A study on the use of the Osstell apparatus to evaluate pedicle screw stability: An in-vitro study using micro-CT

Evaluating stiffness of gastric wall using laser resonance frequency analysis for gastric cancer

Tumor stiffness is drawing attention as a novel axis that is orthogonal to existing parameters such as pathological examination. We developed a new diagnostic method that focuses on differences in stiffness between tumor and normal tissue. This study comprised a clinical application of laser resonance frequency analysis (L-RFA) for diagnosing gastric cancer. L-RFA allows for precise and contactless evaluation of tissue stiffness. We used a laser to create vibrations on a sample's surface that were then measured using a vibrometer. The data were averaged and analyzed to enhance accuracy. In the agarose phantom experiments, a clear linear correlation was observed between the Young's modulus of the phantoms (0.34-0.71 MPa) and the summation of normalized vibration peaks (Score) in the 1950-4050 Hz range (R2 = 0.93145). Higher Young's moduli also resulted in lower vibration peaks at the excitation frequency, signal-to-noise (S/N) ratios, and harmonic peaks. We also conducted L-RFA measurements on gastric cancer specimens from two patients who underwent robot-assisted distal gastrectomy. Our results revealed significant waveform differences between tumor and normal regions, similar to the findings in agarose phantoms, with tumor regions exhibiting lower vibration peaks at the excitation frequency, S/N ratios, and harmonic peaks. Statistical analysis confirmed significant differences in the score between normal and tumor regions (p = 0.00354). L-RFA was able to assess tumor stiffness and holds great promise as a noninvasive diagnostic tool for gastric cancer.

Nondestructive acoustic modal analysis for assessing bone screw stability: An ex vivo animal study

Conventional insertion torque and pull-out tests are destructive and unsuitable for clinical bone screw fixation. This study evaluates screw stability using acoustic modal analysis (AMA) and Periotest compared to traditional methods in an ex vivo animal model. Titanium self-tapping screws (STS) and nonself-tapping screws (N-STS) were implanted in the proximal tibia of 12 rabbits. Four testing methods were used to assess screw stability: peak insertion torque (PIT) during implantation, AMA for natural frequency (NF), Periotest for Periotest value (PTV), and pull-out test for peak pullout force (PPF). Euthanization was performed at 0 (primary stability), 4, and 8 weeks (secondary stability). No significant difference in primary stability was found between STS and N-STS except for AMA (STS: NF 2434 ± 67 Hz, N-STS: NF 2572 ± 43 Hz; p = 0.62). Secondary stability increased significantly over time for both screw types (4-week: NF 3687 ± 36 vs. 3408 ± 45 Hz, PTV 1.4 ± 1.6 vs. -1.5 ± 1.8, PPF 236 ± 29 vs. 220 ± 34 N; 8-week: NF 3890 ± 39 vs. 3613 ± 31 Hz, PTV -3.2 ± 2.5 vs. -2 ± 4.3, PPF 248 ± 25 vs. 289 ± 28 N). Higher NF values for given PTV/PPF indicate potential clinical advantages. Significant differences between primary and secondary stabilities suggest osteointegration was mainly achieved in the 4-week group.

Evaluation of bone integrity around the acetabular cup using noninvasive laser resonance frequency analysis

