Treating Proximal Tibial Growth Plate Injuries Using Poly(Lactic-co-Glycolic Acid) Scaffolds

Sustained release of MAPK14-targeting siRNA from polyelectrolyte complex hydrogels mitigates MSC osteogenesis in vitro with potential application in growth plate injury

The growth plate is a cartilage structure at the end of long bones which mediates growth in children. When fractured, the formation of bony repair tissue known as a "bony bar" can occur and cause limb deformities. There are currently no effective clinical solutions for the prevention of the bony bar formation or regeneration of healthy growth plate cartilage after a fracture. This study employs previously developed alginate/chitosan polyelectrolyte complex (PEC) hydrogels as a sustained release vehicle for the delivery of short-interfering RNA (siRNA). Specifically, the siRNA targets the p38-MAPK pathway in mesenchymal stem cells (MSCs) to prevent their osteogenic differentiation. In vitro experimental findings show sustained release of siRNA from the hydrogels for 6 months. Flow cytometry and confocal imaging indicate that the hydrogels release siRNA to effectively knockdown GFP expression over a sustained period. MAPK-14 targeting siRNA was used to knockdown the expression of MAPK-14 and correspondingly decrease the expression of other osteogenic genes in MSCs in vitro over the span of 21 days. These hydrogels were used in a rat model of growth plate injury to determine whether siMAPK-14 released from the gels could inhibit bony bar formation. No significant reduction of bony bar formation was seen in vivo at the one concentration of siRNA examined. This PEC hydrogel represents a significant advancement for siRNA sustained delivery, and presents an interesting potential therapeutic delivery system for growth plate injuries and other regenerative medicine applications.

3D bioprinted hydrogel/polymer scaffold with factor delivery and mechanical support for growth plate injury repair

Introduction: Growth plate injury is a significant challenge in clinical practice, as it could severely affect the limb development of children, leading to limb deformity. Tissue engineering and 3D bioprinting technology have great potential in the repair and regeneration of injured growth plate, but there are still challenges associated with achieving successful repair outcomes. Methods: In this study, GelMA hydrogel containing PLGA microspheres loaded with chondrogenic factor PTH(1-34) was combined with BMSCs and Polycaprolactone (PCL) to develop the PTH(1-34)@PLGA/BMSCs/GelMA-PCL scaffold using bio-3D printing technology. Results: The scaffold exhibited a three-dimensional interconnected porous network structure, good mechanical properties, biocompatibility, and was suitable for cellchondrogenic differentiation. And a rabbit model of growth plate injury was appliedto validate the effect of scaffold on the repair of injured growth plate. The resultsshowed that the scaffold was more effective than injectable hydrogel in promotingcartilage regeneration and reducing bone bridge formation. Moreover, the addition ofPCL to the scaffold provided good mechanical support, significantly reducing limbdeformities after growth plate injury compared with directly injected hydrogel. Discussion: Accordingly, our study demonstrates the feasibility of using 3D printed scaffolds for treating growth plate injuries and could offer a new strategy for the development of growth plate tissue engineering therapy.

Roles of Local Soluble Factors in Maintaining the Growth Plate: An Update

The growth plate is a cartilaginous tissue found at the ends of growing long bones, which contributes to the lengthening of bones during development. This unique structure contains at least three distinctive layers, including resting, proliferative, and hypertrophic chondrocyte zones, maintained by a complex regulatory network. Due to its soft tissue nature, the growth plate is the most susceptible tissue of the growing skeleton to injury in childhood. Although most growth plate damage in fractures can heal, some damage can result in growth arrest or disorder, impairing leg length and resulting in deformity. In this review, we re-visit previously established knowledge about the regulatory network that maintains the growth plate and integrate current research displaying the most recent progress. Next, we highlight local secretary factors, such as Wnt, Indian hedgehog (Ihh), and parathyroid hormone-related peptide (PTHrP), and dissect their roles and interactions in maintaining cell function and phenotype in different zones. Lastly, we discuss future research topics that can further our understanding of this unique tissue. Given the unmet need to engineer the growth plate, we also discuss the potential of creating particular patterns of soluble factors and generating them in vitro.

