Lymphoscintigraphic Monitoring of the Lower Limb Lymphatic System Response to Bone Fracture and Healing

Lymphatic platelet thrombosis limits bone repair by precluding lymphatic transporting DAMPs

In the musculoskeletal system, lymphatic vessels (LVs), which are interdigitated with blood vessels, travel and form an extensive transport network. Blood vessels in bone regulate osteogenesis and hematopoiesis, however, whether LVs in bone affect fracture healing is unclear. Here, we investigate the lymphatic draining function at the tibial fracture sites using near-infrared indocyanine green lymphatic imaging (NIR-ICG) and discover that lymphatic drainage insufficiency (LDI) starts on day one and persists for up to two weeks following the fracture in male mice. Sufficient lymphatic drainage facilitates fracture healing in male mice. Furthermore, we identify that lymphatic platelet thrombosis (LPT) blocks the draining lymphoid sinus and LVs, causes LDI, and inhibits fracture healing in male mice, which can be rescued by a blood thinner. Moreover, unblocked lymphatic drainage decreases neutrophils and increases M2-type macrophages of the hematoma niche to support osteoblast (OB) survival and bone marrow-derived mesenchymal stem cell (BMSC) proliferation via transporting damage-associated molecular patterns (DAMPs) in male rats. Lymphatic platelet thrombolysis also benefits senile fracture healing in female mice. These findings demonstrate that LPT limits bone regeneration by impeding lymphatic transporting DAMPs. Together, these findings represent a way forward in the treatment of bone repair.

A novel therapy for fracture healing by increasing lymphatic drainage

Background

The musculoskeletal system contains an extensive network of lymphatic vessels. Decreased lymph flow of the draining collecting lymphatics usually occurs in clinic after traumatic fractures. However, whether defects in lymphatic drainage can affect fracture healing is unclear.

Methods

To investigate the effect of lymphatic dysfunction on fracture healing, we used a selective VEGFR3 tyrosine kinase inhibitor to treat tibial fractured mice for 5 weeks versus a vehicle-treated control. To ensure successfully establishing deceased lymphatic drainage model for fractured mice, we measured lymphatic clearance by near infrared indocyanine green lymphatic imaging (NIR-ICG) and the volume of the draining popliteal lymph nodes (PLNs) by ultrasound at the whole phases of fracture healing. In addition, hindlimb edema from day 0 to day 7 post-fracture, pain sensation by Hargreaves test at day 1 post-fracture, bone histomorphometry by micro-CT and callus composition by Alcian Blue-Hematoxylin/Orange G staining at day 14 post-fracture, and bone quality by biomechanical testing at day 35 post-fracture were applied to evaluate fracture healing. To promote fracture healing via increasing lymphatic drainage, we then treated fractured mice with anti-mouse podoplanin (PDPN) neutralizing antibody or isotype IgG antibody for 1 week to observe lymphatic drainage function and assess bone repair as methods described above.

Results

Compared to vehicle-treated group, SAR-treatment group significantly decreased lymphatic clearance and the volume of draining PLNs. SAR-treatment group significantly increased soft tissue swelling, and reduced bone volume (BV)/tissue volume (TV), trabecular number (Tb.N), woven bone and biomechanical properties of fracture callus. In addition, anti-PDPN treated group significantly reduced the number of CD41+ platelets in PLNs and increased the number of pulsatile lymphatic vessels, lymphatic clearance and the volume of PLNs. Moreover, anti-PDPN treated group significantly reduced hindlimb edema and pain sensation and increased BV/TV, trabecular number (Tb.Th), woven bone and biomechanical properties of fracture callus.

Conclusions

Inhibition of proper lymphatic drainage function delayed fracture healing. Use of a anti-PDPN neutralizing antibody reduced lymphatic platelet thrombosis (LPT), increased lymphatic drainage and improved fracture healing.

The translational potential of this article

(1) We demonstrated lymphatic drainage function is crucial for fracture healing. (2) To unblock the lymphatic drainage and prevent the risk of bleeding and mortality by blood thinner, we demonstrated PDPN neutralizing antibody is a novel and safe way forward in the treatment of bone fracture healing by eliminating LPT and increasing lymphatic drainage.

