EFFECT OF INJURIOUS COMPRESSION OF THE SUPERFICIAL ZONE AND DEEPER ZONES OF HUMAN ARTICULAR CARTILAGE EXPLANTS OF DEGENERATIVE KNEE AND ANKLE JOINTS *(**)Rolauffs B, *DiMicco M, *Kisiday J, *Fitzgerald J, *Frank E, **Margulis A, **Kuettner KE, **Cole AA, Grodzinsky, A *M.I.T., Cambridge, MA, 77 Massachusetts Ave. NE 47-377, Cambridge, MA 02139
[email protected] **Rush Medical College, Chicago, Illinois, U.S.A.
(MPa)
Superficial Deeper Zones Zone
Fig. 4 Talus Peak stress.
(MPa)
disks from the superficial zones showed significantly lower peak stresses then disks from deeper zones Peakstress Human Knee Collins II during Injury during injury (Fig. 5), and both 14.0 Superficial Zone 12.0 superficial and deeper zone peak stress Deeper Zones 10.0 were comparable in disks from Collins 8.0 II tali and distal femora (Fig. 5). After 6.0 4.0 injury, the re-measured thickness was 2.0 significantly decreased 0.0 Medial Condyle Lateral Condyle Groove Fig. 5 Distal Femur Peak Stress in all disks. Surprisingly, with this choice of injurious compression, the equilibrium modulus remained unchanged in all talus disks and in all superficial zone disks of the degenerative distal femur (Fig. 6). Deeper zones disks of the distal femur showed a significant increase in equilibrium stiffness of the medial condyle and a slight (not significant) increase of the lateral condyle and the femoral groove (Fig. 6). The initial dynamic stiffness was significantly lower in all superficial zone disks and for all frequencies examined (Fig. 6) when compared to deeper zone disks (Fig. 6). Interestingly, the dynamic stiffness of deeper zone medial condyle was significantly lower than the stiffnesses of the lateral condyle or the femoral groove (Fig. 6). Comparing knee- and ankle-joints, the dynamic stiffness of superficial and deeper zone talus disks (Collins II) were significantly higher than the stiffnesses of superficial and deeper zones distal femur disks (Collins II). After injury, the dynamic stiffness of superficial and deep femoral and superficial talus was significantly increased. Deeper zone talus disks remained unchanged (Fig. 6). Collins II
(MPa)
Collins 0-I
1
0.8 0.5
0.3
0.2 0.1
Initial Dynamic Stiffness Dyn. Stiffness after Injury
1
Superficial Zone Dynamic Stiffness Human Groove Collins II 16 14 12 10 8 6 4 2 0 1
0.8 0.5
0.3
0.8
0.5
0.3 0.2
1
0.1
Dyn. Stiffness after Injury
1
Superficial Zone
0.8
0.5
0.3 0.2
0.1
Deeper Zones f (Hz)
Initial Dynamic Stiffness Dyn. Stiffness after Injury
0.8 0.5
0.3
0.2 0.1
1
Superficial Zone
Deeper Zones f (Hz)
Initial Dynamic Stiffness
0.2 0.1
Dynamic Stiffness Human Lateral Condyle Collins II 16 14 12 10 8 6 4 2 0 (MPa)
Dynamic Stiffness Human Medial Condyle Collins II 16 14 12 10 8 6 4 2 0
Dynamic Stiffness Human Talus Collins II (MPa)
(MPa)
Deeper Zones
Superficial Deeper Zones Zone
(MPa)
Superficial Zone
tali showed peak stresses similar to superficial disks derived from degenerative tali Collins II. In contrast, deeper zones disks showed 10.0 significantly higher peak stresses in 8.0 6.0 cartilage derived from degenerative tali 4.0 Collins II (Fig. 4). 2.0 Similar to talus disks, distal femur 0.0
Peakstress Human Talus during Injury 12.0
(MPa)
µm
Introduction Mechanical injury to articular cartilage leads to an increased risk of osteoarthritis (1), a degenerative joint disease, which exhibits different prevalences for different joints (2). Both mechanical injury and osteoarthritis affect the superficial zone of articular cartilage (3-5) but little is known of the effect of mechanical injury on degeneratively changed cartilage. The objective of this study was to examine the effects of injurious compression on the mechanical properties of the superficial and deeper zones of cartilage of degenerative human knee- and ankle joints. Methods Explant & Culture: Within 48 hours of death, two human knee- and four ankle-joints were opened. Two distal femora and two tali were graded on the scale of Collins (1949), modified by Muehlemann (1997), as Collins II and two tali as Collins 0-I. Full thickness articular cartilage explants were harvested from the weight-bearing areas of both medial and lateral condyles, the femoral groove and the talus dome. In degenerative joints (Collins II) cartilage was harvested from the remaining, macroscopically intact looking surface. Explants were cultured for five days in low-glucose Human Explant Thickness DMEM, 10% FBS and Ascorbate. 1200 Following culture, explants were 1000 punched into disks 3mm in diameter 800 600 (femor n=36, talus n=48). 400 Immediately before mechanical 200 testing each individual disk was 0 manually dissected into superficial Talus Medial Lateral Groove Condyle Condyle (S) and deeper zones (D) (measured Fig. 1 Explant thickness (average SE) thickness shown in Fig.1). Mechanical Testing & Injury: All superficial and deeper zone disks were analyzed individually in uniaxial unconfined compression with an incubator-housed tissue loading device (6). All disks were subjected to three sequential compression steps at 10%, 12.5%, 15% strain. The resulting equilibrium loads at these strains were used for computation of the unconfined compression modulus. At 15% offset strain disks were subjected to 1.5% dynamic strain amplitude at 1.0, .8, 0.5, 0.3, 0.2, 0.1 Hz for computation of dynamic stiffness. Equilibrium Modulus +SE Human Talus After 20 minutes unconfined re1.2 Initial Modulus swelling, a 50% injurious Modulus after Injury 1.0 compression at 100% per second was 0.8 applied, followed by 5 minutes unconfined re-swelling. All disk 0.6 thicknesses were re-measured and 0.4 immediate re-measurement of the 0.2 static and dynamic compressive stiffness followed. Control disks were 0.0 Superficial Deep Superficial Deep subjected to the same biomechanical Collins 0-I Collins II assessment minus Fig. 2 Talus Equilibrium Modulus. injurious compression. RESULTS Mechanical Testing: The calculated equilibrium modulus differed significantly (p
