Abstract
Introduction
There is interest in minimally invasive solutions that reduce osteoarthritic symptoms and restore joint mobility in the early stages of cartilage degeneration or damage. The aim of the present study was to evaluate the Biolox®delta alumina-zirconia composite as a counterface for articulation against live cartilage in comparison to the clinically relevant CoCrMo alloy using a highly controlled in vitro ball-on-flat articulation bioreactor that has been shown to rank materials in accord with clinical experience.
Methods
The four-station bioreactor was housed in an incubator. The dual axis concept of this simulator approximates the rolling-gliding kinematics of the joint. Twelve 32 mm alumina-zirconia composite femoral heads (Biolox®delta, CeramTec GmbH, Germany) and twelve 32 mm CoCrMo femoral heads (Peter Brehm GmbH, Germany) made up the testing groups. Each head articulated against a cartilage disk of 14 mm diam., harvested from six months old steers. Free-swelling control disks were obtained as well. Testing was conducted in Mini ITS medium for three hours daily over 10 days applying a load of 40 N (∼2 MPa). PG/GAG was determined using the dimethylmethylene blue (DMMB) assay. Hydroxyproline was analyzed by high performance liquid chromatography coupled to a mass spectrometer. Additionally, at test conclusion, chondrocyte survival was determined using Live/Dead assay. Histological analysis was performed using a modified Mankin score. The effect of articulating material (ceramic, CoCrMo) on the various outputs of interest was evaluated using ANOVA. Blocking was performed with respect to the animals. The Mankin scores were compared using the Kruskal–Wallis test.
Results
Cells stayed alive during the course of the 3-week experiment with cell survival values close to or at 80% at test completion. There was no difference between ceramic and free swelling control tissue. However, cell count values were inferior for CoCrMo in the superficial zone (p= 0.003). Tested tissue suffered mostly structural abnormalities. In many samples, the superficial layer was disturbed (and sometimes absent), but deeper layers were little affected. The average Mankin scores were in the range of 2 (out of 14) for both materials (p=0.772; Fig. 1). PG/GAG content in medium was highest for CoCrMo (Fig. 2). Though despite a 10% difference between CoCrMo and ceramic, this did not manifest in statistical significance (p=0.315). Similarly, hydroxyproline release into medium was higher for CoCrMo than ceramic (Fig. 3). This difference (28%) was statistically significant (p=0.024).
Discussion
Overall, the results indicate that ceramic-on-cartilage induces less tissue and cell damage than metal-on-cartilage. However, only the hydroxyproline measurements reached statistical significance, partially due to a large variation within both material groups. Current understanding of cartilage wear is still incomplete. While studies have utilized the coefficient of friction against artificial materials as a surrogate wear marker, the best way to determine wear in in-vitro experiments is not well-established. Here, we used the matrix components proteoglycan and hydroxyproline to predict cartilage damage, but further work is necessary to elucidate the mechanobiological reasons for damage. In summary, from this study, Biolox®delta ceramic is generally superior to CoCrMo in the articulation against hyaline cartilage.
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