Cadaver validation of intensity-based ultrasound to CT registration.

A method is presented for the rigid registration of tracked B-mode ultrasound images to a CT volume of a femur and pelvis. This registration can allow tracked surgical instruments to be aligned with the CT image or an associated preoperative plan. Our method is fully automatic and requires no manual segmentation of either the ultrasound images or the CT volume. The parameter which is directly related to the speed of sound through tissue has also been included in the registration optimisation process. Experiments have been carried out on six cadaveric femurs and three cadaveric pelves. Registration results were compared with a "gold standard" registration acquired using bone implanted fiducial markers. Results show the registration method to be accurate, on average, to 1.6 mm root-mean-square target registration error.

Radiation dose for pedicle screw insertion. Fluoroscopic method versus computer-assisted surgery.

STUDY DESIGN: Comparison of the radiation dose between the traditional fluoroscopic approach and computed tomography (CT)-based computer-assisted surgery for pedicle screw placement was determined. OBJECTIVES: To evaluate the radiation dose delivered by fluoroscopy-controlled pedicle screw placement versus insertion guided by computer. To define the CT computer-assisted protocol, involving lower radiation exposure for the patient, that still provides acceptable image quality. SUMMARY OF BACKGROUND DATA: There are no published data describing the dose delivered in CT-based image-guided surgery, and there are few studies in which the organ dose and the effective dose delivered during pedicle screw insertion that is performed traditionally with fluoroscopic control are described. METHODS: Dose measurements were performed on two types (REMAB and RANDO) of anthropomorphic phantoms. Thermoluminescent dosimeters were used to measure the organ dose. Both phantoms were exposed to the fluoroscopic x-ray beam. The representative intraoperative scenario was determined by observation of 20 consecutive surgical interventions featuring pedicle screw implantation. For the CT dose measurement only, the REMAB phantom was used with two types of CT scanners. Three scanning protocols were evaluated: sequential, spiral optimized, and sequential optimized. Optimization of the scanning protocol included changes of anode current. The CT images were subsequently processed to achieve three-dimensional reconstruction of the lumbar spine for the computer-assisted intervention. RESULTS: Organ and effective doses were higher in any of the CT examinations than in the fluoroscopic procedure. There was a slight difference between doses registered during optimized spiral scanning and doses in the calculated optimized sequential CT protocol. Optimized sequential scanning was associated with an effective dose 40% lower than that in nonoptimized sequential scanning. The small anatomic structures of the spine could be easily recognized on each of the three-dimensional reconstructions, and all of them were suitable for use in computer-assisted surgery. CONCLUSIONS: Percutaneous pedicle screw insertion in the lumbar region of the spine, performed using fluoroscopic control, requires a lower radiation dose than do CT scans necessary for computer-assisted surgery. The CT radiation dose can be significantly decreased by optimization of the scanner settings for computer-assisted surgery. The advantages of computer-assisted surgery justify CT scans, when based on correctly chosen indications.

Evaluation of accuracy in ankle center location for tibial mechanical axis identification.

Many surgical computer-assisted systems use mechanical axis identification as a reference for their computations. The goal of this study was to compare three methods to determine the location of the distal point of the tibial mechanical axis, based on percutaneous digitization of definite anatomical landmarks. In particular, we evaluated the accuracy of the identified tibial mechanical axis and the repeatability of the obtained results. Tests performed by four surgeons on cadaveric knees showed that the variability in identifying the ankle center using two out of the three methods presented introduced an inaccuracy in the mechanical axis identification of around 1 degrees. This makes their use suitable for computer-assisted systems.

Novel computer-assisted fluoroscopy system for intraoperative guidance: feasibility study for distal locking of femoral nails.

