peripheral nerve compression - neuropathy

Tibialis Posterior Neuropathy

Michael E. Graham, DPM, FACFAS

What is TPN?

• Pathologic condition of the tibialis posterior nerve.

• Wide variety of symptoms.• MUST be differentiated from “peripheral

neuropathy”• Let’s discuss treatment options.

Pathway of plantar foot nerves.

What happens when your big toe touches something, how do you feel it?

Following the chemical reaction from the big toe to your brain and back again in a matter of seconds.

Sensory Nerves in the big toe

However these signals don’t travel superficially but traverse deep into the foot.

Let’s take a closer look.

The medial hallucis

ditial branch is a

terminal extension

form the medial

plantar nerve.

Abductor Hallucis Brevis Muscle

• Could be a big source of trouble if it crushes the plantar nerves.

• Its function is to stabilize the medial column of the foot, i.e. the 1st ray.

• What would happen if this patient had a hypermobile medial column?

The medial along with

lateral plantar

nerves enter in

to the porta

pedis -

tunnel leading to

the tar

sal tunnel.

The porta pedis is a very concerning area.

As the medial and lateral plantar nerves travel towards the spine their path is transformed from horizontal to vertical.

Porta Pedis

• Tunnel is created mostly from fibers attaching the abductor hallucis muscle belly to the calcaneus along with dense connective tissue similar to the flexor retinaculum.

Porta Pedis

Constriction of the Porta Pedis

• Let’s think about what is in the porta pedis-– Medial & Lateral Plantar

nerves– Medial & Lateral Plantar

arteries– Medial & Lateral Plantar

veins

Contents within the porta pedis in a rectus foot.

LN

MA

MVLV

MN

LA

There is plenty of room and every thing is functioning normally.

LN = Lateral Plantar nerveMN = Medial Plantar nerveLV= Lateral Planar VeinMV = Medial Plantar VeinLA = Lateral Plantar ArteryMA = Medial Plantar Artery

What could possible happen to the structures within the porta

pedis if it was constricting with every step taken or constantly

constricted while standing?

Contents within the porta pedis are crushed due to dislocation of the talus on the tarsal mechanism.

LN

MA

MV

LV

MN

LA

Abductor Hallucis Muscle Calcaneus

There is less room and the structures are compressed decreasing blood flow and altering the natural function.

Effects of TaloTarsal Dislocation During the Gait CycleWhat happens to the porta pedis

Porta Pedis during

swing phase or

non-weightbearing

Porta Pedis during mid-stance in a dislocation of

the talotarsal joint/weightbearing

LN

MA

MVLV

MN

LA

LN

MA

MV

LV

MN

LA

Excessive Force

Now we have shown what can happen to the nerve travelling

through the porta pedis.

Let’s take a look at the neurovascular canal within the flexor retinaculum.

Compression of the porta pedis.

• Constricts blood flow to the plantar aspect of the foot.

• This will build up the pressures proximally within the tarsal tunnel.

• This will lead to more destruction proximally.

Rectus Rearfoot AlignmentThese feet will NOT place additional strain on the porta pedis or combined

/ individual chambers within the flexor retinaculum.

What happens if the hindfoot is not properly aligned?

This will place a tremendous amount of destructive forces on the contents of the porta pedis & tarsal tunnels.

Normal Talotarsal Alignment

Articular facets are alignedSinus tarsi is openNormal CymaNormal Talar declination angleNormal navicular height

Normal to abnormal alignmentSinus tarsi partially collapses/obliterates

Talotarsal Dislocation

• The articular facets of the talus are no longer aligned with the articular facets of the calcaneus.

• Incomplete dislocation is present.

• A pathologic event has occurred, this is NOT a self-resolving condition.

• It requires physical intervention.

Obviously it is important that nothing compresses the nerves within the porta pedis or tarsal tunnel.

Nerves exit the porta pedis and quickly

enter the distal aspect of the tarsal tunnel.

Distal Tarsal Tunnel

• As the nerves travel proximally they pass deep to the flexor digitorium longus tendon and enter into the distal aspect of the tarsal tunnel.

Flexor Retinaculum - roof of tarsal tunnel.

• Purpose:• Retinaculum is more for the

tendons than for the nerves.• In a hypermobile hindfoot it will

have a

s t r e t c h placed on it.

This tissues will either thin out OR

react to these abnormal forces by thickening. The thicker the tissues the less likely it is to fail. However, due to the chonicity of walking the tissues cannot prevent the hypermobility.

Flexor Retinaculum/Laciniate Ligament

• Proximal attachment with the deep fascia of lower leg

• Distal attachments are with the plantar fascia and the abductor hallucis muscle

Flexor Retinaculum- 4 canals

• Tibialis Posterior• Flexor Digitorium

Longus• Posterior-

Artery/nerve/vein• Flexor Hallucis Longus

Imagine what is occurring to the flexor retinaculum.

• It is being pulled apart• The distal end is being

pulled by the abductor hallucis muscle and the plantar fascia.

