Distraction

GOOD MORNING

DISTRACTION OSTEOGENESIS

PRESENTED BY DR RISSHI BHATT

GUIDED BY PROF.HOD.DR.S.M.AGRAWAL

CONTENT INTRODUCTION HISTORY BIOMECHANICAL PARAMETER BIOLOGIC PARAMETER CLASSIFICATION SEQUENTIAL PERIOD OF DO STAGES OF # HEALING EFFECT OF DO ON SKELETAL MUSCLE EFFECT OF DO ON PERIPHERAL NERVE EFFECT OF DO ON TMJ DISTRACTION DEVICES INDICATION & CONTRAINDICATION

TREATMENT PLANNING COMPLICATION CONCLUSION REFRENCES

INTRODUCTION

Samchukov et al., 1998 described

Distraction osteogenesis as a biologic process of new bone formation between the surfaces of bone segments that are gradually separated by incremental traction

The traction generates tension that stimulates new bone formation parallel to the vector of distraction

HISTORY AND EVOLUTION

DO evolved from three procedures

skeletal traction

bone segment fixation

osteotomy tech.

First described by CODIVILLA in 1905 on femur

GAVRIL ILIZAROV (1951)

Ilizarov effects :

1. tension stress effect

2. influence of blood supply

ILIZAROV’S EXPERIMENTS

Stable fixation with preserved axial micromotion generates membranous bone formation.

Preservation of osteogenic tissue during osteotomy.

Bone regenerates within the distraction gap is always formed along the vector of applied traction.

Bone formation depends on both rate and rhythm

0.5mm/day : premature consolidation

1.5mm/day : local ischemia

Blood supply must be proportional to mechanical loading.

Mc Carthy & colleagues were the first to clinically apply extra oral distraction osteogenesis on four children with congenital abnormalities.

Latency period – 7 days

Distraction – 1mm/day in two increments

Consolidation – 10 weeks

Guerrero (1990) devolped his mid symphyseal mandibular widening technique.

Molina & Ortiz simplified the method of Mc Carthy

- corticotomy with medial cortex intact

- one pin fixation on either side

BIOMECHENICAL PARAMETERS

1. Extrinsic

2. Intrinsic

3. Device orientation

4. Vector orientation

BIOLOGICAL PARAMETERS

1. Osteotomy

2. Latency period

3. Fixation

4. Direction of distraction

5. Rate and rhythm

6. Consolidation

7. Proportional relationship between loading

and newly formed bone

DISTRACTION DEVICE CLASSIFICATION

Craniofacial Distraction Devices

External Internal

Bone borne

Subcutaneous

Intraoral

1. Bone borne

2. Tooth borne

1. Unidirectional

2. Bidirectional

3. Multidirectional

Distraction device classification

Unidirectional device

Bidirectional device

Multidirectional device

Intra oral device

Sequential periods of DO:

1. osteotomy

2. latency

3. distraction

4. consolidation

5. remodeling

Bone physiology

Process of bone formation is called osseogenesis

Intramembranous

Endochondral

6 steps of # healing:

- impact

- induction

- inflammation

- soft callus

- hard callus

- remodeling

HOW DISTRACTON OSTEOGENESIS WORKS

The bone is a viscoelastic material, which means

that it has viscous as well as elastic properties,.  A

series of mechanical tests have revealed its

Young’s Modulus. Which is pertinent information

for the design of the distraction device. Young’s

modulus of bone has been found to be 19.4 GPa

longitudinally and 15.0 GPa transversely.

    Young’s Modulus for collagen is found to be

approximately 1000 MPa, and after about 3-4 %

strain, the collagen no longer acts elastically; it

only deforms plastically. Because the strain

acting on the soft tissue in the distraction gap,

during distraction osteogenesis, is much greater

than this value. The collagen will plastically

deform at the projected value of approximately 1

mm per day. 

