Potential risk of cartilage damage in double bundle ACL reconstruction: impact of knee flexion angle and portal location on the femoral PL bundle tunnel

The aim of this study was to compare the impact of knee flexion angle and the level of the medial drilling portal on a potential damage to the subchondral bone in double bundle ACL reconstruction, drilling the femoral PL tunnel through an accessory medial portal. We hypothesized that a knee flexion angle of 70° and 90° or a high accessory medial portal will result in a potential damage to the subchondral bone of the lateral femoral condyle. In a sawbone knee model, the medial portal location was standardized as 0 mm above the meniscus (low portal) and 10 mm above the meniscus (high portal). Femoral PL bundle tunnels were drilled at three different knee flexion angels: 70°, 90°, and 110° of knee flexion. For each portal, ten specimens were used for every flexion angle. Drilling the PL tunnel through the high medial portal at a knee flexion angle of 70° resulted in damage of the subchondral bone plate in all specimens. At 110° of flexion the distance of the tunnel exit to the subchondral bone plate was significantly higher than at 70° of flexion for both the groups, drilling through the high and low medial portal (P < 0.05). Drilling through the low portal did not result in bone plate damage at 90 and 110° of knee flexion angle. Drilling of the femoral PL bundle tunnel through a high medial portal at low knee flexion angles may damage the subchondral bone of the lateral compartment. In ACL reconstruction restoring the AM and PL bundle separately, high medial portal drilling should be avoided. We recommend drilling of the femoral PL bundle tunnel through a low medial portal in high knee flexion.