INTRODUCTION
BONE HEALING
Events in fracture healing are responsible for debridement,
stabilization, and ultimately remodeling of the fracture site.
Healing can take place either primarily, in the presence of rigid
fixation, or secondarily in the absence of a rigid fixation.
PRIMARY BONE HEALING
· Occurs with direct and intimate contact between the fracture
fragements.
· The new bone grows directly across the compressed bone
ends to unite the fracture.
· Primary cortical bone healing is very slow and cannot bridge
fracture gaps.
· There is no radiographic evidence of a bridging callus with
this mode of healing.
· It usually occurs approximately 2 weeks from the time of
surgery.
· This is the only method of healing with rigid compression
fixation of the fracture.
· Rigid fixation requires direct cortical contact and an intact
intramedullary vasculature.
SECONDARY HEALING
It denotes mineralization and bony replacement of a
cartilage matrix with a characteristic radiographic
appearance of callus formation.
· The greater the motion at the fracture site, the greater will
be the quality of the callus.
· This external bridging callus adds stability to the fracture
site by increasing the bone width.
· This occurs with casting and external fixation as well as
intramedullary nailing of the fracture.
Fracture healing
There are three main phases of fracture healing
A. INFLAMMATORY PHASE
·In the inflammatory stage, a hematoma develops within
the fracture site during the first few hours and days.
· Inflammatory cells (macrophages, monocytes,
ly mphocytes, and polymorphonuclear cells) and
fibroblasts infiltrate the bone under prostaglandin
mediation.
· This results in the formation of granulation tissue,
ingrowth of vascular tissue, and migration of
mesenchymal cells.
· The primary nutrient and oxygen supply of this early
process is provided by the exposed cancellous bone
and muscle.
B. REPARATIVE PHASE
This phase lasts several months.
· The fracture hematoma is then invaded by
chondroblasts and fibroblasts, which lay down the
matrix for the callus.
· Initially a soft callus is formed, composed mainly of
fibrous tissue and cartilage with small amounts of bone.
· Osteoblasts are then responsible for mineralization of
this soft callus, converting in to a hard callus of woven
bone and increasing the stability of the fracture
· This type of bone is immature and weak in torque and
therefore cannot be stressed.
C. REMODELLING STAGE
· It takes months to years.
· It consists of osteoclastic and osteoblastic activities that
results in replacement of immature disorganized bone
with a mature organized bone.
· The medullary canal gradually reforms.
There is resorption of bone from the convex surface
and new bone formation on the concave surface.
IMPLANTS
& PROSTHESIS in ORTHOPAEDICS
STRESS-SHARING DEVICE
· It permits partial transmission of load across the
fracture site.
· This results in micromotion at the fracture site, thus inducing secondary healing
with callus formation.
· Eg:- casts, rods and intramedullary nails.
STRESS- SHEILDING DEVICES
· It shields the fracture site from stress by
transferring stress to the device.
· The fracture ends of the bone are held under
compression and there is no motion at the fracture site.
· Hence resulting in primary bone healing without callus
formation.
· Eg:-compression plattinG
BONE SCREWS
A bone screw is used for internal fixation more often
than any other implant
Though it appears as a simple device, it has a great
deal of complex design.
It has four functional parts: Head, Shaft, Threads and
Tip.
HEAD
· The screw head serves as an attachment for the screw
driver.
· Is essential while removing and insertion of the
screw.
· The undersurface of the screw is the countersink.
SHAFT
The shaft is the smooth part of the screw between the
head and the thread
RUN-OUTS
It is the spot where the shaft ends and the thread
begins.
THREAD
It is wrapped around the core which provides the main
support of
the screw.
PITCH
It defines the distance between the adjacent threads
LEAD
The distance the screw will advance with each turn, the
lead is therefore equal to the pitch.
PRINCIPLE
It provides interfragmentary compression which improves mechanical stability of
internal fixation between bone fragments by minimizing the effect of torsion,
shear and bending forces.
FUNCTION
It is used either to fasten plates or similar devices on
to the bones or as lag screws, to hold together fragements of bones.
TYPES OF SCREWS
CORTICAL SCREWS
· It is a machine type of screw.
· The threads are smaller (in diameter) and are closely
placed ( lower pitch).
