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At least 289 records · Page 16Linked to original sources
PubMed2003

Hydroxyapatite composite resin cement augmentation of pedicle screw fixation.

Pedicle screw stability is poor in osteopenic vertebrae attributable, in part, to low screw-bone interface strength. The current authors examined cement augmentation using a low curing temperature hydroxyapatite and bis-phenol-A glycidol methacrylate-based composite resin. This cement may stiffen the screw-bone interface and reduce the harmful effects associated with polymethylmethacrylate regarding temperature and toxic monomer. Thirty-five lumbar vertebrae from human cadavers were instrumented with pedicle screws, with one pedicle previously injected with cement and the other as the control. Caudocephalad toggling of +/- 1 mm for 1600 cycles was applied to the pedicle screws, and the resulting forces supported by the implant-bone interface were captured by a load cell. A curve was constructed from the peak caudal load for each cycle and three mechanical measures parameterized this curve: (1) initial load; (2) rate of load decay during the first 400 cycles; and (3) final load. The initial load increased by 16% as a result of cement augmentation, the final load increased by 65%, and the rate of load decay decreased by 59%. Cement augmentation of pedicle screws increased the stiffness and stability of the screw-bone interface.

Analysis of Variance↗
PubMed1994

Pedicle screws and bone mineral density.

STUDY DESIGN: Thirty-five consecutive patients who underwent surgeries for decompression, and one-level fusions with Cotrel-Dubousset pedicle screws for spinal canal stenosis were included in this study. The relationship between bone mineral density of the lumbar spine and the rate of successful fusion and screw problems was studied. OBJECTIVES: Bone mineral density of the third lumbar vertebral body was measured by quantitative computed tomography preoperatively, and the degree of osteoporosis was graded by radiographic films of lumbar spines. The films were followed with anteroposterior and lateral dynamic radiographic examinations of lumbar spines. These examinations were evaluated clinically after surgery. Follow-up duration was at least 19 months, with a mean of 28 months. SUMMARY OF BACKGROUND DATA: The mean bone mineral density of all the patients was 117.1 mg/mL (SD = 42.5). The rate of successful fusion was 88.6%, the non-union rate was 5.7%, and the rate of fusions that were undetermined was 5.7%. The incidence of screw loosening occurred in 5.7% of the patients, screw breakage occurred in 5.7% of patients, and symptomatic screws related to non-union were present in 5.7% of patients. The degree of bone mineral density or radiographic gradings of osteoporosis and the successful fusion or the incidence of symptomatic screws, which were defined as screws related to non-union, were not related. METHODS: The patients were divided into two groups. One group consisted of 12 patients who had less than 100 mg/mL of bone mineral density, with a mean of 72.0 mg/mL (SD = 21.2). The other group consisted of 23 patients who had more than 100 mg/mL of bone mineral density, with a mean of 140.6 mg/mL (SD = 30.0). The rate of successful fusion or non-union and the rate of screw problems such as screw loosening or screw breakage were compared in the two groups. The presence of bony trabeculation in grafted bone is the most important criterion for successful fusion. RESULTS: A statistical difference did not occur between the two groups. Non-union, screw breakage, and screw loosening were observed in patients with both increased and decreased bone mineral density and those with increased and decreased grade osteoporosis. Radiographic grading of osteoporosis was not correlated to bone mineral density, but patients with unexpected bone mineral density were frequent in this series. CONCLUSIONS: The use of decompression and pedicle screws for spinal canal stenosis due to degenerative lumbar disorders can be done safely with one-level fusion in patients with decreased bone mineral density if patients with grade III osteoporosis are excluded. Bone mineral density is more reliable than radiographic grading to evaluate the degree of osteoporosis and should be included in the preoperative evaluation of patients with osteoporosis.

Bone Density↗
PubMedDate not supplied

The effect of screw type on the fixation of depressed fragments in tibial plateau fractures.

