Computer-assisted guidewire insertion for hip fracture fixation

Results of femoral neck screw fixation in 112 under 65-years-old at a minimum 2 years' follow-up

INTRODUCTION

Failure rates for screw fixation in femoral neck fracture in young patients are often high, with risk of aseptic femoral head osteonecrosis and non-consolidation. The present study sought to identify factors for success or failure of internal fixation according to: 1) initial treatment; 2) initial reduction quality; and 3) population characteristics.

HYPOTHESIS

The study hypothesis was that population, fracture type, initial treatment and reduction quality can predict survival.

MATERIAL AND METHODS

A retrospective study included all cases of femoral neck fracture in under 65-years-old treated by screwing in our center: i.e., 112 patients. Patient characteristics, time to surgery were collated; surviving patients were followed up at a minimum 24 months. Reduction quality was assessed on X-rays in 3 dimensions and cervico-diaphyseal angle.

RESULTS

Mean follow-up was 5.3±3.0 years [range, 2.0-13.6 years]. At 2 years, 23 of the 112 patients (20.5%) had developed complications: 10 osteonecroses (8.9%) and 13 non-unions (11.6%). Known hip osteonecrosis risk factors showed no significant association with survival. Failure rates were significantly higher in unstable (Garden≥3) than stable (Garden≤2) fracture: HR=2.77 [95%CI: 1.09-7.02]; p=0.025. There was no significant association with time to treatment (≤6 hours): HR=1.08 [95%CI: 0.46-2.54]; p=0.86. On 2-year radiographs, mean shortening on the z-axis was 12.3±4.8mm [-0.7 to 26.2], 8.5±5.0mm [-6.8 to 23.9] on the x-axis, and 6.4±6.1mm [-6.3 to 25.3] on the y-axis. There was a significant negative correlation between z shortening and HOOS pain component (r=-0.38; p=0.005), a non-significant negative correlation with quality of life (r=-0.20; p=0.16), and a significant negative correlation with sports activity (r=-0.28; p=0.039).

CONCLUSION

The present series showed lower rates of complications and of arthroplasty than in the literature. Internal fixation seemed to be indicated even at an interval of 6 hours or more.

LEVEL OF EVIDENCE

IV, retrospective study.

Tissue Structure Updating for In Situ Augmented Reality Navigation Using Calibrated Ultrasound and Two-Level Surface Warping

OBJECTIVE

In minimally invasive surgery (MIS), in situ augmented reality (AR) navigation systems are usually implemented using a glasses-free 3D display to represent the preoperative tissue structure, and can provide intuitive see-through guidance information. However, due to changes in intraoperative tissue, the preoperative tissue structure is not able to exactly correspond to reality, which influences the precision of in situ AR navigation. To solve this problem, we propose a method to update the tissue structure for in situ AR navigation in such way to reflect changes in intraoperative tissue.

METHODS

The proposed method to update the tissue structure is based on the calibrated ultrasound and two-level surface warping technologies. Firstly, the particle filter-based calibration is implemented to perform ultrasound calibration and obtain intraoperative position of anatomical points. Secondly, intraoperative positions of anatomical points are inputted in the two-level surface warping method to update the preoperative tissue structure. Finally, the glasses-free real 3-D display of the updated tissue structure is finished, and is superimposed onto a patient by a translucent mirror for in situ AR navigation.

RESULTS

we validated the proposed method by simulating liver tissue intervention, and achieved the tissue updating accuracy of 92.86%. Furthermore, the targeting error of AR navigation based on the proposed method was also evaluated through minimally invasive liver surgery, and the acquired mean targeting error was 1.92 mm.

CONCLUSION

The results demonstrate that the proposed AR navigation method is effective.

SIGNIFICANCE

The proposed method can facilitate MIS, as it provides accurate 3D navigation.

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

OBJECTIVE

Accurate insertion of a guidewire under image intensifier guidance is a fundamental skill required by orthopaedic surgeons. This study investigated how image intensifier distortion, which is composed of pin-cushion and sigmoidal components, changed the apparent trajectory of a guidewire, and the resulting deviation between the intended and actual guidewire tip position.

MATERIALS AND METHODS

Intraoperative image intensifier images for 220 consecutive patients with hip fractures were retrospectively corrected for distortion using a global polynomial method. The deviation between the intended and actual guidewire tip positions was calculated. Additional distortion parameters were tested using an image intensifier produced by a different manufacturer, and a flat-panel c-arm.

