A comparative study of a new "off-centre:off-centre" technique of transtibial ACL reconstruction with "centre:centre" transportal ACL reconstruction.

Background & Introduction: A Single Bundle ACL Reconstruction aims at placing Tibial and Femoral attachment sites of graft from Centre of Native Tibial Foot-print to Centre of Native Femoral Footprint. In tibial tunnel independent Transportal Reconstruction, where the two points are chosen separately, the objective is easily achievable. In Tibial tunnel dependent Transtibial ACL reconstruction, Capture of Centre of femoral tunnel is dictated by Trajectory of Tibial Tunnel. Heming et al. remarked that a TT technique could produce tunnel centred in the both the tibial and femoral footprint but only if a starting point "prohibitively close" to the joint line with a correspondingly short tibial tunnel were used. A new technique wherein authors aim to place the mouths of Tibial & Femoral tunnel at off-centre location, taking care to contain these tunnels still within native footprints to achieve a tunnel which is of adequate length and does not come too close to the joint and saves MCL from violation.

Objective: To study the clinic-radiological outcome of a new "Off-centre to Off-centre" method of Transtibial Reconstruction and compare the results with "centre to centre" method of Transportal reconstruction.

Methods: A prospective randomised comparative study of consecutive 75 clinico-radiological cases of ACL tear with definitive clinical symptoms of knee instability who underwent arthroscopic ACL reconstruction by Same Arthroscopy Surgeon was conducted between 2016 and 2018. A modification, as described herein below, was used in Transtibial technique with placement of centre of mouth of internal opening of tibial tunnel "off-centre" that allowed a predictable capture of Femoral Footprint in "off-centre" location without tunnel being too close to joint line. Only those cases were included in which the mouths of tunnel were completely contained within footprints. Capture of footprints was verified during arthroscopy. 11 cases were excluded because either the native footprint was not clearly delineated, or surgeon failed to completely contain the mouth of tunnel/socket within the delineated footprint of tibia or femur. Hence 64 patients, 32 each in Transtibial & Transportal group were enrolled into the study. The results were analysed with the objective to arrive at recommendations for improving capture of anatomical footprints at both ends by Transtibial technique.

Results: There were no statistically significant differences in Clinical outcome scores. However there were statistically significant differences in length of Femoral Tunnel, Obliquity of Femoral tunnel as well as Femoral Tunnel Placements. Likewise, Tibial Tunnel Angle in AP & Lateral View as well as Tibial tunnel placement were also significantly different.

Conclusion: It is concluded that tunnels follow much different trajectories in the bones in two techniques and trying to apply "Centre of Tibial footprint to Centre of Femoral footprint" philosophy of Transportal technique may be imprudent for Transtibial Technique. An "Off-centre to Off-centre but contained within Footprints" may afford a more predictable and reliable capture of anatomical foot prints without any adverse effect on outcomes.