The ability of various screw types to stabilize depressed tibial plateau fractures was determined in a biomechanical study using a Sawbones model. Two sizes of both cancellous and cortical screws were evaluated for both supportfrom below and through the depressed fragment. As a general trend, cancellous bone screws provided a greater resistance to fragment displacement than cortical bone screws, and screws with a smaller thread diameter provided greater resistance to displacement than screws of the same thread type with a larger diameter. These results agree with the accepted standard that cancellous screws provide better fixation for tibial plateau fractures, but also are counterintuitive in that smaller screws provided greater fixation than larger screws of the same type.

Analysis of Variance↗
PubMed2001

Clinical validation of computer assisted pelvic surgery using ultrasound. A percutaneous safe technique with low radiation exposure.

This study presents early results of the clinical experience of computer assisted surgery (CAS) applied to percutaneous iliosacral screwing. The results of these 10 first cases (4 patients) are compared to an historical series of 51 cases (30 patients). The CAS technique shows better screw placement without outside bone screw and a very low radiation exposure.

Adolescent↗
PubMedDate not supplied

Cervical plates: comparison of physical characteristics and in vitro pushout strength.

BACKGROUND CONTEXT: There are many cervical plates available to the spine surgeon today. A single plate design may not be appropriate for every clinical situation. It is important for the surgeon to understand the differences of these plating systems. Plate systems are known to fail by screw pullout from the bone, screw and plate breakage and a less frequent but clinically observed screw pushout from the plate. Pushout testing of the screws from the plate have not previously been subjected to study. PURPOSE: This compares the features of cervical plating systems and the strength of the locking mechanisms to allow the surgeon to make a knowledgeable choice of plating system. STUDY DESIGN: This is a review of descriptive geometric characteristics of cervical plate systems and a biomechanical evaluation of locking mechanism screw pushout strength. METHODS: Physical characteristics of each plate were determined. Features of plates and screws were cataloged. Each of the test plate systems had a different locking mechanism. Biomechanical testing of the locking mechanism-screw-plate constructs was performed to determine the pushout strength of the fixation screw from the plate-locking mechanism. RESULTS: Physical characteristics of the plating systems, including lengths, widths, shortest screw lengths and distance from edge of plate to nearest screw, were determined. Biomechanical testing showed significant differences in pushout strength, in part explained by the type of locking mechanism. CONCLUSIONS: Biomechanical screw pushout data demonstrate that a significant range of pushout strengths exist across the available cervical plate systems today. Knowing the physical characteristics of the cervical plating systems available may allow the selection of a plate best suited for a given clinical situation.

Biomechanical Phenomena↗
PubMedDate not supplied

Tailor's bunion: clinical evaluation and correction by distal metaphyseal osteotomy with cortical screw fixation.

Fifth metatarsal distal metaphyseal osteotomy represents a very common surgical procedure performed for tailor's bunion deformity. The authors advocate using a cortical bone screw for fixation device offers many advantages over conventional devices (i.e., Kirschner wire). The purpose of this paper is to offer a means to thoroughly evaluate tailor's bunion deformity clinically, biomechanically, and radiographically. This will allow the podiatric surgeon to choose a procedure of choice to correct the deformity. The technique of fifth metatarsal distal metaphyseal osteotomy with cortical bone screw fixation using AO4 principles is fully described.

Biomechanical Phenomena↗
PubMed1995

Biomechanical analysis of bone mineral density, insertion technique, screw torque, and holding strength of anterior cervical plate screws.

The bone mineral density (BMD) of 99 cadaveric cervical vertebral bodies (C3-7) was determined using dual x-ray absorptiometry. The vertebral bodies were randomly assigned to receive either a unicortical (51 bodies) or bicortical (48 bodies) Caspar cervical plating screw. The initial insertion torque was measured using a digital electronic torque wrench, and the force required to withdraw the screw from the vertebral body was determined. The mean BMD for the total group of 99 was 0.787 +/- 0.154 g/cm2, the mean insertion torque was 0.367 +/- 0.243 newton-meters, and the mean pullout force was 210.4 +/- 158.1 newtons. A significant correlation was noted between BMD and torque (p < 0.0001, r = 0.42), BMD and pullout force (p < 0.0001, r = 0.54), and torque and pullout force (p < 0.0001, r = 0.88). Although the BMD of the unicortical and biocortical groups was equivalent (p = 0.92), the insertion torque and pullout force differed significantly (p = 0.02 and p = 0.008, respectively) for the unicortical and bicortical groups. A holding index for each screw and insertion technique was defined as the product of the BMD and insertion torque. The calculated holding index and resultant pullout force were significantly correlated for both techniques of screw insertion (r = 0.92), and a significant difference in holding index was observed with unicortical versus bicortical screw placement (p = 0.04). The determination of BMD and measurement of insertion torque to create a unique holding index provides an assessment of bone-screw interaction and holding strength of the screw, both of which impact on the resultant stability of cervical instrumentation. As the number of cervical plating systems increases, the determination of a holding index for various screws and insertion techniques may assist in the comparison of cervical instrumentation.