· The core diameter is relatively large and provides
the necessary strength.
· The smaller pitch increases the holding power.
· Threads are cut in the pilot hole before the screw is
inserted.
· The elastic reaction vital to hold the bone surfaces
together, comes from elastic deformation of the bone rather than the screw.
•
· Advantage : more engagement of screw threads in to the bone is
possible because taps provide four cutting flutes, micro- motion of bone is
less likely to occur, therefore these procedures better hold the screw.
Disadvantages: it require extra step
in operative procedure and because rather smooth track is established, it is
more likely to loosen by backing out when it is subjected to cylindrical;
stress.
CANCELLOUS SCREW
· It is a modified wooden type of screw.
· It has larger threads and a higher pitch as compared
to the cortical screws.
· The core diameter which is smaller than the shaft,
provides a greater surface area for purchase of the screw threads on the bone.
· It is inserted in to an untapped pilot hole.
Uses: used as fastening devices such as plates in metaphyseal and
epiphyseal
areas
Advantages:
i.
Holding power in fine trabecular bone is more.
ii. Tapping is not usually required because cancellous
bone is fairly soft and easily deformed.
iii. As the screws penetrate, it compressesthe bone to
either side, thereby increasing the bone density in thE
immediate vicinity of the thread, this improves the
holding power.
iv. Typically they have smooth shank in poetion
immediately adjacent to screw head so that an
automatic lag effect occurs without having to overdrill
the near cortex
Disadvantage: when used without a plate they are more
prominent
CANNULATED SCREWS
· It
is used for precise insertion in metaphyseal or epiphyseal site over a guide wire.
· This reduces the problem of having to remove and
reposition an incorrectly placed screw.
· The guide wire also maintains the reduction and
controls the fracture fragments.
· Cancellous cannulated screws come in large
and small sizes.
· Large screws are used to fix fractures of the femoral
neck, femoral condyle and tibial plateau.
· Small cannulated screws are used for distal radius, distal humerus, distal and proximal
tibia, carpals and scaphoid.
Advantages: it needs less soft tissue
dissection.
Disadvantages: screws are weaker than
non cannulated
screw particularly in small fragment size, they break more easily when removal
is attempted
THE HERBERT SCREW
· It is an specialized implant to achieve intrafragmentary compression.
· In this unique device there is no head and threads are
present at both the ends of the screws with a pitch differential between the
leading and trailing screws.
Principle: intrafragmentary compression is achieved the differences in the threads.
LAG SCREW
It is the most effective way to achieve compression
between two bony fragments.
· It pulls the fragments together producing pressure at
the
fracture line.
· Compression between the fracture fragments increases
the friction force so that interfragmentary motion is less
likely and therefore strengthens the structure.
· It achieves this by producing purchase on the distal
fragment while being able to turn freely in the
proximal.
Lag screw principle:
1. The screw must glide freely through the near fragment
and engage only the far fragment.
2. Whenever a screw crosses a fracture line it should be
inserted as a lag screw.
3. Two small screws produce a more stable fixation than
one large screw.
· The lagging technique can be applied to virtually all
of screws. In diaphyseal fractures a cortical
screw is applied as a lag screw.
· In epiphyseal or metaphyseal fractures cancellous screws are applied.
· To effect maximal interfragmentary compression, lag screw must be inserted in to the
centre of the fragments and at right angles to the fracture plane.
Uses: in communited fractures, in metaphyseal area, to achieve
inter fragemental compression &
stability.
Disadvantages: it does not provide great deal of
strength, if while doing screw is inserted at an acute angle to fracture plane
then as it is tightened it introduces a shearing moment and tends to displace
the fragements causes loss of
reduction.
•
NAILS
INTERLOCKING NAILS
The intramedullary nailing techniques which are in common use today. They
are derivd mainly from Gerhard kuntsher.
Biomechanics: interlocking nails
act as internal splints, serving as load sharing devices stabilizing fracture fragements and maintaining
alignment while permitting slight bending during functional activities, a
thicker nailmay not allow bending by
allowing the movement of the adjacent joints, rehabilitation is concurrent with
treatment and stress shielding is minimal.
FRACTURE HEALING FOLLOWING NAILING
The peripheral circulation is generally maintained
however, the
remaining process causes additional damage.
