Inside this Edition:

• Radix Marker
• Aurora and Intramedullary Nailing
• New Aurora Volume
• Research: Tools and TUM
• Polaris Vicra
• Accuracy
• Events

NDI InFocus February 2008

NDI Web Links:

• Computer-Assisted Therapy & NDI
• Polaris Optical Tracking
• Ear Nose Throat (ENT))
• Spine Surgery
• Orthopaedics
• Passive and Active Technology

Radix - The Clear Choice In Passive Technology

In computer-assisted therapy (CAT), passive tracking technology is a popular choice due to the advantages it offers over active tracking. Instruments do not require wires tethering them back to a control unit or independent power sources such as batteries, which add cost and weight to the instruments. Passive technology allows for the design of simple, light-weight instruments giving maximum freedom to the end-user. Current generation passive tools use spherical, retro-reflective markers that reflect infrared light emitted by illuminators mounted on the Position Sensor.

The spherical markers described above were originally designed to meet the needs of the major CAT market at the time – Neurosurgery. Since then, CAT has seen strong growth into other areas. ENT and Spine surgery have seen substantial adoption of CAT. In addition, the acceptance of CAT in Orthopaedic trauma and Arthroplasty is growing rapidly. As such, the passive technology is being used in new environments, with slightly different requirements and drivers. For example, contamination of the spherical markers is a minor issue in Neurosurgery due to relatively clean procedures and small incisions. However, in Orthopaedics, marker contamination is certainly a viable consideration.

NDI is developing a new passive tracking technology designed specifically for harsh surgical environments. The Radix™ Marker is a clear, solid-plastic, retro-reflective lens designed to work with the Polaris and Polaris Spectra Position Sensors. The surface of the marker is a smooth plastic hemisphere which naturally sheds liquid contamination. In the event that contamination does collect on the marker to the point where tracking is interrupted, the marker is easily cleaned and tracking quickly resumed. Contamination of a marker is also easy to visually identify, allowing the user to quickly diagnose a problem and efficiently clean the marker.

The Radix Marker also has the unique characteristic of being inherently resistant to partial occlusions. Partial occlusions occur when the line-of-sight between a marker and the Position Sensor is partly blocked by some other object. One way this can occur is if solid debris blocks part of the marker surface. For spherical retro-reflectors this condition may lead to loss of tracking, as the Position Sensor will reject the affected marker.

With Radix technology, a partial occlusion covering one side of a marker will be reproduced, or 'mirrored' on the opposite side. This results in a symmetrical occlusion, leading to little effect on the calculation of the marker centroid and less tendency for the marker to be rejected.

The Radix Marker is responding to new demands placed on navigation tracking technology when used in challenging environments.

The robust performance of the marker minimizes surgical interruptions, allowing the surgical team to focus on the therapy rather than the technology. Consider Radix when choosing a passive marker for your next application.

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