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. 2022 Dec 19:10:967411.
doi: 10.3389/fbioe.2022.967411. eCollection 2022.

Hourglass-shaped grafts are superior to conventional grafts for restoring knee stability and graft force at knee flexion angle of 30° following anterior cruciate ligament reconstruction: A finite element analysis

Huizhi Wang  1 , Chaohua Fang  1   2 , Mingzhu Tao  1 , Qinyi Shi  1 , Kaixin He  1 , Cheng-Kung Cheng  1
Affiliations

Hourglass-shaped grafts are superior to conventional grafts for restoring knee stability and graft force at knee flexion angle of 30° following anterior cruciate ligament reconstruction: A finite element analysis

Huizhi Wang et al. Front Bioeng Biotechnol. .

Abstract

Background: Anterior cruciate ligament reconstruction (ACLR) using a generally columnar graft is considered the gold standard for treating anterior cruciate ligament ruptures, but such grafts cannot replicate the geometry and mechanical properties of the native anterior cruciate ligament. Purpose: To evaluate the effectiveness of an innovative hourglass-shaped graft versus a traditional columnar graft for restoring joint stability and graft force, while avoiding notch impingement following anterior cruciate ligament reconstruction. Methods: Finite element models of a human knee were developed to simulate ① An intact state, ② anterior cruciate ligament reconstruction using columnar grafts with different diameters (7.5-12 mm in 0.5 mm increments), ③ anterior cruciate ligament reconstruction using columnar grafts with different Young's moduli (129.4, 168.0 and 362.2 MPa) and ④ anterior cruciate ligament reconstruction using hourglass-shaped grafts with different Young's moduli. The knee model was flexed to 30° and loaded with an anterior tibial load of 103 N, internal tibial moment of 7.5 Nm, and valgus tibial moment of 6.9 Nm. The risk of notch impingement, knee stability and graft forces were compared among the different groups. Results: This study found that columnar grafts could not simultaneously restore knee stability in different degree of freedoms (DOFs) and graft force to a level similar to that of the intact knee. The anterior tibial translation and graft force were restored to a near-normal condition when the internal tibial rotation was over-restrained and valgus tibial rotation was lax. A graft diameter of at least 10 mm was needed to restore knee stability and graft force to physiological levels, but such large grafts were found to be at high risk of notch impingement. In contrast, the hourglass-shaped graft was able to simultaneously restore both knee stability and graft force at knee flexion of 30° while also having a much lower risk of impingement. Conclusion: Under knee flexion angle of 30°, an hourglass-shaped graft was better able to restore joint stability and graft force to a near-physiological level than columnar grafts, while also reducing the risk of notch impingement.

Keywords: ACL reconstruction; graft force; graft geometry; knee stability; notch impingement.

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Conflict of interest statement

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Three dimensional model of a cadaveric knee. (A) Intact knee; (B) Knee after ACL reconstruction using a columnar graft. The transparent model shows the fixation of the graft to the bone tunnel using an endoscrew. One end of the endoscrew was tied with the graft while the outside surface of the screw was tied with the inside wall of the bone tunnel. LCL, lateral collateral ligament; MCL, medial collateral ligament.
FIGURE 2
FIGURE 2
(A) Loading conditions and (B) Measurement of the minimum width of the space between the femoral notch and tibial plateau (Lmin). L1 was plotted as a line tangent to the tibial plateau and parallel to L2 and L2 was tangent to the top contour of the femoral notch. ITM, internal tibial moment; VTM, valgus tibial moment; ATL, anterior tibial load.
FIGURE 3
FIGURE 3
Models of the ACL and grafts. (A) Native ACL; (B) Hourglass-shaped ACL; (C) Columnar grafts with different diameters (D).
FIGURE 4
FIGURE 4
Plot of RImP for columnar grafts with different diameters and the hourglass-shaped graft.
FIGURE 5
FIGURE 5
Comparison of a conventional columnar graft to an hourglass-shaped graft for restoring knee stability and ligament force. The values were standardized against an intact knee. D8 signifies a graft diameter of 8 mm. ATT, anterior tibial translation; ITR, internal tibial rotation; VTR, valgus tibial rotation.
FIGURE 6
FIGURE 6
Comparison of a conventional columnar graft (diameter 10 mm, Young’s moduli = 129.4 MPa) to an hourglass-shaped graft for restoring knee stability and ligament force, with varying position of graft fixation in the femoral tunnel (10 mm vs. 20 mm) for the conventional ACLR. GraftInFT20 means the graft length inside the femoral tunnel was 20 mm. The values were standardized against an intact knee. ATT, anterior tibial translation; ITR, internal tibial rotation; VTR, valgus tibial rotation.
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