Foundation: Distraction Regenerate” http://www.globalmednet.com/do-cdrom/Biol/Histomor/rh07.htm

Strain

- physiologic - 2000-3500

- hyper physiologic - > 10,000

Woven lamellar bone - 2000 microstrains

Trabecular pattern - 20,000 microstrains

Fibrous - 200,000 microstrains

Multiple increments - higher extent of bone formation

> 20,000 - chondroid formation

-Ulrich Mayer et al

STRAIN - stimulatory effects

increased callus formation

increased osteoblast proliferation

20,000 microstrains with 10 cycles/day – fast results

AUTOMATED DISTRACTORS

-Ulrich Mayer et al

OSTEOTOMY

Division of bone in two segments

Triggers bone healing ( # healing )

- recruitment of osteoprogenitor cells

- osteoinduction

- osteoconduction

LATENCY PERIOD

Period from bone division to onset of tractionRepresents time allowed for callus formation

Sequence of events

-Hematoma

-Clot -Bone necrosis at the ends of # segments

Ingrowths of vasoformative elements & cellular proliferation

Stage of inflammation ( 1-3 days )

clot is replaced by granulation tissue

5 th day minicellular network of growing

capillaries is formed In medullary canals of both

# segments.

granulation tissue is converted to fibrous tissue

Cartilage also replaces the granulation tissue – more

towards periphery

Inflammation leads to soft callus stage

-callus formation is the response of determined

osteoprogenitor cells originating in periosteum and

endosteum

- it depends on many factors like:

cytokines and growth factors

- role of callus formation

Enlarges the diameter of segments

Serves as solid base for new bone formation

DISTRACTION PERIOD

Application of traction forces to osteotomised bone

segments.

Bone segments are gradually pulled apart resulting in

formation of new bone tissue with in progressively

increasing inter segmentary gap.

Normal # healing:

-fibrocartilagenous tissue of

soft callus is replaced by

osteoblasts into hard

callus.

- stage hard callus lasts for

3-4 months followed by

remodeling.

Distraction :

-normal process of healing

is interrupted by

application of gradual

traction which leads to

microenvironment.

- changes at cellular and

sub cellular level

- growth stimulating effect

- shape forming effect

Growth stimulating effect:

- prolongation of angiogenesis

- increased fibroblast proliferation

Shape forming effect:

- causes altered phenotypic expression of fibroblasts

( distraction fibroblast )

- polarization of these distraction fibroblasts parallel to

vector of distraction.

- soft callus becomes longitudinally oriented along the axis

of distraction

Between 3-7 day of distraction capillaries grow into

fibrous tissue

During the 2nd week of distraction primary

treabeculae begins to form

Osteogenesis is started at existing bone wall and

progress towards the center of distraction gap.

By the end of 2nd week osteoid begins to mineralize

CONSOLIDATION PERIOD

Time between cessation of traction and removal

of distraction devices.

This period represents the time required for

complete mineralization

Distraction regenerate forms predominantly via

membranous ossification.

REMODELING PERIOD

Period from the application of full functional

loading to the complete remodeling of

newly formed bone.

Last stage of cortical reconstruction normalizes

the bony structure ( 1 year )

EFFECT OF DISTRACTION ON SKELETAL MUSCLES

Muscle orient in a plane parallel to distraction force & adapt with compensatory regeneration.

( Guerrirre & co workers )

Sarcomere is the smallest unit of muscle contraction.

Force devolped by muscle during isometric

contraction is dependent on sarcomere length.

During distraction fibers of the attached muscles

undergo incremental gradual stretching of muscle

fibers which in turn stretches the sarcomeres

increasing their length.

Diminishes the number of

connecting bridges between

actin and myosin,

compromising muscle

function.

To preserve muscle function

sarcomeres must return to

optimal range.

Slower rate leads to good muscle adaptation but early consolidation.

Maintain the balance.(.75mm – 1mm per day)

More fractioned rhythm leads to less muscle injury

Mizumoto & coworkers

Amount of distraction:

10%-12% - no damage (only stretching)10%-20% - muscle growth>20% - irreversible muscle damage

20% - critical point

Nerve supply

Blood supply

EFFECT OF DISTRACTION ON PERIPHERAL NERVES

Distraction osteogenesis may result in

serious complications including peripheral

nerve injury.

