Principle of internal and external fixation: Plates, screws, intramedullary nail, types of external fixation

1. Principle of Internal
&
External Fixation
Presenter: Dr. Kisan Nepali

2. Historical Background
• Term Osteosynthesis: Albin Lambotte, Belgian surgeon
• Father of modern internal and external fixation.
• Devised external fixator and
numerous different plates and screws.
• (Arbeitsgemeinschaft Fur Osteosynthesefragen)- set their goal
to improve the outcome of injured patient.

3. Fracture fixation Principle:
1. Identification / recognition of fracture
2. Fracture reduction to restore anatomic relationship.
3. Fracture fixation providing absolute or relative stability
4. Preservation of blood supply to soft tissues and bone.
4. Early and safe mobilization of the injured part and the patient as a whole.

4. Goal of fracture fixation
• Full restoration of function of the injured limb.
• Implants
- Provide a temporary support.
- To maintain alignment during the fracture healing, and
- To allow for a functional rehabilitation.

5. Fracture Reduction
• Restoring anatomical relationships
• Realignment of a displaced fracture
Reduction Method
1. Metaphyseal and diaphyseal fractures
usually need functional reduction.
2. Joint fracture need anatomical reduction.

6. Reduction of Meta and Diaphyseal fracture
• The functional anatomy is restored (length, alignment
and rotational axis).
• The load bearing axis of the extremity is restored
(especially important in the lower limb).

7. • The joint surface is restored anatomically.
Gaps and steps in the articular surface
must be avoided.
• Gaps: means that there is some space
between two adjacent main articular
fragments.
• Steps: means that there is difference
between the levels of two main
articular fragments.
• The axial alignment is restored.
Reduction of articular fracture

8. Stability
Relative stability
• Movement at fracture site.
• No interfragmentary compression at fracture
site. It is achieved by splinting or bridging, eg.
elastic nails.
• Callus formation.
• Indirect bone healing is achieved

9. Absolute stability
• No movement at the fracture site.
• Achieved by interfragmentary
compression, eg. Lag screws,
compression plate, Tension band.
• No callus formation.
• Direct bone healing is achieved
Cutting cone mechanism.
Lag screw
Compression screw
Tension Band

10. Preservation of blood supply –soft tissue
• Only devitalized and dead tissue removed.
• Preserve good soft tissue envelope around bone
• Minimal and gentle soft tissue handling
• Keep exposed tissues moist
• MIPO technique

11. Preserving blood supply -bone
• Reducing Periosteal stripping
• Indirect reduction
• Using implant saving blood supply (LC DCP, locking plates, ring fixators)
• Implant : leave least footprints

12. Early and safe mobilization
• Immediately after surgery
• Elevation of limb
• positioned above the level of the heart to minimize swelling.
• Early joint motion: Use of CPM machine

13. Early and safe mobilization
• Partial weight bearing
• Adequate pain control
• Thrombosis prophylaxis
• Early recognition of complications

14. External fixation
• A device placed outside the skin that stabilizes bone fragments with
pins or wires connected to bars.

15. Indication of External Fixation
1. Fractures with soft tissue damage
2. Polytrauma – damage control surgery
3. Skeletal infection
4. Corrective surgery

16. External fixators implants:
A. Schanz screws
B. Steinmann pins
C. Clamps
D. Rods

17. 1. Schanz screws
• Different lengths
• Different diameters
• Self-tapping
• Self-drilling
Tip—drill hole
Thread—engages in far cortex of
bone.
Shaft—engages in near cortex of
bone.
Top—quadrangular top firmly holded
by
T-handle.

18. Drilling Tapping
Drilling refers to creating a smooth
hole in a material with a drill and
motor.
Tapping is the action that creates a
thread into the side of the hole.
Drilling Tapping combination

19. 2. Steinmann Pins
• Unthreaded and threaded
• With a sharp tip
• Through body of bone, e.g. calcaneus, tibial head, etc
• Use: Skeletal traction

20. • Combining pin-to-rod
• Closed
• Open
• Combining rod-to-rod
• Only rod-to-rod
• Rod-to-pin which can be combined with pin fixation
Clamps

21. 4. Rods
• to link pins with clamps
• Rods come in steel, or carbon fiber, in different lengths
and diameters,
• to stabilize the frame by linking pins, via
clamps.

