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PubMed1988

[Observations on optimizing the mechanical properties of osteosynthesis screws].

According to two agreeing standards, the mechanical requirements for bone screws consist of a minimum breaking torque and of the minimum angle of rotation to failure of 180 degrees. Apparently it has been overlooked that these requirements admit austenitic steels with a very low yield strength, which reach the required torque at fracture only by the work-hardening brought about during the torsion test. As a high yield strength is a prerequisite of a stable fixation, a formulation is proposed which guarantees not only a high elastic torque but also an adequate work of deformation in the plastic state as an insurance against embrittlement.

Biomechanical Phenomena↗
PubMedDate not supplied

Alternative bone expansion technique for immediate placement of implants in the edentulous posterior mandibular ridge: a clinical report.

PURPOSE: The aim of this study was to evaluate the effectiveness of a split-crest bone augmentation technique performed for immediate implant placement in thin edentulous posterior mandibular ridges. MATERIALS AND METHODS: In the present study, 125 implants were placed in posterior mandibular ridges of 30 patients. The mandibular buccal walls were split, expanded, and grafted with a combination of platelet-rich plasma and Cerasorb. The split segments were held in place by cortical bone screws. Before loading, periodontal status was checked, implant stability was evaluated with the Periotest, and panoramic radiographs and computerized tomography scans were obtained. Second-stage surgery (cover screw removal and healing abutment placement) was performed after 3 to 4 months. RESULTS: All implants osseointegrated successfully and underwent loading after 4 months. Optimal healing occurred 3 to 4 months earlier than the usual 6 to 9 months required, and no lip paresthesia was noted. DISCUSSION: Although onlay-inlay grafts, sandwich osteotomies, guided bone regeneration, piezoelectricity, and alveolar distraction have been indicated for augmentation in the posterior mandibular region, each of these techniques involves risks and complications. The crest-splitting bone expansion technique enables single-stage immediate implant placement and lateral ridge augmentation in thin crests and may prevent neurosensorial deficiencies. CONCLUSIONS: The split-crest surgical technique is a valid reconstructive procedure for sharp posterior mandibular ridges. If performed using platelet-rich plasma and Cerasorb, it can shorten the osseointegration period.

Alveolar Ridge Augmentation↗
PubMed1994

Evaluation of methods of internal fixation of transverse patella fractures: a biomechanical study.

Biomechanical testing was performed to evaluate five techniques of internal fixation of transverse patella fractures. Using cadaveric lower extremities, transverse osteotomies of the patella were performed, and the simulated fractures were fixed with the following techniques: the modified tension band, anterior tension band with a supplemental cerclage wire (the Pyrford technique), tension band with cancellous bone screws, Pyrford technique with cancellous screws, and cancellous screws alone. The fixation techniques were evaluated by measuring the separation of the fracture fragments during loading to produce a physiologic range of motion (90 degrees flexion to full extension). All techniques functioned adequately, with no fracture gap exceeding 1 mm. The tension band with screws technique performed significantly better than did the modified tension band, with an average fracture gap approximately half that of the traditional modified tension band technique. Mechanically, the addition of the screws to the tension band techniques reduces fracture separation by providing compression throughout the range of motion and by resisting the tensile loading during terminal extension.

Aged↗
PubMedDate not supplied

Comparison of pullout strength of small-diameter cannulated and solid-core screws.

The purpose of this study was to determine the difference in pullout strength between cannulated and solid-core small-diameter bone screws. Cannulated screws from different manufacturers were compared against solid-core screws with 2.0-mm, 2.4-/2.5-mm, and 3.0-mm diameters. A synthetic material made to simulate bicortical bone was used as the test medium. The screws were extracted under servohydraulic control. There was no statistically significant difference between any of the cannulated and solid-core 2.0-mm screws used in this study (P <.05). In the 2.4-/2.5-mm screw tests, both of the cannulated screw designs had a significantly higher pullout strength when compared with the solid-core screw (P <.05). In the testing of 3.0-mm screw test, 1 of the cannulated screw designs showed a significantly higher pullout strength than the other cannulated and solid-core screws that were tested (P <.05). The results of this study suggest that small-diameter cannulated bone screws are similar in mechanical pullout strength to solid-core screws.

Bone Screws↗
PubMed1989

T-Screw. A new bone fixation device.

The T-Screw was patented in 1984. A 5-year study was begun in 1980, and FDA approval was granted in 1985. Detailed results of this clinical study will be reported in a later paper. The purpose of this paper is to introduce the device. The authors have found that early return to normal function and wearing shoes has been possible when using T-Screws for fixation of podiatric osteotomies. The screw appears to accelerate bone healing and has numerous applications throughout the foot. The authors believe that its ease of application and removal as well as its ability to generate rigid, compressive fixation makes it an excellent alternative to current fixation devices.

Bone Screws↗
PubMed1994

Stability of the elevated fragment in tibial plateau fractures. A radiographic stereophotogrammetric study of postoperative healing.