Resonance frequency analysis (RFA) is valuable for assessing implant status. In a previous investigation, acetabular cup fixation was assessed using laser RFA and the pull-down force was predicted in an in vitro setting. While the pull-down force alone is sufficient for initial fixation evaluation, it is desirable to evaluate the bone strength of the foundation for subsequent fixation. Diminished bone quality causes micromotion, migration, and protracted osseointegration, consequently elevating susceptibility to periprosthetic fractures and failure of ingrained trabecular bone. Limited research exists on the evaluation of bone mineral density (BMD) around the cup using RFA. For in vivo application of laser RFA, we implemented the sweep pulse excitation method and engineered an innovative laser RFA device having low laser energy and small dimensions. We focused on a specific frequency range (2500-4500 Hz), where the peak frequency was presumed to be influenced by foundational density. Quantitative computed tomography with a phantom was employed to assess periprosthetic BMD. Correlation between the resonance frequency within the designated range and the density around the cup was evaluated both in the laboratory and in vivo using the novel laser RFA device. The Kruskal-Wallis test showed robust correlations in both experiments (laboratory study: R = 0.728, p < 0.001; in vivo study: R = 0.619, p < 0.001). Our laser RFA system can assess the quality of bone surrounding the cup. Laser RFA holds promise in predicting the risk of loosening and might aid in the decision-making process for additional fixation through screw insertion.

Impact of screw tip design on screw anchorage: mechanical testing and numerical simulation

BACKGROUND

Screw loosening is a commonly reported issue following spinal screw fixation and can lead to various complications. The initial cause of screw loosening is biomechanical deterioration. Previous studies have demonstrated that modifications in screw design can impact the local biomechanical environment, specifically the stress distribution on bone-screw interfaces. There are several different designs of screw tips available for clinically used pedicle screws; however, it remains unclear whether these variations affect the local stress distribution and subsequent screw anchorage ability.

METHODS

This study conducted comprehensive biomechanical research using polyurethane foam mechanical tests and corresponding numerical simulations to investigate this topic. Models of pedicle screw-fixed osteoporotic polyurethane foam were created with two different clinically used screw tip designs (flat and steep) featuring varying tip lengths, taper angles, and diameters, as well as identical flank overlap areas and thread designs. The anchorage ability of the different models was assessed through toggle and pull-out test. Additionally, numerical mechanical models were utilized to compute the stress distributions at the screw and bone-screw interfaces in the different models.

RESULTS

Mechanical tests revealed superior anchorage ability in models utilizing flat-tipped screws. Furthermore, numerical modeling indicated improved anchorage ability and reduced stress concentration tendency in these models.

CONCLUSION

Changes in screw tip design can significantly impact the biomechanical anchoring capability of screws. Specifically, flatter tip pedicle screws may mitigate the risk of screw loosening by alleviating stress concentration on bone-screw interfaces.

Incomplete insertion of pedicle screws triggers a higher biomechanical risk of screw loosening: mechanical tests and corresponding numerical simulations

Screw loosening is a widely reported issue after spinal screw fixation and triggers several complications. Biomechanical deterioration initially causes screw loosening. Studies have shown that incomplete insertion of pedicle screws increases the risk of screw breakage by deteriorating the local mechanical environment. However, whether this change has a biomechanical effect on the risk of screw loosening has not been determined. This study conducted comprehensive biomechanical research using polyurethane foam mechanical tests and corresponding numerical simulations to verify this topic. Pedicle screw-fixed polyurethane foam models with screws with four different insertion depths were constructed, and the screw anchoring ability of different models was verified by toggle tests with alternating and constant loads. Moreover, the stress distribution of screw and bone-screw interfaces in different models was computed in corresponding numerical mechanical models. Mechanical tests presented better screw anchoring ability with deeper screw insertion, but parameters presented no significant difference between groups with complete thread insertion. Correspondingly, higher stress values can be recorded in the model without complete thread insertion; the difference in stress values between models with complete thread insertion was relatively slight. Therefore, incomplete thread insertion triggers local stress concentration and the corresponding risk of screw loosening; completely inserting threads could effectively alleviate local stress concentration and result in the prevention of screw loosening.