Tissue engineering in growth plate cartilage regeneration: Mechanisms to therapeutic strategies

The repair of growth plate injuries is a highly complex process that involves precise spatiotemporal regulation of multiple cell types. While significant progress has been made in understanding the pathological mechanisms underlying growth plate injuries, effectively regulating this process to regenerate the injured growth plate cartilage remains a challenge. Tissue engineering technology has emerged as a promising therapeutic approach for achieving tissue regeneration through the use of functional biological materials, seed cells and biological factors, and it is now widely applied to the regeneration of bone and cartilage. However, due to the unique structure and function of growth plate cartilage, distinct strategies are required for effective regeneration. Thus, this review provides an overview of current research on the application of tissue engineering to promote growth plate regeneration. It aims to elucidates the underlying mechanisms by which tissue engineering promotes growth plate regeneration and to provide novel insights and therapeutic strategies for future research on the regeneration of growth plate.

A 3D printed mimetic composite for the treatment of growth plate injuries in a rabbit model

Growth plate injuries affecting the pediatric population may cause unwanted bony repair tissue that leads to abnormal bone elongation. Clinical treatment involves bony bar resection and implantation of an interpositional material, but success is limited and the bony bar often reforms. No treatment attempts to regenerate the growth plate cartilage. Herein we develop a 3D printed growth plate mimetic composite as a potential regenerative medicine approach with the goal of preventing limb length discrepancies and inducing cartilage regeneration. A poly(ethylene glycol)-based resin was used with digital light processing to 3D print a mechanical support structure infilled with a soft cartilage-mimetic hydrogel containing chondrogenic cues. Our biomimetic composite has similar mechanical properties to native rabbit growth plate and induced chondrogenic differentiation of rabbit mesenchymal stromal cells in vitro. We evaluated its efficacy as a regenerative interpositional material applied after bony bar resection in a rabbit model of growth plate injury. Radiographic imaging was used to monitor limb length and tibial plateau angle, microcomputed tomography assessed bone morphology, and histology characterized the repair tissue that formed. Our 3D printed growth plate mimetic composite resulted in improved tibial lengthening compared to an untreated control, cartilage-mimetic hydrogel only condition, and a fat graft. However, in vivo the 3D printed growth plate mimetic composite did not show cartilage regeneration within the construct histologically. Nevertheless, this study demonstrates the feasibility of a 3D printed biomimetic composite to improve limb lengthening, a key functional outcome, supporting its further investigation as a treatment for growth plate injuries.

Growing Pains: The Need for Engineered Platforms to Study Growth Plate Biology

Growth plates, or physis, are highly specialized cartilage tissues responsible for longitudinal bone growth in children and adolescents. Chondrocytes that reside in growth plates are organized into three distinct zones essential for proper function. Modeling key features of growth plates may provide an avenue to develop advanced tissue engineering strategies and perspectives for cartilage and bone regenerative medicine applications and a platform to study processes linked to disease progression. In this review, a brief introduction of the growth plates and their role in skeletal development is first provided. Injuries and diseases of the growth plates as well as physiological and pathological mechanisms associated with remodeling and disease progression are discussed. Growth plate biology, namely, its architecture and extracellular matrix organization, resident cell types, and growth factor signaling are then focused. Next, opportunities and challenges for developing 3D biomaterial models to study aspects of growth plate biology and disease in vitro are discussed. Finally, opportunities for increasingly sophisticated in vitro biomaterial models of the growth plate to study spatiotemporal aspects of growth plate remodeling, to investigate multicellular signaling underlying growth plate biology, and to develop platforms that address key roadblocks to in vivo musculoskeletal tissue engineering applications are described.

A new method for modeling rabbit growth plate injury for the study of tissue engineering scaffolds

Establishing a suitable animal model of growth plate injury is necessary to evaluate the effect of tissue engineering scaffolds on repairing the injured growth plate. However, the currently used animal models have limitations. Therefore in this study, we reported and evaluated a new modeling method termed the longitudinal disruption method, which is to make a longitudinal defect in the region of growth plate. In order to compare this new method with the traditional transverse disruption method, we constructed the models by both methods, respectively. To observe whether bone bridges were formed, histological sections were analyzed by HE and Masson staining at three weeks after modeling. The HE and Masson staining results showed the formation of bone bridges in both groups, implying that the two methods successfully injured the growth plate. However, it was unclear whether the exact injury to growth plate caused by both methods was consistent. Therefore, in order to evaluate the accuracy and precision of modeling method, the X-ray and micro-CT were performed immediately after modeling. The percentages of accurate defect position in the longitudinal and transverse modeling groups were 88.89% and 55.56%, respectively. The micro-CT results revealed irregularly shaped defect cross sections in the transverse modeling group, whereas the defects in the longitudinal modeling group had regular shapes. The mean defect areas were 10.06 ± 0.86 and 12.30 ± 2.13 mm² in the longitudinal and transverse modeling groups, respectively, while the difference between the actual area and the expected area were -1.94 ± 0.86 mm² and -7.70 ± 2.13 mm², respectively, showing the high precision of this new method. Altogether, we successfully demonstrated a new method for establishing a rabbit model of growth plate injury,which provides a simple and rapid modeling process, good modeling effect, high modeling accuracy, and convenient scaffold implantation. The new method provides an effective animal model for tissue engineering research on the repair and regeneration of injured growth plate.

