ELECTRIC STIMULATION

Dr. V. Giridhar Boyapati

USES

Treatment of Non union

Pseudoarthrosis

Failed fusion

Enhancement of fresh fracture healing

Treatment of AVN

Loosened prosthesis

ELECTRIC STIMULATION

Results in a series of biochemical events:

changes in the ion binding at membranes

changes in enzymatic activity ( c AMP)

Modification in mitochondrial activity

Alteration in macromolecular synthesis like collagen,RNA,

proteoglycans

Mechanical stressed bone generates an electric potential.

Areas of compression > Electronegative

Areas of tension > Electropositive

These stress generated potentials are due to :

1. Piezoelectric property

2. streaming potentials

CHEMICAL

MECHANICAL

THERMAL STIMULUS > Electric stimulus

> change in the cellular micro environmental

conditions

> callus formation

ELECTRIC STIMULATION

cathode

Ideal current 0.001-1 micro A / mm2

Ideal voltage 0.1- 10 mV / Cm

Amperage of more than 30 micro amp causes

osteonecrosis

Anode causes local tissue necrosis

ELECTRICALLY INDUCED OSTEOGENESIS

Around the cathode : pO2 is decreased

pH is increased

Produce hydrogen peroxide

• Bone grows best at hypoxic environment

• Active areas of bone growth and repair are electronegative

• Electric stimulation > stimulate Adenyl cyclase a hormone

receptor with in the membrane > cyclic AMP levels raise >

• stimulate DNA synthesis and cell division,

• tissue and cell proliferation,

• increased collagen synthesis,

• increase mineralisation,

• interfere with PTH activation,

• altered prostaglandin synthesis.

• specific changes in genetic transcription

BIOLOGICAL RESPONSE

Augmentation of normal reparative process in bone.

Endochondral or / and Inramembranous bone is formed.

Electrically stimulated bone is indistinguishable from that formed

by trauma and mechanical stimulation.

Fresh fractures, ostetomies or cortical defects show early

enhancement of bone, osteoid, and mechanical strength.

Most successful osteogenic model is with Intramedullary implant

model with proximate electrodes.

MODE OF ACTION

DIRECT INTERACTION OF ELECTRIC CURRENT WITH

CELLS

Electric field may displace membrane bound ions and

influence ionic fluxes with in the cell

calcium ion influx changes

calcium release from intracellular stores

Electrochemical relaxation of cell membrane

INDIRECT INTERACTION MECHANISM

Faradic electrochemical reaction near the electrode

Decrease local oxygen concentration

change in pH

CELLULAR RESPONSE MECHANISM

Mechanical interaction with peptide hormones like PTH;

it changes calcium fluxes, release adenyl cyclase and

phosphodiesterase > cyclic AMP > DNA and protein

synthesis.

Mechanical forces alter PGE2 > cyclic AMP

Electric fields effect adenyl cyclase and PGE2 > cyclic

AMP

Alter response of bone cells to PTH

NON ELECTROMAGNETIC RESPONSE

Electrode can provide a mechanical stimulus arising

from muscle activity and locomotion, producing a

osteogenic response.

Reactivity to implant material produce hypertrophic

osteogenic response.

BIOLOGY OF ELECTRICAL STIMULATION

• Musculoskeletal tissues respond to biophysical stimuli, including

weight-bearing, pulsed ultrasound, and electrical and electromagnetic

fields.

• Physiologically, endogenous electrical potentials and currents are

generated in these tissues when damaged and terminate when healed

• It is thought that these are part of a complex signaling network maintaining

normal bone remodeling and fracture healing.

• This current may provide a biophysical input to connective tissue cells

regarding the mechanical adequacy and needs of the extracellular matrix

(ECM)

• Nonunions,is a continuous lag phase.

• In these cases, devices that produce electric or electromagnetic field

tend to improve and amplify the physiological healing response by

driving electric or electromagnetic currents through damaged tissues.

