Orthopedic surgery has traditionally depended on mechanical instruments such as saws and chisels for bone cutting. While effective, these tools often cause friction and stress, potentially harming surrounding tissues and extending recovery times.
In pursuit of a more delicate solution, medical engineers have turned their attention to laser technology. Lasers, which operate without physical contact, can significantly reduce mechanical pressure, thus lowering the risk of microcracks in bones. This precision is particularly beneficial for advanced procedures, including the insertion of customized 3D-printed joint implants.
However, adapting lasers for hard tissue has been challenging. While effective for soft tissues, lasers have struggled to penetrate dense bone. Until recently, laser osteotomy could only achieve cuts of up to 3 centimeters, insufficient for major orthopedic operations like total knee arthroplasty, which requires cuts of about 6 centimeters.
Innovative Laser Design
The challenge isn't merely about increasing laser power. Dr. Ferda Canbaz from the University of Basel explains that amplifying energy could lead to bone charring, adversely affecting healing. Instead, the research team focused on altering the laser's shape. Conventional surgical lasers, such as the Er:YAG, emit energy most intensely at the center, leading to V-shaped cuts that lose focus and energy as they deepen.
To overcome this limitation, researchers developed a "top hat" beam profile, allowing energy to be distributed evenly across its width before tapering off. This uniform energy distribution enhances cutting efficiency and speed, as noted by doctoral student and lead author Mingyi Liu. The flat bottom of the cut prevents the trench walls from sapping the laser's strength, enabling deeper penetration.
Advancements in Joint Implant Surgery
The team successfully tested their redesigned Er:YAG laser on thick bovine femur bones. To prevent tissue charring, they used a micro-jet of water and blasts of compressed air during the cutting process. The results, recently published in a scientific journal, signify a substantial advancement.
While traditional Gaussian lasers typically achieved a depth of about 2.6 centimeters, the top hat laser cut down to 4.45 centimeters, nearing the necessary depth for significant joint resurfacing surgeries. Notably, microscopic analysis revealed that the bone's cellular structure remained intact and healthy at the cut edges.
Despite this progress, the laser is not yet ready to replace mechanical saws in operating rooms. The speed of the cut remains a significant challenge, with the top hat laser removing approximately 0.42 cubic millimeters of bone per second, compared to 11 cubic millimeters per second with a conventional saw.
Nonetheless, the remarkable depth achieved opens exciting possibilities for clinical applications. The research team is now focused on refining the robotic delivery system for use in living, vascularized tissues. Dr. Canbaz emphasizes the importance of adapting the system for the complex conditions within the body while safeguarding surrounding tissues.