Abstract
Cup implantation is a critical stage during THR Surgery. It is mainly because of the rudimentary mallet-based impaction technique, whereby mal-positioning and unknown forces are present. There are some technological attempts to solve this problem partially: dealing with mal-positioning while patient remains subjected to non-standardized impaction forces.
Our comprehensive approach to the problem allows the surgeon to monitor cup positioning and perform controlled insertion with a completely known force profile. Positioning is monitored by means of IMU (Inertial Measurement Unit) technology, while placement is controlled by force feedback and vibratory insertion device. Both technological building blocks (IMU and vibratory insertor) are embedded on a single device containing signal processing and automatic control strategies. This mechatronic device is called BMD3.
This work covers the entire device development life cycle illustrated in figure 1: the roadmap starts at the conceptual inspiration through scientific investigation and concept proof/demonstration up to the BMD3 prototype.
Smooth insertion was the main purpose initially; this led to concept demonstration by means of electrical and pneumatic actuated devices. They employ low-amplitude/high-frequency vibratory input forces into the Acetabular Cup to explore constant sliding in the microscale. Although successful, it was noted that there is optimization potential as vibration is used to decrease friction resistance and either impose or prevent specific shape modes on the pelvic structure. A scientific investigation on frictional and structural behavior allowed us to define suitable instrumentation for an automatic insertion strategy (figure 2a).
Our technical solution to the smooth insertion problem involves positioning monitoring by means of IMU, simultaneously available to the surgeon while using this tool. An operating procedure was proposed to reliably map and feedback surgeon's movement in the OR (Operating Room) space. Concept demonstration was also performed for this additional feature before complete device integration, see figure 2b.
Three main subsystems compose the BMD3: PPU (Power and Processing Unit); Mechatronic Handle; and Replaceable Head. The Replaceable Head allows 1kHz and 20kHz operating ranges; each implemented on a specific mechanism detachable from the Mechatronic Handle. A user (surgeon) may choose one of these versions according to the insertion strategy adopted.
The Mechatronic Handle houses sensors, initial signal conditioning stages, and surgeon interaction interfaces like: Thin Film Transistor screen for visual positioning feedback; and a pushbutton for OR space mapping setup. The Mechatronic Handle itself is an interface between Replaceable Head and the PPU. Every insertion and positioning strategy may be updated directly at the PPU; firmware updates deal with real-time processing of pressure, IMU, and vibration measurements.
Conclusions of the work summarize intangibles such as inspiration and insights on THR improvement spots; scientific analysis; and technology to the effective problem approach.
