ACL graft with extra-cortical fixation rotates around the femoral tunnel aperture during knee flexion

Junjun Zhu; Brandon Marshall; Xin Tang; Monica A Linde; Freddie H Fu; Patrick Smolinski

doi:10.1007/s00167-021-06703-8

ACL graft with extra-cortical fixation rotates around the femoral tunnel aperture during knee flexion

Knee Surg Sports Traumatol Arthrosc. 2022 Jan;30(1):116-123. doi: 10.1007/s00167-021-06703-8. Epub 2021 Sep 9.

Authors

Junjun Zhu¹, Brandon Marshall², Xin Tang³, Monica A Linde⁴, Freddie H Fu^{4

2}, Patrick Smolinski^{5

6}

Affiliations

¹ School of Mechatronic Engineering and Automation, Shanghai University, Shanghai, 200444, China.
² Department of Mechanical Engineering and Material Science, University of Pittsburgh, Pittsburgh, PA, 15213, USA.
³ Department of Orthopedic Surgery, West China Hospital/Medical College, Sichuan University, Chengdu, 610041, China.
⁴ Department of Orthopaedic Surgery, University of Pittsburgh School of Medicine, 3471 Fifth Avenue, Suite 1011, Pittsburgh, PA, 15213, USA.
⁵ Department of Orthopaedic Surgery, University of Pittsburgh School of Medicine, 3471 Fifth Avenue, Suite 1011, Pittsburgh, PA, 15213, USA. patsmol@pitt.edu.
⁶ Department of Mechanical Engineering and Material Science, University of Pittsburgh, Pittsburgh, PA, 15213, USA. patsmol@pitt.edu.

PMID: 34499210
DOI: 10.1007/s00167-021-06703-8

Abstract

Purpose: An understanding of the behavior of a new ACL graft in the femoral tunnel during knee motion and external loading can provide information pertinent to graft healing, tunnel enlargement, and graft failure. The purpose of the study was to measure the percentage of the tunnel filled by the graft and determine the amount and location of the graft-tunnel contact with knee motion and under external knee loads.

Methods: Single bundle anatomical ACL reconstruction was performed on six cadaveric knees. Specimens were positioned with a robotic testing system under: (1) passive flexion-extension, (2) 89-N anterior and posterior tibial loads, (3) 5-N m internal and external torques, and (4) 7-N m valgus moment. The knees were then dissected, repositioned by the robot and the geometry of the femoral tunnel and graft were digitized by laser scanning. The percentage of tunnel filled and the contact region between graft and tunnel at the femoral tunnel aperture were calculated.

Results: The graft occupies approximately 70% of the femoral tunnel aperture and anterior tibial loading tended to reduce this value. The graft contacted about 60% of the tunnel circumference and the location of the graft-tunnel contact changed significantly with knee flexion.

Conclusion: This study found that the graft tends to rotate around the tunnel circumference during knee flexion-extension and contract under knee loading. The "windshield-wiper" and "bungee cord" effect may contribute to femoral tunnel enlargement, affect graft healing, and lead to graft failure. There can be a considerable motion of the graft in the tunnel after surgery and appropriate rehabilitation time should be allowed for graft-tunnel healing to occur. To reduce graft motion, consideration should be given to interference screw fixation or a graft with bone blocks, which may allow an earlier return to activity.

Keywords: ACL reconstruction; Bungee cord effect; Femoral tunnel; Graft motion; Windshield–wiper.

MeSH terms

Anterior Cruciate Ligament*
Biomechanical Phenomena
Cadaver
Femur* / surgery
Humans
Knee Joint / surgery
Range of Motion, Articular
Tibia