It has been observed that the small vessels grow in to
the existing gaps
between the bones and the nail is an astonishingly short
period of
time from where they penetrate in to the neighbouring
malperfused cortical bone and initiate endosteal bone formation.
Tilt nails gives the best results.
The healing of well done closed nailing and the shaft of
tibia or the femur depends on the fracture geometry and the level of fracture
healing in a biological process helped by mechanical stability.
INDICATIONS
1) All closed fractures of tibia
2) Aseptic non union
3) Pathological fractures
4) Deformity correction
5) Septic non union
6) Open fractures up to grade 3 tibial diaphyseal fractures
7) Limb lengthening procedures
8) Arthrodesis
Advantages:
Fractures fixed with intramedullary nails displayed higher
values for blood flow in the whole bone and at the
fracture
site which remained elevated for longer time than these
managed with rigid plate fixation.
ü For the weight
bearing bones, intramedullary nailing is a
fixation because the location of the rod in intramedullary
canal virtually guarantees proper axial alignment
Disadvantages
ü The size of the intramedullary canal may limit the
size of the
nail that can be used, this limits the bending strength
of the
nail unless extensive reaming performed.
ü Intramedullary nails particularly
reamed nails interfere with
the endosteal blood supply, which makes up to 90% of
vascular supply to diaphysis of long bone.
•
TYPES OF NAILS
1. REAMED NAILS
The classic reamed nail is hollow open section nail of kunscherz. Reaming provides
precise fit for nail in intramedullary canal, thereby
reducing the incidence of nail in correction and improving the stability of the
fixation.
Reaming permits the use of longer nails which are
stronger than the smaller ones.
2. Non reamed nails
Single, non reamed, non locking nails have been designed
for most of long bones including femur, tibia, humerus and foreram bones.
Single non reamed nails are easy to insert and
associated with improved preservation of endosteal blood supply and rapid revascularization.
There disadvantages include an increase likelihood of
impaction during driving and because smaller nails must be used.
3. Locking nails
They have single non locking nails absolute. The only
advantage of non locking single nails are their simplicity and low cost.
•
•4. Specialized nails
These are based on locking principle;
i.
Gamma nails: developed in a short designs for fixation of intratrochanteric fractures. Now they
are available in long devices that function like reconstructive nail.
•
•
•
•PINS
•STEINMENN PINS
Steinmann pins are rigid stainless steel pins of varying
lengths, 4-
6mm in diameter. After insertion a special stirrup is
attached to
the pin. The bohler stirrup allows the direction of the traction to
be varied without turning the pin in the hole.
•
They are now a days threaded rather than the ones that
are
smooth, smooth pins tend to loosen rapidly, so they slip
in and
out, leading to soft tissue infection or osteomylitis of bone
•
•
Indications
They are
mainly used for traction through the femur, tibia, calcaneus
Complication
· Pin traction infection
· Ligamentous damage
· Damage to epiphyseal growth plates when used in children
· Depressed scars
•
DENHMANS PIN
The denhman pin is identical to Steinmann pin accept for a
short raised threaded length situated towards the end.
This threaded portion engages the bone cortex and
reduces
the risk of pin sliding.
This type of pin is particularly suitable for use in cancellous
bone such as calcaneus or osteoporotic bone.
NEUFELD PIN
It is advantageous in elderly, medically unstable
patients
with impacted and non displaced femoral neck fractures.
•
•
•TENSION BAND WIRING
If a fracture is to unite, it requires mechanical
stability, which is obtained by compression of the fracture fragments.
· Conversely, distraction or tension interferes with
fracture healing. Therefore, tension forces on a bone must be neutralized or,
more ideally, converted into compression forces to promote fracture healing.
· This is especially important in articular fractures, where
stability is essential for early motion and a good functional outcome.
· In fractures where muscle pull tends to distract the
fragments, such as fractures of the patella or the olecranon, the application of
a tension band will neutralize these forces and even convert them into
compression when the joint is flexed.
· Similarly, a bone fragment can be avulsed at the
insertion of a tendon or ligament.
· Examples include the greater tuberosity of the humerus the greater trochanter of the femur, or the
medial malleolus.
Here, too, a tension band can reattach the avulsed
fragment, convert tensile force into compression force allowing
immediate motion of the joint.
