Peter Messmer

Comparison of different registration methods for surgical navigation in cranio-maxillofacial surgery

BACKGROUND Surgical navigation requires registration of the pre-operative image dataset with the patient in the operation theatre. Various marker and marker-free registration techniques are available, each bearing an individual level of precision and clinical practicability. In this study the precision of four different registration methods in a maxillofacial surgical setting is analyzed. MATERIALS AND METHODS A synthetic full size human skull model was registered with its computer tomography-dataset using (a) a dentally mounted occlusal splint, (b) the laser surface scanning, (c) five facial bone implants and (d) a combination of dental splint and two orbital bone implants. The target registration error was computed for 170 landmarks spread over the entire viscero- and neurocranium in 10 repeats using the VectorVision2 (BrainLAB AG, Heimstetten, Germany) navigation system. Statistical and graphical analyses were performed by anatomical region. RESULTS An average precision of 1mm was found for the periorbital region irrespective of registration method (range 0.6-1.1mm). Beyond the mid-face, precision linearly decreases with the distance from the reference markers. The combination of splint with two orbital bone markers significantly improved precision from 1.3 to 0.8mm (p<0.001) on the viscerocranium and 2.3-1.2mm (p<0.001) on the neurocranium. CONCLUSIONS An occlusal splint alone yields poor precision for navigation beyond the mid-face. The precision can be increased by combining an occlusal splint with just two bone implants inserted percutaneously on the lateral orbital rim of each side.

Internal Fixation of Unstable Proximal Humerus Fractures With an Anatomically Preshaped Interlocking Plate: A Clinical and Radiologic Evaluation

BACKGROUND We evaluated the outcome after internal fixation of unstable or displaced proximal humerus fractures with a new fixed-angle implant. METHODS Prospective consecutive study with a 1-year clinical follow-up in 119 of 137 patients (87%; mean 68 +/- 15 years; 31 two-, 47 three-, and 41 four-part fractures). RESULTS One year postoperatively, the range of motion of the injured side demonstrated on average four-fifths of the function of the contralateral side. Ninety-five percentage of patients (n = 114) could dress themselves independently with no or only slight restriction. The mean disabilities of the arm, shoulder, and hand score was 21 (range, 0-62). The absolute and relative Constant score significantly (p < 0.001) improved from 56 +/- 18 (75% +/- 21%) at 6 months postoperatively to up to 65 +/- 18 (82% +/- 18%) at 12 months postoperatively. The initial fracture configuration did not have a significant influence on clinical outcome or complications. Twenty-six patients (22%) underwent a reintervention because of a clinical problem or subjective complaint, which led to total or relevant relief of problems in 23 patients (87%). Radiologic follow-up revealed a significant correction of the mean fragment angles (p < 0.001) postoperatively compared with initial postcrash radiographs. The precision of intraoperative reduction had a significant impact on the patients disabilities of the arm, shoulder, and hand scoring (p = 0.02). A comparison of the last evaluable radiographs with the intraoperative intensifier images revealed a mean loss of reduction over time of </=2 degrees. CONCLUSIONS The angular stability of the fixed-angle interlocking plate could be proven radiologically in this clinical series. This fixation system seems to be a promising alternative in the treatment of displaced or unstable proximal humerus fractures. Clinical outcome can be further improved by avoiding certain minor errors in operative technique.

Fluoroscopic guidance versus surgical navigation for distal locking of intramedullary implants a prospective, controlled clinical study

A prospective controlled clinical study was performed to compare fluoroscopic guidance with fluoroscopy-based surgical navigation for distal locking of intramedullary implants. Forty-two patients with fractures of the lower extremity treated by intramedullary nailing were divided in two groups: distal locking either with fluoroscopic guidance (group I) or with surgical navigation (group II). The average fluoroscopic time to insert one interlocking screw with fluoroscopic guidance was 108 s compared with 7.3s in the navigation group. The average procedure time to insert one interlocking screw in group I was 13.7 min compared with 17.9 min in group II. The drill bit failed to pass through the interlocking hole in one patient from group II. There was no significant difference in the technical reliability between both groups. Fluoroscopic times to achieve equivalent precision are reduced with fluoroscopy-based surgical navigation compared with fluoroscopic guidance. Fluoroscopy-based surgical navigation is recommended for intraoperative guidance in situations where reduction of exposure to radiation is considered advantageous over the increase of procedure time.

