Fracture healing after reamed and unreamed intramedullary nailing in sheep tibia

Endosteal Vasculature Dominates Along the Tibial Cortical Diaphysis: A Quantitative Magnetic Resonance Imaging Analysis

OBJECTIVE

Disrupted blood supply has been proposed as an underlying cause for delayed union in tibial shaft fractures (OTA/AO 42). Although tibial blood supply has been qualitatively evaluated, quantitative studies are lacking. The purpose of this project was to quantify the relative contribution of the endosteal supply to the tibial diaphysis.

METHODS

The superficial femoral artery of 8 fresh frozen cadaveric matched pair lower extremities was cannulated. The nutrient artery was ligated at its proximal branch point in experimental limbs. Pregadolinium and postgadolinium enhanced magnetic resonance imaging was performed with high resolution fat-suppressed ultrashort echo time magnetic resonance imaging sequences. Perfusion was assessed in 3 zones (outer, central, and inner cortex) for the proximal, middle, and distal diaphysis, respectively, using custom software to quantify and compare signal intensity between experimental and control limbs.

RESULTS

On average, the endosteal system supplied 91.4% (±3.9%) of the cortex and was the predominant blood supply for the inner, central, and outer thirds. The dominance of the endosteal contribution was most pronounced in the inner two-third of the cortex, with more than 97% loss of perfusion. Disruption of the nutrient artery also resulted in 76.3% (±11.2%) loss of perfusion of the outer one-third of the cortex.

CONCLUSION

This quantitative study revealed a predominance of endosteal blood supply to all areas (inner, middle, and outer thirds) of the tibial diaphyseal cortex. To prevent delayed bone healing, surgeons should take care to preserve the remaining periosteal vascular network in fracture patterns in which the nutrient artery has likely been disrupted.

In vivo evaluation of a magnesium-based degradable intramedullary nailing system in a sheep model

The biocompatibility and the degradation behavior of the LAE442 magnesium-based intramedullary interlocked nailing system (IM-NS) was assessed in vivo in a comparative study (stainless austenitic steel 1.4441LA) for the first time. IM-NS was implanted into the right tibia (24-week investigation period; nails/screws diameter: 9 mm/3.5 mm, length: 130 mm/15-40 mm) of 10 adult sheep (LAE442, stainless steel, n=5 each group). Clinical and radiographic examinations, in vivo computed tomography (CT), ex vivo micro-computed tomography (μCT), mechanical and histological examinations and element analyses of alloying elements in inner organs were performed. The mechanical examinations (four-point bending) revealed a significant decrease of LAE442 implant stiffness, force at 0.2% offset yield point and maximum force. Periosteal (new bone formation) and endosteal (bone decline) located bone alterations occurred in both groups (LAE442 alloy more pronounced). Moderate gas formation was observed within the LAE442 alloy group. The CT-measured implant volume decreased slightly (not significant). Histologically a predominantly direct bone-to-implant interface existed within the LAE442 alloy group. Formation of a fibrous tissue capsule around the nail occurred in the steel group. Minor inflammatory infiltration was observed in the LAE442 alloy group. Significantly increased quantities of rare earth elements were detected in the LAE442 alloy group. μCT examination showed the beginning of corrosion in dependence of the surrounding tissue. After 24 weeks the local biocompatibility of LAE442 can be considered as suitable for a degradable implant material.

STATEMENT OF SIGNIFICANCE

An application oriented interlocked intramedullary nailing system in a comparative study (degradable magnesium-based LAE442 alloy vs. steel alloy) was examined in a sheep model for the first time. We focused in particular on the examination of implant degradation by means of (μ-)CT, mechanical properties (four-point bending), clinical compatibility, local bone reactions (X-ray and histology) and possible systemic toxicity (histology and element analyses of inner organs). A significant decrease of magnesium (LAE442 alloy) implant stiffness and maximum force occurred. Moderate not clinically relevant gas accumulation was determined. A predominantly direct bone-to-implant contact existed within the magnesium (LAE442 alloy) group compared to an indirect contact in the steel group. Rare earth element accumulation could be observed in inner organs but H&E staining was inconspicuous.

Non-osteotomy and osteotomy large animal fracture models in orthopedic trauma research

Large animal fracture models are important in the field of orthopedic trauma research. New implants are tested in animals before being implanted into humans. Large animals like sheep or swine often are more properly to simulate conditions in humans, e.g. biomechanical demands, compared to rodents. Cited articles mainly analyze shock or fracture healing. Both osteotomy and non-osteotomy fracture models have been used in the past. However, comparative studies are rare and clear recommendation when to use which model are missing. This review will summarize large animal fracture models putting special emphasis on non-osteotomy fracture models.

[Effect of intramedullary reaming and nailing on the production of growth factors in the femur fracture callus in rats]

INTRODUCTION

Many studies have been conducted to determine the different effects that reaming or intramedullary nailing have on fracture healing, but there is no evidence in the literature of the effect of intramedullary reaming on osteogenesis. We performed a prospective study to analyse the effect of intramedullary reaming and nailing on the production of growth factors during the process of fracture healing in the femur of rats.

MATERIAL AND METHODS

A transverse mid-shaft non-comminuted femur fracture was produced in 64 rats; 34 rats did not receive any treatment, and a standardized surgical procedure was performed on 30 rats, by exposing the left knee, reaming the medullary canal from distal to proximal, and then fixing the fracture with a steel pin. The rats were sacrificed at the 24th hour, 4th, 7th and 15th days after the fracture. The amount of growth factors that appeared in the callus fracture was measured using histopathology studies. The primary categorical variables analysed were PDGFA, TGF2 and TGFβ-R2. These variables were analysed in each group at the different sacrifice times.

RESULTS

The results of the primary variables of the study, stratified by the time until sacrifice, showed no statistically significant differences.

DISCUSSION

Even if the presence of an intramedullary wire facilitates the fracture repair and the stabilising the bridge of bone between both edges of the fracture site, no evidence was found that reaming changes the expression of the growth factors studied (PDGFA, TGFβ-R2 and TGFβ2) during the callus formation in rats.

What is the effect of compartment syndrome and fasciotomies on fracture healing in tibial fractures?

Acute compartment syndrome (ACS) in tibial diaphyseal fractures has been associated with such complications as infection, delayed fracture healing or non-union, sensory and motor deficits, deformities, and poor functional outcome. Essential condition of an uncomplicated recovery is early diagnosis with prompt decompression. A comprehensive review of the literature was performed to evaluate the impact of compartment syndrome and leg fasciotomies on the time to fracture union and the incidence of delayed union and non-union in tibial diaphyseal fractures. A total of 16 articles, which included 245 tibial fractures complicated with compartment syndrome were analysed. There were statistically significant differences in the time to healing, being longer by 4.90 weeks (p<0.001), and in the rates of delayed union or non-union (55% versus 17.8%) (p<0.001) when these fractures were compared to tibial fractures without compartment syndrome. Patients with ACS of the tibia undergoing leg fasciotomies should be informed about the increased risk of impaired fracture healing and longer time to union.