Basic Study Of Applying Shear Wave Elasticity For Early Diagnosis Of Osteoarthritis

Part1.The clinical value of traditional ultrasonography in evaluatingknee cartilage degenerationObjective: To explore the clinical value of traditional ultrasonography by studying the correlation between ultrasonographic semi-quantitative evaluation system and clinical symptoms for osteoarthritis, and compare it with radiography.Method: This study includes 63 patients(63 knee) who went to the Orthopaedic outpatient department of our hospital due to knee pain, those with a surgery or injury history of the knee were excluded. Ultrasonographic and radiographic examination were performed, and Kazam system and Kellgren–Lawrence system were adopted to evaluate the severity of osteoarthritis. VAS scale and WOMAC questionnaire were adopted to evaluate the severity of clinical symptoms. Then, the correlation between ultrasonography,radiography and clinical symptoms were analyzed and compared. The interobserver agreement for ultrasonographic semi-quantitative evaluation system were analyzed.Results: The correlation coefficient between ultrasonographic grading and VAS, WOMAC score were 0.813 and 0.898 respectively. The correlation coefficient between radiographic grading and VAS, WOMAC score were 0.707 and 0.733 respectively. The correlation coefficient between ultrasonography and radiography was 0.859, ultrasonography is more sensitive for detecting early stage osteoarthritis. The Kappa coefficient between ultrasonographic grading and radiographic grading was 0.777. The interobserver agreement for evaluating early stage osteoarthritis is comparatively insufficient.Conclusion: Ultrasonography can clearly show the morphological change of cartilage of femoral trochlear and condyle. The diagnostic value of ultrasonography is better than radiography. The interobserver agreement of ultrasonographic grading is good. However, the sensitivity and interobserver agreement of ultrasonography for early stage osteoarthritis diagnosis is insufficient and could be improved by combining ultrasonography with shear wave elastography technique.Part 2. The influence of tissue thickness on shear wave elastographymeasurementObjective: To study The influence of tissue thickness on shear wave elastography(SWE)measurement, explore the feasibility of using SWE to measure the Young’s modulus of thinplate shaped tissues.Methods: Three batches of gelatin-agar phantoms with different agar concentrations(2%, 2.5% and 3%) were made for SWE test. Each batch consisted of 6 phantoms with different thickness(3, 6, 8, 15, 30 and 50mm). The only currently available commercial SWE machine(Aixplorer) was used for measuring the Young’s modulus of gelatin-agar phantoms. HFVS mechanical property test was adopted for reference.Results: The Young’s modulus of phantoms with thickness of 50, 30, and 15 mm measured by SWE were similar. When the thickness was less than 15 mm, the SWE results began to decrease. And this trend became more significant with further decrease of the phantom’s thickness. The result of HFVS test was close to that of 50, 30 and 15 mm phantoms measured by SWE. It indicates that currently available SWE machines can get the real Young’s modulus of thick phantoms. But bias will appear when SWE is used to measure thin phantom. The thinner the phantom is, the more significant the bias is.Conclusion: Tissue thickness has a significant influence on SWE result. Currently available SWE machine is only suitable for measuring the Young’s modulus of thick tissues. Improvement is need if we want to use SWE to detect the early stage cartilage degeneration in osteoarthritis.Part 3. Finite element analysis of using shear wave elastography todetect early stage cartilage degenerationObjective: To study the shear wave propagation in cartilage like structures, and the feasibility of using shear wave elastography(SWE) to detect early stage cartilage degeneration by finite element analysis(FEA).Method: Cartilage like thin-plate finite element model and theoretical model were established in Abacus. Then following situations were simulated:(1) the change of cartilage thickness;(2) two-layer structure of cartilage and subchondral bone;(3) the presence of a 0.8*0.8mm focal degeneration with Young’s modulus change in cartilage. The influence of above situations on shear wave speed were investigated.Result:(1) The FEA result confirmed that the tissue thickness could retard the shear wave speed, which was in accordance with SWE results of Part 2. This influence could be minimized by establishing new formula.(2) In the two-layer structure, inferior stiff tissue will accelerate the shear wave speed. The influence would be more significant with the decrease of superior tissue thickness. The frequency and length of shear wave had an effect on the influence.(3) The small focal change of Young’s modulus in cartilage will influence the shear wave speed.Conclusion:(1) The structure of cartilage will significantly influence the shear wave propagation, and could be rectified by some strategies.(2) Using SWE to detect the focal Young’s modulus change due to cartilage degeneration is feasible and sensitive.