University of Basel improves safety of laser bone surgery

13 Dec 2023

Optical feedback for both depth of cut and tissue type makes laser osteotomy more accurate.

Bone machinists: better outcomes for patients

The process, termed laser osteotomy, could eventually replace conventional techniques, and has been investigated as a way to simplify surgery for spinal conditions. But at present ways to ensure that the laser technique makes only the cuts desired and leaves surrounding tissues untouched have remained challenging.

A project at the University of Basel has now demonstrated a laser osteotomy platform in which optical techniques provide feedback on the depth of cut being made and the composition of the nearby tissues, and reported the results in Lasers in Surgery and Medicine.

"The special thing about our system is that it controls itself, without human interference," said Ferda Canbaz from Basel's Biomedical Laser and Optics Group (BLOG).

The new work builds on previous studies at BLOG into the use of OCT as means to guide the laser during an osteotomy procedure. In September 2023 the group demonstrated an OCT-assisted system which integrated a fiber-based Er:YAG osteotomy laser with a long-range swept-source OCT system, to enable real-time depth feedback during laser osteotomy.

The group has now added a laser-induced breakdown spectroscopy (LIBS) system to the platform, able to differentiate tissue types by analyzing the plasma generated on the tissue by a nanosecond Nd:YAG laser. As a result the system is designed to allow simultaneous monitoring of depth of cut and tissue type during an osteotomy operation.

New cutting shapes possible

In operation the platform deploys the three individual lasers in sequence and focused on the same spot, with the first being for LIBS analysis of the area, according the project team.

"The first laser serves as a tissue sensor, in that it scans the surroundings of the site where the bone is to be cut," commented the University of Basel. "Pulses are sent with this laser to the surface at regular intervals, vaporizing a tiny bit of tissue each time. The composition of this vaporized tissue is measured with a spectrometer and an algorithm creates a map that shows where the bones are located and where the soft tissue is."

A second Er:YAG laser then begins the actual bone cutting procedure, directed at the places where bone rather than soft tissue has been identified. A third laser in a long-range Bessel-beam OCT sub-system then monitors the depth of the cut, imaging at depths of up to 26 millimeters, and checks that the cutting laser is not penetrating more deeply than planned.

"The coaxial integration of various feedback systems yields superior accuracy in deep laser ablation compared to alternative configurations," said the project in its paper. "This represents a significant technological advancement toward utilizing laser osteotomy in minimally invasive surgery."

In trials using femur bones and tissue from pigs, the results showed successful real‐time tissue differentiation and visualization without any visible thermal damage or carbonization, according to the team.

The next steps will involve making the platform more compact, with the ultimate goal of fitting it within an endoscope to carry out minimally invasive operations. Cutting in a controlled manner using lasers also permits new cutting shapes to be applied, so that a bone implant could perhaps be physically interlocked with the existing bone without the need for additional fixatives.

“One day we might be able to do without bone cement completely," said Ferda Canbaz.