Positioning and Stabilization of a minimally invasive Laser Osteotome Manuela Eugster1, Philippe C. Cattin3, Azhar Zam2, Georg Rauter1 1BIROMED-Lab, 2BLOG, 3CIAN, all from the Dept. of Biomedical Engineering, University of Basel
Background
Challenge
Goal: Replacing conventional mechanical bone cutting tools by a robotic laser endoscope while changing the setup from an open surgery to minimally invasive surgery.
System Setup: The robotic endoscope 1 is guided by a serial robot 2 . The endeffector 3 at the tip of the endoscope contains the laser optics and the laser beam exits the end-effector perpendicular to the bone.
First Application: Unicompartmental knee arthroplasty…
3 A
D
1 R
2
D
[1]
… is a surgical treatment for unicompartmental osteoarthritis. Nowadays, bone resection is executed using surgical instruments such as oscillating saws and drills.
Compared with mechanical tools, Laser Osteotomy provides… • • • •
Faster bone healing[2],[3] Cutting with higher precision[4] and good depth control Higher flexibility in the planar ablation geometry[4] Smaller cut width
D
Main Challenges: Accuracy: The positioning and stabilization of the end-effector requires high accuracy A (0.25 ) in order to enable a good performance of the laserosteotome for enabling continuous cuts through point-wise ablation (laser diameter 0.5mm). R Registration: The relative pose between the laser optics and the bone surface has to be determined in order to enable cutting at the desired location.
Combining Laser Osteotomy with a robotic tool for minimally invasive surgery allows… • • • •
Smaller incisions → faster healing and less damage Precise cutting-geometry and depth Improved planning → more possibilities and increased coherence A less extensive tool assortment in the operational theatre
D
Disturbance compensation: Several disturbances such as patient motion, movement artefacts from the robotic components and vibrations have to be suppressed.
Methods
Results
Concept: A bone-attached six bar mechanism with integrated actuation for positioning. Robotic Endoscope
Patella
2 1
Design Synthesis: An exhaustive search algorithm was used to find the optimal design parameters of the mechanism which correspond to the maximal workspace.
Actuation: Femur
max
Sliders Linear rails Legs Rotatory joints Anchoring point
, ,
,
s.t. :
Laser
3
,r,
,
Laser
Bowden cable Pre-tension spring Tibia
[EP 17177760.0]
This bone-attached mechanism is a six bar mechanism. The main components are: the body of the end-effector 1 and two legs 2 on each side. Additionally, the legs on each side are connected to a respective anchoring point 3 which is rigidly fixed on the bone surface and which is building the base of the mechanism. Mobility: When fixed to the base, the mechanism can move in the plane with 3 degrees of freedom. During insertion and retraction the legs can be folded away, making the mechanism suitable for minimally invasive surgery. 3
Parameter Leg length
Unit mm
Lower limit
Upper limit
Rail length Rail distance Anchoring distance
mm mm mm
15 4 15
35 15
Outcome: • Optimal parameters: , , • Reachable workspace: • Cut length: 30 / 40
2⋅
, 1.5 ⋅ Footprint 40
First Prototypes:
Insertion and Retraction
Rotation around z-axis
Translation along x-axis
1
Translation along y-axis
3
35
x
2
y
z
Decoupling: When fixed to the bone, the end-effector can be decoupled from the robotic → For example by releasing endoscope and move on its own.
1
2
115
the tension of the tendon-driven links
End-effector Laser
Robotic Endoscope Bone Surface
Decouple
3:1 Prototype
1:1 Prototype
References [1] [2] [3] [4]
[Online]. Available: http://pennstatehershey.adam.com/content.aspx?productId=115&pid=3&gid=100225, [Accessed: 31 Aug- 2016] Baek, K.-W et al., “A comparative investigation of bone surface after cutting with mechanical tools a3nd Er: YAG laser”, Lasers in surgery and medicine, 47, 426-432, Rajitha Gunaratne, G. D., et al. ,“A review of the physiological and histological effects of laser osteotomy”, Journal of Medical Engineering & Technology, 41.1, 1-12, 2017 Baek, K.-W et al., “Clinical applicability of robot-guided contact-free laser osteotomy in cranio-maxillo-facial surgery: in-vitro simulation and in-vivo surgery in minipig mandibles”, British Journal of Oral and Maxillofacial Surgery, 53, 976-98, 2015 [5] Eugster et al., “Positioning and Stabilisation of a Minimally Invasive Laser Osteotome”, The Hamlyn Symposium on Medical Robotics, 10, 21-22, 2017
Funding Werner Siemens-Foundation, Zug, Switzerland
[email protected]