DEVICES

Several electric stimulatory devices are employed , varying in the number

of coils, the electromagnetic intensity, the pulse frequency, the duration of

electric current administration,and the location of the coils. A device

employing a :

Direct electric current (DC),

Capacitive coupling (CC),

Inductive coupling (IC)

• Irrespective of the stimulant device used, a final common pathway exists

in the molecular cascade of healing stimulation by ES, that is,

1. Increase in the intracellular calcium,

2. Resulting in increased intracellular calmodulin

3. cell proliferation

• Local growth factors like Transforming growth factor (TGF) β1,

causes proliferation and differentiation of osteochondral cells and in the

stimulation of extracellular matrix (ECM) deposition

DIRECT CURRENT

Implantation of one or multiple cathodes into the bone

An anode is typically placed on the skin over the fracture site and a 5 to

100μA current is delivered.

In 1981, Brighton et al. published a case series using direct electrical

stimulation via four cathodes surgically implanted into a fracture

nonunion site for 12 weeks They found that four 20-μA cathodes applied

for 12 weeks produced solid bony union in 76.8% union.

Direct electrical current has also been used to promote healing of

Spinal fusion,

Ankle fusions and

Charcot foot reconstructions.

An electrochemical reaction occurring at the cathode is thought to

result in the osteogenic effects of direct electrical stimulation.

A Faradic reaction at the cathode has been shown to lower oxygen

concentration, increase pH, and produce hydrogen peroxide.

Decrease in oxygen concentration has been found to enhance osteoblastic

activity and decrease osteoclastic activity.

The direct electrical current also results in increased proteoglycan and

collagen synthesis.

Hydrogen peroxide may stimulate macrophages to release vascular

endothelial growth factor (VEGF), an angiogenic factor that is critical

for osteogenesis.

CAPASITATIVE COUPLING

Capacitive coupling is a noninvasive technique that involves placing

two electrodes on the skin overlying the fracture such that the

fracture site lies between the electrodes.

An alternating current is then used to create an electrical field within

the fracture site.

Potentials of 1-10 V at frequencies of 20-200 kHz are applied to the

electrodes, which result in the development of electric fields of 1-

100 mV/cm at the fracture site.

Brighton et al. found that the electrical field strength played a major role in

determining the proliferation of bone cells when exposed to a capacitive

coupling electric field.

Korenstein et al. found that there was a dose-dependent response to

capacitive coupled fields whereby Bone cell proliferation depend on :

1. Electrical field strength

2. Time the bone cells are exposed to the electrical field

Wang et al. found that capacitive coupling up-regulates the mRNA

expression for bone morphogenic proteins (BMPs)2, 3, 4, 5, 6, 7, and 8, as

well as gremlin and noggin.This increase in the production of growth

factors that are important for the proliferation and differentiation of

osteoblastic cells and influences osteogenesis.

Chemical pathway by which capacitive coupling acts on the bone cell to cause

proliferation and osteogenesis is signal transduction results from calcium ion

translocation through voltage-gated calcium channels that leads to

increases in prostaglandin

cytosolic calcium, and

activated calmodulin

INDUCTIVE COUPLING

Inductive coupling relies on the use of a pulsed electromagnetic field

(PEMF) device that is placed on the skin over the fracture site .

The PEMF consists of a wire coil through which a current is passed and a

magnetic field is generated. The magnetic field, in turn, induces an electrical

field within the fracture site.

The size of the electrical field that is induced within the fracture site is

dependent on the magnitude of the magnetic field and the physical

characteristics of the tissues surrounding and within the fracture site.

Induced magnetic fields varying from 0.1 to 20G have been used to produce

electrical fields varying from 1 to 100 mV/cm within bone

INVASIVE WEIGHT BEARING

DIRECT

CURRENT YES PERMITTED

CAPASITATIVE

COUPLINGNO PERMITTED

INDUCTIVE

COUPLINGNO NOT PERMITTED

COMPARING ELECTRICAL STIMULATION

AND BONE GRAFTING

Brighton and et al. have compared CC, DC, and bone grafting in a total of

271 patients. In a multivariate analysis, controlling for several prognostic

variables such as the type of nonunion (atrophic vs. hypertrophic), the

radiologic fracture pattern, and whether the fracture was closed or open, they

found no differences in the probability of healing of the nonunion.

When no such potential risk factors for a non-healed nonunion were present,

the probabilities of a nonunion being healed by 10 months were

99% for CC

96% for DC

99% for bone grafting

PEMS promotes organization and consolidation in delayed union.

PEMF treatment of osteoblasts in the active proliferation stage accelerates

cellular proliferation, enhanced cellular differentiation, and increased bone

tissue-like formation.

