Bone-material interface characteristics of absorbable interlocking intramedullary rods for treatment of long bone shaft fracture*⋆

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Abstract

BACKGROUND:

Absorbable orthopedic implant material can be degraded and absorbed in vivo, which avoids second operation to remove it, and may play a role in stimulating fracture healing.

OBJECTIVE:

To observe bone-material interface characteristics of absorbable interlocking intramedullary rods (AIIRs) for treatment of long bone shaft fracture.

DESIGN, TIME AND SETTING:

A randomized grouping and comparative observation. The experiment was performed in the Animal Laboratory, Zhongshan Medical School from March to September 2003.

MATERIALS:

A total of 15 hybrid dogs, aged 10-12 months, weighing 13-15 kg, were used for the animal models of tibial shaft fracture.

METHODS:

The 15 hybrid dogs were randomly divided into 2 groups. In the experimental group (n=9), a hole was drilled at the slope beneath the tibial plateau to reach the medullary cavity. The cavity was enlarged by an appropriate drill to confirm the size of the cavity. The absorbable polyamide intramedullary rods were inserted from the hole in tibial superior extremity, and the fracture was anatomically reduced with the rod passing through the fracture. Two locking nails, which were cylinder polyamide rods, were respectively located 2 cm from the cutting site, in the distal and proximal ends. Auxiliary plaster external fixation was performed for 4 weeks. In the control group (n=6), quincunx intramedullary nails of the same diameter with 4 pre-drilled holes were accordingly inserted into the cutting segment, and 2 screws were locked in the distal and proximal ends, respectively. Auxiliary plaster external fixation was performed for 4 weeks.

MAIN OUTCOME MEASURES:

The general and histological changes of the intramedullary bone-material interface were observed 4, 8, 12 weeks after the operation.

RESULTS:

In the experimental group at 4 weeks, intramedullary rod was intact and smooth, with no embrittlement, closely attaching to the internal surface of medullary cavity, and no obvious gap was observed; there was a layer of fibrous connective tissue on its surface, and considerable cancellous bone and red myeloid tissue were formed beneath the connective tissue; at 8 weeks, a lightly red layer of smooth cancellous bone fibrous membrane was observed, spanning the fracture, with considerable cancellous bone surrounding outside; at 12 weeks, the fracture was completely fused, with no gap between the medullary cavity and the material, and no breakage on the locking nail. The polyamide rods were intact and smooth, not softened. There were cancellous bone and bone marrow components filled in the medullary cavity, outside the rod. However, in the control group, there was always a gap between the bone-material interface during the healing process, and no obvious bone trabecula was observed around the material.

CONCLUSION:

AIIRs can better fix the fractures of dog tibial shaft. The material matches tightly with the medullary cavity, and stimulates new bone growth without toxicity.

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