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Optical and electromagnetic tracking systems represent the two main technologies integrated into commercially-available surgical navigators for computer-assisted image-guided surgery so far. Optical Tracking Systems (OTSs) work within the optical spectrum to track the position and orientation, i.e., pose of target surgical instruments. OTSs are characterized by high accuracy and robustness to environmental conditions. The main limitation of OTSs is the need of a direct line-of-sight between the optical markers and the camera sensor, rigidly fixed into the operating theatre. Electromagnetic Tracking Systems (EMTSs) use electromagnetic field generator to detect the pose of electromagnetic sensors. EMTSs do not require such a direct line-of-sight, however the presence of metal or ferromagnetic sources in the operating workspace can significantly affect the measurement accuracy. The aim of the proposed review is to provide a complete and detailed overview of optical and electromagnetic tracking systems, including working principles, source of error and validation protocols. Moreover, commercial and research-oriented solutions, as well as clinical applications, are described for both technologies. Finally, a critical comparative analysis of the state of the art which highlights the potentialities and the limitations of each tracking system for a medical use is provided.

Background: Technological tools as robotic devices and wearable sensors can provide accurate and repeatable measurements of physical variables (e.g., position, velocities, forces) which can be used for quantitative and qualitative assessment of movement analysis and upper limb motor performance. Objective: The study aims to propose a quantitative and qualitative assessment of upper limb motor performance by means of seven kinematic parameters recorded by a passive mechatronic device in patients who underwent a surgical procedure for ligament reconstruction following acromioclavicular joint dislocation. Method: Five patients (mean age: 40 ± 12 years) with acromioclavicular joint dislocation were enrolled. A passive end-effector mechatronic device characterized by 7 degrees of freedom and designed for the assessment of upper limb motor performance - especially for measuring the hand position in three-dimensional space - was used. The Constant-Murley score and seven kinematic parameters were used as clinical outcome measure and quantitative and qualitative assessment, respectively. Results: The preliminary results of this study show no significant differences between the impaired arm and unimpaired arm: the end-effector passive mechatronic device used in this study is able to provide an overall assessment of the upper limb motor performance following shoulder impairment. Conclusion: The motion tracker can be easily used as effective tool for quantitative and qualitative assessment of upper limb motor performance, even several years after the surgical operation.

Stereotactic navigation has an increasingly wide use in spinal surgery. The use of this technology has improved the accuracy of the surgical procedures and reduced the incidence of iatrogenic neurovascular injuries.

Low invasive techniques for the treatment of lumbar disk herniation are still a subject of debate and interest in the field of vertebral surgery. We present a critical review of 80 cases of percutaneous nucleotomy performed from 1989 to 1999 at the First Orthopaedic Clinic in Pisa. The analysis of the results confirms the usefulness of this method for lumbar disk hernias in young patients who precisely meet the indications for surgery. Furthermore, automised percutaneous nucleotomy did not provoke collapses in the intervertebral space or instability in the functional units following the emptying of the nucleus. Post-operative magnetic resonance imaging revealed, in all cases, the creation of a discal scar.

A number of interspinous devices (ISD) have been introduced in the lumbar spine implant market. Unfortunately, the use of these devices often is not associated with real comprehension of their biomechanical role. The aim of this paper is to review the biomechanical studies about interspinous devices available in the literature to allow the reader a better comprehension of the effects of these devices on the treated segment and on the adjacent segments of the spine. For this reason, our analysis will be limited to the interspinous devices that have biomechanical studies published in the literature.

Interspinous devices are in the class of medical devices that can be implanted in the lumbosacral spine using a minimal and often mini-invasive approach. Because their use has boomed over the last decade, we can state with confidence that this technological sector attracts a great deal of interest in a quest for techniques and materials able to reduce the invasiveness of the surgical procedure and increase its general bio-compatibility. An initial classification of interspinous devices from a biomechanical viewpoint may be carried out by assessing the rigidity of the distraction element (Table 1, Appendix). This identifies devices that are inaccurately categorized as nondeformable, involving the insertion of material with high mechanical rigidity into the space between the spinous process, where the distraction between the spinous processes may be considered constant. In other devices, a material with a shock-absorbing function is inserted between the spinous processes, which then undergoes appreciable elastic or visco-elastic deformation under physiological loads to increase bone implant compliance. In parallel with this sub-category, there are also devices that work by rigid stabilization of the interspinous space where stable posterior interspinous fusion is brought about by applying autologous or homologous bone and cruentation of the spinous processes. Clinical trials on interspinous devices available in the literature show a good relationship between the benefits for the patient and the use of resources in the disease treatment. Nevertheless, there is still margin for clinical investigation and for the establishment of verification and validation procedures of these devices in order to clearly define the relationship between the effects on the biomechanics of the functional unit and the clinical indications of such devices.