PEMF has role in stimulating protein synthesis, which have effect in gene

regulation.Up-regulation of mRNA levels and protein synthesis for growth

factors has also been observed with the application of PEMS. This

enhances cellular repair and synthesis of extracellular proteins, which have

role in differentiation and growth.

Recent series of Simons et al.(2003) and Punt et al.(2008)

Daily duration of therapy 12 hrs / day schedule to be effective and compliant for

patients as well.

In their series, >90% success was achieved.

Infection has no detrimental effect on fracture healing but gap between fracture

ends and distance between coils are important factors.

Distance between coils has worked by producing coil effects across fracture

ends. They work by generation of electromagnetic field leading to stimulation of

osteosynthesis.

Best nonunion to be treated by this method is one without any other complication

such as infection.

Compound fractures in need of dressing with gap or loss of bony fragment will

be difficult to be managed by this modality.

CONTRAINDICATIONS

Segmental bone loss at the fracture site

Synovial pseudoarthrosis

Infected nonunions

Poor mechanical stability of the fracture site.

In these clinical scenarios, surgical management to bone graft defects,

eradicate infection, or stabilize the fracture with internal fixation is

required before electrical stimulation can be considered.

Electrical stimulation should be thought of as an adjunct to, not a

replacement for, standard fracture care.

Current evidence from randomized trials is insufficient to conclude a benefit

of electromagnetic stimulation in improving the rate of union in patients with a

fresh fracture, osteotomy, delayed union, or nonunion.

Current evidence is insufficient to conclude a benefit of electromagnetic

stimulation on time to healing in tibial stress fractures.

Current evidence is insufficient to attribute a reduction in pain to

electromagnetic stimulation in patients with a fracture or osteotomy;

Electromagnetic stimulation results in short but not long-term (i.e., four

weeks or more) increases in scintimetric healing activity with no impact on

fracture redisplacement rates in non operatively treated

Bone density is improved in patients undergoing femoral intertrochanteric

osteotomy

Monitoring Electric property of bone is useful for diagnosing

delayed and early non-union of bones and may enable the clinician

to change the line of treatment.

Electric properties like :

Impedence

Mutual Inductance

Resonant frequency

Conductance

• Patients with abnormal healing due to various complications impedance

at the time of fracture union was lower than that at the first week.

• The impedance showed significant difference at week 1, 4 and 6.

• Conductance can be a marker of fracture healing at week 8. There is no

significant difference between the values of conductance at week 4 and 6

• This suggests that inductance and conductance can be used for the early

diagnosis of delayed unions.

SCAPHOID FRACTUREAND

NONUNION

Treatment of scaphoid non-union presently includes ongoing

immobilization, bone grafting, various internal fixators, and combinations of

these. Ultimately it may become necessary to insert a prosthetic scaphoid.

The use of pulsing electromagnetic fields and capacitively coupled

electric fields, both of which methods claim a high rate of success.

One Study has suggested that the combined use of a bone graft plus

electrical stimulation has a higher rate of success than either method

alone.

Osterman et al, state in their review article of scaphoid non-union that

the most appropriate indication for the use of electrical stimulation is in

those patients who have failed the previous bone grafting and in

whom the scaphoid has remained relatively aligned.

Frykman and Adams on 44 and 54 scaphoid nonunions, respectively, showed

that 69%to 80% of un-united fractures that presented more than six months

after injury, healed using PEMF stimulation and a thumb spica cast.

Patients were treated for at least three months or until the fracture had united.

Nonunions with radiological evidence of avascular necrosis 73% to 89%

Acute scaphoid fractures by up to 30%.

The healing of tibial and radial fractures was found to be significantly

accelerated in two prospective, randomised, double-blind trials as an adjunct to

conventional treatment.

IMPACTED HIP FRACTURES

72 yr female IT #, Fixation was done. Later she developed

septicemia and hip abcess. Implant removed. X-rays

showing non union of impacted fracture. Electrical

stimulation using a capacitively coupledsystem. Over the six

month course of treatment, she was able to walk without

support.

FRACTURE TREATMENT

PAINFUL HIP PROSTHESIS

In 1985 Ascherl reported clinical evidence of tightening in loosened hip

prostheses using pulsed electromagnetic fields. Using a clinical scoring

system, he reported a success rate of 69.5% in 348 loosened

arthroplasties.

