Stainless Steel Screws Research Articles

Pleomorphic Malignant Fibrous Histiocytoma at the Site of an Arthroscopic Reconstruction of the Anterior Cruciate Ligament

P reviously regarded as a distinct tumor type representing the most common adult soft-tissue sarcoma1,2, the term malignant fibrous histiocytoma is now reserved for a small group of undifferentiated pleomorphic sarcomas3. The tumor is most often primary, but rare cases of secondary malignant fibrous histiocytoma in burn scars4-8 or infected or noninfected surgical scars9-12 have been reported (see Appendix). Secondary malignant fibrous histiocytoma has been described in contact with prostheses13-28, osteosynthesis material29-35, or implanted Dacron grafts36. Malignant degeneration of benign tumors35, Paget disease37, osseous infarcts38, or fibrous dysplasia39 also has been reported (see Appendix). We report a unique case of a patient with soft-tissue malignant fibrous histiocytoma that developed on the medial side of the knee six years after arthroscopic reconstruction of the anterior cruciate ligament with use of the patellar tendon. D uring a soccer game in June 1993, a nineteen-year-old man experienced an indirect injury to the right knee that caused a rupture of the anterior cruciate ligament. A magnetic resonance imaging scan confirmed the diagnosis. An arthroscopic reconstruction of the anterior cruciate ligament was carried out in October 1993 with use of the patellar tendon. Stainless-steel (alloy-316L) screws (with a diameter of 6.5 mm) were used for the femoral and tibial fixation. The rest of the intra-articular examination was normal, and the postoperative course was uneventful. In 1995, a hemarthrosis developed in the right knee subsequent to a new injury. The knee was stable, and the hemarthrosis resolved with symptomatic treatment. In 1997, the patient experienced a locking episode of the right knee, which was found to be caused by a bucket-handle tear of the medial meniscus at …

Craniovertebral Junction Realignment for the Treatment of Basilar Invagination With Syringomyelia: Preliminary Report of 12 Cases

Twelve selected patients, eight males and four females aged 14 to 50 years, with syringomyelia associated with congenital craniovertebral bony anomalies including basilar invagination and fixed atlantoaxial dislocation, and associated Chiari I malformation in eight, were treated by atlantoaxial joint manipulation and restoration of the craniovertebral region alignment between October 2002 and March 2004. Three patients had a history of trauma prior to the onset of symptoms. Spastic quadriparesis and ataxia were the most prominent symptoms. The mean duration of symptoms was 11 months. The atlantoaxial dislocation and basilar invagination were reduced by manual distraction of the facets of the atlas and axis, stabilization by placement of bone graft and metal spacers within the joint, and direct atlantoaxial fixation using an inter-articular plate and screw method technique. Following surgery all patients showed symptomatic improvement and restoration of craniovertebral alignment during follow up from 3 to 20 months (mean 7 months). Radiological improvement of the syrinx could not be evaluated as stainless steel metal plates, screws, and spacers were used for fixation. Manipulation of the atlantoaxial joints and restoring the anatomical craniovertebral alignments in selected cases of syringomyelia leads to remarkable and sustained clinical recovery, and is probably the optimum surgical treatment.

Screw fixation of the syndesmosis: a cadaver model comparing stainless steel and titanium screws and three and four cortical fixation

We assessed syndesmotic set screw strength and fixation capacity during cyclical testing in a cadaver model simulating protected weight bearing. Sixteen fresh frozen legs with artificial syndesmotic injuries and a syndesmotic set screw made of stainless steel or titanium, inserted through three or four cortices, were axially loaded with 800 N for 225,000 cycles in a materials testing machine. The 225,000 cycles equals the number of paces taken by a person walking in a below knee plaster during 9 weeks. Syndesmotic fixation failure was defined as: bone fracture, screw fatigue failure, screw pullout, and/or excessive syndesmotic widening. None of the 14 out of 16 successfully tested legs or screws failed. No difference was found in fixation of the syndesmosis when stainless steel screws were compared to titanium screws through three or four cortices. Mean lateral displacement found after testing was 1.05 mm (S.D. = 0.42). This increase in tibiofibular width exceeds values described in literature for the intact syndesmosis loaded with body weight. Based on this laboratory study it is concluded that the syndesmotic set screw cannot prevent excessive syndesmotic widening when loaded with a load comparable with body weight. Therefore, we advise that patients with a syndesmotic set screw in situ should not bear weight.

