latur presentation final version

8/8/2019 Latur Presentation Final Version

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Selection Of Implants In Vogue

DR.D.J. ARWADE

M.S.,D.Ortho., F.R.C.S. (ENG. & EDIN.), DIP.N.B. (Ortho)

y Ex-Chairman, Implants Committeey Formerly Head, Dept.Of Ortho. GovernmentMedical College, Miraj,

y Prof. & Head, Dept.Of Ortho. Orthopaedic &Trauma Hospital,SarvamangalPratisthan,Miraj,y Consultant Ortho.Surgeon, Sanjeen Hospital, Sangli 416416.

C/o Sanjeen Hospital

Gulmohar Colony,Sangli 416 416

Maharashtra State

Phone No.0233 2322541

Cell :9422411639

[email protected]


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SELECTION OF IMPLANTS IN VOGUE Page 2

Selection Of Implants In Vogue

Introduction:

Implants with many modifications are being flooded into the market everyday.

Orthopaedic manufactures have modified implants to have their unique identity

and possibly to avoid the restraints of copy-right protection laws and also to suit

the demands of an individual surgeon.

The Ortho.Surgeon is at a loss to understand the rationale behind these variationsand is at times confused to make a proper selection from the available varieties.

The problem could be substantially simplified if parameters involved are well

understood.

Sir HughOwen Thomas in 1886 saidthe crying evil of our art is that much of our

surgery is too mechanical. There is a hankering to interfere which thwarts the

inherent tendency to recover. We want knowledge that will aid repair, not better

mechanics.

125 years have passed since then, but we have neither mastered mechanics nor

the tissue repair. So Sir Watson Jones in 1962warned us Even if the decision is

made to operate, there is still a wide choice of appliances in relation to both

materials &design. If the implant surgery fails due to breakage, corrosion or

inadequate fixation, the result is often disastrous.

Every fracture is different. Considering patientsage,sex, occupation and

demands,one implant is best suited for a particular type of fracture.

A study is made of common implants in vogue, highlighting points to be

considered in selection of the right implant and also rationalizing their variations.


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Implants:

1)Bone Plates:

Following points should be considered before selecting a plate:

1. Noncompressive /compressive/DCP/LCDCP/LCP.

2. Thickness.

3. Length.

4. Central clear space.

5. Holes configuration.

6. Workmanship-such as polishing, burrs, pitsetc.

It is noted that holes in the plate present serious sites of weakness. The existing

market plates (fig.1) show no uniformity regarding the central clear space.As a

result; the central hole may override or be very close to the fracture area. This

hole can not be screwed and thus the plate stands at a risk of breakage at this

hole due to fatigue.

A.O. specifies 26 mm central clear space while the holes are 16 mm apart.

BISdoesntseem to have similar specification today.

Thickness should be minimum 3mm for long bone plates; Otherwise plate stands

risk of bending or breakage during usage.

In case of DCP (Dynamic Compression Plate) /LCDCP(Low Contact Dynamic

Compression Plate) plates,one should check oblique and horizontal gliding

portions in order to have proper dynamization, as the screw is tightened.


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In case of LCP (Locked Compression Plate), apart from dynamization, there is a

static threaded portion in the hole which allows locking of screw head, as the

screw is tightened.

Length of the plate will obviously vary as per the anatomy of the fracture.By and

large 3 to 4 screws should be on either side of fracture.

Also one should meticulously visualize plates for scratch marks, burrs& pits.

2) Screws:

Following points should be considered for selection of a screw:

1. Type-self-tapping/nonself-tapping.

2. Width-4.5mm/3.5mm/2.5mm.

3. Threads per inch (TPI).

4. Thread profile.

5. Head slots.

6. Tip flute.

7. Length accuracy.

8. Workmanship.

Requirements of a screw are-

1. Relative ease of insertion.

2. Good purchase of bone so that it will not pull out during usage.

3. Strong enough to withstand tensional, torsional&shear stresses.

4. Capable of easy removal when situation arises.

The varieties of cortical screw heads that exist today is single slot , single slot with

central depression, crossedslots, Philips recessed crossed slots, hexagonal


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recessed slot & AO star shaped recessed slot(fig.2) .This would require minimum

six different types of screw drivers & similar self-holding screw drivers, to be able

to fix one unselected screw on the operation table. Besides hexagonal slots of

different companies are not identical, thereby creating additional difficulties at

surgery.

