Dynamic Fixation Research Articles

A Comparative Study to Assess the Preoperative Thickness of Lateral Trochanteric Wall as a Predictor of Postoperative Lateral Wall Fracture in Intertrochanteric Fracture Treated by Dynamic Hip Screw

The aim of this study was to assess the preoperative thickness lateral trochanteric wall as a predictor of postoperative lateral wall fracture in intertrochanteric fracture treated by dynamic hip screw fixation. A Radiograph based Comparative study involved 66 patients with intertrochanteric fracture treated by dynamic hip screw fixation. All patients had an intact lateral wall preoperatively and were AO/OTA 31 A1 and AO/OTA 31 A2 fractures. Mean age of the patients was 75 years. All patients were followed up with x-ray at 1 month and 6 months postoperatively. Age, gender, side of fracture, type of fracture as per AO/OTA classification, the pre-operative thickness of the lateral trochanteric wall, the tip-apex distance and the status of the trochanteric wall after 6 months from surgery were subjected to analysis. Radiographs were retrieved from the Picture Archive and Communication System and thickness of the lateral wall calculated. Measurements were corrected for magnification using the radiological magnification factor. Of the 66 patients, a fracture of the lateral wall occurred in 26 patients (39.39%). The lateral was intact in 40 patients (60.61%). The mean pre-operative thickness of the lateral wall of the 26 patients with a lateral wall fracture was 17.8 mm (SD-6.45) compared to 26.9 mm (SD-6.93) in 40 patients without a lateral wall fracture. The mean thickness of trochanteric wall in 39 patients with A1 fracture was 27.5 mm (SD=7.17) whereas the mean thickness in A2 type fracture (27 cases) was 17.3 mm (SD=4.88).74.07% of patients with A2 type fracture developed a fracture of the lateral wall whereas only 15.38% of A1 type fracture had a fracture of lateral wall after a six months follow-up. Factors like age at the time of operation, gender, side of fracture, tip-apex distance (if less than 25 mm) has no significant relation with development of post-operative lateral wall fracture. In summary, when the lateral wall thickness is less than 20.55 mm there is significantly high chance of lateral wall getting fractured if fixed with a DHS alone.

The mid- to long-term effect of Wallis lumbar interspinous dynamic stabilization on the adjacent segment degeneration

Objective: To explore the mid- to long-term effect of Wallis interspinous dynamic stabilization system on the adjacent segment degeneration. Methods: From March 2009 to June 2010, in Department of Orthopedics, Beijing Luhe Hospital, Capital Medical University, 24 patients with L4-5 monosegmental lumbar disc herniation were treated with posterior lumbar decompression combined with Wallis interspinous dynamic fixation. Clinical outcomes were evaluated with visual analogue score (VAS) (back pain), VAS (leg pain) and oswestry disability index (ODI) score. Intervertebral disc height (IDH) and range of motion (ROM) of the upper and lower adjacent segments were measured on X-ray. The degneration of lumbar intervertebral disc was evaluated on MRI. paired-t test was used to compare preoperative VAS, ODI, IDH, ROM and the degeneration of lumbar intervertebral disc with those at the final follow-up. Results: Twenty patients had a mean follow-up time of (65.2±4.7) months. At the final follow-up, VAS (back pain), VAS (leg pain) and ODI showed significant improvement (all P<0.01). At the final follow-up, IDH of the upper and lower adjacent segment showed no significant difference compared with those preoperatively (P>0.05); ROM of the upper adjacent segment increased (P<0.05), while ROM of the lower adjacent segment did not change significantly compared with that preoperatively (P>0.05). The degeneration of intervertebral discs at the upper and lower segments showed no significant changes at the final follow-up (P>0.05). Conclusions: Posterior decompression combined with Wallis interspinous dynamic stabilization system for monosegmental lumbar disc herniation can achieve satisfactory clinical results. More than five years' follow-up confirmed that the Wallis system will not accelerate adjacent segment degeneration.

