Effect of implant crestal position on primary stability before and after loading: an in vitro study / Efeito do posicionamento crestal do implante na estabilidade primária antes e após carga: um estudo in vitro

Introduction: Primary stability is one of the goals of modern implant dentistry and if achieved, reduces treatment time for prosthetic rehabilitation and the number of interventions made in patients mouth. Several companies state as protocol for connical conection implants, a subcrestally positioning. Objective: This in vitro study aimed to evaluate the effect of placing a conical connection implant equicrestally and subcrestally on static and loading condition in two types of bone density. Material and method: A total of 200 bone cylinders were extracted from femur of pigs, standardized by means of x-rays and computerized microtomography scan (microCT) and separated in low and high density specimens. The implants were placed on the center of the bone cylinders and were evaluated before and after loading by means of microCT and histomorphometry. Result: The results showed that placing the evaluated implant subcrestally provided better primary stability and performance on static and loading situations on low and high density bone. Conclusion: Placing implant subcrestally improve primary stability outcomes under loading and static situations.

Introdução: A estabilidade primária é um dos objetivos da implantodontia moderna e, caso atingida, reduz o tempo de tratamento para a reabilitação protéticas e o número de intervenções realizadas. Diversas empresas preconizam a posição subcrestal no uso de implantes com conexão cônica interna. Objetivo: Este estudo in vitro avaliou o efeito do posicionamento de implantes de conexão conica interna sub e equicrestal sob condições estáticas e em função, considerando dois tipos de densidades ósseas. Material e método: um total de 200 espécimes de osso extraído do femur de suínos e padronizados por meio de radiografias e microtomografias computadorizadas foram separados em densidade alta e baixa. Implantes foram instalados no centro dos especimes e for a avaliados por meio de microCT e histomorfometria. Resultado: Os resultados demonstraram que a colocação de implante subcrestalmente promoveu melhor estabilidade primária e performance em todas as situações, irrespectivamente à densidade óssea. Conclusão: A colocação de implantes subcrestalmente melhora a estabilidade primária em todas as situações, sendo indicada quando da utilização de conexões cônicas internas.

Mechanical Equation Verification and Mechanical Property Analysis of the TC4 Self-Tapping Bone Screw / 医用生物力学

Objective To test the validity for mechanical equation of the TC4 self-tapping bone screw and analyze the influence of bone screw parameters on its mechanical properties. Methods In order to derive the equation of self-tapping and pull-out for bone screw, the physical model of bone screw-polyurethane foam block was built. By reference of ASTMF543-07 standard specification and test method for metallic medical bone screw, the mechanical verification tests of selected conical head shallow thread locking bone screw (HAZ) and conical head deep thread locking bone screw (HBZ) with different diameters were performed on Instron E3000 mechanical testing machine, and the data of self-tapping force, self-tapping torque and pull-out force from 5 groups of bone screws were tested respectively. Results The calculated and measured values were basically the same, except for a few points with large individual errors. The average error of the two values was 11.02%, so the theoretical calculation formula was highly credible. The bone screw with a larger diameter or a higher tooth height would require greater self-tapping force and pull-out force. Conclusions The research results provide the calculation basis for mechanical properties of bone screw and the research direction for optimization and improvement of bone screw in future.

Dual pitch titanium-coated pedicle screws improve initial and early fixation in a polyetheretherketone rod semi-rigid fixation system in sheep / 中华医学杂志(英文版)

