Metal artifacts from titanium and steel screws in CT, 1.5T and 3T MR images of the tibial Pilon: a quantitative assessment in 3D

Evaluation of Pedicle Screw Position on Computerized Tomography Using Three-Dimensional Reconstruction Software

Background and Objectives: Recent advances in intraoperative navigation systems have improved the accuracy of pedicle screw placement in spine surgery. However, many hospitals have limited access to these advanced technologies due to resource constraints. In such settings, postoperative computed tomography (CT) evaluation remains crucial for assessing screw placement and related potential complications. Metal artifacts in CT scans often compromise the diagnostic accuracy. This study aimed to develop and validate three-dimensional (3-D) reconstruction software to enhance screw localization accuracy and facilitate its practical clinical application. Materials and Methods: This study included two phases: 3-D software development utilizing specific threshold values of Hounsfield units for titanium screws followed by internal validation. For validation, fifty pedicle screws were inserted into porcine lumbar vertebrae with random violation (superior, inferior, medial, or lateral). Three fellowship-trained surgeons evaluated screw positions using both conventional CT bone window settings and the developed software. Additional clinical validation involving 386 pedicle screws from cervical to lumbar spine was performed by two surgeons. Results: The software demonstrated significantly higher specificity (83% vs. 63%) and positive predictive value (96% vs. 91%) compared to conventional CT bone window settings, while maintaining 100% sensitivity and negative predictive value. Interobserver reliability was excellent for both methods (0.961 for bone window vs. 0.990 for software). In clinical validation, the software showed superior intraobserver (0.83 vs. 0.74) and interobserver reliability (0.855 vs. 0.513) compared to picture archiving and communication system (PACS) workstation evaluation. Conclusions: The developed software provides improved accuracy and reliability in pedicle screw position evaluation through distinct screw outline visualization and metal artifact reduction. Its equipment-independent nature and cost-effectiveness make it particularly valuable for clinical implementation.

Quantification of metallic artifact on CT associated with titanium pedicle screws

Background

In dogs undergoing vertebral column stabilization, post-operative computed tomography (CT) evaluates implant placement. The impact on the interpretation of metallic artifact associated with titanium implants in dogs remains to be established. Our objective was to quantify metallic artifact on CT associated with titanium pedicle screws.

Methods

The study design included an in vitro model and a retrospective review of 11 dogs with vertebral column stabilization. Twenty four titanium pedicle screws (6 each: 2.0 mm, 2.7 mm, 3.5 mm, and 4.5 mm) were inserted into a 20% ballistic gel, and CT scan of the construct was performed. Three blinded raters used a bone window to measure the maximum width (effective size) of each screw, one rater measured effective size using an ultrawide window and 45 titanium pedicle screws (3×2.0 mm, 5×2.7 mm, 30×3.5 mm, and 7×4.5 mm) in 11 clinical cases. Effective size measurements were compared to actual screw sizes.

Results

The effective size was 26.9-43.8%, 9.2-18.5%, and 21.1-30.5% larger than the actual size for the in vitro system (bone window), in vitro system (ultrawide window), and clinical cases, respectively. The mean gross difference for the in vitro measurements varied by implant size (p < 0.001) and was positively correlated with implant size (r = 0.846), but the mean percentage difference was negatively correlated with implant size (p < 0.001). Overestimation was larger for the in vitro model bone window compared to the ultrawide window (p < 0.001) and clinical cases (p = 0.001).

Conclusion

Metallic artifact associated with titanium pedicle screws on CT resulted in an overestimation of screw size. This information might aid in the interpretation of implant placement on post-operative imaging.

Radiation myelopathy following stereotactic body radiation therapy for spine metastases

PURPOSE

Stereotactic body radiation therapy (SBRT) is now considered a standard of care treatment option in the management of spine metastases. One of the most feared complications of spine SBRT is radiation myelopathy (RM).

METHODS

We provided a narrative review of RM following spine SBRT based on review of the published literature, including data on spinal cord dose constraints associated with the risk of RM, strategies to mitigate the risk, and management options for RM.

RESULTS

There are limited published data of cases of RM following spine SBRT with detailed spinal cord dosimetry. The HyTEC report provided recommendations for the point maximal dose (Dmax) for the spinal cord that is associated with a < 5% risk of RM for 1-5 fractions spine SBRT. In the setting of spine SBRT reirradiation after previous conventional external beam radiation therapy (cEBRT), factors associated with RM are: SBRT spinal cord Dmax, cumulative spinal cord Dmax, and the time interval between previous RT and SBRT reirradiation. There are various strategies to mitigate the risk of RM, including accurate delineation of the spinal cord (or thecal sac), strict adherence to the recommended spinal cord dose constraints, and robust treatment immobilisation set-up and delivery. Limited effective treatment options are available for patients who develop RM, and these include corticosteroids, hyperbaric oxygen, and bevacizumab; however, none have been supported by high quality evidence.

