OTA 1997 Posters - Scientific Basis for Fracture Care

Intramedullary Locked Nailing with Diastasis in Rat Femora - A Pseudarthrosis Model

Roel Bierling, Kari Indrekvam, Oliver Grundnes, Anders Mölster

Haukeland University Hospital, Bergen, Norway

The aim of this study was to create an experimental model for a diaphyseal pseudarthrosis, if possible both a hypertrophic and an atrophic version.

Material and Methods: Twenty-four male Wistar rats weighing 340g (330-360) underwent transverse osteotomies in the left femur. Two mm bone was removed, and the medullary canal was reamed to 1.8mm. A 30mm nail with a 1.8mm diameter was introduced and locked proximally and distally. Locking was performed with dental root burrs manually drilled via preformed holes in the nails from a lateral opening of the femoral cortex and directly through the medial cortex. Lateral fixation was established with dental composite. A spacer in the osteotomy site was used temporarily to maintain 2 mm diastasis.

The rats were randomized into 2 groups, one received steel nails, the other polyacetal nails. Radiographs in lateral and a-p-projections were taken postoperatively and after 4 and 8 weeks. At 8 weeks postoperatively, blood flow and metabolism in the two femora were measured, and the animal was sacrificed. Histologic preparations were made from the pseudarthrotic area. Blood flow was measured with Ce 141 labeled microspheres (diameter 15um) which were injected in the left carotid, with comparison between the pseudarthrotic segment of femur in hypertrophic and atrophic specimens, and between total diaphysis in operated and control femora, respectively. Bone metabolism in total femora was measured with Sr 85 injected 48 hours before the animal was sacrificed.

Results:

	atrophic pseudarthr.	hypertrophic pseudarthr.	union	technical failure	sum
steel	6	2	1	3	12
polyacetal	1	3	4	4	12
sum	7	5	5	7	24

Technical failure was due to loosening of the proximal interlocking screw or a fracture of the femoral neck, resulting in collapse of the diastasis or rotational instability. Blood flow was significantly higher in the hypertrophic non unions compared with the atrophic type p<0.005), and in the operated femoral diaphysis compared with the control femur in all pseudarthrotic cases ( p=0.01). Metabolism was slightly elevated in femora with hypertrophic callus compared with atrophic, but the difference was not statistically significant (p=0.07).

Discussion: Atrophic and hypertrophic pseudarthrosis can be created with diastasis and use of rigid or flexible nails, respectively. The significantly higher levels of blood flow, and a tendency towards higher frequency of union with flexible nailing is felt to express stimulation of bone formation by movements of the bone ends, while a diastases in a rigid situation results in atrophic pseudarthrosis. The method needs technical improvements, which are currently applied. This model may be of value for studies of the development, properties, and possible treatment of the two types of non union.