Arthroscopic Fixation of Matrix-Associated Autologous Chondrocyte Implantation: Importance of Fixation Pin Angle on Joint Compression Forces

Purpose: The aim of the study was to investigate the effect of pin fixation perpendicular and 30 degrees tilted to the matrix surface on the joint compression forces. Methods: In a porcine knee model, joint compression forces were recorded with a digital pressure sensor above the medial meniscus and with axial compression of 100 N by use of a material testing machine. The forces were recorded for an intact femoral condyle, as well as a standardized cartilage defect of 25 X 20 mm, after matrix-associated autologous chondrocyte implantation (m-ACI) (BioSeed C; Biotissue Technologies, Freiburg, Germany), fixed by use of a conventional suture technique and pin fixation with a biodegradable pin perpendicular and 30 degrees tilted to the matrix surface. Results: In knees with cartilage defects, the peak compression forces (mean, 824 kPa) were significantly increased compared with the intact knee joint (564 kPa). After m-ACI implantation with a chondral suture (581.3 kPa) and perpendicular pin fixation, the joint compression forces of the cartilage defect were significantly decreased (630.7 kPa). There were no significant differences compared with the intact knee. After 30 tilted pin insertion, mean joint compression forces were significantly increased (1,740 kPa). Conclusions: This study shows that after chondral suture and perpendicular pin fixation, there are no increased compression forces in the knee joint in comparison to an intact knee. Thirty degree tilted pin insertion contributes to increased joint compression forces. Clinical Relevance: A tilted insertion during pin fixation in m-ACI should be avoided because it may lead to increased joint compression forces, especially after cartilage defect lesions on the tibial side.