Aims: Clinical methods do not provide direct quantitative information about cartilage functional properties. We have developed a novel handheld ultrasound indentation instrument for the diagnosis of articular cartilage degeneration. This study investigates the feasibility and reproducibility of the instrument to evaluate cartilage properties in situ. Methods: Osteochondral blocks (n=18) were prepared from lateral patellar groove (LPG), medial condyle (FMC) and medial tibial (MTP) of bovine knee. In ultrasound indentation, cartilage is indented with an ultrasound transducer. For the determination of cartilage dynamic modulus, tissue thickness and deformation are calculated using ultrasound and stress is measured with strain gauges. High-resolution material tester was used for reference mechanical tests. Cartilage glycosaminoglycan (GAG) content was determined using digital densitometry. Results: Cartilage dynamic modulus was efþciently detected with the novel instrument (r=0.913 with reference values). Dynamic modulus was signiþcantly (p< 0.05) higher at LPG (10.14±3.11 MPa) than at FMC (4.63±1.32 MPa) or MTP (2.92±1.38 MPa). Ultrasound reßection coeff. from the articular surface was signiþcantly smaller at MTP (2.04±0.73%) than at FMC (4.22±0.88%) or LPG(4.43±0.83%). Reproducibility (standardized coeff. of variation) was 3.0%, 5.2% and 1.7% for thickness, dynamic modulus and ultrasound reßection coeff. Cartilage GAG content correlated positively with dynamic modulus (r=0.678) but it was not related with the ultrasound reßection coeff. (r=0.294, p=0.24). Conclusions: Manual measurements were reproducible and the instrument can be used in situ to detect topographical variation of cartilage mechano-acoustic properties. This study establishes a step towards clinical arthroscopic use.

Aims: Fourier transform infrared imaging (FTIRI) is a new quantitative imaging technique for direct visualization of chemical constituents. Our goal was to investigate the suitability of FTIRI to characterize material properties of articular cartilage (AC) and its ability to indirectly determine biomechanical characteristics of AC. Methods: Cylindrical AC samples (dia.=3.7 mm, n=6) with different stages of osteoarthrosis (OA) were prepared from bovine patellae and mechanical properties of AC were determined with a highresolution material testing device to determine Youngñs modulus (stiffness) at equilibrium (E). After biomechanical testing, one piece of the sample was processed for the histological grading of OA and the other piece was processed for FTIRI. Measurements were conducted from air-dried cryosections. Degree of cartilage degeneration was characterized by the integrated area of amide I and II absorbance. Water content of the specimen was determined from the remaining tissue by measuring the wet and dry weight of the sample. Results: Histological Mankinñs grades of the samples ranged from 0 to 7 indicating that cartilage samples showed only mild to moderate OA. FTIRI absorption showed high correlations with histological grading (r=−0.928) and water content (r=−0.980). Also, average infrared absorption of AC correlated highly linearly with E (r=0.826). Conclusions: Present results show that FTIRI offers a new tool for structural evaluation of AC quality and chemical composition. FTIR correlated well with the histological and biomechanical þndings. Technique offers a new approach to optically determine cartilage constituents. In addition to in vitro research FTIR can be coupled to arthroscopic þber optic probe in order to diagnose cartilage structure and composition in vivo.