Inferior alveolar nerve injury

direct

- intraoperative manipulation

- contact with fixation devices

indirect

- compression by postoperative odema

- constriction of medullary canal

Adaptation of peripheral nerves to distraction

peripheral nerve trunks are highly resistant to stretching

15% lengthening - early degenerative changes of myelinated nerves, swelling of schwan cells

20% lenthening - similar changes in non

myelinated nerves

20% -50% lengthening – wallerian degeneration

Regeneration of nerve fiber during consolidation

No acute injury with 10 mm distraction

Mild IAN changes in 10-15 % nerve fibers

- samchukov et al

TMJ ALTERATIONS DURING DISTRACTION

Different biological responses:

Compression – permanent degenerative changes

Adaptive joint remodeling

Functional adaptation to the changing environment

Distraction devices

Extra oral devices

Unidirectional devices: mandibular lengthening was possible in one direction only distraction was determined by the angle between Frankfurt horizontal plane and distraction device cannot be adjusted after insertion

Bidirectional devices

allows distraction in two directions as well

as adjustment of angle between two arms of the device.

single or double level osteotomy is possible.

Multidirectional devices

essential component of these devices are angulation joints and two geared rods of variable lengths.

in bidirectional devices the middle joint is simple hinge whereas in multidirectional devices it is multifunctional double ball joint.

device can be adapted according to individual anatomic situations.

Semi-rigid extra oral distraction devices

Intra oral distraction

In 1996 Chin and Toth described the feasibility and potential advantages of using intra oral devices for distraction osteogenesis.

Intraoral distraction devices

MD – DOS Device ROD custom distractor device Buried bidirectional telescopic mandibular

distractor Multiaxis intra oral distractor New spiral distractor Distractor with micro hydraulic cylinder

MD – DOS DEVICE - Morrice Mommarts

Started clinical application of this device in 1997

Consists of four major components

PFU – posterior fixation unit

AFU - anterior fixation unit

Spacer

DU - distractor unit

Posterior end of PFU is fixed in ascending ramus.

Depth of PFU penetration is controlled by PFU

screw length and bar spacer.

Anterior end of PFU is connected to posterior end of DU by hinge which allows DU to rotate along vertical axis.

Anterior end of DU is connected to AFU which is basically a modified five hole plate.

ROD intra oral custom distractor device

programmed along a desired vector.

there are five categories of ROD devices.

with ROD device it is possible to distract first and than decompensate the teeth.

Device fabrication

Distractor device consists of three components

Anterior activated expander , male and female attachments.

Male attachment is soldered to the crowns.

Male attachment also have vertical slots for wire fixation.

Female part is soldered to expansion screw

The intra oral attachment allows prefabrication of

device presurgically and cementation of

distractor device prior to osteotomy with removal

of distractor screws with the female part.

The vector planning ROD lab. alignment tool was devolved to properly position the distractor bilat.

Buried Bidirectional Telescopic Mandibular Distractor

Most of the current intra oral devices are

unidirectional with limited possibilities of

intraoperative adjustments.

BTMD has mediolateral offset with an adjustable screw allowing intraoperative adjustment of distractor vector and postop correction of midline occlusal discrepancies.

BTMD is stainless steel device that can be attached to mandible with upto 1.9 to 2.3 mm monocortical or bicortical screws

Activation is done by transmucosal approach.

BTMD has also shown its use in mandibular defect reconstruction.

Multiaxial intra oral distractor

Distractor that allows distraction in more than one direction

Requirement of such distractor are:

- should provide independent horizontal and

vertical distraction

-allows gradual changes between horizontal and

vertical axis

Basic unit of such distractor:

angulation gear – allows angulation change of 15’ vertical distractor is attached to posterior fixation

plate by a clamp horizontal distractor is attached to anterior fixation

plate

Spiral Distractor

Several authors suggest that mandible grows in archival fashion which has been hypothesized to be along logarithmic spiral.

Based on this information semi buried distractor with curvilinear vector was devolved.

By placing the osteotomy and device at mandibular ramus the archival path of distraction would mimic the logarithmic spiral of mandibular growth.