In a similar study in 1988, Kennedy reported a 55% success rate

Brighton and Pollack demonstrated that capacitively coupled electrical fields

were as effective as inductively induced fields in the treatment of non-unions in

long bones in humans.

80 yr female with parkinson disease, operated with AMP. 5 months later disability and pain.

Arthrograms revealed dye between the upper three centimeters of the femoral component

and the femur on the lateral aspect. Cultures taken at the time of the arthrogram were

sterile.

6 months electric stimulation. Repeat Arthrogram revealed no migration of the dye beyond

the joint space.

Fifteen patients with painful hip prostheses were exposed to pulsed electric

fields for eight hours per day over a period of six to twelve months and

followed with a clinical scoring system for four years.

In twelve of the fifteen there was clinical improvement as measured by a

modified Harris Hip score.

Three of the twelve went on to revision surgery because of insufficient relief

of pain and the remaining nine avoided further surgery

Overall success rate of 60% at four years.

OSTEOPOROSIS

Use of pulsed electromagnetic fields, induced at a

physiological frequency and intensity, to prevent

osteoporosis.

Using treatment regimen of 1 hr per day of pulsed

electromagnetic fields, produced an osteogenic dose

response to induced electric power, with maximum

osteogenic effect between 0.01 to 0.04 tesla per sec.

Response showed decrease of intracortical remodeling,

inhibition of endosteal resorption and stimulation of both

endosteal and periosteal new bone formation.

OSTEOARTHRITIS

Positive results in terms of pain reduction and bone healing by the

application of pulsed electromagnetic fields to damaged or painful tissues

and osteoarthritic joints, regardless of method of stimulation.

Potential for favorable restorative transcriptional and biochemical effects of

applied fields on the cells of bone and cartilage and their surrounding tissue

structures.

1. In contrast to other physiotherapy modalities which may invoke

hyperthermia and proteolytic enzyme activity which increases cartilage

destruction, and potentially induces swelling, pulsed electromagnetic field

applications may be applied athermally

2. Application enhance chondrocyte activation in such a way so as to promote

proteoglycan and collagen synthesis.

3. Application could help with repair of bone damage, which may be causing or

perpetuating the disease to some extent.

4. Unlike drugs, pulsed electro-magnetic field effects may be prolonged, as well

as efficacious. Konrad et al (1996) , reported that the benefits of applying pulsed

electromagnetic field therapy for aseptic loosening of total hip prostheses were

still noticeable one year after completion of treatment

5. Unlike drugs, no side-effects of pulsed electromagnetic fields have been

reported in the literature.

6. Anti-inflammatory and pain reducing properties might prove equally valuable

in preserving joint integrity.

ARTHRODESIS

HIGH RISK

INDIVIDUALS

Standard arthrodesis

protocol of bone

grafting and internal

fixation is

supplemented with

implantable electric

stimulator.

SPINAL FUSION

Dwyer et al. were the first to show that adjunctive electrical stimulation

improved the fusion rate of a diagnostically varied group of patients

undergoing both anterior and posterior spinal fusion.

DEVISES :

Direct current

Capacitive coupling

Inductive coupling

Indicated in ‘Difficult to Fuse’ spine fusion population consisting of:

• One or more previous fusion attempts;

• Multi level procedures;

• Grade II or worse spondylolisthesis

• Risk factors, consisting of obese patients, smokers, diabetics

Randomized study compared 28 patients undergoing posterior spinal fusion

without stimulation and 31 patients with DCES. The stimulated group was

found to have a successful fusion rate of 81% compared with 54% in the

non-stimulated group.

Failure rates of lumbar fusion is about 20-40%.

IMPLANTABLE SPINAL FUSION STIMULATOR

SPF battery provides a

constant current for a

minimum of 6 months.

Safe with MRI of 1.5 tesla

or less

AVASCULAR NECROSIS

Electrical stimulation has been shown experimentally to

enhance osteogenesis and neovascularization as well as to

alter osseus turnover.