The principle is ,if there is going to be a large torque, hexagonal slot is preferred

as the torque is divided into 1/6th at each angle, so the chances of screw driver

slippage and hand wobble are eliminated.In a pre-tapped hole, ordinary screw

driver will do the job quite satisfactorily. The different thread patterns of bone

screws are 32, 20 and 14TPI. It is presumed that 32 TPI screws are no more in use.

Presently 20 TPI cortical screws and 14 TPI cancellous screws are in vogue.

The purchase of screw depends on edge width pattern of thread and hole size. 20

TPI would appear ideal for cortical bone, since six threads would engage in both

cortices.

Flute: There are two types of flutes for the self-tapping screws. V-type and right

angle type (Fig 3).BIS (Beauro of Indian Standards) dont specify the depth and the

length of V-flute. Various screws from the market show flutes extending from one

thread to ten threads. Poor tap requires considerable force for the insertion of a

screw. As a result hand wobbles and hole would become oblong.Further extra

force required could damage the screw threads also.

Right angle flute is preferred since it has better cutting edge.Besides the bone grit

gets pushed back easily, avoiding damage to the threads.

Length of thescrew: Two methods of length measurement exist in the market.

One measures the screw length, from the sloping edge of head to the tip while

other measures the screw from the top of the head to the tip.Thiscreatesconfusion, since the same screw may be sold under two different

lengths.


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The length of the screw should be measured from the base of the head to the tip,

asthis is the functional length. Top of the screw head can be flat or dome shaped.

As a result, the measurement would vary when taken from the top of the head.

3)Cancellous Screw:

Following points should be considered:

1. Head.

2. Thread type-V-type, Asymmetric, Buttressed.

3. Thread length.

4. Tip.

5. Tap.

To match the cortical screws, the cancellous screws also have variance in head

&threadpattern. Head is in 3 types viz. single slot, cross slot and hexagonal

recessed slot. The hexagonal recessed slot is preferred since there is large torque

during introduction of the cancellous screw.

The existing screws are manufactured under following thread patterns- V- thread,

Asymmetrical thread and Buttressed thread (fig.4). BIS specification says that the

cancellous screw should have 5 degrees slope on the head side and 25 degrees

slope on the tip side. The concept is V- type of threaded screw would go in easily

and pull out easily. The asymmetrical threaded screw would go in easily but will

not come out easily. The buttressed threads screw will have better bone purchasesince more bone is contained in between the threads but its thin threads stand a

risk of damage during insertion.


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4) Washers:

There are varieties of washers (fig. 5) available.

Consider following aspects:

1. Shape-Square, Round or Oval.

2. Diameter of central hole.

3. Split or unsplit.

The square washers have different dimensions and also have different

dimentionsof the central hole. As a result, they are not exchangeable. Hence the

assembly should be checked before surgery.

Splitting the washer reduces the strength by 80% hence split washer should not

be preferred.

Spring washer would maintain the hold of the screw, provided the washer retains

its resilience under pressure.

5) Dynamic Hip Screw (DHS):

Consider following points:

1. Thread length-16 mm, 32mm

2. Shaft-DHS (rectangular), hexagonal, slotted.

3. Telescopywith the tube plate.

4. Match with the top nut.

Since DHS assembly is in vogue, one has to be aware of all the problems that mayarise with this nail during surgery.

Two types of thread lengths(16 mm& 32mm) are available.16mm short length

threaded screw should be used for trans-cervical & sub-capital fracture neck


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femur.32 mm long threaded screw is suited for basal & per-trochanteric fractures.

It gives better purchase in the head & neck.

Three types of shafts designs were in the market(rectangular,hexagonaland

slotted). There is less bother for assembling screw &tube plate if one is using

DHS.Other two types have practically become extinct. Pre-operative trial fitting is

essential to make sure that screw and barrel plate engage into one another and

there is free telescopy.

Also it is essential to make sure that the top nut engages in the shaft properly

otherwise compression cannot be achieved with it on the operation table.