CONCLUSION

RM is a rare but devastating complication following SBRT for spine metastases. There are strategies to minimise the risk of RM to ensure safe delivery of spine SBRT.

In Silico Biomechanical Evaluation of WE43 Magnesium Plates for Mandibular Fracture Fixation

Titanium fixation devices are the gold standard for the treatment of mandibular fractures; however, they present serious limitations, such as non-degradability and generation of imaging artifacts. As an alternative, biodegradable magnesium alloys have lately drawn attention due to their biodegradability and biocompatibility. In addition, magnesium alloys offer a relatively high modulus of elasticity in comparison to biodegradable polymers, being a potential option to substitute titanium in highly loaded anatomical areas, such as the mandible. This study aimed to evaluate the biomechanical competence of magnesium alloy WE43 plates for mandibular fracture fixation in comparison to the clinical standard or even softer polymer solutions. A 3D finite element model of the human mandible was developed, and four different fracture scenarios were simulated, together with physiological post-operative loading and boundary conditions. In a systematic comparison, the material properties of titanium alloy Ti-6Al-4V, magnesium alloy WE43, and polylactic acid (PLA) were assigned to the fixation devices, and two different plate thicknesses were tested. No failure was predicted in the fixation devices for any of the tested materials. Moreover, the magnesium and titanium fixation devices induced a similar amount of strain within the healing regions. On the other hand, the PLA devices led to higher mechanical strains within the healing region. Plate thickness only slightly influenced the primary fixation stability. Therefore, magnesium alloy WE43 fixation devices seem to provide a suitable biomechanical environment to support mandibular fracture healing in the early stages of bone healing. Magnesium WE43 showed a biomechanical performance similar to clinically used titanium devices with the added advantages of biodegradability and radiopacity, and at the same time it showed a remarkably higher primary stability compared to PLA fixation devices, which appear to be too unstable, especially in the posterior and more loaded mandibular fracture cases.

Computed Tomography in Limb Salvage and Deformity Correction-3D Assessment, Indications, Radiation Exposure, and Safety Considerations

Computed tomography (CT) is an essential tool in orthopedic surgery but is known to be a method with that entails radiation exposure. CT increases the risk of developing fatal cancer, which should not be underestimated. However, patients with bone defects and/or deformities must frequently undergo numerous investigations during their treatment. CT is used for surgical planning, evaluating callus maturation, alignment measurement, length measurement, torsion measurement, and angiography. This study explores the indications in CT scans for limb lengthening and deformity correction and estimates the effective radiation dose. These results should help avoid unnecessary radiation exposure by narrowing the examination field and by providing explicit scanning indications. For this study, 19 posttraumatic patients were included after the bone reconstruction of 21 lower limbs. All patients underwent CT examinations during or after treatment with an external ring fixator. The mean effective dose was 3.27 mSv, with a mean cancer risk of 1:117,014. The effective dose depended on the location and indication of measurement, with a mean dose of 0.04 mSv at the ankle up to 6.8 mSv (or higher) for vascular depictions. CT evaluation, with or without 3D reconstruction, is a crucial tool in complex bone reconstruction and deformity treatments. Therefore, strict indications are necessary to reduce radiation exposure-especially in young patients-without compromising the management of their patients.

Biomaterial design strategies to address obstacles in craniomaxillofacial bone repair

Biomaterial design to repair craniomaxillofacial defects has largely focused on promoting bone regeneration, while there are many additional factors that influence this process. The bone microenvironment is complex, with various mechanical property differences between cortical and cancellous bone, a unique porous architecture, and multiple cell types that must maintain homeostasis. This complex environment includes a vascular architecture to deliver cells and nutrients, osteoblasts which form new bone, osteoclasts which resorb excess bone, and upon injury, inflammatory cells and bacteria which can lead to failure to repair. To create biomaterials able to regenerate these large missing portions of bone on par with autograft materials, design of these materials must include methods to overcome multiple obstacles to effective, efficient bone regeneration. These obstacles include infection and biofilm formation on the biomaterial surface, fibrous tissue formation resulting from ill-fitting implants or persistent inflammation, non-bone tissue formation such as cartilage from improper biomaterial signals to cells, and voids in bone infill or lengthy implant degradation times. Novel biomaterial designs may provide approaches to effectively induce osteogenesis and new bone formation, include design motifs that facilitate surgical handling, intraoperative modification and promote conformal fitting within complex defect geometries, induce a pro-healing immune response, and prevent bacterial infection. In this review, we discuss the bone injury microenvironment and methods of biomaterial design to overcome these obstacles, which if unaddressed, may result in failure of the implant to regenerate host bone.

