Knee surgery tool given FDA approval following development with Sagentia Innovation

With 510(k) clearance from the FDA, Fremont, California-based THINK Surgical can now market TMINI, a wireless robotic handpiece designed to assist surgeons in performing total knee replacement. 

Following a CT-based three-dimensional surgical plan, the TMINI robotic handpiece automatically compensates for surgeon hand movement to locate bone pins along precisely defined planes. Cutting guides are then connected to the bone pins for accurate bone resection. Along with ease of use, TMINI can replace many instruments used for knee replacement surgery.

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Cambridgeshire-based consultants Sagentia Innovation were chosen by THINK Surgical to act as primary development partners of TMINI. Part of their remit required them to develop the turnkey subsystem (TMINI robotic handpiece, battery charger), which involved electrical, mechanical, and software design from concept through to verification, pilot builds and transfer to manufacture.

A key element of TMINI is the pairing interaction between a camera placed over the site of the operation and the handpiece. Tim Frearson, Sagentia Innovation TMINI project manager explained that latency was a challenge.

“To achieve the required high-performance control while managing the latency associated with the pose measurements from the optical tracking system, we had to introduce a configurable filter into the motion control loop which executes on the TMINI,” he said. “This filter is used to manage the control system’s response to delayed input from the optical tracking system while still allowing the control system itself to provide a strong disturbance rejection.” 

Frearson added that the size and weight of the TMINI hand piece presented another challenge that required the management of competing requirements, such as balancing ease of use with available power, motor torque, and battery life.

“This led to a highly constrained and complex electromechanical design, which required innovative solutions to meet the sterilisation needs of the hand piece, management of fixed and moving wires, and connectivity of mating interfaces,” he said. “We tackled these challenges through theoretical modelling, proof of principle prototypes, confidence testing, and design iteration.”

The device’s battery – the TMINI Smart Cell - will not operate the TMINI hand piece unless it has sufficient battery capacity to complete one full surgical procedure, Frearson said, adding that the electronics and software of the TMINI Smart Cell have been designed so that the battery capacity needs to be above a specified threshold otherwise it will not allow pairing to the tracker during setup.