Bicortical Screws Research Articles

Use of Locking Plate and Screws for Triple Pelvic Osteotomy

To evaluate the efficacy and complication rate associated with use of a purpose-specific locking triple pelvic osteotomy (LTPO) plate. Prospective study. Dogs (n = 9; 15 hips). Physical examination, plain film radiography, computed tomography (CT) of the pelvis, and coxofemoral arthroscopy were performed before unilateral triple pelvic osteotomy (TPO) or staged bilateral TPO. Radiographs were taken after each procedure and 3-5, 6-8, and ≥12 weeks postoperatively. Pelvic width was measured at 3 locations to evaluate pelvic canal narrowing. No screw loosening occurred. Complications occurred in only 1 hip (7%) where pullout of the locking plate-screw construct from the caudal iliac segment occurred because of a fracture of the cis-cortex; the dog made a full recovery after a salvage procedure. There was no significant reduction in the cranial pelvic width but a small reduction at the level of the acetabuli and ischiatic tuberosities was noted 3-5 weeks after the 2nd TPO. The LTPO plate was associated with a lower complication rate than previously reported for TPOs using Slocum canine pelvic osteotomy plates (CPOP) and warrants further investigation. Pullout of the caudal plate-screw construct is a complication specific to LTPO implants. Bicortical screw purchase is recommended to prevent fracture of the cis-cortex and implant pullout.

A biomechanical study comparing plate fixation using unicortical and bicortical screws in transverse metacarpal fracture models subjected to cyclic loading

The use of bicortical screws to fix metacarpal fractures has been suggested to provide no added biomechanical advantage over unicortical screw fixation. However, this was only demonstrated in static loading regimes, which may not be representative of biological conditions. The present study was done to determine whether similar outcomes are obtained when cyclic loading is applied. Transverse midshaft osteotomies were created in 20 metacarpals harvested from three cadavers. Fractures were stabilised using 2.0 mm mini fragment plates fixed with either bicortical or unicortical screw fixation. These fixations were tested to failure with a three-point bending cyclic loading protocol using an electromechanical microtester and a 1 kN load cell. The mean load to failure was 370 N (SD 116) for unicortical fixation and 450 N (SD 135) for bicortical fixation. Significant differences between these two constructs were observed. A biomechanical advantage was found when using bicortical screws in metacarpal fracture plating.

Lateral Mass Screw Complications

Retrospective, consecutive patient series. To quantify the risks and the complications associated with screw fixation devices of the cervical spine. The usefulness of lateral mass internal fixation has been well documented in the clinical setting. However, there is a paucity of studies examining the complications associated with these devices in a degenerative clinical setting. From 1999 to 2007, 225 consecutive patients underwent posterior cervical fixation using a screw-plate and polyaxial screw-rod implant systems. There were 105 women and 120 men (age range: 45 to 84 y; mean, 68 y). In all patients, the surgical indication was cervical spondylosis with myelopathy. Mean follow-up interval was 18 months (range: 12 to 72 mo). Screw position was evaluated by computed tomography scanning postoperatively in all patients. Clinical and radiographic outcome was assessed at each visit after surgery. Intraoperative complications include fracture of lateral mass in 27 screws placement and nerve irritation in 3 bicortical screws. Early complications include hematoma formation in 2 cases and C5 root palsy in 5 cases after spinal canal decompression. Late complications include pseudarthrosis in 6 cases and screw pull-out in 3 cases. There were no cases of spinal cord or vertebral artery injury, infections, deaths, or adjacent segment disease. All patients had radiographic union, and no patient developed mechanical implant failure requiring removal of instrumentation. Reoperation was required in 14 (6.2%) cases because of nerve injury, hematoma formation, pseudarthrosis, and screw pull-out. Our clinical findings indicate that lateral mass fixation can be used safely with minimal complications and low rate of morbidity for cervical myelopathy treatment.

Surgical management of large mandibular ameloblastoma in Jamaica

The aim of this paper is to present the two cases with extensive ameloblastomas of the mandible requiring immediate reconstruction. Patients with mandibular ameloblastomas diagnosed histopathologically were treated in Kingston Public Hospital Jamaica with segmental mandibulectomy and immediate reconstruction with iliac crest bone graft and reconstruction plates. Mechanical stability was adequately achieved by the use of 2.7 mm thick titanium reconstruction plates and bicortical screw osteosynthesis which should be removed 6 months–1 year later in order to allow the bone to heal along biomechanical principles. The two patients presented in this paper are male with the age of 24 and 38. Both patients recovered well. The facial nerve was not affected in any patient treated extra orally. The functional and esthetic results are satisfactory for the patients.