•
•
•EXTERNAL FIXATORS
In the management of limb injuries, external skeletal
fixations,
wide variety of applications, now has a firm place in
the
armamentarium of technique available to trauma surgeon.
External fixations is a method of immobilizing fractures
by means
of pins passed through the skin and bone.
In external fixation a minimum of metal exists inside
the tissues,
and the fracture elements are will realigned, distracted
or
compressed.
•
INDICATIONS:
1. Compound fractures
2. Closed fractures with severe associated soft tissue
injuries;
compartment syndrome
3. Limb injuries requiring plastic and vascular
procedures.
4. Stress shielding device to protect internal fixation
5. Infected non unions
6. Poly traumatized patients
7. Selected fractures of the pelvis
There are two types main types of external fixators: Pin fixator
and Ring fixator
•
PIN FIXATOR
· They are applied quickly to stabilize most diaphyseal fractures.
· Also wound access is adequate for management of
soft tissue injuries.
•
•
Disadvantages:
1. The fracture needs to be reduced before constructing
the frame.
2. The presence of a fixed bar, limits adjustability of
the
frame to control angulatory and rotatory deformities,
3. It does not allow axial loading at the fracture site.
4. There is high incidence of delayed union and non
union.
5. Not suitable for ankle and pelvis fractures.
•
RING FIXATOR
· In this mode of external fixator, the frames have a
major role to play in complex reconstructions.
· These frames replicate the structure of a long tubular
bone and are somewhat like exoskeletal.
•
The bone is stabilized by tensioned wires acting like
an elastic band.
· The frame gives stability for the fracture.
•Fracture
healing is better than in the pin fixator as weight bearing produces micromovements that favour faster healing
•
DISADVANTAGES:
1. They are heavy and cumbersome
2. It is a time consuming procedure
3. There is a risk of neurovascular damage as the pins
and wires transverse the entire thickness of the bone.
4. Oedema is a commoner occurrence in unilateral frames.
•USES
1. Progressive deformity correction
2. Limb lengthening and
3. Management of non union.
•
Basic components of an external fixator
· Bone screws or pins
· Clamps
· Couplings
· Central body
· Compression-distraction system
•
1. The pin (schanz
screw, half pins)
· The stabilizing hold on a bone segment is obtained
through a
specialized bone pin that does not pass much beyond the
far
cortex
· This pin has threads at one end and a rounded tip at
the
other end.
· The half pin is a main stay of the external fixator. It is a
modified cortical screw and it is only used as a hold
fast, it
does not exert intrafragmentary compression as cortical
screws.
· A Steinmann pin is also used which passes through the
bone.
2. The clamp
It provides a connection between the pins and the other
components of the fixator.
· There are two types, in the first type an indiviual pin is fastened to
the frame by a single pin tube articulation.
The second type can attach a group of pins together and
attach them to the main frame.
•
3. The central body
· The central body, a connecting rod or a tube is the mian structure of the fixator.
· Increasing the number of rods, increases the rigidity
of the frame.
•
4. Compression-distraction system
· The compression- distraction assembly can be fixed to
the
main structure in special circumstances.
· These devices are useful to apply compression at the
fracture surface or bone interface.
•
5. Frames
· The three dimensional structure built with the
components of a fixator system is called a fixator frame, construct, or
a fixator configuration.
· Types of frame are: unilateral, unilateral uniplanar, unilateral biplanar,bilateral, bilateral uniplanar, bilateral biplanar, modular.
•
•
•
Unilateral uniplanar
frame
· It is a best suitable stabilization frame in regions
where the local topography, anatomy and functional considerations make the
erection of the double frame or a triangulated assembly impossible.
· The stiffness of this frame in the saggital plane is is higher than in the
bilateral uniplanar.
· The increased stiffness neutralizes most bending
forces which tend to cause displacement of the fragements.
· Indications: The frame is useful in stabilising humeral shaft, the ulna and radius
and fracture femur and tibia.
·
•
Advantage: Walking is greatly
facilitated and the patient can square or sit crossed legged, fewer skin entry
holes reduce the possibility of bacterial contamination and the number of
scars.