Absorptiometry, Photon↗
PubMed2001

Incomplete humeral condylar fractures in the dog.

The details of eight dogs (11 elbows) referred to the authors with lameness relating to elbow pain associated with incomplete fracture of the humeral condyle were reviewed. In all cases, a diagnosis was reached by radiographic examination, with the pathognomonic feature being a radiolucent line, in the sagittal plane, through the condyle. Treatment involved placement of a transcondylar bone screw with or without bone tunnels being created parallel to this implant. Six dogs (nine elbows) made a complete recovery without subsequent complications.

Animals↗
PubMed2006

A comparison of pullout strength for pedicle screws of different designs: a study using tapped and untapped pilot holes.

STUDY DESIGN: The pullout strengths of various pedicle screw designs are compared using tapped and untapped pilot holes. OBJECTIVE: The objective of this study is to compare the pullout strength of various pedicle screw designs. The designs are compared using tapped and untapped pilot holes. By using several different screw designs, it is possible to gain an understanding of whether there is a correlation between tapping a pilot hole and the ultimate pullout strength. SUMMARY OF BACKGROUND DATA: Most bone screws originally developed were intended to be installed in a pretapped pilot hole. This same technology has been carried over to the development of more modern bone screws for use in spinal fixation applications. Many pedicle screws in use today are still intended to be installed in a tapped hole. Preparing the vertebrae and tapping of a pilot hole involve additional trauma to the patient as well as increased operating time. METHODS: Pedicle screws from various manufacturers are installed in tapped and untapped pilot holes and then loaded to failure. A uniform synthetic material was used to provide a consistent test of each screw design by eliminating variability seen in bone. RESULTS: Tapping pilot holes did not increase the pullout strength of the screws tested in this study. It was observed during testing that tapping some of the holes degraded the material. This degradation led to pullout strengths that were lower than in the untapped case, and generally larger standard deviations. CONCLUSIONS: The pullout strength was not increased by tapping for the screws in this study. Screws placed in untapped holes generally had higher pullout strengths and lower standard deviations. The results of this study suggest that tapping does not increase pullout strength in bone with densities near 20 lb/ft3, which correlates with low density cancellous or osteoporotic bone.

Biomechanical Phenomena↗
PubMed1996

Herbert screw fixation of scaphoid fractures.

We reviewed the records of 431 patients who had open reduction and internal fixation of the scaphoid performed by one surgeon (TJH) over a 13-year period. The Herbert bone screw provided adequate internal fixation without the use of plaster immobilisation, promoting a rapid functional recovery. On average, patients returned to work 4.7 weeks after surgery and wrist function was significantly improved, even when the fracture failed to unite. Healing rates for acute fractures were better than those reported for plaster immobilisation and were independent of fracture location. In the case of established nonunions, healing depended on the stage and location of the fracture, but the progress of arthritis was halted and carpal collapse significantly improved. Internal fixation of the scaphoid using the Herbert bone screw, although technically demanding, has few complications and appears to offer significant advantages over other methods of treatment.

Acute Disease↗
PubMed1997

[Use of the Herbert screw with the freehand method for osteosynthesis of acute scaphoid fracture].

