DR. ARPAN CHAUDHARY 3rd YEAR PG RESIDENT, M.S. ORTHOPAEDICS SCREWS-HEAD, SHAFT, TIP, RUN OUT, THREAD, TYPES OF SCREWS, CORTICAL SCREW, CANCELLOUS SCREW, CANNULATED CANCELLOUS SCREW, THE HERBERT SCREW, DYNAMIC HIP SCREW, PEDICAL SCREW, BIOABSORBABLE SCREW, LAG SCREW PRINCIPLE, TENSION BAND WIRING, GOETZE-RHINELANDER-BOHLER METHOD REFERENCE- ANAND THAKUR

1. Bone Screws
SCREW IS A DECICE WHICH CONVERTS ROTATIONAL FORCES
INTO LINEAR MOTION.
ARPAN CHAUDHARY

2. It serves to hold or more objects and to lag.
A bone screw has four functional parts: head, shaft, thread, and tip.

3. Screw head:
- Screwdriver proper engagement is essential.It apply torque.

4. 1. Single slot head : A slot extends across the diameter of the head. It is also
difficult to align the screwdriver without visualization of the slot.
2. Cruciate head(fearson screw head): Two slots at right angles provide a wider
contact area than in the single slot design.
3. Phillips head: The recessed cross: slot provides a secure grip on the screw head.
On the negative side, the torque transmission is somewhat dependent of axial thrust.
4. Recessed hexagonal head (Hex head): The hexagonal head driver makes a
strong and alignment-insensitive connection with the screw and offers a good lateral guidance
that allows ‘blind’ insertion and removal.
- The flats of the hex screwdriver and hex–recess are oriented tangentially to the applied
force(Fig. F-a).
- May strip resulting in expansion of the screw head with application of excessive torque.
This happens when the screwdriver is worn out.
5. Tox 6 star drive head : advantages of the hex but offers a better resistance to
stripping, as the flats are orientated more perpendicularly to the applied force.
- Causes minimum stress and and least deformation of socket.

5. The screw head serves two functions.
1. It provides the means of applying torque
(twisting force) to the screw.
1. Acts as stop - the translational motion of the
screw stops – tension – compression.

6. Countersink
The countersink, or the undersurface of the head, is either conical or hemispherical.
1. CONICAL : inserted centred and perpendicular to the hole in a plate. If
set to any other angle, the undersurface does not adapt well.
2. A HEMISPHERICAL HEAD: Allows the screw to be angulated in all directions within a washer or
the screw hole of a plate.
- Its only disadvantage : prominence when used without a plate.
-The hemispherical shape is an integral part of the self-compressing plate design.
CONICAL
HEMISPHERICAL
Misfit 0.13 degree

7. THE SHAFT:
- The shaft/shank is the smooth link between the head and the thread.
- Screws with long shafts are used as lag screws.
RUN OUT:
- Represents a location of significant stress concentration (stress riser) because of abrupt
changes in the diameter and presence of sharp corners.
- The screw may break at the run out during insertion if
it is incorrectly centred over the hole or is not
perpendicular to the plate.
- The run out of a fully threaded screw used to be
of the same diameter as that of outside diameter
of the screw thread.
Undercutting or reducing the diameter of the ‘run out’ has also reduced the risk of
bone splitting.

8. THREAD
 Visualized as long wedge encircling the core.
 Standard screw has single thread, but screws can have two or more sets of threads.
 Double threaded screw advances twice as fast as single thread.
Thread diameter (outside diameter) : The larger the outside diameter, the greater the
resistance to pull-out.
1) V thread : more stress at sharp corner.provide more shear force and compression
force also.
- Shear force also promotes bone resorption, having lesser pull out strength.
2) Buttress thread : Slanted 45degree on leading age,trailing edge is perpendicular
or at 5-7 degree incluined.
- Less stress at rounded corner..
- Less stress force and more compression for prtovides great pull out strength.
3) Butress with cutting edge: cutting mechanisum imprecies and course threads
cxauses microfractures.
- As thred cut bone derbis push backin hole-friction-generate heat-requires higher
torque.

