Adaptation of post-traumatic angiogenesis in the rabbit knee by apposition of torn ligament ends

Immunomodulatory biomimetic nanoparticles target articular cartilage trauma after systemic administration

Post-traumatic osteoarthritis (PTOA) is one of the leading causes of disability in developed countries and accounts for 12% of all osteoarthritis cases in the United States. After trauma, inflammatory cells (macrophages amongst others) are quickly recruited within the inflamed synovium and infiltrate the joint space, initiating dysregulation of cartilage tissue homeostasis. Current therapeutic strategies are ineffective, and PTOA remains an open clinical challenge. Here, the targeting potential of liposome-based nanoparticles (NPs) is evaluated in a PTOA mouse model, during the acute phase of inflammation, in both sexes. NPs are composed of biomimetic phospholipids or functionalized with macrophage membrane proteins. Intravenous administration of NPs in the acute phase of PTOA and advanced in vivo imaging techniques reveal preferential accumulation of NPs within the injured joint for up to 7 days post injury, in comparison to controls. Finally, imaging mass cytometry uncovers an extraordinary immunomodulatory effect of NPs that are capable of decreasing the amount of immune cells infiltrating the joint and conditioning their phenotype. Thus, biomimetic NPs could be a powerful theranostic tool for PTOA as their accumulation in injury sites allows their identification and they have an intrinsic immunomodulatory effect.

The novel epiligament theory: differences in healing failure between the medial collateral and anterior cruciate ligaments

According to current literature, 90% of knee ligament injuries involve the medial collateral ligament or the anterior cruciate ligament. In contrast to the medial collateral ligament, which regenerates relatively well, the anterior cruciate ligament demonstrates compromised healing. In the past, there were numerous studies in animal models that examined the healing process of these ligaments, and different explanations were established. Although the healing of these ligaments has been largely investigated and different theories exist, unanswered questions persist.

Therefore, the aim of this article is 1) to review the different historical aspects of healing of the medial collateral ligament and present the theories for healing failure of the anterior cruciate ligament; 2) to examine the novel epiligament theory explaining the medial collateral ligament healing process and failure of anterior cruciate ligament healing; and 3) to discuss why the enveloping tissue microstructure of the aforementioned ligaments needs to be examined in future studies.

We believe that knowledge of the novel epiligament theory will lead to a better understanding of the normal healing process for implementing optimal treatments, as well as a more holistic explanation for anterior cruciate ligament healing failure.

Comparison between Operative and Non-Operative Treatment of the Medial Collateral Ligament: Histological and Ultrastructural Findings during Early Healing in the Epiligament Tissue in a Rat Knee Model

The medial collateral ligament of the knee joint is one of the most commonly injured ligaments of the knee. Recent data have shown that the thin layer of connective tissue covering the ligament, known as the epiligament, is essential for its nutrition and normal function, as well as its healing after injury. The aim of the present study was to investigate and compare the changes in the epiligament of the medial collateral ligament which occurred during operative and non-operative treatment throughout the first month after injury. We used 27 male Wistar rats randomly allocated to three groups. In the 9 rats belonging to the first group, the medial collateral ligament was fully transected and left to heal spontaneously without suture. In the 9 rats belonging to the second group, the transected ends were marked with a 9–0 nylon monofilament suture. The 9 rats in the third group were used as normal controls. Three animals from each group were sacrificed on days 8, 16, and 30 after injury. Light microscopic analysis was performed on semi-thin sections stained with 1% methylene blue, azure II, and basic fuchsin. Transmission electron microscopy was used to study and compare the ultrastructural changes in the epiligament. The statistical analysis of the obtained data was performed using the Kruskal-Wallis H test and Mood’s median test. The normal structure of the epiligament of the medial collateral ligament was presented by fibroblasts, fibrocytes, adipose cells, mast cells, collagen fibers, and neuro-vascular bundles. On days 8 and 16 postinjury, the epiligament appeared hypercellular and returned to its normal appearance on the thirtieth day postinjury. The electron microscopic study revealed the presence of different types of fibroblasts with the typical ultrastructural features of collagen-synthetizing cells. The comparative statistical analysis on the respective day showed that there was no statistically significant difference in the number of cells between spontaneously healing animals and animals recovering with suture application. These data further prove that spontaneous healing of the medial collateral ligament yields similar results to surgical treatment and may be used as a basis for the development of treatment regimens with improved patient outcome.

Medial collateral ligament and partial anterior cruciate ligament transection: mRNA changes in uninjured ligaments of the sheep knee

Following knee ligament injury, clinical and experimental investigations usually focus on the injured ligament, and uninjured ligaments of the same joint are largely ignored and presumed to remain unchanged. The purpose of this study was to characterize changes in mRNA levels for a relevant subset of molecules in the uninjured knee ligaments following combined unilateral medial collateral ligament (MCL) and partial anterior cruciate ligament (ACL) transection in sheep. Semiquantitative reverse transcription-polymerase chain reaction was performed for collagen types I, III, and V; matrix metalloproteinase-13 (MMP-13); and tissue inhibitor of metalloproteinase-1 for both injured and uninjured knee ligaments at 6 and 12 weeks after injury. Collagen type I, III, and V mRNA levels were significantly increased in MCL scars at 6 weeks as well as in the uninjured lateral collateral ligament and the anteromedial band of the ACL (AM-ACL). MMP-13 mRNA levels were also elevated in the MCL at 6 and 12 weeks and in the AM-ACL 6 weeks after injury. In contrast, significant changes in the posterior cruciate ligament were not detected at either time point, indicating specificity in the transient alterations. These results suggest that following injury, responses occur in uninjured ligaments that are specific although transient in nature. These responses may be an adaptive attempt to preserve function until the scar tissue can stabilize the mechanical environment following injury.

The angiogenic peptide vascular endothelial growth factor (VEGF) is expressed during the remodeling of free tendon grafts in sheep

BACKGROUND

Angiogenesis is important for the remodeling of autologous tendon grafts. A sheep model was used to examine the expression of the angiogenic peptide vascular endothelial growth factor (VEGF) in autologous tendon grafts after anterior cruciate ligament (ACL) reconstruction.

METHODS

Merino sheep underwent ACL reconstruction with an autologous Achilles tendon split graft. VEGF and its receptors, the Fms-like tyrosine kinase receptor (FLT-1, VEGFR-1) and the kinase insert domain-containing receptor KDR (VEGFR-2/FLK-1) were detected immunohistochemically. Reverse transcription-polymerase chain reaction (RT-PCR) was performed to detect which of the different VEGF splice forms are expressed during ACL remodeling.

RESULTS

At 6 weeks, light microscopy showed zones with hypocellular necrotic graft tissue in the central part surrounded by hypercellular and hypervascularized reparative tissue invading the former graft tissue from the periphery. In contrast to the necrotic tissue, all cell types of the reparative tissue labeled strongly positive for VEGF. The VEGF receptors FLT-1 and KDR could be detected on endothelial cells of blood vessels. At 12 weeks, the complete graft diameter showed an increased vascular density (anti-factor VIII immunoreactivity), but zones of non-remodeled former graft tissue could not be found. Fusiform fibroblasts labeled strongly for VEGF. At 24 weeks, VEGF immunostaining decreased, and at 52 and 104 weeks, the grafts were largely VEGF-negative. RT-PCR supported the immunohistochemical results regarding VEGF expression and showed further that the splice variants VEGF(120 )and VEGF(164) are expressed during angiogenesis during the remodeling of tendons.

CONCLUSION

We conclude that the angiogenic peptide VEGF plays a role in tendon graft remodeling.