Cannulated Screw Fixation of Jones Fractures

Background Traditional nonsurgical treatment of Jones fractures has high rates of delayed union, nonunion, and refracture. Internal fixation has become the treatment of choice in athletes and active patients. Purpose The purpose of this study was (1) to review the short- and long-term clinical results of cannulated screw fixation of Jones fractures and (2) to perform a biomechanical evaluation of fatigue failure characteristics of several types of screws used in the fixation of Jones fractures. Study Design Retrospective case series and in vitro biomechanical study. Methods Ten male and 5 female patients with Jones fractures fixed with cannulated screws ranging from 4 mm to 6.5 mm in diameter were evaluated by chart review, review of radiographs, and telephone interview. Mean follow-up from surgery to phone survey was 34 months. Screws ranging in size from 2.7 mm to 7.3 mm, both cannulated and noncannulated, stainless steel and titanium, were tested in the laboratory by cyclic loading to 250 N up to a maximum of 200 000 cycles. Results Mean time to healing as shown on radiographs and by full activity after surgery were 7.3 and 7.9 weeks, respectively. All patients were able to return to their previous levels of activity. Screw fatigue data showed that the number of cycles to failure increased with increasing screw diameter. For 4-mm screws, mean number of cycles to failure was 4308 for cannulated titanium screws, 22 012 for cannulated stainless steel screws, and 44 523 for noncannulated stainless steel screws. Conclusions In our patients, cannulated screw fixation of Jones fractures was a procedure that was reliable, had low morbidity, and afforded athletes a quick return to activity. Clinical Relevance The laboratory study suggests that the largest screw possible should be used for surgical fixation of these fractures and that screws less than 4 mm in diameter should be used with caution.

Design of a head fixation device for experiments in behaving monkeys

We have designed a new device for head fixation of behaving monkeys. The fixation device consists of a duralumin head ring mounted with four screw holders. It is firmly fixed to the animal’s skull with four stainless steel screw pins. The head ring is then attached to a primate chair in any desirable position and angle using a set of adjustable plates. The device has been used for behavioral training that requires accurate gaze monitoring and for recording single-unit activity over a several-month period. The advantage of our device is that it is simple to use; it can be attached readily without major surgical procedures and it can be quickly removed when experiments are not running. This head fixation system is suitable for behavioral experiments and single-unit recording studies. It may also be applicable for studies on functional imaging of the macaque brain, by constructing it of non-magnetic materials.

Differential morphine effects on short- and long-latency laser-evoked cortical responses in the rat

Evoked potential and ensemble neuronal activities were used to study the responses of the primary sensorimotor cortex (SmI) to noxious CO 2 laser irradiation of the middle part of the tail in conscious behaving rats. The hypothesis that systemic morphine treatment preferentially attenuates the longer-latency laser-evoked cortical responses was also tested. Laser-evoked potentials (LEPs) and multiple single-unit (SU) activities were, respectively, recorded from chronically implanted stainless-steel screws and microwire electrodes. When examined individually, many SmI neurons showed either short-latency (<100 ms) or long-latency (300–500 ms) responses to laser irradiation. These neurons are widely dispersed in the tail region and hind limb region of the SmI, and also in the forelimb and head regions of the primary motor cortex (MI). Quantitatively, a higher percentage of neurons in the SmI tail region responded with shorter latencies compared to those in the SmI hind limb region or in the MI. When responses of many simultaneously recorded SU were examined together, short-latency and long-latency SmI ensemble activities matched the LEP1 and LEP2, respectively. Systemic morphine significantly attenuated the long-latency but not the short-latency component in both LEPs as well as ensemble neuronal activity in the tail region of the SmI. These effects were blocked by naloxone pretreatment.

