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Dr.S.V.Hari krishnan PGT , M.S .(Ortho)
INTRAMEDULLARY NAILING BASIC CONCEPTS
Learning Objectives Introduction Evolution Classification Biomechanics Applications Special Circumstances Recent Advances
Introduction Fracture stabilized by one of two systems
Compression Splinting
Intramedullary fixation - internal splinting Splintage -micro motion between bone & implant Relative stability without interfragmentary compression. Entry point - distant from fracture site – hematoma retained. Closed reduction and fixation (biological)
Evolution
1st generation Splints(1˚)
Rotational stability minimal
Closed fit Longitudinal slot
along entire length
Eg –K nail , V nail
2nd generation • Locking screw - improved rotational stability •Non- slotted. •Eg-russel taylor nail, delta nail
3rd generation •Fit anatomically as much as possible•Aid insertion and stability• Titanium alloy •Eg-trigen nail, universal femoral nail nails with multiple curves ,multiple fixation systems•Tibial nail with malleolar fixation
Classification Entry Portals :
Centromedullary K nail
Cephalomedullary Gamma nail Russell taylor nail PFN
Condylocephalic nail Ender nail
Direction :
AntegradeRetrograde
Centromedullary Nails First generation
Contained within medullary canal
Usually inserted from piriformis fossa
Proximal locking bolts - transverse or oblique in pertrochanter
Requires LT be attached to proximal fragment for adequate # stabilization
Cephalomedullary Nails second generation nails
More efficient load transfer than SHS
Shorter lever arm of IM device decreases tensile strain on implant - low risk of implant failure
screws/blade inserted cephald into femoral head and neck. Gamma nail Recon nail
C o n d y l o c e p h a l i c F i x a ti o n Elastic stable intramedullary nailing (ESIN) - primary definitive
paediatric fracture care . 3 – point fixation or bundle nailing. Elastic and small - micro-motion for rapid fracture healing. Flexible -insertion through a cortical window. Examples :
Lottes nails Rush pins Ender nails
Morote nails Nancy nails Prevot nails Bundle nails
Opposite Apex of curvature - at level of fracture site.
Nail diameter - 40% of narrowest medullary canal diameter
Entry point - opposite to one another
Used without reaming.
Commonest biomechanical error is lack of internal support.
Schneider nail [ solid, four fluted cross section and self broaching ends.
Harris condylocephalic nail [curved in two planes, and designed for percutaneous, retrograde fixation of extra capsular hip fractures.
Lottes tibial nail specially curved to fit tibia, and has triflanged cross section.
Ender Nails Solid pins with oblique tip and an eye
in flange at or end
Designed for percutaneous, closed treatment of extra capsular hip fractures
Rush Nails Intended for fractures of diaphyseal or metaphyseal fractures of long bones like femur, tibia, febula, humerus, radius and ulna.
Pointed tip facilitates easy insertion.
Curve at top prevents rotation and stabilizes fracture.
Bundle Pinning C- or S – shaped, act like spring. Principle introduced by hackethal. Many pins are inserted in to bone until
jammed within medullary cavity to provide compression between nails and bone.
Bending movements neutralized, but telescoping and rotational torsion not prevented
Applications Diaphyseal fractures of long bones
High proximal and low distal fractures of long bones
Floating hip, floating knee, floating elbow.
Aseptic and septic non-union
Osteoporotic long bone fractures
Pathological fractures
Open fractures up to grade IIIA
Contraindications Narrow and anomalous medullary canal
Open growth plates
Prior malunion - prevents nail placement
History of intramedullary infection
Associated ipsilateral femoral neck or acetabular fracture (relative)
Mechanics (K Nail) Elastic deformation or “elastic locking”
of nail within medullary canal
Adequate friction of nail in both fracture fragments
To achieve elastic impingement- “V” profile or even better “clover-leaf”
design.