EXPERIMENTAL STUDY OF ANTERIOR CORRECTION AND FIXATION TECHNIQUES FOR SPINAL DEFORMITIES

Objective. To assess spinal mobility with different extents of intervertebral disc resection, strength of screw fixation in vertebral bodies depending on placement techniques, and potentials for augmentation of screw fixation with bone cement. Material and Methods. Eighteen young human cadaveric models of thoracolumbar spines were used. Discs with different extents of discectomy were exposed to rapture and torsion load. Mechanical stability of screw fixation using different placement techniques and augmentation with bone cement was assessed. Results. The highest spinal mobility was observed after total discectomy with posterior longitudinal ligament dissection. Two-rod fixation system proved to be the most stable one, and bicortical screw placement – the most preferable. Bone cement augmentation increases mechanical stability of screws inserted into vertebral bodies.

Minimally-invasive fixation of distal extra-articular femur fractures with locking plates: Limitations and failures

Minimally-invasive fixation using a locking plate and early motion is normal practice. However, technical errors and pitfalls are common. This surgery has a set of rules that encompass both the mechanics of the internal fixation system and the implantation itself. If these rules are not strictly followed, alignment defects and/or early failure of the fixation can occur. We analysed four cases of clinical failure that were encountered after minimally-invasive distal femoral extra-articular fixation with locking plates. The following rules must be followed with this technique: extra-articular fracture, minimally-invasive approach, long plate alternating between locking screw and empty hole (five holes on either side of fracture), bi-cortical screws, placement of locking screws near a complex fracture but away from a simple fracture. Osteoporotic bone, obesity that interferes with the instrumentation, articular fracture, horizontal fracture line and surgeon experience are all limitations of this minimally-invasive technique.

Etiology and Revision Surgical Strategiesin Failed Lumbosacral Fixation of AdultSpinal Deformity Constructs

Retrospective case analysis. The purpose of this study was to evaluate the etiology and salvage strategies of failed lumbosacral fixation in adult spinal deformity patients. When extending a long spinal deformity fusion to the sacrum, the lumbosacral junction is a common site for implant problems and pseudarthrosis. Clinical and radiographic results of 33 patients (26 women/seven men; average age, 53.5 years; range, 21-73) diagnosed and treated for lumbosacral fixation failure between 1995 and 2007 were reviewed. Twenty-one of the 33 patients underwent revision surgery at one institution for these failures and were followed postoperatively for more than 2 years (average, 50.7 months). Twenty-nine of these 33 patients had two sacral screws, two patients one sacral screw, and two patients none. Bicortical sacral screws were placed in 18 patients, only 12 had distal fixation to the sacral screws (bilateral iliac screws, n = 9; others, n = 3). Seventeen of 19 patients without distal fixation to the sacral screws had screw loosening/pullout at L5 or S1. Anteriorly at L5-S1: 4/6 bone grafts collapsed, 5 of 15 intervertebral discs without anterior column support collapsed, and two of 12 titanium cages subsided into the endplates. Rod breakage between L5 and S1 (n = 9) was seen only in patients with distal fixation to the sacral screws. Nineteen of 21 revision patients received two bicortical sacral screws, whereas 20 received distal fixation to the sacral screws consisting of bilateral iliac screws in 16. Nineteen patients received anterior column support at L5-S1. Fifteen of 21 revision patients achieved solid fusion at ultimate follow-up; however, six had additional rod breakage or dislodgement at the lumbosacral junction. With long fusions to the sacrum in the treatment of spinal deformity, the use of bilateral S1 screws alone may allow for screw loosening/pullout and/or L5-S1 cage/graft collapse/subsidence. Adding bilateral iliac screws and an anterior structural cage/graft at L5-S1 will protect the S1 screws, but may still allow L5-S1 rod breakage/dislodgement because of lumbosacral pseudarthrosis. Revision surgery in these patients remains a challenge.