22. External Fixator constructs
• Uni-plane
• Bi-plane
• Multi-plane
• Ring

23. Uniplanar Fixators
Uniplanar fixator single Bar
Uniplanar fixator Z frame
Uniplanar fixator Double stacked

24. Types of external fixators
1.Modular system
can be applied anywhere
• individual bone fracture or
• joint bridging fractures.
• optimal for temporary use.
It is rapidly applied without need
for intraoperative x-rays and can
be adjusted later.

25. 2.Ring fixator
To achieve complex corrections in several planes, or just fracture stabilization.
Corrective procedures:
• Lengthening of shortened limbs.
• Correction of (rotational) deformities.
• Segemental bone transport.

26. Distraction Osteogenesis
• Inherent capacity of bone tissue to regenerate and
remodel according to the mechanical and tension forces to
which it is gradually submitted .
• Uses:
• limb length discrepancies,
• bone deformities secondary to trauma,
• infections or malformations,
• as a compensation after surgical excision of bone
tumors

27. 3. Hybrid system
• combination of two types of fixator,
• such as a half-ring fixator plus unilateral
external fixator system.
• Uses: fix periarticular fractures.

28. Method of Increasing Stability
• Pins
• Large Diameter
• More pins
• Closure to fracture site
• Bars
• Closer to limb
• More bars
• Rings
• Smaller is stiffer
• Use smallest diameter ring possible
but allow for swelling
• More rings = more stable

29. External fixation advantages
• Minimal damage to blood supply
• Minimal damage to soft tissues
• Fixation is away from site of injury
• Good option when significant infection risk.

30. Complication
• Neurovascular injury
• Pin loosening
• Pin tract infection
• Joint stiffness
• Malaligment
• Malunion
• Nonunion.

31. Internal Fixation
Stabilizes fracture ends of bone by implantation of various appliances: wires, pins,
rods, nails, plates or screw.
Principle
• To promote early active pain free movement and full weight bearing of
affected limb.
• Prevent fracture disease (Muscle atropy, Joint stiffness, Tissue adhesions,
Osteoporosis)

32. Indications of internal fixation
• Displaced intra-articular fractures
• Axial, angular or rotational instability that cannot be controlled by closed methods.
• Open fracture
• Polytrauma.
• Associated neurovascular injury.

33. Internal fixators
• Pins & Wire Fixation
• Screw fixation
• Plates and screw fixation
• Intramedullary nail

34. Pin and Wire Fxation
K-Wire and Steinmann Pin
• Resistance to bending load is poor
• So supplemented by bracing/casting
• Inserted percutaneously or with limited open reduction.
• Use:
• Provisional Fracture fixation
• Definitive Fracture fixation: Hand, forearm, foot.

35. Screw Fixation
• Screw is a device that convert
rotational force into linear motion.
• A screw has a core about which is
wrapped a spiral surface.
• 4 parts:
• Head
• Shaft
• Thread
• Tip
Lead = Pitch * No. of start
Purchase

36. Screw Head:
• attachment for screwdriver through recesses
• Arrest forward motion
• If head is threaded:- screw locks in plate– provide angular stability.
• There is also a countersink for buttress which prevent sinking of head into
bone.
Recess types:
A. Single slot head B. Cruciate Head C. Philips Head D. Recessed Hexagonal head E. New socket and driver tip (Star Drive)

37. Types of screws
1. Machine Screws
1. Threaded whole length
2. Self tapping
3. Cross section : V
Use: Fasten Hip compression screw device to SOF.
2. ASIF screw
• Designed for osteosynthesis
• Thread fully/partially.
• Cross section: Buttress.
• Self tapping, non tapping.
3. Malleolar screw
• Cortical screw, Partially threaded, trocar tip

38. Cortical Screw Cancellous screw
Modification of Machine screw Wood screw
Core diameter More Less
Thread depth Lesser More
Pitch Lesser More
Tip Simple Cork screw
Cutting flutes Absent Present
Solid or cannulated Mainly solid Both

39. Lag screw
• Compression between two bone fragments
• Achieves by providing purchase on the distal fragment while being able to turn
freely in the proximal.
• Use : simple spiral and oblique fracture.

