Mechanical load applied by Intraosseous Transcutaneous Amputation Prosthesis (ITAP) during walking on level and sloped treadmill: A case study.

This proof of concept study presents a method to collect and analyse kinetic data from one participant with a transfemoral amputation fitted with a percutaneous osseointegrated implant walking on a level and sloped treadmill. We describe the construction of and results from a bespoke wireless six axis load cell built into one participant's prosthetic assembly. The load cell does not clinically compromise the participant in any way and is an initial milestone in the development of a light-weight wireless load cell for use with percutaneous osseointegrated implants. In this case, it is the first time that kinetic data from a participant fitted with an Intraosseous Transcutaneous Amputation Prosthesis has been published. We propose that the data can be used to model the load transfer to the host bone, with several clinically significant applications. The raw dynamic data are made available and quasi-static load cases for each functional phase of gait are presented. Peak forces obtained in the medio-lateral (X), cranio-caudal (Y) and antero-posterior (Z) axes over level ground respectively were -243.8 N (0.24 BW), 1321.5 N (1.31 BW) and -421.8 N (0.42 BW); uphill were -141.0 N (0.14 BW), 1604.2 N (1.59 BW), -498.1 N (0.49 BW); downhill were -206.0 N (0.20 BW), 1103.9 N (1.09 BW), -547.2 N (0.54 BW). The kinetics broadly followed able bodied gait patterns with some gait strategies consistent in participants with other implant designs or prosthetic socket connections, for example offloading the artificial limb downhill.

Design and characterization of a novel permanent magnet synchronous motor used in a growing prosthesis for young patients with bone cancer.

Approximately 50 child sarcomas are treated with limb salvage surgery each year in the United Kingdom. These children need an extendable implant that can be lengthened periodically to keep pace with the growth in the opposite limb. Surgically, invasive devices have been used for the past 30 years with intrinsic problems of infection and long-term recurrent trauma to the patient. To eliminate problems associated with the invasive device, a noninvasive extendable prosthesis was developed. The magnetically coupled drive technology used for this prosthesis was a synchronous motor with a gear-driven telescoping shaft. In this design the motor configuration was in two parts: a rotating magnet (rotor) that fitted inside the prosthesis where space was limited and the stator, which was an external device used to extend the prosthesis remotely as the patient grew. This compact external drive produced a focused magnetic flux that required no cooling and operated on a single-phase power supply. The extending mechanism in the implant was able to overcome up to 1300 N force, which is the tension force exerted by the soft tissues during the lengthening procedure. The device has been successfully implanted in 50 patients.

Correlation of radiographic and telemetric data from massive implant fixations.

One proximal femoral replacement (PFR) and two distal femoral replacements (DFR) used in tumoural limb salvage were instrumented to measure axial force in the femoral shaft and at the tip of the intramedullary stem in vivo. The prostheses were implanted in suitable subjects and regular recording sessions held over 2 years for each subject. The ratio of the tip force to the shaft force increased with time in all 3 subjects, albeit at different rates, indicating that a greater proportion of the load was being transmitted along the prosthesis stem. The aim of this study was to correlate these changes with bone remodelling observed radiographically over the same period. Radiographs were analysed using a computer-assisted method to quantify bone width, radiolucent line width and relative bone density. The analysis showed the development of radiolucent lines at the bone-cement interface and a decrease in the lateral to medial ratio of bone density near the transection site. For the PFR, the mean width of the radiolucent area alongside the proximal fifth of the stem on the lateral side increased from 0 to 0.67 mm over the 2 years. The tip to shaft ratio correlated significantly with radiolucency on the lateral side of the stem. Both the DFRs became loose within 2 years but the PFR has remained in situ for 13 years to date. The correlations found thus far suggest that it may be possible to establish relationships between load transfer (and therefore loosening in the fixation) and radiographic data, with possible application to advance warning of clinical loosening in stemmed implants.

The use of a bone-anchored device as a hard-wired conduit for transmitting EMG signals from implanted muscle electrodes.

The use of a bone-anchored device to transmit electrical signals from internalized muscle electrodes was studied in a sheep model. The bone-anchored device was used as a conduit for the passage of a wire connecting an internal epimysial electrode to an external signal-recording device. The bone-anchored device was inserted into an intact tibia and the electrode attached to the adjacent M. peroneus tertius. "Physiological" signals with low signal-to-noise ratios were successfully obtained over a 12-week period by walking the sheep on a treadmill. Reliable transmission of multiple muscle signals across the skin barrier is essential for providing intuitive, biomimetic upper limb prostheses. This technology has the potential to provide a better functional and reliable solution for upper limb amputee rehabilitation: attachment and control.