Systemic and local ibandronate enhance screw fixation

The trauma involved with inserting implants into bone leads to an activation of the inflammatory response and an activation of osteoclasts. In addition, apoptosis of osteocytes in the surrounding area has been implicated in further activation of osteoclasts. If the balance between resorption and bone formation shortly after implantation favours resorption, an impairment of early fixation might ensue. Because bisphosphonates inhibit resorption, this study analyses whether they can improve early fixation. Stainless steel screws (M 1.7) were inserted into the tibiae of 76 male Sprague-Dawley rats. Daily subcutaneous injections of ibandronate (3 μg) or saline were given to 20 rats. The remaining rats received ibandronate or saline directly applied into the drill hole before the screw was inserted. Tibiae were harvested at 14 days. Mechanical tests were performed on 50 tibiae. Systemically treated tibiae were tested for pull-out strength alone. Locally treated tibiae were tested for either pull-out or torque resistance. The remaining 18 tibiae were prepared for histology. Systemic ibandronate increased the pull-out force at failure by 30% ( p=0.04). Local treatment increased the force at failure by 15% ( p=0.02) and stiffness by 28% ( p=0.01). In the removal torque measurements, local ibandronate increased the torque-moment at failure by 60% ( p=0.04), and the maximum friction moment by 51% ( p=0.04). Energy for turning the screw 1/4 revolution was increased by 68% ( p=0.02). These results demonstrate that early remodeling events plays an important role in screw fixation, and that systemic or local bisphosphonate treatment could be an effective pharmacological path to improve early implant fixation.

Electrochemical assessment of some titanium and stainless steel implant dental alloys

Commercially pure titanium alloy, Ti-6Al-4V alloy and stainless steel screw implants were evaluated in both Ringer and synthetic saliva physiological solutions at body temperature by EIS (Electrochemical Impedance Spectroscopy) with immersion times of 30 d. Results were simulated as a sandwich system composed by four capacitors-resistances connected in series with the solution resistance. A model explaining the results in terms of the porosity and thickness of four different layers, was proposed.

Surface immobilized bisphosphonate improves stainless-steel screw fixation in rats

An increase in the mechanical fixation in bone of metallic biomaterials is considered advantageous in joint replacement and fracture surgery. Different approaches to improve fixation may be e.g. surface roughening, Ca-mineral coating or surface immobilization of growth factors or drugs. In the present work, bisphosphonate, a class of drugs that inhibit bone resorption, was immobilized onto stainless-steel screws. The screws were first roughened and coated with immobilized and cross-linked fibrinogen. Subsequently, an N-bisphosphonate, pamidronate, was immobilized onto fibrinogen, and another N-bisphosphonate, ibandronate, adsorbed on top of this. The so coated screws were inserted into the tibiae of eight male Sprague-Dawley rats. Another eight rats received screws prepared in the same way, but without the bisphosphonate coating. Pullout strength tests were performed after 2 weeks of implantation. The results showed a 28% ( p=0.0009) higher pullout force and 90% increased pullout energy for the bisphosphonate coated screws, and support the idea that surface immobilized bisphosphonates can be used to improve biomaterials fixation in bone.

Drug release kinetics and fronts movement studies from methyl methacrylate (MMA) copolymer matrix tablets: effect of copolymer type and matrix porosity

Several methyl methacrylate (MMA) copolymers have recently been proposed as an alternative for the formulation of controlled-release matrix tablets. Copolymers were synthesised by free radical copolymerisation of methyl methacrylate with starch or cellulose derivatives and were alternatively dried by oven or freeze-drying techniques. Both the chemical composition and the drying technique were demonstrated to have a considerable influence on the physical properties of the copolymers. The present investigation was focused on the elucidation of the drug release mechanism from MMA copolymer matrices, using anhydrous theophylline as model drug. Drug release experiments were performed from free tablets. Radial drug release and fronts movement were also evaluated using special devices consisting of two Plexiglass ® discs joined by means of four stainless steel screws. Mathematical analysis of release data was performed using Higuchi, Korsmeyer and Peppas equations and fronts movement was investigated using a colorimetric technique. The drug release rate and the relative positions of the fronts were studied as functions of the type of copolymer and the initial porosity of the tablets. Drug release was controlled mainly by diffusion and the release rate was found to be affected by the drying method and related to the area exposed to the dissolution medium. Three distinct fronts (water uptake, complete wetting, erosion) were observed during the release process and the dynamics of fronts movement confirmed the diffusional mechanism.

Bioabsorbable screw fixation in coracoclavicular ligament reconstruction.