· Disadvantages: There is no
possibility of improving th reduction
alignment once the frame is completed, also there is vulnerability of the
anterior tibial crest; should
infection occur the strongest portion of the tibia can be severly damaged
Unilateral biplanar
frame
· It is the most stable of the unilateral frames and it
is well for
the treatment of tibial fractures since a large surface of that
bone is subcutaneous.
· Pins are inserted at various positions without going
through
muscles, tendons, nerves or vessels.
A unilateral biplanar frame is useful for prolonged application of the fixator in the presence of
bone loss or severe soft tissue damage
•
Bilateral uniplanar frame
· Depending upon the stability produced by the lag
screws, the bilateral uniplanar frame is either
applied with a axial compression or used simply to neutralize bending and
shearing forces.
· In the presence of a bone defect or severe communition, one
cannot apply compression for fear of producing
shortening.
· The stability of this frame is improved by prestressing the Steinmann
within each main fragement.
· The symmetry of the bilateral uniplanar assembly has offers
certain mechanical advantages over the unilateral uniplanar frame, it almost
completely eliminates lateral movements of the fragments and it allows for
uniform distribution of stress on the cortices and the external structure of
the frame.
•
Bilateral biplanar frame
· It offers greater torsional stability than other frames, with
only a few additional pins.
· The frame is useful in the presence of a large bony
defect
and in achieving arthrodesis of the knee and elbow.
· This configuration neutralizes the bending movements
in the
ventrodorsal or saggital plane, which is of great advantage
in the postoperative mobilization of the lower extremity
after
arthrodesis of the knee joint.
•
Modular frame
· Unilateral uniplanar frame requires pins to be placed in a particular order
and does not allow any variation to accommodate soft tissue conditions nor does
it permit secondary correction without new pin placement.
· In a modular frame which is a modification of the
unilateral uniplanar frame, the pins are
inserted as local condition demand.
· The modular frame gives unnprecendented freedom of pin placement and permits the positioning of
pins in different planes according to the anatomy and nature of soft tissue
damage.
· An example of the usefulness of this frame is the
external fixation of the humerus, where damage to the
radial nerve is avoided by applying the pins in two planes at right angles to
each other.
BONE PLATES
Bone plates are like internal splints holding together
the fracture
ends of the bone.
The bone plates can be classified in to four groups
1. Neutralization plates
2. Compression plates
3. Buttress plates
4. Condylar plates
NEUTRALIZATION PLATES
· A neutralization plate acts as a ‘bridge
PRINCIPLE:
1. It transmits various forces from one end of the
bone to the other, bypassing the area of the
fracture.
· Functions:
1. Acts as a mechanical link between the healthy
segments of bone above and below the fracture,
such a plate does not produce any compression at
the fracture site.
2. Used in combination with a lag screw also
counteracts the torsional, bending, and shearing
forces that tend to disrupt the screw, allowing
mobilization of the extremity.
3. The most common clinical application of the
neutralization plate is to protect the screw fixation
of a short oblique fracture or a communited
fracture of a long bone.
•
COMPRESSION PLATES
· A compression plate produces a locking force across a
fracture site to which it is applied
This effect
occurs according to newton’s third law(action and
reaction are equal and opposite).
· The plate is
attached to a bone fragement. It is then pulled
across the fracture site by a device, producing tension in the plate. As a
reaction to this tension, compression is produced at the fracture site across
which the plate is fixed.
The direction
of the compression force is parallel to the
plate.
•
•
The role of compression plate
1. Compaction of the fracture to force together the interdigitating spicules of bone and increase
the stability of the construct.
2. Reduction of the space between the bone fragments to
decrease the gap to be bridged by a new bone.
3. Protection of the blood supply through enhanced
fracture stability.
4. Friction, which at the fracture surfaces resists the
tendency of the fragements to slide under
torsion or shear. This is advantageous as plates are not particularly effective
in resisting torsion.
•BUTTRESS PLATE
FUNCTIONS
1. The mechanical function of this plate is to
strengthen (buttress) a weakened cortex.
2. It prevents the bone from collapsing during the
healing process.
3. It is designed with a large surface area to
facilitate wider distribution of the load.
•
PRINCIPLE
1. In order to prevent shearing at the fracture site or
displacement of the fracture fragments bringing about widening of the articular surface, it is
necessary to apply a plate from the diaphysis across the outer surface of the metaphyseal-epiphyseal fragment.
