tailieunhanh - Total Knee Arthroplasty - part 8

Hình trụ bên trong được instrumented với thiết bị cảm căng thẳng trong khi hình trụ bên ngoài đã được cố định xương [25]. Bộ chuyển đổi này đã được sử dụng để đo lường các lực lượng chày ở đầu gối tử thi bình thường và đã được đưa vào thông qua một phẫu thuật cắt 1 cm gần hệ thống nguyên mẫu điện tử thay thế | 283 45 Chapter 45 The Electronic Knee - . Colwell Jr. D. D. D Lima cylinders. The inner cylinder was instrumented with strain gages while the outer cylinder was fixed to bone 25 . This transducer was used to measure tibial forces in normal cadaver knees and was inserted through a 1-cm resection of the proximal tibia. A prototype electronic tibial replacement system was also developed using radiofrequency transmission of data which demonstrated comparable accuracy in measuring the location and magnitude of tibiofemoral compressive forces 26 . This telemetry system was found to accurately transmit the signal through bone cement and soft tissues with a range of approximately 2 m. Technical Details Transducers. A titanium alloy revision tibial prosthesis design was instrumented with force transducers a microtransmitter and an antenna. The tibial-force transducers were manufactured by NK Biotechnical and have been described previously 3 and have been used in cadaveric studies 24 27 . The tibial tray consists of upper and lower halves separated by support posts below which lie the load cells located at the four corners of the tibial tray. By measuring the force on each load cell and the total axial load the location of center of pressure can be determined. In addition the distribution of forces between the medial and the lateral compartments can be calculated. Figure 45-1 demonstrates the location of the multichannel transmitter and the hermetic feed-through antenna o Fig. 45-1 . Telemetry. The microtransmitter receives the analog signal through leads from the load cells and is connected to the transmitting antenna. The microtransmitter was developed by Microstrain Burlington VT entirely from off-the-shelf surface-mount integrated circuits. The requisite bridge signal conditioning the multiplexer the A D analog-to-digital converter and the programmable gain and filter functions were combined on a single chip AD7714 Analog Devices Norwood MA . The AD7714 features three