Compressible in two directionsDirections right angles to each other
V Nail Clover Leaf Nail
Compressible in only one direction
Elastic Compressibility Of Clover – Leaf Nail
Solid Nail Elastic Nail
Not occupy full width of medullary canal
Nail with elastic cross section adjust to constrictions of medullary canal.
Grosse – Kempf nail Russell – Taylor nail Brooker–Wills nail
Biomechanics of deforming forces
D
F = Force Bending moment = F x D
D
PlateIM Nail
Bending moment for plate greater due to force being applied over larger distance.
D = distance from force to implant.
Comparision• Nail cross section round• Resisting loads equally in all
directions.
• Plate cross section rectangular resisting greater loads in one plane versus the other
Cortical contact
- compressive loads borne by bony cortex
- compressive loads transferred to
interlocking screws (“four-point bending of screws ”)
+ -
Ideal Intramedullary Nail Strong and stable - maintain alignment and position
Prevent rotation - interlocking transfixing screws
Promote union - contact-compression forces at fracture surfaces
Accessible for easy removal
Pre Requisites Adequate preoperative planning
Patient tolerance to a major surgical procedure
Availability of nails of suitable length and diameter
Suitable instruments, trained assistants, and optimal hospital conditions
Closed nailing techniques - whenever possible
Pre Operative Planning
Biplaner Radiographic Images
• Bone Morphology• Canal Dimensions
• Fracture Personality• Comminution• Fracture Extensions
Length Of Nail
• Radiographs of contra lateral femur (magnified)
• Traction radiographs (comminuted #)
• Palpable greater trochanter to lateral epicondyle.
• TMD (tibial tubercle–medial malleolar distance) for tibial nail
Diameter Of Nail
• Narrowest portion of femoral canal at femoral isthmus – lateral radiograph
• 1.0 to 1.5 mm greater in diameter than anticipated nail diameter.
Nail Length Preoperative radiographs of fractured long bone
with proximal and distal joints
AP radiograph of opposite normal limb at a tube distance of 1meter
Kuntscher measuring device : Ossimeter used to measure length and width Magnification is taken in to account
Biomechanics Stability determined by
Nail design Number and orientation of locking screws Distance of locking screw from fracture site Reaming or non reaming Quality of bone
IM nails assumed to bear most of load initially,gradually transfer it
to bone as fracture heals.
Nail Design Factors contributing to biomechanical profile :
Material properties Cross-sectional shape Diameter Curves Length and working length Ends of nail
Nail design Material properties
Titanium alloy and 316l stainless steel.
Modulus of elasticity Titanium alloy – same as
cortical bone SS – twice as cortical bone
CROSS SECTIONAL SHAPE
Determines bending and torsional strengths
Polar moment of inertia Circular nail diameter Square nail edge length High in nails with sharp corners or
fluted edges
A-schneider B-diamond C-sampson fluted D-kuntscher E-rushF-ender G-mondyH-halloran i-huckstepJ-AO/ASIFK-grosse –kempf L-russell-taylorJ,k,l-now commonly used
Nail diameterNail diameter affects bending rigidity solid circular nail,
Bending rigidity third power of nail diameter (D3)
Torsional rigidity fourth power of diameter (D4)
Large diameter with same cross-section are both stiffer and stronger than smaller ones.
Nail curves Long bones have curved medullary cavities
Nails contoured to accommodate curves of bone Straight, curved or helical Average radius of curvature of femur - 120(±36) cm.
Complete congruency minimizes normal forces and hence little frictional component to nail’s fixation.