Background@#Reports on the efficacy of modifications to the thread design of pedicle screws are scarce. The aim of the study was to investigate initial and early fixation of pedicle screws with a plasma-sprayed titanium coating and dual pitch in the pedicle region (dual pitch titanium-coated pedicle screw [DPTCPS]) in a polyetheretherketone (PEEK) rod semi-rigid fixation system.@*Methods@#Fifty-four sheep spine specimens and 64 sheep were used to investigate initial ( "0-week" controls) and early (postoperative 6 months) fixation, respectively. Sheep were divided into dual pitch pedicle screw (DPPS), standard pitch pedicle screw (SPPS), DPTCPS, and standard pitch titanium-coated pedicle screw (SPTCPS) groups. Specimens/sheep were instrumented with four screws and two rods. Biomechanical evaluations were performed, and histology at the implant-bone interface was investigated.@*Results@#At 0-week, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (557.0 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.61, P < 0.05; 622.6 ± 25.2 vs. 459.1 ± 19.1 N, t = 3.43, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (343.4 ± 16.5 vs. 237.5 ± 12.9 N, t = 3.52, P < 0.05; 343.4 ± 16.5 vs. 289.9 ± 12.8 N, t = 3.12, P < 0.05; 124.7 ± 13.5 vs. 41.9 ± 4.3 cycles, t = 2.18, P < 0.05; 124.7 ± 13.5 vs.79.5 ± 11.8 cycles, t = 2.76, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (1.8 ± 0.13 vs. 3.76 ± 0.19 mm, t = 2.29, P < 0.05; 1.8 ± 0.13 vs. 2.46 ± 10.20 mm, t = 2.69, P < 0.05). At post-operative 6 months, mean axial pull-out strength was significantly higher for the DPTCPS and SPTCPS than the SPPS (908.4 ± 33.6 vs. 646.5 ± 59.4 N, t = 3.34, P < 0.05; 925.9 ± 53.9 vs. 646.5 ± 59.4 N, t = 3.37, P < 0.05). On toggle-testing, the DPTCPS was significantly more resistant than the SPPS and SPTCPS (496.9 ± 17.9 vs. 370.3 ± 16.4 N, t = 2.86, P < 0.05; 496.9 ± 17.9 vs. 414.1 ± 12.8 N, t = 2.74, P < 0.05; 249.1 ± 11.0 vs.149.9 ± 11.1 cycles, t = 2.54, P < 0.05; 249.1 ± 11.0 vs.199.8 ± 7.2 cycles, t = 2.61, P < 0.05). On cyclic loading, maximum displacement was significantly lower for the DPTCPS than the SPPS and SPTCPS (0.96 ± 0.11 vs. 2.39 ± 0.14 mm, t = 2.57, P < 0.05; 0.96 ± 0.11 vs. 1.82 ± 0.12 mm, t = 2.73, P < 0.05). Resistance to toggle testing (370.3 ± 16.4 vs. 414.1 ± 12.8 N, t = 3.29, P < 0.05; 149.9 ± 11.1 vs.199.8 ± 7.2 cycles, t = 2.97, P < 0.05) was significantly lower and maximum displacement in cyclic loading (2.39 ± 0.14 vs.1.82 ± 0.12 mm; t = 3.06, P < 0.05) was significantly higher for the SPTCPS than the DPTCPS. Bone-to-implant contact was significantly increased for the DPTCPS compared to the SPPS (58.3% ± 7.0% vs. 36.5% ± 4.4%, t = 2.74, P < 0.05); there was no inflammatory reaction or degradation of coated particles.@*Conclusion@#DPTCPSs might have stronger initial and early fixation in a PEEK rod semi-rigid fixation system.

Avulsion Fracture of the Posterior Cruciate Ligament from Femoral Insertion Occurred in a Patient with Residual Poliomyelitis: A Case Report

Avulsion fracture of the posterior cruciate ligament from its femoral insertion is quite rare, particularly in adults, and the treatment guidelines have not been established. A 68-year-old female patient with residual poliomyelitis presented with an avulsion fracture of the femoral insertion of the posterior cruciate ligament after a falling accident and was treated with arthroscopic headless compression screw fixation and pull-out suture of the avulsed ligament. We report this case with a relevant discussion of this type of injury.

Delayed Lateral Row Anchor Failure in Suture Bridge Rotator Cuff Repair: A Report of 3 Cases

Compared to single row repair, use of lateral row anchors in suture bridge rotator cuff repair enhances repair strength and increases footprint contact area. If a lateral knotless anchor (push-in design) is inserted into osteoporotic bone, pull-out of the lateral row anchor can developed. However, failures of lateral row anchors have been reported at several months after surgery. In our cases, even though complete cuff healing occurred, delayed pull-out of the lateral row anchor in the suture bridge repair occurred. In comparison to a conventional medial anchor, further biomechanical evaluation of the pull-out force, design, and insertion angle of the lateral anchor is needed in future studies. We report three cases with delayed pull-out of lateral row anchor in suture bridge rotator cuff repair with a literature review.