Sweep Pulse Excitation Method for Enhancing Photoacoustic Elastic Waves at Different Laser Irradiation Parameters

Laser remote sensing using a sweep pulse excitation method, in which a laser beam is irradiated at the same repetition frequency as the natural frequency, for enhancing photoacoustic elastic waves through resonance effect has been studied. The sweep pulse excitation method, which is based on the principle of detecting natural frequency fluctuations, such as hammering tests, can detect natural frequencies in the audible sound region with low average laser power and contribute to the convenience and low cost of an installation strength diagnosis of fastening bolts. In this study, we investigated the dynamics of the swept excitation method for optimization by evaluating the dependence of the laser irradiation conditions (pulse width, spot size, and average power) on different metal disc samples. We discovered that the magnitude of the photoacoustic elastic wave is proportional to the absorption of laser power, and the spatiotemporal dynamics can be explained through thermal diffusion phenomena. These findings contribute to the development of laser-sensing technology based on photoacoustic elastic waves.

Systems Biology in Periodontitis

Systems biology is a promising scientific discipline that allows an integrated investigation of host factors, microbial composition, biomarkers, immune response and inflammatory mediators in many conditions such as chronic diseases, cancer, neurological disorders, and periodontitis. This concept utilizes genetic decoding, bioinformatic, flux-balance analysis in a comprehensive approach. The aim of this review is to better understand the current literature on systems biology and identify a clear applicability of it to periodontitis. We will mostly focus on the association between this condition and topics such as genomics, transcriptomics, proteomics, metabolomics, as well as contextualize delivery systems for periodontitis treatment, biomarker detection in oral fluids and associated systemic conditions.

Replacement of Destructive Pull-out Test with Modal Analysis in Primary Fixation Stability Assessment of Spinal Pedicle Screw

BACKGROUND

Pedicle screw fixation devices are the predominant stabilization systems adopted for a wide variety of spinal defects. Accordingly, both pedicle screw design and bone quality are known as the main parameters affecting the fixation strength as measured by the pull-out force and insertion torque. The pull-out test method, which is recommended by the standards of the American Society for Testing and Materials (ASTM), is destructive. A non-destructive test method was proposed to evaluate the mechanical stability of the pedicle screw using modal analysis. Natural frequency (ω_n) extracted from the modal analysis was then correlated with peak pull-out force (PPF) and peak insertion torque (PIT).

METHODS

Cylindrical pedicle screws with a conical core were inserted into two different polyurethane (PU) foams with densities of 0.16 and 0.32 g/cm3. The PIT and PPF were measured according to the well-established ASTM-F543 standard at three different insertion depths of 10, 20, and 30 mm. Modal analysis was carried out through recording time response of an accelerometer attached to the head of the screw impacted by a shock hammer. The effect of the insertion depth and foam density on the insertion torque, natural frequency, and pull-out force were quantified.

RESULTS

The maximum values of ω_n, 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 estimated at 332 Hz, 16 N.cm, and 127 N, respectively, within the low-density PU at the depth of 10 mm. The higher value of ωn was originated from higher bone screw stability and thus more fixation strength. According to the regression analysis outcomes, the natural frequency (ω_n) was linearly dependent on the PIT (ω_n=14 PIT) and also on the PPF (ω_n=1.7 PPF). Coefficients of variation as the results of the modal analysis were significantly less than those in conventional methods (i.e. pull-out and insertion torque).

CONCLUSION

The modal analysis was found to be a reliable, repeatable, and non-destructive method, which could be considered a prospective alternative to the destructive pull-out test that is limited to the in-vitro application only. The modal analysis could be applied to assess the stability of implantable screws, such as orthopedic and spinal screws.

Modal Analysis of the Ancillary During Femoral Stem Insertion: A Study on Bone Mimicking Phantoms

The femoral stem primary stability achieved by the impaction of an ancillary during its insertion is an important factor of success in cementless surgery. However, surgeons still rely on their proprioception, making the process highly subjective. The use of Experimental Modal Analysis (EMA) without sensor nor probe fixation on the implant or on the bone is a promising non destructive approach to determine the femoral stem stability. The aim of this study is to investigate whether EMA performed directly on the ancillary could be used to monitor the femoral stem insertion into the bone. To do so, a cementless femoral stem was inserted into 10 bone phantoms of human femurs and EMA was carried out on the ancillary using a dedicated impact hammer for each insertion step. Two bending modes could be identified in the frequency range [400-8000] Hz for which the resonance frequency was shown to be sensitive to the insertion step and to the bone-implant interface properties. A significant correlation was obtained between the two modal frequencies and the implant insertion depth (R² = 0.95 ± 0.04 and R² = 0.94 ± 0.06). This study opens new paths towards the development of noninvasive vibration based evaluation methods to monitor cementless implant insertion.