OBJECTIVES: Orthopaedic procedures that use fluoroscopy require intraoperative mental navigation of the surgical tools in a three-dimensional space. Moreover, because of their reliance on real-time monitoring, such procedures are frequently associated with increased x-ray exposure. The goal of this study was to develop a computer-guided surgical navigation system based on fluoroscopic images that not only facilitates direction of surgical tools within anatomy, but also provides constant feedback without the need for radiologic updates. To evaluate the feasibility of the new technology, the authors used it on cases requiring distal locking of femoral nails. METHODS: The hardware components of the system include an instrumented C-arm, optoelectronic position sensor, stereotactic tools, and custom-made software. Computer integration of these devices permitted C-arm alignment assistance and real-time navigation control without constant x-ray exposure. The nails were locked in a variety of media, including plastic femurs, dry human femoral specimens, human cadavers, and one clinical case. Unreamed femoral nail sizes ranged from 9/340 to 12/400. Radiographs were taken to confirm that screws were positioned correctly, and fluoroscopic time associated with the locking procedure was recorded. RESULTS: All distal holes were locked successfully. In eight (11 percent) of seventy-six holes, the drill bit touched the canal of the locking hole, albeit with no damage to the nail and no clinical consequences. The fluoroscopy time per pair of screws was 1.67 seconds. CONCLUSIONS: The developed system enables the physician to precisely navigate surgical instruments throughout the anatomy using just a few computer-calibrated radiographic images. The total radiation time per procedure can be significantly reduced because additional x-ray exposure is not required for tool navigation.

Three-dimensional measurement of cemented femoral stem stability: an in vitro cadaver study.

OBJECTIVE: To compare the in vitro stability of two cemented hip stem designs: Stem I was a collarless, double-tapered, highly polished implant; Stem II had a collar and matt finish. BACKGROUND: Stability of the femoral component of a hip implant is important for its long-term clinical success. Excessive migration or cyclic motion can increase the risk of early implant failure. METHODS: The stems were implanted in paired human cadaver femurs, and custom-designed micromotion sensors were used to measure three-dimensional motions of the stems at proximal, middle and distal locations during simulated in vivo loading cycles. RESULTS: This study found that despite 'rigid' fixation, cemented stems exhibit detectable motions under a limited number of cycles of simulated physiologic loads. At four times the donor body weight, Stem I showed a subsidence of 90 microm, compared to 25 microm of Stem II (P<0.05). In contrast, the proximal end of Stem II exhibited greater cyclic motions in the medial-lateral direction (P<0.05). CONCLUSIONS: The different motion patterns could be due to the design differences, such as surface finish and geometry. RelevanceImplant design is an important factor related to the behavior of the cement/bone interface and the overall success of the implant. This study compares in vitro micromotion of two cemented femoral prostheses with differing proximal designs.

Fluoroscopy as an imaging means for computer-assisted surgical navigation.

OBJECTIVE: Intraoperative fluoroscopy is a valuable tool for visualizing underlying bone and surgical tool positions in orthopedic procedures. Disadvantages of this technology include the need for continued radiation exposure for visual control, and cumbersome means of alignment. The purpose of this article was to highlight a new concept for a computer-assisted freehand navigation system that uses single intraoperatively acquired fluoroscopic images as a basis for real-time navigation of surgical tools. MATERIALS AND METHODS: Optoelectronic markers are placed on surgical tools, a patient reference, and the fluoroscope to track their position in space. Projection properties of the fluoroscope are acquired through an initial precalibration procedure using a tracked radiopaque phantom grid. Corrections are applied to compensate for both the fluoroscope's image intensifier distortions and the mechanical bending of the C-arm frame. This enables real-time simulation of surgical tool positions simultaneously in several single-shot fluoroscopic images. In addition, through optoelectronically tracked digitization of a target viewpoint, the fluoroscope can be numerically aligned at precise angles relative to the patient without any X-ray exposure. RESULTS: This article shows the feasibility of this technology through its use in cadaver trials to perform the difficult task of distal locking of femoral nails.

Computer-assisted fluoroscopy-based reduction of femoral fractures and antetorsion correction.

OBJECTIVE: Intra-operative fluoroscopy is a valuable tool for visualizing underlying bone, implant, and surgical tool positions in orthopedics. It has brought about the minimally invasive surgical technique of intramedullar nailing to fix femoral shaft fractures. However, the limited field of view and two-dimensional property of fluoroscopic images aggravate intra-operative control of surgical parameters. The purpose of this article is to introduce a surgical navigation system based on fluoroscopy that provides missing information for the procedure of femoral fracture fixation. MATERIALS AND METHODS: Optoelectronic markers are placed on a surgical drill, involved bone fragments, the femoral nail, and the fluoroscope to track their positions. Projection properties of the fluoroscope are acquired through an initial precalibration. The relative positions of bone fragments, implants, and surgical tools are displayed superimposed simultaneously and in real time on multi-planar intra-operative fluoroscopic images. This is achieved by computer simulation of X-ray projections that have taken place with acquisition of the fluoroscopic images. In addition, a method has been developed that allows contactless measurement of three-dimensional anatomic landmarks, based on their representation in fluoroscopic images. In combination with optoelectronic tracking, this enables dynamic calculation of important surgical parameters such as femoral antetorsion. RESULTS: A pilot surgery showed that fracture reduction can benefit from the developed computer-assisted method. An in-vitro study on computer-assisted measurement of femoral antetorsion demonstrated the high degree of precision of this technique.