40. • If the screw purchases in both
cortices, it cannot produce
interfragmentary compression.
Perpendicular screw placement

41. Herbert screw
• In small bones, such as the scaphoid, self
compressing, double pitch screws can be used.
• These are usually cannulated.
• As the fine pitch of the thread on the head engages
the bone, it travels less far on turning than the
coarse-pitched tip and so compression is applied
across the fracture plane.
• used in scaphoid, capitellum, radial head and in
osteochondral fractures.

42. Poller screws a/k/a blocking screw
• Effectively serving as a surrogate cortex in areas with insufficient nail-
cortex contact
• Stability against translation and angulation

43. Dynamic Hip Screw
Principle:
Sequential collapse at the fracture site
when joint is loaded.
Uses: Intertrochanteric fracture
Basal neck fracture

44. Tension Band principle
• In eccentrically loaded bone, Tensile force --- converted to compressive force on
convex side—accompanied by placing a tension band (wire, bone plate) across the
fracture line of convex side of the bone.
• Use: Olecranon, patellar fracture

45. Plates
• Like internal splints.
• Two mechanical function
1. It transmits force from one end of a bone to the other, bypassing thus
protecting the area of fracture.
1. Holds the fracture together while maintaining the proper alignment of the
fragements throughout the healing process.

46. Classification: Function
1. Neutralization
2. Compression
3. Buttress
4. Bridge
Bridge Plate
Compression plate

47. Neutralization Plate
• A protection plate neutralizes bending and rotational forces to protect
a lag screw fixation
Reduce the fracture and fix the
fracture with one or more lag
screws.
The appropriately contoured plate is
applied to the bone and screws inserted in
a neutral mode.

48. Compression plate
• It negate torsional, bending and shearing
forces and create compression across the
fracture site either through external tension
device or through specially designed self
compression holes in the dynamic compression
plate design.
• These holes exerts compression through
translation of plate as the screw engage.
USE: Type A shaft #, Transverse short oblique #

49. Dynamic Compression plate
Principle:
self compression plate due to the special geometry of screw hole
which allow the axial compression.

50. LC DCP
• Further development of DCP
• The evenly distributed undercuts reduces the contact area between
bone and plate to minimum. This significantly reduces impairment of
the blood supply of the underlying cortical bone. Undercuts also
allows for the formation of a small callus bridge.

51. Locking Compression Plate
A fixed angle construct where screw head is locked with plate
Principle:
Internal external fixator: Do not require friction between plate and bone for
stabilitiy unlike DCP.
Stability occur at screw plate interface : Increase pull-out strength of screw.
No contact between plate and bone : do not hamper periosteal vascularity.
Healing by secondary intention, callus formation

52. DCP LC-DCP
Under cuts Absent Present
Hole distance Even Uneven
Bending force distribution Even uneven
Cross section and stiffness Minimum at plate hole Uniform
Blood supply More affected Minimally affected
Magnitude of compression Less More
Bone ingrowth at fracture site Less More
Stress riser More Less
Stess shielding More less
Lag screw placement freedom 25° longitudinal and 7° sideway 40° longitudinal and 7° sideway

53. Conventional vs locking head screws
• They provide more stability in osteoporotic bone by reducing the risk of screw pullout and
over tightening of the screws.
• Well reduced fractures stay reduced
• Unicortical screws may be used
• The plate does not need to be perfectly contoured to the bone
• As the plate is not pressed against the bone, the periosteum is not compromised
• Compression at fracture site is not produced.

54. Buttress Plate
• Negate compression and shear force that occur at metaphyseal-epiphyseal #
• Used in conjunction with interfragmentary screw fixation.
• Feature:
• Plate is anchored to main stable fragement
• Correct contouring is mandatory.
• Screw should be inserted so that they adhere to the shoulder of the
screw hole closest to the fracture line to prevent axial deformation with
loading.

