Reamed and Nonreamed Intramedullary Nailing on Fracture Healing
Reference: Chapman M.W., CORR, 355S pg S230-280, 1998
– 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
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%.
– Interesting review of the topic.