Lymphatic platelet thrombosis limits bone repair by precluding lymphatic transporting DAMPs

Lymphatic vessels (LVs) interdigitated with blood vessels, travel and form an extensive transport network in the musculoskeletal system. Blood vessels in bone regulate osteogenesis and hematopoiesis, however, whether LVs in bone affect fracture healing is unclear. Here, by near infrared indocyanine green lymphatic imaging (NIR-ICG), we examined lymphatic draining function at the tibial fracture sites and found lymphatic drainage insufficiency (LDI) occurred as early as two weeks after fracture. Sufficient lymphatic drainage facilitates fracture healing. In addition, we identified that lymphatic platelet thrombosis (LPT) blocks the draining lymphoid sinus and LVs, caused LDI and then inhibited fracture healing, which can be rescued by a pharmacological approach. Moreover, unblocked lymphatic drainage decreased neutrophils and increased M2-like macrophages of hematoma niche to support osteoblast (OB) survival and bone marrow-derived mesenchymal stem cell (BMSC) proliferation via transporting damage-associated molecular patterns (DAMPs). These findings demonstrate that LPT limits bone regeneration by blocking lymphatic drainage from transporting DAMPs. Together, these findings represent a novel way forward in the treatment of bone repair.

Interactions of B-lymphocytes and bone cells in health and disease

Bone remodeling occurs through the interactions of three major cell lineages, osteoblasts, which mediate bone formation, osteocytes, which derive from osteoblasts, sense mechanical force and direct bone turnover, and osteoclasts, which mediate bone resorption. However, multiple additional cell types within the bone marrow, including macrophages, T lymphocytes and B lymphocytes influence the process. The bone marrow microenvironment, which is supported, in part, by bone cells, forms a nurturing network for B lymphopoiesis. In turn, developing B lymphocytes influence bone cells. Bone health during homeostasis depends on the normal interactions of bone cells with other lineages in the bone marrow. In disease state these interactions become pathologic and can cause abnormal function of bone cells and inadequate repair of bone after a fracture. This review summarizes what is known about the development of B lymphocytes and the interactions of B lymphocytes with bone cells in both health and disease.

Managing Lymphedema in Fracture Care: Current Concepts and Treatment Principles

Lymphatic flow plays a notable role in the regulation of bone formation and remodeling. Chronic accumulation of the lymph fluid within tissues may lead to issues with proper bone healing after fractures, emphasizing the importance of proper management of lymphedema after trauma. Many associated risk factors place patients at risk for lymphedema, including previous surgery with nodal dissection, radiation therapy, infection, malignancy, family history of congenital lymphedema, and trauma. The benchmark imaging technique for the diagnosis of lymphedema is lymphoscintigraphy. Other modalities include duplex ultrasonography, CT, and MRI. First-line conservative treatment of lymphedema is compression. Complete decongestive therapy or complex physical therapy, also known as decongestive lymphatic therapy (DLT), has shown positive results in reducing lymphedema. Surgical interventions aim to either reconstruct and restore function of the lymphatic system or debulk and reduce tissues and fluids. Understanding the significance of lymphedema on bone healing and techniques available to recognize it are important factors in preventing delay in diagnosis and ensuring proper management of lymphedema after trauma.