Machine Learning-Based Diagnosis in Laser Resonance Frequency Analysis for Implant Stability of Orthopedic Pedicle Screws

Evaluation of the initial stability of implants is essential to reduce the number of implant failures of pedicle screws after orthopedic surgeries. Laser resonance frequency analysis (L-RFA) has been recently proposed as a viable diagnostic scheme in this regard. In a previous study, L-RFA was used to demonstrate the diagnosis of implant stability of monoaxial screws with a fixed head. However, polyaxial screws with movable heads are also frequently used in practice. In this paper, we clarify the characteristics of the laser-induced vibrational spectra of polyaxial screws which are required for making L-RFA diagnoses of implant stability. In addition, a novel analysis scheme of a vibrational spectrum using L-RFA based on machine learning is demonstrated and proposed. The proposed machine learning-based diagnosis method demonstrates a highly accurate prediction of implant stability (peak torque) for polyaxial pedicle screws. This achievement will contribute an important analytical method for implant stability diagnosis using L-RFA for implants with moving parts and shapes used in various clinical situations.

Laser resonance frequency analysis of pedicle screw stability: A cadaveric model bone study

There is no evaluation method currently available to assess intraoperative pedicle screw fixation (PSF) strength. In this study, we established a laser-based resonance frequency analysis (RFA) system with high-speed, noncontact, quantitative measurements of PSF. Clinical investigations in the future can assess surgical failure risk of implants. We investigated the characteristics of the laser RFA and compared them with the conventional methods. We inserted a pedicle screw in the vertebral pedicle of human cadaver or model bone, followed by screw pull-out, peak torque, implant stability quotient (ISQ) value obtained by the magnetic dental RFA system, and fixation force of laser RFA. We compared the outcomes using best-fit linear or logarithmic approximations. For the model bone study, the resonance frequency (RF) versus peak torque/pull-out force (POF) demonstrated strong correlations using logarithmic approximation (vs. peak torque: R = 0.931, p < .001, vs. POF: R = 0.931, p < .001). RF strongly correlated with the ISQ value using linear approximation (R = 0.981, p < .001). For the cadaveric vertebrae study, the correlation coefficients between RF and the peak torque/POF were significant regardless of approximation method (peak torque: logarithmic: R = 0.716 vs. linear: R = 0.811; p < .001) (POF: logarithmic: R = 0.644 vs. linear: R = 0.548; p < .05). Thus, the results of this study revealed a constant correlation between RFA and conventional methods as a measurement validation, predicting favorable support for intraoperative PSF. RFA has the potential to be a new index for evaluating the implant fixation force.

Factors Affecting Pedicle Screw Insertional Torque in Spine Deformity Surgery

STUDY DESIGN

Retrospective observational study of consecutive patients.

OBJECTIVE

We sought to: (1) clarify the key factors predominantly associated with the insertional torque of pedicle screws; (2) compare the optimal factors for pedicle screw insertion to obtain rigid screw fixation in patients with adult spinal deformity (ASD) and in those with adolescent idiopathic scoliosis (AIS); (3) determine the optimal screw/pedicle ratio (S/P) to obtain rigid pedicle screw fixation.

