Benchtop Positional Accuracy Assessment of a Robotic-Assisted Surgical System Using Digital Image Correlation

Kelly L Mote, Thomas W McDowell IV, Joseph Wyss

DePuy Synthes Joint Reconstruction, Warsaw, IN

Disclosures: Kelly L Mote (3A-DePuy Synthes), Thomas W McDowell (3A-DePuy Synthes), Joseph Wyss (3A-DePuy Synthes)

INTRODUCTION

Robotic-assisted surgery has the potential to increase the surgical accuracy of Total Knee Arthroplasty’s (TKA) compared to conventional instrumentation. The overall accuracy of a Robotic-Assisted system is dependent on multiple contributing factors including the accuracy of the registration of key anatomical landmarks, patient size, cut execution, user variability and the ability of the system to position the saw or end effector. During the development of the VELYS™ Robotic-Assisted Solution it was determined that in addition to more wholistic cadaveric assessments of accuracy including all these variables, there was a need to verify the specific capabilities of the system. i.e. how accurately the system could position the saw assessing both angular and distance displacement. To do this a novel Accuracy Test Bench was developed. The test bench functions as simulated use, allowing for a large range of anatomical variation in bone size, positioning, and leg flexion in a controlled precise manner.

METHODS

The Accuracy Test Bench (figure 1) is a mechanical representation of a single leg anatomy and developed with gauged femur and tibia bone models defining the anatomical landmark locations (pre-operative) and respective cut planes (post-operative) using removable bone pins. Three tibia and femur bone model sizes were used to represent the default (nominal), minimal and maximum parameters of the surgical system for a size 5 TKA implant (ATTUNE^® Knee System) for a single trial per system.

The leg was aligned to 90° Flexion and 0°Varus/Valgus and landmarks were acquired to compute the surgical plan.

An optical measurement system, ARAMIS 4M Adjustable Base Camera, referred to as the DIC, was used to track the position of the saw blade of the surgical system to the cut planes of the bone models on the test bench. Tracking markers were placed on the bone models and scanned using the DIC and associated software (PONTOS Live). The CAD model of the scanned part was imported and tacked to the component. Theoretical cut planes were built on each of the cut plane surfaces of the models and coordinate systems were built on each plane. Tracking markers were placed on the saw handpiece and scanned, and the CAD was imported using the same method as the bone models. Four calibration points on the saw blade were probed using a custom probe and offset to create theoretical top and bottom saw blade planes. Coordinate systems were built on top and bottom blade planes for positional measurements. The linear deviations were then measured from the saw blade to the plane to the bone model. The angular deviation was measured between the normal of the saw blade and cut plane.

The surgical robot moved through 6 faceted cut positions (5 femoral, 1 tibial) according to its surgical cut plane position and the PONTOS Live software tracked the body of the saw and the bone models to calculate the linear distance and angular deviation (figure 2). The 5 femoral cuts were the Distal, Anterior, Posterior, Posterior Chamfer and Anterior Chamfer and the single Tibia cut was the Tibial resection.

RESULTS

A single trial was conducted for 5 systems using 3 bone model sizes (size 5 minimum, maximum, and nominal) with an overall pooled linear positional accuracy of 0.326 ±0.249 mm and pooled angular positional accuracy of 0.365± 0.611°. Where pooled denotes the combination of all systems and bone models. The five femoral and singular tibial resection presented the following linear and angular positional accuracies: Distal (0.334 ± 0.257mm and 0.172 ± 0.471°), Anterior (0.370 ± 0.240mm and 0.168 ± 0.879°), Posterior (0.366 ± 0.301mm and 0.526 ±0.701°), Posterior Chamfer (0.156 ± 0.182mm and 0.593 ± 0.461°), Anterior Chamfer (0.458 ± 0.233mm and 0.311 ± 0.676°) and Tibia (0.269 ± 0.184mm and 0.419 ± 0.224°) (figure 3).

DISCUSSION

A novel test bench was created to allow for the evaluation of predetermined surgical plans to characterize the positional accuracy of the VELYS™ Robotic-Assisted Solution's end effector. The bench removes the user variability and landmark acquisition variability to directly assess the accuracy of the surgical system. When controlling for these variables, the system was found to be highly accurate with average linear and angular deviation of sub 1 mm and sub 1°.

SIGNIFICANCE/CLINICAL RELEVANCE

The results of this study demonstrate the capabilities and accuracy of the VELYS Robotic-Assisted Solution to drive to specific defined points and gives confidence that given accurate data from the registration it will be highly accurate in clinical use.

benchtop positional accuracy assessment of a robotic assisted surgical system

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