Second-Look Arthroscopic Assessment and Clinical Results of Modified Pull-Out Suture for Posterior Root Tear of the Medial Meniscus

PURPOSE: To identify the structural integrity of the healing site after arthroscopic repair of a posterior root tear of the medial meniscus by second-look arthroscopy and to determine the clinical relevance of the findings. MATERIALS AND METHODS: From January 2005 to December 2010, 20 consecutive patients underwent arthroscopic modified pull-out suture repair for a posterior root tear of the medial meniscus. Thirteen patients were available for second-look arthroscopic evaluation. The healing status of the medial meniscus was classified as complete healing, lax healing, scar tissue healing, and failed healing. We evaluated the correlation between the clinical symptoms and second-look arthroscopic findings. Clinical evaluation was based on the Lysholm knee scores and Hospital for Special Surgery (HSS) scores. RESULTS: There were 4 cases of complete healing, 4 lax healing, 4 scar tissue healing, and 1 failed healing. The healing status of the repaired meniscus appeared to be related to the clinical symptoms. Patients who achieved complete tissue healing had no complaint. The healing status exhibited no relationship with age, mechanical axis, degree of subluxation, and symptom duration. The mean Lysholm score improved from 34.7 preoperatively to 75.6 at follow-up and the mean HSS score also significantly increased from 33.5 to 82.2. CONCLUSIONS: We achieved 4 complete and 8 partial healing (lax or scar) of the medial meniscus in this retrospective case series of posterior horn meniscus root repairs performed by 1 surgeon. Further research is needed to clarify why all patients showed clinical improvement despite findings of partial healing on second-look arthroscopy.

Modified Pull-out Suture in Posterior Root Tear of the Medial Meniscus: Using a Posteromedial Portal

In cases with root tear of the medial meniscus posterior horn, the meniscus usually can be repaired by a pull out suture technique. However, there is difficulty in manipulating a suture hook via the anteromedial portal and looking through the arthroscopic camera via anterolateral portal in the narrow medial joint space at the same time. This article describes a modified simple pull out suture technique for root tear of the medial meniscus posterior horn using a posteromedial portal that provides a safe and easy handling of the suture hook. Our indications of this technique used in patients with Outerbridge 1-2 arthritic change and minimal varus axis change. Benefits of this technique are simple, less invasive, and reduced operation time by simultaneous suture with a hook via posteromedial portal and pulling of a string with grasper. It may reduce the possibility of an additional chondral or meniscal injury.

Minimum 1 Year Results of Arthroscopic Pull-out Repair for Posterior Root Tear of Medial Meniscus / 대한스포츠의학회지

This study is to evaluate clinical and arthroscopic second-look results of arthroscopic repairs of posterior root tears of medial meniscus which may cause loss of circumferential hoop tension and extrusion of meniscus. From October 2006 to May 2009, fifty-eight patients (59 knees) underwent arthroscopic pull-out repairs. Clinical results were evaluated using Hospital for Special Surgery (HSS) score and International Knee Documentation Committee (IKDC) score for 12-month follow-up. Second-look arthroscopy was done to evaluate meniscal healing in 21 cases. Magnetic resonance imaging (MRI) was performed to assess status of repaired meniscus and tibial tunnel position in 9 patients. Average preoperative HSS score and IKDC score of 59 cases were 69.5 and 36.0, respectively. Average postoperative HSS score and IKDC score of 59 cases had been changed into 90.3 (p<0.001) and 66.8 (p<0.001), respectively. Second-look arthroscopies revealed complete or incomplete healing except one case. Two patients showed increased one grade according to the Kellgren-Lawrence radiologic classification system and others showed no change. Of 9 patients who performed MRI, six patients showed complete healing. The average position of tibial tunnel was 4.8 mm anterior and 5.7 mm medial to center of posterior cruciate ligament. Arthroscopic pull-out repair technique using transtibial tunnel seems to be simple and effective procedure for posterior root tear of medial meniscus. Further evaluation of arthroscopic repair of posterior root tear of medial meniscus should be needed to prove the effectiveness on the prevention of osteoarthritis of knee.