The purpose of this study is to evaluate the biomechanical properties of stainless steel and bioabsorbable screw fixation of the clavicle to the base of the coracoid. Seven matched pairs of fresh frozen shoulders were prepared by removing all soft tissue except the acromioclavicular and coracoclavicular ligament complexes. The shoulders were randomly selected and fixed with 4.5-mm stainless steel (SS) screws, while contralateral shoulders were fixed with 4.5-mm poly L-lactic acid polymer (PLLA) screws. Pullout strength, stiffness, and elongation to failure were measured using an Instron Mechanical Tester (Model 4202). The average pullout strength of 720.6 +/- 244.9 N of the metal screws was not statistically different (p = 0.089) from that of the biodegradable screws of 580.4 +/- 188.6 N. The pullout strengths exerted by both these screws exceeded the reported strength (500 N) of the intact coracoclavicular complex indicating adequate initial pullout strength for coracoclavicular fixation.

The stainless steel screw as an orthopaedic implant

AbstractThe study reported here dealt with the metallographical inspection and analysis of corrosion behavior of screws for mild Slipped Capital Femoral Epiphysis (SCFE), which is a serious orthopedical problem in early adolescence. The screws were fabricated from low carbon, austenitic grade stainless steel type 316L (AISI) with 1600 ppm of nitrogen (316LN2). They were clinically tested in a nearly 25‐year‐long study where patients in early adolescence were operated with these screws with the fixation in situ. Since the results obtained in all patients were similar, we present the results obtained in screws removed after 3 years of implantation from a 14‐year‐old boy. Metallographical inspection results reveal that a low content of carbon in the SS 316LN2, and annealing this material at a high temperature ensures the monophasic microstructure of austenitic grains. In the grains twin bands that appeared during mechanical deformation were observed. As the hardness measured at the stalk (262 HV) was lower than that measured at the head of the screw (293 HV) it was concluded that cold mechanical deformation of the head was much more extensive than that of the stalk. Accordingly, corrosion of the head could be more probable than that of the stalk. Corrosion behavior of the screw in simulated physiological media (0.9% NaCl solution), carried out by the electrochemical method, gave an Ecorr of −0.124 V (vs. SCE), corrosion current density of 21 nA/cm2, and corrosion rate of 0.010 ± 0.005 mpy. This low corrosion rate indicates that SS 316LN2 expresses relatively high corrosion resistance in a saline solution. However, potentiodynamic polarization measurements, where the specimen was driven to more than 1.8 V above the Ecorr., showed that in the region between −0.1 and 0.15 V the specimen corroded, while around 0.2 V a small valley appeared where passivation proceeded. The narrow passive region between 0.15 and 0.25 V indicated that chlorides prevented the formation of thick protecting films. With potentials more positive than 0.3 V the passivating film broke down and the specimen began to corrode. These data indicate that SS 316LN2 can not be effectively protected by passivation since it is not corrosion resistant in a chloride containing environment.

Slippage between screwdriver and bone screw.

Cortical 3.5-mm stainless steel screws with hexagonal heads and corresponding screwdrivers from two manufacturers were investigated. Measurement of dimensions and torsional testing were done to study slippage between the screw and the driver bit. There were only small differences in dimensions between the manufacturers. Ultimate torque values obtained were at the level of 2.7 N-m where reaming of the screw socket took place. Additional rotation resulted in approximately (1/2) of the maximum torque. Subsequent torque testing in the opposite direction, corresponding to removal of the screw, revealed that the torque values were equally low in that direction. Additional insertion and removal of bone screws with hexagonal sockets are hampered after only one episode of slippage. It is justified to consider new shapes of drive bits and corresponding screw head sockets, such as a fluted multiedge configuration.