RESULTS

Deviation was approximately 1 cm if the guidewire was aimed from the extremity of the image and almost 0 if the entry point was only 20% from the centre (p < 0.001). The direction of deviation was different for left and right hips, with average deviations measuring 3 mm proximal and 5 mm distal respectively (p < 0.001). The flat-panel c-arm almost completely eliminated distortion.

CONCLUSIONS

Image intensifier distortion significantly altered the intended trajectory of a guidewire, with guidewires aimed from the image periphery more affected than guidewires aimed from the centre. Furthermore, for right hips, guidewires should be aimed distal to their intended position, and for left hips they should be aimed proximal to achieve their desired position. The flat-panel c-arm eliminated the effect of distortion; hence, it may be preferable if precision in guidewire positioning is vital.

2D projection-based software application for mobile C-arms optimises wire placement in the proximal femur - An experimental study

PURPOSE

A new software application can be used without fixed reference markers or a registration process in wire placement. The aim was to compare placement of Kirschner wires (K-wires) into the proximal femur with the software application versus the conventional method without guiding. As study hypothesis, we assumed less placement attempts, shorter procedure time and shorter fluoroscopy time using the software. The same precision inside a proximal femur bone model using the software application was premised.

METHODS

The software detects a K-wire within the 2D fluoroscopic image. By evaluating its direction and tip location, it superimposes a trajectory on the image, visualizing the intended direction of the K-wire. The K-wire was positioned in 20 artificial bones with the use of software by one surgeon; 20 bones served as conventional controls. A brass thumb tack was placed into the femoral head and its tip targeted with the wire. Number of placement attempts, duration of the procedure, duration of fluoroscopy time and distance to the target in a postoperative 3D scan were recorded.

RESULTS

Compared with the conventional method, use of the application showed fewer attempts for optimal wire placement (p=0.026), shorter duration of surgery (p=0.004), shorter fluoroscopy time (p=0.024) and higher precision (p=0.018). Final wire position was achieved in the first attempt in 17 out of 20 cases with the software and in 9 out of 20 cases with the conventional method.

CONCLUSIONS

The study hypothesis was confirmed. The new application optimised the process of K-wire placement in the proximal femur in an artificial bone model while also improving precision. Benefits lie especially in the reduction of placement attempts and reduction of fluoroscopy time under the aspect of radiation protection. The software runs on a conventional image intensifier and can therefore be easily integrated into the daily surgical routine.

Patient-specific core decompression surgery for early-stage ischemic necrosis of the femoral head

Introduction

Core decompression is an efficient treatment for early stage ischemic necrosis of the femoral head. In conventional procedures, the pre-operative X-ray only shows one plane of the ischemic area, which often results in inaccurate drilling. This paper introduces a new method that uses computer-assisted technology and rapid prototyping to enhance drilling accuracy during core decompression surgeries and presents a validation study of cadaveric tests.

Methods

Twelve cadaveric human femurs were used to simulate early-stage ischemic necrosis. The core decompression target at the anterolateral femoral head was simulated using an embedded glass ball (target). Three positioning Kirschner wires were drilled into the top and bottom of the large rotor. The specimen was then subjected to computed tomography (CT). A CT image of the specimen was imported into the Mimics software to construct a three-dimensional model including the target. The best core decompression channel was then designed using the 3D model. A navigational template for the specimen was designed using the Pro/E software and manufactured by rapid prototyping technology to guide the drilling channel. The specimen-specific navigation template was installed on the specimen using positioning Kirschner wires. Drilling was performed using a guide needle through the guiding hole on the templates. The distance between the end point of the guide needle and the target was measured to validate the patient-specific surgical accuracy.

Results

The average distance between the tip of the guide needle drilled through the guiding template and the target was 1.92±0.071 mm.

Conclusions

Core decompression using a computer-rapid prototyping template is a reliable and accurate technique that could provide a new method of precision decompression for early-stage ischemic necrosis.

Enhanced cephalomedullary nail lag screw placement and intraoperative tip-apex distance measurement with a novel computer assisted surgery system

OBJECTIVE

The goal of this study was to evaluate the ability of a novel computer assisted surgery system to guide ideal placement of a lag screw during cephalomedullary nailing and then accurately measure the tip-apex distance (TAD) measurement intraoperatively.

DESIGN

Retrospective case review.

SETTING

Level II trauma hospital.

PATIENTS

The initial 98 consecutive clinical cases treated with a cephalomedullary nail in conjunction with a novel computer assisted surgery system were retrospectively reviewed.

INTERVENTION

A novel computer assisted surgery system was utilized to enhance lag screw placement during cephalomedullary nailing procedures. The computer assisted surgery system calculates the TAD intraoperatively after final lag screw placement.

