Stiffness and shape of the ACL graft affects tunnel enlargement and graft wear



Tunnel enlargement and graft rupture are common complications associated with ACL reconstruction (ACLR). This study aims to explore how variations in graft stiffness and shape affect the strain energy density (SED) around bone tunnel entrances and stress on the graft and subsequently influencing the level of tunnel enlargement and graft wear.


Finite element ACLR models were developed using different graft stiffnesses (323 N/mm, 545 N/mm and 776 N/mm) and shapes (circular and elliptical). The models were subjected to a combined loading of 103 N anterior tibial load, 7.5 Nm internal tibial moment, and 6.9 Nm valgus tibial moment at joint flexion of 30°. SED at tunnel entrances and stresses on the graft was recorded and compared among the different models.


Increasing the graft stiffness resulted in greater stress on the graft (17.2, 24.4 and 31.7 MPa for graft stiffnesses of 323 N/mm, 545 N/mm and 776 N/mm), but had little effect on the SED reduction around the tunnel entrances. Changing the cross section of the graft from circular to elliptical caused an additional reduction in SED (56.8 vs 2.8 kJ/m3) at the posterior zone of the femoral tunnel entrance and increased the stress on the graft (31.7 MPa vs 38.9 MPa).


This study recommends using ACL grafts with lower stiffness and a circular cross section to reduce tunnel enlargement and graft wear following ACLR.

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Cadaveric experiments for model validation were performed at MSRC, University of Pittsburgh. The authors would like to thank Dr. Savio L-Y. Woo for his kind support in sourcing samples and equipment. We would also like to thank Dr. Jonquil R. Mau and Dr. Huijun Kang for their help with robotic testing. Mr. Colin McClean is acknowledged for his assistance with editing this manuscript.


This research did not receive any specific grant from funding agencies in the public, commercial, or not-for-profit sectors.

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Correspondence to Cheng-Kung Cheng.

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The authors have no conflicts of interest to disclose.

Ethical approval

All procedures performed in this study involving human cadaveric knees were approved by the Committee for Oversight of Research and Clinical Training Involving Decedents in the University of Pittsburgh (CORID No. 222) and were in accordance with the 1964 Helsinki Declaration and its later amendments or comparable ethical standards. This article does not contain any studies with animals performed by any of the authors.

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Wang, H., Zhang, B. & Cheng, CK. Stiffness and shape of the ACL graft affects tunnel enlargement and graft wear. Knee Surg Sports Traumatol Arthrosc 28, 2184–2193 (2020).

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  • Finite element analysis
  • ACLR
  • ACL graft
  • Bone tunnel enlargement
  • Graft wear