Instructive cartilage regeneration modalities with advanced therapeutic implantations under abnormal conditions

The development of interdisciplinary biomedical engineering brings significant breakthroughs to the field of cartilage regeneration. However, cartilage defects are considerably more complicated in clinical conditions, especially when injuries occur at specific sites (e.g., osteochondral tissue, growth plate, and weight-bearing area) or under inflammatory microenvironments (e.g., osteoarthritis and rheumatoid arthritis). Therapeutic implantations, including advanced scaffolds, developed growth factors, and various cells alone or in combination currently used to treat cartilage lesions, address cartilage regeneration under abnormal conditions. This review summarizes the strategies for cartilage regeneration at particular sites and pathological microenvironment regulation and discusses the challenges and opportunities for clinical transformation.

Enlightenment of Growth Plate Regeneration Based on Cartilage Repair Theory: A Review

The growth plate (GP) is a cartilaginous region situated between the epiphysis and metaphysis at the end of the immature long bone, which is susceptible to mechanical damage because of its vulnerable structure. Due to the limited regeneration ability of the GP, current clinical treatment strategies (e.g., bone bridge resection and fat engraftment) always result in bone bridge formation, which will cause length discrepancy and angular deformity, thus making satisfactory outcomes difficult to achieve. The introduction of cartilage repair theory and cartilage tissue engineering technology may encourage novel therapeutic approaches for GP repair using tissue engineered GPs, including biocompatible scaffolds incorporated with appropriate seed cells and growth factors. In this review, we summarize the physiological structure of GPs, the pathological process, and repair phases of GP injuries, placing greater emphasis on advanced tissue engineering strategies for GP repair. Furthermore, we also propose that three-dimensional printing technology will play a significant role in this field in the future given its advantage of bionic replication of complex structures. We predict that tissue engineering strategies will offer a significant alternative to the management of GP injuries.

Update on premature physeal closure. Diagnosis and treatment

PURPOSE OF REVIEW

Premature Physeal Closure (PPC) is the most common consequence of a mostly posttraumatic, physeal injury. They are of utmost importance because they can significantly alter physeal function and lead to disorders such as limb length discrepancies and angular deformities.

RECENT FINDINGS

The type of physeal fracture has not demonstrated a solid predictive value in the formation of PPC, especially in the knee where almost any type of fracture can produce it. The detection of physeal damage with imaging tests (simple radiology and MRI) is very accurate; however, their predictive capacity to foretell which injury will generate a physeal bridge is still poor. For this reason, it is not advisable to make surgical decisions at the first medical assessment. Direct surgical management of PPC's (resection-interposition technique) has generally shown high unpredictability. Nevertheless, the latest interposition materials (chondrocytes and mesenchymal stem cells) showed promising results.

SUMMARY

PPC is an often devastating consequence of physeal injury and as such deserves further research. To date little is known about etiopathogenesis, risk factors and natural history among other aspects. Until direct surgery offers more consistent results, acute osteotomies and bone distraction for progressive correction continue to be the most widespread treatments for PPCs.

Periosteal incarceration versus interposition adipose tissue grafting in physeal fractures: pilot study in immature rabbits

Purpose

The purpose of this study is to evaluate bar formation following physeal fracture with incarcerated periosteum or adipose tissue graft using radiographic and histological methods in an immature rabbit model.

Methods

Ten-week-old rabbits underwent induced proximal tibia physeal fractures with a contralateral sham. Fractures had periosteum (n = 5) or adipose tissue (n = 5) interposed. Radiographs were compared over time by tibial medial-lateral side difference (TMLSD)(mm), femoral-tibial angle and tibia plateau angle, and physeal bars evidence. MicroCT was performed, growth plates reconstructed, and physeal area calculated and normalized to same animal contralateral physes. Physeal disruption and chondrocyte organization were evaluated histologically.

