Image intensifier distortion influences a surgeon's ability to aim guidewires during orthopaedic procedures

Optimizing implant positioning in total hip arthroplasty via the direct anterior approach: The role and technique of conventional traction table and fluoroscopy

BACKGROUND

Precise implant positioning during total hip arthroplasty (THA) is an important factor influencing dislocation rate and long-term implant survival. Although a special carbon fiber traction table for THA improves the accuracy of implant positioning, it is too expensive. We aimed to report the accuracy of cup positioning and complication rate in patients undergoing THA via the direct anterior approach using a conventional noncarbon fiber traction table, which is generally used for osteosynthesis of femoral fractures.

METHODS

This retrospective study included 101 patients who received primary THA via the direct anterior approach using a conventional traction table with fluoroscopy between July 2022 and October 2024. Two observers evaluated radiological outcomes using postoperative anteroposterior X-rays. The intraclass correlation coefficients of cup positioning angles were calculated (inclination: 0.92, anteversion: 0.89 for intra-observer agreement; inclination: 0.91, anteversion: 0.85 for inter-observer agreement). Complications were defined as dislocation, periprosthetic fracture, ankle fracture, implant loosening, nerve injury, surgical site infection, deep vein thrombosis, and revision surgery for any reason.

RESULTS

Radiographic analysis showed an average cup inclination of 38.1° ± 4.1° (99.0% within Lewinnek's safe zone). The average cup anteversion was 12.0° ± 4.7° (97.0% within Lewinnek's safe zone). None of the patients experienced any complications.

CONCLUSION

The use of a conventional traction table to perform THA using fluoroscopy may not interfere with precise cup positioning. This technique, which does not require a special carbon fiber traction table for THA, could be a feasible alternative for performing THA at general hospitals.

Image Correlation Between Digitally Reconstructed Radiographs, C-arm Fluoroscopic Radiographs, and X-ray: A Phantom Study

OBJECTIVE

Digitally reconstructed radiographs (DRRs) are planar two-dimensional (2D) X-rays derived from a three-dimensional (3D) computed tomography (CT) dataset. DRRs allow the simulation of radiographs of all desired views and facilitate preoperative planning. However, orthopedic surgeons rely on C-arm fluoroscopic imaging during surgery to verify fracture reduction and implant placement. Pincushion distortion represents a technical limitation of fluoroscopic imaging, resulting in a greater distance between points at the periphery of the image compared to the center. This project, therefore, aimed to assess the image correlation between digitally reconstructed radiographs (DRRs) and fluoroscopic imaging (C-arm) using conventional radiographs (X-ray) as a control.

METHODS

A 3D-printed cubic prototype and an anatomical humerus bone model were used. C-arm fluoroscopic radiographs and conventional X-ray images were taken in an anteroposterior (AP) view at 10-degree steps while rotating the objects from 0 to 90 degrees. CT scans were made and used to compute and export DRRs in AP view at 10-degree rotational steps from 0 to 90 degrees. The surface area (cm2) was measured and compared between the different modalities. For automated image analysis of the anatomical humerus model, matching (%) between modalities was calculated using the structural similarity index (SSIM).

RESULTS

The overall regression was statistically significant in all models, with an R2 >0.99 when comparing all three imaging modalities of the prototype. Surface correlation in the anatomical humerus model was R2 0.99 between X-ray and C-arm and R2 0.95 between C-arm and X-ray to DRRs, respectively. The SSIM was highest for comparing DRR and C-arm images (0.84±0.01%).

CONCLUSIONS

The study indicates a strong agreement between digitally reconstructed radiographs and X-ray/C-arm images. DRRs, therefore, represent a valuable tool for research and clinical application.

Quantitative assessments of image intensifier distortion induced by weak (Sub-Gauss) magnetic fields during fluoroscopically-guided procedures

BACKGROUND

Fluoroscopically-guided procedures at our hospital have been aborted due to sigmoidal distortion (S-distortion) when an image intensifier (II) system is used in a surgical environment distant from any apparent sources of strong magnetic fields, such as a nearby magnetic resonance imaging (MRI) scanner. Clearly, current clinical practice fails to account for the impact of ambient weak magnetic fields and/or other contributing factors on S-distortion induction.

PURPOSE

This study attempts to quantitatively assess the threshold level of magnetic field, along with other potential factors, that can induce intolerable S-distortion during image-intensified fluoroscopically-guided procedures. We will also discover the origins of such level of magnetic field in typical surgical facilities and provide our practical mitigation strategies accordingly.

METHODS

Ten surgical facilities and their accessory equipment (e.g., surgical tables) were screened using an AC/DC gaussmeter for the distribution and magnitude of magnetic field (magnetic flux density). A 'hot spot' of magnetic field was identified to further investigate the induction of S-distortion by scanning a titanium rod phantom using a GE OEC 9900 Elite II system placed at increasing distance from the 'hot spot' corresponding to decreasing magnetic field experienced by the II. The measurements were compared to that on a 'cold spot', and a GE flat panel detector (FPD) fluoroscopy was used as the negative control. Rod phantoms made of various magnetic susceptible materials (titanium, steel, aluminium, and copper) were scanned to explore the potential effects of implant material on S-distortion. An upper extremity anthropomorphic phantom was imaged on various surgical tables to mimic clinical sceneries. The GE II model and Siemens ARCADIS Orbic II model were compared to evaluate if S-distortion induction varied among different II models. Two metrics, angle of rotation (θ) and deviation/length ratio, were used to quantify the degree of S-distortion. Three designs of external magnetic shielding were evaluated for mitigating S-distortion.

