Intrapartum fetal oxygen saturation monitoring in congenital fetal heart block

Precutaneous Kirschner wire fixation of displaced Gartlands types II and III supracondylar fractures with image guidance remains a preferred procedure for most orthopaedic units. Various K-wire configurations have been in use, but recent objective evaluation of pin stability has favoured two techniques; the 2 crossed pins placed from the medial and lateral epicondyles, and 2 parallel lateral pins when the former technique is impracticable because of swelling. We reviewed patients who had K-wire fixation precutaneously over a 2-year period (Feb 1996 to Feb 1998). There were 44 children, 30 males, 14 females, ages between 1-15 years. 19 patients had (medial and lateral pins) 15, (2 parallel lateral) and 10 patients (2 lateral crossed) precutaneous pin placement respectively. Their postoperative course indicated that maximum stability was obtained with two opposite crossed pins, followed by the 2 paralleled pin method. These observation determined the choice of technique by the surgeons who operated on these patients.     

The role of anteromedial foraminotomy and the uncovertebral joints in the stability of the cervical spine. A biomechanical study

STUDY DESIGN: The biomechanical role of the cervical uncovertebral joint was investigated using human cadaveric spines. Sequential resection of cervical uncovertebral joints, including clinical anteromedial foraminotomy, was conducted, followed by biomechanical testing after each stage of resection. OBJECTIVES: To clarify the biomechanical role of uncovertebral joints and clinical anteromedial foraminotomy in the cervical spine and their effects on interbody bone graft stability. SUMMARY OF BACKGROUND DATA: Although the biomechanical role of the cervical uncovertebral joints has been considered to be that of a guiding mechanism in flexion and extension and a limiting mechanism in posterior translation and lateral bending, there have been no studies quantifying this role. According to results in quantitative anatomic studies, anatomic variations exist in uncovertebral joints, depending on the vertebral level, articular angulation, and relative height of the joints. METHODS: Fourteen human functional spinal units at C3-C4 and C6-C7 underwent sequential uncovertebral joint resection, with each stage of resection followed by biomechanical testing. The uncovertebral joint was divided anatomically into three parts on each side: the posterior foraminal part, the posterior half, and the anterior half. The loading modes included torsion, flexion, extension, and lateral bending. A simulated anterior bone graft construct was also tested after each uncovertebral joint resection procedure. RESULTS: Significant changes in stability were observed after sequential uncovertebral joint resection in all loading modes (P < 0.05). The biomechanical contribution of uncovertebral joints decreased in the following order: the posterior foraminal part, the posterior half, and the anterior half. Unilateral and bilateral foraminotomy most affected the stability of the functional spinal unit during extension, causing a 30% and 36% decrease in stiffness of the functional spinal unit, respectively. The effect was less in torsion and lateral bending. After sequential resection, there was a statistically significant difference between decreases in torsional stiffness at C3-C4 and C6-C7 (P < 0.05). The stiffness of the simulated bone graft construct decreased progressively during flexion and lateral bending after each foraminotomy (P < 0.05). Increased bone graft height of 79% returned stability to the preforaminotomy level. CONCLUSIONS: This is the first study to quantitate the biomechanical role of uncovertebral joints in cervical segmental stability and the effect at each intervertebral level. The effect differs because of anatomic variations in uncovertebral joints. The major biomechanical function of uncovertebral joints includes the regulation of extension and lateral bending motion, followed by torsion, which is mainly provided by the posterior uncovertebral joints. This study highlights the clinical assessment of additional segmental instability attributed to destruction of the uncovertebral joints during surgical procedures or by neoplastic lesions.     