DHS Tubeplate:

Consider following aspects for DHS tube plate:

1. Length of tube.

2. Length of plate.

3. Location of holes.

4. Compression slot, if it exists at the end hole.

Like DHS screw, it is essential to check that tube plate and screw assembly

telescope freely into each other. Otherwise fracture may be splinted apart and

may lead to delayed or nonunion.

Also important is to check length of the barrel. If the barrel is too long, there will

be limited telescopy (Fig.6).


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6) KuntscherNail:

Through this nail isnt much in usein big towns, it is still used in mofussal places

&also for economic reasons.

Consider:

1. Tip.

2. Slot.

3. Flute.

4. Diameter along the shaft.

5. Surface smoothness.Intra-medullary nail is an efficient form of internal fixation

of long bones &is widely practiced.

Two types of tips are seen blunt &sharp. The former is preferred. The sharp tip

may cause pricking pain in the buttock.

Slot sizes vary a lot. If the slot is narrow, extractor hook may not engage in it and

may pose a problem in extraction of the nail.

Nail is at times wider in the center than at the ends and may get jammed in the

medullary cavity if not checked beforehand.

7) InterlockingNail for Tibia:

Points to consider:

1. Herzogbend, angle&location.

2. Length of the nail.

3. Locking screw holes-diameter & location.

4. Proximal threaded end.

Herzog bend location and angle are found to vary from batch to batch and

company to company. Herzog bend should be located at the distance from the


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point of tibial insertion to the point where the tibial condyles join the diaphysis.

The angle should be 11 degrees.

Locking screw hole, if not in the Centre, will form the serious site of weakness.

Nail stands risk of fracture at that location. Also if hole is too big, locking screw

/bolt may wobble in it and break.

It is essential to check that the conical driver/impactor and proximal threads of

the nail engage into each other. Otherwise there is difficulty in introduction and

extraction of the nail.

Also if the nail has slot & flute, one should check that the extractor hook engages

into the slot & diameter of the nail is uniform throughout the fluted nail length

(Fig.7).

8) InterlockingNail for Femur:

Same considerations apply as of tibia nail. Instead of Herzog bend, one has to

study the anterior bow & side of fracture.Proximal locking is done by using a jig,

hence the jig should fit well and drill holes in the jig and nail should match

properly.

9) AustinMooreProsthesis:

Following parameters should be studied:

1. Head diameter (checked with the template).

2. Smoothness of the head.

3. Location of tail.

4. Width of the tail at the base.

5. Collar of prosthesis.

Head diameter has been found to vary by +1 mm to -1mm, than has been marked

on the prosthesis. It is better to check the size by template before inserting the

prosthesis.


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Smoothness of the head head diameters in various axis should be identical and

surface should have mirror finish. Many prosthesis are so rough that a cobbled

feel is noted to the palpating palm. Such implant would cause erosion of the

acetabulum and hence rejected.

At times, tails have been attached in a cantilever fashion to the head (Fig.8). This

would produce varus strain on the prosthesis in vivo and would lead to loosening

or the tail may fracture at the junction with the collar. Further collar of the

prosthesis should be concave on the undersurface, so as to make snug fit on the

cut femoral neck.

Width of the tail should be looked into. It should be optimal to the Indian femora;

otherwise femur stands a chance of shattering on impaction.

10) SquareNail forUlna&Radius:

Consider following points:

1. Tip-trocar or gliding type.

2. Diameter-2mm, 2.5mm, 3.0mm.

3. Extraction/Impaction end.

The principle is that the fracture fragments must be held in apposition by the nail

big &strong enough to prevent side to side, angulatory and rotatory motions. The

square nails are available in the sizes of 2mm, 2.5mm and3.0mm.

In a circle, if the square is to give rotational stability it is the diagonal whichshould confirm with diameter of the circle.

In a 2mm square the effective diagonal is 2.82mm.If the diagonal were to be

2mm, and then the sides of the square would be 1.41mm which is a manufactural


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impossibility.So we are in a situation where we are measuring the surface and

hoping that the unknown diagonal would be effective (Fig.9).

Instead, a triangular nail should be preferred.In an equilateral triangle, all sides

would be 2.0mm and 3 angles would give enough rotational stability.

11) Blount Staple:

Should be studied for:

1. Length.

2. Thickness of the legs.

The blount staples are produced in the sizes of , 3/4, 1 and 1 etc. BISmeasures the outside width of the staple (Fig.10). The orthopaedic surgeon is

interested in the effective inside width of the staple, as the stability of the staple

fixation depends on the inside bone mass.