SUMMARY OF BACKGROUND DATA

Rigid pedicle screw fixation is mandatory to perform corrections for spinal deformities properly and to allow successful fusion after surgery. The fixation depends mainly on screw position accuracy and patient bone quality. Traditionally, spinal surgeons have decided the screw size, trajectory, and tapping size based on their intuition. Insertional torque has been indicated as useful to predict screw fixation strength, and is correlated with screw pullout strength and frequency of postoperative screw loosening.

METHODS

We compared insertion torque at L1-L3 levels of 324 screws in 68 patients with ASD and 58 screws in 32 patients with AIS. We assessed the association between screw/pedicle ratio and insertion torque by constructing a spline curve.

RESULTS

Pedicle and screw diameter correlated positively with insertion torque in patients with either ASD or AIS. The optimal screw/pedicle ratio to obtain rigid pedicle screw fixation in patients with ASD was close to, but less than one, and, by contrast, was about 1 to 1.25 in patients with AIS.

CONCLUSION

We propose the concept of an optimal S/P ratio for obtaining rigid pedicle screw fixation during spinal corrective surgery, which is different for patients with ASD and patients with AIS. The S/P ratio is useful for deciding the appropriate diameter screw for each case in preoperative planning.Level of Evidence: 4.

Resonance frequency analysis with two different devices after conventional implant placement with ridge preservation: A prospective pilot cohort study

BACKGROUND

Primary and secondary implant stability is of high importance for survival and success of dental implants in the short and long term. Measurements of implant stability during healing provide the opportunity to monitor the course of the osseointegration process.

PURPOSE

To compare implant stability quotient (ISQ) by resonance frequency analysis (RFA), recorded with two different devices after implant placement.

MATERIALS AND METHODS

Patients with the need of single tooth extraction in posterior sites of the maxilla and the mandible were treated in a surgical center. All patients received additional augmentation with a bovine bone substitute and platelet-rich fibrin (PRF) after atraumatic tooth extraction. After a healing period of 10 weeks, 28 self-tapping titanium-implants were placed. Implant stability was recorded with two different devices (Osstell and Penguin) at the time of implant insertion (T0), 10 days later (T1), and after 7 (T2), or 17 weeks (T3).

RESULTS

No implant was lost, and no postoperative complication occurred during follow-up. Patient cohort comprised 9 female (32.1%) and 19 male patients (67.9%), with a mean age of 52.8 years, 64.3 years, respectively. Mean overall insertion torque was 43.6 Ncm at implant placement with no significant difference between implant location, age, or gender. No patient dropped out. During observation period, a significant increase in mean ISQ was recorded with both devices. Significant positive correlations between insertion torque and ISQ were recorded with both devices at T0, T2, and T3. No significant differences were observed in ISQ-values between both devices, and measuring directions at any point of measurement.

CONCLUSIONS

Within the limitations of this cohort study, both devices were suitable for RFA-measurement and revealed comparable results. Due to the cordless design, handling of the Penquin device was more comfortable. Reusability of the Penguin MultiPeg-transducers may offer an additional benefit with regard on ecological aspects.

Comparison of the Pull-Out Strength between a Novel Micro-Dynamic Pedicle Screw and a Traditional Pedicle Screw in Lumbar Spine

OBJECTIVE

This study aimed to investigate the strength of a novel micro-dynamic pedicle screw by comparing it to the traditional pedicle screw.

METHODS

Forty-five lumbar vertebrae received a traditional pedicle screw on one side and a micro-dynamic pedicle screw on the other side as follows (traditional group vs micro-dynamic group): 15 vertebrae underwent instant pull-out testing; 15 vertebrae underwent 5000-cyclic fatigue loading testing; and 15 vertebrae underwent 10,000-cyclic fatigue loading testing and micro-computed tomography (micro-CT) scanning. The peek pull-out force and normalized peek pull-out force after instant pull-out testing, 5000-cyclic and 10,000-cyclic fatigue loading testing were recorded to estimate the resistance of two types of screws. Bone mineral density was recorded to investigate the strength of the different screws in osteoporotic patients. And the semidiameter of the screw insertion area on micro-CT images after fatigue were compared to describe the performance between screw and bone surface.