Distal interphalangeal joint arthrodesis comparing tension-band wire and Herbert screw: a biomechanical and dimensional analysis

Thirty cadaveric distal interphalangeal joints (15 male and 15 female joints) were prepared with either a Herbert screw or a tension-band wire technique to simulate an arthrodesis. To elucidate mechanical differences between these constructs, the strength of the specimens was determined for three-point anteroposterior and lateral bending and for axial torsion. The Herbert screw demonstrated significantly greater anteroposterior bending strength and greater torsional rigidity when compared to the tension-band wire technique. For dimensional analysis, the height and width of each distal phalanx was measured prior to fixation, 4 mm from the distal tip of the bone (the region that must accommodate the large-diameter threads of the Herbert screw). Results indicated that the mean height of the distal phalanx (3.55 mm) is smaller than the diameter of the screw (3.90 mm). Fracture or thread penetration at the tip of the distal phalanx during screw placement occurred in 25 of the specimens overall and in all the female phalanges, often resulting in stretching or violation of the nail bed. Despite fracture or screw penetration, the Herbert screw appears to offer additional strength that may be clinically important for joint arthrodesis.     

Flexural and Torsional Properties of Pultruded Fiber Reinforced Plastic I-Profiles

Experimental determination of the full section flexural and torsional properties of pultruded fiber reinforced plastic I-profiles is described. Based on beam theory approximations, test configurations for determining the various section properties are established. Tests were conducted on three different I-profiles with a range of span-to-depth ratios. Major and minor axis flexural rigidities and flexural moduli, determined from three- and four-point bending tests, show close correlation. Major and minor axis transverse shear rigidities and shear moduli show significant variation, due to differing effective areas of the cross section resisting transverse shear and differing fiber content and orientation in the web and flanges. St. Venant torsional shear moduli, determined from uniform torsion tests, are consistent but significantly greater than the transverse shear moduli, which may be due to variations in fiber content, orientation, and lay up. Warping torsional rigidities, determined from nonuniform torsion tests, are consistent with values deduced from minor axis flexural rigidities, indicating that the influence of shear deformation on restrained torsional warping is insignificant.     

APhA drug treatment protocols: management of patients with generalized anxiety disorder.APha Psychiatric Disorders Panel

STUDY DESIGN: The multidirectional stability potential of anterior, posterior, and combined instrumentations applied at L1-L3 was studied after L2 corpectomy and replacement with a carbon-fiber implant. OBJECTIVES: To evaluate the biomechanical characteristics of short-segment anterior, posterior, and combined instrumentations in lumbar spine tumor vertebral body replacement surgery. SUMMARY OF BACKGROUND DATA: The biomechanical properties of many different spinal instrumentations have been studied in various spinal injury models. Only a few studies, however, investigate the stabilization methods in spinal tumor vertebral body replacement surgery. METHODS: Eight fresh frozen human cadaveric thoracolumbar spine specimens (T12-L4) were prepared for biomechanical testing. Pure moments (2.5 Nm, 5 Nm, and 7.5 Nm) of flexion-extension, left-right axial torsion, and left-right lateral bending were applied to the top vertebra in a flexibility machine, and the motions of the L1 vertebra with respect to L3 were recorded with an optoelectronic motion measurement system after reconditioning. The L2 vertebral body was resected and replaced by a carbon-fiber cage. Different fixation methods were applied to the L1 and L3 vertebrae. One anterior, two posterior, and two combined instrumentations were tested. Load-displacement curves were recorded and neutral zone and range of motion parameters were determined. RESULTS: The anterior instrumentation provided less potential stability than the posterior and combined instrumentations in all motion directions. The anterior instrumentation, after vertebral body replacement, showed greater motion than the intact spine, especially in axial torsion (range of motion, 10.3 degrees vs 5.5 degrees; neutral zone, 2.9 degrees vs. 0.7 degrees; P < 0.05). Posterior instrumentation provided greater rigidity than the anterior instrumentation, especially in flexion-extension (range of motion, 2.1 degrees vs. 12.6 degrees; neutral zone, 0.6 degrees vs. 6.1 degrees; P < 0.05). The combined instrumentation provided superior rigidity in all directions compared with all other instrumentations. CONCLUSIONS: Posterior and combined instrumentations provided greater rigidity than anterior instrumentation. Anterior instrumentation should not be used alone in vertebral body replacement.     

