Biomechanical aspects of lower limb torsional deformation correction with the Ilizarov external fixator.

The correction of torsional deformities with the Ilizarov apparatus is accompanied by rotational and translational displacement, which affects the biomechanics of the bone fragments. Understanding the biomechanical factors will assist in designing the optimal treatment strategy and mechanical properties of the fixator, thus shortening the duration of treatment and improving the outcomes. In order to determine the impact of different types of derotators on the kinematics of bone fragments in Ilizarov apparatus, physical models were studied. Translational and derotational displacement was measured using non-contact method (Optotrak Certus Motion Capture System). The results of the studies conducted on physical models have shown that regardless of the type of the derotator, the divergence between the applied angle of derotation and the obtained angle of rotation relative to fragments needs to be taken into account. Transverse displacement of fragments occur by 3.5 mm to approximately 9 mm, depending on the angle of derotation. For correction of rotational deformities up to 30°, it is advisable to use the type Z derotators because of its higher accuracy of derotation. Different types of derotators can affect the biomechanical conditions in the regenerating bone tissue through different kinematics characteristics.

Clinical requirements for an ultrasound-based tool navigator for minimally interventional procedures.

BACKGROUND: The past years showed a considerable progress in the development of imaging and navigation systems to support minimal-invasive surgery. However, these methods do not always meet actual clinical requirements of surgeons. They often cause technical and logistic efforts and considerable costs. Purpose of our study was the development of a navigation system relying on simple, familiar and cheaper components. It is based on two-dimensional ultrasound visualization, is quickly applicable to a wide range of minimal-invasive interventions, and is easily to be learned. MATERIAL/METHODS: The imaging system is composed of widely used, well-accepted components and relies only upon conventional two-dimensional sonography using a navigated ultrasound probe, a navigated surgical instrument, and a coordinate tracker, combined with new custom-made navigation software. Accuracy tests were performed, possible error sources were mentioned and the easy and safe handling of this system was demonstrated. RESULTS: Our custom-made software integrates information about the three-dimensional position of an instrument into a two-dimensional ultrasonic image. On-screen navigation aids are offered to reach a sonographically depicted target structure. These navigation aids are easily to be learned and make the use of this system very comfortable. The system shows a mean three-dimensional error of only 0.9+/-0.2 mm. CONCLUSIONS: Our navigation system combines several advantages: as to visualization, it relies solely on the familiar two-dimensional ultrasound image, its use is easy, it is more economic than comparable ultrasound navigation systems, and it can be used in a wide range of minimal-invasive interventions.

Development of prototype for navigated real-time sonography for the head and neck region.

BACKGROUND: To date, few imaging methods have been established for the head and neck region, in particular for soft tissues, that allow adequate visualization and simultaneously adequate real-time orientation. METHODS: We report a new method using a navigated ultrasound device and a navigated surgical instrument that allows--even in the absence of bony landmarks--appropriate visualization and reliable orientation in real time. RESULTS: The practical applicability of the system was tested. Good handling and acceptance of the system could be shown. The "3-dimensional error" derived from the deviations in all 3 dimensions lies at 0.64 mm. CONCLUSIONS: With this ultrasound-guided navigated procedure, an accurate approach of soft tissue structures with a surgical instrument is possible. Changes of the situs are represented in real time.

Improving surgical precision--application of navigation system in orthopedic surgery.

Navigation systems track objects with precision expressed as root mean square equalling even up to 0.15 mm. Application of navigation system combined with imaging technique makes surgical operations less invasive, which results in the reduced risk of infection, smaller scar and a shorter time of rehabilitation. Imaging techniques allow surgeon to create individual virtual models for virtual surgery planning. Navigation system tracks the positions of surgical tools in relation to the patient's coordinate systems. Medical imaging enables low-invasive surgery, whereas the position of surgical instruments is monitored on screen. The paper presents a newly developed computer-aided surgical system consisting of ultrasonographic probe and tracking system to measure bone geometry, design surgical scenario virtually and follow it intraoperatively. The system assists surgeon to correct bone deformities. The paper presents the results of several accuracy tests, which demonstrate good repeatability and accuracy.

A new experimental measurement and planning tool for sonographic-assisted navigation.

In this study, we present a new 2.5-dimensional ultrasonic navigation system for measuring axes, lengths, and torsions preoperatively, intraoperatively, and postoperatively. The system comprises an ultrasound unit with a 5-MHz linear probe (TELEMED Echoblaster 128; Telemed, Vilnius, Lithuania) and a navigation system (OrthoPilot; B. Braun Aesculap, Tuttlingen, Germany) with a Polaris camera (Northern Digital, Waterloo, Canada). Specialized software developed for this application allows for selecting any body region on a virtual 3D skeleton. With a virtual ultrasound probe, planes needed for measurements can be defined. For each section, the respective surface contour of the bone, which is also shown in the ultrasound image, is displayed. Alternatively, the clinician can use established standard sections. Finally, the required length, axes, and torsions are defined. The accuracy and precision of the system were tested using a plastic model. The measurements of length, torsion, and axis values were accurate to -0.1 +/- 0.3 mm (95% CI), 0.1 degree +/- 0.2 degree (95% CI), and 0.0 degree +/- 0.006 degree (95% CI), respectively. The precision variances for length, torsion, and axis were 1.17 mm (standard deviation) and 0.94 degree and 0.66 degree. These results suggest that the new sonographic method is more accurate than conventional radiographic techniques.