Curvilinear vector is chosen by VTO

Distractor with Micro Hydraulic Cylinder

Device is based on the concept of hydraulic pump.

it consists of two major parts

- cylinder

- piston

Both piston and cylinder have integrated fixation plates with two holes for bone fixation using conventional 3.5 mm bicortical screws

Depending on situation both incremental and continuous distraction can be applied

Indications of Distraction Osteogenesis

Children or infants with severe retrognathia associated with a syndrome (Pierre Robin syndrome, Treacher Collins syndrome) Unilateral hypoplasia of the mandible (Hemifacial microsomia)

Mandibular hypoplasia due to trauma and/or ankylosis of the temporomandibular joint

Nonsyndromic mandibular hypoplasia associated with a dental malocclusion where movement of mandible required is >10mm

Mandibular transverse deficiency associated with a dental malocclusion and dental crowding

Severe obstructive sleep apnea in patients who are morbidly obese

Shortened vertical height of the alveolar bone to receive an implant

Contraindications of Distraction Osteogenesis

Patients who are unable or unwilling to comply with the distraction schedule

Infants < 6 months of age due to fragility of bones to place distraction devices

Inadequate bone surface to accept distraction device

Inadequate bone surface area to provide regeneration of bone

Caution must be exercised in patients who have undergone radiation therapy. This is because of delayed bone formation due to reduced number of stem cells

Caution must be exercised in elderly patients because of the decreased number of mesenchymal stem cells

Treatment planning

History Records Patient expectations Distraction device selection Predistraction, intradistraction and

postdistraction treatment objectives Determination of vector Distraction protocol

Distraction device selection

External Internal

External devicesAdvantages : multidirectional excellent control of bone segment available in longer lengths easier to place and maintain simple to remove

Disadvantages :

skin scarring

poor patient compliance

Intaoral devices

Advantages :

no scarring

better patient compliance

Disadvantages :

difficult to place risk of injuries to nerves, vessels and tooth

buds second surgical procedure is required for

removal

Lack of availability of multidirectional devices

Factors for device selection

• desired lengthening• desired angular correction• vector• psychological requirements of patients

Lengthening capabilities

Lengthening capabilities

To achieve desired amount of lengthening and angular correction appropriate length of distractor must be selected.

Ratio of amount of device activation and observed amount of distraction can go as high as 2:1

Incorporation of angular correction further decreases total amount of linear distraction

Direction of distraction

Based on type of deformity and main goal of positional changes.

If only ramus or body lengthening is required unidirectional distractor would be utilized.

If simultaneous ramus and body lengthening is required, distractor may be placed according to the following formula:

Pin placement angle = 180 – gonial angle x ramus def / total def Pin placement angle = angle between vector of distraction and mandibular plane

Amount of Distraction:

The amount of distraction can be determined by simply drawing a triangle two sides of which represents the amount of mandibular corpus and ramus shortening respectively.

The angle between these two sides is the gonial angle and third side indicates amount of distraction. This can be calculated by using the formula:

Distraction amount = Dc + Dr – 2 (Dc x Dr) x Cos aDc = Corpus deficiencyDr = Ramus deficiencyA = Gonial angle

Amount of distraction

In case of simultaneous maxillary defficiency amount of maxillary correction is also included in calculation.

If deformity correction requires mandibular lengthening in combination with gonial angle change or transverse change, multidirectional distractor is required.

Bone ends should be separated by 10 mm before starting angular correction.

Double level osteotomy can be performed in difficult cases.

Orthodontics

Predistraction orthodontics

Intradistraction orthodontics

Postdistracrtion orthodontics

The distraction vector defines the desired direction that the distal segment must move during lengthening.

VECTOR PLANNING

Despite precise planning the actual distal segment movement is difficult to predict and is affected by various forces:

osteotomy design

osteotomy location

distracton device orientation

masticatory muscle influence

occlusal interferences

distraction device adjustment

orthodontically applied forces

Distraction device orientation

Device should be placed parallel to vector

vertically

horizontally

obliquely

Biomechanical effects of distraction device orientation

Mandible is V shaped when viewed in transverse plane, anatomic axis of right and left sides of mandible are not parallel to each other or to desired direction of distraction.