Assessment of 3-dimensional magnetic resonance imaging fast low angle shot images for computer assisted spinal surgery.

The objective of this research was to determine whether a fast 3-dimensional (3-D) gradient echo magnetic resonance imaging (MRI) sequence could be used to acquire images suitable for image guided surgery of the spine. The main difficulty with MRI is that inhomogeneities in the static magnetic field lead to geometric distortions in the images. We used a very fast 3-D MRI sequence with a wide bandwidth and short echo time (TE) to minimize these distortions. Fiducial markers that could be localized in MRI and computed tomography (CT) images and in physical space were attached to a phantom in order to assess the accuracy of a landmark based registration method. The effect of varying the MRI parameters on image contrast was also investigated. The results demonstrate that the registration can be undertaken with an accuracy of 0.4 mm using the 3-D MRI. This is comparable to the accuracy of 0.3 mm obtained with CT and is a significant improvement over the accuracy of the 2-D MRI techniques (> 1.0 mm). In vivo images demonstrating good contrast between the spine and surrounding soft tissues such as fat, intervertebral disks, and cerebrospinal fluid were obtained. The MRI acquired using the sequence described in this article shows promise for use in computer assisted surgery of the spine.

The relationship of the orientation of the transverse acetabular ligament and acetabular labrum to the suggested safe zones of cup positioning in total hip arthroplasty.

BACKGROUND: There is a need to develop and validate a method for establishing cup orientation that is patient specific and independent of the anterior pelvic plane. It is our hypothesis that the transverse acetabular ligament and acetabular labrum can be used to do this. The objective of this study is to define the orientation of the plane formed by the transverse acetabular ligament and acetabular labrum and to examine whether these local landmarks lie within the limits of acceptance for cup positioning. METHODS: Twenty-five consecutive patients, who were being investigated for labral tears with a MRI arthrogram of the hip, were enrolled in this prospective study. The orientation of the transverse acetabular ligament-labrum plane was determined by manually selecting points on the transverse acetabular ligament and labrum. The best-fit plane through these points was determined and its operative orientation expressed with respect to a constructed pelvic coordinate system. RESULTS: The operative anteversion of the transverse acetabular ligament-labrum plane ranged from 5.3-36.1 inverted exclamation mark (mean 23.0 inverted exclamation mark + or - 7.4 inverted exclamation mark standard deviation). The inclination ranged from 38.4-50.3 inverted exclamation mark (mean 45.6 inverted exclamation mark + or - 3.2 inverted exclamation mark standard deviation). CONCLUSIONS: The transverse acetabular ligament and acetabular labrum offer a possible solution to the many difficulties involved in cup placement during total hip arthroplasty. This paper highlights the variation in the orientation of these local acetabular landmarks and questions the logic of a set target for cup positioning.

A radical approach to minimally invasive total hip replacement: surgical technique and pre-clinical test data.

Currently total hip replacement surgery using minimally invasive techniques is a fast developing field. However, all reports concern adaptations of surgical techniques with adapted instruments using conventional implants. These conventional implants limit the minimal invasiveness to some extent. In this paper a new system is reported featuring a new surgical approach, new instrumentation and a new implant design. The purpose of this study was to introduce the system and to assess the feasibility of the system in terms of stability, range of motion and wear characteristics. The pre-clinical tests indicated that the factor of safety for this type of design is smaller than for conventional implants. However, the results show adequate performance of the system, which suggests that further development and testing is justified to advance the system for clinical use.

[Digital method of assessing bone radiographs]. / Metoda cyfrowej oceny radiogramów kosci.

The computerized method of bone radiographs assessment has been presented. The radiographs were taken by standard technique with the aluminum wedge on the film and known exposition parameters as energy, time and the distance between the source and the subject. Specially designed software served to evaluate the intensity of film darkening. The method may be particularly useful for quantitative assessment of the callus in the healing phase of fractured bone. It may also be an alternative method (as cheaper one) to QCT or DPX in bone density evaluation in patients with metabolic bone diseases.