Results

Radiographic: After 6 weeks, physeal bars formed in both periosteum (4 of 4) and fat groups (3 of 5). The periosteum group showed a significant increase in the TMLSD between immediate post-op and 10 days later (p = 0.028); but, after 6 weeks, TMLSD change was not significantly different between the three groups (p = 0.161). MicroCT: The normalized physeal area of every physis in the fat group was more than 0.9 (0.99 ± 0.06). Only half of the periosteum group was over 0.9 (0.81 ± 0.24). Histology: Physeal disruption was seen by microscopic evaluation in none of the sham group, all 4 in the periosteum group and 4 of 5 in the fat group.

Conclusions

Fat interposition may prevent, or at least delay, the onset of bars across a fractured physis compared to periosteum, but it is not completely protective.

Molecular characterization of physis tissue by RNA sequencing

The physis is a well-established and anatomically distinct cartilaginous structure that is crucial for normal long-bone development and growth. Abnormalities in physis function are linked to growth plate disorders and other pediatric musculoskeletal diseases. Understanding the molecular pathways operative in the physis may permit development of regenerative therapies to complement surgically-based procedures that are the current standard of care for growth plate disorders. Here, we performed next generation RNA sequencing on mRNA isolated from human physis and other skeletal tissues (e.g., articular cartilage and bone; n = 7 for each tissue). We observed statistically significant enrichment of gene sets in the physis when compared to the other musculoskeletal tissues. Further analysis of these upregulated genes identified physis-specific networks of extracellular matrix proteins including collagens (COL2A1, COL6A1, COL9A1, COL14A1, COL16A1) and matrilins (MATN1, MATN2, MATN3), and signaling proteins in the WNT pathway (WNT10B, FZD1, FZD10, DKK2) or the FGF pathway (FGF10, FGFR4). Our results provide further insight into the gene expression networks that contribute to the physis' unique structural composition and regulatory signaling networks. Physis-specific expression profiles may guide ongoing initiatives in tissue engineering and cell-based therapies for treatment of growth plate disorders and growth modulation therapies. Furthermore, our findings provide new leads for therapeutic drug discovery that would permit future intervention through pharmacological rather than surgical strategies.

Regenerative Medicine Approaches for the Treatment of Pediatric Physeal Injuries

The physis, or growth plate, is a cartilaginous region at the end of children's long bones that serves as the primary center for longitudinal growth and characterizes the immature skeleton. Musculoskeletal injury, including fracture, infection, malignancy, or iatrogenic damage, has risk of physeal damage. Physeal injuries account for 30% of pediatric fractures and may result in impaired bone growth. Once damaged, cartilage tissue within the physis is often replaced by unwanted bony tissue, forming a "bony bar" that can lead to complications such as complete growth arrest, angular or rotational deformities, and altered joint mechanics. Children with a bony bar occupying <50% of the physis usually undergo bony bar resection and insertion of an interpositional material, such as a fat graft, to prevent recurrence and allow the surrounding uninjured physeal tissue to restore longitudinal bone growth. Clinical success for this procedure is <35% and often the bony bar and associated growth impairments return. Children who are not candidates for bony bar resection due to a physeal bar occupying >50% of their physis undergo corrective osteotomy or bone lengthening procedures. These approaches are complex and have variable success rates. As such, there is a critical need for regenerative approaches to not only prevent initial bony bar formation but also regenerate healthy physeal cartilage following injury. This review describes physeal anatomy, mechanisms of physeal injury, and current treatment options with associated limitations. Furthermore, we provide an overview of the current research using cell-based therapies, growth factors, and biomaterials in the different animal models of injury along with strategic directions for modulating intrinsic injury pathways to inhibit bony bar formation and/or promote physeal tissue formation. Pediatric physeal injuries constitute a unique niche within regenerative medicine for which there is a critical need for research to decrease child morbidity related to this injurious process.