When viewed in sagittal plane, the inferior border of mandible is often not parallel to maxillary occlusal plane which is primary plane of reference for ant. mandibular distraction.

If distraction was placed parallel to the inferior border of the mandible, elongation occurred horizontally with opening or obliteration of gonial angle.

If distraction was placed obliquely to both ramus and body, neomandible maintained original form with preservation of gonial angle.

Laskin suggests planning distractor placement

preoperatively to achieve desired results.

Distractors placed parallel to the mandible with out regard to desired direction of distraction create reactive forces leading to following clinical problems:

bending of distractor device loosening of fixation screws

bone resorption

joint compression

The magnitude of lateral displacement tendency is proportional to amount of mandibular lengthening and mandibular arch angle.

Placement of distractor parallel to direction of distraction eliminates the tendency of lateral displacement of proximal segment.

If the distraction cannot be placed parallel to direction of distraction and lateral displacement tendency cannot be corrected they should be compensated either by acute correction or gradually incorporating a hinge element to lengthening device.

The vertical relationship between the distal mandibular segment and maxilla during distraction is another important consideration.

An increase in lower anterior facial height occurs when the vector of distraction is oriented parallel to mandibular plane instead to the maxillary ccclusal plane.

Vertical increase in lower anterior facial height may manifest as development of anterior /posterior open bite.

The amount of open bite is proportional to the amount of distraction.

Increase in angle between occlusal plane and vector = increased vertical deviation from desired ( open bite )

To prevent the development of open bite distractor should be placed as possible to desired direction of distraction, usually maxillary occlusal plane.

But open bite can still develop due to extrinsic and intrinsic factors.

Extrinsic factors: rigidity of distractor stability of screws

Intrinsic factors: soft tissue tension bone quality anatomy of mandible

Influence of masticatory muscles

Soft tissue traction due to physiologic muscle activation may contribute to distal segment instability.

Occlusal interferences

Should be corrected orthodontically

Distraction device activation

Depends on dimensional capability of device

Future growth and overcorrection

Skeletal age and future growth potential must be considered for distraction planning

The amount of distraction required is based on

careful assessment of mandible followed by compensation by growth standards or norms for particular race, sex, and facial skeleton maturity.

Surgical Therapy…..

• The orthodontist and the surgeon must have open communication throughout the entire planning process

• They must share the same treatment objectives

• Osteotomy cutShould be decided before hand with the help of imaging studies

• Osteotomy cut. Where do you place it? …

If the mandible is … Osteotomy cut Distrator plane

Deficient in ramus height

Superior to angle of mandible on ramus

Vertical plane

Deficient in body length Anterior to angle of mandible

Horizontal plane

Combination of both? Anterior and/or superior to angle of mandible?

Oblique plane??

Preoperative work up…..

Osteotomy / Corticotomty

Osteotomy: Division of bone in two segments

Corticotomy: Cancellous bone is kept intact

or

Subtotal / incomplete osteotomy

corticotomy

circumferential

external

External extended

Depending on number

Single Double

Depending on type of correction

Lengthening Widening Alveolar

Ramus

Angle

Corpus

interdental Post.to teeth

Midline

B/W lateral and canine

Horizontal

segmental

corticotomy

osteotomy

Distraction

Before device placement

After device placement

To start with

Distraction protocol

External extended

Preserves vascularity and tooth buds

Cancellous bone is spared

6-8 mm of inner cortical bone remains intact

Ramus osteotomy

Vertical, downward and inward ramus distraction

Required in hemifacial microsomia and other syndrome cases

Angular osteotomy

Downward and forward lengthening

Osteotomy is prepared from distal of 2nd molar down to inferior border of mandible.

10 – 12 mm of lingual cortex is cut with bur protecting the 3rd molar

Ridge corticotomy is done in oblique and anterior direction and than sharply turned posterior to angle of mandible.

Device is placed, marked and removed.

