Intramedullary Nailing Basic Principles Presented by Michael Sochacki
Intramedullary Nailing Basic Principles Presented by Michael Sochacki, MD Developed by Rahul Banerjee, MD
A locked IM Nail has what advantage over an unlocked nail? A. Higher union rate B. Lower incidence of immediate post-op malrotation C. Shorter OR time D. Less radiation exposure E. Higher rate of maintenance of reduction
Which of the following is the stiffest IM nail? • A. Ender pin • B. 10 mm diameter cannulated titanium nail • C. 9 mm diameter solid titanium nail • D. 8 mm diameter cannulated stainless steel nail • E. 8 mm diameter solid stainless steel nail
ANSWER • B. 10 MM DIAMETER CANNULATED TITANIUM NAIL
Intramedullary Nail • Functional Requirements • Design Features • Biology (Reaming)
Functional Requirements Maintain the alignment of a fractured or weakened bone until healed • Length • Rotation • Coronal alignment • Sagittal alignment
Functional Requirements How does the IM nail accomplish the functional requirements? 1. Internal Splint to Resist Bending Load sharing device (implant works with bone)
Functional Requirements How does the IM nail accomplish the functional requirements? 1. Internal Splint to Resist Bending 2. Locking Screws Resist Fracture Rotation and Shortening
Nail Design Features • Nail stiffness is ideal when loads are distributed throughout entire length. – Minimizes stress risers • At locking screws • Along nail bone interface
Design Features Internal Splint to Resist Bending Compared to a plate, a nail location is closer to the anatomic axis of the bone. The shorter moment arm results in reduced bending loads seen by the implant. Moment arm length
Design Features Internal Splint to Resist Bending Mechanics of a nail are similar in frontal and lateral planes • Nail cross section is round resisting loads equally in all directions. • Plate cross section is rectangular resisting greater loads in one plane versus the other.
Design Features Internal Splint to Resist Bending Nail Geometry - Longitudinal Curvature - Cannulation - Interlocking
Design Features: Longitudinal Curvature Early nail designs were straight Newer designs match shape of bone with slight mismatch
Design Features: Cannulation • Allows insertion over a guidewire • Reduction of intramedullary pressure while inserting the nail
Design Features: Interlocking – Original Gerhard Küntscher designs relied on a frictional fit between nail and bone
Interlocking Nails – Original Gerhard Küntscher designs relied on a frictional fit between nail and bone. – Advancements in image intensifiers in the late 1960’s made it possible to interlock IM nails.
Design Features: Interlocking Thanks to Peter Trafton
Design Features: Interlocking 5 mos Thanks to Peter Trafton
Biology Locking Elements: • Screws • ‘Shear Pin’ – Core diameter (Ø) is very important – Thread Depth is not the critical feature • Minimal Screw Pullout loads
Biology • Intramedullary Nailing is biologically friendly – Minimally invasive – No direct exposure of fracture – Load-sharing device
Reaming • Why do we ream? – Increases blood flow and healing response – Allows placement of larger nail…. but!
Reaming • Too much reaming can be dangerous! • Leung, JBJS (Br) 1996 – Osteocutaneous necrosis by aggressive reaming ultimately resulting in osteomyelitis
Reaming • Old School = Ream to “chatter” and place largest nail possible
Biology • Reaming must balance placement of an appropriately sized nail with encouraging the blood flow and biologic response • New School = LIMITED REAMING
Biology • What is LIMITED REAMING? • Think of the reamer as a “rotating intramedullary sound – to determine the normal canal diameter – not to change it very much. ” – B. Brumbach
Reaming • Limited Reaming – Hupel et. al. 1996, 2001 • Better viability and blood flow with limited reaming – Ziran et. al. 2004 • Limited reaming acceptable in open fractures
Reaming • General Principles – Sharp reamer – Full speed rotation, but slow advancement – Limited reaming • Pass reamer limited (2 -3 at most) number of times to determine canal size and encourage biology
Summary • Functional requirements of IM Nail – Resist bending, rotation, translation • How? – Internal Splint on biomechanical axis – Interlocking elements (ESSENTIAL) • Biology – Limited reaming
THANK YOU
SWOTA : 2010 Resident Course - Fundamentals of Fracture Care Principles of Intramedullary Nailing Helpfulness of Material A) Worst B) Bad C) OK D) Good COMMENTS Please E) Best
SWOTA : 2010 Resident Course - Fundamentals of Fracture Care Principles of Intramedullary Nailing Quality of Presentation A) Worst B) Bad C) OK D) Good COMMENTS Please E) Best
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