9. 4) locking screw thread:
- Shallower threads.
- Resists only pull out strength and does not produce compression b/w plate and
bone.
5) Bone screw fastner:
Supertior to conventional butress thread.
- Pushes bone chips in its front and out of cortex.
- Its threads distribute axial loads to multiple thread faces.

10. THE CORE
-The core diameter, also known as the inside or root.
-Represents the narrowest diameter of the screw across the base of the threads.
-It is also the weakest part of the screw.
-The smaller the root diameter, the greater the tendency
to shear off during insertion and removal.
- The root diameter of the screw and its constituent
material are the two factors which limit the torque
that can be applied.
PITCH & Lead
- The distance between the adjacent threads.
- A cortical screw with a fine thread has a small pitch 1.75mm (or 40.5 tpi),
- A cancellous screw with a coarse thread has a large pitch 2.,75MM (or 9.2 tpi).
-The stronger the bone (cortex), the smaller the pitch; the weaker the bone (cancellous), the
larger the pitch.
Lead - the distance screw travels on a complete turn.

11. THE TIP
There are five types of tips of bone screws.
1) SELF TAPPING – has thread cutting device called “FLUTE”.It cuts the bone over which
screw advances.
- Needs pilot hole, No pretapping.fit tight.
- Its tip has no purchase on distal cortex(due to
flute)
- So, Screw length should be selected than in which fluted segmeant protrudes beyond distal
cortex.
- Reinsertion should be manual.
2) NON SELF TAPPING - lacks a thread-cutting device.
-Threads precut in pilot hole with TAP – So, greater ‘effective torque’ can be produced when the
screw is inserted. This results in higher interfragmental compression.
- Offers great pullout reasistance & than the fluted self-tapping tip and provides better purchase
on the distal cortex.

12. 3) Corkscrew tip
- A corkscrew tip is used in cancellous screws where the tip clears pre-drilled hole.
- The cancellous screw forms its own by compressing the thin walled trabecular bone.
-Inadequate for cortical bone.
4)TROCAR TIP
- The trocar does not produce a true thread but rather displaces the bone as it advances.
- The ‘malleolar’ screw has a trocar tip which is well suited for soft cancellous bone of the distal
tibia and medial malleolus.
-Other are Schanz screws, and locking bolts for intramedullary nails.
5) Self-drilling self-tapping tip
- This screw complements MIIPO and used only in locked internal fixator plate hole.
- Sharpened tip and tap followed by it - increases the cutting performance and reduces the
resistance and heat generation once the drilling tip penetrates the bone.
-No possibility of measuring the exact screw length – So,monocortical insrtion
-Better purchase in osteoporotic bone and metaphyseasl region.

13. Size of pilot hole
Screw size Drill bit for
Thread hole Gliding hole
4.5 3.2 4.5
3.5 2.5 3.5
2.7 2.0 2.7
1.5 1.0 1.5

14. Screw types
 CORTICAL SCREWS AND
 CANCELLOUS SCREWS
 CORTICAL SCREWS
-MACHINE TYPE
-SMALLER THREADS,
-LOWE PITCH (40.5tpi)
-LARGE CORE DIAMETER
-SMALLER PITCH HIGHER HOLDING POWER
-THREADS CUT WITH TAP OR ST TIP (THREAD CUTTING TYPE)
-HIGHER SURFACE AREA
-FULLY THREADED SCREW
1.5mm-phalanx
2.7 mm-mwtacarpals and phalanx
3.5-radius,ulna,fibula,clavicle
4.5-humerus,tibia,femur