Acute small intestinal inflammation results in persistent lymphatic alterations

Inflammatory bowel disease (IBD) has a complex pathophysiology with limited treatments. Structural and functional changes in the intestinal lymphatic system have been associated with the disease, with increased risk of IBD occurrence linked to a history of acute intestinal injury. To examine the potential role of the lymphatic system in inflammation recurrence, we evaluated morphological and functional changes in mouse mucosal and mesenteric lymphatic vessels, and within the mesenteric lymph nodes during acute ileitis caused by a 7-day treatment with dextran sodium sulfate (DSS). We monitored whether the changes persisted during a 14-day recovery period and determined their potential consequences on dendritic cell (DC) trafficking between the mucosa and lymphoid tissues. DSS administration was associated with marked lymphatic abnormalities and dysfunctions exemplified by lymphangiectasia and lymphangiogenesis in the ileal mucosa and mesentery, increased mesenteric lymphatic vessel leakage, and lymphadenopathy. Lymphangiogenesis and lymphadenopathy were still evident after recovery from intestinal inflammation and correlated with higher numbers of DCs in mucosal and lymphatic tissues. Specifically, a deficit in CD103⁺ DCs observed during acute DSS in the lamina propria was reversed and further enhanced during recovery. We concluded that an acute intestinal insult caused alterations of the mesenteric lymphatic system, including lymphangiogenesis, which persisted after resolution of inflammation. These morphological and functional changes could compromise DC function and movement, increasing susceptibility to further gastrointestinal disease. Elucidation of the changes in mesenteric and intestinal lymphatic function should offer key insights for new therapeutic strategies in gastrointestinal disorders such as IBD. NEW & NOTEWORTHY Lymphatic integrity plays a critical role in small intestinal homeostasis. Acute intestinal insult in a mouse model of acute ileitis causes morphological and functional changes in mesenteric and intestinal lymphatic vessels. While some of the changes significantly regressed during inflammation resolution, others persisted, including lymphangiogenesis and altered dendritic cell function and movement, potentially increasing susceptibility to the recurrence of gastrointestinal inflammation.

Lymphatic Contribution to the Cellular Niche in Heterotopic Ossification

OBJECTIVE

The objective of this study was to determine the contribution of lymphatic tissue to heterotopic ossification (HO).

BACKGROUND

HO is the pathologic development of ectopic bone within soft tissues often following severe trauma. Characterization of the tissue niche supporting HO is critical to identifying therapies directed against this condition. Lymphangiogenesis is upregulated during incidents of trauma, thereby coincident with the niche supportive of HO. We hypothesized that lymphatic tissues play a critical role in HO formation.

METHODS

Mice underwent hindlimb Achilles' tendon transection and dorsal burn injury (burn/tenotomy) to induce HO. The popliteal and inguinal lymph nodes were excised ipsilateral to the tenotomy site. Flow cytometry and immunostaining were used to quantify and localize lymphoendothelium. MicroCT was used to quantify HO.

RESULTS

Enrichment of mature lymphatic tissues was noted 2 weeks after injury at the tendon transection sites when compared with the contralateral, intact tendon based on LYVE1+ tubules (10.9% vs 0.8%, P < 0.05). Excision of the inguinal and popliteal nodes with draining popliteal lymphatic vessel significantly decreased the presence of mature lymphoendothelium 2 weeks after injury (10.9% vs 3.3%, P < 0.05). Bone-cartilage-stromal progenitor cells (CD105+/AlphaV+/Tie2-/CD45-/CD90-/BP1-) were also significantly decreased after lymph node excision (10.2% vs 0.5%, P < 0.05). A significant decrease was noted in the volume of de novo HO present within the soft tissues (0.12 mm vs 0.02 mm).

CONCLUSION

These findings suggest that lymphatic vessels are intimately linked with the de novo formation bone within soft tissues following trauma, and their presence may facilitate bone formation.

T Lymphocytes Influence the Mineralization Process of Bone

Bone is a unique organ able to regenerate itself after injuries. This regeneration requires the local interplay between different biological systems such as inflammation and matrix formation. Structural reconstitution is initiated by an inflammatory response orchestrated by the host immune system. However, the individual role of T cells and B cells in regeneration and their relationship to bone tissue reconstitution remain unknown. Comparing bone and fracture healing in animals with and without mature T and B cells revealed the essential role of these immune cells in determining the tissue mineralization and thus the bone quality. Bone without mature T and B cells is stiffer when compared to wild-type bone thus lacking the elasticity that helps to absorb forces, thus preventing fractures. In-depth analysis showed dysregulations in collagen deposition and osteoblast distribution upon lack of mature T and B cells. These changes in matrix deposition have been correlated with T cells rather than B cells within this study. This work presents, for the first time, a direct link between immune cells and matrix formation during bone healing after fracture. It illustrates specifically the role of T cells in the collagen organization process and the lack thereof in the absence of T cells.

