Inra medullary nailing - basic concepts

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