Mediolateral Differences of Proteoglycans Distribution at the ACL Tibial Footprint: Experimental Study of 16 Cadaveric Knees

This study aimed to identify the staining pattern of ACL attachment blended with cartilage of the medial tibial plateau at the tibial insertion and histologically characterize the tibial footprint. Sixteen fresh frozen cadaveric knees (mean age: years) were used for this study. The specimens were bisected in the coronal plane, in accordance with the fiber orientation of the ACL tibial attachment. Adjacent sections were then stained with hematoxylin and eosin (H&E) to observe the morphology of the ACL insertion and with fast green and Safranin-O protocols to evaluate for collagen and proteoglycans (PG). The insertion area on the tibial footprint was divided into five zones in the medial to lateral direction, which was determined by division of the section from most prominent medial tibial spine to most lateral margin of ACL attachment. Then rectangular area with a vertical length that is twice the width of respective five zones was set. Stained areas of all images were quantified positively by using ImageJ software, and the value for staining area measured was defined in percentage by multiplying whole image area by 100. The mean proportion of Safranin-O staining is significantly greater nearer to the medial tibial spine (59% in zone 1, 32% in zone 2, 13% in zone 3, 13% in zone 4, and 4% in zone 5, ). The medial section of the tibial insertion area grew in size and increased in PG staining with more densely organized collagen arrangement with more fibrocartilage cells. The ACL tibial insertion showed a medially eccentric staining pattern by histological evaluation of the ACL attachment to cartilage. Our histological results of the eccentric biomaterial property in the medial tibial spine of ACL insertion area can be considered in making a more functional anatomic tibial tunnel placement.

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