Femoral nail designs have considerably less curve, with radius ranging from 150 to 300 cm
Im nails - straighter (larger radius) than femoral canal
Nail curves Angle of herzog :
11o bend in AP direction at junction of upper 1/3rd and lower 2/3rd of tibia nail
Mismatch in radius of curvature – Distal anterior cortical perforation more reaming required during insertion
Hoop stress Circumferential expansion stress
during nail insertion Larger hoop stress can split bone
Hoop stress reduction : Use flexible nails Over-ream entry hole by 0.5 to 1 cm Selection of ideal entry point
Posterior - loss of proximal fixation
Ideal - posterior portion of piriformis fossa
Anterior - generates huge forces, can lead to bursting of proximal femur
Nail length
A-Total nail length - Anatomical length B-working length - length between proximal and
distal point of firm fixation to bone
Working lengthAffected by various factors Type of force (Bending ,Torsion ) Type of fracture Interlocking and dynamization Reaming Weight bearing
Nail length Shorter working length stronger fixation
Transverse fracture has a shorter working length than comminuted fracture
Torsional stiffness 1/ to l
Bending stiffness 1/ to l2
Surgeon’s techniques to modify “ l ” Medullary reaming Interlocking
Extreme ends K-nail
Slot/eye in ends for extraction One end tapered to facilitate insertion .
Holes for interlocking screws
Some nails have slots near distal end for placement of anti rotation screw
Anterior slot- Improved flexibility
Posterior slot - Increased bending strength
Non-slotted -Increased torsional stiffness and strength in smaller sizes
Interlocking of nail Recommended for most cases of IM nailing.
Principle : Resistance to axial and torsional forces depends on screw – bone interface Length of bone maintained even in bone defect.
Number of interlocks : Fracture location Amount of fracture comminution Fit of nail within canal.
Placing screws in multiple planes - reduction of minor movement
Interlocking screw Location of distal locking screws affects
biomechanics of fracture
Distal locking screws Closer to fracture site - less cortical contact -
increased stress on locking screws Distal from fracture site - fracture becomes more
rotationally stable
Interlocking screws positioned at least 2 cm from fracture provides sufficient stability
Poller /blocking screws
Corrects mal-alignment.
Centers IM nail.
Planned and inserted before IM nail insertion.
Saggital or coronal plane.
Static locking Screws placed proximal and distal to fracture site
Restrict translation and rotation at fracture site.
Acts as a “bridging fixation”
Indications : Communited Spiral Pathological fractures Fractures with bone loss Atropic non union
Dynamic locking Screws inserted only at one end (short fragment)
Unlocked end stabilized by snug fit inside medullary cavity (long fragment)
Prerequisite: at least 50% cortical circumferential contact
Indications Fractures with good bone contact Non unions
With axial loading , working length in bending and torsion is reduced - improving nail-bone contact
Dynamisation “Weaken stability” Never done in progressive normal healing
Indications Established nonnunion Pseudoarthrosis
Caution: premature dynamisation adds to shortening, instability and non-union.
Dynamisation Primary Dynamisation
Dynamic locking of axially and rotationally stable fractures at time of initial fracture fixation
Secondary Dynamisation Removing interlocking screw from longer
fragment / moving proximal interlocking screw from static to dynamic slot in nail
Done in long bone delayed union and nonunion
Reamed Versus Unreamed Endosteal thermo-necrosis & endosteal cortical blood supply disruption
Minimized by using sharp reamers with deep cutting flutes. Reaming - slow and smooth.
Endosteal blood supply regenerates rapidly - high healing rates in reamed nails.
No difference in infection rates
No overall difference in time to union
Reamed Versus Unreamed Reamed nail :
High chance of embolization of bone marrow fat to lungs but this phenomenon is limited & transient
Fat extravasation greatest during insertion of nail in medullary cavity
Not dependent upon increased intra medullary pressure
Reamed nailing generally report no statistical difference in pulmonary complications as compared to unreamed nailing
Open intramedullary nailing
Primary indication : Failure to do closed nailing Nonunions Fractures requiring intramedullary fixation in existing
internal fixation device.
Advantages : Less expensive equipment required than for closed nailing.
No special fracture table / preliminary traction
Absolute anatomical reduction
Direct observation of bone - undisplaced / undetected comminution
Improved rotational alignment and stability.
