title: Ultrasound indentation of bovine knee articular cartilage in situ.
abstract: We have earlier developed a handheld ultrasound indentation instrument for the diagnosis of articular cartilage degeneration. In ultrasound indentation, cartilage is compressed with the ultrasound transducer. Tissue thickness and deformation are calculated from the A-mode ultrasound signal and the stress applied is registered with the strain gauges. In this study, the applicability of the ultrasound indentation instrument to quantify site-dependent variation in the mechano-acoustic properties of bovine knee cartilage was investigated. Osteochondral blocks (n=6 per site) were prepared from the femoral medial condyle (FMC), the lateral facet of the patello-femoral groove (LPG) and the medial tibial plateau (MTP). Cartilage stiffness (dynamic modulus, E(dyn)), as obtained with the ultrasound indentation instrument in situ, correlated highly linearly (r=0.913, p<0.01) with the values obtained using the reference material-testing device in vitro. Reproducibility (standardized coefficient of variation) of the ultrasound indentation measurements was 5.2%, 1.7% and 3.1% for E(dyn), ultrasound reflection coefficient of articular surface (R) and thickness, respectively. E(dyn) and R were site dependent (p<0.05, Kruskall-Wallis H test). E(dyn) was significantly higher (p<0.05, Kruskall-Wallis Post Hoc test) in LPG (mean+/-SD: 10.1+/-3.1MPa) than in MTP (2.9+/-1.4MPa). In FMC, E(dyn) was 4.6+/-1.3MPa. R was significantly (p<0.05) lower at MTP (2.0+/-0.7%) than at other sites (FMC: 4.2+/-0.9%; LPG: 4.4+/-0.8%). Cartilage glycosaminoglycan concentration, as quantified with the digital densitometry, correlated positively with E(dyn) (r=0.678, p<0.01) and especially with the equilibrium Young's modulus (reference device, r=0.874, p<0.01) but it was not associated with R (r=0.294, p=0.24). We conclude that manual measurements are reproducible and the instrument may be used for detection of cartilage quality in situ. Especially, combined measurement of thickness, E(dyn) and R provides valuable diagnostic information on cartilage status.
authors.affiliation: Department of Clinical Physiology and Nuclear Medicine, Kuopio University Hospital and University of Kuopio, POB 1627, FIN-70211, Kuopio, Finland. mikko.laasanen@uku.fi
authors.forename: Mikko S
authors.initials: MS
authors.lastname: Laasanen
authors.forename: Simo
authors.initials: S
authors.lastname: Saarakkala
authors.forename: Juha
authors.initials: J
authors.lastname: Töyräs
authors.forename: Jani
authors.initials: J
authors.lastname: Hirvonen
authors.forename: Jarno
authors.initials: J
authors.lastname: Rieppo
authors.forename: Rami K
authors.initials: RK
authors.lastname: Korhonen
authors.forename: Jukka S
authors.initials: JS
authors.lastname: Jurvelin
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000000981:diagnostic imaging* / Q000378:metabolism; D002417:Cattle; D003720:Densitometry; D004548:Elasticity; D004867:Equipment Design; D005240:Feasibility Studies; D006025:Glycosaminoglycans / Q000378:metabolism; D007719:Knee Joint / Q000000981:diagnostic imaging* / Q000378:metabolism; D015203:Reproducibility of Results; D014463:Ultrasonography / Q000295:instrumentation
chemical_list: D006025:Glycosaminoglycans