Analysis of the external fixator pin-bone interface

External fixator pins were inserted into tibiae of dogs under four in vivo loading conditions to examine the mechanism of pin loosening. Pins were quantitatively measured for pin torque resistance, and the pin tracts were studied radiographically and histologically. The pins holding an unstable fracture had more gross pin loosening. Pins also may become loose under static loads. Radiographic lucency of 1 mm or more in the cortical bone around a pin was evidence of gross pin loosening. Histologic examination showed that tight pin tracts were characterized by a lack of bone remodeling. Loose pin tracts were characterized by extensive bone resorption and inflammatory infiltrates. Pin loosening can be detected radiographically. Pin insertion technique is important to improve the initial pin torque resistance to minimize pin loosening. Sixty-nine percent of pins with an initial torque resistance of less than 68 Ncm became grossly loose compared with only 9% of pins with an initial torque resistance greater than 68 Ncm, regardless of the experimental group. Unstable external fracture fixation is another important factor in producing pin loosening. Pins loaded under unstable fracture fixation had the highest incidence of gross loosening. When applying an external fixator, the fracture rigidity should be critically evaluated and, if necessary, protected weight bearing must be introduced initially to minimize pin loosening.     

Free Vibration of Three-Dimensional Orthotropic Uniform Shear Beam-Columns with Generalized End Conditions

The free vibration analysis of asymmetrical three-dimensional (3D) uniform shear beam-columns with generalized boundary conditions (semirigid flexural and torsional restraints, lateral bracings, and lumped masses at both ends) subjected to an eccentric end axial load in addition to a linearly distributed eccentric axial load along its span is presented in a classic manner. The five coupled governing equations of dynamic equilibrium (i.e., two shear equations, two bending moment equations, and the pure torsion moment equation) are sufficient to determine the natural frequencies and modal shapes. The proposed model which is an extension of a 2D model presented previously by the writer includes the simultaneous 3D coupling effects among the lateral deflections, deformations of the cross section along the member (shear, torsional and rotational), the translational, rotational and torsional inertias of all masses considered, an eccentric end axial load in addition to a linearly distributed axial load along its span, and the end restraints. Deformations caused by shear forces and pure torsion are considered. The effects of axial deformations, warping torsion and torsional stability are not included. The proposed model shows that the dynamic behavior of 3D shear beam-columns is highly sensitive to the coupling effects just mentioned, particularly in members with both ends free to rotate. Analytical results indicate that except for doubly symmetric members with concentric axial loads and with perfectly clamped ends, the natural frequencies and modal shapes of 3D shear beam-columns are determined from the eigenvalues of a full 8×8 matrix, rather than from the uncoupled equations of transverse (or shear-wave equations) and torsional moment equilibrium. Two comprehensive examples are presented that show the effectiveness of the proposed method.     

Hydroxyapatite coated external fixation pins: an experimental study

A sheep model was developed for the implantation of 84 bicylindrical stainless steel external fixation pins. One-half of the pins were coated with hydroxyapatite, and the rest remained uncoated. A set of 6 pins with the same coating was implanted in the lateral side of the left tibias of 14 sheep, the final insertion torque was measured, and a monolateral external fixator was assembled on the pins. The medial tibial middiaphysis then was exposed and a 5-mm resection osteotomy was done. Sheep were euthanized 6 weeks after surgery, radiographs were taken, and the initial extraction torque was measured on 4 pins from each sheep. Undecalcified sectioning and histologic and histomorphometric analyses were done on the remaining 2 pins. Radiographic pin tract rarefaction was significantly lower in the hydroxyapatite coated pins compared with the uncoated pins. Group average insertion torque was 960 +/- 959 Nmm in the hydroxyapatite coated pins and 709 +/- 585 Nmm in the uncoated pins. Group average initial extraction torque was 1485 +/- 1308 Nmm and 298 +/- 373 Nmm, respectively. Bone pin contact was 85.7% +/- 8.9% and 50.3% +/- 20.4%, respectively, in hydroxyapatite coated and uncoated pins. Bone between the threads was 95.6% +/- 5.7% and 80% +/- 8.7%, respectively, in hydroxyapatite coated and uncoated pins. Hydroxyapatite coating was effective for improving the bone-to-pin interface.     