Primary stability of unicompartmental knee arthroplasty under dynamic flexion movement in human femora

BackgroundThe objective of our study was to evaluate the impact of a trabecular stem fixation versus a cortical teeth fixation technique on the primary stability of cemented unicompartmental femoral components under dynamic flexion movement loading conditions in human femora. MethodsTen fresh-frozen human knees of a mean donor age of 73.9years were used to perform medial unicompartmental knee arthroplasty under a less invasive parapatellar surgical approach. The femora were divided into two groups of matched pairs based on comparable trabecular bone mineral density. To assess the primary stability, a new method based on a combination of dynamic flexion movement, double-peak loading simulating stair climbing, kinematic analysis of the femoral component migration relative to the bone and an evaluation of the cement layer by fragments cut through the implant-cement-bone interface in the sagittal plane of the medial condyle was introduced. FindingsFor the “trabecular stem fixation” technique the mean load to failure was 2340 (SD 650) N and for “cortical teeth fixation” it was 1080 (SD 455) N, with a substantially enhanced dynamic fixation strength for the “trabecular stem fixation” (p=0.008). In the distal area the cement layer of the “trabecular stem fixation” showed a significant decreased thickness compared to the “cortical teeth fixation” (p=0.029), while a substantially deeper cement penetration (p=0.044) has been achieved for the “trabecular stem fixation”. InterpretationFrom our observations, we conclude that there is a significantly enhanced primary stability with a “trabecular stem fixation” compared to a “cortical teeth fixation” technique of cemented unicompartmental femoral components, in terms of dynamic failure load and migration characteristics.

Effect of illuminance and spectrum on peripheral obstacle detection by pedestrians

Obstacle detection is an important visual task for pedestrians. An experiment was carried out to measure the ability to detect peripheral obstacles under variations of illuminance and scotopic/photopic luminance ratio and with older and younger test participants. The LED array used in this work enabled scotopic/photopic ratio to be varied whilst chromaticity was held constant. The tests employed a full-scale model with dynamic fixation and walking to better simulate pedestrian experience than in past work. Detection performance increased with illuminance, reaching a plateau at 2.0 lux. A higher scotopic/photopic ratio improved obstacle detection but only at the lowest illuminance used in this study (0.2 lux). Older participants showed poorer obstacle detection performance than younger participants but again only at the lowest illuminance.

Secondary intramedullary nailing following external fixation for open tibial shaft fractures

Objective To explore the clinical efficacy of secondary unreamed intramedullary nailing following primary external fixation for open tibial shaft fractures. Methods From March 2011 to June 2014, we treated 28 open tibial shaft fractures. They were 17 men and 11 women, aged from 21 to 62 years(average, 38. 2 years). After thorough debridement, the tibia was stabilized temporarily with external fixation. The wounds were handled with primary closure or secondary repair with skin grafts or tissue flaps. After the wounds healed, the external fixation was replaced by unreamed intramedullary nailing. Fracture union and complications were documented. The clinical efficacy was evaluated at the final follow-ups according to the Johner-Wruhs scoring system. Results All the 28 patients were followed up for 12 to 18 months(average, 13. 5 months). Bony union was achieved in all after 4 to 15 months(average, 4. 9 months). Delayed union was observed in 4 cases which were healed after dynamic fixation. There was no deep infection, nail breakage, malunion or limb shortening in any one. Mild knee pain was reported by 5 cases after surgery. According to the Johner-Wruhs criteria, 18 cases were excellent, 7 good, and 3 moderate, giving an excellent to good rate of 89. 3%. Conclusion Primary external fixation and secondary unreamed intramedullary nailing can result in good fracture union with satisfactory biomechanical stability and favorable early rehabilitation in the treatment of open tibial shaft fractures. Key words: Tibial fractures; Fracture fixation, intramedullary; External fixator

Role of locking dynamic hip screw fixation in the treatment of osteoporotic intertrochanteric fractures

Role of locking dynamic hip screw fixation in the treatment of osteoporotic intertrochanteric fractures