2. Such a plate acts as a buttress or retaining wall. A
buttress plate applies a force to the bone which is perpendicular to the flat
surface of the plate.
A buttress plate is used to maintain the bone length or
to
support the depressed fracture fragments.
· Commonly used in fixing epiphyseal and metaphyseal fractures.
· There are two types of buttress plates T-plate or
L-plate
·T-plate is used for fixation of the distal radius and tibial plateau, also used
to fix fractures of the tibial pilon and the distal humerus.
CONDYLAR PLATE
Its main application is in the treatment of intra articular distal femoral
fractures.
FUNCTIONS:
1. It maintains the reduction of the major intra articular fragments hence
restoring the anatomy of the joint surface.
2. It also rigidly fixes the metaphyseal components to the
diaphyseal shaft, permitting early mobility of the extremity.
3. It can function as both the neutralization plate as
well as the buttress plate.
· A condylar plate is used to fix a proximal femoral osteotomy and intercondylar fracture of the
femur
•
Discussion:
- Gilberty & Bateman in
1974, reported use of bipolar prosthesis;
- rationale was that erosion and protrusion of acetabulum would be less
because motion is present between metal head & polyethylene socket
(inner
bearing), as well as between metallic cup & acetabulum (outer bearing),
since cup is not fixed in bone;
- theory that distribution of shear forces between the inner and
outer bearings will spare acetabular surface from wear and erosion;
- acetabular wear is diminished
through reduction of total amount of motion that occurs between the acetabular cartilage and
metallic outer
shell
by the interposition of a second low-friction interbearing within the implant;
- because of compound bearing surface, bipolar designs provide
greater overall range of motion than either unipolar designs or conventional THR;
- made available with a 22 or 32 mm diameter head;
Recent modifications:
- axis of metallic and polyethylene cups are now
eccentric so that with loading of hip, metallic cup rotates laterally than
medially, and thus
avoids
fixation in varus position and avoids
impingement of head on edge of cup, which causes frx of poly bearing insert and dislocation;
-
Indications:
- femoral
neck fracture:
- due to the risks of osteolysis, many orthopaedist are reluctant to
insert bipolar components and instead insert unipolar componenets:
- salvage procedure in revision
THR surgery:
- indications:
- massive acetabular deficiencies which
do not permit secure fixation of the acetabular component;
- hip
instability from deficiency of abductors is a relative indication because
bipolar component is intrinsically more stable than fixed
component;
- if patient has
no abductor musculature, bipolar implant provides added stability against
dislocation compared w/ THR;
•Relative Contra-indications:
- DDH:
- further technical point is that a
bipolar prosthesis may not do well if the acetabular souricil angle is greater
than 15 deg;
- most
dysplastic acetbuli will have a high sourcil angle;
- in these cercumstances the acetabulum should be reamed
deeply, and if necessary bone grafted superiorly;
Complications:
- degree of inner bearing motion decreases over time;
- acetabular migration:
- bipolar implants in revision acetabular surgery usually
migrate, especially in soft bone such as that in rheumatoid arthritis or
against bone graft;
- migration and pain are occasional
problems with bipolar implants in young patients requiring total hip
replacement;
- osteolysis:
- this is any especially prevelant complication due to
the thinness of the polyethylene bearing surface (between the inner and out
components);
- bipolar components shed twice as
many polyethylene particles as are found in fixed acetabular
components;
- young active patients are at high
risk for osteolysis, and in these
patients a 22 mm head should be used
•Hip
resurfacing
•Total
- resurfacing arthroplasty Charnley 1948
using Teflon
bearings – poor wear
1960 –Townley – metal on polyurethane articulation – high wear –
later replaced by metal on polyethylene
1967 – Muller – metal on metal bearings
1970 – Gerhard – metal on Vitallium
1st Generation poly fails: thin poly & large femoral
heads
•1988-
Weber – Metasul bearing – high Co-Cr
alloy
•1991:
Heinz Wagner- 2nd gen. Hip
resurfacing with titanium shell & metasul inlay
Contemporary
hip resurfacing
1.Bearing surface containing high carbon Co – Cr alloy
2. Cementless acetabulum with press fit
component without screws
3. Cemented femoral component
4. Diameter approximates diameter of native femoral head
& designed to avoid notching of femoral neck.
