D. C. Wirtz

Fluoroscopy-based 3-D reconstruction of femoral bone cement: a new approach for revision total hip replacement

In revision total hip replacement the removal of the distal femoral bone cement can be a time consuming and risky operation due to the difficulty in determining the three-dimensional (3-D) boundary of the cement. We present a new approach to reconstruct the bone cement volume by using just a small number of calibrated multiplanar X-ray images. The modular system design allows the surgeon to react intraoperatively to problems arising during the individual situation. When encountering problems during conventional cement removal, the system can be used on demand to acquire a few calibrated X-ray images. After a semi-automatic segmentation and 3-D reconstruction of the cement with a deformable model, the system guides the surgeon through a free-hand navigated or robot-assisted cement removal. The experimental evaluation using plastic test implants cemented into anatomic specimen of human femoral bone has shown the potential of this method with a maximal error of 1.2 mm (0.5 mm RMS) for the distal cement based on just 4-5 multiplanar X-ray images. A first test of the complete system, comparing the 3-D-reconstruction with a computed tompography data set, confirmed these results with a mean error about 1 mm.

Fluoroscopic navigation system for hip surface replacement

Metal-on-metal hip resurfacing arthroplasties represent an alternative to total hip arthroplasties for young and active patients, enabling the preservation of intact femoral bone and therefore improving the prognosis for future hip joint replacements. Follow-up studies have shown that the main reasons for early implant failure are mal-orientation of the implant stem in relation to the femoral neck axis, and notching of the femoral neck during femoral head preparation, as well as by exposed cancellous bone after implantation. A computer-assisted planning and navigation system for the implantation of femoral hip resurfacing implants has been developed which supports the surgeon during intraoperative fluoroscopy-based planning and navigation of implant positioning. This paper presents the results of a cadaver study performed to evaluate the systems functionality and accuracy.

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.

Funktionalität und Genauigkeit eines fluoroskopischen Navigationssystems zur Implantation von Hüftkopf-Oberflächenersatzprothesen: Eine Anatomiestudie

INTRODUCTION Resurfacing arthroplasty represents an alternative method to total hip replacement especially for the young and active patient. The main reasons for early implant failure are mal-positioning of the femoral component and notching of the femoral neck during femoral head preparation. MATERIAL AND METHODS In the context of a cadaver study of formalin-fixed cadaveric full body specimens 6 DUROM -Hip-Resurfacing prosthesis have been implanted under navigation control. The aim of the study was an evaluation of the functionality and accuracy of the computer-assisted planning and navigation system on the basis of a navigation module library from Surgitaix AG Aachen, Germany. RESULTS The main angulation error between planning (135.2 +/- 3.6 degrees ) and navigation (136.2 +/- 2.8 degrees ) was 1.9 +/- 1.1 degrees , the main anterior offset error between planning (2.2 +/- 1.3 mm) and navigation (2.7 +/- 2.3 mm) was 1.2 +/- 1.9 mm. The main distance error between planning and navigation was 2.7 +/- 1.3 mm. The mean time for all five planning and navigation steps was 20.2 +/- 2.5 min. Against the background of a acetabular bone-saving approach in all 6 cases the smallest possible femoral component could be implanted. CONCLUSION The computer-assisted fluoroscopic planning and navigation system for hip resurfacing showed within the scope of this cadaver study first promising results. The system approaches a practicable intraoperative planning with a high accuracy in operative implementation. Nevertheless, the potential benefit has to be evaluated in further clinical studies, especially from the perspective of a possible integration of this navigation system into the clinical work-flow. Further studies should consider a fluoroscopic-assisted range of motion assessment under consideration of an additional cup-module to enhance the postoperative range of motion after hip resurfacing procedures.