Improved Commercially Pure Titanium Obtained by Laser Directed Energy Deposition for Dental Prosthetic Applications

The objective of this study was to evaluate the viability of the cp-Ti obtained through the laser-directed energy deposition (LDED) technique as a material for dental prostheses through an evaluation of the microstructural, mechanical, and electrochemical properties. Additionally, the material resulting from LDED is also compared with the same alloy employed for milling in the dental restorative industry. The results obtained show that both materials have good overall performance for biomedical applications according to the ISO 22674 and ISO 10271 dentistry standards. Both materials have high corrosion resistance, typical of this alloy. However, commercially pure titanium grade 4 obtained by LDED present a higher mechanical performance than the ones resulting from the milling technique: 7% increment of ultimate tensile strength, 12.9% increment of elongation after fracture and 30% increment of toughness. This improved mechanical performance can be attributed to microstructure modification inherent to the LDED process.

A novel MRI compatible mouse fracture model to characterize and monitor bone regeneration and tissue composition

Over the last years, murine in vivo magnetic resonance imaging (MRI) contributed to a new understanding of tissue composition, regeneration and diseases. Due to artefacts generated by the currently used metal implants, MRI is limited in fracture healing research so far. In this study, we investigated a novel MRI-compatible, ceramic intramedullary fracture implant during bone regeneration in mice. Three-point-bending revealed a higher stiffness of the ceramic material compared to the metal implants. Electron microscopy displayed a rough surface of the ceramic implant that was comparable to standard metal devices and allowed cell attachment and growth of osteoblastic cells. MicroCT-imaging illustrated the development of the callus around the fracture site indicating a regular progressing healing process when using the novel implant. In MRI, different callus tissues and the implant could clearly be distinguished from each other without any artefacts. Monitoring fracture healing using MRI-compatible implants will improve our knowledge of callus tissue regeneration by 3D insights longitudinal in the same living organism, which might also help to reduce the consumption of animals for future fracture healing studies, significantly. Finally, this study may be translated into clinical application to improve our knowledge about human bone regeneration.

Current controversies in management of fracture neck femur in children: A review

Paediatric femur neck fracture is an uncommon injury and is known for high rate of complications. This in turn, can have significant impact on development of hip and overall function of the child. Controversy prevails in many areas of management and it still remains a difficult injury to manage. Through this paper, an attempt has been made to summarize the current concepts in management and suggest current recommendations regarding the controversies so that these injuries can be managed judiciously. A systematic review was done as per PRISMA guidelines using pre-defined inclusion and exclusion criteria. 18 studies with better scientific evidence after quality assessment were included in the systematic review. Current trends and Controversial issues in management were then identified and discussed. It was observed that existing literature is inconclusive regarding several aspects of management of this injury with no clear guideline available. However, certain recommendations useful for decision making could be made. These injuries should be managed aggressively with operative fixation at the earliest and one should not hesitate to open reduce if acceptable alignment is not obtained after one or two gentle closed manipulations. Choice of implant and their configuration in neck can vary depending on age and weight of patient, type of injury and surgeon's preference. Initial fracture displacement could be considered to be most predictive for development of osteonecrosis of the femoral head, whereas, role of surgical decompression, type of fixation and timing of surgery is still debatable. Functional outcome is primarily affected by osteonecrosis of the femoral head, nonunion and severe coxa vara, whereas mild coxa vara, shortening, and premature closure of physis when considered alone, don't have significant influence on functional outcome in short term. Treatment of fracture neck femur in children is still controversial in many aspects and needs further research. It should be understood that complications can occur regardless of the method of treatment and might reveal their full impact many years after injury. Hence, a guarded prognosis should be explained to the parents and care-givers at the time of injury.