MAIN OUTCOME MEASURES

The ideal TAD was considered to be within a range of 5mm-20mm. The ability of the computer assisted surgery system (CASS) to assist in placement of a lag screw within the ideal TAD was evaluated. Intraoperative TAD measurements provided by the computer assisted surgery system were then compared to standard postoperative TAD measurements on PACS (picture archiving and communication system) images to determine whether these measurements are equivalent.

RESULTS

79 cases (80.6%) were available with complete information for a retrospective review. All cases had CASS TAD and PACS TAD measurements >5mm and<20mm. In addition, no significant difference could be detected between the intraoperative CASS TAD and the postoperative PACS TAD (p=0.374, Wilcoxon Test; p=0.174, paired T-Test). A cut-out rate of 0% was observed in all patients who were treated with CASS in this case series (95% CI: 0 - 3.01%).

CONCLUSIONS

The novel computer assisted surgery system tested here is an effective and reliable adjunct that can be utilized for optimal lag screw placement in cephalomedullary nailing procedures. The computer assisted surgery system provides an accurate intraoperative TAD measurement that is equivalent to the standard postoperative measurement utilizing PACS images.

LEVEL OF EVIDENCE

Therapeutic Level IV.

A motion compensation method for bi-plane robot-assisted internal fixation surgery of a femur neck fracture

Bi-plane robots have been widely applied in clinical use to place cannulated screws for internal fixation surgery of femur neck fractures, which is performed precisely and automatically using two online fluoroscopic images. However, the setup procedure of the bi-plane robot is empirical, and physicians usually have to re-run the setup procedure, exposing the patient to high doses of radiation in clinical applications. In this article, a motion compensation method is proposed by a novel use of the binocular vision principle to improve the bi-plane robot setup using two doses of radiation within 2 min. The entry point, exit point, and angle errors of the three-dimensional trajectory reconstruction are 1.23 ± 0.39 mm, 1.49 ± 0.49 mm, and 0.33° ± 0.23°, respectively. The motion compensation method significantly reduces the dose of radiation and the operation time of the setup procedure and has acceptable accuracy.

Accuracy of the surgeon's eye: use of the tip-apex distance in clinical practice

Tip-apex distance is a well described method for assessment of screw placement in dynamic hip screw fixation of proximal femoral fracture. A distance of <25mm is associated with a significantly lower rate of cut out of the fixation device. Measurement is frequently performed retrospectively, although there has been no demonstration as to what accuracy the surgeon has of estimating tip-apex distance from image intensifier images, whilst scrubbed in theatre. Thirty-one clinicians working within orthopaedic departments were tested in their ability to identify adequacy of tip-apex distance on a series of image intensifier images. Level of seniority, awareness of the concept of tip-apex distance and use of the concept in clinical practice were each assessed. The accuracy in identifying the correct TAD was 82.5% in consultants, 83.8% in registrars and 71.1% in Senior house officers (SHO). The method was used in clinical practice by 50% of consultants, 89% of registrars and none of the SHOs.

Accuracy of the lesser trochanter for guiding lag screw insertion in hip fracture management

The goal of this study was to evaluate the accuracy of the lesser trochanter for entry of lag screw placement in the fixation of hip fractures. Radiographs of the pelvis with both hips in 50 Chinese patients were analyzed to determine the accuracy of using the lesser trochanter as a reference landmark for inserting lag screws. The femoral neck was divided into 4 parts, and the second distal part was classified as the safe zone. Cobb angles of 125° and 130° were used as representative lag screw insertion angles, referencing the lateral cortex of the lesser trochanter for measurement, and insertion tracks were drawn on the neck of the femur. The accuracy of lag screw placement in the defined safe zone was evaluated. Accuracy of placement in the safe zone for entry points at the superior tip, apex, and inferior tip of the lesser trochanter were 78%, 39%, and 0%, respectively, for the 125° Cobb angle. Rates for the superior tip, apex, and inferior tip of the lesser trochanter were 31%, 74%, and 6%, respectively, for the 130° Cobb angle. The entry point at the level of the inferior tip of the lesser trochanter had incidence rates of 95% and 71% for cutout for 125° and 130° screws, respectively. The authors found that the superior tip of the lesser trochanter was a good reference point for 125° lag screw insertion and that the apex of the lesser trochanter was a good reference point for 130° lag screw insertion. Entry at the level of the inferior tip of the lesser trochanter has a very high rate of cutout and should be avoided.