RESULTS

The bone mineral density showed a weak correlation with peek pull-out force (r = 0.252, P = 0.024). The peek pull-out force of traditional pedicle screw after 10,000-cyclic fatigue loading were smaller than that of instant pull-out test in both osteoporotic (P = 0.017) and healthy group (P = 0.029), the peek pull-out force of micro-dynamic pedicle screw after 10,000-cyclic fatigue loading was smaller than that in instant pull-out test in osteoporotic group (P = 0.033), but no significant difference in healthy group (P = 0.853). The peek pull-out force in traditional group and micro-dynamic group underwent instant pull-out testing (P = 0.485), and pull-out testing after 5000-cyclic fatigue loading testing (P = 0.184) did not show significant difference. However, the peek pull-out force in micro-dynamic group underwent pull-test after 10,000-cyclic fatigue loading testing was significantly greater than that measured in traditional group (P = 0.005). The normalized peek pull-out force of traditional groups underwent instant pull-out testing, pull-out test after 5000-cyclic and 10,000-cyclic fatigue loading testing significantly decreased as the number of cycles increased (P < 0.001); meanwhile, the normalized peek pull-out force of micro-dynamic groups remained consistent regardless of the number of cycles (P = 0.133). The semidiameter after the fatigue loading test of the traditional screw insertion area was significantly larger than that of the micro-dynamic screw insertion area (P = 0.013).

CONCLUSION

The novel micro-dynamic pedicle screw provides stronger fixation stability in high-cyclic fatigue loading and non-osteoporotic patients versus the traditional pedicle screw, but similar resistance in low-cycle fatigue testing and osteoporotic group vs the traditional pedicle screw.

Feasibility of using tapping torque during lumbar pedicle screw insertion to predict screw fixation strength

BACKGROUND

Rigid pedicle screw fixation is mandatory for achieving successful spinal fusion; however, there is no reliable method predicting screw fixation before screw insertion. The purpose of the present study was to investigate the efficacy of measurement of tapping torque to predict pedicle screw fixation.

METHODS

First, different densities of polyurethane foam were used to measure tapping torque. The insertional torque during pedicle screw insertion and axial pullout strength were measured and compared between under-tapped and same-tapped groups. Next, for in vivo study, the tapping and insertional torque of lumbar pedicle screws using the cortical bone trajectory technique were measured intraoperatively in 45 consecutive patients. Then, correlations between tapping torque, the bone mineral density of the femoral neck and lumbar vertebrae, and insertional torque were investigated.

RESULTS

Ex vivo tapping torque significantly correlated with the insertional torque and pullout strength regardless of tapping sizes (r = 0.98, p < 0.001). The mean in vivo tapping and insertional torque were 1.48 ± 0.73 and 2.48 ± 1.25 Nm, respectively (p < 0.001). Insertional torque significantly correlated with tapping torque and two BMD parameters, and the correlation coefficient of tapping torque (r = 0.83, p < 0.001) was higher than those of femoral neck BMD (r = 0.59, p < 0.001) and lumbar BMD (r = 0.39, p < 0.001).

CONCLUSIONS

Tapping torque is a reliable predictor of pedicle screw fixation and allows surgeons to improve the integrity of the bone-screw interface by making modification prior to actual screw insertion.