Imaging IGF-I uptake in growth plate cartilage using in vivo multiphoton microscopy

Bones elongate through endochondral ossification in cartilaginous growth plates located at ends of primary long bones. Linear growth ensues from a cascade of biochemical signals initiated by actions of systemic and local regulators on growth plate chondrocytes. Although cellular processes are well defined, there is a fundamental gap in understanding how growth regulators are physically transported from surrounding blood vessels into and through dense, avascular cartilage matrix. Intravital imaging using in vivo multiphoton microscopy is one promising strategy to overcome this barrier by quantitatively tracking molecular delivery to cartilage from the vasculature in real time. We previously used in vivo multiphoton imaging to show that hindlimb heating increases vascular access of large molecules to growth plates using 10-, 40-, and 70-kDa dextran tracers. To comparatively evaluate transport of similarly sized physiological regulators, we developed and validated methods for measuring uptake of biologically active IGF-I into proximal tibial growth plates of live 5-wk-old mice. We demonstrate that fluorescently labeled IGF-I (8.2 kDa) is readily taken up in the growth plate and localizes to chondrocytes. Bioactivity tests performed on cultured metatarsal bones confirmed that the labeled protein is functional, assessed by phosphorylation of its signaling kinase, Akt. This methodology, which can be broadly applied to many different proteins and tissues, is relevant for understanding factors that affect delivery of biologically relevant molecules to the skeleton in real time. Results may lead to the development of drug-targeting strategies to treat a wide range of bone and cartilage pathologies.NEW & NOTEWORTHY This paper describes and validates a novel method for imaging transport of biologically active, fluorescently labeled IGF-I into skeletal growth plates of live mice using multiphoton microscopy. Cellular patterns of fluorescence in the growth plate were completely distinct from our prior publications using biologically inert probes, demonstrating for the first time in vivo localization of IGF-I in chondrocytes and perichondrium. These results form important groundwork for future studies aimed at targeting therapeutics into growth plates.

Percutaneous tibial physeal fracture repair in small animals: technique and 17 cases

OBJECTIVES

To retrospectively describe cases treated via percutaneous tibial physeal fracture repair (PTPFR), using intra-operative fluoroscopy (IFL) or digital radiography (DR). To describe a technique ("spiking"), used to treat tibial tuberosity avulsion fractures.

METHODS

Clinical data of 14 dogs and three cats were included. The "spiking" technique was described.

RESULTS

Intra-operative fluoroscopy (n = 11) and DR (n = 6) were successfully used in 11 tibial tuberosity avulsion fractures, one combined proximal physeal and tibial tuberosity avulsion fracture, and five distal tibial/fibular physeal fractures. Surgery times ranged from eight to 54 minutes. The "spiking" technique was successfully applied in six tibial tuberosity avulsion fracture cases. Return to function was at a mean (± standard deviation) of 1.9 (± 1.6) weeks. Long-term (>12 months; n = 17) follow-up was available at a mean of 40.6 (± 13.4) months. Major complications consisted of skin irritation from a pin (distal tibia / fibula physeal fracture case; 8 weeks post-PTPFR), and a bilateral grade II medial patella luxation (tibial tuberosity avulsion fracture case; 1.5 years post-PTPFR). One case developed a mild tibial tuberosity avulsion fracture re-avulsion. All conditions in these three cases were not of clinical concern at follow-up and final outcome was graded as good in these and excellent in the other 14 cases.

CLINICAL SIGNIFICANCE

Percutaneous tibial physeal fracture repair can be considered as a technique to treat tibial physeal fractures. The "spiking" technique was successfully applied in six dogs. A larger, prospective case series is indicated to provide additional clinical information.

Physeal fractures about the knee

While some fractures may be managed similarly in adults and children, physeal fractures are uniquely limited to the pediatric population and require special consideration. Although physeal fractures about the knee are relatively rare, they are occurring more frequently due to increasing youth participation in sports and high-energy recreational activities. The evaluation and management of distal femoral and proximal tibial physeal fractures are similar to one another, but fractures of the tibial spine and tibial tubercle are approached somewhat differently. A thorough understanding of the pertinent developmental anatomy is critical for correlating the clinical findings with the imaging work-up, and for anticipating the most common and the most serious complications of each fracture. Diagnosis is usually made with appropriate plain radiographs with advanced imaging often used for preoperative planning. In general, fracture pattern and degree of displacement determine the need for surgical intervention and the overall outcome. While a variety of fixation techniques or constructs may be used, because of the importance of restoring physeal and articular anatomy for avoidance of growth disturbance and degenerative joint disease, respectively, achieving anatomic, rigid fixation is of greater importance than with many other fracture locations in the growing skeleton.