Chondrocyte death after drilling and articular screw insertion in a bovine model

Abstract

Intra-articular screws are used for internal fixation of osteochondral fragments after fracture or osteochondritis dissecans. This causes cartilage injury potentially leading to chondrocyte death. We have visualised/quantified the hole and zone of cell death (ZCD) in cartilage after drilling/insertion of various articular screws. Using an exvivo bovine model with transmitted light and confocal laser scanning microscopy (CLSM), the holes and ZCD following drilling/insertion of articular screws (cortical screw, headless variable pitch metallic screw, headless variable pitch bioabsorbable screw) were evaluated. In situ chondrocyte death was determined by live/dead cell viability assay. An imaging/quantification protocol was developed to compare hole diameter and ZCD from drilling/insertion of screws into cartilage. The effect of saline irrigation during drilling on the ZCD was also quantified. Screw insertion created holes in cartilage that were significantly (P≤0.001) less than the diameters of the equipment used. With a 1.5mm drill, a ZCD of 580.2±124μm was produced which increased to 637.0±44μm following insertion of a 2mm cortical screw although this was not significant (P>0.05). The ZCD from insertion of the variable pitch headless screws (diam. 3.5mm) was lower for the metallic compared to the bioabsorbable design (800.9±159 vs 1,236.4±212μm, respectively; P<0.01). The ZCD from drilling was reduced ∼50% (P<0.001) by saline irrigation. Cartilage injury during intra-articular screw fixation caused a ZCD around the hole irrespective of screw design. Saline irrigation significantly reduced the ZCD from drilling into cartilage.