Mandibular Sub-Apical Osteotomy as Adjunctive in Maxillary Rehabilitation With Dental Implants

Severe maxillary atrophy is still a challenge in dental implants rehabilitation, because the Class III relationship is secondary to mandibular auto-rotation and anterior maxillary bone loss. Also, gravity forces mandibular soft tissues to descend increasing the lip to lower tooth show and lower facial third aging look. This study analyzes the functional and cosmetic results of including a mandibular sub-apical osteotomy with infero-posterior repositioning in the patient treatment planning combined with maxillary edentulous rehabilitation. Ten patients (6 female and 4 male) aged between 45-65 years old (average 52.3) underwent maxillary dental implants insertion to treat edentulism combined with anterior mandibular osteotomy to reposition the bony-dental segment inferiorly and posteriorly. The dental implants were either standard fixtures or zygoma implants placed as anterior as possible to eliminate the anterior crossbite or anterior canti-lever. The mandibular sub-apical osteotomies were performed through small incisions, minimal periosteal detachment and were fixated with bicortical screws. Some posterior mandibular fixtures were combined for maxillo-mandibular rehabilitation. All 10 patients were treated 3-D and the evaluation included clinical, radiograph and photograph analysis, pre- and postoperative; all patients were followed for a minimum of 12 months. The mean value for the anterior segment posterior and inferior repositioning was calculated postoperatively base on the lateral and PA cephalic radiographs. All patients were treated with provisional dental maxillary rehabilitation the day of the surgery. All final rehabilitations were installed within 5 months and remarkable esthetics improvement, Class I occlusions and ideal tooth-to-lip (-2 mm) relation were obtained. In the sub-apical osteotomy the posterior reposition was 4 to 7 mm (average 5.8 mm) and 3 to 5 mm (average 4.2 mm) of intrusion. This procedure was combined with zygoma (30) and conventional (27) implants in maxillary atrophy and conventional implants (37) in posterior edentulous mandibular area. No patients had intra- or postoperative complications. Mental nerve paresthesia was present in 2/10 and resolved in the following 6 months. The mandibular sub-apical osteotomy represents an excellent adjunctive surgical procedure to include in the treatment planning of total maxillary edentulous patients. This surgical alternative it is a highly predictable procedure, improves the esthetics, decreases the antero-posterior relation and helps occlusion biomechanics.

Medial Malleolar Fractures: A Biomechanical Study of Fixation Techniques

Fracture fixation of the medial malleolus in rotationally unstable ankle fractures typically results in healing with current fixation methods. However, when failure occurs, pullout of the screws from tension, compression, and rotational forces is predictable. We sought to biomechanically test a relatively new technique of bicortical screw fixation for medial malleoli fractures. Also, the AO group recommends tension-band fixation of small avulsion type fractures of the medial malleolus that are unacceptable for screw fixation. A well-documented complication of this technique is prominent symptomatic implants and secondary surgery for implant removal. Replacing stainless steel 18-gauge wire with FiberWire suture could theoretically decrease symptomatic implants. Therefore, a second goal was to biomechanically compare these 2 tension-band constructs. Using a tibial Sawbones model, 2 bicortical screws were compared with 2 unicortical cancellous screws on a servohydraulic test frame in offset axial, transverse, and tension loading. Second, tension-band fixation using stainless steel wire was compared with FiberWire under tensile loads. Bicortical screw fixation was statistically the stiffest construct under tension loading conditions compared to unicortical screw fixation and tension-band techniques with FiberWire or stainless steel wire. In fact, unicortical screw fixation had only 10% of the stiffness as demonstrated in the bicortical technique. In a direct comparison, tension-band fixation using stainless steel wire was statistically stiffer than the FiberWire construct.

Can We Trust Ex Vivo Mechanical Testing of Fresh–Frozen Cadaveric Specimens? The Effect of Postfreezing Delays