Breaking strength retention and histologic effects around 1.3-mm. ORTHOSORB polydioxanone absorbable pins at various sites in the rabbit

Absorbable 1.3-mm polydioxanone (ORTHOSORB) pins were implanted in 75 New Zealand White rabbits in three sites: within the lateral subcutaneous tissue parallel to the femur, down the femoral intramedullary canal, and mediolaterally across the femoral condyles (transcondylar). Pins were harvested at periodic intervals up to 56 and 365 days for mechanical and histologic analyses, respectively. Mechanical analyses were performed by loading the pin in double shear. Histologic analyses were performed on the pin and surrounding tissue. Histologic observations revealed a typical nonspecific foreign-body reaction at all implant sites that resolved at 1 year after resorption of the pin. On histologic examination, there was complete resorption of the pin material in the subcutaneous site by day 182, and there was complete resolution of all response to the pin in six of nine rabbits by day 365. In the intramedullary site, pin material was completely resorbed, based on histologic examination, in five of six rabbits by day 182, and there was complete resolution of the response to the pin in eight of nine rabbits by day 365. The pin material was completely resorbed based on histologic examination of the transcondylar site by day 210, and there was complete resolution of the response to the pin in four of six rabbits by day 270 and in four of nine rabbits by day 365. No enlarged pin tracks or sinus formations were observed in or near the implants sites. The average initial shear strength as 171.4+/ 5.1 MPa, and the breaking strength retention decreased with increasing implantation time. Pins from the subcutaneous regions maintained above 97% of their initial strengths at 28 days, and those from the intramedullary canals maintained above 92%. At later times the strength of the pins implanted in the intramedullary canal decreased more rapidly than those from the subcutaneous region. Overall, the average breaking strength of the subcutaneous pins was significantly greater than that of the intramedullary pins at all time points beyond 14 days. These data indicate that the pins exhibited a strength retention profile sufficient to allow normal healing of bone without enlarged pin tracts, allergic reactions, or sinus formations.     

Mechanical properties of perforated and partially demineralized bone grafts

Changes in flexural rigidity and compression strength of 18 sheep tibias were investigated after laser perforation and partial demineralization. Test bones were divided into three groups: Group 1, no treatment; Group 2, laser hole grid; and Group 3, laser hole grid and partial demineralization. Starting in the anterior direction at the tibial tuberosity, the flexural rigidity was determined using a nondestructive four-point bending test. The elliptical distribution of the flexural rigidity before and after a specific treatment was compared. After the bending test, a cylindrical center section of each test bone was loaded axially to failure to determine subsequent changes in compression strength. Results showed that perforation alone produced minimal reduction of rigidity and insignificant changes in compression strength. However, additional partial demineralization resulted in larger reductions. In compression testing, perforated and partially demineralized bone specimen showed marked decrease of the ultimate failure stress. The observed increase in failure strain appeared to be related to compression of the laser holes. The findings of this study suggest that partial demineralization and perforation can be applied to diaphyseal bone grafts and that their decreased mechanical properties are a function of the bone volume reductions produced by both processes.     

Retrospective diagnostics of congenital cytomegalovirus infection performed by polymerase chain reaction in blood stored on filter paper

OBJECTIVE: External reference points, particularly Kirschner pins (K-wire), placed in the region of the nasion have been shown to improve the accuracy of maxillary vertical repositioning. Although no complications associated with this technique have been reported, there is a potential for injury to the anterior cranial fossa or frontal sinus. The purpose of this study was to measure the shortest distance from the nasion to the anterior cranial fossa and from the nasion to the frontal sinus. These measurements were used to establish anatomic guidelines governing safe placement of external reference point pins. STUDY DESIGN: Twenty-seven cadaver heads were sectioned in the midsagittal plane for gross study. Using a Boley gauge, two specific measures were obtained: (1) distance from deepest depression of nasion to the most anterior and inferior projection of the anterior cranial fossa, and (2) distance from nasion to the most inferior aspect of the frontal sinus. All measurements were made in the midsagittal plane. RESULTS: The average distance from nasion to anterior cranial fossa was 16.9 mm (range 13.0 to 20.0 mm) and the smallest distance, 13.0 mm, was seen in two specimens. The average distance from nasion to the frontal sinus was 6.2 mm (range 2.0 to 10.0 mm) and the smallest distance, 2.0 mm, was seen in three specimens. CONCLUSION: Based on our findings, we recommend the following: (1) place pin to a depth of no more than 8 mm into bone, (2) place pin 5 to 10 mm inferior to soft tissue nasion, and (3) place pin in an anterosuperior to posteroinferior direction (i.e., roughly perpendicular to the nasal dorsum). When these anatomic guidelines are followed, one would expect minimal morbidity associated with the placement of ERP pins.     

