Evaluation of cartilage defects with near-infrared spectroscopy (NIR): an ex vivo study.

Damaged cartilage undergoes complex changes in composition, histological structure, and mechanical properties. Near-infrared-spectroscopy (NIR spectroscopy) is an important method to measure changes in composition of complex composites. The present study was aimed at evaluating NIR spectroscopy as a means to quantitate tissue alterations in low grade cartilage defects. Fresh medial femoral condyles from female sheep were collected. Cartilage defects were graded according to the International Cartilage Repair Society (ICRS). Specimens were examined by a NIR spectroscopy device (spectral range of 1100-1700 nm). Absorption spectra were calculated from the reference and measurement spectra. As indicator for cartilage composition the ratio (absorption ratio, AR) of the two main absorption bands in this region was calculated. Mechanical stiffness was measured as Shore A. Water-, glycosaminoglycan-, and collagen content and histological grade (Mankin score) were determined. The NIR absorption in ICRS grade 1 defects (AR=2.1+/-0.1) was significantly higher than in intact cartilage (AR=1.5+/-0.1). ICRS grade 2 specimens tended to a higher NIR absorption. NIR absorption correlated significantly with Mankin score (R=0.896), water content (R=0.845), and mechanical stiffness (R=0.877). Initial cartilage degeneration correlates with changes in NIR absorption, indicating NIR spectroscopy to reflect complex structural changes in degenerated cartilage. The data suggest that NIR spectroscopy could be useful for in situ detection of early cartilage defects.

Mechanical behavior of intact and low-grade degenerated cartilage.

Young's modulus, elastic and plastic deformation, mechanical hardness and load at failure were determined for low-grade degenerated hyaline cartilage in a porcine model. Osteochondral plugs from the medial condyle of 30 female pigs were used. Cartilage defects were classified using the International Cartilage Repair Society (ICRS) protocol. Mechanical hardness was measured using a Shore A testing device. Total stiffness and plastic deformation was evaluated in the range 50-200 N using a 5-mm indenter. The load at failure was then determined. ICRS grade I specimens showed significantly lower stiffness than grade 0 specimens. ICRS grade 0 specimen showed no significant plastic deformation within the load range 25-100 N. In degenerated cartilage, plastic deformation started at a significantly lower load (50 N). The Young's modulus at 25 N in ICRS grade 0 specimens (18.8 MPa) was significantly higher than in grade I (11.1 MPa) or grade II (10.5 MPa) specimens. Intact cartilage showed significantly higher tension at failure and mechanical Shore A hardness. Young's modulus and tension at failure showed strong correlation. Cartilage degeneration is associated with a significant loss of elasticity and mechanical stress resistance. Shore hardness measurement is an adequate method for rapid biomechanical evaluation of cartilage specimens.

Karl Fischer titration and coulometry for measurement of water content in small cartilage specimens.

This study evaluated the efficiency of Karl Fischer titration and coulometry for measurement of water content in small intact and defective cartilage specimens. Cartilage from the main weight-bearing zone of the medial condyle of 38 fresh sheep knees was used. Of these, 20 condyles had an intact cartilage, while defects (14 grade I and 4 grade II) were found in the rest. The mechanical hardness was determined as Shore A. Cartilage specimens of approximately 5 mg were analyzed in special devices for moisture measurement and then continuously heated up to 105 degrees C. The actual measurement was performed in an electric cell (coulometry). An electrode was laminated with hygroscopic phosphorus pentoxide. In the electrochemical reaction, H and O are liberated from the electrode. The requirement for electric energy correlates with the amount of water in the specimen. The water content in intact cartilage was 66.9%. Grade I (72.6%) and grade II (77.8%) defects had significantly higher water content. Significantly higher and faster spontaneous evaporation was observed in cartilage defects at room temperature. The water content and spontaneous water evaporation correlated with significantly lower mechanical hardness. The experimental design (combined method of thermogravimetry, Karl Fischer titration, and coulometry) was sufficient for evaluating the water content in small cartilage specimens. It is also possible to measure the temperature-dependent water liberation from cartilage specimens.