A-mode ultrasound-based intra-femoral bone cement detection and 3D reconstruction in RTHR

Due to the difficulty of determining the 3D boundary of the cement-bone interface in Revision Total Hip Replacement (RTHR), the removal of the distal intra-femoral bone cement can be a time-consuming and risky operation. Within the framework of computer- and robot-assisted cement removal, the principles and first results of an automatic detection and 3D surface reconstruction of the cement-bone boundary using A-mode ultrasound are described. Sound propagation time and attenuation of cement were determined considering different techniques for the preparation of bone cement, such as the use of a vacuum system (Optivac®, Biomet). A laboratory setup using a rotating, standard 5-MHz transducer was developed. The prototype enables scanning of bisected cement-prepared femur samples in a 90° rotation range along their rotation axis. For system evaluation ex vivo, the distal femur of a human cadaver was prepared with bone cement and drilled (Ø 10 mm) to simulate the prosthesis cavity in a first approximation. The sample was cut in half and CT scanned (0.24 mm resolution; 0.5 mm distance; 0.5 mm thickness), and 3D voxel models of the manually segmented bone cement were reconstructed, providing the ground truth. Afterwards, 90° segments of each ex-vivo sample were scanned by the A-mode ultrasound system. To obtain better ultrasound penetration, we used coded signal excitation and pulse compression filtering. A-mode ultrasound signal detection, filtering and segmentation were accomplished fully automatically. Subsequently, 3D voxel models of each sample were calculated. Accuracy evaluation of the measured ultrasound data was performed by ICP matching of each ultrasound dataset (∼8000 points) to the corresponding CT dataset and calculation of the residual median distance error between the corresponding datasets. Prior to each ICP matching, an initial pre-registration was calculated using prominent landmarks in the corresponding datasets. This method yielded a median distance error in the region of 0.25 mm for the cement-bone interface in both femur halves.

Mittelfristige Behandlungsergebnisse der posttraumatischen Alloarthroplastik des Kniegelenks beim geriatrischen Patienten

BACKGROUND Due to the increasing prevalence of elderly people in Germany, the number of geriatric fractures will continue to increase. Typical geriatric skeletal and physical changes are osteoporosis, arthrosis, and reduced ability of coordination. Altogether, these factors may lead to a failure of a performed osteosynthesis, or may make the classical fracture treatment of reduction and internal fixation appear to be impossible. The aim of this study was to examine the results of peri-knee fractures treated directly or within 3 months by implantation of a knee prosthesis. MATERIAL AND METHODS 15 geriatric patients could be identified who were treated in the described way in the last 4 years. The follow-up time was 39 months. The knee injury occurred in all cases after a banal trauma. RESULTS 14 patients could be examined by applying the HSS scoring system. We furthermore checked the operative management and postoperative course. The patients reached a good score level and showed few complications. CONCLUSION For elderly patients, the primary knee arthroplasty after periarticular fractures of the knee is a valid treatment option. Nevertheless, the surgeon has to identify those fractures which are impossible to treat by a classical osteosynthesis. Furthermore, the application of the appropriate knee prosthesis, regarding the degree of hinge constrainment or augmentation of the tibial or femoral bone stock, is important.

Computer-assisted optimization of correction osteotomies on lower extremities.

Automated methods are presented for the planning of correction osteotomies and osteosynthesis on lower extremities. Intraoperative calibrated X-ray images and kinematic measurements using optical tracking systems are the basis for the identification of the individual anatomy of the patient. The correction input of the surgeon, together with optimization algorithms, allows the calculation of the position and orientation of the osteotomies and the repositioning of the bone fragments. A navigation module supports the surgeon during the execution of osteotomies and repositioning, as well as osteosynthesis. So far, the approach has been evaluated in laboratory trials and ex vivo tests.

[Bilateral Dislocation Fracture of the Humeral Head (Right AO 11C3.3; Left AO 11A1.3) without Direct Trauma Due to First Clinical Manifestation of Seizure - a Case Report and Review of the Literature].