Improvement of the Bone–Screw Interface Strength with Hydroxyapatite-Coated and Titanium-Coated AO/ASIF Cortical Screws

To evaluate whether coating AO/ASIF screws with osteoconductive materials can improve bone-screw fixation. Ninety-six AO/ASIF 4.5-millimeter cortical screws were divided into four paired groups and implanted in the femurs and tibiae of six sheep: Group A = standard stainless steel screws; Group B = stainless steel screws coated with highly crystalline hydroxyapatite; Group C = stainless steel screws coated with low crystalline hydroxyapatite; Group D = titanium screws coated with titanium. The screws were implanted according to the standard AO technique to an insertion torque of 2,000 Newton-millimeters. Sheep were killed at one, three, and twelve months after surgery. Extraction torque was measured on six screws from each group selected at random at time of each euthanization. Morphologic analysis of the bone-screw interface was performed on the remaining screws. At each euthanization the extraction torque of Group A was lower than that of the other groups (p < 0.0001). At three and twelve months the extraction torque of Group B was higher than that of Group D (p = 0.002). Morphologic results showed extensive bone-screw gap in Group A. Optimal osteointegration was observed in Groups B and C. Osteointegration of Group D was higher than that of Group A and lower than that of Groups B and C. It was demonstrated that AO/ASIF screws coated with osteoconductive materials achieve optimal fixation strength, even in the early phase. This fixation strength was significantly higher than that of the standard screws.

Hydroxyapatite coating improves fixation of pedicle screws

We investigated the effects of hydroxyapatite (HA) coating on the purchase of pedicle screws. A total of 23 consecutive patients undergoing lumbar fusion was randomly assigned to one of three treatment groups. The first received uncoated stainless-steel screws, the second screws which were partly coated with HA, and the third screws which were fully coated. The insertion torque was recorded. After 11 to 16 months, 21 screws had been extracted. The extraction torque was recorded. Radiographs were taken to assess fusion and to detect loosening of the screws. At removal, the extraction torques exceeded the upper limit of the torque wrench (600 Ncm) for many HA-coated screws. The calculated mean extraction torque was 29 ± 36 Ncm for the uncoated group, 447 ± 114 Ncm for the partly-coated group and 574 ± 52 Ncm for the fully-coated group. There were significant differences between all three groups (p &lt; 0.001). There were more radiolucent zones surrounding the uncoated screws than the HA-coated screws (p &lt; 0.001). HA coating of pedicle screws resulted in improved fixation with reduced risk of loosening of the screws.

Strength comparison of allogenic bone screws, bioabsorbable screws, and stainless steel screw fixation

Allogenic bone screws are new to the fixation market and have yet to be tested against current fixation materials. An in vitro comparison of the same sizes of stainless steel, bioabsorbable, and allogenic bone screws was undertaken to assess screw resistance to the forces of bending, pullout, and shear. Using aluminum plates to support the screws, forces up to 1000 Newtons were applied to six to eight samples of each type of screw. During each test, stainless steel screws withstood the maximum force that could be exerted by the testing apparatus without failing (bending, 113.9 +/- 11.8 N mean +/- SE; pullout 999.1 +/- 33.7 N; and shear, 997.5 +/- 108.8 N). In each test, compared to bioabsorbable screws, allogenic bone screws failed faster (pullout, allogenic: 12.4 +/- 1.1 seconds vs. bioabsorbable, 120.6 +/- 13.8 seconds; p = .001; bending, allogenic: 53.4 +/- 4.8 seconds vs. bioabsorbable, 201.9 +/- 11.1 seconds; p = .001; shear, allogenic 13.5 +/- 1.4 seconds vs. bioabsorbable, 43.8 +/- 0.9 seconds; p = .001) under equivalent (pullout: bioabsorbable, 385.0 +/- 18.4 N vs. allogenic, 401.0 +/- 35.9 N; p = .001) or lower (bending, allogenic: 4.7 +/- 0.2 N vs. bioabsorbable, 11.0 +/- 0.9 N; p = .675; shear, allogenic: 312.1 +/- 15.5 N vs. bioabsorbable 680.9 +/- 8.5 N; p = .001) loads, and in a highly variable fashion. Overall, the bioabsorbable screws withstood the forces of bending, pullout, and shear better than the allogenic screws, and stainless steel screws outperformed both bioabsorbable and allogenic screws. Despite these results, allogenic screws could still be useful in compliant patients who would benefit from their osteoconductive properties.

A Technique for Permanent Malar Implant Fixation

A common problem with every shape and size of malar/cheek implant is movement, either immediate or delayed, from its desired position on the malar bone. Once the pocket has been created and the implant inserted, suturent bolsters must be tried with limited success to prevent immediate slippage of the implant. Postoperatively, delayed implant mobility can occur anytime and is particularly annoying to the patient when the cheek is palpated. From the success of miniplating of facial fractures, a technique has been developed that allows the immediate, permanent fixation of the silastic implant to the facial skeleton with stainless steel screws.