Posttraumatic edema of the lower extremities: evaluation of the lymphatic vessels with magnetic resonance lymphangiography

OBJECTIVE

To assess for the first time the morphology of the lymphatic system in patients with posttraumatic edema of the lower extremities by magnetic resonance (MR) imaging using the interstitial lymphangiography technique

MATERIALS AND METHODS

Six patients with posttraumatic edema in eight of their 12 lower extremities were examined by MR lymphangiography. Eighteen mL of gadoteridol and one mL of mepivacainhydrochloride 1% were subdivided into 10 portions and injected intracutaneously. MR imaging was performed with a 1.5-T system equipped with high-performance gradients. For MR lymphangiography, a 3D-spoiled gradient-echo sequence was used.

RESULTS

In five of the eight (63%) traumatized lower extremities, enlarged lymphatic vessels were detected, with the largest diameter measuring 5 mm. Additionally, a fast lymphatic outflow was observed in seven of the eight (88%) traumatized legs with enhancement of the inguinal lymph nodes already in the first image acquisition 15 minutes after contrast material injection. In two of the eight (25%) traumatized lower extremities, an extensive network of collateral lymphatic vessels was detected at the level of the calf. In both extremities, lymphatic collateralization involved not only the epifascial but also the subfascial lymphatic system. In one patient, who sustained a trauma of the left lower leg with tibial fracture, a small aneurysmatic widening of 7 mm could be detected at the middle level of the calf.

CONCLUSION

MR lymphangiography is a safe and accurate minimal-invasive imaging modality for the evaluation of the lymphatic circulation in patients with posttraumatic edema of the lower extremities. If the extent of lymphatic damage is unclear at the initial clinical examination or requires a better definition for optimal therapeutic planning, MR lymphangiography is able to identify the anatomic and physiological derangements and to establish an objective baseline.

T and B cells participate in bone repair by infiltrating the fracture callus in a two-wave fashion

Fracture healing is a regenerative process in which bone is restored without scar tissue formation. The healing cascade initiates with a cycle of inflammation, cell migration, proliferation and differentiation. Immune cells invade the fracture site immediately upon bone damage and contribute to the initial phase of the healing process by recruiting accessory cells to the injury site. However, little is known about the role of the immune system in the later stages of fracture repair, in particular, whether lymphocytes participate in soft and hard callus formation. In order to answer this question, we analyzed femoral fracture healing in mice by confocal microscopy. Surprisingly, after the initial inflammatory phase, when soft callus developed, T and B cells withdrew from the fracture site and were detectable predominantly at the femoral neck and knee. Thereafter lymphocytes massively infiltrated the callus region (around day 14 after injury), during callus mineralization. Interestingly, lymphocytes were not found within cartilaginous areas of the callus but only nearby the newly forming bone. During healing B cell numbers seemed to exceed those of T cells and B cells progressively underwent effector maturation. Both, osteoblasts and osteoclasts were found to have direct cell-cell contact with lymphocytes, strongly suggesting a regulatory role of the immune cells specifically in the later stages of fracture healing.

Gall bladder visualization in lymphoscintigraphy

BACKGROUND

The aim of this study was to evaluate gall bladder visualization in lymphoscintigraphy of extremities.

METHODS AND RESULTS

Thirteen patients who had prediagnoses of lymphedema and were referred for lower extremity lymphoscintigraphy to our department were retrospectively evaluated. Lower extremity lymphoscintigraphy with Tc-99m sulfur colloid was performed on the patients, and planar images of the lower extremity and abdominal region were taken in early phase and late phase (at the 24th hour) routinely. Lymphoscintigraphy results of eight patients were normal regarding lymphatic flow or lymph nodes; however, additional pathologic tracer accumulations in gall bladder were observed, which disappeared at 24th hour images in three patients. Five patients had various pathologies regarding lymph flow or lymph nodes. However, there were no patients with gall bladder activity except those three patients who had casual anamnesis of fasting prior to the exam.

