Evaluation of the theoretical optimal angle of the tibial tunnel in transtibial anatomic posterior cruciate ligament reconstruction by computed tomography

BACKGROUND: “Killer turn” effect is a critical explanation for the recurrent posterior laxity following transtibial posterior cruciate ligament (PCL) reconstruction, which affected by the angle of the tibial tunnel. Meanwhile, excessive tunnel angle would have an adverse impact on the healing of tendon to bone. The purpose was to evaluate the theoretical optimal angle of the tibial tunnel in transtibial anatomic PCL reconstruction. METHODS: The measurements were performed on CT sagittal plane, including the thickness of cancellous bone (L1), the theoretical optimal angle of the tibial tunnel (TOA, which was measured between tibial plateau and the extension cord connecting the center of PCL insertion site with a point 5 mm superior from marrow cavity vertex), L2 - the distance from anterior tunnel aperture to anterior end of tibial plateau, L3 - the distance from anterior tunnel aperture to tibial tuberosity (lowest edge of patellar ligament attachment). RESULTS: The value of TOA and L3 were 35.4 ± 7.9 ° and 26.8 ± 11.4 mm, respectively. L1 and L2 were higher in males than females (L1, P = 0.002; L2, P = 0.046). Regarding age, L1, TOA, L2 and L3 were higher in the 46–60 years group than 31–45 years group (P = 0.02, P = 0.001, P = 0.038, P = 0.032, respectively). With regard to height, L1 was lower in group I - < 1.66 m than group II - 1.66 to 1.75 m and group III - > 1.75 m (I v II, P = 0.015, I v III, P = 0.026). L2 was also lower in group I than group II and group III (I v II, P = 0.026, I v III, P = 0.006). TOA and L3 showed no significant differences among sex and height groups (P > 0.05). CONCLUSIONS: TOA (35.4 ° ± 7.9 °) and L3 (26.8 ± 11.4 mm) could be used as a reference for ideal tibial tunnel placement in transtibial anatomic PCL reconstruction, so as to prevent recurrent PCL laxity and ensure good graft healing. However, further clinical validation is needed.