Metal artefacts severely hamper magnetic resonance imaging of the rotator cuff tendons after rotator cuff repair with titanium suture anchors

BACKGROUND

The rate of retear after rotator cuff surgery is 17%. Magnetic resonance imaging (MRI) scans are used for confirmative diagnosis of retear. However, because of the presence of titanium suture anchors, metal artefacts on the MRI are common. The present study evaluated the diagnostic value of MRI after rotator cuff tendon surgery with respect to assessing the integrity as well as the degeneration and atrophy of the rotator cuff tendons when titanium anchors are in place.

METHODS

Twenty patients who underwent revision surgery of the rotator cuff as a result of a clinically suspected retear between 2013 and 2015 were included. The MRI scans of these patients were retrospectively analyzed by four specialized shoulder surgeons and compared with intra-operative findings (gold standard). Sensitivity and interobserver agreement among the surgeons in assessing retears as well as the Goutallier and Warner classification were examined.

RESULTS

In 36% (range 15% to 50%) of the pre-operative MRI scans, the observers could not review the rotator cuff tendons. When the rotator cuff tendons were assessable, a diagnostic accuracy with a mean sensitivity of 0.84 (0.70 to 1.0) across the surgeons was found, with poor interobserver agreement (kappa = 0.12).

CONCLUSIONS

Metal artefacts prevented accurate diagnosis from MRI scans of rotator cuff retear in 36% of the patients studied.

SPECT/CT arthrography

Single photon emission CT (SPECT)/CT arthrography, the combination of CT arthrography and late phase bone SPECT/CT, has been developed in 2011 and so far used in knee, ankle and wrist joints. SPECT/CT offers functional information about increased bone turnover in combination with morphological details. Compared with SPECT/CT alone, additional intra-articular contrast enables the assessment of cartilage, menisci, ligaments and loose bodies. SPECT/CT arthrography is a promising alternative technique for the evaluation of internal derangement of joints in patients with MR contraindications and/or metallic implants. In this article, we review and report our 5-year experience with this technique illustrated with patient examples and give a perspective for future applications.

[Fixed angle carbon fiber reinforced polymer composite plate for treatment of distal radius fractures : Pilot study on clinical applications]

BACKGROUND

The clinical implementation of a new carbon-fiber-reinforced polyetheretherketon (PEEK) plate for distal radius fractures might offer advantageous properties over the conventional metallic devices. This includes similar elastic modulus to cortical bone, radiolucency, low artifacts on MRI scans and the lack of metal allergies.

OBJECTIVE

The aim of this study was to evaluate the clinical results at 6-week and 12-month follow-up using either a new fixed angle (monoaxial) PEEK plate system or a fixed angle (polyaxial) titanium plate.

METHODES

We included 26 patients (mean age 59.3) with displaced fractures of the distal radius (all AO types). Radiological and functional outcomes were measured prospectively at a 6-week and 12 month follow-up.

RESULTS

We documented no cases of hardware breakage or significant loss of the surgically achieved fracture reduction with the usage oft the new PEEK device. Operating time was 101.0 min using PEEK versus 109.3 min in titanium plates, recorded times were including preparation, draping, and postoperative processing (ns, p 0.156). At the 6-week follow up the PEEK plate showed a trend for better range of motion and functional results (DASH-score, Mayo-wrist score, VAS) with no statistical significance. Results of 12 month follow up with PEEK showed comparable results with corresponding studies examining titanium plate after this period.

CONCLUSION

First experience with PEEK plate osteosynthesis demonstrate quick clinical implementation with good clinical outcome and the advantage of excellent postoperative radiological assessment. At early follow-up PEEK even showed a trend for improved functional results.

Biodegradable magnesium Herbert screw - image quality and artifacts with radiography, CT and MRI

Background

Magnesium alloys have recently been rediscovered as biodegradable implants in musculoskeletal surgery. This study is an ex-vivo trial to evaluate the imaging characteristics of magnesium implants in different imaging modalities as compared to conventional metallic implants.

Methods

A CE-approved magnesium Herbert screw (MAGNEZIX®) and a titanium screw of the same dimensions (3.2x20 mm) were imaged using different modalities: digital radiography (DX), multidetector computed tomography (MDCT), high resolution flat panel CT (FPCT) and magnetic resonance imaging (MRI). The screws were scanned in vitro and after implantation in a fresh chicken tibia in order to simulate surrounding bone and soft tissue. The images were quantitatively evaluated with respect to the overall image quality and the extent and intensity of artifacts.