Study of torsion defects of the lower limbs using computerized tomography

January, 1990, to July, 1993, the torsional defects of the lower limbs were studied at the Department of Radiology of the Istituto Ortopedico Rizzoli, Bologna. Ninety-three patients were examined, all of them affected with congenital or acquired (posttraumatic and/or iatrogenic) torsional defects. The torsional angles, i.e., the anteversion acetabulum angle, the anteversion femoral neck angle and the tibial torsion angle, were measured as follows: the patients were laid supine with their limbs either in intrarotation with the patella perpendicular to the table (62 patients) or in neutral rotation with the feet in the pace position (31 patients). The images were always analyzed at the console by two different radiologists in the following days. The electronic lines for measuring torsional angles were drawn by the two radiologists ex novo on the previously acquired CT images. No statistically significant differences were observed between the two groups of patients. The measures were independent of limbs position and the interobserver differences were bigger in children and in the measurement of femoral neck anteversion angle; however, these differences decreased by about 50% with better console use. CT, thanks to its feasibility, has replaced conventional (direct or indirect) radiology to study the torsional defects of the lower limbs. Moreover, CT is extremely useful not only for early disease diagnosis (location, rotation degree and associated joint deformities), but also for treatment planning, be it surgical or conservative.     

A comparative evaluation of halo pin designs in an immature skull model

To design an improved halo pin for use in pediatric patients, three commonly used halo pins were evaluated with a mechanical testing apparatus and segments of prepared fetal calf skull. The pins were driven through the bone segments while the load at the bone-pin interface was measured. New pins were designed with respect to pin tip and flange width and similarly compared. Mean maximum loads to penetration, normalized for bone segment thickness, were 55.6 N/mm for the PMT Corporation pin, 61.5 N/mm for the Bremer pin, and 73.6 N/mm for the Ace pin. Four new, short tipped pins were designed and compared with the Ace pin, and there was no significant difference. Finally, four new pins were designed with varying flange widths. Mean maximum loads, normalized for bone segment thickness, were 68.9 N/mm for the 4.2 mm flange, 72.2 N/mm for the 4.7 mm flange, 92.9 N/mm for the 5.2 mm flange, and 96.4 N/mm for the 5.7 mm flange. The findings of this investigation are clinically important because they may help to explain the variability in the complication rates seen with the use of different halo systems in children. The three halo pins currently on the market have different pin designs, including tip lengths and flange distances, which contribute to the difference in load to penetration for each pin. The new, wide flanged, short tipped halo pin design might decrease the complication rate of halo use in children by providing an improved capacity to resist penetration despite increased loads of application.     

Transient osteoporosis of the hip in pregnancy

STUDY DESIGN: Fresh calf lumbar spines were used to perform flexibility tests in multiple loading directions to compare the stabilizing effects of anterior and posterior rigid instrumentations. OBJECTIVE: To compare the biomechanical flexibility of anterior and posterior instrumentation constructs using an unstable calf spine model. SUMMARY OF BACKGROUND DATA: Unstable burst fractures of the thoracolumbar spine can be managed anteriorly or posteriorly. Controversy persists, however, on the merit of anterior fixation versus that of posterior fixation in terms of how much stability can be achieved. METHODS: Fifteen fresh calf spines (L2-L5) were loaded with pure unconstrained moments in flexion, extension, axial rotation, and lateral bending directions. After removal of L3-L4 disc and endplates to create an 1.5-cm anterior and middle column defect, testing was performed on five specimens after anterior Kaneda rod fixation, anterior University Plate fixation, or posterior ISOLA pedicle screw fixation (AcroMed, Cleveland, OH). Testing was repeated after inserting a polymethylmethacrylate block to stimulate an interbody anterior graft with instrumentation. RESULTS: All fixation devices provided a significant stabilizing effect in flexion and lateral bending. In extension, all constructs except ISOLA (AcroMed) without graft were stiffer than the intact specimen. In axial rotation with no graft, only the Kaneda device significantly reduced the flexibility from that of the intact specimen. The interbody graft provided additional rigidity to the ISOLA (AcroMed) instrumentation construct in flexion and extension and to the Kaneda construct in lateral bending. There was no significant effect of grafting in axial rotation. CONCLUSIONS: A short, transpedicular instrumentation, such as ISOLA (AcroMed), provided less rigid fixation in flexion and extension without the anterior structural graft. The Kaneda rod and University plate with grafting provided a significant stabilizing effect in all directions compared with the intact specimen. When no graft was inserted, the Kaneda device was more effective in preventing axial rotation than the other devices. In lateral bending, the University plate provided more rigid fixation than the Kaneda device without grafting.     

