OrthoNet

Reamed and Nonreamed Intramedullary Nailing on Fracture Healing

Reference: Chapman M.W., CORR, 355S pg S230-280, 1998

Main Message

- Intramedullary nailing has mechanical and biologic effects on fracture healing. The mechanical effects are known well documented; the biologic effects are less well understood (as are the implications of these on fracture healing). The molecular biologic effects have not been studied.

Points of Interest

Mechanics - influenced by nail geometry and stiffness
- geometry includes longitudinal shape, transverse diameter, cross sectional shape, slot
- stiffness influenced by material properties
- most are made of 316L stainless steel or titanium
- the modulus of elasticity of titanium is half that of stainless steel, but the ultimate strength is about 1.6 times that of stainless steel
- cross sectional area is important - moment of inertia increases by the FOURTH power of the radius, so as the diameter increases, the moment of inertia increases very quickly
- the main mechanical advantage of reaming is that a larger diameter nail can be inserted, which will be stronger, and will have a longer contact area through the isthmus

Biologic

Pulmonary Effects of Reaming
- European studies showed a large difference in pulmonary problems with reaming; these results have not been reproduced in North American studies which have showed no difference in both animal models (Schemitsch - canine model) or clinically (Bosse - retrospective study of 453 patients, Chapman - prospective study of 82 patients).

Bone Vascularization Effects of Reaming
- cortex in the mid-diaphysis receives the inner 2/3 from endosteal vessels, the outer 10-30% from the periosteum
- the larger you ream, the more the total blood flow and cortical blood flow is reduced acutely.
- a strong hyperemic reaction is induced by reaming however.
- nails that tightly fit the inner cortex interfere more with revascularization
- muscle coverage is important for increasing bone perfusion if there has been soft tissue loss (open fracture)
- both reamed and unreamed nails create a zone of avascularity within the inner part of the cortical bone. This avascular zone of the cortical bone is smaller in unreamed nails acutely and at 6 weeks, but the difference decreases in time. The differences seem to be pretty small - 51% vs 62%, 40% vs 51%.

Thoughts….
- Interesting review of the topic.