PEEK Rods for Posterior Lumbar Fixation: Pros and Cons: The First French Series

Introduction The ideal lumbar spine fixation system should provide sufficient stability while preserving natural posturing and spinal alignment with limited risk of adjacent level degeneration. While rigid fixation systems may contribute to stress shielding in anterior column increasing consecutively adjacent segment degeneration, Polyetherethrketone (PEEK) Rods provide a modulus of elasticity close to cancellous bone that may decrease these risks. Biomechanical studies comparing rigid fixation using titanium Rods with PEEK Rods posterior systems have shown a comparable intervertebral stability with the two systems nevertheless PEEK was associated with a lower risk of screw mobilization in poor bone, an increased anterior physiological load and a reduced stress on bone-screw interface that may predict lower risk of adjacent level degeneration. We performed a retrospective study in a french cohort of patients who underwent posterior lumbar fixation using PEEK Rods to investigate clinical indications and clinical outcomes in real life settings. Material and Methods Between June 2011 and July 2014, 48 patients who underwent posterior lumbar fixation using PEEK Rods were included in our study for retrospective review. Surgery was performed using 5,5mm pre-bent PEEK Rods with Titanium monoaxial screws for 1 to 4 level posterior lumbar fixation with a maximum length of 160 mm. Clinical outcomes were assessed using Oswestry Disability Index (ODI), reoperation rate, complications, radiographs and MRI. The patients satisfaction was also evaluated using the Patient Satisfaction Index (PSI). Results The population included 28 males and 20 females with an average age of 61 years. The main indication for surgery was spinal decompression with stabilization (44,6%). A majority of patients (29/60,4%) presented surgical antecedents including recurrent disc herniation, posterior decompression, posterior fusion with instrumentation and stabilization with interspinous devices. Patients underwent surgery on one (18/37,5%) or multiple levels (30/62,5%). Patients had surgery with anterior cages for fusion (PLIF), posterior dynamic fixation or hybrid systems combining fusion and non-fusion. The most frequent surgeries were performed on L4L5S1 as hybrid systems. At 2 years follow-up, the mean ODI score was improved by 29% (from 67% to 38%) and the mean PSI was 1,8 on a scale ranging from 1 to 4 (1: completely satisfied. 4: same or worse condition than before surgery). There was no reoperation for 89,7% patients, no migration for 94,7%, no screw breakage for 84,2% (never for one single level fixation) and no rod breakage. We reported 15% patients with post-operative adjacent level degeneration. For 21% patients with pre-operative signs, the degeneration was no more observed on the last MRI evaluation after 2 years. Conclusion PEEK Rods provide a safe and effective system that can be either used as a fusion system promoting anterior fusion with decreased risk of implant failure, as dynamic system protecting adjacent levels, or as hybrid system combining both advantages, with a stability comparable to Titanium rods. Further studies on larger populations and longer term follow-up are needed to confirm these data.

Fratture esposte di omero e di gomito

Humeral and elbow fractures are much rarer than those of the lower limbs and represent about 10% of all fractures. We performed a review of the literature and reported our experience in the management of these fractures. The technique mainly depends on the degree of exposure and contamination of the wound as happens for other fractures. From a close examination of the literature, which is really small, it appears that the main treatment for humeral fractures remains external fixation as an emergency stabilisation, and as final solution in case of severe mortification of muscle tissue. In case of distal humeral fracture or, in particular, of articular injuries classified as Gustilo I and II, a stable surgical treatment with plates or bone graft or dynamic fixator can be indicated for early mobilisation. In case of proximal forearm articular fractures with moderate bone exposition, the patient can be treated by stable ulnar fixation and radial reconstruction (if needed, with radial head prosthesis), if managed within six hours after the injury.

Evaluation of the biomechanical stability of lumbar dynamicly fixed by socket track pedicle screws