Laser Resonance Frequency Analysis: A Novel Measurement Approach to Evaluate Acetabular Cup Stability During Surgery

Artificial joint acetabular cup stability is essential for successful total hip arthroplasty. However, a quantitative evaluation approach for clinical use is lacking. We developed a resonance frequency analysis (RFA) system involving a laser system that is fully contactless. This study aimed to investigate the usefulness of laser RFA for evaluating acetabular cup stability. First, the finite element method was performed to determine the vibration mode for analysis. Second, the acetabular cup was press-fitted into a reamed polyurethane cavity that replicated the human acetabular roof. The implanted acetabular cup was vibrated with pulse laser irradiation and the induced vibration was detected with a laser Doppler vibrometer. The time domain signal from the vibrometer was analyzed by fast Fourier transform to obtain the vibration frequency spectrum. After laser RFA, the pull-down force of the acetabular cup was measured as conventional implant fixation strength. The frequency of the first highest amplitude between 2 kHz and 6 kHz was considered as the resonance peak frequency, and its relationship with the pull-down force was assessed. The peak frequency could predict the pull-down force (R² = 0.859, p < 0.000). Our findings suggest that laser RFA might be useful to measure acetabular cup stability during surgery.

Experimental Evaluation of Screw Pullout Force and Adjacent Bone Damage According to Pedicle Screw Design Parameters in Normal and Osteoporotic Bones

This paper proposes an optimum design of the pedicle screw with respect to bone density and variables of the screw design. First, pedicle screws are designed and manufactured with design variables including the core diameter and conical angle that affect the pullout force of the pedicle screw. Variables of bone density are also classified into two groups, namely grade 10 (0.16 g/cc) with osteoporotic bone density and grade 20 (0.32 g/cc) with normal bone density. The effect of each parameter on the pullout force and relationship between the pullout force and screw designs are investigated. Furthermore, bone damage after fixation failure or insertion in the patient body is considered separately from the pullout strength. Therefore, cross sectional images of the artificial bone are observed to analyze the degree of damage after the pullout test of the pedicle screw by using micro-CT (computed tomography). The region and degree of bone damage are quantitatively analyzed. The effects of the core diameter and conical angle of the pedicle screw on the pulling force, bone damage, and fracture behavior are analyzed via the aforementioned experiments and analysis. An optimal pedicle screw design is suggested based on the experimental results.

Quantitative CT-based bone strength parameters for the prediction of novel spinal implant stability using resonance frequency analysis: a cadaveric study involving experimental micro-CT and clinical multislice CT

BACKGROUND

To predict conventional test forces (peak torque and pull-out force) and a new test force (implant stability quotient [ISQ] value of a spinal pedicle screw) from computed tomography (CT) parameters, including micro-architectural parameters, using high-resolution micro-CT and clinical multislice CT (MSCT) in human cadaveric vertebrae.

METHODS

Micro-CT scans before/after screw insertion (n = 68) and MSCT scans before screw insertion (n = 58) of human cadaveric vertebrae were assessed for conventional test forces and ISQ value. Three-dimensional volume position adjustment between pre-insertion micro-CT and MSCT scans and post-insertion scans (micro-CT) was performed to extract the volume of the cancellous bone surrounding the pedicle screw. The following volume bone mineral density and micro-architectural parameters were calculated: bone volume fraction, bone surface density (bone surface/total volume (BS/TV)), trabecular thickness, trabecular separation, trabecular number, structure model index, and number of nodes (branch points) of the cancellous bone network/total volume (NNd/TV) using Spearman's rank correlation coefficient with Bonferroni correction.

RESULTS

Conventional test forces showed the strongest correlation with BS/TV: peak torque, ρ = 0.811, p = 4.96 × 10^-17(micro-CT) and ρ = 0.730, p = 7.87 × 10^-11 (MSCT); pull-out force, ρ = 0.730, p = 1.64 × 10^-12 (micro-CT) and ρ = 0.693, p = 1.64 × 10^-9 (MSCT). ISQ value showed the strongest correlation with NNd/TV: ρ = 0.607, p = 4.01 × 10^-8 (micro-CT) and ρ = 0.515, p = 3.52 × 10^-5 (MSCT).

CONCLUSIONS

Test forces, including the ISQ value, can be predicted using micro-CT and MSCT parameters. This is useful for establishing a preoperative fixation strength evaluation system.