Computer modeling of the pathomechanics of spastic hip dislocation in children.

Spastic muscles about the hip cause subluxation, dislocation, and lead to acetabular dysplasia. Spastic hip disease occurs when the muscles about the hip exert forces that are too high or in the wrong direction or both. To determine the role of the hip forces in the progression of spastic hip disease and the effect of both muscle-lengthening and bony reconstructive surgeries, a computerized mathematical model of a spastic hip joint was created. The magnitude and direction of the forces of spastic hips undergoing surgery were analyzed preoperatively and postoperatively to determine which procedure is best suited for the treatment of spastic hip disease. The muscle-lengthening procedures included (a) the adductor longus, (b) the psoas, iliacus, gracilis, adductor brevis, and adductor longus, and (3) the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus. The bony reconstructive and muscle-lengthening procedures included (a) lengthening the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus combined with changing femoral neck anteversion from 45 to 10 degrees , (b) lengthening of the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus combined with changing neck-shaft angle from 165 to 135 degrees , and (c) lengthening of the psoas, iliacus, gracilis, adductor brevis, adductor longus, semimembranosus, and semitendinosus combined with changing femoral neck anteversion from 45 to 10 degrees and neck-shaft angle from 165 to 135 degrees . Results show that a child with spastic hip disease has a hip-force magnitude 3 times that of the a child with a normal hip in the normal physiologic position. Based on this mathematical model the best to normalize the magnitude of the hip-joint reaction force, the muscles to be lengthened should include the psoas, iliacus, gracilis, adductor brevis, and the adductor longus. To normalize the direction of the hip force, the extremity should be positioned in the normal physiologic position. The impact of decreasing the femoral anteversion or femoral neck-shaft angle or both had little additional effect on the direction or magnitude of hip forces.

[The method of computer-assisted orthopedic surgery based on two-dimensional fluoroscopy: the principles of action]. / Metoda komputerowego wspomagania zabiegów ortopedycznych wykorzystujaca dwuwymiarowe obrazy fluoroskopowe--zasada dzialania.

Surgical instruments play a major role in orthopedic surgery; usually they are controlled visually at the operation. In certain situations additional device to control instrument is needed. The aim of this paper is to present theoretical foundations, create prototype and give initial assessment of computer assisted orthopedic surgery system. Two-dimensional fluoroscopy was the base for system functioning. Lab tests and first applications in the operating room are presented. Precision of the system found allows for its use in orthopedic surgery with television monitoring.

Acetabular volume.

Reconstructive acetabular osteotomies can affect the acetabular volume. Volume mismatch between the femoral head and the acetabulum should be an important consideration but is rarely evaluated before hip reconstruction. Accurate measurement of the volume of the acetabulum is difficult because of the unusual shape and spatial orientation of the acetabulum. In this study, we used three techniques (physical, two-dimensional computed tomography, and three-dimensional computed tomography reconstruction) to determine the volume of 18 pig, four sheep, and 15 model acetabulae. A comparison of pre- and post-Pemberton osteotomy volumes of three dysplastic acetabulae models and two patients with developmental dysplasia of the hip also was performed. The results indicate that accurate, reproducible volume determinations can be made by using all three techniques, and that certain data-selection modes can reduce the patient's exposure to radiation. In addition, we observed an increase in the volume of the acetabulum after the Pemberton osteotomy.

A new approach to computer-aided spine surgery: fluoroscopy-based surgical navigation.

A new computer-based navigation system for spinal surgery has been designed. This was achieved by combining intraoperative fluoroscopy-based imaging using conventional C-arm technology with free-hand surgical navigation principles. Modules were developed to automate digital X-ray image registration. This is in contrast to existing computed tomography- (CT) based spinal navigation systems, which require a vertebra-based registration procedure. Cross-referencing of the image intensifier with the surgical object allows the real-time image-interactive navigation of surgical tools based on one single registered X-ray image, with no further image updates. Furthermore, the system allows the acquisition and real-time use of multiple registered images, which provides an advanced multi-directional control (pseudo 3D) during surgical action. Stereotactic instruments and graphical user interfaces for image-interactive transpedicular screw insertion have been developed. A detailed validation of the system was performed in the laboratory setting and throughout an early clinical trial including eight patients in two spine centers. Based on the resulting data, the new technique promises improved accuracy and safety in open and percutaneous spinal surgery.