Volume rendering of three-dimensional fluoroscopic images for percutaneous scaphoid fixation: an in vitro study

Percutaneous fixation of scaphoid fractures offers potential advantages to cast treatment but can be difficult to perform with conventional two-dimensional imaging. This study aimed to evaluate the use of a novel navigation technique using volume-rendered images derived from intraoperative cone-beam computed tomography imaging, without the need for typical patient-based registration. Randomized in vitro trials in which a guidewire was inserted into a scaphoid model were conducted to compare volumetric navigation to conventional fluoroscopic C-arm (n = 24). Central wire placement, surface breach, procedure time, drilling attempts, and radiation exposure were compared between groups. Compared to conventional percutaneous insertion, navigation achieved equal or significantly better placement of the guidewire with fewer drilling attempts and less radiation exposure. On average, navigation took 74 s longer to perform than the conventional method, which was statistically significant but clinically irrelevant. This evaluation suggests that the technology is promising and may have many clinical benefits including improved fixation placement, fewer complications, and less radiation exposure. The intraoperative workflow is more efficient and eliminates the need for preoperative computed tomography, image segmentation, and patient-based registration typical of traditional navigated procedures.

Training femoral neck screw insertion skills to surgical trainees: computer-assisted surgery versus conventional fluoroscopic technique

BACKGROUND

: Femoral neck fractures are among the most common orthopaedic injuries impacting the health care system. Surgical management of such fractures with cannulated screws is a commonly performed procedure. The acquisition of surgical skills necessary to perform this procedure typically involves learning on real patients with fluoroscopic guidance. This study attempts to determine if a novel computer-navigated training model improves the learning of this basic surgical skill.

METHODS

A multicenter, prospective, randomized, and controlled study was conducted using surgical trainees with no prior experience in surgically managing femoral neck fractures. After a training session, participants underwent a pretest by performing the surgical task (screw placement) on a simulated hip fracture using fluoroscopic guidance. Immediately after, participants were randomized into either undergoing a training session using conventional fluoroscopy or computer-based navigation. Immediate posttest, retention (4 weeks later), and transfer tests were performed. Performance during the tests was determined by radiographic analysis of hardware placement.

RESULTS

Screw placement by trainees was ultimately equal to the level of an expert surgeon with either training technique. Participants who trained with computer navigation took fewer attempts to position hardware and used less fluoroscopy time than those trained with fluoroscopy. When those trained with fluoroscopy used computer navigation at the transfer test, less fluoroscopy time and dosage was used. The concurrent augmented feedback provided by computer navigation did not affect the learning of this basic surgical skill in surgical novices. No compromise in learning occurred if the surgical novice trained with one type of technology and transferred to using the other.

CONCLUSIONS

The findings of this study suggest that computer navigation may be safely used to train surgical novices in a basic procedure. This model avoids using both live patients and harmful radiation without a compromise in the acquisition of a 3-dimensional technical skill.

Accuracy study of new computer-assisted orthopedic surgery software

PURPOSE

The new computerized system is based on image analysis and designed to aid in orthopedic surgeries by virtual trajectory of the guide wire, intra-operative planning and various measurements. Validation of the accuracy and safety of any computer-aided surgery system is essential before implementing it clinically. We examined the accuracy of guide-wire length and angle measurements and fusion of multiple adjacent images (panoramic view image, PVI(®)) of the new software.

METHODS

This is a 2-part study. Part I: twenty guide wires were drilled to various depths in a synthetic femur model and the results obtained by the software measurements were compared with manual measurements by a caliper and a depth gauge. Part II: a sawbone femur shaft was osteotomized and various inclinations of > 10° to the varus or valgus angles were tested. The manually obtained measurements of angles and lengths were compared to the new computerized system software PVI.

RESULTS

There was a significant positive linear correlation between all groups of the computerized length and the control measurements (r>0.983, p<0.01). There was no significant difference among different distances, angles or positions from the image intensifier. There was a significant positive linear correlation between the angle and length measurement on the PVI and the control measurement (r>0.993, p<0.01).

CONCLUSIONS

The new computerized software has high reliability in performing measurements of length using an aiming, positioning and referring device intra-operatively.

Three-dimensional computer-assisted navigation for the placement of cannulated hip screws. A pilot study

PURPOSE

Medial femoral neck fractures are common, and closed reduction and internal fixation by three cannulated screws is an accepted method for the surgical treatment. Computer navigation for screw placement may reduce fluoroscopy time, the number of guidewire passes and optimise screw placement.

