Subchondral screw abutment: does it harm the joint cartilage? An in vivo study on sheep tibiae

Purpose Subchondral screw abutment in osteosynthesis of joint fractures is an effective method to achieve sufficient screw grip. In this study we investigated if subchondral screw placement is possible without harming the overlying subchondral plate and joint cartilage iatrogenic. Materials and Methods A 3.5-mm conventional steel screw was placed in the tibia of ten sheep in distances between 1 and 7 mm beneath the joint cartilage. After a follow up of two and four months, evaluation of the subchondral bone and joint cartilage was performed by means of a histological osteoarthritis score, HRpQCT imaging and determination of the glycosaminoglycan content in the cartilage. The control group was the contralateral knee of the same animal. Results Histomorphometric evaluation of the Mankin osteoarthritis score revealed no significant difference compared to the control after two (p = 0.102) and four months (p = 0.429). No correlation between distance of the screw to the cartilage and histological scoring was found (p = 0.658, R2 = 0.04 after two months and p = 0.171, R2 = 0.18 after four months). HRpQCT measurements of the subchondral thickness between screw and cartilage after two (p = 0.05) and four months (p = 0.424) showed no significant difference. Mean glycosaminoglycan content in the treatment group compared to the control after two months (p = 0.25) and four months (p = 0.523) was not significant different. Conclusion In conclusion subchondral screw abutment did not damage the joint cartilage after a two- and four-month follow up in this sheep model.