Wireless technologies and their use in the medical field have become much more widespread and important in the last decade. Whether it is a doctor carrying a personal digital assistant, the hospital WLAN, RFID asset tracking systems, telemetry-based Point-of-Care systems, or implanted wireless devices, wireless systems play an important role in the underlying technologies utilized by a hospital. Conversely, wireless technologies are not widely used in computer assisted orthopaedic surgery (CAOS), mainly due to their poor performance in the operating room (OR). The large amount of metallic interference found in the OR can severely degrade wireless signals. This can cause failure in wireless digital communication and large errors in 3-D tracking when using wireless signals for 3-D positioning.

We have developed a wireless positioning system based on ultra wideband (UWB) technology which achieves mm-range 3-D dynamic accuracy and can be used for intraoperative tracking in CAOS systems. This system can be used to track smart surgical tools in the OR and also for registration of bones and conventional (non-smart) surgical tools. UWB technology also has the potential for high data rate digital communication. The potential of highly accurate 3-D tracking combined with high data rate digital communication make UWB an attractive wireless technology for future CAOS systems and provides a strong backbone for smart surgical tools.

We have run various experiments with our UWB system in an OR both during orthopaedic surgeries and when the OR was empty. We have obtained time domain and frequency domain data, which has been analyzed to show the effects of transmitting UWB wireless signals in the OR. The implications of the OR environment on 3-D positioning accuracy and also high data rate digital communication will be presented. The final conclusions show the potential of UWB for wireless smart surgical tools which can be tracked in real-time with mm-range and even sub-mm range 3-D accuracy.

Wireless technologies applied to the medical field have grown both in prevalence and importance in the past decade. Various applications and technologies exist underneath the telemedicine umbrella including Point-of-Care systems where electrocardiographs, blood pressure, temperature, and medical image data are recorded and transmitted wirelessly, which enables remote patient monitoring from inside hospitals, personal residences, and virtually any location with access to satellite communication. Another widespread application for wireless systems in hospitals is asset tracking, typically done with RFID technology. Wireless technologies have not been widely used in computer assisted orthopaedic surgery (CAOS) because of the limitations in terms of overall 3-D accuracy.

We have developed a wireless positioning system based on ultra wideband technology (UWB) which achieves mm-range 3-D dynamic accuracy and can be used for intraoperative tracking in CAOS systems. Current intraoperative tracking technologies include optical and electromagnetic tracking systems. The main limitations with these systems include the need for line-of-sight in optical systems and the limited view volume and susceptibility to metallic interference in electromagnetic tracking systems. UWB indoor positioning does not suffer from these effects. Until this point, the main limitation of UWB indoor positioning systems was its limitation in 3-D real-time dynamic accuracy (10–15 cm as opposed to the required 1–2 mm).

We have developed a UWB indoor positioning system which achieves dynamic 3-D accuracy in the range of 5–6 mm for a non-coherent approach and 0.5–1 mm for a coherent approach (transmitter and receiver use the same clock signal). The integration of this tracking system with smart surgical tools opens up a plethora of exciting intraoperative applications including picking landmarks, 3-D bone and instrument registration, real-time wireless pressure sensing used for ligament balancing in TKA, and real-time A-mode ultrasound bone morphing. The UWB tracking system will be presented along with its integration into smart surgical tools and surgical navigation.

Many nonoperative techniques exist to alleviate pain in unicompartmental osteoarthritic knees including physical therapy, heel wedges and off-loading knee braces [1]. Arthritic knee braces are particularly effective since they can be used on a regular basis at home, work, etc. Previous knee brace studies focused on their ability to stabilize anterior cruciate ligament (ACL) deficient knees. A standard technique for analyzing brace effectiveness is the use of an athrometer to look at the range-of-motion. Although this is helpful, it is more useful to use X-ray or fluoroscopy techniques to analyze the in vivo 3-D conditions of the femur and tibia. One method for doing this is Roentgen Steroephotogrammetric Analysis, which uses a calibration object and two static X-rays to perform 3-D registration of the femur and tibia. This technique is limited to static and typically non-weight bearing analysis.

We have analyzed five patients with moderate to severe osteoarthritis in both step up and step down activities with two different knee braces and also without a knee brace. Fluoroscopy of the five patients performing these activities was obtained as well as a CT scan of the knee joint for each patient. 3-D models of the femur and tibia were obtained from manual segmentation and overlaid to the fluoroscopy images using a novel 3-D to 2-D registration method [2]. This allowed analysis of 3-D in vivo weight bearing conditions. This work builds off of an analysis where 15 patients were analyzed in vivo during gait with and without knee braces [3].

All five patients experienced substantially less pain when performing the step up and step down activities with a knee brace versus without a knee brace. It should be noted that none of the five patients were obese, which can limit brace effectiveness. Preliminary results show that medial condyle separation was increased by 1.4–1.6 mm when using a knee brace versus not using a knee brace during the heel-strike and 33% phases of step up and step down activities. Also, the condylar separation angle was reduced by an average of 1.5–2.5°. Finally, consistently less condylar separation was seen during step down versus step up activities (0.5–1 mm), which can be attributed to a greater initial impact force on the knee joint during step down versus step up activities.