Osteotomy is completed with spreader

Device is placed

Closure is done

Corpus osteotomy

Horizontal and forward lengthening

Inferior border channel retractor is placed between 2nd and 3rd molar.

Mandible is than transected through both buccal and lingual cortex at inferior border, vertically upto 3mm of inferior alveolar canal

Outer cortex is than sectioned

Protecting the lingual periosteum saw is placed upside down and osteotomy is carried through alveolar crest, sup. Inf. to 3mm superior to canal.

6 mm medial bone is kept intact

Device is placed

Closure is done with small aperture at the top of incision to facilitate vertically placed chisel , which is placed to give final cut followed by complete closure

Mandibular widening

Complete osteotomy is done midline between central incisors below the roots of incisors.

Alveolar bone is than sectioned with bur taking care of teeth and gingiva

If teeth are very close the alveolar bone and gingiva,lingual cortex is green fractured with expansion forceps device.

Postoperative details

What should the surgeon watch for after the placement of distractor ?

During the distraction phase, the patient should be seen every 2-3 days to monitor the advancement and to intercept any potential occlusal discrepancies

During the consolidation phase, the patient should be seen on a weekly basis to monitor healing and ossification of the regenerate

In bilateral expansion of the mandible, the

patient should be distracted until a slight class

III dental occlusion exists (edge-edge incisal

relationship)

In a unilateral expansion, a slight over

correction of the mandibular midline is

recommended to overcome the deficient soft

tissue envelope

COMPLICATIONS

A complication is an unexpected deviation from the treatment plan that, with out appropriate correction will lead to worsening of existing, development of a new, or recurrence of the initial pathologic process

Mistake

Mistake is an inattentive action that results in a deviation of the course of treatment, thereby leading to the development of a complication

Potential mistakes

Iatrogenic

Patient related

Potential complications

Axial deviation

Axial deviation of distracted segment can result from various mistakes.

-inappropriate size and strength of device -inadequate osteotomy level -inadequate device orientation -inadequate hinge placement -inaccurate placement of device -comminuted osteotomy

Correction of axial deviation begins with elimination of main cause of this deviation.

-replacement of distracter device

-repositioning hinge axis

-reorientation

-additional surgery

Soft tissue overstretching

Blood vessels

rare

least tolerant to compressive forces

lead to ischemia

Adjacent joints

degenerative changes

Skin

scaring and necrosis

Infection

incidence is 5-30%, more with extra oral devices

Distraction vs OsteotomyDistraction Osteotomy

Need for bone grafting Not necessary even for defects > 20 mm

Necessary for defects >10 mm

Control over movement 3 Dimensional 2 Dimensional

On infants and children Can be done Think about perma-nent teeth and suffi-ciency of bone

Distortion and loading of the TMJ

Does not cause Risk of causing

Damage to the inferior alveolar nerve

Does not cause Risk of causing

Increasing ramus height

Possible Not Possible

Cost Expensive (distractors and equipment )

Relatively inexpensive

Time Takes time Quick Fix Method

Distraction vs osteotomiesThe argument contnues….

While traditional mandibular osteotomies, such as the bilateral sagittal split osteotomy, will always have a place, distraction osteogenesis allows a surgeon to treat patients who are unable or unwilling to undergo a traditional osteotomy

Distraction osteogenesis is a highly predictable and reliable method of increasing the bone in a deficient mandible

With technology advancements, the distraction devices become smaller and more sophisticated making distraction movements more precise

One of the current controversies involves using distraction osteogenesis instead of the traditional bilateral sagittal split osteotomy

Some authors have gone so far as to state that the bilateral sagittal split osteotomy is an obsolete procedure with no place in current practice

In reality, traditional mandibular osteotomies will always have a place; however, distraction osteogenesis provides the surgeon with another option in treating a wide variety of mandibular deficiencies

References

1. Craniofacial distraction osteogenesis – Mikhail L. Samchukov, Jason B. Cope, Alexander M. Cherkashin

2. Distraction of the craniofacial skeleton – Joseph G. McCarthy.

3. Oral and maxillofacial surgery – Peter Wardbooth.

4. Oral and maxillofacial surgery – Fonceca.