55. Anti-Gliding plate
• Types of buttress plate
• 1/3rd tubular plate used
• Applied in lower 1/3rd Fibula
fracture
• Prevents displacement of tip of
fibula

56. Bridge Plate
• Bridge plating techniques are used for multifragmentary long bone
fractures where intramedullary nailing or conventional plate fixation is
not suitable.
• The plate provides relative stability by fixation of the two main
fragments, achieving correct length, alignment, and rotation. The
fracture site is left undisturbed and fracture healing by callus
formation is promoted.

57. Working Length
• the length between the 2 screws closest to the fracture on each end of
the fracture.
• decreasing the working distance increases the stiffness of the fixation
construct

58. MIPO
• The traditional ORIF results in extensive soft tissue dissection and
periosteal injury and are associated with hight rates of infection,
delayed union, and non-union.
• Because of these drawbacks, research and development to the
invention of new plates called “BIOLOGICAL PLATE” and new surgical
procedure, one of which is “MINIMALLY INVASIVE PLATE
OSTEOSYNTHESIS”

59. • In this technique, only the normal bone cortexes, both proximal and distal to the
fracture site, are exposed for positioning the plate and inserting the screws, while
the fracture site is not explored so that osteogenic tissues surrounding the fracture
are well protected and their blood supply is also preserved.
• Relative stability

60. Intramedullary nail
• Nail is an internal splint that allows axial forces to be transmitted from
on end of bone to other.
• This is a load sharing implant.

61. • Classification:
Centromedullary nail: For example, k-nail, V-nail
Cephalomedullary nail: For example, proximal femoral nail
Condylocephalic nail: For example, Ender’s nail
Interlocking nail.

62. Cross section of nail:
• Cloverleaf- K-nail
• V-shaped- V-nail
• Square shaped -Talwalkar square nail

63. Generation of nail:
1st generation nail: Only internal splintage but no rotational stability, e.g. K-nail, V-
nail.
2nd generation nail: Rotational stability with, entry from piriformis fossa, e.g.
interlocking nail
3rd generation nail: Trochanteric entry, e.g. PFN, recon nail.

64. Working length of nail:
Distance between two points on either side of fracture where metal firmly grips the
bone.
Working length determines:
• Bending stiffness: It is inversely proportional to square of working length.
• Torsional stiffness: It is inversely proportional to working length.

65. Hoop stress:
When a nail is inserted into medullary canal, a circumferential expanding force
generated on cortex of bone is called hoop stress. This may lead to fracture of bone.
To reduce hoop stress:
• Over-reaming of canal
• Use undersize nail
• flexible nail
• Proper entry point.

66. Anteroposterior (a) and lateral (b) radiographs of nonunion of a right femur fracture before dynamization. Both figures
show measurements of callus diameter and diaphysis diameter that are used to determine the callus-to-diaphysis ratio
Dynamization of nail:
• The production of micromovement at fracture site without any deformation when
limb is loaded is called dynamization.
• Done at 6–10 weeks after fracture fixation.
• Prerequisite: Minimal callus around fracture site.
• Done by removal of static bolt from longer fragment (for minimal instability).

67. Interlocking nail
• These are cylindrical nails of various bends and angulations
with proximal and distal holes for bolts.
• Principle: 3-point contact.
• Mode of use:
• If only dynamic bolts are applied; it act as load sharing
implant, e.g. useful in transverse or short oblique fractures.
• If only static bolts are applied; it act as load bearing
implant, e.g. useful in comminuted fractures.

68. Reamed nailing Unreamed nailing
Nail diameter Larger diameter Lesser diameter
Working Length (WL) Increased working length No change in working length
Stability More Lesser
Endosteal or medullary blood supply Hamepered Intact
Healing of fracture Periosteal callus Both periosteal and endosteal callus
Thermal necrosis Present Absent
Bone graft fracture site Present No
Risk of fat embolism Present No
Chance of infection More chances No
Use in compound fracture No Yes

69. Summary
Following principle of Fracture fixation is important:
1. To ensure fracture heals well and properly
2. To ensure patient returns to normal function as quickly as possible
3. To reduce early and late complication of fracture

70. References
• AO principle of fracture fixation
• Rockwoods and Green Fracture in Adults, 8th Edition
• Campbell’s operative orthopedics , 12th edition
• The Elements of Fracture Fixation, 2nd Edition
• Bedside clinics in orthopedics
• Internet & Related articles