Delayed lubricin injection improves cartilage repair tissue quality in an in vivo rabbit osteochondral defect model

Osteochondral lesions (OCL) are common among young patients and often require surgical interventions since cartilage has a poor capacity for self-repair. Bone marrow stimulation (BMS) has been used clinically for decades to treat OCLs, however a persisting challenge with BMS and other cartilage repair strategies is the inferior quality of the resulting fibrocartilaginous repair tissue. Lubrication-based therapies have the potential to improve the quality of cartilage repair tissue as joint lubrication is linked to local cartilage tissue strains and subsequent cellular responses including death and apoptosis. Recently, a full length recombinant human lubricin (rhLubricin) was developed and has been shown to lower friction in cartilage. This study investigated the effect of a single delayed injection of rhLubricin on cartilage repair in an in vivo rabbit OCL model using gross macroscopic evaluation, surface profilometry, histology, and tribology. Moderate improvement in macroscopic scores for cartilage repair were observed. Notably, quantitative analysis of Safranin-O histology showed that rhLubricin treated joints had significantly higher glycosaminoglycan content compared to saline treated joints, and there were no differences in repair integration between groups. Furthermore, rhLubricin treated joints had significantly lower friction coefficients tested across three sliding speeds compared to saline treated joints (rhLubricin: 0.15 ± 0.03 at 0.1 mm/s to 0.12 ± 0.03 at 10 mm/s, Saline: 0.22 ± 0.06 at 0.1 mm/s to 0.19 ± 0.05 at 10 mm/s). Overall, a single delayed injection of rhLubricin improved the quality and lubricating ability of the repair cartilage tissue without inhibiting repair tissue integration.