15.  Cancellous screw
Wood type
Core diameter less –large threads
Higher pitcgh
Greater surface area for purchase
No need for tap
Pilot holes equals to core
Better fixation in soft cancellos bone
Fully threaded – cannulated or non cannulated
Partially threaded –cannulated or non
cannulated
4mm – humerus condyles
6.5mm – tibia and femoral condyles

16. Cannulaed screws
- Insertion in metaphyseal and epiphyseal region
- Guide wire use – accurately visualise path
- maintain reduaction and control fracture fragements
- guide wire position cane be changed without
enlarging hole and w/o sacrificing bone strength.
CANNULATED CANCELLOUS SCREW
LARGE IN – femoral neck
- femoral condyles
- tibial plateau
SMALL IN - distal radius and humerus
- distal and proximal tibia
- scaphoid
- A cannulated screw for cancellous bone should be self-cutting and self-tapping. The screw tip
cuts only when rotated clockwise and is blunt when turned counterclockwise (removal
direction).

19. THE HERBERT SCREW
- Interfragmentary compression
- No head and threads are present at both ends of the screw, with a pitch differential.
-the coarser pitch moves the screw a greater distance through bone with each turn than does
the finer pitch.
-In absence of a screw head it is possible to insert this screw through articular surfaces
Current indications include fractures of the carpal scaphoid, capitellar fractures, radial head
fractures, osteochondral fractures, osteochondritis dissecans, and small joint
arthrodesis,NAVICULAR fracture,fifth metatarsal fracture.GT fracture.

20. DYNAMIC HIP SCREW
INTERFERANCE SCREW

21. BIOABSORBABLE SCREW
PEDICAL SCREW
- Provides excellent longitudinal compression –
distraction, torsional, sagital stability.
- Large pitch in distal shaft - purchase in the
cancellous bone.
- Small pitch of prox. Shaft - engages cortical bone
of pedicle.
- Polyaxial head.
- Provides threee column stability.

22. Screw used to compress fracture(lag screw),
to hold a plateagainst bone(placement screw)
or to buttress a fracture.
The lag Screw
- Its a technique of insertion nota screw.
- The most effective way to achieve compression between two bone fragments.
- It pulls the fragments together producing pressure across the fracture line.
- Distal purchae, prximally free.

23. Lag screw principle
The screw must glide freely through the near fragment and engage only the far fragment
● Whenever a screw crosses a fracture line it should be inserted as a lag screw
● Two small screws produce a more stable fixation than one large screw

24. -In diaphyseal fractures a cortical screw is applied as a lag screw – proximal gliding hole.
-In the cancellous bone of epiphyseal or metaphyseal fractures, cancellous screws are
employed.
- The unthreaded portion of the shaft,so that the threaded portion will engage only the far
fragment.
- Distance from # at far cortex longest - Screw grip strongest
- Holding strenghth increases

25. Screw fixation alone can provide adequate stability only if the fracture length is at least two to
three times the diameter of the bone, thus permitting fixation with a minimum of two screws.
(A) It follows that only long oblique and long spiral fractures can be stabilized with lag screws
alone, and this is possible only in short tubular bones such as phalanges, metacarpals and
metatarsals
(B)The third use of a screw is to buttress a fracture: a lateral wedge fracture is buttressed at its
tip with a cortical screw and a washer.

26. Wires
stainless steal, pure titaniumor its alloys, cobalt-chrome alloys.
STRENGTH : cobalt chrome alloy > steel wires.
FATIGUE RESISTANCE : multifilaments >> monofilaments.
TWO PROCESS : Annealing-wire-lower tansile strenght.
: Cold working.
In wire the gauge number decreases as diameter increases.
The ratio of any diameter to the next is 1.123.
 Factors affecting strength of wire:
- Twisting wire
- Knots-decreases strength 30%, and also with repeated bending.
Application of wire
● Twist wire to apply tension and not to obtain reduction
● Incorrectly applied wire will
—break during application
—break in the primary twist
● Correctly applied wire will
—untwist
—break in substance

27. A. One end of the wire is passed through a loop in the other end and kinked
backward for temporary fixation: ‘bend-back’ technique.
B. A variation of this technique with one end of the wire passed under itself and
against the underlying bone.
C. Helical twisting of the wire ends at a high pitch for temporary or definitive
fixation .