Chronic post-traumatic osteomyelitis of the lower extremity: comparison of magnetic resonance imaging and combined bone scintigraphy/immunoscintigraphy with radiolabelled monoclonal antigranulocyte antibodies

Abstract Objective. A retrospective study of the validity of combined bone scintigraphy (BS) and immunoscintigraphy (IS) using 99mTc-labelled murine antigranulocyte antibodies (MAB) and magnetic resonance imaging (MRI) in chronic post- traumatic osteomyelitis. Design and patients. The results of MRI and combined BS/IS of 19 lesions in 18 patients (13 men, 5 women; mean age 45 years, range 27–65 years) were independently evaluated by two radiologists and one nuclear medicine physician with regard to bone infection activity and extent. The patient group was a highly selective collection of clinical cases: the average number of operations conducted because of relapsing infection was eight (range 2–27), the average time interval between the last surgical intervention and the present study was 6.5 years (range 3 months to 39 years), and from the first operation was 14 years (range 1.5–42 years). Interobserver agreement on MRI was measured by kappa statistics. Sensitivity, specificity, accuracy, positive predictive value (PPV) and negative predictive value (NPV) were calculated for MRI and the nuclear medicine studies. Results. For MRI/nuclear medicine, a sensitivity of 100%/77%, a specificity of 60%/50%, an accuracy of 79%/61%, a PPV of 69%/58% and a NPV of 100%/71% were calculated. Four MR examinations were false positives because of postsurgical granulation tissue. A high degree of interobserver agreement was found on MRI (κ=0.88). A low-grade infection was missed on two scintigrams, while four were false positive because of ectopic haematopoietic bone marrow, and in one examination the anatomical distortion resulted in an inaccurate assignment of the uptake leading to false positive findings. Image analysis was frequently hindered by susceptibility artefacts due to residual abrasions of metallic implants after removal of orthopaedic devices (15/18 patients); this led to limited assessment in 17% (3/18 patients). Conclusion. Acute activity in a chronic osteomyelitis can be excluded with high probability if the MRI findings are negative. In the first postoperative year fibrovascular scar cannot be distinguished accurately from reactivated infection on MRI and scintigraphy may improve the accuracy of diagnosis. MRI is more sensitive in low-grade infection during the later course than combined BS/IS. Scintigraphic errors due to ectopic, peripheral, haematopoietic bone marrow can be corrected by MRI.

Posterior pelvic ring fractures: Closed reduction and percutaneous CT-guided sacroiliac screw fixation

PurposeTo assess the midterm results of closed reduction and percutaneous fixation (CRPF) with computed tomography (CT)-guided sacroiliac screw fixation in longitudinal posterior pelvic ring fractures.MethodsThirteen patients with 15 fractures were treated. Eleven patients received a unilateral, two a bilateral, screw fixation. Twenty-seven screws were implanted. Continuous on-table traction was used in six cases. Mean radiological follow-up was 13 months.ResultsTwenty-five (93%) screws were placed correctly. There was no impingement of screws on neurovascular structures. Union occurred in 12 (80%), delayed union in 2 (13%), and nonunion in 1 of 15 (7%) fractures. There was one screw breakage and two axial dislocations.ConclusionSacroiliac CRPF of longitudinal fractures of the posterior pelvic ring is technically simple, minimally invasive, well localized, and stable. It should be done by an interventional/surgical team. CT is an excellent guiding modality. Closed reduction may be a problem and succeeds best when performed as early as possible.

A whole-body registration-free navigation system for image-guided surgery and interventional radiology.

RATIONALE AND OBJECTIVES To develop and test an image-guided navigation system in which the base of reference is taken from the imaging modality, here, a helical CT scanner. METHODS An optical digitizer together with a calibration device is used to measure the transformation matrix between the digitizer reference system and a CT reference system. During intervention, it tracks radiological and surgical tools with tool references. A specific software visually integrates the current tool position with the corresponding image information. In vitro accuracy tests were performed. RESULTS With helical CT, freehand positioning accuracy was 1.9 +/- 1.1 mm (mean +/- SD) in vitro (n = 718). CONCLUSIONS The navigation system developed by the authors appears to be feasible for radiological interventions as well as for minimally invasive surgery. It is not limited to a certain procedure, can be used in every region of the body, and is functional after imaging. Intraprocedural scans can be integrated immediately.