Enhanced fixation with hydroxyapatite coated pins

Three groups of seven patients had external fixation of middiaphyseal tibial fractures using uncoated pins, uncoated bicylindrical pins, and hydroxyapatite coated bicylindrical pins, respectively. All fractures were fixed with six pins, and all fractures united. Median pin insertion torque was 0.6, 1.2, and 1.3 Nm in the three groups, respectively. Median extraction torque was 0.1, 0.1, and 2.1 Nm, respectively. Both types of stainless steel pins showed a lower extraction torque than insertion torque in all cases, whereas the mean extraction torque in the hydroxyapatite coated pins was unchanged. Seven of the 14 patients receiving uncoated pins had pin tract infection, compared with none of the patients receiving hydroxyapatite coated pins. Hydroxyapatite coating of external fixation pins increases stability and thereby reduces the risk for pin tract infection and mechanical failure of fracture fixation.     

Stability of posterior spinal instrumentation and its effects on adjacent motion segments in the lumbosacral spine

STUDY DESIGN: An in vitro biomechanical analysis of three anterior instability patterns was performed using calf lumbosacral spines. Stiffness of the constructs was compared, and segmental motion analyses were performed. OBJECTIVES: To clarify the factors that alter the stability of the spinal instrumentation and to evaluate the influence of instrumentation on the residual intact motion segments. SUMMARY OF BACKGROUND DATA: Recently, many adverse effects have been reported in fusion augmented with rigid instrumentation. Only few reports are available regarding biomechanical effects of stability provided by spinal instrumentation and its effects on residual adjacent motion segments in the lumbar-lumbosacral spine. METHODS: Eighteen calf lumbosacral spine specimens were divided into three groups according to instability patterns--one-level, two-level, and three-level disc dissections. Six constructs were cyclically tested in rotation, flexion-extension, and lateral bending of intact spines, of destabilized spine, and of spines with four segmental posterior instrumentation systems used to extend the levels of instability (Cotrel-Dubousset compression hook and three transpedicular screw fixation systems). During each test, stiffness values and segmental displacements were measured. RESULTS: The rigidity of the instrumented construct increased as the fixation range became more extensive. Although application of the instrumentation effectively reduced the segmental motion of the destabilized vertebral level, the motion at the destabilized level tended to increase as the number of unstable vertebral levels increased, and the fixation range of the instrumentation became more extensive. Instrumented constructs produced higher segmental displacement values at the upper residual intact motion segment when compared with those of the intact spine. In contrast, the instrumented constructs decreased their segmental displacement values at the lower residual intact motion segment with higher magnitude of the translational (shear) motion taking place compared with the intact spine in flexion-extension and lateral bending. These changes in the motion pattern became more distinct as the fixation range became more extensive. CONCLUSIONS: As segmental spinal instrumentation progresses from one level to three levels, the overall torsional and flexural rigidity of the system increases. However, segmental displacement at the site of simulated instability becomes more obvious. Application of segmental instrumentation changes the motion pattern of the residual intact motion segments, and the changes in the motion pattern become more distinct as the fixation range becomes more extensive and as the rigidity of the construct increases.     