Objective To investigate the stability of lumbar single-level dynamicly fixed by socket track pedicle screws after decompression. Methods Socket track pedicle screws are made of titanium-alloy, swing like universal screw within the scope of 18° in the sagittal plane and 8° in the horizontal plane. Motion constraints were due to the hole which the screw goes through. Six pig spines (L1-5) were tested by applying a pure moment of 4.018 Nm in 3 directions of loading. The range of motion (ROM) of the following groups underwent different surgical procedures was measured: (1) intact; (2) dynamic fixation 1 (decompression by total laminectomy and instrumentation with socket track pedicle screws); (3) dynamic fixation 2 (decompression by total laminectomy and bilateral facetectomy while instrumentation with socket track pedicle screws); (4) instability resulted from decompression (decompression by total laminectomy plus bilateral facetectomy without any rod); (5) hybrid fixation (decompression by total laminectomy and bilateral facetectomy while instrumentation with 2 socket track pedicle screws connected with 2 unilateral pedicle screws ). Results Compared with the intact specimens (in flexion, extension, lateral bending and rotation, corresponding angular displacements were 1.84°±0.75°, 1.55°±0.34°, 2.2°±1.07°, 2.06°±0.76° respectively), the ROM of segment L3, 4 of each group were significantly restricted except for axial rotation. In flexion, extension and lateral bending, the ROM was reduced to 0.71°±0.39°, 0.46°±0.18°, 0.85°±0.66° in dynamic fixation 1 group; 0.79°±0.43°, 0.71°±0.20°, 1.17°±0.48° in dynamic fixation 2 group and 0.63°±0.50°, 0.37°±0.19°, 0.54°±0.60° in hybrid fixation group. The rotation ROM of dynamic fixation 1 group and hybrid fixation group were decreased to 1.50°±0.64° and 1.22°±0.36°, whereas the ROM of dynamic fixation 2 had a non-significant reduction to 1.85°±0.67°. The extension and rotation ROM of dynamic fixation 2 increased significantly comparing to dynamic fixation 1 group; the extension, lateral bending and axial rotation ROM of hybrid fixation group were reduced comparing to the state of dynamic fixation 2 group. Conclusion The dynamic instrumentation of single-level lumbar spine with socket track pedicle screws could offer stability in all directions. The flexion, extension, lateral bending and rotation ROM of spine with dynamic instrumentation after total laminectomy and bilateral facetectomy could be reduced. Key words: Lumbar vertebrae; Bone screws; Biomechanics

Clinical Follow-Up after Treatment of Degenerative Lumbar Disease by Posterior Dynamic Stabilizing Technique

Introduction: Technique of dynamic fixation for treatment of lumbar degenerative has been developed in avoidance of possible adjacent level degeneration. The dynamic rod, consists of titanium alloy cable cord and polyetheretherketone shell, of K-rod posterior dynamic rod system provides flexible feature that mobility preservation of instrumented level shall be achieved. Clinical research for the usage of K-rid system has not been reported with evidence-based support. This retrospective study was aimed to report clinical outcome of K-rod posterior dynamic rod system utilized for degenerative lumbar disease. Methods: Fifty patients with lumbar degenerative disease ranged from L3 to S1 have been enrolled. Dynamic and hybrid (dynamic rod accompanied by rigid rod) fixations of K-rod system were adequately selected for patients after discectomies of diseased intervertebral discs. Clinical evaluations including Japanese Orthopedidc Association Scores (JOA), Oswestry Disability Index (ODI), and Visualized Analogue Scale (VAS) have been conducted pre- and post-operatively. Results: In the follow-up period (12-36 months, mean 26.4 months), great improvements in JOA, ODI, and VAS were respectively 73.34%, 37.18%, and 77.35% in dynamic fixation group, while those in hybrid fixation group were respectively 76.37%, 30.5%, and 71.68%, with no statistical difference between the two groups. Significantly reduced mobility has been observed in hybrid fixation group compared with its preoperative status. Conclusions: Current follow-up report of K-rod posterior dynamic rod system represented acceptable clinical satisfactory. The preserved mobility of instrumented segment based on sufficient biomechanical stability can successfully achieve pain relief and functional restoration.

Conversion arthroplasty after failed dynamic hip screw fixation of intertrochanteric fractures

Background Failed treatment of intertrochanteric fractures typically leads to profound functional disability and pain. Factors that guide the choice of salvage treatment include the anatomic site of nonunion, the quality of the remaining bone and articular surface, and patient factors (such as age and activity level). Patients and methods Between 2010 and 2013, 30 patients (seven women and 23 men) with a mean age of 60 years (range: 50–70 years) were treated at the Orthopedic Department of Beni Suef University, following failure of internal fixation with dynamic hip screw of intertrochanteric fracture, using prosthetic replacement (12 bipolar hemiarthoplasty and 18 total hip replacement). The average follow-up was 14 months (range: 3–26 months). Results At the end of follow-up, nine hips had excellent results, 11 had good result, five had fair results, and five had poor results according to Harris hip score. Conclusion Hip arthroplasty is an effective salvage procedure after the failed treatment of an intertrochanteric fracture in older patients.