Hence BIS should modify its specifications and advicemanufacturersaccordingly.

As far as surgeon is concerned, he should actually measure inside width and

select the staple accordingly.

Discussion:

Louis Pasteur said, The greatest mischief of the mind is to believe in things,

bybelieving, we will see them to be so.From the above descriptions of individual

implants and their appraisals, two approaches emerge to this problem.

1) Designspecification: Manufacturers should give due weightage to thefollowing points:

A)The designs should be theoretically perfect in terms of location, strength andvariations in bone /implant properties as materials.

B) Functional needs of the implant-

y Immobilization of crucial (healing) areas.y Sustain direct stresses on permitted mobility.


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y Transfer progressive stresses to the developed bone.y Abuttment of fracture fragments with utmost precision.y Allowing mobility to bring in normal functions as closely as feasible.

2) Implants would continue to be available with variations, may be substantially in

a narrow range. Awareness to involved parameters in 1) above and their order of

importance to make a selective utilization can be of great help to orthopaedic

surgeons.

It is stressed that before fixing the implant, Orthopaedic surgeon should make

sure that he has adequate & proper instrumentation to do the fracture fixation

with that implant.

He should be wary of using loaner sets, as some crucial instruments may be

missing & some may be blunted or wornout making the job difficult and

imprecise.

As far as possible he should use implants of branded/ISO (Indian standards

organization) registered company. Implants should be marked with laser etching-

the name and logo of the company, the batch no. , specifications of metal and

implant design, etc.

Also note should be made in the case paper regarding the implant specifications

and the identity of the manufacturer. This would protect him in consumer court,

in case he is unfortunate enough to face the suit for implant failure.


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Summary:

There are many variations of the same implant in the market. Orthopaedic

surgeon is at a loss to choose the proper implant. In certain situations some

implants are better suited than others. So it is essential to have clear

understanding in selecting a proper implant.

This article analyses common implants for their variations and rationalizes their

specific uses highlighting some of the obscure defects.

It is hoped that proper selection of the implant will reduce the operative

difficulties and incidence of implant failure and thereby ensuing frustration to the

surgeon.

References:

1. ARWADED.J. (1984) fractured implants. Indian J.Ortho.18:117.2. A.O. /A.S.I.F. (1977) -Synthes R.-Original instruments of the Swiss

association for the study of internal fixation-Rob Mathys Co.

InstituteStraumannA.G., page 8.

3. Indian standards institution:I. Specification for Bone-Plate, Sherman type,I.S.5170-JUNE 92

II. Specification for Screws, Bone,I.S.5393-FEB 91III. Specification for Prosthesis Hip,I.S.5394-AUG 91IV. Specification for Nail, Bone,Kuntschner ,I.S.5395-MAR 94V. Specification for Staple Epiphyseal,Orthopaedic,I.S.6289-AUG 91

VI. Specification for Metal Bone Screws Part 1, 2, 3, and 4. ,I.S.9829-JUNE 92VII. Specification for Nail,Square,Ulna,I.S.10727-FEB 91

VIII. Specification for Nail, Square, Radius. ,I.S.10728-FEB 91IX. Specification for Bone, Plate, Dynamic Compression,I.S.12088-JUNE 92X. A.J.THAKUR-intramedullarynailing, the elements of fracture fixation,

Churchilllivingstone.1997,Page 81.


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LEGENDS

Fig.1) Bone plates showing varying central clear spaces. Note the second

and the bottom plates do not have central clear space.

Fig.2) Varieties of cortical screw heads.

Fig.3) Right angled and v type flutes of the cortical screws.

Fig.4) V, Asymmetrical and Buttress threads of cancellous screws.

Fig.5) Unmatched various square and round washers.

Fig.6) DHS screw with variable length tube plates showing variable

telescopy.

Fig.7) Interlocking nails showing varying slots & flutes.

Fig.8) A.M. Prosthesis showing cantilever effect due to tail in an eccentric

location.

Fig.9) ConceptofSquare Nail for Ulna & Radius to give rotational stability

shown diagrammatically.

Fig.10) Blount staple measurementsas shown inBIS standard & actual

measurement of the staples showing discrepancy.

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