Jens Geerling

A comparison of plates with and without locking screws in a calcaneal fracture model.

Background: We compared different plates in an experimental calcaneal fracture model under biocompatible loading. Methods: Four plates were tested: a plate without locked screws (Synthes), and three different plates with locked screws (Newdeal, Darco, Synthes). Synthetic calcanei (Sawbone) were osteotomized to create a fracture model, and the plates were fixed onto them. Seven specimens for each plate model were subjected to cyclic loading (preload 20 N, 1,000 cycles with 800 N, 0.75 mm/s), and load to failure (0.75 mm/s). Motion, forces, plastic deformation of the plate, and consequent depression of the posterior joint facet were analyzed. Results: During cyclic loading, all plates with locked screws showed statistically significant lower displacement in the primary loading direction than the plates without locked screws. Mean values (mm) of maximal displacements for each plate during cyclic loading were as follows: Synthes, 3.5; Darco, 4.5; Newdeal, 5.0; Synthes without locked screws, 7.5; (p < 0.001). No statistically significant differences between the plates were found in relation to loads to failure and corresponding displacement. Conclusion: This is the first biomechanical study to assess the stability of different plates currently in use in our practice for the fixation of calcaneal fractures. Our results showed that plates with locked screws provided greater stability during cyclic loading than the plate without locked screws.

Intraoperative 3D imaging in calcaneal fracture care-clinical implications and decision making.

BACKGROUND In operative calcaneal fracture care malposition of screws and joint line incongruity frequently remain unrecognized using fluoroscopy intraoperatively, and are frequently only recognized on postoperative computed tomography scans. The purpose of this study was to analyze the feasibility and utility of a new C-arm-based three-dimensional imaging technology for calcaneal trauma care. METHODS The C-arm-based three- dimensional imaging device (ISO-C-3D) was used in 32 patients during a 2-year period. Patients were indicated for open reduction and internal fixation using standard techniques and fluoroscopy. After reduction and implant placement was determined to be correct, the ISO-C-3D procedure was performed. The time for setup and use, and the consequences were recorded. An assessment was obtained from the surgeon regarding the feasibility and the adequacy and quality of the data provided, using a Visual Analog Scale. RESULTS The average total time required for ISO-C-3D use was 610 seconds. The information obtained from the scan led the surgeon to alter the reduction or screw placement during the procedure in 41% of the patients. Surgeons rating according to a Visual Analog Scale: feasibility 9.5, accuracy and quality 9.2, clinical benefit 8.2. CONCLUSION Intraoperative three- dimensional visualization with the ISO-C-3D provides important information in the operative treatment of calcaneal fractures which cannot always be obtained from plain films or standard fluoroscopy alone. The use of the device adds minimal time to the overall procedure, and was found to be extremely useful in evaluating reduction and implant position intraoperatively in calcaneal fractures.

Computer-assisted fracture reduction of pelvic ring fractures: an in vitro study.

A newly developed software module for computer-assisted surgery based on a commercially available navigation system allows simultaneous, independent registration of two fragments and real-time navigation of both fragments while reduction occurs. To evaluate the accuracy three fracture models were used: geometric foam blocks, a pelvic ring injury with disruption of the symphysis and the sacroiliac joint, and a pelvic ring fracture with symphysis disruption and a transforaminal sacral fracture. One examiner did visual and navigated reduction and in all experiments the end point was defined as anatomic reduction. Residual displacement was measured with a magnetic motion tracking device. The results revealed a significantly increased residual displacement with navigated reduction compared with visual control. The differences were low, averaging 1 mm for residual translation and 0.7° for the residual rotation, respectively. Residual displacement was small in both set-ups and may not be clinically relevant. Additional development of the software prototype with integration of surface registration may lead to improved handling and facilitated multifragment tracking. Use in the clinical setting should be possible within a short time.

Navigated pedicle screw placement: Experimental comparison between CT- and 3D fluoroscopy-based techniques

Objective: Even with CT-based navigation, the misplacement rate for pedicle screws is reported to be as high as 10%. Using fluoroscopy-based 3D navigation, misplacement rates of 1.7 to 6% occur. The purpose of this study was to compare the accuracy of CT-based and Iso-C-based navigation in an experimental context. Methods: A foam spine model and the SurgiGATE® navigation system were used. First, a determination of point accuracy measured the difference between the real positions of markers placed on selected vertebrae and their positions as determined by the navigation system. In the verification mode, the pointer is placed exactly on the markers displayed on the monitor screen, and the deviation of the pointer tip and marker is measured in reality using a caliper. Secondly, pedicle accuracy was measured using pre-drilled holes for pedicle screws. A trajectory was planned into the visible hole and the navigated pointer was placed. Results: The measured accuracy for the markers showed a statistically significant difference between the results with CT and Iso-C navigation for one of six markers placed on the vertebra. Iso-C-based navigation demonstrated a lower mean deviation of 0.5 mm, compared to 1 mm with CT-based navigation. The deviation within the pre-drilled holes was lower when using the Iso-C3D scan. Using Iso-C3D navigation, 76.6% of the measurements showed no deviation at the entrance point, compared with 43% when using CT-based navigation. Also, with Iso-C3D navigation, 78.3% of the inserted pedicle awls hit the defined trajectories in the pre-drilled holes correctly, compared to 66.6% with CT-based navigation. Conclusion: The overall image-to-reality accuracy for CT- and Iso-C-based navigation was assessed in the described experimental setup. An apparent tendency towards higher accuracy with Iso-C-based navigation was evaluated; however, the differences were not significant.