Assessment of Mortality in Postoperative Hip Fractures in a Rural Tertiary Care Centre

Background: Peritrochanteric hip fractures in elderly people leads to prolonged immobilization and increased risk of death. Elderly people having co morbidities such as diabetes, hypertension and cardiovascular diseases, along with hip fractures results in increase the mortality of the patients post operatively1,2. The objective of this study is to determine the relation of mortality during one year post operative period after hip surgery to associated co morbidities. Methods: In this retrospective study patients aged 60 and above admitted during the period from April 2014 to June 2015 in the department of orthopaedics at a rural tertiary care centre for surgical intervention for peri trochanteric hip fractures were included. A sample size of 56 patients operated during this period was considered in this study. Results: Out of 56 patients operated, 9 patients died during first year post operative period.Of them 4 were males and 5 females. 2 patients died in first one month of follow up, one due to aspiration pneumonia and second patient from septicaemia. 3 patients died in first 3 months of follow up due to deep vein thrombosis leading to pulmonary embolism, cardiac failure and cerebro-vasular accident. 4 patients died due to cardiac failure between 3 months to one year postoperative period. Out of 9 death 4 were in hospital 3 in home, one in old age home and one person in unknown place. In 9 deaths 3 patients had bipolar prosthesis,2 dynamic hip screws fixation, 2 with proximal femoral locking compression plate, 2 with proximal femoral nailing and 1 with Austin Moore prosthesis. Death of patients more than 75 years were 5 and between 65-74 years was 4. Conclusion: Hip fractures are one of the common causes of increasing mortality in elderly population. However early recognition of patients with hip fracture and admission to hospital, prompt identification of the co morbidities and treating them with early surgery and mobilization would geatly reduce the risk of morbidity and mortality.

Comparative study between Dynamic Condylar Screw and Locking Plate Fixation in fractures of distal femur in adults-A study of 30 cases

Background: The aim of treatment of the distal femoral fractures has been a balance between the goal of anatomical alignment and need for early function of limb. Objective: 1. To compare the rigidity of fixation achieved. 2. To compare the restoration of anatomical joint surface. Methodology: 30 patients of distal femoral fractures admitted to Department of Orthopaedics, at Government Medical College, Rajindra Hospital, Patiala. Only those cases were selected where ORIF is indicated like in patients with displaced intra-articular fractures, multiple injuries, severe ipsilateral limb injuries, displaced extra-articular supracondylar fractures, pathological fractures and most open fractures. Results: Among 30 patients, 16 cases (54%) sustained A type and 14 cases (46%) suffered type C supracondylar fracture as per AO classification. In DCS group, most (80%) of the patients had A type of fracture. In LCP group, most (75%) of the patients had C type of fractures. Bone grafting was done in 8 (24%) cases at the time of primary fixation of fractures. In DCS group bone grafting was done in two cases and in LCP group in 6 cases. In the DCS group, we had 2 cases (6%) in which only one inter fragmentary screw and 1 case in which 2 inter fragmentary screws were fixed in the distal fragment along with DCS lag screw and plate to give additional support. Conclusion: LCP is the implant of choice in comminuted fractures of distal end of femur and in elderly patients DCS can be used in distal femur fractures only when there is an uncomminuted bone stock of atleast 4 cm above the intercondylar notch. Key Words: Supracondylar, Intercondylar, Inter fragmentary screws, Bone grafting

The Impact of Nitinol Staples on the Compressive Forces, Contact Area, and Mechanical Properties in Comparison to a Claw Plate and Crossed Screws for the First Tarsometatarsal Arthrodesis

