Utilization of the AO LockingRatNail in a Novel Rat Femur Critical Defect Model

Surgical Classification for Preclinical Rat Femoral Bone Defect Model: Standardization Based on Systematic Review, Anatomical Analysis and Virtual Surgery

Though surgical techniques profoundly influence in vivo experiments, significant heterogeneity exists in current surgeries for inducing rat femoral bone defects. Such variations reduce the reproducibility and comparability of preclinical studies, and are detrimental to clinical translation. The purposes of this study were: (1) to conduct a systematic review of rat femoral defect models, summarizing and analyzing the surgical techniques; (2) to analyze surgical design and potential pitfalls via 3D anatomy and virtual surgeries for fostering future precision research; and (3) to establish a surgical classification system, for improving the reproducibility and comparability among studies, avoiding unnecessary repetitive experiments. The online database PubMed was searched to identify studies from January 2000 to June 2022 using keywords, including rat, femur, bone defect. Eligible publications were included for a review of surgical methods. Anatomical analysis and virtual surgeries were conducted based on micro-CT reconstruction of the rat femur for further investigation and establishment of a classification system. A total of 545 publications were included, revealing marked heterogeneity in surgical methods. Four major surgical designs were reported for inducing defects from the proximal to distal femur: bone tunnel, cortical window, segmental defect, and wedge-shaped defect. Anatomical analysis revealed potential pitfalls hindering efficient clinical translation. A classification system was established according to the anatomical region, surgical design, and fixation devices. This systematic review in combination with 3D analysis and virtual surgery provides a general overview of current surgical approaches to inducing femoral defects in rats, and establishes a surgical classification facilitating preclinical research of quality and translational value.

A bioactive synthetic membrane improves bone healing in a preclinical nonunion model

OBJECTIVES

High energy long bone fractures with critical bone loss are at risk for nonunion without strategic intervention. We hypothesize that a synthetic membrane implanted at a single stage improves bone healing in a preclinical nonunion model.

METHODS

Using standard laboratory techniques, microspheres encapsulating bone morphogenic protein-2 (BMP2) or platelet derived growth factor (PDGF) were designed and coupled to a type 1 collagen sheet. Critical femoral defects were created in rats and stabilized by locked retrograde intramedullary nailing. The negative control group had an empty defect. The induced membrane group (positive control) had a polymethylmethacrylate spacer inserted into the defect for four weeks and replaced with a bare polycaprolactone/beta-tricalcium phosphate (PCL/β-TCP) scaffold at a second stage. For the experimental groups, a bioactive synthetic membrane embedded with BMP2, PDGF or both enveloped a PCL/β-TCP scaffold was implanted in a single stage. Serial radiographs were taken at 1, 4, 8, and 12 weeks postoperatively from the definitive procedure and evaluated by two blinded observers using a previously described scoring system to judge union as primary outcome.

RESULTS

All experimental groups demonstrated better union than the negative control (p = 0.01). The groups with BMP2 incorporated into the membrane demonstrated higher average union scores than the other groups (p = 0.01). The induced membrane group performed similarly to the PDGF group. Complete union was only demonstrated in groups with BMP2-eluting membranes.

CONCLUSIONS

A synthetic membrane comprised of type 1 collagen embedded with controlled release BMP2 improved union of critical bone defects in a preclinical nonunion model.

Evaluation of Femoral Bone Fracture Healing in Rats by the Modal Damping Factor and Its Correlation With Peripheral Quantitative Computed Tomography

Introduction

Monitoring the progress of fracture healing is essential in order to establish the appropriate timing that ensures adequate bone strength for weight-bearing. In the present experimental study on a rat model of femoral fracture healing, the measurement of bone density and strength by peripheral quantitative computerized tomography (pQCT) was correlated with the modal damping factor (MDF) method.

Methods

Four groups of 12 male six-month-old Wistar rats each were anesthetized and submitted to baseline femoral pQCT and MDF scanning, followed by aseptic midshaft osteotomy of the right femur which was fixed by a locking intramedullary nail technique. The animals were left to recover and re-scanned following euthanasia of each group after six, eight, 10, and 12 weeks, respectively. The parameters measured by the pQCT method were total bone mineral density (BMD) and polar strength strain index (SSIp).