CONCLUSION

The fasting state of the patients might be the cause of gall bladder visualization during the lymphoscintigraphy of the extremities with sulfur colloid.

Complete decongestive physical therapy in a patient with secondary lymphedema due to orthopedic trauma and surgery of the lower extremity

BACKGROUND AND PURPOSE

This case report describes a patient who developed lower-extremity lymphedema secondary to orthopedic trauma and surgery and reports the response to complete decongestive physical therapy (CDP), with 8 treatment sessions over 3 months.

CASE DESCRIPTION

The patient was a 56-year-old man who sustained a right ankle displaced fibular fracture, underwent open reduction internal fixation surgery 12 days later, and developed lymphedema 4 months postinjury. The patient's impairments of the right lower extremity included increased girth, decreased ankle range of motion, and increased pain. Due to these impairments and the inability to fit into normal footwear, the patient limited activities such as ambulating long distances and climbing stairs. This limited activity restricted him from participating in his normal lifestyle activities such as walking his dog in the community and performing all necessary work duties.

OUTCOMES

Using the truncated cone formula to measure limb volume, the limb volume of the right (involved) lower extremity decreased 368 mL as a result of CDP. The percentage of difference in limb volume between the right and left lower extremities at the initial examination was 9%, and it was reduced to less than 1% at discharge. He was independent with his home program in order to maintain the results of therapy.

DISCUSSION

Physical therapist management of secondary lymphedema due to orthopedic trauma and surgery of the lower extremity was effective in decreasing circumferential girth measurements and decreasing limb volume, thereby improving gait and allowing the patient to fit into his work and leisure shoes. The patient reported improvement in his ability to perform all work activities, and he returned to his prior level of participation in the community.

Lymphangiogenesis, myeloid cells and inflammation

The lymphatic system is essential for the maintenance of tissue fluid balance, immune surveillance and the absorption of fatty acids in the gastrointestinal tract. The lymphatic circulation is also a key player in disease processes such as cancer metastasis, lymphedema and various inflammatory disorders. With the identification of specific growth factors for lymphatic endothelial cells and markers that distinguish blood and lymphatic vessels, as well as the development of in vivo imaging technologies that provide new tools to examine the lymphatic drainage function in real time, many advancements have been made in lymphatic vascular research during the past few years. Despite these significant achievements, our understanding of the role of lymphatics in disease processes other than cancer metastasis is still rather limited. The current review will focus on the recent progress made in studies of lymphatics in inflammatory disorders.

The healing of tibial fracture and response of the local lymphatic system

BACKGROUND

Damage of tissues by mechanical injury and inflammation is followed by reaction of the regional lymphoid tissue, lymphatics, and lymph nodes. In our previous lymphoscintigraphic studies, we showed that closed fractures of a lower limb cause reaction of the local lymphoid tissue. There was dilation of lymphatics draining the site of the fracture and enlargement of inguinal lymph nodes. These changes persisted even after clinical healing of the fracture. In the long-lasting nonhealing fractures, the lymphoscintigraphic pictures were different. The draining lymphatics became obliterated, and the lymph nodes disappeared.

METHODS

In this study, we tried to correlate the lymphoscintigraphic images, reflecting the immune events at the fracture site, with the immunohistochemical observations of the biopsy specimens obtained during corrective operations from the healing and nonhealing fracture gaps. Thirty-eight patients with closed fracture of the tibia without traumatic skin changes were studied.

RESULTS

We confirmed that closed tibial fracture evokes response of the regional lymphatic system. Normal fracture healing with immune cell infiltrates and foci of ossification was accompanied by dilated lymphatics and enlarged lymph nodes. Prolonged nonhealing fracture with lack of cellular reaction in the gap proceeded with decreased mass of lymph nodes.

CONCLUSION

This study provides evidence for existence of a functional axis between wound of bone and surrounding soft tissue and the local lymphatic (immune) system. We hypothesize that the fast healing is regulated by influx into the wound of lymph node regulatory cells, whereas prolonged healing causes gradual exhaustion of the regional lymph node functional elements, and reciprocally impairment in sending regulatory cells to the fracture gap.