A more flattened bone tunnel has a positive effect on tendon–bone healing in the early period after ACL reconstruction

  • Fengyuan Zhao
  • Xiaoqing Hu
  • Jiahao Zhang
  • Weili Shi
  • Bo Ren
  • Hongjie Huang
  • Yingfang AoEmail author



The purpose of this study was to evaluate whether a flattened bone tunnel has a positive effect on the tendon–bone healing (TBH) process in the early period after anterior cruciate ligament (ACL) reconstruction.


Seventy-two New Zealand White rabbits were randomly allocated into two groups, the flattened tunnel (FT) group and the conventional round tunnel (RT) group. We compared the cross-sectional areas and diameters of the bone tunnels between the two groups through computed tomography (CT) scanning. TBH results between the two groups were assessed by histological analysis, micro-CT scanning and biomechanical tests at 4 weeks, 8 weeks and 12 weeks after operation.


The cross-sectional areas of the bone tunnels between the two groups were almost the same. However, the shape of bone tunnels in the FT group was more flattened. A faster cellular and collagen remoulding process were found in the FT group. Semiquantitative histological analysis of Safranin O staining showed that there was more fibrocartilage formation in the interface region in the FT group (P < 0.05). Sirius Red staining showed that the tissues in the interface areas were more intense in the FT group. Micro-CT scanning showed that more new bone formation could be found in the interface region in the FT group. The biomechanical tests also showed that FT ACL reconstruction will result in a stronger regenerated tendon–bone interface.


Our study found that a flattened bone tunnel accelerated TBH in the early period after ACL reconstruction surgery in a rabbit model, which lays the groundwork for further clinical practice of this ACL reconstruction method.


Anterior cruciate ligament Flattened Tendon-bone healing Ribbon-like 



Anterior cruciate ligament


Flattened tunnel


Round tunnel


Tendon–bone healing


Computed tomography


Region of interest


Bone volume/total volume






Confidence interval


Intraclass correlation coefficient



The authors gratefully acknowledge Jiying Zhang, BS, Xiaoning Duan, BS and Xin Fu, BS for active participation in histological experiments.

Author contributions

Fengyuan Zhao carried out the ACL reconstruction surgery in rabbits, participated in the histological analysis and drafted the manuscript. Xiaoqing Hu designed of the study, performed the statistical analysis and carried out the micro-CT scanning. Jiahao Zhang participated in the histological analysis and measured the cross-sectional areas and diameters of bone tunnels. Weili Shi also measured the cross-sectional areas and diameters of bone tunnels and participated in the micro-CT analysis. Bo Ren did the biomechanical tests of specimens. Hongjie Huang participated in the calculation of the areas and diameters of bone tunnels. Yingfang Ao conceived of the study, and participated in its design and coordination and helped to draft the manuscript. All authors read and approved the final manuscript.


No external funding was used.

Compliance with ethical standards

Conflict of interest

The authors declare that they have no conflict of interest.

Ethical approval

This article does not contain any studies with human participants performed by any of the authors.

Supplementary material

167_2019_5420_MOESM1_ESM.pdf (158 kb)
Supplementary material 1 (PDF 158 KB)
167_2019_5420_MOESM2_ESM.docx (15 kb)
Supplementary material 2 (DOCX 14 KB)
167_2019_5420_MOESM3_ESM.docx (14 kb)
Supplementary material 3 (DOCX 14 KB)


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Copyright information

© European Society of Sports Traumatology, Knee Surgery, Arthroscopy (ESSKA) 2019

Authors and Affiliations

  1. 1.Institute of Sports Medicine, Beijing Key Laboratory of Sports InjuriesPeking University Third HospitalBeijingPeople’s Republic of China

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