研究目的
To demonstrate the capability of a fiber optic microindenter sensor to discriminate between healthy and slightly degenerated human articular cartilage samples, specifically for early osteoarthritis diagnosis.
研究成果
The FBG microindenter effectively discriminates between healthy (Outerbridge grade 0) and early degenerated (grade 1) human cartilage, showing statistically significant differences in stiffness parameters. The viscoelastic model fits well for both healthy and osteoarthritic tissue, indicating its general applicability. The small dimensions of the indenter enable potential endoscopic use, offering an objective alternative to subjective haptic evaluation. However, it does not significantly differentiate between grades 1 and 2, suggesting limitations for more advanced degeneration. Future studies should explore broader comparisons and in vivo validation.
研究不足
The study was conducted in vitro, which may not fully replicate in vivo conditions. The force measurement has a lower detection limit of 2.5 mN due to static friction, limiting sensitivity for very soft tissues. The sample size was small (seven specimens, with varying numbers per grade), and variability due to age, gender, and spatial differences in cartilage could affect results. The system cannot distinguish between Outerbridge grades 1 and 2 with statistical significance. Future work is needed for comparisons with other grading methods like Mankin score and for in vivo applications.
1：Experimental Design and Method Selection:
The study used a fiber optic microindenter based on a Fiber Bragg Grating (FBG) sensor for stress-relaxation indentation measurements on human cartilage samples. A viscoelastic Maxwell-Wiechert model with two elements (three springs and two dampers) was applied to fit the relaxation data and extract stiffness and time parameters.
2：Sample Selection and Data Sources:
Seven human tibia plateau specimens from donors undergoing knee replacement were used. From each specimen, three samples with different Outerbridge grades (0, 1, and 2) were extracted based on visual and haptic inspection by an experienced surgeon. Samples were stored in phosphate buffered saline (PBS) at 4°C before measurements.
3：List of Experimental Equipment and Materials:
Equipment included a fiber optic microindenter (silica glass optical fiber with FBG), a piezo stage (HERA
4：1, PI GmbH), a fast interrogator (I4, FAZ technologies ltd.), a high precision scale (KB1200-2 N, Kern & Sohn GmbH), a capillary for the indenter, cement glue (Cerastil V336, Panacol), a goniometer for sample alignment, and a desktop computer for control and data acquisition. Materials included human cartilage samples and PBS solution. Experimental Procedures and Operational Workflow:
6 The sensor head was positioned orthogonally to the cartilage surface. Stepwise indentation was performed: the indenter was moved in 40 μm steps at 333 μm/s speed, with 240 s relaxation after each step, for a total of eight steps up to 320 μm depth. Bragg wavelengths of the indenter and a temperature reference sensor were measured at 1 kHz rate. Data were post-processed to compensate for temperature effects and converted to force using a linear model.
5：Data Analysis Methods:
Relaxation data were fitted with a double exponential function (Prony series) to extract stiffness (Ke, K1, K2) and time (τ1, τ2) parameters. Statistical analysis (ANOVA) was performed on stiffness parameters at maximum indentation depth to assess differences between Outerbridge grades.
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