Three different methods can be described:

1. Non-invasive pulsed electromagnetic-field stimulation

2. Direct-current stimulation of the necrotic area through

insertion of an electrode at the time of a core decompression

3. Non-invasive direct-current stimulation by capacitive

coupling after a core decompression

Stimulation with pulsed electromagnetic fields (PEMFs) has

been shown to be useful for enhancing bone repair and for

exerting a chondro protective effect on articular cartilage.

Electric stimulation was performed in combination with core

decompression (CD); although the results obtained were good, it

was not possible to demonstrate any statistically significant

advantage of the combined treatment as against treatment with

CD alone.

Results of the studies suggest that an early instrumental

diagnosis at the onset of the disorder and the immediate use of

PEMFs enables better clinical results.

Lesions in early stage respond well to treatment with PEMFs

and, in the majority of cases, as far as Ficat II, are capable of

preventing the progression of the disease.

Ficat stage -III does not constitute a real indication for this treatment.

Idiopathic lesions seem more sensitive to PEMF therapy as compared

with secondary forms, because the therapies responsible of the disease

cannot be interrupted.

Initial stages of the AVN are dominated by the ischemic and

inflammatory component; which is responsible for the joint pain, edema,

and degradation of the cartilage.

PMEF produces pain relief mediated by the anti inflammatory action of

the PEMFs that enables resolution of the joint edema.

Strong anti inflammatory effects of PEMFs causes an increase of adenylyl

cyclase activity and a reduction of superoxide anion production, as a result

of receptors located on the neutrophil surface.

This anti inflammatory action has been demonstrated on the sinoviocytes

and chondrocytes.The binding plays a fundamental role on the

inflammatory response and promotes new vessel formation and limits the

extension of the necrotic area, resulting from ischemia.

PEMFs exert a chondroprotective effect in vivo on osteoarthritis,which may

play a fundamental role in the treatment of early stages of osteonecrosis of

the femoral head by limiting the damage induced by inflammation and

preserving cartilage and subchondral bone exerting a short term effects.

PEMF has effects firstly on angiogenesis and then on osteogenesis.

In association with core decompression, biophysical stimulation enhances the osteo-

integration of autologous bone grafts, stimulates the local production of growth

factors, and favors the osteogenic activity of osteoblasts reducing the bone

reabsorption by interfering with the activation of the parathyroid hormone receptor,

thus decreasing the recruitment and differentiation of osteoclasts.

Stimulation with PEMFs may be a good opportunity to resolve the disease or at

least to delay the time until joint replacement becomes necessary.

Alternating electromagnetic field using a screw implant to the

weak bone in the femoral head is to speed up bone regeneration

in case of avascular necrosis of the femoral head.

A BISS (bipolar induction screw system), as the depicted ASNIS

screw with integrated coil and electrodes is used.

ASNIS screw is only suitable for the case where the femoral

head show sclerosis and no collapse on cancellous bone . This

means, as long as the cartilage of the femoral head is not

damaged, the electro-stimulation therapy with the ASNIS-s

screw can be applied.

When the cartilage is ruptured and the femoral head shows

flattening, other therapies such as a total hip replacement have

to be considered.

GALVANIC CORROSION OR

BATTERY EFFECT

Some implant systems use several metals for different components. For example, Co-Cr rods may attach to titanium alloy screw heads, or Co-Cr rods and screw heads may attach to titanium alloy screw shanks.

This matching of dissimilar metals raises the concern of galvanic (bimetal) corrosion, also known as the battery effect.

An electrochemical effect occurs when two dissimilar metals, also known as a “couple,” are placed in an ionic bath.

An electric potential is created and ions flow from the anode metal, which is more resistant to corrosion and oxidation to the cathode metal.

Less resistant metal will undergo greater corrosion.

The strength of the effect is proportional to the difference in the electrochemical properties of the metals, called the “anodic index,” and can be measured by the electromotive force.

Galvanic corrosion can lead to

pain,

inflammatory responses,

metallosis, and

device failure.

For this reason, bimetallic systems designed to be used in corrosive environments should have an anodic index of 0.15 or less.

For galvanic corrosion to occur, the following three conditions must be met:

dissimilar metals,

electrical contact, and

a path for ion exchange.

All three conditions are present when medical devices are placed in the body.

Galvanic corrosion may be minimized by lessening the impact of

environmental factors through a process called Passivation. During this process, the surface of the implant is coated with a shielding layer, usually by formation of oxides, which will resist ion exchange.