Results

Fracture healing progressed over time and at 12 weeks post-osteotomy there was no statistically significant difference between the osteotomized right and the control left femurs regarding MDF, BMD, and SSIp measurements. The highest correlations for the osteotomized femurs were observed between MDF and BMD (r = -0.647, P = 0.043), and between MDF and SSIp (r = -0.350, P = 0.321), at 10 weeks postoperatively. The high to moderate correlations between MDF and BMD, and between MDF and SSIp respectively, support the validity of MDF in assessing fracture healing.

Conclusions

Based on our findings in this fracture healing animal model, the results from the MDF method are reliable and correlate highly with the total BMD and moderately with the SSI polar values obtained by the pQCT method of bone quality measurement. Further studies are needed which may additionally support that the MDF method can be an attractive portable alternative to monitor fracture healing in the community.

An overview of de novo bone generation in animal models

Some of the earliest success in de novo tissue generation was in bone tissue, and advances, facilitated by the use of endogenous and exogenous progenitor cells, continue unabated. The concept of one health promotes shared discoveries among medical disciplines to overcome health challenges that afflict numerous species. Carefully selected animal models are vital to development and translation of targeted therapies that improve the health and well-being of humans and animals alike. While inherent differences among species limit direct translation of scientific knowledge between them, rapid progress in ex vivo and in vivo de novo tissue generation is propelling revolutionary innovation to reality among all musculoskeletal specialties. This review contains a comparison of bone deposition among species and descriptions of animal models of bone restoration designed to replicate a multitude of bone injuries and pathology, including impaired osteogenic capacity.

The Masquelet technique: Current concepts, animal models, and perspectives

Bone reconstruction within a critical-sized defect remains a real challenge in orthopedic surgery. The Masquelet technique is an innovative, two-step therapeutic approach for bone reconstruction in which the placement of a poly (methylmethacrylate) spacer into the bone defect induces the neo-formation of a tissue called "induced membrane." This surgical technique has many advantages and is often preferred to a vascularized bone flap or Ilizarov's technique. Although the Masquelet technique has achieved high clinical success rates since its development by Alain-Charles Masquelet in the early 2000s, very little is known about how the process works, and few animal models of membrane induction have been developed. Our successful use of this technique in the clinic and our interest in the mechanisms of tissue regeneration (notably bone regeneration) prompted us to develop a surgical model of the Masquelet technique in rats. Here, we provide a comprehensive review of the literature on animal models of membrane induction, encompassing the defect site, the surgical procedure, and the histologic and osteogenic properties of the induced membrane. We also discuss the advantages and disadvantages of those models to facilitate efforts in characterizing the complex biological mechanisms that underlie membrane induction.

Development of a Three-Dimensional (3D) Printed Biodegradable Cage to Convert Morselized Corticocancellous Bone Chips into a Structured Cortical Bone Graft

This study aimed to develop a new biodegradable polymeric cage to convert corticocancellous bone chips into a structured strut graft for treating segmental bone defects. A total of 24 adult New Zealand white rabbits underwent a left femoral segmental bone defect creation. Twelve rabbits in group A underwent three-dimensional (3D) printed cage insertion, corticocancellous chips implantation, and Kirschner-wire (K-wire) fixation, while the other 12 rabbits in group B received bone chips implantation and K-wire fixation only. All rabbits received a one-week activity assessment and the initial image study at postoperative 1 week. The final image study was repeated at postoperative 12 or 24 weeks before the rabbit scarification procedure on schedule. After the animals were sacrificed, both femurs of all the rabbits were prepared for leg length ratios and 3-point bending tests. The rabbits in group A showed an increase of activities during the first week postoperatively and decreased anterior cortical disruptions in the postoperative image assessments. Additionally, higher leg length ratios and 3-point bending strengths demonstrated improved final bony ingrowths within the bone defects for rabbits in group A. In conclusion, through this bone graft converting technique, orthopedic surgeons can treat segmental bone defects by using bone chips but with imitate characters of structured cortical bone graft.