Scaphoid fracture is, in most cases, usually still treated conservatively. The disadvantages of long-term immobilization are stiffness of the wrist joint, loss of strength and higher costs. The osteosynthesis of the scaphoid fracture with the Herbert bone screw restores the exact form and length and the normal position of the scaphoid to the other carpal bones. It prevents non-unions, arthrosis and other late complications. The Freehand method is used as a percutaneous technique without utilization of a jig. The scaphoid fracture is treated with closed reduction and osteosynthesis is performed with the Herbert bone screw. The percutaneous technique preserves the inter- and intracarpal ligaments, the vascular supply and the articular surfaces of the scaphoid. Osteosynthesis by the Freehand method is sufficiently stable to withstand early functional moves on the first postoperative day.

Adult↗
PubMedDate not supplied

The effect of screw holes on bone strength.

Internal fixation devices continue to be used in the fixation of foot and ankle fractures and osteotomies. Because of the increased use of fixation techniques, postoperative care following removal of internal fixation devices assumes a vital role in the success of these procedures. Using 10 fibulas from 5 cadavers, the authors tested the resistance of 5 intact fibulas and 5 contralateral fibulas with one 3.5-mm. drill hole to bending forces. The mean load at failure of the intact fibulas was 360.86 N (range 181.69-800.14 N), whereas the mean load at failure of the drilled fibulas was 215.20 N (range 66.49-600.61 N). The drilled fibulas displayed failure with the application of 59.63% of the mean load applied to the intact fibulas at failure (p = 0.007).

Aged↗
PubMed2001

Proximal interphalangeal arthrodesis in 22 horses.

The purpose of this study was to evaluate a new method of internal fixation technique for pastern arthrodesis. Pastern arthrodeses are performed commonly in horses with chronic osteoarthritis of the pastern joint or, in cases of acute traumatic injury to the pastern, in which the weightbearing bony column must be restored. Chronic osteoarthritis of the pastern is a frequent cause of lameness in the equine athlete and is evidenced by chronic lameness localised to the pastern joint, and supported radiographically by periosteal proliferation and loss of joint space. Nonsurgical and surgical treatments have both been described in the literature. Complications following pastern arthrodesis have been reported on several occasions and appear to focus on excessive periarticular exostoses and increased time in a cast due to prolonged time to bony fusion. The hospital records of horses presenting for pastern arthrodesis to the Rood and Riddle Equine Hospital in Lexington, Kentucky, were reviewed and 22 met criteria for inclusion in the study. Horses with chronic osteoarthritis of the proximal interphalangeal joint or horses with an acute traumatic injury to the pastern undergoing pastern arthrodesis with one of the following techniques were included in the study. Horses with severe comminution of the middle phalanx were excluded. Three 5.5 mm cortical bone screws placed in lag fashion alone or in combination with a 4 or 3 hole dynamic compression plate affixed with 4.5 mm cortical bone screws were compared. A lower limb fibreglass cast was applied in all cases. Period in cast, time to return to intended use, complications encountered and outcome were evaluated. Seven of the 8 hindlimbs treated with the combination technique became sound. Three out of 6 of the front limbs treated with the combination technique became sound. Four of the 5 horses with hindlimbs, and one of the 2 with front limbs, treated with screws only returned to their intended use. The type of internal fixation did not appear to influence the overall number of horses returning to the intended level of performance. The period spent in cast and the time to return to soundness were decreased in horses operated on using the combination technique. We concluded that, in the immediate postoperative period, the combination of the parallel screw technique with a dorsally-applied dynamic compression plate provides the most stable and secure fixation, minimising motion, expediting bone remodelling and therefore favouring rapid fusion of that joint.

Animals↗
PubMed1997

[Scaphocapitate dislocation-fracture of the wrist joint in the setting of multiple injury].

Scaphocapitate fracture syndrome (SCFS) as part of perilunar distortion injuries (PL, PLF) in the human wrist is still remarkably rare. The diagnosis is determined by careful physical and radiological examinations, including conventional radiographs. Computed tomography can be helpful in detecting such lesions. In our opinion, the high risk of post-traumatic arthrosis because of carpal instability in a osteoligamental injury requires operative reconstruction in nearly all cases. We report the possibility of operative treatment in a case of scaphocapitate fracture syndrome (Fenton) by implantation of 2-mm mini-bone screws, while the use of K-wires or Herbert bone screws has been described in former articles.