• This causes major constriction and compression of the structures within the flexor retinaculum.

Contents 3rd tunnel in the flexor retinaculum in a rectus foot.

TPA

TPV

TPN

There is plenty of room and every thing is functioning normally.Tib. Post. N

erve

In response a thicker Flexor Retinaculum will occur to try and overcome these stretching forces.

• Well, this will immediately compress the underlying nerves which flattens it.

• Flattening of the nerve not only crushes the nerve fibers it also decreases the blood flow within the nerve.

• Think of standing on a garden hose or repeated stepping on a garden hose say 7,000 a day for 50 years.

• Maybe after doing this for so long there could be damage to the nerve?

Comparison- there is stretched placed on these structures as the talus slips off the tarsal mechanism.

Normal Abnormal

Talotarsal instability is not kind to the structures within the tarsal tunnel.

Contents 3rd tunnel in the flexor retinaculum with talotarsal instability.

MA

MV

PN

There is compression of the neurovascular structures.

During WalkingHowever, as soon as the heel touches the ground the talus

slips off the tarsal mechanism and the excessive abnormal

forces begin to take effect on the structures within the tarsal

tunnels.

With no weight on the foot there are no

abnormal forces acting on the structures within

the tarsal tunnels.

DID YOU KNOW

Active person takes 8,500 steps/day

A 50 year old has taken

152,022,500

steps.

Just think about all that damage being inflicted onto the nerves.

Eventually Damage occurs to the nerve

• The outer most fibers are affect first

• Due to the constricted blood flow within the nerve the outer most is first to loose the blood flow.

• Also the physical trauma to the nerve damages the myelin sheath decreasing nerve impulses.

Nerve Injury cycle.

During the walking cycle the nerve is intermittently compressed.

Nerve Injury cycle.

While standing the nerve is

continuously compressed.

If the chemical signal is able to pass through the porta pedis and the tarsal tunnel it will continue

up the leg

Eventually the nerve signal travels proximally up the leg...

…that if its allowed to pass through the porta pedis and tarsal tunnel.

How can we fix this problem?

• Observation?• Shoes?• Arch supports/Orthotics?• Pills- vitamin supplements, nerve

“desensitizers” (lyrica, cymbalta, gabapentin)• Microvas?• Magnets?• Nerve Testing?

This is an internal problem that demands an internal solution!

• The nerve damage is a secondary condition not primary.

• Diabetes, alcoholism, and chemotherapy are not going to make this condition any better but they can make it worse. Even if controlled there is no evidence of improved/cure nerve disease.

Tarsal Tunnel Pressures- What do we know?

Neutral STJ 2 (0-7) mmHgMaximally pronated 32 (12-60) mmHgPronation = significantly increases pressure within

the tarsal tunnel with every step taken

Kumar et al: Evaluation of Various Fibro-Osseous Tunnel Pressures in Normal Human Subjects. Indian J Physiol Pharmaol, 32:139-145, 1988

Trepman et al.:Effect of Foot & Ankle Position on Tarsal Tunnel Compartment Pressure. Foot Ankle Int. 20:721-726, 1999

Barker et al: Pressures Changes in the Medial & Lateral Plantar and Tarsal Tunnels Related to Ankle Position: A Cadaver Study. Foot Ankle Int 28:250-254, 2007

Rosson et al: Tibial Nerve Decompression in Patients with Tarsal Tunnel Syndrome: Pressures in the Tarsal, Medial Plantar, and Lateral Plantar Tunnels. Plast Reconstr Surg 124:1202-1210, 2009

Increased Tarsal Tunnel Pressures

What do we know?

• A pressure of 20 – 30 mmHg has been shown to impair intraneural blood flow

– Gelberman et al: Tissue Pressure Threshold for Peripheral Nerve Viability. Clin Orthop Relat Res 285-291, 1983

– Rydevik et al: Effects of graded comprssion of intraneural blood flow. An in vivo study on rabbit tibial nerve. J Hand Surg AM 6:3-12, 1981

Nerve Strain/Tension

What do we know?

• Pronation increases the strain/tension on the posterior tibial nerve

– Francis et al: Benign Joint Hypermobility with Neuropathy: Documentation and Mechanism of Tarsal Tunnel Syndrome. J Rheumatol 14:577-581, 1987

– Daniels et al: The Effects of Foot Position and Load on Tibial Nerve Tension. Foot Ankle Int. 19:73-78, 1998

Nerve Strain/Tension

What do we know?

• 8% venular flow obstructs• 15% complete arterial occlusion occurs

– Kwan el al: Strain, stress, and stretch of peripheral nerve. Acta Orthop Scand, 83:267-272, 1992

– Lundborg, G, Rydevik, B: Effects of stretching the tibial nerve of the rabbit. JBJS 55B:390-401, 1973

Nerve Strain/Tension

What do we know?

• 6 % Strain decreases the amplitude of the action potential which recovers after removal of the strain.