Because embalming has been demonstrated to decrease the mechanical integrity of bone, most investigators favor fresh-frozen specimens for biomechanical evaluation. However, little is known about how the integrity of fresh--frozen specimens may change during biomechanical testing or may be affected by standard practices in testing. The purpose of this study was to evaluate how the time after removal from a freezer may affect the mechanical properties of fresh--frozen diaphyseal bone. Matched pairs of nonosteoporotic fresh--frozen human cadaveric femora were thawed before instrumentation with bicortical screws. Matched femora were reserved for either control or delayed use. Each specimen received standard diaphyseal bicortical screws (six or more in each group). At specified time points, screws were axially pulled out following the guidelines of ASTM F543-07. Test groups were stored in air (21 ± 0.5°C) for 16, 50, or 90 hours. In the control group, screws were pulled out at 16 hours, which corresponds to the minimum elapsed time for specimen thawing, instrumentation, potting, and biomechanical test initiation. This represents the baseline mechanical properties of the fresh--frozen bone at the inception of any biomechanical test. The 90-hour group corresponds to the time needed to cycle a construct 300,000 times at a physiological test frequency of 1 Hz. This corresponds approximately to 2 to 4 months of in vivo loading. A midpoint of 50 hours was also tested, representing approximately 180,000 cycles. Failure for all specimens occurred as a result of bone failure at the screw-to-bone interface. There was a decrease in screw pullout strength as exposure time in air increased. The 50-hour test group showed a 9% decrease in screw pullout strength as compared with the 16-hour control group (P = 0.81). However, the 90-hour test group showed a 30% decrease in screw pullout strength as compared with the 16-hour control group (P = 0.04). This study indicates that when using fresh-frozen cadaveric bone in biomechanical tests to simulate the orthopaedic clinical setting, specimen exposure time should be considered. The timing of testing should be kept constant between specimens to allow for a proper comparison. Furthermore, for fresh--frozen cadavers, the physical properties of bone may be detrimentally affected in biomechanical testing that exceeds the 50-hour time point after removal from the freezer.

An In Vitro Evaluation of Rigid Internal Fixation Techniques for Sagittal Split Ramus Osteotomies: Setback Surgery

The aim of this study was to evaluate the biomechanical features of 3 different methods of rigid internal fixation for sagittal split ramus osteotomy for mandibular setback in vitro. Sixty polyurethane replicas of human hemimandibles were used as substrates, simulating a 5-mm setback surgery by sagittal split ramus osteotomy. These replicas served to reproduce 3 different techniques of fixation, including 1) a 4-hole plate and 4 monocortical screws (miniplate group), 2) a 4-hole plate and 4 monocortical screws with 1 additional bicortical positional screw (hybrid group), and 3) 3 bicortical positional screws in a traditional inverted-L pattern (inverted-L group). After fixation, hemimandibles were adapted to a test support and subjected to lateral torsional forces on the buccal molar surface and vertical cantilever loading on the incisal edge with an Instron 4411 mechanical testing unit. Peak loadings at 1, 3, 5, and 10 mm of displacement were recorded. Means and standard deviation were analyzed using analysis of variance and Tukey test with a 5% level of significance, and failures during tests were recorded. Regardless of the amount of displacement and direction of force, the miniplate group always showed the lowest load peak scores (P < .01) compared with the other fixation techniques. The hybrid group demonstrated behavior similar to the inverted-L group in lateral and vertical forces at any loading displacement (P > .05). Molar load tests required more force than incisal load tests to promote the same displacement in the mandibular setback model (P < .05). For mandibular setback surgery of 5 mm, this study concluded that the fixation technique based on the miniplate group was significantly less rigid than the fixation observed in the hybrid and inverted-L groups. Mechanically, adding 1 bicortical positional screw in the retromolar region in the miniplate technique may achieve the same stabilization offered by inverted-L fixation for mandibular sagittal split ramus osteotomy setback surgery in vitro.

A Biomechanical Evaluation of Bicortical Metal Screw Fixation Versus Absorbable Interference Screw Fixation After Coracoid Transfer for Anterior Shoulder Instability

The purpose was to evaluate the load to failure of 2 coracoid fixation techniques after transfer of the coracoid to the anterior glenoid neck. Ten cadavers (mean age, 87 years; range, 74 to 96 years) underwent the Bristow conjoined tendon tenodesis technique as described by Boileau et al. (bioabsorbable interference screw fixation of a coracoid bone plug) in 1 shoulder and the Latarjet-Patte coracoid transfer popularized by Walch (fixation with 2 screws through a larger piece of the coracoid) in the opposite shoulder. The force on the conjoined tendon required to pull the coracoid off of the anterior glenoid was recorded, along with the mode of construct failure. The median ultimate failure load was 110 N (range, 35 to 170 N) in the interference screw group and 202 N (range, 95 to 300 N) in the bicortical screw group (P = .002). The mode of failure of the interference screw technique was complete avulsion of the bone plug from the socket in 6 cases (60%) and fracture of the bone plug in 4 (40%). The mode of failure of the bone block technique was a vertical fracture through both screw holes in 7 cases (70%), a horizontal fracture through the distal screw hole in 2 (20%), and an intratendinous rupture of the conjoined tendon in 1 (10%). Fixation of a coracoid bone block to the anterior glenoid neck with 2 bicortical metal screws is stronger than fixation of a coracoid bone plug with an absorbable interference screw. These data may influence surgeons' decisions regarding coracoid fixation as well as postoperative rehabilitation after coracoid transfer.