Primary stability of orthodontic miniscrews inserted into femurs of osteopenic rats

Aim: To test the hypothesis that bone quality may affect the stability of anchorage devices implanted in a rat model. Methods: Twenty male Wistar rats were divided into 2 groups: Group 1 (rats treated with FK506) and Group 2(rats treated with saline solution vehicle). The immunosuppressant tacrolimus was used with the intention of causing a condition of osteopenia in Group 1. A total of 20 orthodontic mini-implants were used. One mini-implant was inserted in the right femur of each rat. After sacrificing the animals, blocks of bone tissue containing the mini-implants were removed for mechanical pull-out tests to be performed in a universal test machine at a crosshead speed of 0.5 mm/s. The maximum insertion force values and pull-out test were recorded and submitted the nonparametric analyses including the Kruskal-Wallis test and Mann-Whitney tests (p<0.05). The test for Pearson’s correlation was used to verify the correlation between bone mineral density and the pull-out test. The dose of FK506 was 2 mg/kg/day. Densitometric analysis was performed to observe the effect of FK506 on the bone mineral density. Results: The mean insertion force values were similar in both groups, with no statistically significant difference between them (P > 0.05). The mean pull-out force values were higher in Group 2 than in Group 1, with statistically significant difference between the groups (P < 0.05). Conclusions: Bone quality may affect the stability of mini-implants. Orthodontic mini-implants did not present good primary stability in a rat model with osteopenia.

Evaluation of insertion of torque and pull-out strength of mini-screws according to different thickness of artificial cortical bone / 대한치과교정학회지

OBJECTIVE: The purpose of this study was to evaluate the mechanical performance of mini-screws during insertion into artificial bone with use of the driving torque tester (Biomaterials Korea, Seoul, Korea), as well as testing of Pull-out Strength (POS). METHODS: Experimental bone blocks with different cortical bone thickness were used as specimens. Three modules of commercially available drill-free type mini-screws (Type A; pure cylindrical type, Biomaterials Korea, Seoul, Korea, Type B; partially cylindrical type, Jeil Medical, Seoul, Korea, Type C; combination type of cylindrical and tapered portions, Ortholution, Seoul, Korea), were used. RESULTS: Difference in the cortical bone thickness had little effect on the maximum insertion torque (MIT) in Type A mini-screws. But in Type B and C, MIT increased as the cortical bone thickness increased. MIT of Type C was highest in all situations, then Type B and Type A in order. Type C showed lower POS than Type A or B in all situations. There were statistically significant correlations between cortical bone thickness and MIT, and POS for each type of the mini-screws. CONCLUSION: Since different screw designs showed different insertion torques with increases in cortical bone thickness, the best suitable screw design should be selected according to the different cortical thicknesses at the implant sites

The Treatment of Gynecomastia using Ultrasound-Assisted Liposuction with Pull-Out Method or Excision through Periareolar Incision

PURPOSE: Gynecomastia is an abnormal increase in the volume of the male breast. Patients affected by gynecomastia with significant glandular enlargement may respond to suction alone and/or sharp dissection and excision. The purpose of this report is to introduce the indications and results of authors' two techniques. METHODS: The diameter of parenchyme was determined by a pinch test after liposuction. For the parenchymal diameter less than 4cm, ultrasound-assisted liposuction was performed, in conjunction with the "pull- out technique" to effectively remove the fibrofatty tissue of the male breast through a single 5-7mm incision. For the parenchymal diameter more than 4cm, ultrasound-assisted liposuction and excision were applied through 2.5cm periareolar approach. RESULTS: A total of 94 patients (185 breasts) underwent the operation from October 2000 to October 2003 and mean follow-up period was 12 months. The volume of aspirates ranged from 50 to 450 cc per breast. There were no major complications such as skin flap necrosis. Five reoperations were performed for 1 hypertrophic scar, 2 under-resected and 2 hematoma cases. The patient's satisfaction was high and most of them were pleased with the shape of the breasts and scars. CONCLUSION: These procedures can minimize scars and reduce the incidence of contour problem such as saucer deformity, and provides consistent results. Patients can return to full activities in 48 hours. It can be offered as an option for the treatment of gynecomastia.

Comparison of different ways of pulling out ureter double-J stent in females / 重庆医科大学学报

Objective:To compare the different ways of pulling out ureter double-J stent in females.Methods:172 female patients requiring urter double-J stent for different cases were chosen,including upper urinary calculus(150 cases),hydronephrosis with urterostenosis(14 cases),Ormond’s syndrome(3 cases) and postradiotherapy of uterine cervix cancer(5 cases).These cases were divided into three groups with different ways of pulling out the urter double-J stent.Results:The achievement ratio of cystoscope(100%) and rat-tooth forceps(98.1%) were higher than the blood vessel forceps(92.1%).Conclusion:The cystoscope operation requires the special equipment and cost more money and time.Compared to the blood vessel forceps,using the rat-tooth forceps to pull out the female ureter double-J stent is safe and more effective.