METHODS

In the context of a sawbone study, a computer-assisted planning and navigation system based on 3D-imaging for guidewire placement in the femoral neck was tested to improve screw placement. Three screws were inserted into 12, intact, femoral sawbones using the conventional technique and into 12, intact, femoral sawbones guided by the computer-based navigation system. Guidewire and subsequent screw placement in the femoral neck were evaluated.

RESULTS

Use of the navigation system resulted in a significant reduction of the number of drilling attempts (p≤0.05) and achieved optimised accuracy of implant placement by attaining significantly better screw parallelism (p≤0.05) and significantly enlarged neck-width coverage by the three screws (p≤0.0001). Computer assistance significantly increased the number of fluoroscopic images (p≤0.001) and the operation time (p≤0.0001).

CONCLUSIONS

Three-dimensional computer-assisted navigation improves accuracy of cannulated screw placement in femoral neck while increasing the number of fluoroscopic images and operation time. Additional studies including fractured sawbones and cadaver models with the goal of reducing operation time are indispensable before introduction of this navigation system into clinical practice.

Femoral neck shortening and varus collapse after navigated fixation of intracapsular femoral neck fractures

OBJECTIVE

Assessing femoral neck shortening (FNS) and varus collapse after internal fixation of femoral neck fractures using computerized navigation (CN).

DESIGN

Retrospective cohort study.

SETTINGS

Academic Level I trauma center.

PATIENTS AND METHODS

Forty-one patients who had healed femoral neck fractures treated with CN between the years 2003 and 2008. Average age was 65 years (range, 14-91 years). Thirty-six patients had nondisplaced fractures and five had displaced fractures.

INTERVENTION

Screws were placed using CN in an inverted triangle formation Follow-up films were digitized into a PACS system, calibrated, and analyzed using CAD software.

OUTCOME MEASURES

The following parameters were recorded: abductor lever arm shortening (termed x), corresponding vertical femur shortening (termed y), and the resultant femoral neck shortening vector (z). Fifteen patients were available for clinical outcome measures by the means of SF-12 survey

RESULTS

Significant FNS of the x component (greater than 5 mm) occurred in 30 of 42 (71%) patients with severe shortening (greater than 10 mm) in 25% of the patients. Significant y shortening occurred in 43% of the patients and severe shortening in 17%. Overall (z) femoral neck shortening occurred in 56% of the patients with severe shortening in 22% of patients. Varus collapse (greater than 5°) did not occur in any patient. Screw pullout (greater than 5 mm) occurred in 17 (41%) patients. Seven patients required late (greater than 6 months) arthroplasty postoperatively. FNS did not significantly correlate with fracture type, quality of reduction, age, or neck shaft angle. SF-12 results were negatively correlated with overall FNS.

CONCLUSIONS

Our results show a high degree of FNS associated with the use of CN for fixation of femoral neck fractures, similar to recently published series using nonnavigated implants. However, no varus collapse occurred in our series. Our preliminary clinical data show a trend toward an adverse effect of FNS on quality-of-life measures.

Evaluation of a new computer-assisted surgical planning and navigation system based on two-dimensional fluoroscopy for insertion of a proximal femoral nail: an experimental study

Pertrochanteric femoral fractures are common and intramedullary nailing is an accepted method for their surgical treatment. Accurate placement of the implant is essential to ensure fixation. The conventional technique can require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on two-dimensional fluoroscopy for guide wire placement in the femoral neck has been developed, in order to perform intramedullary pertrochanteric fracture fixation using the proximal femoral nail (PFNA). The planning process was supported by a 'zero-dose C-arm navigation' system. The PFNA was inserted into 12, intact, femoral sawbones guided by the computer-based navigation, and into 12, intact, femoral sawbones using a conventional fluoroscopic-assisted technique. Guide wire and subsequent blade placement in the femoral neck was evaluated. The computer-assisted technique achieved a significant decrease in the number of required fluoroscopic images and in the number of guide wire passes. The obtained average blade placement accuracy in the femoral neck was equivalent to the conventional technique. The operation time was significantly longer in the navigation-assisted group. The addition of computer-assisted planning and surgical guidance to the intramedullary nailing of pertrochanteric femoral fractures offers a number of clinical benefits based on the results of this sawbone study. Further studies including fractured sawbones and cadaver models with extension of the navigation process to all steps of PFNA introduction and with the goal of reducing operation time are indispensable before integration of this navigation system into clinical practice.

