Optical sensing assists orthopedic surgery

11 Jan 2022

Survey led by Tyndall National Institute indicates how evolving optics techniques can meet clinical needs.

Cases of orthopedic surgery already account for a substantial number of medical procedures, and the number will increase further as populations grow older and skeletal wear and tear continues.

Optical sensing and measurement techniques have already made inroads into this sector, assisting surgeons and clinicians with both pre-op assessment and with the carrying out of surgical procedures, so improving patient outcomes.

Examples have included a LED-based technique from Fraunhofer IWU to measure patients' leg lengths and improve the fit of replacement hip joints, and an opto-electronic system developed at Hebrew University of Jerusalem to monitor and detect minute changes in the trajectory of the guide-wire employed during surgery.

A new review led by Tyndall National Institute and published in Journal of Biomedical Optics has surveyed the current and future uses of optical sensing in orthopedic surgical devices, and concluded that the sector presents both opportunities and challenges for the biomedical optics community.

"Various unmet clinical needs in orthopedic surgery could potentially be addressed by optical spectroscopy or imaging, which come in many different forms depending on the light–tissue interaction being sensed," noted the report. "They include diffuse reflectance that depends on the light absorption and elastic scattering of the tissue; OCT that images tissue microstructures; and fluorescence and Raman inelastic scattering that report molecular signatures."

The review considered specific potentially optics-enabled orthopedic techniques in its survey, including total hip arthroplasty, or joint replacement, in which a drill incorporating optical sensing would assist surgeons to select drilling locations that avoid damage to the patient's neurovasculature.

"An optical sensor within the drill tip would report on whether the drill is encountering blood vessels or nerves, and also sense the bone/tissue interface to warn of potential periosteum breach," said the report.

"There are, however, several challenges to this approach. The drill bits used in hip arthroplasty have a hollow core, which is well suited for fiberoptic placement, but large-core multimode glass fibers that are commonly used for such sensing have limited bend radius. More flexible plastic fibers might be an option, but may have limited lifetime in the harsh drilling environment."

Other procedures such as fixation of fractured clavicles would also benefit from such tooling, since they also hinge on prescribed safe drilling angles and zones, while lumbar decompression might be assisted by optical guidance during the bone shaving technique used to relieve pressure on the spinal canal.

Significant opportunities for optical devices in surgical tools

These applications will place complementary demands on the optical sensing being employed. The report suggests that requirements for use in orthopedic surgery will include a field of view 1.5 to 2 x the diameter of the drill and spatial resolution of 0.1 x 0.1 millimeters, in addition to the need for accurate differentiation of the different tissue types encountered.

Integration with other modalities could also be a significant advance during minimally invasive surgeries, paralleling similar developments underway in robotic ophthalmic surgery and brain surgery.

"We envision that the integration of optics within orthopedic tools would use primarily the native optical properties of bone and surrounding soft tissues to provide near real-time feedback on upcoming structures, or signaling when only a thin layer of bone remains," noted the survey.

"The need for such additional guidance will only expand with evolving minimally invasive and percutaneous procedures, so there are significant opportunities for further development of optical devices integrated into orthopedic surgical tools."