Background The optimal fixation method for the first tarsometatarsal arthrodesis remains controversial. This study aimed to develop a reproducible first tarsometatarsal testing model to evaluate the biomechanical performance of different reconstruction techniques. Methods Crossed screws or a claw plate were compared with a single or double shape memory alloy staple configuration in 20 Sawbones models. Constructs were mechanically tested in 4-point bending to 1, 2, and 3 mm of plantar displacement. The joint contact force and area were measured at time zero, and following 1 and 2 mm of bending. Peak load, stiffness, and plantar gapping were determined. Results Both staple configurations induced a significantly greater contact force and area across the arthrodesis than the crossed screw and claw plate constructs at all measurements. The staple constructs completely recovered their plantar gapping following each test. The claw plate generated the least contact force and area at the joint interface and had significantly greater plantar gapping than all other constructs. The crossed screw constructs were significantly stiffer and had significantly less plantar gapping than the other constructs, but this gapping was not recoverable. Conclusions Crossed screw fixation provides a rigid arthrodesis with limited compression and contact footprint across the joint. Shape memory alloy staples afford dynamic fixation with sustained compression across the arthrodesis. A rigid polyurethane foam model provides an anatomically relevant comparison for evaluating the interface between different fixation techniques. Clinical Relevance The dynamic nature of shape memory alloy staples offers the potential to permit early weight bearing and could be a useful adjunctive device to impart compression across an arthrodesis of the first tarsometatarsal joint. Therapeutic, Level V: Bench testing.

Dynamic Distraction External Fixation for Contracture of the Metacarpophalangeal Joint.

Metacarpophalangeal (MP) joint contractures are common after traumatic injury, and can be difficult to manage. After surgical capsulectomy, it remains challenging to maintain motion that was obtained at the time of surgery. Our group uses a novel, prefabricated digital external fixator to provide both distraction, and motion therapy across the MP joint after surgical treatment of MP contracture. The purpose of this technique is to demonstrate the effectiveness of an adjunctive dynamic distraction external fixator for the maintenance of joint motion after surgical treatment of MP contractures of the border digits.

TITANIUM IMPLANTS IN SPINE SURGERY: PROMISING DIRECTIONS

The current lineup of titanium implants and structures used in spine surgery is presented by meshes, cages, telescopic implants, transpedicular screws, plates and dynamic fixation systems. The review incorporates evolution of application and positive and negative properties of implants.

Letter to the Editor concerning “Systematic review of the effect of dynamic fixation systems compared with rigid fixation in the anterior cervical spine” by Campos RR, Botelho RV (Eur Spine J. 2014 Feb; 23(2):298–304)

We read, ‘‘Systematic review of the effect of dynamic fixation systems compared with rigid fixation in the anterior cervical spine’’ by Campos RR, Botelho RV [1], who should be congratulated for their literature review; nevertheless, we would like to point out several issues. The worse fear about using dynamic plates would be the clinical impact of lordosis loss; as shown by Ghahreman and colleagues who analyzed ABC use [2], even though there is a partial loss (around 50 %) of gained lordosis after surgery, there is still a global lordotic gain, which may explain why changes in cervical angles do not affect clinical outcome in the study. The second fear is about adjacent segment irritation and subsequent early degeneration (which may just happen because of the surgery itself) as with axial dynamic plates there may be plate invasion of the disc space (not any longer with modern designs), which seems to be caused mainly because of surgical technique, and as such can be prevented when using the DOC plate by turning it [3], and when using the ABC the screws should be placed as far as possible from the adjacent level. Once addressed these two issues, the main criticism about the review is the global approach of considering all types of dynamic plates as working identically: no distinction is made among several types of dynamic plates, as they are different not only from static plates but also among them, depending on the dynamism based on rotational or axial (uni-DOCor bilateral-ABC)—the latter also has a combined dynamism. This is important because of the three RCT studies for two level ACDF, while one study shows no difference in clinical outcome or fusion speed of static (CSLP) against rotational (Atlantis) or unidirectional axialangular dynamic plate (Premier), others favor dynamic both with C-TEK [4] (better clinical outcomes) and ABC [2] (faster fusion, including not only two but also at onelevel); further more, even dynamic plates obtain same or superior fusion results with fibular allograft compared to with autologous crest plus static [4]. Finally, the best way of assessing usefulness may be to examine complications—particularly those requiring reoperation—decrease, which should be looked at more carefully as this could be one of the mainstones for advising the use of dynamic plates; translational plates seem to decrease the rate of pseudoarthroses [3, 4].