Navigated percutaneous pelvic sacroiliac screw fixation: Experimental comparison of accuracy between fluoroscopy and Iso-C3D navigation

Percutaneous sacroiliac screw fixation is technically demanding and can result in complications mainly related to imaging problems. Furthermore, the conventional technique performed using fluoroscopic control is associated with a long radiation exposure. The purpose of this study was to evaluate the accuracy of two navigation technologies used in traumatology; fluoroscopy and Iso-C3D navigation. A total of 40 screws were placed (20 with Iso-C3D, 20 with 2D fluoroscopy) at levels S1 and S2. With both technologies, all S1 screws could be placed correctly, but four (10%) incorrect placements were seen at S2 with fluoroscopy navigation. With all Iso-C3D navigated drillings, no perforation was seen. Iso-C3D navigation therefore proved superior to 2D fluoroscopy navigation for sacroiliac screw fixation in an experimental set-up designed to assess accuracy.

Navigated Iso-C3D-based percutaneous osteoid osteoma resection: A preliminary clinical report

Minimally invasive osteoid osteoma resection under computer tomography (CT) guidance has yielded good results and has become a viable alternative to open surgical procedures. Limited visualization of the actual drill position under CT guidance can frequently result in inadequate and malpositioned drilling, especially at lesions located in less accessible anatomic regions. With the conventional CT-guided drilling technique, sterility and general operative management poorly correlate with standard operating room conditions, and are at risk of intra- and postoperative complications. The new Iso-C3D® imaging device provides intraoperative multiplanar reconstructions. Adequate image quality and implementation in navigation systems were described for numerous indications. On the basis of multiplanar reconstructions, minimally invasive navigated techniques under three-dimensional surgical tool control become possible, which is not the case under fluoroscopic or CT-based navigation. We report on our first three cases of navigated Iso-C3D® osteoid osteoma resection. A minimally invasive resection of the nidus was possible under permanent multiplanar image control. No complications were encountered and all patients reported successful outcomes. Minimally invasive-based navigation offered an effective and reproducible surgical approach. Dependence on CT imaging for proper positioning and complications associated with use away from the operating room environment can be avoided.

Intraoperative Pedography: A Validated Method for Static Intraoperative Biomechanical Assessment

Background: A new device was developed to perform intraoperative static pedography. The purpose of this study was to validate the introduced method by a comparison with the standard method for dynamic and static pedography. Methods: A device known as Kraftsimulator Intraoperative Pedographie® (KIOP®) was developed for intraoperative placement of standardized forces to the sole of the foot. Pedographic measurements were done with a custom-made mat that was inserted into the KIOP® (Pliance®, Novel Inc., St. Paul, MN, USA). Validation was done in two steps: (1) comparison of standard dynamic pedography walking on a platform, standard static pedography in standing on a platform, and pedography with KIOP® in supine position in 30 healthy volunteers, and (2) comparison of static pedography in standing position, pedography with KIOP® supine awake, and pedography with KIOP® supine with 30 patients under anesthesia. Individuals who had operative procedures at the knee or distal to the knee were excluded. The different measurements were compared (one-way ANOVA, t-test; significance level 0.05). Results: No significant differences were found among all measurements for the hindfoot compared to midfoot-forefoot force distribution. For the medial compared to lateral force distribution and the 10-region-mapping, significant differences were found when comparing all measurements (steps 1 and 2) and when comparing the measurements of step 1 only. No differences were found for these distributions when comparing the measurements of step 2 alone or when comparing the measurements of step 1 and 2 without the platform measurements of step 1 (dynamic walking pedography and static standing pedography). No significant differences in the force distributions were found in step 2 when comparing subjects without anesthesia, with general anesthesia, and with spinal anesthesia. Conclusions: The KIOP device allows a valid static intraoperative pedography measurement. No statistically significant force distribution differences were found between standing subjects and anesthetized subjects in the supine position.

Computer Assisted Pelvic Surgery: Registration Based on a Modified External Fixator

A fundamental step in Computer Assisted Surgery (CAS) is the registration, when the preoperative virtual data and the corresponding operative anatomy of the region of interest are merged. To provide exact landmarks for anatomical registration, a tubular external fixator was modified. Two intact pelvic bones (one artificial foam pelvis and one cadaver specimen) were used for the experimental setup. Registration was carried out using a standardized protocol for anatomy-based registration in the control group; anatomical registration was achieved using a modified external fixator in the study group. This external fixator had titanium fiducials wedged into the fixator carbon tubes serving as landmarks for paired-point registration. The tubes were used for surface registration. The standard anterior pelvis fixator assembly was augmented with additional bilateral tubes oriented towards the posterior, enabling registration of the sacroiliac areas. The accuracy of registration was checked by “reversed verification”, where the examiner used only the screen display to control the virtual position of the pointer tip in relation to selected landmarks. By virtual matching, the real distance was measured with a digital caliper. We defined the verification as “accurate” when the residual distance was less than 1 mm; “acceptable” when it was between 1 mm and 2 mm; and “insufficient” when it exceeded 2 mm. The paired T-test with significance levels of p < 0.05 was used for statistical analysis. The anatomical registration based on the external fixator landmarks was statistically as accurate as that obtained using anatomical landmarks on the pelvic bone. This study concludes that the external fixator, a conventional tool in the management of acute traumatic pelvic instability, can also be useful for landmark registration in CAS.