Accidental Falls↗
PubMed1997

Comparative pull-out strength of tapped and untapped pilot holes for bicortical anterior cervical screws.

STUDY DESIGN: This biomechanical study analyzed the axial pull-out strength of tapped versus untapped pilot holes for bicortical screws in the anterior cervical spine. OBJECTIVE: To determine which pilot hole preparation method was mechanically better. SUMMARY OF BACKGROUND DATA: Tapping pilot holes in the lumbar spine was previously shown significantly to reduce pull-out strength of pedicle screws. No study was found investigating the effect of tapping on pilot holes for anterior cervical bicortical screws. METHODS: Twenty-five unembalmed human cadaveric cervical vertebrae (C3-C7) were tested. Two identical pilot holes were drilled into each vertebra: one pilot hole was tapped, and the control pilot hole was not tapped. A fully threaded cortical bone screw was inserted into each pilot hole. Screw pull-out strength was determined using a servocontrolled hydraulic materials testing system and an axial load cell. Force-deformation and failure curves were obtained. RESULTS: There were no statistically significant differences between the axial pull-out strength of tapped and untapped pilot holes at any vertebral level. Mean force to-failure was 386 +/- 42 N in the untapped pilot holes and 397 +/- 48 N in the tapped pilot holes. CONCLUSIONS: Tapping a pilot hole for bicortical screws of the anterior cervical spine neither weakens nor strengthens the axial pull-out strength of fully threaded cortical bone screws. Tapping may be unnecessary; however, it may be desirable in patients with dense bone to cut the thread profile into the bone or if the screws have dull tips and threads.

Adult↗
PubMed1996

Unrecognized chondral penetration by a Herbert screw in the scaphoid.

The Herbert bone screw as developed by T. Herbert in the early 1980s has been used in the treatment of scaphoid fractures and nonunions. Reports on clinical efficacy have been accompanied by discussions of technical difficulties. This study determines if the curvilinear surface of the proximal pole of the scaphoid leads to errors in screw length and penetration into the joint. The screw was inserted in cadaveric wrists using the technique described by Herbert. Plain x-ray films were taken in the anteroposterior and lateral planes and fluoroscopy was used through 360 degrees. From the imaging studies, we decided whether subchondral penetration of the screw had occurred. The scaphoids were then dissected and the dorsal poles inspected. In our six specimens, two screws were found to be penetrating subchondral bone. The plain x-ray films were accurate in five of six specimens. Fluoroscopy was accurate in all six. Fluoroscopy during placement of the Herbert screw may decrease the rate of subchondral penetration.

Bone Screws↗
PubMed1995

Screw osteolysis after cementless total knee replacement.

A comparative radiographic review of 217 cementless total knee replacements was done 4 years after surgery to look for radiographic change at the screw-bone interface. There were 102 Miller Galante I knee prostheses, 59 Miller Galante II prostheses, and 56 Anatomic Modular Knee prostheses studied. If the appearance of the screw-bone interface had changed, this was classified according to the width of the lucency. Two hundred sixty-five of the 851 screws that were studied showed some evidence of change, with 185 (21.7%) of the screws showing a cavitary appearance change. The AMK prosthesis showed the higher incidence of cystic and cavitary changes. Polyethylene debris is thought to be responsible for generation of osteolysis and the radiographic appearance change. Design of the components and particularly the polyethylene attachment mechanisms may be responsible for the differences in the frequencies of osteolysis.

Bone Screws↗
PubMed2002

Biomechanical evaluation of fixation of clavicular fractures.

Reproducible fractures of the midshaft of the clavicle were created in 14 fresh frozen human cadaveric clavicles. Under the three-point bending loading by a materials testing machine, the load to failure of fixation of the clavicular fractures treated with steel reconstruction plates (five specimens) and Herbert cannulated bone screw (nine specimens), was compared with a group control formed by five specimens of clavicles without osteosynthesis material. No statistically significant differences were observed between the three groups. In consequence and in terms of biomechanics, in clavicular acute fractures, both plating and intramedullary Herbert cannulated bone screw may be utilized in the treatment of these lesions.

Adult↗