Vibration arthrometry in the patients with failed total knee replacement

This is a preliminary research on the vibration arthrometry of artificial k nee joint in vivo. Analyzing the vibration signals measured from the accele rometer on patella, there are two speed protocols in knee kinematics: 1) 20 degrees/s, the signal is called "physiological patellofemoral crepitus (PP C)", and 2) 67 degrees/s, the signal is called "vibration signal in rapid k nee motion", The study has collected 14 patients who had revision total kne e arthroplasty due to prosthetic wear or malalignment represent the failed total knee replacement (FTKR), and 12 patients who had just undergone the p rimary total knee arthroplasty in the past two to six months and have curre ntly no knee pain represent the normal total knee replacement (NTKR). FTKR is clinically divided into three categories: metal wear polyethylene w ear of the patellar component, and no wear but with prosthesis malalignment , In PPC, the value of root mean square (rms) is used as a parameter; in vi bration signals in rapid knee motion, autoregressive modeling is used for a daptive segmentation and extracting the dominant pole of each signal segmen t to calculate the spectral power ratios in f < 100 Hz and f > 500 Hz. It was found that in the case of metal wear, the rms value of PPC signal is far greater than a knee joint with polyethylene wear and without wear, i.e ., PPC signal appears only in metal wear. As for vibration signals in rapid knee motion, prominent time-domain vibration signals could be found in the FTKR patients with either polyethylene or metal wear of the patellar compo nent. We also found that for normal knee joint, the spectral power ratio of dominant poles has nearly 80% distribution in f < 100 Hz, is between 50 % and 70 % for knee with polyethylene wear and below 30 % for metal wear, whe reas in f > 500 Hz, spectral power ratio of dominant poles has over 30 % di sribution in metal wear but only nonsignificant distribution in polyethylen e wear, no wear, and normal knee. The results show that vibration signals i n rapid knee motion can be used for effectively detecting polyethylene wear of the patellar component in the early stage, while PPC signals can only b e used to detect prosthetic metal wear in the late stage.