Comparative study of different intraoperative 3-D image intensifiers in orthopedic trauma care.

INTRODUCTION Recently, isocentric C-arm fluoroscopy (Iso-C 3D) has been introduced as a precise imaging modality for intraoperative evaluation and management of fractures and osteosyntheses. The Siemens Iso-C 3D collects multiple fluoroscopic images during a 190-degree arc of rotation around the anatomic region of interest and reconstructs them into sagittal, axial, and coronal planes. Like the Iso-C 3D, the new Ziehm Vario 3D imaging system reconstructs images in multiple planes, but only requires a 136-degree arc of rotation. The purpose of this study was to compare the image quality and range of applicability of these two imaging systems. METHODS All the tests were performed on a human cadaver. In the first part of the experiment, different bones and joints were scanned in their native condition using both the Iso-C 3D and Vario 3D. In the second part of the experiment, scans were performed in the same anatomic regions after simulated fractures and subsequent fixation. In some cases, suboptimal placement of hardware was intentionally undertaken. Direct visualization of the fracture construct and in certain cases computed tomographic (CT) imaging served as the gold standard. The scans from both imaging systems were analyzed using a DICOM viewer by five orthopedic trauma surgeons randomized and blinded to the study. The evaluation was based on the overall image quality, delineation of cancellous and cortical bone, delineation of joint surfaces, presence of artifacts, visualization quality of intra-articular incongruities, quality of reduction and implant positioning, and clinical applicability of the scan. These items were rated using a visual analog scale and a points system. A total of 55 3D scans were made and evaluated. RESULTS There was no significant difference between the two imaging systems in terms of the overall image quality, delineation of cancellous and cortical bone, and the presence of artifacts. The delineation of joint surfaces was significantly better visualized with the Iso-C 3D. Furthermore, Iso-C 3D scans demonstrated a higher overall clinical applicability than Vario 3D images. However, the Vario 3D was able to provide superior quality with scans of the shoulder joint and the adipose tissue. There was no significant difference in the visualization of intra-articular incongruities, quality of reduction, and implant positioning. CONCLUSION Although the Iso-C 3D imaging system was superior in delineating the joint surfaces, the image quality, and the overall clinical applicability, the study revealed that both devices provided 3D images with sufficient quality to the surgeon to assess clinically relevant questions, including the quality of fracture reduction and implant positioning. On the other hand, the Ziehm Vario 3D is capable of doing scans of the shoulder area, which could not be taken with the Siemens Iso-C 3D because of the isocentric design.

Differences in the mechanical properties of calcaneal artificial specimens, fresh frozen specimens, and embalmed specimens in experimental testing

Background. Artificial calcanei, fresh-frozen cadaver specimens, and embalmed cadaver specimens were compared in experimental testing under biocompatible loading to clarify the biocompatibility of artificial calcaneal specimens for implant testing. Methods. Two different artificial calcaneal bone models (Sawbone™, Pacific Research Laboratories, Vashon, WA, and Synbone™, Synbone Inc., Davos, Switzerland), embalmed cadaver calcaneal specimens (bone density, 313.1 ± 40.9 g/cm 2 age, 43.8 ± 7.9 years), and fresh-frozen cadaver calcanei (bone density, 238.5 ± 30.0 g/cm 2 age, 44.4 ± 8.2 years) were used for testing. Seven specimens of each model or cadaver type were tested. A mechanical testing machine (Zwick Inc., Ulm, Germany) was used for loading and measurements. Cyclic loading (preload 20 N, load was increased every 100 cycles by 100 N from 1,000 to 2,500 N, 0.5 mm/s) and load to failure (0.5 mm/s) were performed. The loads were applied through an artificial talus in a physiological loading direction. The displacement of the posterior facet in the primary loading direction was measured. Results. The four different specimen groups showed different stability and different displacement in the primary loading direction during cyclic loading. The variation of the maximal displacement in the primary loading direction for the entire cyclic loading was higher in artificial specimens than in the cadaver specimens. Conclusions. Artificial calcanei (Sawbone™, Synbone™) showed different biomechanical characteristics than cadaver bones (embalmed and fresh-frozen) in this experimental setup with biocompatible cyclic loading. These results do not support the use of artificial calcanei for biomechanical implant testing. Fresh-frozen and embalmed specimens seem to be equally adequate for mechanical testing. The low variation of mechanical strength in the unpaired cadaver specimens suggests that the use of paired specimens is not necessary.