Results

In all modalities, the artifacts generated by the magnesium screw had a lesser extent and were less severe as compared to the titanium screw (mean difference of artifact size of solo scanned screws in DX: 0.7 mm, MDCT: 6.2 mm, FPCT: 5.9 mm and MRI: 4.73 mm; p < 0.05). In MDCT and FPCT multiplanar reformations and 3D reconstructions were superior as compared with the titanium screw and the metal-bone interface after implanting the screws in chicken cadavers was more clearly depicted. While the artifacts of the titanium screw could be effectively reduced using metal-artifact reduction sequences in MRI (WARP, mean reduction of 2.5 mm, p < 0.05), there was no significant difference for the magnesium screw.

Conclusions

Magnesium implants generate significantly less artifacts in common imaging modalities (DX, MDCT, FPCT and MRI) as compared with conventional titanium implants and therefore may facilitate post-operative follow-up.

Electronic supplementary material

The online version of this article (doi:10.1186/s12880-017-0187-7) contains supplementary material, which is available to authorized users.

Can MRI accurately detect pilon articular malreduction? A quantitative comparison between CT and 3T MRI bone models

BACKGROUND

Pilon fracture reduction is a challenging surgery. Radiographs are commonly used to assess the quality of reduction, but are limited in revealing the remaining bone incongruities. The study aimed to develop a method in quantifying articular malreductions using 3D computed tomography (CT) and magnetic resonance imaging (MRI) models.

METHODS

CT and MRI data were acquired using three pairs of human cadaveric ankle specimens. Common tibial pilon fractures were simulated by performing osteotomies to the ankle specimens. Five of the created fractures [three AO type-B (43-B1), and two AO type-C (43-C1) fractures] were then reduced and stabilised using titanium implants, then rescanned. All datasets were reconstructed into CT and MRI models, and were analysed in regards to intra-articular steps and gaps, surface deviations, malrotations and maltranslations of the bone fragments.

RESULTS

Initial results reveal that type B fracture CT and MRI models differed by ~0.2 (step), ~0.18 (surface deviations), ~0.56° (rotation) and ~0.4 mm (translation). Type C fracture MRI models showed metal artefacts extending to the articular surface, thus unsuitable for analysis. Type C fracture CT models differed from their CT and MRI contralateral models by ~0.15 (surface deviation), ~1.63° (rotation) and ~0.4 mm (translation).

CONCLUSIONS

Type B fracture MRI models were comparable to CT and may potentially be used for the postoperative assessment of articular reduction on a case-to-case basis.

Bone Regeneration after Treatment with Covering Materials Composed of Flax Fibers and Biodegradable Plastics: A Histological Study in Rats

The aim of this study was to examine the osteogenic potential of new flax covering materials. Bone defects were created on the skull of forty rats. Materials of pure PLA and PCL and their composites with flax fibers, genetically modified producing PHB (PLA-transgen, PCL-transgen) and unmodified (PLA-wt, PCL-wt), were inserted. The skulls were harvested after four weeks and subjected to histological examination. The percentage of bone regeneration by using PLA was less pronounced than after usage of pure PCL in comparison with controls. After treatment with PCL-transgen, a large amount of new formed bone could be found. In contrast, PCL-wt decreased significantly the bone regeneration, compared to the other tested groups. The bone covers made of pure PLA had substantially less influence on bone regeneration and the bone healing proceeded with a lot of connective tissue, whereas PLA-transgen and PLA-wt showed nearly comparable amount of new formed bone. Regarding the histological data, the hypothesis could be proposed that PCL and its composites have contributed to a higher quantity of the regenerated bone, compared to PLA. The histological studies showed comparable bone regeneration processes after treatment with tested covering materials, as well as in the untreated bone lesions.

The Utility of a Digital Virtual Template for Junior Surgeons in Pedicle Screw Placement in the Lumbar Spine

This study assessed the utility of three-dimensional preoperative image reconstruction as digital virtual templating for junior surgeons in placing a pedicle screw (PS) in the lumbar spine. Twenty-three patients of lumbar disease were operated on with bilateral PS fixation in our hospital. The two sides of lumbar pedicles were randomly divided into “hand-free group” (HFG) and “digital virtual template group” (DVTG) in each patient. Two junior surgeons preoperatively randomly divided into these two groups finished the placement of PSs. The accuracy of PS and the procedure time of PS insertion were recorded. The accuracy of PS in DVTG was 91.8% and that in HFG was 87.7%. The PS insertion procedure time of DVTG was 74.5 ± 8.1 s and that of HFG was 90.9 ± 9.9 s. Although no significant difference was reported in the accurate rate of PS between the two groups, the PS insertion procedure time was significantly shorter in DVTG than in HFG (P < 0.05). Digital virtual template is simple and can reduce the procedure time of PS placement.