Lubricin

Objective: To determine if lubricin was present in the surface layer of repair cartilage formed after autologous chondrocyte implantation (ACI). Design: Forty-three biopsies of repair tissue were taken from patients who had been treated with ACI 8 to 68 months previously (mean of 18.0 ± 14.4 months); 30 had flaps of periosteum and 13 of Chondro-Gide. Cryopreserved sections were stained with hematoxylin and eosin, toluidine blue, and immunostained for lubricin and type II collagen. The quality of repair tissue was scored via OsScore, and clinical improvement in patients was assessed via change in Lysholm score. Normal/control cartilage was studied for comparison (n = 5). Results: Patients’ Lysholm scores improved from 48.1 ± 17 preoperatively to 69.5 ± 21.5 posttreatment. The thickness of repair tissue was 2.9 ± 1.7 mm compared with 2.3 ± 0.6 mm for control cartilage, with an OsScore of 6.7 ± 1.6 (8.9 ± 1.2 for controls). Ninety-eight percent of biopsies had staining for lubricin, with 84% having some in the surface layer (60% of periosteal treated and 100% of Chondro-Gide treated). The improvement in Lysholm score was not significantly different in patients with lubricin present at the surface compared with those without. Conclusion: Lubricin was present in almost all samples of repair tissue formed post ACI, often in the surface layer, resembling the distribution that is seen in normal cartilage. The presence of lubricin in the upper layer is likely to have implications for the functioning of the tissue because, via its mucin-like repeats, it appears capable of reducing the friction that could arise in articulating joints.