Biomechanical comparison of unilateral semi-rigid and dynamic stabilization on ovine vertebrae.

Using the unilateral pedicle screw fixation was thought to decrease the stiffness of the fixed segments. Various prospective, randomized studies were performed to determine whether unilateral pedicle screw fixation provides the necessities of bilateral fixation in one- or two-segment lumbar spinal fusion. In this study, four different unilateral pedicle screw fixation systems were evaluated to determine which one best approximated an intact spine with respect to biomechanics and kinematics. The four groups included an intact group, a unilateral facetectomy group with no fixation, a unilateral semi-rigid pedicle screw fixation group with a poly-ether-ether-ketone rod, and a unilateral dynamic pedicle screw fixation group. The bone mineral densities of all specimens were measured and specimens were matched with groups randomly. Flexion, lateral bending, and axial rotation tests were performed to compare the groups. For the flexion, lateral bending, and axial rotation tests, the best biomechanical outcomes were in the control group. The unilateral facetectomy group had the poorest performance and was not stable enough, compared with the control group. The dynamic and semi-rigid groups showed performance closer to that of the control group. The biomechanical responses of these two groups were also in good agreement, showing no significant statistical differences. Based on these test results, it is concluded that the unilateral dynamic and semi-rigid pedicle screw fixations can be used to provide stability to the vertebrae.

Serum B-Type Natriuretic Peptide: A Potential Marker for Neoplastic Edema in Brain Tumor Patients?

Compression fractures at adjacent mobile segments have been reported as adjacent segment disease under trauma in several studies. In this study, the occurrence of fractures at the adjacent segment was evaluated experimentally under trauma.Static testing of different fixation systems was performed to show their biomechanical performances. The ovine vertebrae fixed with rigid, dynamic, and semirigid systems were used as test samples. The stiffness values of the systems were obtained by testing the vertebrectomy models under compression bending, lateral bending, and torsion tests. In addition, their effects on the adjacent segments were experimentally evaluated within a drop mechanism. A free-fall drop mechanism was designed and manufactured. Next, 3.5-kg, 5-kg, and 7-kg weights were released from 1 m above the test samples to generate compression fractures. The occurrence of compression fractures was observed with the use of radiograph of test samples, which were obtained before and after the drop test.Dynamic and semirigid systems have advantages compared with rigid systems as the result of their lower stiffness values. Radiographs showed that epiphysis fractures occurred at fixed and adjacent mobile segments, which were fixed with semirigid fixation. In addition, dynamic fixation well preserved the fixed and adjacent mobile segments under trauma.The dynamic system with a polyetheretherketone rod can better preserve both adjacent and fixed segments. However, because of the cantilever beam effect, the semirigid system exhibits a great disadvantage.

Experimental Evaluation of the Developmental Mechanism Underlying Fractures at the Adjacent Segment

Compression fractures at adjacent mobile segments have been reported as adjacent segment disease under trauma in several studies. In this study, the occurrence of fractures at the adjacent segment was evaluated experimentally under trauma. Static testing of different fixation systems was performed to show their biomechanical performances. The ovine vertebrae fixed with rigid, dynamic, and semirigid systems were used as test samples. The stiffness values of the systems were obtained by testing the vertebrectomy models under compression bending, lateral bending, and torsion tests. In addition, their effects on the adjacent segments were experimentally evaluated within a drop mechanism. A free-fall drop mechanism was designed and manufactured. Next, 3.5-kg, 5-kg, and 7-kg weights were released from 1 m above the test samples to generate compression fractures. The occurrence of compression fractures was observed with the use of radiograph of test samples, which were obtained before and after the drop test. Dynamic and semirigid systems have advantages compared with rigid systems as the result of their lower stiffness values. Radiographs showed that epiphysis fractures occurred at fixed and adjacent mobile segments, which were fixed with semirigid fixation. In addition, dynamic fixation well preserved the fixed and adjacent mobile segments under trauma. The dynamic system with a polyetheretherketone rod can better preserve both adjacent and fixed segments. However, because of the cantilever beam effect, the semirigid system exhibits a great disadvantage.