The masquelet induced membrane technique with BMP and a synthetic scaffold can heal a rat femoral critical size defect

Long bone defects can be managed by the induced membrane technique together with autologous bone graft. However, graft harvest is associated with donor site morbidity. This study investigates if a tricalcium phosphate hydroxyapatite scaffold can be used alone or in combination with bone active drugs to improve healing. Sprague Dawley rats (n = 40) were randomized into four groups. (A) scaffold, (B) BMP-7, (C) BMP-7 + scaffold, and (D) BMP-7 + scaffold + systemic bisphosphonate at 2 weeks. Locked femoral nailing was followed by 6 mm segment removal and implantation of an epoxy spacer. At 4 weeks, the spacers were removed and the defects grafted. Eleven weeks later, the bones were explanted for evaluation with radiography, manual assessment, micro-CT, histology, and Fourier Transform Infrared spectroscopy (FTIR). Isolated scaffolds (A) did not heal any defects, whereas the other treatments led to healing in 7/10 (B), 10/10 (C), and 9/10 (D) rats. Group D had greater volume of highly mineralized bone (p < 0.01) and higher bone volume fraction (p < 0.01) compared to all other groups. A synthetic scaffold + BMP-7 combined with a bisphosphonate improved the callus properties in a rat femoral critical size defect, compared to both BMP-7 and scaffold alone or the two combined.

Expandable Proximal Femoral Nails (EPFNs) in Elderly Patients

PURPOSE

The purpose was to study the performance of expandable proximal femoral nails (EPFNs) for the treatment of unstable intertrochanteric fractures in elderly patients.

PATIENTS AND METHODS

Eighty-four patients were treated with a newly designed EPFN and followed up for one year.

RESULTS

The mean operating time was 50.1 ± 3.2 min and the mean blood loss was 112.3 ± 5.3 ml. Patients were treated with EPFNs of 220 mm (n = 24), 240 mm (n = 59), and 340 mm (n = 1) length. At six months postoperatively, the Harris Hip Score was 74.5 ± 5.3. At the end of follow up, 75% of patients completely recovered their preoperative function and resumed their normal activities. Seven patients died within one year postoperatively. During the operation, one patient experienced proximal femoral diaphyseal slight crack fracture. This crack fracture was treated by using a long EPFN (340 mm). Two patient developed screw cut-outs, which were solved by reoperation. And one developed deep infection resolved favorably by the appropriate antibiotic treatment. Implant failure, deep venous thrombosis, fat embolism, secondary fracture, and nonunion were not encountered.

CONCLUSIONS

In conclusion, the results of the EPFNs were satisfactory in most elderly patients with unstable intertrochanteric fracture. However, during the inflation period, the pressure on the nail must be monitored carefully in order to prevent a crack fracture.

APPLICATION OF DENDRIMER/PLASMID hBMP-2 COMPLEXES LOADED INTO β-TCP/COLLAGEN SCAFFOLD IN THE TREATMENT OF FEMORAL DEFECTS IN RATS

Purpose: Plasmid loading into scaffolds to enhance sustained release of growth factors is an important focus of regenerative medicine. The aim of this study was to build gene-activated matrices (GAMs) and examine the bone augmentation properties. Methods: Generation 5 polyamidoamine dendrimers (G5 dPAMAM)/plasmid recombinant human bone morphogenetic protein-2 (rhBMP-2) complexes were immobilized into beta-tricalcium phosphate (β-TCP)/type I collagen porous scaffolds. After cultured with rat mesenchymal stem cells (rMSCs), transfection efficiencies were examined. The secretion of rhBMP-2 and alkaline phosphatase (ALP) were detected to evaluate the osteogenic properties. Scanning electron microscopy (SEM) was used to observe attachment and proliferation. Moreover, we applied these GAMs directly into freshly created segmental bone defects in rat femurs, and their osteogenic efficiencies were evaluated. Results: Released plasmid complexes were transfected into stem cells and were expressed, which caused osteogenic differentiations of rat mesenchymal stem cells (rMSCs). SEM analysis showed excellent cell attachment. Bioactivity of plasmid rhBMP-2 was maintained in vivo, and the X-ray observation, histological analysis and immunohistochemistry (IHC) of bone tissue demonstrated that the bone healing in segmental femoral defects was enhanced by implantation of GAMs. Conclusions: Such biomaterials offer therapeutic opportunities in critical-sized bone defects.