Biomechanical study of the effectiveness of unilocking T-plate systems for prophylactic internal fixation of the radial osteocutaneous donor site

Introduction: Prophylactic internal fixation (PIF), with a bone plate in either the anterior (over the section defect) or posterior (on intact cortex) position, has substantially reduced the incidence of fracture at the donor site of the radial osteocutaneous free flap. This study uses the sheep tibia model to compare the effectiveness of new T-shaped titanium plates utilising a unilocking screw system with a 3.5 mm steel plate and bicortical screw fixation system commonly applied for PIF.

Is a Single Miniplate at the Inferior Border Adequate in the Management of an Angle Fracture of the Mandible?

This prospective study evaluates the efficacy of using a single miniplate at the inferior border in the management of a displaced angle fracture. Case series with chart review. Pt. B.D. Sharma University of Health Sciences. Fifty-two patients with angle fracture of the mandible were evaluated. All fractures were displaced. The displacement of fracture was assessed on panoramic radiography by measuring the displacement of the inferior alveolar canal. Fractures with displacement greater than 2 mm were included in the study. Fixation with a 4-hole noncompression miniplate along the inferior border and 2 bicortical screws on each side of the fracture was done. Among these 52 patients, 20 sustained isolated angle fracture, 2 sustained bilateral angle fracture, and 30 sustained angle fracture associated with contralateral parasymphysis or body fracture. Five patients (9.5%) experienced complications. All were considered minor and did not require hospitalization. Two had a slight occlusal discrepancy requiring selective occlusal grinding, and 2 minor infections were managed by incision and drainage. One patient suffered from paresis of the facial nerve that resolved itself after 3 months. Based on this single study, at a single institution, we can conclude that outcomes are acceptable in our patients, but there is very limited ability to generalize the results to different practice settings. Because of these limitations, a multicenter study with an appropriate comparison group is required to substantiate a more generalizable conclusion of efficacy of this single miniplate at inferior border.

Inadvertent Screw Stripping During Ankle Fracture Fixation in Elderly Bone

Poor screw purchase because of osteoporosis presents difficulties in ankle fracture fixation. The aim of our study was to determine if cortical thickness, unicortical versus bicortical purchase, and bone mineral density are predictors of inadvertent screw stripping and overtightening. Ten paired cadaver ankles (average donor age, 81.7 years; range, 50-97 years) were used for the study. Computed tomography scanning with phantoms of known density was used to determine the bone density along the distal fibula. A standard small-fragment, 7-hole, one-third tubular plate was applied to the lateral surface of the fibula, with 3 proximal bicortical cortical screws and 2 distal unicortical cancellous screws. A posterior plate, in which all 5 screws were cortical and achieved bicortical purchase, was subsequently applied to the same bones and positioned so that the screw holes did not overlap. A torque sensor was used to measure the torque of each screw during insertion (Ti) and then stripping (Ts). The effect of bone density, screw location, cortical thickness, and unicortical versus bicortical purchase on Ti and Ts was checked for significance (P < .05) using a general linearized latent and mixed model. We found that 9% of the screws were inadvertently stripped and 12% were overtightened. Despite 21% of the screws being stripped or being at risk for stripping, we found no significant predictors to warn of impending screw stripping. Additional work is needed to identify clinically useful predictors of screw stripping.