Five cases of fracture of the lateral tibial condyle of the split-depression type were treated by elevation of the depressed fragment, bone grafting and cancellous bone screws. During the operation, tantalum markers were inserted into the depressed fragment and the tibial metaphysis for radiographic stereophotogrammetric analysis. Postoperatively a plaster cast was applied for one month and weightbearing was not allowed for 3 months. In three cases, a depression of the elevated fragment, at the most 2.8 mm, recurred during the first month after operation. This was not considered to be significant and more aggressive postoperative mobilisation may be warranted.

Adult↗
PubMed2005

Modified Sauvé-Kapandji procedure for disorders of the distal radioulnar joint in patients with rheumatoid arthritis.

BACKGROUND: The Sauvé-Kapandji procedure has become popular for the treatment of disorders of the distal radioulnar joint in patients with rheumatoid arthritis, but this procedure is impossible to perform in patients with poor bone quality in the distal part of the ulna. We have modified the procedure for patients with poor bone quality in the distal part of the ulna. The modified procedure involves resecting the distal part of the ulna, making a drill-hole in the ulnar cortex of the distal part of the radius, rotating the resected portion of the ulna 90 degrees , inserting it into the distal part of the radius, and fixing it at that site with use of an AO cancellous-bone screw. In the present report, we describe the new operative technique and report the results after a minimum duration of follow-up of three years. METHODS: This operation was performed in fifty-six patients (sixty-six wrists) with rheumatoid arthritis. The mean age at the time of the operation was 59.3 years. The mean duration of follow-up was forty-eight months. Patients were evaluated in terms of wrist pain, grip strength, and range of motion. Radiographic evaluation included calculation of the carpal translation index to assess the extent of ulnar translation of the carpus. RESULTS: Osseous union was achieved in all cases. Wrist pain resolved or decreased in all patients. The mean total range of forearm rotation increased from 144 degrees preoperatively to 167 degrees at the time of the most recent follow-up (p < 0.01). The mean carpal translation index did not change after the operation. CONCLUSIONS: The modified Sauvé-Kapandji procedure results in rigid fixation of the grafted bone. The technique provides sufficient osseous support of the carpus even in patients with rheumatoid arthritis and poor bone quality in the distal part of the ulna.

Arthritis, Rheumatoid↗
PubMed1987

A new material (single crystal sapphire screw) for internal fixation of the mandibular ramus.

A new single crystal sapphire bone screw which has favourable properties such as chemical stability, mechanical strength and biocompatibility, was applied for rigid internal fixation of the sagittal split osteotomies in 86 cases since 1982. Radiographic findings supported the excellent biocompatibility of the material; there was no noticeable bone loss around the screw and the excellent bone adaptation to the threaded portion was observed. The screws can mechanically support the split mandibular rami until bone union occurs. Complications due to the screw were not encountered in follow-up periods of 0.5-3.5 years.

Aluminum↗
PubMed1988

Stability of simultaneous maxillary intrusion and mandibular advancement: a comparison of rigid and nonrigid fixation techniques.

This study examines the short-term stability of bimaxillary surgery following Le Fort I impaction with simultaneous bilateral sagittal split osteotomies and mandibular advancement using two standard techniques of postsurgical fixation. Fifteen adults had skeletal plus dental maxillomandibular fixation, and fifteen adults had rigid internal fixation using bone plates in the maxilla and bicortical bone screws between the proximal and distal segments in the mandible. The group with rigid internal fixation did not undergo maxillomandibular fixation. Radiographic cephalograms were analyzed during the postsurgical period to evaluate skeletal and dental stability. There was no statistical difference in postsurgical stability with rigid internal fixation or skeletal plus dental maxillomandibular fixation other than the vertical position of the maxillary molar; the skeletal plus dental maxillomandibular fixation group had a significant amount of postsurgical intrusion of the maxillary molar when compared with the rigid internal fixation group. Although the other measures showed no statistically significant difference between the experimental groups, the amount of variability in postsurgical stability in the group with skeletal plus dental maxillomandibular fixation was greater than that found in the group with rigid internal fixation.

Bone Plates↗
PubMed1994

Stress analysis of a canine spinal motion segment using the finite element technique.

Canine models have been frequently employed to investigate the in vivo effects of a surgical procedure. Various studies indicate that canine models can provide a successful in vivo biological model for these studies. Use of canine models for the biomechanical studies of the spine, however, have been questioned because of different loading conditions on the canine and human spines originated from posture differences between canine and human. Similarities between the stress distributions within the canine and human motion segments under physiological loads will strengthen the use of canine models for the studies of spine biomechanics. In the present study, finite element models of the canine intact and stabilized motion segments were developed to investigate these aspects. Comparison of model predicted flexion angle, axial stiffness, and facet contact force for the canine intact L6-L7 motion segment revealed good agreement with the corresponding parameters experimentally measured under the similar loading conditions. Similar stress distributions within the intact canine and human models were found from the predicted results in response to the physiological load. Stabilizing and stress-shielding effects of a pedicle screw-plate-type fixation device [variable spinal plating (VSP)] on the stabilized motion segment were also similar for the canine and human stabilized models. Furthermore, maximum stresses in the pedicle screws were found at the junction between the bone screw and the integrated nut of the inferior screw in both the canine and human stabilized models. This corresponds to the location of pedicle screw breakage reported in the literature. These findings suggest that a canine is a suitable model for the biomechanical studies of the lumbar spine.