Prevents torquing and twisting in segmental fractures
In nonunions, opening of medullary canals of sclerotic bone is easier.
DISADVANTAGES :
Skin scars
Fracture hematoma evacuated.
Bone shavings created by reaming medullary canal often are lost.
Infection rate increased.
Rate of union decreased.
If a locking nail is used, locking is difficult without image intensification
Nailing in open fractures If initial debridement adequate and timely , definitive stabilization with reamed
intramedullary nailing
with severe soft tissue injuries that require a second debridement, temporary external fixation reasonable
increased risk of infection after use of external fixation pins longer than 2 weeks followed by reamed intramedullary nailing.
Rapid initial management approach allows delayed conversion to a medullary implant at 5 to 10 days.
Nailing in open fractures Fractures with delay in initial debridement of more than 8 hours
- staged nailing.
Acceptable complication rate (11 % infection rate in type iii open fractures)
No relationship between infection rate, non union with timing of nailing or associated soft tissue injury
Aseptic non unions
Without bone defects - primary im nailing or exchange nailing if well aligned
With bone defects - im nailing with bone grafting
corticocancellous graft material - harvested with ria(little donor morbidity)
Exchange nailing Biological effects :
Reaming of medullary canal – promotes union
Mechanical effects : Larger-diameter intramedullary nail – improved stability
Exchage nail – atleast 1mm larger than previous nail
Canal reaming until osseous tissue observed in reaming flutes
Removal of current intramedullary nail
Reaming of medullary canal
Placement of an larger intramedullary nail
Septic non union Main aim - eradicating infection
Osseous stability important in management of infected nonunion
Stabilization with antibiotic impregnated cement coated nail after serial debridement.
Cement nail elute high concentration of antibiotic in local sites for up to 36 weeks.
Antibiotic impregnated cement nail
Nailing in damage control orthopaedics (DCO)/early total care (ETC)
In polytrauma , early femoral stabilization decreases incidence of severe fat embolism and pulmonary complications (ARDS).
Nailing with reaming will not increase pulmonary complications
Early intramedullary nailing may be deleterious and is associated with elevation of certain proinflammatory markers - (il)-6.
Early external fixation of long bone fractures followed by delayed intramedullary nailing – high risk patients.
Nailing in damage control orthopaedics (DCO)/early total care (ETC)
50% (↓) in mortality patients who underwent femoral shaft fracture stabilization beyond 12 hours
This timing was hypothesized to allow for adequate resuscitation
Exact and optimal timing of femoral shaft fracture nailing remains unclear in polytrauma(esp. Chest injuries)
Removal Timing controversial
Indications : Patient request(after union) Pain, swelling secondary to backing out of implant. Infected nailing
Full weight bearing immediately after removal
Femoral nail removed after 24-36 months , tibial nail 18-24 months
Failure When fracture healing is delayed or nonunion occurs.
IM nails usually fail in predictable patterns. Unlocked nails
fail at fracture site or through a screw hole or slot. Locked nails
screw breakage or fracturing of nail at locking hole sites(proximal hole of distal interlocks )
Recent advances Biodegradable polymers
Nickel-titanium shape-modifiable alloys can improve stability as they change shape after
insertion and recover curvature as they warm.
IM nails coated with bmp
Conclusion Implant of choice in diaphyseal fractures
Multiple factors determine final construct stiffness, should be understood and considered when choosing IM nail
Ideal intramedullary nail is yet to be invented
Bibliography
Campbell operative orthopaedics 12th edition
Rockwood and green – fractures in adults 8th edition
Elements of fracture fracture fixation – anand J.Thakur(3rd edition)
History of intramedullary nailing ,matw R. Bong, M.D., Kenneth J. Koval,m.D., And kenneth A. Egol, M.D., Bulletin of NYU hospital for joint diseases • volume 64, numbers 3 & 4, 2006