, 2) Group PEMF: without Steffee, with pulsed electromagnetic fields, 3) Group INST: with Steffee, without pulsed electromagnetic fields, 4) Group PEMF + INST: with Steffee, with pulsed electromagnetic fields. At the end of 24 weeks, the dogs were killed, and L4-L7 segments were tested biomechanically without instrumentation. Radiographs and quantitative computed tomography assessed the condition of the fusion mass. Stress shielding was induced in the anterior vertebral bodies of L6 with the Steffee plates; bone mineral density was increased with the addition of pulsed electromagnetic fields, regardless of the presence or absence of fixation. A decrease in flexion and bending stiffness was observed in the Group INST; pulsed electromagnetic fields did increase the flexion stiffness regardless of the presence or absence of fixation, although this was not statistically significant. Use of pulsed electromagnetic fields has the potential to minimize device-related vertebral-bone mineral loss.

Posterior Cervical Fixation for Fracture and Degenerative Disc Disease

There are numerous newer techniques that have been developed for the internal fixation of the cervical spine in recent years. Wiring techniques are still appropriate for posterior stabilization of the cervical spine. The halo vest is still widely used for the conservative management of cervical fractures and for postoperative external immobilization. The authors stress that the surgical indications for more modern rigid implants should be adhered to strictly. These implants also should be selected by weighing their advantages versus potential risks. In the upper cervical spine, the surgeon may choose traditional wiring methods and newer C1-C2 screw fixation, occipitocervical plate fixation. For the lower cervical spine, triple wiring technique or lateral mass plating may be used. The surgeon must choose an appropriate device based on the mechanism of injury, pathoanatomy of the lesion, and familiarity with the device, keeping in mind that the goals of internal fixation are stabilization, reduction and maintenance of alignment, early rehabilitation and perhaps enhancement of fusion rates, and avoidance of use of an external halo vest.

The effect of instrumentation on human spinal fusion mass.

This study is a prospective histomorphometric evaluation of human spinal fusion bone using video dimensional analysis. Little information exists regarding the biology of fusion mass (FM) and the effect that instrumentation has on FM quality. Concerns regarding potential for "stress shielding" of FM with rigid implants have arisen. The goal of this study was to determine what effect spinal implants have on the quality and metabolism of FM bone. Fifty-six patients underwent surgeries to remove spinal implants or extend a fusion after pulse-dose labeling with fluorochrome. Twelve patients had undergone fusions without instrumentation. Duplicate biopsies of FM and iliac crest (IC) were obtained and evaluated blindly for mineralized volume, trabecular thickness, mineralization rate, and bone formation rate. Iliac crest, instrumented FM, and noninstrumented FM were compared. Instrumental FM had superior material properties relative to noninstrumented FM or IC. No significant difference in metabolic activity was present. Instrumentation does not lead to FM "stress-shielding."

Comparative Postoperative Infection Rates in Midfacial Trauma Using Intermaxillary Fixation, Wire Fixation, and Rigid Internal Fixation Implants

• The use of rigid internal fixation implants in the repair of midfacial fractures requires more extensive bone exposure, soft-tissue manipulation, and operative time. We wished to determine the relative contribution of this method of repair to postoperative infection rates. Midfacial trauma cases occurring between the years 1984 and 1991 at the University of Iowa Hospitals and Clinics, Iowa City, were reviewed. Patients were grouped according to method of repair (intermaxillary fixation, open reduction with wire fixation, or open reduction with rigid internal fixation plates). postoperative infection data (wound infections, sinusitis, etc) were obtained by chart review and telephone interview. Minimum follow-up for inclusion in the study was 3 months, with an average follow-up for all groups of 28.8 months. We found no significant difference in the rate, or the type, of postoperative infections in all three groups. We conclude that rigid internal fixation implants do not contribute increased postoperative infection rates in midfacial trauma. (Arch Otolaryngol Head Neck Surg.1993;119:308-309)

Histological observations of coated and prestressed dental implants under flexible or rigid loading conditions

Hydroxyapatite-coated and hydroxyapatite-prestressed titanium implants were implanted under load-free, flexible-loaded and rigid-loaded conditions in dog mandibula in vivo. The bone response, bone contact and the quality of the coating were evaluated histologically and histometrically. Hydroxyapatite coating on titanium implants enhanced the bone apposition. The bone contact can still be present while the coating is resorbed. Gingiva contact with the coating led to a faster degradation of the coating. There was no significant difference in bone contact between hydroxyapatite-coated and -prestressed implants with regard to the loading systems: rigid, flexible and load-free. All three implants showed the highest amount of bone contact apically. Only at the mesial side of the implant did the flexible element show rather high amounts of bone contact compared to the rigid and load-free implants. The hydroxyapatite coating more or less degraded during the implantation period. The degree of degradation varied in the implant itself, between the implants and between the animals.