RESULTS

We identified static magnetic fields up to 2500 µT and 70 µT on the floor and at 1-meter height, respectively, in random locations of surgical facilities. A large variation of magnetic field (64 ± 20 µT) was detected on the surface of surgical tables, with background magnetic fields of ∼35 µT. Quantitative assessments demonstrated that even weak magnetic fields at sub-Gauss level (<100 µT) could induce noticeable distortion artifacts, deemed unacceptable (θ > 4°). S-distortion was independent of the implant material being imaged but dependent on the II model - the threshold magnetic fields (4° distortion induction) were as low as 47 µT and 94 µT for the GE and Siemens II models. Mitigation possibilities of S-distortion include relocating the II to an area with subthreshold magnetic fields and shielding the II utilizing cylindrical mu-metal shields with an extension for alleviating the effect of openings.

CONCLUSIONS

This work demonstrates that ambient sub-Gauss magnetic fields originating from any possible sources in a surgical environment have to be carefully considered when performing an image-intensified fluoroscopically-guided procedure, because such weak magnetic fields are likely able to induce unacceptable S-distortion artifacts in the acquired X-ray images leading to undesirable surgical outcomes.

Magnetically Controlled Growing Rods: Influence on Intraoperative Fluoroscopic Imaging: A Case Report

CASE

A 7-year-old boy with severe congenital scoliosis and impending thoracic insufficiency syndrome underwent uneventful single magnetically controlled growing rod (MCGR) insertion and removal of his ipsilateral rib-based distraction implants at our institution. Intraoperative fluoroscopy imaging revealed an artifactual bend (S-distortion) of the rod actuator after placement. This artifact was eliminated by moving the image intensifier further from the patient.

CONCLUSION

We attributed the S-distortion to influences of magnetic fields within the MCGR actuator onto the image intensifier. Surgeons should be aware of such implications which can lead to misleading imaging artifacts. This is a first reported case of such incident with MCGR.

Are We Being Fooled by Fluoroscopy? Distortion May Affect Limb-Length Measurements in Direct Anterior Total Hip Arthroplasty

BACKGROUND

Distortion is an intrinsic phenomenon associated with image-intensified fluoroscopy that is both poorly understood and infrequently appreciated by orthopedic surgeons. Little information exists regarding its potential influence on intraoperative parameters during orthopedic surgery, let alone during direct anterior (DA) total hip arthroplasty (THA). The purpose of this study was to quantify the amount of potential error caused by fluoroscopic distortion during DA THA.

METHODS

Intra-operative fluoroscopic pelvic images from 74 DA THAs were reviewed by two independent readers. All images were obtained using the same fluoroscopic C-arm unit with a radiopaque grid attached to the image intensifier. The vertical distortion from a straight central horizontal line at the peripheries of images were measured and summed to yield the combined vertical distortion similar to how a surgeon calculates a side to side comparison of limb lengths. Simple linear regression was used to evaluate associations between total distortion and patient demographics, operating theaters, and various operative parameters.

RESULTS

The average combined distortion was 10.0mm (range 2.0-20.0mm). There was a significant difference in the average distortion observed in different theaters (P < .001). There was no association between distortion and patient demographics or fluoroscopic time (all, P > .05).

CONCLUSION

Fluoroscopic distortion is unpredictable and can cause a substantial amount of error when comparing limb lengths during DA THA. This is a critical finding as this amount of inaccuracy could lead to unintended implant positioning and limb-length discrepancies if unaccounted for.

Accuracy of radiographic measurement techniques for the Taylor spatial frame mounting parameters

Aim

The correction accuracy of the Taylor Spatial Frame (TSF) fixator depends considerably on the precise determination of the mounting parameters (MP). Incorrect parameters result in secondary deformities that require subsequent corrections. Different techniques have been described to improve the precision of MP measurement, although exact calculation is reportedly impossible radiologically. The aim of this study was to investigate the accuracy of intraoperative and postoperative radiographic measurement methods compared to direct MP measurement from TSF bone mounting.

Methods

A tibial Sawbone® model was established with different origins and reference ring positions. First, reference MPs for each origin were measured directly on the frame and bone using a calibrated, digital vernier calliper. In total 150 MPs measured with three different radiographic measurement techniques were compared to the reference MPs: digital radiographic measurements were performed using soft-copy PACS images without (method A) and with (method B) calibration and calibrated image intensifier images (method C).

Results

MPs measured from a non-calibrated X-ray image (method A) showed the highest variance compared to the reference MPs. A greater distance between the origin and the reference ring corresponded to less accurate MP measurements with method A. However, the MPs measured from calibrated X-ray images (method B) and calibrated image intensifier images (method C) were intercomparable (p = 0.226) and showed only minor differences compared to the reference values but significant differences to method A (p < 0,001).

Conclusion

The results demonstrate that MPs can be accurately measured with radiographic techniques when using calibration markers and a software calibration tool, thus minimizing the source of error and improving the quality of correction.