A faster method for 3D/2D medical image registration—a simulation study

3D/2D patient-to-computed-tomography (CT) registration is a method to determine a transformation that maps two coordinate systems by comparing a projection image rendered from CT to a real projection image. Iterative variation of the CTs position between rendering steps finally leads to exact registration. Applications include exact patient positioning in radiation therapy, calibration of surgical robots, and pose estimation in computer-aided surgery. One of the problems associated with 3D/2D registration is the fact that finding a registration includes solving a minimization problem in six degrees of freedom (dof) in motion. This results in considerable time requirements since for each iteration step at least one volume rendering has to be computed. We show that by choosing an appropriate world coordinate system and by applying a 2D/2D registration method in each iteration step, the number of iterations can be grossly reduced from n6 to n5. Here, n is the number of discrete variations around a given coordinate. Depending on the configuration of the optimization algorithm, this reduces the total number of iterations necessary to at least 1/3 of its original value. The method was implemented and extensively tested on simulated x-ray images of a tibia, a pelvis and a skull base. When using one projective image and a discrete full parameter space search for solving the optimization problem, average accuracy was found to be 1.0 +/- 0.6(degrees) and 4.1 +/- 1.9 (mm) for a registration in six parameters, and 1.0 +/- 0.7(degrees) and 4.2 +/- 1.6 (mm) when using the 5 + 1 dof method described in this paper. Time requirements were reduced by a factor 3.1. We conclude that this hardware-independent optimization of 3D/2D registration is a step towards increasing the acceptance of this promising method for a wide number of clinical applications.

A CT Database for Research, Development and Education: Concept and Potential

Both in radiology and in surgery, numerous applications are emerging that enable 3D visualization of data from various imaging modalities. In clinical practice, the patients images are analyzed on work stations in the Radiology Department. For specific preclinical and educational applications, however, data from single patients are insufficient. Instead, similar scans from a number of individuals within a collective must be compiled. The definition of standardized acquisition procedures and archiving formats are prerequisite for subsequent analysis of multiple data sets.Focusing on bone morphology, we describe our concept of a computer database of 3D human bone models obtained from computed tomography (CT) scans. We further discuss and illustrate deployment areas ranging from prosthesis design, over virtual operation simulation up to 3D anatomy atlases. The database of 3D bone models described in this work, created and maintained by the AO Development Institute, may be accessible to research institutes on request.

Protrusion of hardware impairs forearm rotation after olecranon fixation. A report of two cases.

Tension-band wire fixation is a common surgical technique that is used in the treatment of olecranon fractures and during osteotomies1-3. A number of problems that are specifically related to the use of Kirschner wires have been identified, including wire migration, skin ulceration, and the need for hardware removal4-6. We found only one published article that described diminished forearm rotation following the use of the tension-band technique7. Fig. 1 A patient with impaired forearm rotation after tension-band wire fixation of an olecranon osteotomy. A: The true lateral radiograph shows no evidence of undue penetration of the Kirschner wires into the soft tissues (arrow). B: Kirschner-wire protrusion (arrow) as seen in the three-dimensional model derived from the computed tomography scan. Impingement of the wires with the soft tissues is highly probable. We observed several instances of limitation of forearm rotation following tension-band wire fixation of the olecranon at our medical center (Division of Trauma Surgery, University Hospital of Zurich). Hence, we evaluated computed tomography scans of these patients and developed a computational simulation model with use of three-dimensional computed tomography reconstruction of the elbow. Unlike other authors who studied cadaver elbows3,6-9, we employed a virtual three-dimensional bone model to demonstrate the anatomy of the proximal aspect of the ulna and to simulate Kirschner-wire placement. One hundred and seventeen consecutive patients (seventy-one men and forty-six women) who had undergone internal fixation of the olecranon between April 2003 and November 2004 were retrospectively analyzed. The average age of the patients was 52.1 years (range, twenty-five to eighty-eight years). Of the 117 patients, forty-one underwent osteotomy of the olecranon for exposure of an intra-articular fracture of the distal aspect of the humerus and seventy-six had fixation of an olecranon fracture. The …

Image Fusion for Intraoperative Control of Axis in Long Bone Fracture Treatment

Background:The incidence of malalignment after long bone fracture fixation is reported to be between 0 and 37%. Modern fracture treatment strives towards closed reduction and minimally invasive fracture fixation, thus not exposing the fracture itself. Hence, the occurrence of malalignment might even be higher than previously reported and quite frequently even necessitate secondary operations. Minimally invasive techniques rely heavily on intraoperative fluoroscopy. However, fluoroscopic images have small cross-sections and consequently limit intraoperative visualization of the limb to individual segments only. Under these circumstances, correct alignment of fragments in long bone fractures is often compromised.Methods:We present a new software prototype using an absolute reference panel to concatenate two or more discontinuous fluoroscopic images into one single panoramic picture. The reference panel is placed on the operating table under the limb to be examined. Prior to digital picture fusion, the software applies non-linear distortion, picture scaling and de-rotation algorithms to the fluoroscopic images.Results:The presented software runs on a notebook and processes images generated by a commercially available mobile C-arm within seconds. The reliability of alignment in the panorama picture is found to be numerically adequate and the technique appropriate for clinical use.Conclusion:This method aims to improve the intraoperative visualization in minimally invasive osteosynthesis and therefore diminish malalignments in long bone fracture treatment.