Type-II external fixation, using new clamps and positive-profile threaded pins, for treatment of fractures of the radius and tibia in dogs

A new external fixation system for repair of fractures of the radius and tibia was developed that uses positive-profile threaded pins. This system allows for addition of a fixation clamp between 2 installed clamps, predrilling of pin holes through a drill sleeve, use of positive-profile threaded pins in all locations, and easier application of full pins. Type-II external fixators were applied, using this system, to fractures in 10 client-owned dogs, and outcome was evaluated. All fractures healed without complications. Duration of surgery, mean time until radiographic evidence of a bridging callus, and mean time until removal of the external fixator were shorter, and frequency of pin loosening were less than with other techniques. Pin loosening was uncommon. This system provides an important improvement in external skeletal fixation.     

Strength of fixation with transosseous sutures in rotator cuff repair

The effect of various configurations of placement of transosseous sutures on the immediate strength of fixation was studied in forty-five fresh-frozen humeri from cadavera of older individuals (mean age at the time of death, sixty-three years). The ultimate strength (the strength to failure) was significantly greater (p < 0.05) when the sutures were placed at sites more distal to the tip of the greater tuberosity or when the sutures were tied over a wider bone bridge. Cortical augmentation with use of a plastic button through which the transosseous sutures were tied increased the ultimate strength approximately 1.9-fold. The increase in the ultimate strength of the transosseous repair corresponded significantly with the increasing mean thickness of the cortical bone as the sutures were placed more distally along the lateral aspect of the humerus. We concluded that the strength of the fixation of a rotator cuff repair can be increased by placing the transosseous sutures at least ten millimeters distal to the tip of the greater tuberosity and by tying them over a bone bridge that is at least ten millimeters wide. When bone is very osteoporotic, cortical augmentation with a readily available plastic button strengthens the repair.     

Complications in connection with venous port systems: prevention and therapy

OBJECTIVE: To assess the effects of graded intramedullary reaming and nailing on the healing pattern of segmental diaphyseal fractures using male Wistar rats. STUDY DESIGN: In male Wistar rats we produced two standardized, partial osteotomies with an eight-millimeter intermediary fragment in the femoral diaphysis. The osteotomies were subsequently manually broken. In Group A, intramedullary reaming was performed to 1.6 millimeters, and the fracture was stabilized with a 1.6-millimeter steel pin. In Group B, the femoral canal was reamed to 2.0 millimeters, and a hollow steel tube of 2.0 millimeters was installed. The rats were allowed free movement. After four, eight, and twelve weeks, eight rats in each group were sacrificed and callus formation, biomechanical properties, and bone blood flow were evaluated. RESULTS: The callus area was relatively constant with time in Group B, whereas a reduction was observed in Group A at twelve weeks. The biomechanical properties increased throughout the experimental period in both groups, and no significant differences between the groups were detected in bending moment, bending rigidity, or fracture energy. Total bone blood flow was substantially increased at four weeks in both groups and decreased throughout the experimental period. In addition, blood flow of the segmental fractured area was substantially increased after four weeks and decreased gradually thereafter. The increases in blood flow tended to be largest in the moderately reamed group. CONCLUSION: This study indicates that the degree of reaming does not significantly affect the healing pattern measured as restoration of mechanical characteristics.     

Structural Characteristics and Applicability of Four-Span Suspension Bridge

A four-span suspension bridge which has two main 2,000 m spans is investigated with respect to the deformation characteristics. Generally, deformation behavior of the four-span suspension bridge is mainly influenced by rigidity of the center tower. This study is focused on properties such as bending and torsional rigidity of the girder, sag ratio, and dead load. The result of this investigation clarified that the lower rigidity under live load than the three-span bridge is caused by the smaller cable spring coefficient of the main span, which is 1/6 of the side span. Nevertheless, the tendency is stable and can be assisted by stiffened rigidity of the center tower. Live load deflection of the girder can be reduced to less than 1/200 of the main span length, which is useful and economical, by stiffening the bending coefficient of the center tower. Moreover, relatively lower rigidity of the center tower is sufficient for the 2,000 m span suspension bridge than for the 1,000 m span case, keeping the same deflection ratio. Three-dimensional sag geometry of the main cable is effective in limiting the torsional deformation, which is an especially important issue for the four-span suspension bridge caused by twist of the center tower.