The “Ligamentization” Process in Anterior Cruciate Ligament Reconstruction

The anterior cruciate ligament (ACL) is a short, stout, intra-articular, extrasynovial structure which acts to control rotational movements and anterior translation of the femur upon the fixed tibia.[1][1] Rupture is a traumatic event, often as a consequence of twisting upon the weight-bearing limb

Background There is little information documenting whether the phenomenon of “ligamentization,” as proposed by Amiel, occurs in the human anterior cruciate ligament after clinically effective reconstruction. To clarify this point, we analyzed biochemical differences between the native anterior cruciate ligament; the patellar, semitendinosus, and gracilis tendons; and anterior cruciate ligaments reconstructed with autografts. Study Design Cohort study; Level of evidence, 2. Methods Fifty patients who underwent arthroscopically assisted anterior cruciate ligament reconstruction using either semi-tendinosus and gracilis tendon or bone-patellar tendon-bone autografts were selected for the study. Samples of grafted tissue were collected during arthroscopy and quantitatively analyzed for collagen content and the amount of reducible and nonreducible crosslinks at 4 to 6 postoperative months in patients with semitendinosus and gracilis tendon grafts and at 11 to 13 months in all patients with semitendinosus and gracilis tendon or bone-patellar tendon-bone grafts. Results The total collagen content and nonreducible/reducible crosslink ratios increased significantly during the postoperative period (P < .05). The dihydroxylysinonorleucine/hydroxylysinonorleucine ratio was 3.11 ± 0.56 in the native anterior cruciate ligament, 1.21 ± 0.47 in the patellar tendon, and 3.59 ± 1.58 in the anterior cruciate ligaments reconstructed with bone-patellar tendon-bone autografts 1 year after surgery. The dihydroxylysinonorleucine/hydroxylysinonorleucine ratio in both semitendinosus and gracilis tendons was less than 1.0. However, in anterior cruciate ligaments reconstructed with semitendinosus and gracilis tendon autografts, it was 2.34 ± 0.98 at 4 to 6 months and 3.43 ± 1.61 at 11 to 13 months after the operation. Conclusions After anterior cruciate ligament reconstruction with autografts, biochemical characteristics of the graft resembled those of the native anterior cruciate ligament. These findings suggest that, regarding the amount of collagen crosslinks and their architecture, the phenomenon of ligamentization occurs in the successfully reconstructed human anterior cruciate ligament within 1 year after operation.

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To longitudinally monitor remodeling of human autograft following anterior cruciate ligament (ACL) reconstruction with DTI. Twenty-eight patients underwent DTI follow-up at 3, 8, and 14months after clinically successful ACL reconstruction with tendon autograft. Among these, 18 patients had a concomitant lateral extra-articular procedure (LET). DTI data from 7 healthy volunteers was also obtained. Diffusion parameters (fractional anisotropy, FA; mean diffusivity, MD; axial diffusivity, AD; and radial diffusivity, RD) were evaluated within the fiber tractography volumes of the ACL graft and posterior cruciate ligament (PCL) in all patients. Data were analyzed using a linear mixed-effects model with post hoc testing using Bonferroni-Holm correction for multiple testing. The effect of additional LET was studied. The ACL graft showed a significant decrease of FA over time (F = 4.00, p = 0.025), while the diffusivities did not significantly change over time. For PCL there were no significant DTI changes over time. A different evolution over time between patients with and without LET was noted for all diffusivity values of the ACL graft with reduced AD values in patients with LET at 8months postoperatively (p = 0.048; adjusted p = 0.387). DTI metrics of the ACL graft differed largely from both native ACL and tendon at 14months postoperatively. Our study has shown the potential of DTI to longitudinally monitor the remodeling process in human ACL reconstruction. DTI analysis indicates that graft remodeling is incomplete at 14months postoperatively. • DTI can be used to longitudinally monitor the remodeling process in human ACL reconstruction. • DTI analysis indicates that autograft remodeling is incomplete at 14months postoperatively. • DTI may be helpful for evaluating new ACL treatments.

The aim of this study was to determine the impact on intra-articular healing of muscle tissue retained on tendon grafts used for anterior cruciate ligament (ACL) reconstruction. In an animal study on 40 New Zealand rabbits, a semi-tendon/semi-muscle graft (SSG) and a total tendon graft (TTG) were individually harvested from the Achilles tendons in each animal. After transecting the ACLs in both knees of each rabbit, SSG and TTG were randomly used on bilateral sides of the knee for ACL reconstruction. After 2, 4, and 8weeks, functional scoring, gross observations, and histological evaluations of the repaired knees were performed (each time point; n=10). Biomechanical testing was conducted on remaining animals at 8weeks (n=10). At 2, 4, and 8weeks after surgery, there were no statistically significant differences in functional scores between the SSG group and TTG group (n.s.). As healing progressed, skeletal muscle on the SSG was gradually absorbed with a corresponding decrease in graft diameter, compared to TTG, at each time point (P<0.001). However, healing and incorporation of the intra-articular graft in the SSG were more apparent than those in the TTG, based on histology. The vascularity and cellularity in the center of the sample were significantly greater in the SSG group than the TTG group at all the time points (P<0.01). At 8weeks, the SSG group's ultimate failure load, yield load, and elongation at failure were significantly less than for the TTG group (P<0.01). There were no significant differences in stiffness between the two groups with biomechanical testing (n.s.). Results of this study indicate that muscle left on tendon grafts promotes intra-articular healing and remodeling of the graft in a rabbit model. However, excessive amounts of retained skeletal muscle weaken tendon graft's strength for ACL reconstruction. Preserving small amounts of muscle on tendon grafts is feasible for improving the biological success of ACL reconstruction in humans.

