IntroductionThese implants are introduced into the boneremote to the fracture site and sharecompressive, bending, and torsional loads withthe surrounding osseous structuresIM nails act as internal splintswith load-sharing characteristics.
HISTORYStimson in 1883 described the insertion of an ivory peg inmedullary canal.Rush brothers described their IM pinning system in 1927.
Gerhard KuntschnerFemoral Nail-1939Stable OsteosynthesisPrinciple of fixation was based on compression between boneand implant
Flexible NailsRush pinsEnder nailsMorote NailsNancy Nails
MechanicsAct by stabilizing fractures with three or four pointcompressionEquilibrium between the tensioned pin and the bonewith its soft attached tissues will hold the alignment.Bending movements are neutralized but telescopiningand rotational torsion are not prevented.
MechanicsElastic Deformation is principle of nail stabilityNail insertion causes radially oriented forceForce is proportional to the contact area between the bone andnailProduced friction stops the nail from pulling out“Elastic Locking”
Elastic LockingBending of the nail (curvature)Cross-sectional shape (particularly the geometry of thesurface of the implant), and its diameterThe corresponding properties of the canal (eg, size, shape,bone quality)
Interlocking NailingThese nails have proximal and distal lockingscrews.The resistance to axial and torsional forcesis mainly dependant on screw boneinterphase.
Interlocking screws placed proximal anddistal to the fracture site restrict translationand rotation at the fracture site; however,minor movements occur between the nailand screws, allowing toggling of the bone.
Screw BreakageWith cortical bone contactweight is transmitted throughbone also.However in its absence fourpoint bending can occur
Implant FailuresUnlocked nails typically fail either at the fracture site orthrough a screw hole or slot.Locked nails fail by screw breakage or fracturing of the nailat locking hole sites, most commonly at the proximal hole ofthe distal interlocks
PATHOPHYSIOLOGY OF NAILINGLocal effectsSystemic effects.These effects are described with reamed nailing.
Local effectsDamage to endosteal blood supplyHeat necrosisWith intact soft tissue envelop reaming increases thecirculation in the surrounding musclesRate of non union is less with reamed nail as compared tounreamed nail.
SystemicReaming causes transient raise of the pulmonary arterial pressureIM instrumentation causes liberation of bone marrow contents toblood streamThey undergo an increase in size due to platelet adhesions
Leads to a transient decrease in perfusionSubsequent cascade reaction follows.
Unreamed nailsIt is said that unreamed nailing is advantageous in treatmentof Gustilo IIIB open fractures.It has got less amount of superficial infection and malunion ascompared to external fixation.
PrinciplesA motor with sub-cutaneous receiver for gradual lengtheningA mechanical function with one way cluches
Advantages over externalfixatorsLimb lengthening by external fixators is associated withproblems such as Pain at the pin tracts Pin tract infections Reduced joint motion and Prolonged fixation time.