TECHNIQUES OF ABSOLUTE AND RELATIVE STABILITY INCLUDING

EXTERNAL FIXATION

PRESENTER:DR.MUNENEFACILITATOR:DR.MUTISO

-Stability : degree of displacement at fracture site induced by load

-Stable fracture : fracture that does not visibly displace under physiological load

-Aim of fracture stabilizationa) Maintain achieved reductionb) Restore stiffness at fracture site(thus allowing

function)c) Minimize pain related to instability at fracture site

-Fracture fixation with absolute stability-there’s no micro-motion at the fracture site under physiological load

-This reduces mechanical stimulus for callus formation

-Fixation with relative stability-aims to maintain reduction and still keep mechanical stimulation for callus formation

-Displacement occurring under load is elastic(reversible)

ABSOLUTE FIXATION-It aims to provide a mechanically neutral environment for fracture healing

-Lack of micromotion results in primary bone healing mechanical stimulus for repair by callus formation

-This also reduces mechanical stimulus for repair by callus formation

-Hence implant must provide and maintain absolute stability for prolonged periods of time

-Without tmt, mobile fragments are stabilized by pain induced contraction of surrounding muscles→ malunion and shortening

-Implants include lag screws and plates

-Skeletal traction: pin inserted along long axis of bone. It helps to align bone fragments by ligamentotaxis and reduced motion.

-External splinting: wood, plastic ,plaster

Skeletal Traction

-Traction on a bone structure by means of a pin or wire surgically inserted into the bone.

- continuous traction is desired to immobilize, position, and align a fractured bone properly during the healing process

Aim of Skeletal Traction• regain normal length and alignment of involved bone

• lessen or eliminate muscle spasms

• relieve pressure on nerves, especially spinal and

• prevent or reduce skeletal deformities or muscle contractures

 Proximal Tibial Pins: - contraindications: - ligament injury to ipsilateral knee; - should never be used in children; - may cause recurvatum injury due to damage of tibial physis; - pins are inserted from lateral side to avoid damaging peroneal nerve;

- pin insertion: proper insertion site: 2.5 cm posterior to & 2.5 cm distal to tibial tubercle; - landmark is to place pin one to two finger breaths below tibial tuberosity in the midportion of the tibia;

- proximal pin placement, places it thru too much cancellous bone, which is weaker;

- distal femoral pin placement, while in stronger cortical bone, risks damage to peroneal nerve as it passes anterior after it passes around fibular neck;

- make a transverse skin incision about 1 cm in length, placed about 3 cm below lesser tuberosity;

Lag Screws

-Stabilizes fracture by compression alone

- Oblique, non comminuted fractures in bones which are not osteoporotic

- Involves placement of one or more screws across an osteotomy site to achieve inter-fragmentary compression

-lag screw is best positioned at right  angles to the fractures plane;

Advantages-Allow for a smaller incision-Don’t have to be removed-Don’t interfere with sydesmotic screws if needed

Disadvantages-lever arm is too small to resist functional

loading(bending/ shearing). Therefore combined with a plate to protect them from these forces

-Lack of tolerance to single overload

PLATES• Combined with screws, they act as splints to protect the screw by

reducing shear or bending forces( hence term protection plate/neutralization plate)

• 5 functional uses of a plate:i. Protection-of the lag screws

ii. Compression-drives ends of fracture together

iii. Tension band-plate placed on tension side of bone

iv. Bridging –used in multifragmentary fractures

v. Buttress:-used in metaphyseal areas(resists axial load by applying force at 90˚ to axis of potential deformity)

•LC-DCP has limited plate-bone contact(plate footprint), hence less impairment of capillary network of the periosteum->relative improvement of cortical perfusion

•Locking compression plates(LCP)-designed in such a way that screws effectively bolt into plate and bone, hence as screw is tightened, bone maintains its position and is not drawn to plate

Implications-Contouring of plates

-Screw angulation and numbers

-Screw diameter and strength

-Minimally Invasive Plate Osteosynthesis (MIPO)-periosteum,angular rigidity,osteoporosis

disadv of plates-prominent lateral screws may cause symptoms or

wound necrosis

- possibility of distal intra-articular screw insertion

-inadequate fixation if distal screws are too short

-may not allow adequate fixation in osteoporotic bone

- may interfere w/ syndesmotic screw insertion (especially when two syndesmoic screws are to be used);

RELATIVE FIXATION-Bone fragments displace in relation to each other

when physiological load is applied across fracture.

-Implants: internal fixators,ext. fixators,IM nails -All allow inter fragmentary movement which can

stimulate callus formation

-Incorrect application leads to excess movement and inhibit bone union

Ext. fixators- External fixation is a method of immobilizing bones to

allow a fracture to heal.

-External fixation is accomplished by placing pins or screws into the bone on both sides of the fracture

-The pins are then secured together outside the skin with clamps and rods. The clamps and rods are known as the "external frame."

Factors influencing stability of fixation: -stiffness of connecting rods

-distance between rods and bone axis

-no, spacing and diameter of schanz screws

Advantages-rigid fixation

-compression, neutralization, or fixed distraction of the fracture fragments

-direct surveillance of the limb and wound status

- associated treatment e.g dressing changes, skin grafting, bone grafting, and irrigation, is possible without disturbing the fracture alignment or fixation

-immediate motion of the proximal and distal joints is allowed

-extremity is elevated without pressure on the posterior soft tissues

-early patient mobilization

-can de done under L.A

- used in infected, acute fractures or non union

Disadvantages-pin tract infection

-expensive equipment

-cumbersome frame(aesthetic)

-fracture through pin tracts

- re fracture after ex-fix removal

-joint stiffness: over a joint e.g pilon fracture

-pin and fixator frame may be difficult to assemble

Complications

-pin tract infection

-neurovascular impairment

-muscle/tendon impairment

-compartment syndrome

-delayed union

IM NAILS

-Classical kuntscher nail- stable against bending and shear forces perpendicular to its long axis. Its confined to simple transverse/oblique fractures

-IM nails are: -unstable against torsional forces -confined for simple transverse or short oblique

fractures which cannot shorten and will inter-digitate to prevent rotation

-Locked IM Nails-withstand torsional forces and axial loading

-Holes are larger than screws

-Stability dependent on diameter of the nail, geometry, number of interlocking screws, spatial arrangement

Internal fixators and bridging plates

-Plating with relative stability should only be used in multi-fragmentary fractures

-Use in simple fractures causes high incidence of delayed or nonunion

-Bridge plating uses the plate as an extramedullary splint, fixed to the two main fragments, while the intermediate fracture zone is left untouched.

-anatomical reduction of the shaft fragments is not necessary.

-direct manipulation risks disturbing their blood supply

• Stiffness of an internal fixation method depends on: -dimensions of the implant

-number and position of screws

-quality of coupling btn screw and plate and btn screw and bone