Volume slicing of cone-beam computed tomography images for navigation of percutaneous scaphoid fixation

PURPOSE

Percutaneous scaphoid fixation (PSF) is growing in popularity as a treatment option for non-displaced fractures. Success of this procedure demands high-precision screw placement, which can be difficult to achieve with standard 2D imaging. This study aimed to develop and test a system for computer-assisted navigation using volume slicing of 3D cone-beam computed tomography (CBCT).

METHODS

The navigated technique involved a distinctive workflow in which a 3D CBCT imager was calibrated preoperatively, circumventing the need for intraoperative patient-based registration. Intraoperatively, a 3D CBCT image was acquired for both preoperative planning and direct navigation using volume-rendered slices. An in vitro study was conducted to compare the navigated approach to two conventional fluoroscopic methods for volar PSF. The surgical goal was to insert a guide wire to maximize both length and central placement.

RESULTS

There was no significant difference in the mean central placement of guide wire, although the variance in central placement was significantly lower using VS navigation (P < 0.01). The lengths of the drill paths were significantly longer for the VS-navigated group compared with one 2D group (P < 0.1). Each navigated trial required only one drilling attempt and resulted in less radiation exposure than conventional C-arm (P < 0.01).

CONCLUSIONS

Volume-sliced navigation achieved a more repeatable and reliable central pin placement, with fewer drilling attempts than conventional 2D techniques. Volume-sliced navigation had a higher number of drill paths within the optimal zone maximizing both length of the path and depth from the surface.

Evaluation of a fluoroscopy-based navigation system enabling a virtual radiation-free preview of X-ray images for placement of cannulated hip screws. A cadaver study

Accurate placement of cannulated screws is essential to ensure fixation of medial femoral neck fractures. The conventional technique may require multiple guide wire passes, and relies heavily on fluoroscopy. A computer-assisted planning and navigation system based on 2D fluoroscopy for guide wire placement in the femoral neck has been developed to improve screw placement. The planning process was supported by a tool that enables a virtual radiation-free preview of X-ray images. This is called "zero-dose C-arm navigation". For the evaluation of the system, six formalin-fixed cadaveric full-body specimens (12 femurs) were used. The evaluation demonstrated the feasibility of fluoroscopically navigated guide wire and implant placement. Use of the novel system resulted in a significant reduction in the number of fluoroscopic images and drilling attempts while achieving optimized accuracy by attaining better screw parallelism and enlarged neck-width coverage. Operation time was significantly longer in the navigation assisted group. The system has yielded promising initial results; however, additional studies using fractured bone models and with extension of the navigation process to track two bone fragments must be performed before integration of this navigation system into the clinical workflow is possible, and these studies should focus on reducing the operation time.

[Evaluation of a 2D fluoroscopy-based navigation system for insertion of femoral neck screws. An experimental study]

INTRODUCTION

The aim of this study was the evaluation of a new computer-assisted planning and navigation system based on 2D-fluoroscopy for guidewire insertion in order to perform cannulated screw placement into the femoral neck. The image acquisition process was supported by a radiation-saving procedure called Zero-dose C-arm navigation.

MATERIAL AND METHODS

In the context of a sawbone study, we performed insertion of 3 cannulated screws positioned under navigation control as well as using the conventional technique in 12 sawbones. Both procedures were performed using open and closed techniques.

RESULTS

The computer-assisted technique significantly reduced the amount of intraoperative fluoroscopic images (open technique: -14±3 images, closed technique: -29.4±6 images). Drilling attempts were reduced in the computer-assisted groups (open technique: -1.2±1 attempts, closed technique: -1.7±1.5 attempts) and the femoral neck area covered by the screws was greater in the navigation-assisted groups (open technique: +32.1±16.3 mm(2), closed technique: +32.6±14.9 mm(2)), There was no difference concerning parallelism of the screws or perforation of femoral neck or head. The operation time was significantly longer in the navigation-assisted groups (open technique: +24.2±2.1 min, closed technique: +22.8±5.8 min).

CONCLUSION

The addition of computer-assisted planning and surgical guidance supported by Zero-dose C-arm navigation can be useful for the fixation of medial femoral neck fractures with cannulated screws. Further studies with the goal of reducing the operation time are indispensable before integrating this navigation system into the clinical workflow.

Reconstruction interlocking nails for ipsilateral femoral neck and shaft fractures: biomechanical analysis of effect of supplementary cannulated screw on intracapsular femoral neck fracture

BACKGROUND

To stabilize the femoral head in ipsilateral femoral neck and shaft fractures, one cannulated screw was supplemented in front of the reconstruction interlocking nail (recon nail).