Early effect of parathyroid hormone (1-34) on implant fixation.

Intermittent systemic administration of parathyroid hormone increases bone formation by stimulating osteoblastic activity. The current study determined how parathyroid hormone (1-34) administration influences the bony fixation of stainless steel screws with time. A screw was implanted in the left tibia and a metal rod was implanted in the right tibia in 30 adult male rats that then were injected three times a week with human parathyroid hormone (1-34) at 60 microg/kg/injection (n = 15) or saline (n = 15). The animals were euthanized after 1, 2, or 4 weeks of treatment. Eight additional rats received only the screw and were euthanized immediately after implantation. No significant effects of parathyroid hormone on body weight change or ash weight of the femurs were seen. The degree of fixation was assessed by measuring pullout strength of the screws. The mean pullout strength immediately after implantation was 12 N. The pullout strength of the group injected with saline was 33 N after 1 week, 23 N after 2 weeks, and 41 N after 4 weeks. The pullout strength of the group injected with parathyroid hormone increased to 43 N after 1 week, 58 N after 2 weeks, and 100 N after 4 weeks. The increase at 2 and 4 weeks was statistically significant. Strength reflects the mechanical properties of the bone within the screw threads. The contralateral tibia with its metal rod was used for blinded histologic assessment. Parathyroid hormone increased the fraction of the metal surface having contract with bone without an intervening soft tissue layer from 45% to 69% after 1 week. The current results suggest that intermittent parathyroid hormone treatment can enhance early implant fixation by enhancing the density of the surrounding bone and by increasing the implant bone contact.

Screw Fixation in Cancellous Osteoporotic Bone – First in Vitro Results with a Novel Augmentation Material

Background: Screw fixation during internal fixation of osteoporotic fractures can be difficult due to severe reduction of bone mass and structure in these patients. Material and Methods: The use of PMMA-bone cement to anchor implants in patients in a “combined osteosynthesis” has empirically been developed. The irreversibility of this methodology is currently limiting it to exceptional use in salvage cases of pathological fractures. A new degradable screw augmentation material was therefore developed on the basis of alkylene bis(oligolactoyl)methacrylates. The mechanical properties of this degradable polymer were tested by pull-out and torque tests in augmenting cancellous stainless steel screws in non-osteoporotic bovine cancellous bone blocks and in polypropylene blocks. In these tests, augmentation was improved significantly by the material. Results: The maximum pull-out force obtained showed an 256% increase compared to the bovine standard system. Screw torques measured were up to 400% higher than this standard for the new material. The in vitro degradation kinetics of the new polymer were tested in a standardized system showing an almost linear weight loss of the material of 2–3% per week between weeks 2 and 16. Conclusion: For further material development improved in vivo and in vitro models must be developed. They should include either considerable overdrilling in normal cancellous bone or human osteoporotic bone.

Tibial Implants: Biomechanical and Histomorphometric Studies of Hydroxyapatite-Coated and Uncoated Stainless Steel and Titanium Screws in Long-Term Ovariectomized Sheep

This study was designed to evaluate osteointegration of HA-coated and uncoated titanium and stainless steel screws in the cortical bone of long-term (24 months) ovariectomized sheep (OVX group), in comparison with Sham-aged sheep (control group). The screws were tested biomechanically (extraction torque) and histomorphometrically (affinity index: Al) 12 weeks after their implantation in tibial diaphyses. Tibial cortical bone parameters showed significant differences between the groups, showing a reduction of the selected parameters in the OVX group. ANOVA showed significant effects for both material and ovariectomy factors on obtained extraction torque (material: F=159.26, p < 0.0005; ovariectomy: F=20.04, p < 0.0005) and Al data (material: F=8.04, p < 0.001; ovariectomy: F=7, 17, p < 0.05). In both groups the extraction torque for coated screws of both materials was significantly higher than for uncoated screws, and uncoated titanium had a better extraction torque than uncoated stainless steel. In the OVX group, the HA-coated stainless steel and titanium Al data were significantly higher than uncoated Al data. In conclusion, the biomechanical and histomorphological results obtained suggest employing HA-coated screws in the presence of osteopenic cortical bone.