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Title: Cells from a GDF5 origin produce zonal tendon‐to‐bone attachments following anterior cruciate ligament reconstruction

Following anterior cruciate ligament (ACL) reconstruction surgery, a staged repair response occurs where cells from outside the tendon graft participate in tunnel integration. The mechanisms that regulate this process, including the specific cellular origin, are poorly understood. Embryonic cells expressing growth and differentiation factor 5 (GDF5) give rise to several mesenchymal tissues in the joint and epiphyses. We hypothesized that cells from a GDF5 origin, even in the adult tissue, would give rise to cells that contribute to the stages of repair. ACLs were reconstructed inGdf5‐Cre;R26R‐tdTomato lineage tracing mice to monitor the contribution ofGdf5‐Cre;tdTom+cells to the tunnel integration process. Anterior−posterior drawer tests demonstrated 58% restoration in anterior−posterior stability.Gdf5‐Cre;tdTom+cells within the epiphyseal bone marrow adjacent to tunnels expanded in response to the injury by 135‐fold compared with intact controls to initiate tendon‐to‐bone attachments. They continued to mature the attachments yielding zonal insertion sites at 4 weeks with collagen fibers spanning across unmineralized and mineralized fibrocartilage and anchored to the adjacent bone. The zonal attachments possessed tidemarks with concentrated alkaline phosphatase activity similar to native entheses. This study established that mesenchymal cells from a GDF5 origin can contribute to zonal tendon‐to‐bone attachments within bone tunnels following ACL reconstruction.

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Author(s) / Creator(s):
 ;  ;  ;  ;  
Publisher / Repository:
Date Published:
Journal Name:
Annals of the New York Academy of Sciences
Page Range / eLocation ID:
p. 57-67
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Background:

    Graft placement is a modifiable and often discussed surgical factor in anterior cruciate ligament (ACL) reconstruction (ACLR). However, the sensitivity of functional knee mechanics to variability in graft placement is not well understood.


    To (1) investigate the relationship of ACL graft tunnel location and graft angle with tibiofemoral kinematics in patients with ACLR, (2) compare experimentally measured relationships with those observed with a computational model to assess the predictive capabilities of the model, and (3) use the computational model to determine the effect of varying ACL graft tunnel placement on tibiofemoral joint mechanics during walking.

    Study Design:

    Controlled laboratory study.


    Eighteen participants who had undergone ACLR were tested. Bilateral ACL footprint location and graft angle were assessed using magnetic resonance imaging (MRI). Bilateral knee laxity was assessed at the completion of rehabilitation. Dynamic MRI was used to measure tibiofemoral kinematics and cartilage contact during active knee flexion-extension. Additionally, a total of 500 virtual ACLR models were created from a nominal computational knee model by varying ACL footprint locations, graft stiffness, and initial tension. Laxity tests, active knee extension, and walking were simulated with each virtual ACLR model. Linear regressions were performed between internal knee mechanics and ACL graft tunnel locations and angles for the patients with ACLR and the virtual ACLR models.


    Static and dynamic MRI revealed that a more vertical graft in the sagittal plane was significantly related ( P < .05) to a greater laxity compliance index ( R2= 0.40) and greater anterior tibial translation and internal tibial rotation during active knee extension ( R2= 0.22 and 0.23, respectively). Similarly, knee extension simulations with the virtual ACLR models revealed that a more vertical graft led to greater laxity compliance index, anterior translation, and internal rotation ( R2= 0.56, 0.26, and 0.13). These effects extended to simulations of walking, with a more vertical ACL graft inducing greater anterior tibial translation, ACL loading, and posterior migration of contact on the tibial plateaus.


    This study provides clinical evidence from patients who underwent ACLR and from complementary modeling that functional postoperative knee mechanics are sensitive to graft tunnel locations and graft angle. Of the factors studied, the sagittal angle of the ACL was particularly influential on knee mechanics.

    Clinical Relevance:

    Early-onset osteoarthritis from altered cartilage loading after ACLR is common. This study shows that postoperative cartilage loading is sensitive to graft angle. Therefore, variability in graft tunnel placement resulting in small deviations from the anatomic ACL angle might contribute to the elevated risk of osteoarthritis after ACLR.

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For Group 1, the whip stitch as well as the locking whip stitch were performed with a novel 2-part needle. For Group 2, the whip stitch was performed with loop suture needle and the locking stitch was krackow with a curved needle. Similarly, for Group 3, the whip stitch was performed with loop suture needle and the locking stitch was krackow with a curved needle (Figure 1). Cyclical testing was performed using a servohydraulic testing machine (MTS Bionix) equipped with a 5kN load cell. A standardized length of tendon, 7 cm, was coupled to the MTS actuator by passing it through a cryoclamp cooled by dry ice to a temperature of -5°C (Figure 2). All testing samples were then pre-conditioned to normalize viscoelastic effects and testing variability through application of cyclical loading to 25-100 N for three cycles. The samples were then held at 89 N for 15 minutes. Thereafter, the samples were loaded to 50-200 N for 500 cycles at 1 Hz. 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