Risk of internal carotid artery injury during C1 screw placement: analysis of 160 computed tomography angiograms

Background contextInjury to the internal carotid artery (ICA) is a potentially catastrophic complication of C1-lateral mass (C1-LM) or C1–C2 transarticular screw insertion. PurposeThis study was designed to determine the risk of injury to the ICA during placement of these screws using computed tomography angiography (CTA). Study designRadiographic analysis using CTA. Patient sampleOne hundred sixty CTAs were examined, for a total of 320 ICAs. Outcome measuresNot applicable. MethodsFine-cut intravenous CTAs with multiplanar and three-dimensional reconstruction were reviewed. The position of the ICA in relation to the anterior cortex (AC) of C1, anterior end of the anterior tubercle (AT), and medial margin of the transverse foramen (TF) was measured bilaterally in three ascending and equidistant levels of the C1-AT. ResultsThe position of the ICA in relation to C1 was variable. The average distance between the ICA and the AC of C1 was only 3.7 mm. Furthermore, 96% of the time the posterior margin of the ICA was located posterior to the anteriormost aspect of the anterior C1 tubercle (average distance, 5.4 mm), making the ICA vulnerable to damage if a drill, tap, or screw was inserted to the depth of the anteriormost portion of the AT as seen on a lateral fluoroscopic or radiographic view. The medial margin of the ICA was located medial to the TF (a location potentially vulnerable to injury with bicortical screw placement) less often at the caudal aspect of the C1-AT (54%) than at its middle or cranial aspect (74% and 75%, respectively). No ICAs were located anterior to the medial 30% of the C1-LM or more medially. ConclusionsBicortical C1-LM or C1–C2 transarticular screw placement carries a potential risk of ICA injury. Given the wide variation in ICA location relative to C1, if bicortical C1 fixation is required, preoperative CTA should be considered to determine the optimal screw trajectory. In general, inferomedially angulated C1-LM screws appear to be safer with respect to the ICA injury than other potential trajectories.

Biomechanical study of a unilocking T-plate system for prophylactic internal fixation of the radial osteocutaneous donor site using the sheep tibia model

Prophylactic internal fixation (PIF), with a bone plate in either the anterior (over the section defect) or posterior (on intact cortex) position, has substantially reduced the incidence of fracture at the donor site of the radial osteocutaneous free flap. This study uses the sheep tibia model to compare the effectiveness of new T-shaped titanium plates utilising a unilocking screw system with a 3.5 mm steel plate and bicortical screw fixation system commonly applied for PIF. Forty matched pairs of adult sheep tibias were tested in torsion and 4-point bending. An osteotomised bone was significantly weaker (p<0.001) than an intact bone in both bending and torsion with a mean loss of 77% and 64% of strength respectively. The tibia withstood much greater bending loads. All of the constructs significantly strengthened an osteotomised bone by a factor of 1.73-2.43 times in bending and 1.54-2.63 in torsion. The 2.4 mm T-plate in an anterior position (section) was the baseline against which other plates in differing positions were compared. The 3.5 mm T-plate section, DCP section and DCP cortex constructs had 41%, 30% and 2% greater mean bending strengths respectively but only the 3.5 mm T-plate section result approached statistical significance (p=0.06). In torsion the DCP section, 3.5 mm T-plate section and DCP cortex constructs had 56% (p=0.01), 27% (p=0.06) and 25% greater mean strengths respectively. When compared to an intact bone the mean bending strength restored by the DCP section (84%) and 3.5 mm T-plate section (87%) constructs was greatest and effectively restored the strength to that of an intact bone (100%). In torsion the mean strength restored by the DCP section (62%), DCP cortex (44%), 3.5 mm T-plate section (40%) and 2.4 mm T-plate (36%) remained significantly less than an intact bone. All of the plate constructs significantly strengthened an osteotomised bone but overall the 3.5 mm T-plate section and DCP section were the strongest constructs and most suitable for PIF. The lighter 2.4 mm T-shaped titanium plate was least effective. The strongest reinforcement in bending and torsion was the 3.5 mm T-plate section and DCP section respectively. The 3.5 mm DCP section plate was significantly stronger (p=0.01) than the 3.5 mm T-plate in torsion and remains the most effective construct for resisting torsional stresses, which are probably the commonest cause of fracture in clinical practice.