• 12% strain produced a complete block and showed minimal recovery

– Wall et al: Experimental stretch neuropathy. JBJS 74B:126-129, 1992

Putting it all together

• Pronation increases pressure within the tarsal tunnel which interrupts intraneural blood flow

• Pronation increases nerve strain/tension

• In a normal amount of pronation• What about a hyperpronating foot• Average person takes 7,000-10,000 steps per day• 50 y.o. has taken roughly 152,022,500 steps

How can we eliminate the hyperpronation?

• Orthotics?• Special Shoes• Braces/splints• Exercises/stretching

Custom-molded “Orthotics”

Internal deformity = Internal Correction

Two Part Study

TaloTarsal DislocationStabilized Hindfoot

With HyProCure

• Pressure Measurements within the – Tarsal Tunnel– Porta Pedis

• Strain of the Posterior Tibial Nerve Elongation in a hyperpronating foot.

• Pressure Measurements within the – Tarsal Tunnel– Porta Pedis

• Strain of the Posterior Tibial Nerve Elongation in a hyperpronating foot.

Part I findings

Pressure Measurements

The Effect of HyProCure Sinus Tarsi Stent on Tarsal Tunnel and Porta Pedis Pressures.Journal of Foot and Ankle Surgery, Volume 50, Issue1 Pages 44-

49, January 2011

Cadaver Set-Up

Tarsal Tunnel

Porta Pedis

 TT Pressures Without HyProCure With HyProCure

% Reduction HyProCure

Specimen No. Neutral

Hyper-Pronated Neutral

Hyper-Pronated

  n = 3 for each reported data value

1 2 31 0 21 31

2 2 15 6 14 9

3 6 21 1 11 46

4 5 21 0 14 34

5 6 31 6 20 34

6 0 26 2 18 30

7 6 38 7 29 25

8 6 35 1 17 53

9 7 68 5 43 37Grand Mean

± 1 S.D. (n = 27) 4 ± 3 32 ± 16 3 ± 3 21 ± 10 34%Range (n =

27) 0 - 13 9 - 72 0 - 8 10 - 53 9 - 53

95% C.I. 3.2 – 5.7 25.6 – 37.9 2.1 – 4.3 16.7 – 24.8

Specimen No. NeutralMaximallyPronated Neutral

MaximallyPronated

HyProCure% Reduction

foot after

HyProCure  n = 3 for each reported data value1 2 27 1 20 262 3 25 5 14 433 1 26 1 14 454 1 16 2 7 575 1 25 2 21 166 1 28 0 19 337 2 32 2 19 428 2 15 2 7 549 5 64 7 44 31

Grand Mean ± 1 S.D. (n =

27) 2 ± 2 29 ± 15 2 ± 2 18 ± 11 38%

Range (n = 27) 0 - 7 10 - 73 0 - 7 5 - 51 16 - 5795% C.I. 1.4 - 2.7 23.0 - 34.5 1.6 - 3.3 14 - 22.8

Porta Pedis Study

Overall Results

29 1832 21

34% reduction- Tarsal tunnel38% reduction- Porta pedis

Part II FindingsStrain on the Tibialis Posterior Nerve

Effect of Extra-Osseous TaloTarsal Stabilization on Posterior Tibial Nerve Strain in Hyperpronating Feet: A Cadaveric EvaluationJournal of Foot and Ankle Surgery, Volume 50, Issue 6 , Pages

672-675, November 2011

9 Cadaver Specimens

  Elongation Strain

% Reduction in

Elongation

 Without

HyProCure®

With HyProCure®

Without HyProCure®

With HyProCure®  

  in mm in %  

           Mean ± 1

S.D. 5.91 ± 0.91 3.38 ± 1.20 26.81 ± 4.6 15.38 ± 5.65 43%

Range 3.02 - 7.19 1.25 - 5.23 12.5 - 33.87 5.24 - 23.57  

Significant Decrease with Talotarsal Stabilization

Why Posterior Tibial Nerve Involvement

• Increased Pressures within both the tarsal tunnel and porta pedis

• Flattening forces acting on the nerve(s)• Strain/elongation forces placed on nerve(s)• Intraneural damage• Vascular impairment• Repetitive Trauma to the nerve fibers

Thoughts

• Patients present with a wide variety of medical backgrounds

• Short/Long-term results of pure decompression*?

• What is the missing piece to the puzzle?• External modalities are less than optimal• Internal stabilization is preferred

*Chaudhry V, Russell J, Belzberg A. Decompressive surgery of lower limbs for symmetrical diabetic peripheral neuropathy. Cochrane Database of Systematic Reviews 2008, Issue 3. Art. No.: CD006152. DOI: 10.1002/14651858.CD006152.pub2.

Next Step-Suggestions

• Early presentation- internal stabilization with HyProCure® as a stand-alone procedure

• Significant symptoms- combined neurolysis decompression along with HyProCure®

to be continued…

Thanks

For more information please visit:

www.HyProCure.com