METHODS

Twenty-eight left sawbone femurs were divided into two groups. The 14 femurs in each group were osteotomized with subcapital or transcervical fractures. The shafts of all femurs were also osteotomized, and 1cm of the distal segmental cortex was excised. Next, all the fractures were treated with static recon nails to concomitantly stabilize both femoral neck and shaft fractures. Additionally, seven subcapital fractures and seven transcervical fractures were supplemented with one cannulated screw in front of the recon nails. All specimens were tested with a Material Testing System machine to investigate the relative stability during uniaxial cyclic compression.

FINDINGS

The subcapital and transcervical fractures supplemented with one cannulated screw could bear more loads than those without screw supplementation (P<0.01 and P<0.01, respectively at any testing interval). Moreover, in the case of the subcapital fractures, the single supplemented cannulated screw could reduce the displacement at 500 N by 24% (P< 0.001). On the other hand, in the case of the transcervical fractures, one supplemented cannulated screw could reduce the displacement at 500 N by 4% (P=0.003).

INTERPRETATION

From the biomechanical viewpoint, the subcapital fractures in combined fractures are recommended to supplement with one cannulated screw in front of the recon nails to eliminate complications associated with stabilization.

Error analysis of marker-based object localization using a single-plane XRII

The role of imaging and image guidance is increasing in surgery and therapy, including treatment planning and follow-up. Fluoroscopy is used for two-dimensional (2D) guidance or localization; however, many procedures would benefit from three-dimensional (3D) guidance or localization. Three-dimensional computed tomography (CT) using a C-arm mounted x-ray image intensifier (XRII) can provide high-quality 3D images; however, patient dose and the required acquisition time restrict the number of 3D images that can be obtained. C-arm based 3D CT is therefore limited in applications for x-ray based image guidance or dynamic evaluations. 2D-3D model-based registration, using a single-plane 2D digital radiographic system, does allow for rapid 3D localization. It is our goal to investigate-over a clinically practical range-the impact of x-ray exposure on the resulting range of 3D localization precision. In this paper it is assumed that the tracked instrument incorporates a rigidly attached 3D object with a known configuration of markers. A 2D image is obtained by a digital fluoroscopic x-ray system and corrected for XRII distortions (+/- 0.035 mm) and mechanical C-arm shift (+/- 0.080 mm). A least-square projection-Procrustes analysis is then used to calculate the 3D position using the measured 2D marker locations. The effect of x-ray exposure on the precision of 2D marker localization and on 3D object localization was investigated using numerical simulations and x-ray experiments. The results show a nearly linear relationship between 2D marker localization precision and the 3D localization precision. However, a significant amplification of error, nonuniformly distributed among the three major axes, occurs, and that is demonstrated. To obtain a 3D localization error of less than +/- 1.0 mm for an object with 20 mm marker spacing, the 2D localization precision must be better than +/- 0.07 mm. This requirement was met for all investigated nominal x-ray exposures at 28 cm FOV, and for all but the lowest two at 40 cm FOV. However, even for those two nominal exposures, the expected 3D localization error is less than +/- 1.2 mm. The tracking precision was +/- 0.65 mm for the out-of-plane translations, +/- 0.05 mm for in-plane translations, and +/- 0.05 degrees for the rotations. The root mean square (RMS) difference between the true and projection-Procrustes calculated location was 1.07 mm. It is believed these results show the potential of this technique for dynamic evaluations or real-time image guidance using a single x-ray source and XRII detector.

Robot-assisted femoral fracture reduction: preliminary study in patients and healthy volunteers

We developed a robot-assisted fracture reduction system (FRAC-Robo) to assist anatomical reduction and to maintain reduction during internal fixation while recording the procedure in a log. We conducted two experiments before using FRAC-Robo clinically. In the first experiment using the FRAC-Robo system, we measured the maximum force and torque required to pull and rotate the limbs of healthy conscious volunteers until they felt pain or abnormality. The average maximum traction force applied to the lower limb was 250.7 N, and the average maximum torque was 5.6 Nm in internal rotation and 7.6 Nm in external rotation for 30 degrees of abduction of hip. In the second experiment, we measured the traction force and rotation torque during the reduction of proximal femoral fractures. The average traction force and rotation torque needed for reduction were 215.9 N and 3.2 Nm, respectively. On the basis of these results, we consider that FRAC-Robo can generate sufficient force and torque to reduce femoral fractures safely.

Correction of lag screw guide pins inappropriately placed during intramedullary hip nailing

INTRODUCTION

Lag screw position is one of the most important controllable factors in trochanteric fracture fixation. However, it is sometimes difficult to handle the lag screw guide pin during intramedullary hip nailing. In this study, causes of guide pin shift and correction of malposition were investigated.

