Session I - Tibia Fractures

New Bone Formation and Cortical Revascularisation after Reamed and Unreamed Tibial Nailing

Martin Runkel, MD, Lothar Rudig, MD, Jürgen Degreif, Prof., MD, Pol Maria Rommens, Prof., MD

Unfallchirurgie Johannes Gutenberg-Universität Mainz, Mainz, Germany

Purpose: The insertion of a reamed nail into a fracture with severe tissue damage affects the medullary circulation considerably. Unreamed nailing is less damaging to the cortical blood supply. It is unclear whether there are differences with regard to bone healing and the remodeling process when comparing reamed and unreamed nailing procedures. For this reason, an animal experiment was performed on sheep.

Materials and Methods: Sixteen black-headed sheep, transverse tibial osteotomy (mid-shaft). In 8 cases no reaming and in 8 cases reaming followed by static interlocking nailing. Postoperative fluorescence staining at 2, 4, 6 and 8 weeks. Total duration: 10 weeks. From the tibial specimens, undecalcified thin sections were prepared. These were photographed using special filter combinations in the fluorescence microscope in such a way that areas of periosteal and interfragmentary callus area could be individually identified; these had been stained with calcein green (4 weeks), alizarin red (6 weeks) or with all 4 fluorochromes (8 weeks). Morphometric documentation of the areas of remodeling callus was possible with computer-aided picture analysis.

By measuring the distance between endosteal cortical limits and the stained osteons in the corticalis, or the thickness of the corticalis, the size of the remaining central avascular cortical zone could be determined.

Results: Periosteal callus (median of the callus area): 4 weeks after unreamed (reamed) nailing - callus area 134 sq mm (95 sq mm). Six weeks after unreamed (reamed) nailing -callus area 162 sq mm (162 sq mm). Eight weeks after unreamed (reamed) nailing - callus area 191 sq mm (180 sq mm). The values after 4 weeks differ significantly (P value 0.014, Wilcoxon test), the other values did not differ greatly. Interfragmentary callus (median of the callus area): 4 weeks after unreamed (reamed) nailing -callus area 12.1 sq mm (5.4 sq mm). Eight weeks after unreamed (reamed) nailing - callus area 15.5 sq mm (10.0 sq mm). The values after 4, 6 and 8 weeks differed statistically significantly (P values 0.010, 0.012, 0.018, Wilcoxon test). Avascular central cortical zone: 4 weeks postoperatively, 51% of the cortical thickness was not revascularised after unreamed nailing, after reamed nailing 62%; after 6 weeks these values were 40% and 51% respectively. The difference between the two groups was statistically significant (P values 0.03, Wilcoxon test).

Discussion: New bone formation: When first measured after 4 weeks the periosteal callus area after unreamed nailing was 1.4x as large as after reamed nailing. In the following weeks, there was not any further relevant difference. The larger callus area observed early in the experiment can be attributed to a better blood supply. The differences were far more pronounced between fragments. Here, it could also be observed that the difference between the two groups diminished over time. Cortical revascularization: Reamed nailing causes greater damage to the cortical circulation initially. Postoperatively a larger area of necrotic tissue remains after reamed than after unreamed nailing.

Conclusion: Due to the advantages in terms of both progress and quantity of bone regeneration and diminished bone necrosis, the application of unreamed nailing can be recommended in particular for open fractures liable to infection and comminuted fractures or in cases of severe soft tissue damage in which a considerable reduction of cortical vascularity due to trauma must be assumed.