THE RELATIONSHIP BETWEEN THE IN VIVO MEASURED STIFFNESS AND THE HISTOLOGICAL STAGE OF DEGENERATION OF HUMAN KNEE ARTICULAR CARTILAGE

Abstract

Purpose: To determine the relationship between the in vivo indentation stiffness and indices of histopathological degeneration of human knee articular cartilage.

Materials and Methods: Cartilage compressive stiffness was measured in 98 patients during in vivo knee arthroscopies. The age of the patients ranged from 21 to 63 years (mean age 29 years). Male to female ratio of the patients was 37:61. The measurements were performed at eight standard sites. No chondropathic or grade I. chondropathic surfaces were measured. An indentation instrument, Artscan 1000, was used for in vivo measurements. Four plugs were harvested from each knee for histological analysis. The stage of cartilage degeneration was assessed according to Mankin histolopathology score. 16 measurements were performed after ACI.

Results: Lateral femoral condyle stiffness (mean + SD; 5.12 ±1.02N) was greater than all other sites and was significantly greater than mean values obtained for medial femoral condyle (4.8 ± 1.22N); medial and lateral trochlea (4.2 + 0.92, 4.6 + 1.27N), medial (3.1 ± 0.66N) and lateral patella (3.3 ± 1.01N); and medial and lateral tibial condyle for all subjects (2.4 ± 1.17N and 3.2 ± 1.16N).

The dynamic modulus of the normal or mildly degenerated cartilage correlated negatively with the Mankin score: r (Spearman) = −0.823, n =

348. All visually degenerated samples were softer (dynamic modulus < 2.9 Mpa) than the visually and histologically normal samples (dynamic modulus = 14.7 + 2.9 MPa). Stiffness at the repaired site was similar to normal cartilage at adjacent sites in the knee.

Conclusion: The high negative correlation between stiffness and the Mankin score suggests that the stage of cartilage degeneration can be quantitatively and indirectly assessed with a hand-held instrument during arthroscopy.