Pull-Out repair of the radial posterior horn tear near the root of the medial meniscus: Technical Note

We reported a new technique to repair of the posterior horn tear near the root of the medial meniscus. The radial posterior horn tear near the root showed total loss of the circumferential hoop tension and was similar to the total meniscectomized state. Efforts should be made to restore the circumferential hoop ten-sion and maintain stable bony insertion. We introduced a pull-out repair technique using ACL guide, suture repair set and two PDS No.1. This technique showed stable fixation and good hoop tension of the meniscus. Pull-out repair into the posterior root seems to be a useful method in the posterior horn tear near the root of the medial meniscus.

Arthroscopic Treatment of Tibia Intercondylar Eminence Comminuted Fracture Used Number 5-nonabsobable Suture Material

PURPOSE: To evaluate effect of modified arthroscopic pull-out suture technique which used number 5-nonabsorbable suture material for tibia intercondylar eminence comminuted fractures. MATERIALS AND METHODS: There were 21 cases of tibia intercondylar emimence fracture which arthroscopic treated at our hospital between 1999 and 2004. However the study population only included 12 cases in which a number 5-nonabsorbable suture material (Ethibond No. 5) was used for tibia intercondylar eminence comminuted fractures and minimum 1-year follow-up has gone. The average follow-up period was 18.5 months (range, 12 to 42 months). Lachman test and KT-2000 athrometer test were evaluated at the pre-and post-operation. Clinical results of all patients were evaluated with the Meyers and Mckeever 's criteria. RESULTS: In all 12 cases, the normal range of motion and sports activities were recovered at the final follow-up. When tested for anterior instability with KT-2000 arthrometer, there were no different between normal knee and operated knee. Clinical results by Meyers and Mckeever's criteria were excellent in 10 patients and good in 2 patients. CONCLUSION: We obtained early mobilization and stable fixation in modified arthroscopic pullout suture technique for tibia intercondylar eminence comminuted fractures. Patients can early return to his job. This technique seems to be one of the effective operative techniques for treatment of tibia intercondylar eminence comminuted fractures.

Arthroscopic Reduction and Pull-out Suture Fixation for the Intercondylar Eminence Fracture of the Tibia

PURPOSE: Meyers-McKeever and Zaricznyj proposed a classification for intercondylar eminence fractures of the tibia. Type III and IV classifications are generally accepted as surgical indications for the fractures. The purpose of the present study was to evaluate the effectiveness of arthroscopic reduction and multiple pull-out suture fixation for displaced intercondylar eminence fractures of the tibia. MATERIALS AND METHODS: Twenty two cases were examined, with a average age of 14(5~23) years, and the average follow-up was 34 months(24 months~6 years). Patients were evaluated according to the Meyers and McKeever criteria, and were scored at 6 weeks, 4 months, 8 months, each year and at the last follow-up. Patients underwent the following evaluations: radiological, range of motion, Lachman test, pivotshift test and the KT 2000 arthrometer. RESULTS: The average union time was postoperative week 9.3(6~12 weeks). According to the Meyers and McKeever criteria, the cases showed the following outcomes at the final follow-up: 19(86.4%) excellent, 2(9.1%) good and 1(4.5%) poor. CONCLUSION: Using the short- and mid-term arthroscopic reduction and multiple pull-out suture fixation procedure for displaced intercondylar eminence fractures of the tibia resulted in 95.5%(19) of cases showing good or excellent outcomes, indicating this procedure is effective.

A Biomechanical Study on the Pull-Out Strength of Pedicle Screw Augmented with Polymethylmethacrylate(PMMA)- Cadaveric Study -

OBJECTIVE: The authors evaluate the differences in the pedicle screw pull-out strength between an unaugmented screw and a screw augmented by high pressurized PMMA in an embalmed human lumbar cadaveric spine. METHODS: Pedicle screws were inserted in the 50 pedicles of cadaver lumbar spine after measuring the bone mineral density(BMD) of the specimens. The pedicle screw was inserted without augmentation on the left pedicle and with augmentation by a vertebral reconstruction with high pressurized PMMA on the right side. The pedicle screw was inserted before the hardening of bone cement on the right side. A computed tomographic scan was done to evaluate the location of the PMMA and PMMA/ screw interface. After that, a screw pullout strength test was performed. RESULTS: There were positive correlations between the pull-out strength and BMD in the control group (r=0.7339). The average pull-out strength of the augmented group was 168% greater than that of the control group(p<0.05). The pull-out strength of the augmented group was correlated with in the volume of the PMMA. CONCLUSION: A pedicle screw that is augmented with PMMA will provide a more rigid fixation than that of an unaugmented screw, especially in the low BMD group of the specimens.