Obtaining rigidity in the neophallus of female-to-male transsexuals: a review of the literature.

In phalloplasty, the use of transplants and implants to obtain sufficient rigidity allowing for sexual penetration is difficult and often has resulted in complications and failure. Resorption, curving, and fracture of autologous cartilage and bone transplants are reported, and rigid implants have a tendency to erode and extrude. Besides, a constantly rigid phallus may serve as a source of embarrassment to the patient. On the other hand, hydraulic prostheses frequently show mechanical failure compared with nonhydraulic implants. For these reasons, some authorities have their patients use external devices for erection. Others fully rely on edema, scar fibrosis, or congestion to give sufficient rigidity. In this review, the literature on baculum implantation--on the use of external devices as well as on the use of no stiffener at all--is discussed.

Osseointegrated Implants and Orthodontics

SUMMARY Bone physiology and metabolism are important considerations for all orthodontic and den- tofacial procedures. Osseointegrated implants are the functional equivalent of an ankylosed tooth. Rigid implants do not move in response to orthodontic force. Osseointegration is a source of firm anchorage applicable to a variety of restorative problems. Periodontal health, functional occlusion, patient comfort, and longterm prognosis can be enhanced by orthodontic treatment utilizing implant anchorage. Under the conditions described, atrophic edentulous ridges may be candidates for space closure.

Strain shielding 12 weeks after femoral reaming and nailing in rats.

The purpose of this study was to investigate the in vivo strain-shielding in rat femora 12 weeks after intramedullary nailing with either flexible or rigid implants. Five days prior to death, unidirectional strain gauge units were implanted on the anterior bone surface bilaterally. Median strain values of reamed only and polyacetal-nailed femora ranged from 67 to 90 percent of the intact side. Removal of polyacetal nails and sham operations gave negligible changes in strain. Strain of the steel-nailed femora was 51 percent of the intact side. Removal of nails increased strain to 91 percent of the intact side. Testing of femora after removal of implants revealed stiffness of 116 and 103 percent of normal in reamed-only and polyacetal-nailed groups, respectively. Stiffness in the steel-nailed group was reduced to 85 percent of normal. None of these changes were statistically significant. This study indicates that rigid intramedullary nails cause strain shielding at the anterior, mid-diaphyseal surface of rat femora 12 weeks after insertion. Removal of rigid implants seems to restore the loading configuration immediately.

Cementless Total Hip Arthroplasty

The differences between prostheses fixed with and without cement are mainly in the design and nature of the surface implant. The shapes of the sockets to be implanted without cement show a wide variety: cylinder, square, conus, and ellipsoid with and without threads. The hemispheric shape, however, which was chosen for the acetabular component of the isoelastic hip joint, does not disturb the natural form and function of the hip joint since the outer surface is closely adapted to the original subchondral bone layer. The noncemented cup is secured by threads, pegs, screws, etc., and by ingrowth of bony tissue in the grooves of the surfaces. Most femoral stems are based on the self-locking principle. All prosthetic models incorporate attempts to increase the surface of the stem (ribs, wings, corrugations, rims, etc.). There is a tendency to use less rigid elastic implants instead of the well known rigid metallic prostheses. The aim is to overcome the problems of stress protection and stress concentration observed with rigid implants. For the biomechanical integration of an implant, the properties of the surface, especially macroporosity and microporosity, are important. Most European models of noncemented endoprostheses are based on macroporosity (porometal, madreporic, etc.). The increase in implant surface area achieved with macroscopic perforations and recesses is relatively minor compared with the possibilities offered by microporosity ("alumine fritée," Proplast, fiber-metal, etc.). The best indication for use of a cementless hip endoprosthesis is in revision arthroplasty. The lost bone stock is replaced by bone grafts, thereby creating a situation comparable with that of a primary arthroplasty. Clinical experience with noncemented hip endoprostheses is, to date, promising, although the observation time for most models is short.

The treatment of squamous-cell carcinoma of the lower lip by rigid implants

A technique of implantation of the lower lip is described. The sources are held in a constant position in relation to each other and to the tumour. The technique has recently been modified to allow after-loading with Iridium 192 wires, reducing the radiation exposure to the operator. No local recurrences or lymph node metastases occurred in 29 of 30 patients with tumours less than 3 cm in diameter observed for three years. The method was much less successful with larger tumours. It is suggested that this is a simple and effective alternative to fractionated external beam radiotherapy.