METHODS

The movements of guide pins during fracture fixation were traced fluoroscopically using 35 embalmed, mainly anteverted femora, angles were measured in the anteroposterior and lateral planes and necessary corrections calculated.

RESULTS

In the proximal anteverted femur, posterior correction of an inappropriately placed guide pin in the lateral plane led to an inferior shift in the anteroposterior fluoroscopic view, and vice versa. Mean anteversion, alpha, beta, and beta' angles were 13.1 degrees (5-29 degrees ), 10.9 degrees (4-18 degrees ), 4.6 degrees (0-10 degrees ) and 4.4 degrees (0-9 degrees ), respectively. The beta' angle was directly proportional to the anteversion angle only, i.e. Y=0.27X+0.65 (R(2)=0.79), p<0.001.

CONCLUSIONS

In the proximal anteverted femur, guide pin shift in the anteroposterior fluoroscopic view occurred during correction of pin position in the lateral plane. The amount of shift was directly related to the amount of anteversion.

Fracture-table-mounted versus bone-mounted dynamic reference frame tracking accuracy using computer-assisted orthopaedic surgery--a comparative study

OBJECTIVE

Fluoroscopy-based computerized navigation systems enable accurate implant placement while reducing radiation exposure. The navigation process normally requires the attachment of a dynamic reference frame (DRF) to a bone, causing additional surgical trauma. The aim of this study was to compare the accuracy of navigation with the DRF either attached to the bone or mounted on the fracture table.

METHODS

We conducted a prospective study on 10 consecutive patients who underwent operative fixation of femoral neck fractures with cannulated screws using computerized navigation. After insertion of the three guide wires, the DRF was moved from the patient's bone to the fracture table. For each screw, angular and translational deviations of the navigated images as compared to the conventional fluoroscopic images were analyzed.

RESULTS

The accuracy of navigated Kirschner wire placement was similar with both techniques, resulting in an average translational error of less than 2 mm in both groups and around 1 degrees in angulation error--both of these accuracy measurements are acceptable and sufficient for the insertion of cannulated screws into the femoral head.

CONCLUSION

Our study suggests that attaching the DRF to a fracture table during navigated femoral neck fixation allows for acceptable accuracy with the possible added benefit of reducing patient morbidity.

Safety of computer-assisted surgery for cannulated hip screws

Computer-assisted orthopaedic surgery has developed considerably during the past few years. Several manufacturers produce hardware and software for use in trauma surgery. Validation of these systems before clinical application is mandatory to be sure they work accurately and safely. The accuracy of surgical performance is highly correlated with the cut-out percentages of hip screws. In a standardized operative setting, three cannulated hip screws were inserted in each of 20 sawbones. The screws were positioned either by fluoroscopic navigation technique or by conventional operative technique depending on randomization. Our primary aim was to assess whether computer-navigated screw fixation is equally safe compared with conventional screw fixation using fluoroscopy. To determine safety, we investigated number of drilling attempts, screw position, and radiation time. Secondary to these safety parameters, we also compared the operating time between the two procedures to assess the efficiency of computer navigation. Statistical analysis showed no differences regarding accuracy of screw position. Computer-assisted surgery resulted in fewer drilling attempts and less radiation time, with a similar operation time. We believe the currently used navigation system is safe and accurate.

Computerized navigation for the internal fixation of femoral neck fractures

BACKGROUND

Accurate placement of cannulated screws is essential to ensure secure fixation of femoral neck fractures. We compared computerized navigation and conventional fluoroscopy with regard to the accuracy of screw placement for the fixation of femoral neck fractures.

METHODS

We retrospectively compared two groups of twenty consecutive patients with a femoral neck fracture who underwent internal fixation with three cannulated screws. Computer-based navigation was used to guide screw placement in one group, and conventional fluoroscopy was used in the other group. Radiographic evaluation included the measurement of screw parallelism and spread, the calibrated distance from the lesser trochanter, and joint penetration. The follow-up period was two years. The rates of complications in both groups were evaluated.

RESULTS

The navigation-assisted group had better screw parallelism and greater spread of the screws. There was a tendency for fewer reoperations and significantly fewer overall complications in the patients in whom computerized navigation was used (p < 0.018).

CONCLUSIONS

Computerized navigation improves the accuracy of cannulated screw placement in the internal fixation of femoral neck fractures. It may provide better mechanical stability and improved fracture outcome.