The incidence of fractures among epileptics is frequent and mostly occurs by direct trauma due to falls caused by seizures. The risk of fractures is estimated to be 50 % higher in epileptics than in the general population. Most of the fractures affect the proximal femora and the hip joint. Dorsal shoulder dislocations occur frequently in epileptics. If they occur bilaterally, this is pathognomonic for seizuring. Besides this, shoulder dislocation and bilateral dislocation fractures of the humeral head, however, are far more rare even among epileptics but pathognomonic for seizure. In this case report we present a female patient with bilateral dislocation fracture of the humeral head due to first clinical manifestation of a tonic-clonic seizure without direct trauma.

Evaluation of a 2D Fluoroscopy-Based Navigation System for Insertion of the Dynamic Hip Screw (DHS): an Experimental Study

Ziel: Die Osteosynthese der lateralen Schenkelhalsfraktur mit einer dynamischen Hüftschraube (DHS) ist ein standardisiertes Verfahren. Ziel dieser Studie war die Evaluation eines neuen computergestützten Fluoroskopie-basierten Planungsund Navigationssystems mit neuartiger integrierter strahlungsfreier Röntgenbildvorschau (sog. „Zero-Dose C-Arm-Navigation“), das den Operateur bei der Implantation der DHS unterstützt. Material und Methoden: Von einem Operateur wurden in 24 intakte Kunstknochen 12 DHS navigiert und 12 DHS in konventioneller Technik implantiert. Beide Verfahren wurden je 6×offen und 6×geschlossen angewandt. Ergebnisse: Die Auswertung zeigte im Vergleich zum konventionellen Vorgehen eine signifikante Reduktion der Anzahl der Röntgenbilder mithilfe des Navigationsmoduls sowohl in der offen (–8,1 ±0,5; p <0,001) als auch in der geschlossen (–12,3 ±3,7; p <0,001) operierten Gruppe. An K-Draht-Bohrungen wurde in den beiden navigierten Gruppen bei jeder Durchführung jeweils nur 1 Versuch benötigt. Die konventionellen Versuchsreihen benötigten beide signifikant mehr Bohrungen (offen: + 1,3 ± 1,2; p <0,05 – geschlossen: + 1,5 ± 1,2; p <0,05). Bezüglich der Präzision ergaben sich keine signifikanten Unterschiede. Im Vergleich zur konventionellen Technik verlängerte sich die OP-Zeit signifikant in der offen navigiert operierten Gruppe (+ 14,6 ±5,4min; p<0,001) als auch in der geschlossen navigiert operierten Gruppe (+ 13±3min; p <0,001). Schlussfolgerung: Das computergestützte fluoroskopische Planungsund Navigationssystem ermöglicht eine intraoperative Planung und sichere und reproduzierbare Umsetzung dieser Planung bei der Implantation der DHS. Vorteile sind die deutliche Reduktion der Strahlenbelastung und der Bohrungen bei gleich bleibender Präzision im Vergleich zum konventionellen Vorgehen. KriAbstract !

Korrektur einer posttraumatischen femoralen Beinverkürzung mit einem intramedullären Distraktionsmarknagel

AIM For the operative adjustment of a leg length shortening and for correcting an angular deformity, an external fixator is the most frequently used technique today. This method may, however, be complicated by painful soft tissue and muscle fixations, pin infections and psychic strain as well as by long treatment duration with the external fixator. The intramedullary skeletal kinetic distractor (ISKD) is an internal lengthening nail, which promises a postoperative course without further complications. METHOD We used the ISKD nail in a 28-year-old traumatised motorcyclist, in whom, after removal of a comminuted femur bone fragment, a leg length shortening of 8 cm resulted. RESULTS After uneventful healing of all fractures and having performed implant removal, we implanted an ISKD nail for femoral lengthening. The following distraction resulted, without considerable complications, in a complete compensation of the leg difference. CONCLUSIONS The ISKD nail is a suitable procedure to compensate for post-traumatic leg length differences, which exhibits, in contrast to the frequently used external fixator, a largely uncomplicated course. It cannot be used to correct a gross transverse or rotational deformity.