mohammad javad ein afshar

Pedicle screw fixation devices are the predominant stabilization systems adopted for a wide variety ofspinal defects. Accordingly, both pedicle screw design and bone quality are known as the main parameters affecting thefixation strength as measured by the pull-out force and insertion torque. The pull-out test method, which is recommendedby the standards of the American Society for Testing and Materials (ASTM), is destructive. A non-destructive test methodwas proposed to evaluate the mechanical stability of the pedicle screw using modal analysis. Natural frequency (ωn)extracted from the modal analysis was then correlated with peak pull-out force (PPF) and peak insertion torque (PIT). Cylindrical pedicle screws with a conical core were inserted into two different polyurethane (PU) foams withdensities of 0.16 and 0.32 g/cm3. The PIT and PPF were measured according to the well-established ASTM-F543standard at three different insertion depths of 10, 20, and 30 mm. Modal analysis was carried out through recordingtime response of an accelerometer attached to the head of the screw impacted by a shock hammer. The effect of theinsertion depth and foam density on the insertion torque, natural frequency, and pull-out force were quantified. The maximum values of ωn, PIT, and PPT were obtained at 2,186 Hz, 123.75 N.cm, and 981.50 N, respectively,when the screw was inserted into the high-density foam at the depth of 30 mm. The minimum values were estimatedat 332 Hz, 16 N.cm, and 127 N, respectively, within the low-density PU at the depth of 10 mm. The higher value of ωnwas originated from higher bone screw stability and thus more fixation strength. According to the regression analysisoutcomes, the natural frequency (ωn) was linearly dependent on the PIT (ωn=14 PIT) and also on the PPF (ωn=1.7PPF). Coefficients of variation as the results of the modal analysis were significantly less than those in conventionalmethods (i.e. pull-out and insertion torque). The modal analysis was found to be a reliable, repeatable, and non-destructive method, which could beconsidered a prospective alternative to the destructive pull-out test that is limited to the in-vitro application only. Themodal analysis could be applied to assess the stability of implantable screws, such as orthopedic and spinal screws.Level of evidence: V

Internal rigid fixation techniques are commonly used to treat maxillofacial fractures by stabilizing bone segments using titanium plates and screws. The current study aimed to compare the biomechanical stability of two maxillofacial screws with different tip designs in vivo.

Six male rabbits were randomly divided into two experimental periods of 0 and 4 weeks. Under general anesthesia, the screws were randomly placed in the tibia bone on both sides of each animal. The pullout test was conducted using a Sentam test device. Data were statistically analyzed using ANOVA.

The average insertion torque for non-self-tapping and self-tapping screws amounted to 4.2±1.7 and 4.8±1.4 Newton/centimeter, respectively (P-value >0.05). The calculated measures for the pullout test demonstrated a significant increase of secondary stability after 4 weeks in comparison to 0 week (P-value<0.001). However, the results among the two screws showed no statistically significant difference in each time point (P-value >0.05).

No significant differences were demonstrated among self-tapping or non-self-tapping maxillofacial screws.

Back pain is a common medical problem. There is no clear cause for the back pain problem so far, but in most cases, spinal instability can be noted. Lumbar spine fixation is performed to treat the problems of low back pain. Spinal fixation can be done with or without surgery. One of the surgical methods is the use of spinal screws in which the strength and stability of the screw are of great importance. The strength and stability of the screw in the bone reduces the time and cost of treatment, reduces the amount of bleeding and accelerates the patient's treatment. In this study, screws were inserted using a digital torque meter. An impact was applied using an impact hammer and resonated sound was recorded using a microphone. The vibration mode of the screw was obtained by processing the signal generated by MATLAB R2017 software and plotting the fast Fourier transform. Finally, tensile test was performed to obtain the ultimate pull-out force. The innovation of this study was to use modal analysis method and to correlate its results with that of the ultimate pull-out force and peak insertion torque. In this study, five screws with different screw depth, and screw thread crest thickness were examined. Also, the effect of self-tapping was investigated. The peak insertion torque, ultimate pull-out strength and natural frequency occurred at 182 Nm, 992 N and 1916 Hz, respectively, for the cylindrical pedicle screw. By comparing the obtained data, results showed a linear relationship between insertion torque and pull-out force of the screws. Due to the lack of significant difference between natural frequency and pull-out force of the self-drilling and non-self-drilling tip screws (comparing between screws number 3 and 4 and between 1 and 5), the use of self-tapping screws can be advantageous. The trend of the dependent parameters in all three methods i.e. insertion torque, pull-out force and natural frequency are the same, indicating the non-destructive advantage of modal analysis in in-vivo surgical application.

The present study was conducted to quantify the relationships between bone drilling process parameters(i.e., feed rate, resting time, exit rate, and drill bit diameter) and drilling outcome parameters (i.e., thrust force andmaximum temperature).

This study utilized 10-cm cortical bovine samples to evaluate the effects of four independent parameters,including drill bit diameters, six different feed rates, three various resting times, and three different exit rates on thrustforce and maximum temperature (MT). A total of 28 stainless steel orthopedic drill bits with a diameter of 2.5 and 3.2mm, as well as an orthopedic handpiece were attached to the 500N load cell and an accurate linear variable differentialtransformer to obtain forces. Moreover, two k-type thermocouples were utilized to record the temperature-time curvenear the drilling site. The data were analyzed using the two-way analysis of variance and post hoc Tukey-KramerHonest test.

Maximum thrust force (MTF) decreased by almost 230% as the drill bit diameter increased from 2.5 to 3.2mm in the lowest feed rate. The MTF showed a 335% increase, whereas a decrease of 69% was observed as the feedrates rose from 0.5 to 3 mm/sec. Moreover, the MT decreased to 67% with an increasing exit rate from 1 to 3 mm/sec.Furthermore, a slight increase was observed in MT when the resting time increased from 0 to 2 seconds (P>0.05).

The desired drilling is drilling with lower thrust force and lower final temperature of bone. Increasing feedrate can cause an increase and decline in thrust force and final temperature, respectively. The highest rates of MT were0.5 and 1 mm/min, and the optimum feed rate would be 1.5 mm/min due to the averaged thrust force. Moreover, theresting time had no significant effects on the final temperature. Attentions to resting time would be useful to provide amore accurate, efficient, and uniform drill hole.Level of evidence: V

Bone drilling is a common step in orthopedic surgery. Thrust force is one of the most important parameters that can influence the quality of bone drilling. The number of drill bit usage has some limitations and it can affect the quality of bone drilling.
The aim of this study was to investigate the limitations of drill bit usage number to increase the bone drilling quality.
Two mid-diaphysis sections of male human cadaveric femora were prepared. Five orthopedic drill bits were used to identify the effects of the usage number. An orthopedic hand piece was attached to the dynamic testing machine. The spindle speed and feed rate of the drill bits were 900 rpm and 0.5 mm/s, respectively. Drill bit usage of 0, 20, 40, 60 and 80 were prepared for scanning electron microscopy (SEM). SEM images were taken to illustrate physical changes on the cutting surfaces of the drill bit.
There was an increase in the thrust force by increasing the number of drill bits usage. Irreversible physical damages were observed in drill bit point angle, frank face, and flutes of drill bits.
The number of drill bits usage has limitation. Drill bits that are similar to the ones of the current study are better to be used no more than 55 times.