28. Instruments to handle wire
● Wire tightener
● Wire passer
● Holding forceps for wire
● Wire bending pliers/
flat-nosed parallel pliers
● Wire cutters

29. Main two procedures:
1) TENSION BAND WIRING.
2) CERCLAGE WIRING.
TENSION BAND WIRING
-PRINCIPLE
● Wire must be applied on the tension surface of the bone
● Wire must be prestressed (tightened)
● Wire must be strong to withstand tension load
● Strong opposite bone cortex must be present to withstand dynamic compressive loads
● Joint movement must be encouraged to improve congruity and compression
‘Wire absorbs the tensile forces, the bone withstands the compressive forces’

30. STATIC AND DYNAMIC COMPRESSION
LOSS OF BONE STOCK / POOR BONE QUALITY – BENDING STRESS-FIXATION FAILURE.

31. The technique can be employed for
 Transverse and comminuted patella fracture,
 Fracture and osteotomy of the femoral greater trochanter,
 The medial and lateral malleolar fractures,
 Fracture of the grater tuberosity of the humerus (especially where
small or osteoporotic fragments are involved),
 Fracture of the distal end of the clavicle
 Olecranon process of the ulna.

33. Cerclage wiring
● Long spiral/oblique fracture > 3 inches.
● Obtain reduction
● Multiple wire loops(not single)
● Contour wires around the bone
● Pull and twist
Always
— Use wire tightener-twister
— Twist in the same direction
— Apply equal tension all wires — unequal tension leads to early wire
breakage
GOETZE-RHINELANDER-BOHLER METHOD

34. Comminuted fractures of the tibia or femur
are successfully treated with an
intramedullary nail and cerclage wire
THEY NEUTRALIZE THE SHEARING FORCES
AND CONVERT THEM TO COMPRESSION
FORCES.
In short, the uses of cerclage wiring are:
● Temporary fixation during the plating of long bones
● Reattachment of a fractured or osteotomized greater trochanter
● As an alternative method when interlocking nailing is not available
● As an adjunct to intramedullary nailing in the presence of one or more butterfly
fragments.

35. PINS
-A surgical pin is a thin straight wire possessing remarkable resistance to bending.
-Martin Kirschner (1879–1942), Heidelberg,first to use thin wires (0.7 mm chromium-plated
steel piano wire) .
The tip of the Kirschner wire is sharp enough to facilitate insertion in the bone.
Two designs:
A. A trocar point with three cutting edges.
B. A diamond point with two bevelled surfaces and
- The trocar point is better suited for insertion in hard cortical bone.
Steinmann pins—are between 1.5 mm (1/16
inch) and 6.5 mm (1/4 inch) in diameter.
K-wires are 0.9 to 1.5 mm (0.035, 0.045, 0.062
inches) in diameter.

36. Kirschner wire insertion
● Always use a power drill to insert a Kirschner wire. The wire bends when it is inserted on a
hand drill.
● Always use a guide to direct the pin and protect the soft during insertion.
● Cutting
— Support the wire.
— Place the cutter jaws at right angles to the wire.
— Bend the wire tip after cutting.
● Wire tip must not touch the plaster cast.
 The jaws of a wire cutter are always placed at right angles to the wire.
 at any other angle, a twisting force develops
 force is transferred to the bone and as a result unintentional fracture can occur in a
small bone, particularly in the cancellous area.

37. The stability depends on three factors that are under surgeon’s control:
1. Size of the pin
2. The distance between the pins along the line of fracture
3. The pins being in the bone on both sides of the fracture.