The Effect of Sacral Decortication on Lumbosacral Fixation in a Calf Spine Model

Animal cadaveric biomechanical study. We hypothesized that increasing bony destabilization of a bovine cadaveric sacrum by anterior pedicle screw penetration and bilateral alar decortication would decrease the amount of load necessary for failure of the construct and result in failure through the decortication sites. Fusion to the sacrum has become commonly used for treatment of neuromuscular scoliosis and fusions in osteoporotic patients. Fixation failure after attempted fusion to the sacrum may be attributed to iatrogenic causes such as S1 screw penetration and sacral ala decortication. Sixteen fresh-frozen 6- to 8-week-old calf spines were tested after instrumentation with pedicle screws and bilateral rods from L2 to S1 using four constructs: (1) S1 screws with posterior-only purchase; (2) S1 screws with bicortical purchase; (3) S1 screws with bicortical purchase and sacral alar decortication; and (4) S1 screws with bicortical purchase, decortication, and iliac fixation. A destructive flexural bending load was applied at L2 to each construct. Ultimate failure moment (Nm) was compared among the four groups, using a one-way analysis of variance combined with Holm-Sidak post hoc test. No significant difference in failure moment was found among groups 1, 2, and 3. The addition of iliac fixation (group 4) significantly increased bending load to failure (P < 0.01), and iliac screw dislodgement was the dominant mechanism of failure. All specimens in group 3 failed with fractures extending through the decortication site. Groups 1 and 2 specimens failed by fracturing through the S1 body. Sacral alar decortication and anterior pedicle screw purchase did not decrease the failure moment in long instrumentation to the sacrum. Pattern of failure was affected, with alar decortication being the site of fracture in each construct in which it was performed. Iliac fixation increased the failure moment under catastrophic loading conditions even when combined with sacral alar decortication and bicortical pedicle screw purchase.

Surgical Treatment of Sagittal Fracture of Mandibular Condyle Using Long-Screw Osteosynthesis

The retrospective study evaluated long-screw (bicortical screw) osteosynthesis used in the surgical treatment of sagittal fracture of the mandibular condyle and compared it with titanium plates and removal of the condylar fragment. Ninety-five patients with sagittal fracture of the mandibular condyle received open surgical treatment from 1997 to 2008. Among these patients, the condylar fragments were fixed with long screws in 56 cases (group A), were fixed with titanium plates in 12 cases (group B), and were completely removed in 24 cases (group C). Follow-up was carried out clinically and radiologically. The clinical features included limitation of mandibular mobility, occlusion disturbance, lateral deviation on mouth opening, joint pain, clicking, facial asymmetry, and patient's subjective evaluation. The radiologic parameters consisted of degree of bony resorption, bony change, change of osteosynthesis material, and shortening of mandibular ramus height. Anatomic reduction and functional restoration were obtained and no severe complication was detected in group A. However, 3 of 14 patients had severe osteoarthrosis and 2 of 14 patients had ankylosis in group B. In group C 3 of 24 patients had mandibular retrusion, 4 of 24 patients had front teeth open bite, 4 of 24 patients had severe osteoarthrosis, and 1 of 24 patients had ankylosis. The long-screw fixation group had a more favorable prognosis than the titanium plate group and the group in which removal of the condylar fragment was performed. The long-screw fixation technique might be suitable for use in the surgical treatment of sagittal fractures of the mandibular condyle.

Biplanar fixation of a locking plate in the diaphysis improves construct strength

BackgroundElevation of a locking plate over the bone surface not only supports biological fixation, but also decreases the torsional strength of the fixation construct. Biplanar fixation by means of a staggered screw hole arrangement may combat this decreased torsional strength caused by plate elevation. This biomechanical study evaluated the effect of biplanar fixation on the torsional strength of locking plate fixation in the femoral diaphysis. MethodsCustom titanium plates were manufactured with either a linear or staggered hole pattern to evaluate planar and biplanar fixation, respectively. Fixation strength under torsional loading was evaluated in surrogates of the femoral diaphysis representative of osteoporotic and non-osteoporotic bone. Furthermore, fixation strength was determined for plate fixation with unicortical or bicortical locking screws. Five specimens per configuration were loaded to failure in torsion to determine their strength, stiffness, and failure mode. FindingsIn osteoporotic bone, biplanar fixation was 32% stronger (P=0.01) than planar fixation when unicortical screws were used and 9% stronger (P=0.02) when bicortical screws were used. In non-osteoporotic bone, biplanar fixation was 55% stronger (P<0.001) than planar fixation when unicortical screws were used and 42% (P<0.001) stronger when bicortical screws were used. InterpretationA biplanar screw configuration improves the torsional strength of diaphyseal plate fixation relative to a planar configuration in both osteoporotic and normal bone. With biplanar fixation, unicortical screws provide the same fixation strength as bicortical screws in non-osteoporotic bone.