Animals↗
PubMed1999

Stability of lumbar fusion with transpedicular fixation determined by roentgen stereophotogrammetric analysis.

STUDY DESIGN: An evaluation of the intervertebral stability of transpedicular instrumentation in posterolateral lumbar fusions by roentgen stereophotogrammetric analysis. OBJECTIVES: To determine the in vivo intervertebral stability of posterolateral lumbar fusions augmented with transpedicular screws and plates. SUMMARY OF BACKGROUND DATA: Transpedicular bone screw systems have been found to be as safe and clinically effective as other types of devices in stabilizing surgery of the spine. Many experimental studies have yielded basic data on the stabilizing implant effect in vitro, but the exact in vivo stabilizing effect on human lumbar vertebrae has not been presented previously. METHODS: In 12 patients, the intervertebral stability of posterolateral fusion in the lower lumbar spine augmented with transpedicular screws and plates was evaluated by serial roentgen stereophotogrammetric analysis with the patients in supine and erect positions 1 year after surgery. RESULTS: Screws in each fused vertebra yielded stable fixation or permitted sagittal intervertebral translations smaller than 1 mm induced by the positional change. A widely decompressed and destabilized vertebra without screw fixation yielded persisting intervertebral translations. CONCLUSIONS: The current study demonstrated the adequacy of in vivo stability of lumbar fusions augmented with transpedicular screws and plates. Sagittal translation seems easier to elicit than movements along the other three-dimensional axes. A widely decompressed and destabilized vertebra without screw fixation increases the risk for persisting intervertebral translations. The roentgen stereophotogrammetric analysis technique described seems to be a good way of comparing the in vivo behavior of different implant systems.

Adult↗
PubMed2002

Design and validation of a surrogate humerus for biomechanical testing.

At present biomechanical testing of fracture plating strategies is conducted using animal or cadaveric whole bone models. This may introduce experimental error into these studies. This communication summarises the design and validation of a novel bone and fibre-reinforced plastic construct conceived to minimise intra-experimental error. A tubular surrogate humerus was produced with dimension and strength matched to that of the human humerus. Bone inserts placed into the wall of the tube allow for the fixation of the plates with bone screws. Three-point bending tests of the flexural rigidity of the surrogate humerus (EI=100.1 (SD 6.0)Nm(2)) showed it to be comparable to the human humerus. Further, pull-out tests of the screws showed that the bone slots adequately mimicked the whole bone scenario. This testing construct will be used for a comparative study of humeral plating techniques.

Animals↗
PubMed1996

Multiple segmental gradual distraction of facial skeleton: an experimental study.

The method of distraction osteogenesis was used to move several facial segments in different directions with formation of new bone. On 3 young adult sheep a Le Fort II osteotomy, combined with circumferential orbital osteotomies, was performed. The periosteum over the osteotomies was preserved. Titanium bone screws were placed as bone markers. The segments were fixed with pins and plates to a combined distraction apparatus in order to advance the segments in different directions. By a gradual distraction, the midface was advanced forward by 30 mm. The left orbit was moved laterally 20 mm and the right orbit was moved forward 20 mm. In both orbits there was a concomitant globe movement. New bone formation in the distracted area was obvious radiographically, clinically, and histologically. In conclusion, multiple segmental distraction is possible in the adult sheep face and may offer three-dimensional (3D), controlled correction of complex face deformities.

Animals↗
PubMed1996

An instrumented spacial linkage for monitoring relative three-dimensional motion between fracture fragments.

A mechanical linkage with electro-magnetic sensors (a displacement transducer) is described, which may be used to measure accurately the relative motion at a bony junction such as a fracture. The linkage may be fixed to bone screws of externally-fixated fractures during routine patient activity, to measure three-dimensional inter fragmentary displacements arising from dynamic loading. Movements of the linkage are monitored by six Hall Effect devices for the six degrees of freedom (three orthogonal translations and three rotations about the translating axes). Measurements are made within error bounds of +/- 0.025 mm and +/- 0.025 deg over a range of 5 mm for the two orthogonal transverse translations, 8 mm for axial translation and 8 deg for the three rotations. Movements at the linkage, remote from the fracture, are then translated mathematically to the fracture site, assuming rigid screw contact with the bone. Displacements of the distal fragment in relation to the proximal, at the fracture center, can then be expressed anatomically through anterior, medial, and distal translations, and rotations in the sagittal, coronal, or transverse planes.

Biomechanical Phenomena↗