BackgroundThe current standard of care to treat a ruptured anterior cruciate ligament (ACL) is ACL reconstruction (ACLR), which involves replacing the torn ligament with a tendon graft. The implanted tendon graft undergoes a graft-maturation process known as ligamentization. However, the synthesis of type III collagen, which is typically found in weaker scar tissue, continues at higher concentrations, and the heterogeneous composition of collagen fibers of varying diameters of native ACL is never restored. Culture-expanded ACL-derived cells reseeded to tendon graft have shown the potential for enhanced ligamentization. We performed in vitro and in vivo studies of the outcomes of ACLR with decellularized tendon grafts reseeded with ACL-derived cells combined with acellularized cruciate ligament matrix (ACLM) powder as a biological scaffold. We hypothesized that this tissue-engineered construct would enhance the graft maturation process and mechanical properties of the graft following ACLR.MethodsACL-derived cells were harvested and isolated from remnants of ruptured ACLs within 4 weeks of injury in patients who had undergone ACLR. An ACLM was prepared from human ACL and posterior cruciate ligament tissues. Forty-five Sprague Dawley rats were randomly divided into 3 groups: a standard allograft group, an ACLM powder-only injection group, and an ACL-derived cells and ACLM powder co-injection group (e.g., target group). ACL-derived cells were mixed with ACLM powder and then injected into the decellularized tendon graft before ACLR.ResultsIn vitro experiments found that combining ACLM powder and ACL-derived cells improved survival and integration of reseeded cells in the tendon extracellular matrix, resulting in the successful transplantation of ACL-derived cells. Animal ACLR experiments confirmed histologically improved structural maturation in cellularity, metaplasia, and restoration of collagen crimping in the graft reseeded with ACL-derived cells and ACLM powder. Enhanced gene expression of type I collagen resulted in superior mechanical properties of the tendon graft compared with the control groups.ConclusionImplantation of a tendon graft reseeded with culture-expanded ACL-derived cells, and ACLM powder enhanced the tendon graft’s maturation process and mechanical properties. We provide in vitro and in vivo proof-of-concept evidence supporting the efficacy of reseeding a tendon graft with ACL-derived cells combined with ACLM powder as a biological scaffold for ACL reconstruction.Graphical Supplementary InformationThe online version contains supplementary material available at 10.1186/s13287-025-04760-1.

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Objective Establish the animal experimental models of anterior cruciate ligament (ACL) reconstruction with remnant preservation and ACL reconstruction without remnant, to investigate whether there is a difference about grafts vascularization and nerve regeneration in different reconstruction methods. Methods The 72 New Zealand rabbits were randomly divided into control group(group A), ACL reconstruction without remnant (group B), ACL reconstruction with remnant preservation (Femoral Tensioning and augmented suture)(group C) and ACL reconstruction with remnant preservation (graft passing ACL remnant sheath) (group D). At 3, 6 and 12 weeks after surgery, the graft tendon near tibial level was harvested to detect the mRNA expressions of vascular endothelial growth factor (VEGF) and growth-associated protein 43 (GAP-43) by real-time fluorescent quantitative polymerase chain reaction (FQ-PCR). Graft cell number and microvascular density (MVD)were evaluated by hematoxylin and eosin (HE) staining and immunohistochemical CD34. Results Postoperative 3, 6 and 12 weeks, VEGF mRNA relative expression in B, C, D group respectively was 1.98±0.48, 2.21±0.73, 2.06±0.14; 4.35±0.45, 3.97±0.24, 4.18±0.63; 1.14±0.62, 1.23±0.06, 1.19±0.35. compared with A group, the difference was statistically significant (P=0.000, P=0.000, P=0.026). B, C, D group had no signifcant difference (P=0.214, P=0.672, P=0.823). GAP-43 mRNA relative expression in B, C, D group respectively was 1.73±0.61, 1.58±0.12, 1.66±0.23; 5.86±1.07, 6.01±0.43, 5.76±0.74; 2.94±0.69, 3.10±0.34, 3.13±0.95. compared with A group, the difference was statistically significant (P=0.000, P=0.000, P=0.000). B, C, D group had no signifcant difference (P=0.634, P=0.138, P=0.275). At each point after operation, there was no signifcant difference in Graft cell number and MVD between B and C, D group (P=0.114, P=0.086, P=0.092; P=0.135, P=0.061, P=0.269). Conclusion Compared with ACL reconstruction without remnant, both two different ways of remnant preservation ACL reconstruction do not show obvious advantages in grafts vascularization and nerve regeneration. Key words: Anterior cruciate ligament reconstruction; Remnant preservation; Vascular endothelial growth factor; Microvessel density; Growth associated protein-43