Arthroscopic Reduction of Bony Avusion of the Posterior Cruciate Ligament from the Tibia using Pull-out PDS

No abstract available.

Treatment of Fracture of the Tibial Intercondylar Eminence with Arthroscopic Pull-Out Suture

The purpose of this study is to demonstrate the effectiveness of arthrocopic treatment for the avulsion fracture of intercondylar eminence of the tibia and of the technique of arthroscopically assisted reduction and fixation through pull-out suture method. Between January 1995 and May 1997, three patients were underwent arthroscopic reduction and suture fixation for type 0 of avulsion fracture of intercondylar eminence of tibia and were followed up. The result of two patients were graded as normal and one as nearly normal by the criteria of the International Knee Documentation Committee(IKDC) rating scale. The advantages of this technique include no retained hardware and ability to treat comminuted fracture(type g ). We describe technique of arthroscopic reduction and suture fixasion for displaced avulsion fractures, including those with comminution of intercondylar eminence of tibia.

Pull - out Strength of Different Multiple Suturing Method of the Cruciate Ligament / 대한정형외과학회잡지

The aim of this study was to measure the immediate pull-out strengths by increasing the number of suture loops and to compare the immediate pull-out strengths of three different suturing techniques. In one group, the number of suture loops increased from 2 to 9 and the suturing technique of multiple loops through the proximal ligament stumps was used. The other group, the three different techniques were transverse, vertical, and criss-cross suture. The ultimate strength for the 2 loops was 16.62 (+/-6.7)N, for the 3 loops was 34.45 (+/-12.5)N, for the 4 loops was 54.80 (+/-17.7)N, for the 5 loops was 74.30 (+/-21.4)N, for the 6 loops was 102.49 (+/-13.5)N, for the 7 loops was 105.05 (+/-24.8)N, for the 8 loops was 129.50 (+/-76.1)N, for the 9 loops was 229.50 (+/-48.7)N. The transverse suture had a mean ultimate strength of 47.38 (+/-14.8)N, where-as the vertical suture failed at 76.94 (+/-26.4)N and the criss-cross suture at 101.82 (+/-25.7)N. Consequently, their strength can be improved by increasing the number of loops and we suggest that the criss-cross suture technique is reliable method for clinical use, because of high failure strength and wider apposition area of bone to ligament.

A study on changes of the Vertebral Pedicles and Mechanical Strengths after Screw Insertion / 대한정형외과학회잡지

Spinal fixation using pedicle screws has recently been the focus of increased attention, but the adequate size of pedicle screw and maximum percentage fill as related to the pedicle diameter and are not well known. The objects of this study were to determine the ideal ratio among pedicle, drill and screw diameter, and to determine the maximum percentage fill of the screw without significant decrease of pull-out strength. The materials used for the experiments were 376 thoracic pedicles obtained from the 38 young pigs, and the diameters of pedicles ranged from 3.0 to 8.5mm. After 40% to 100% drilling as compared to pedicle diameter, screws were inserted carefully, and measurements were taken of the outer pedicle changes and pull-out strengths, and adequate drill and screw sizes as related to the diameters of given pedicles were determined. It was found that pull-out strength was the strongest after 60% drill, and the larger the drill diameter, the smaller the holding power, and the larger the screw diameter, the greater the holding power. Maximum pull-out strength was seen at 80-90% fill with 60% drill. After sequentially drilling each pedicle with increasingly larger drill bits, larger screws could be inserted with pedicle changes such as expansion, cutout, split fracture, and comminuted fracture. after larger drilling up to 100%, pedicle screws with diameters smaller than 115% of measured pedicle diameters could be safly inserted without fracture and significant decrease of pull-out strength. It is concluded that effective percentages of drill and screw diameters to the pedicle diameter are 60% and 80-90% respectively, and pedicle screw up to 115% of measured pedicle diameter can be safely inserted into pedicle without significant decrease of pull-out strength. It is thought that fresh pedicle has elasticity and larger screw can be inserted to the pedicle with strong holding after larger drilling.