Graft Choice for Anterior Cruciate Ligament Reconstruction: Superior Tendon-to-Bone Incorporation With Soft-tissue Autograft Compared With Allograft and Hybrid Graft in a Rat Model

Abstract

Background:

Optimal graft selection for anterior cruciate ligament (ACL) reconstruction (ACLR) remains controversial, particularly regarding tendon-to-bone incorporation and biomechanical performance among autografts, allografts, and hybrid grafts.

Hypothesis:

Autografts demonstrate superior tendon-to-bone healing, biomechanical strength, and functional recovery compared with allografts and hybrid grafts.

Study Design:

Controlled laboratory study.

Methods:

A total of 84 rats underwent ACLR using autograft, allograft, or hybrid grafts (a construct combining autograft and allograft tissues) (n = 21 per group), with an intact group serving as the control group. Grafts were harvested from the peroneus longus tendon. Assessments at 1, 2, 4, and 8 weeks included histology (hematoxylin and eosin; the Masson trichrome staining; immunohistochemistry), gait analysis, micro-computed tomography, and biomechanical testing.

Results:

Histologically, compared with allografts and hybrid grafts, autografts exhibited significantly improved synovial coverage, lower cartilage degeneration (score, autograft vs allograft vs hybrid graft: 10.80 ± 0.84 vs 3.20 ± 0.84 vs 4 ± 0.71; P < .001), improved collagen alignment, reduced inflammation, and enhanced vascularization and tenogenesis, whereas allografts and hybrid grafts exhibited distinct necrosis. Autografts exhibited superior value of bone volume per total volume (femur, autograft vs allograft vs hybrid graft: 5.40 ± 0.55 vs 2.60 ± 0.86 vs 2.69 ± 0.25; P < .001). Gait parameters, including stride length and step height, were restored to near-control levels only in the autograft group (intact control vs autograft: stride length, 3.09 ± 0.40 vs 2.96 ± 0.35; P = .899; step height, 2.67 ± 0.31 vs 2.26 ± 0.35; P = .199). Biomechanically, autografts demonstrated superior stress (autograft vs allograft: 14.86 ± 4.26 vs 2.64 ± 1.35; P < .001), stiffness (autograft vs allograft: 11.21 ± 5.55 vs 3.15 ± 1.55; P = .027), and tensile modulus (autograft vs allograft vs hybrid graft: 31.71 ± 10.35 vs 3.71 ± 1.83 vs 15.07 ± 4.51; P < .001).

Conclusion:

Autografts provided superior tendon-to-bone integration, biomechanical performance, and functional outcomes compared with allograft and hybrid grafts in a rat ACLR model.

Clinical Relevance:

This preclinical study, conducted in a rat model, provides mechanistic evidence that autografts exhibit superior biological incorporation and mechanical integrity, supporting the existing clinical preference for autograft in ACLR and helping inform graft selection.