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Comparison of Magnetic Resonance Imaging Findings in Anterior Cruciate Ligament Grafts With and Without Autologous Platelet-Derived Growth Factors

March 5, 2010

Comparison of Magnetic Resonance Imaging Findings in
Anterior Cruciate Ligament Grafts With and Without
Autologous Platelet-Derived Growth FactorsRupture of the anterior cruciate ligament (ACL) is an injury commonly observed in sports medicine. Return to professional sports occurs at around 6 to 7 months, depending on the sport practiced. In sports medicine this time period is often very long for the athlete; thus methods have been sought to shorten the biological time required for the graft to acquire biomechanical properties similar to the original ACL.

The clinical results of ACL reconstruction and time to return to sports could be improved if the graft healing process is enhanced. In a classic publication on this topic in 1982, Arnoczky and Tarvin1 described the behavior of the graft used in ACL reconstruction in dogs, describing 3 stages in the process of graft metaplasia: incorporation, neoligament formation, and remodeling.2,3

Various authors have tried to study the behavior of the graft in clinical trials, with histology or imaging studies, which experienced a significant boost with the appearance of magnetic resonance imaging (MRI).4-10

In 1995, in a prospective clinical study that relied on second-look arthroscopy to perform a histologic and MRI assessment of the graft at 6, 9, and 12 months of postoperative evolution,11 we described how the patellar tendon graft used in human ACL reconstruction is incorporated. We concluded that the graft maturation takes a long time: 12 months to achieve histology similar to a normal ACL. At 12 months, the MRI study of the graft was homogeneous and hyperintense, without swelling in the bone tunnels. The correlation of the histology with MRI was of great help in establishing a reliable imaging pattern, which allowed us to noninvasively verify the graft healing process.

Weiler et al.12 report correlations between biomechanical properties and vascularity of an ACL graft and MRI in a sheep model.

Clinical applications of autologous platelet-rich plasma gel (PRPG) include maxillofacial surgery, treatment of bone fractures, and tendon repair, reporting excellent outcomes.13-16 Platelets contain different growth factors that facilitate healing. PRPG is a fraction of plasma volume with a platelet concentration above baseline (whole blood). Platelet concentrates contain an enormous amount of activated plateletderived growth factors (PDGFs).17-23

Platelets contain PDGFs, transforming growth factors (TGFs), insulin-like growth factors, epidermal growth factors, vascular endothelial growth factors, and fibroblast growth factors. These factors are involved in the majority of biological remodeling processes in the body. In the specific case of ACL graft, PDGFs, fibroblast growth factor 1, and the various types of TGF- are responsible for accelerating the healing process, as well as increasing the tensile strength of the graft.24-30

Only 2 articles have shown an enhancing effect of treatment with PRPG on the tendon or ligament in humans. In a human study Orrego et al.31 showed an enhancing effect over the graft maturation process as evaluated by MRI signal intensity, without showing a significant effect on the osteoligamentous interface or tunnel widening evolution. In human tenocyte cultures, de Mos et al.32 showed that PRPG stimulates cell proliferation and collagen production.

Currently, it is practically impossible to perform human clinical trials of biomechanical or histologic assessments of the graft’s behavior in ACL reconstruction. For this reason, we decided to practice an indirect and noninvasive assessment in our patients, using MRI. The purpose of our investigation was to study MRI findings in the ACL graft when PRPG was added during surgery, thus allowing future studies correlating MRI findings with histology and ultimate load and strength. We hypothesized that PRPG has a positive effect on cell proliferation and collagen production in the human tendon and plays a key role in the remodeling and repair processes of the graft used in ACL reconstruction.

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