40. Fritz Steinmann (1870–1933), a surgeon in Bern, Switzerland, introduced pins for skeletal
traction in 1908.
Steinmann pins are made in diameters from 3 to 6 mm and in lengths from 150 to 300 mm.
Tip –troacar/diamond point design
Flutes
The shaft - smooth or threaded (As the thread diameter is 0.5 mm larger than the pin)
Common sites for applying skeletal traction :
 Upper end of tibia,
 Lower end of femur,
 Lower end of tibia,
 Calcaneum and
 Olecranon.
Steinmann Pin

41. Steinmann pin insertion
● Always pre-drill a hole with a sharp drill bit.
● Use a power drill. A hand drill or T-handle induces a wobble factor and makes an oval hole
which predisposes to loosening.
● The Steinmann pin tip cuts poorly. Direct insertion into dense bone with power may cause
bone necrosis due to excessive heat production.
● Make skin cuts around the pin exits.
● Never pierce the skin with the pin tip -leads to sinus formation as the dermis is pushed
inside the wound.
● Use a drill sleeve to protect the soft tissue.Cover the sharp end of the pin.
● Ensure that no tension exists on the skin after traction is applied; if necessary make
additional cuts relax the skin to prevent its necrosis.

42. THANK YOU

43. SCREW INSERTION
1)DRILL BIT
RANGE 90-140 DEGREE DRILL ANGLE POINT

45.  Two areas of highest temperature; the bone chips immediately behind the
drilling edges of the drill bit, and in the bit itself.
 After a bone is heated to 44.6°C, temperature elevation causes deactivation of alkaline
phosphatase and the degradation of the collagen-hydroxyapatite bond resulting in
permanent alterations in its mechanical properties
Heat production in drilling
Increase
● Dull drill bit
● Time
● Thick bone
● Excessive thrust and speed
Decrease
● Sharp drill bit with
appropriate cutting angle
● Simultaneous saline irrigation
● Frequent drill bit cleaning
● Drilling large holes in
There are two possible causes of failure.
- The bit may touch an implant or may graze an
instrument and fail;this is an avoidable cause.
- Rotational bending failure following contact
with the far cortex at an unfavourable angle is
an unavoidable cause of failure.

46. Power drill
- Less wobbling occurs if a drill sleeve and power drill are used. A power drill and abundant
coolant are both necessary for good drilling.
- The drill should be rotated in the same direction, even when it is withdrawn from the hole, and
should not be reversed because it will then break.
- If the drill bit jams - removed with the help of a T-handle.
- Irrigation of the hole with saline - Reduces the friction and
- Avoids thermal damage by
cooling the tissue
Good drilling practice
● Use a straight, sharp drill bit of recommended size
● Clean the tip and the flutes frequently.
● Start slowly, establish and maintain the drilling angle.
● Use a drill sleeve.
● Use the power drill; drill with Simultaneous saline irrigation.
● Achieve proper drilling depth; avoid over-penetration

47. A drill sleeve (drill guide) :
1) Used to direct the placement of a drill hole and
2) Simultaneously protect the surrounding soft tissues.
MEASUREMENT OF SCREW LENGTH
A depth gauge is used.
In cortical bone, the appropriate screw length is such that one full thread exits the far cortex.
When inserting a self-tapping cortical screw, the screw tip must protrude further from
the far cortex so that the flutes are clear and at least one complete thread engages the cortex
In cancellous bone the depth gauge is used without the use of countersink..

48. TAPPING
- Cutting an internal thread by means of a multiple-point cutting tool is known as tapping – TAP.
- It is a good practice to make a half back turn after every two forward turns.
- Tapping reduces the incidence of cortical screw failure during insertion and allows a
greater percentage of the applied torque to be converted into compressive force.
WASHER
- A washer is often used with a cancellous screw to prevent the screw
head from burying into the thin cortex overlying the cancellous bone
HOLDING POWER OF SCREW
- The measurement of the pull-out strength and
- The measurement of maximum axial tension that a screw can develop a