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 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.
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 = Lateral Plantar nerve MN MA MN = Medial Plantar nerve LV= Lateral Planar Vein LA LN MV = Medial Plantar Vein LA = Lateral Plantar Artery LV MV MA = Medial Plantar ArteryThere is plenty of room and every thing is functioning normally.
What could possible happen to the structures within the portapedis 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. M M N A L Abductor Hallucis Muscle N L M L A Calcaneus V VThere is less room and the structures are compressed decreasing blood flow and altering the natural function.
Effects of TaloTarsal Dislocation During the Gait Cycle What happens to the porta pedis MN MA M M N A L N LN LA Excessive L A Force L M LV MV V VPorta Pedis during Porta Pedis during mid- swing phase or stance in a dislocation of the talotarsalnon-weightbearing joint/weightbearing
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 AlignmentArticular facets are alignedSinus tarsi is openNormal CymaNormal Talar declination angleNormal navicular height
Normal to abnormal alignment Sinus 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
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. TPN TPA TPVThere is plenty of room and every thing is functioning normally.
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 thesestructures 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. P M N A MV There is compression of the neurovascular structures.
During Walking However, as soon as theWith no weight on the heel touches the ground the foot there are no talus slips off the tarsalabnormal forces acting mechanism and the on the structures excessive abnormal forces begin to take effect on the within the tarsal structures within the tarsal tunnels. tunnels.
DID YOU KNOWActive person takes 8,500 steps/day A 50 year old has taken 152,022,500 steps.
Just think about all that damagebeing 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 iscontinuously compressed.
If the chemical signal is able to passthrough 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 takenKumar et al: Evaluation of Various Fibro-Osseous Tunnel Pressures in Normal Human Subjects. Indian J Physiol Pharmaol, 32:139-145, 1988Trepman et al.:Effect of Foot & Ankle Position on Tarsal Tunnel Compartment Pressure. Foot Ankle Int. 20:721-726, 1999Barker 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, 2007Rosson 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
Two Part Study Stabilized Hindfoot TaloTarsal Dislocation With HyProCure• Pressure Measurements • Pressure Measurements within the within the – Tarsal Tunnel – Tarsal Tunnel – Porta Pedis – Porta Pedis• Strain of the Posterior • Strain of the Posterior Tibial Nerve Elongation in Tibial Nerve Elongation in a hyperpronating foot. a hyperpronating foot.
The Effect of HyProCure Sinus Tarsi Stenton Tarsal Tunnel and Porta Pedis Pressures.Journal of Foot and Ankle Surgery, Volume 50, Issue1 Pages 44- 49, January 2011 Part I findingsPressure Measurements
Effect of Extra-Osseous TaloTarsal Stabilization on Posterior Tibial Nerve Strain in Hyperpronating Feet: A Cadaveric Evaluation Journal of Foot and Ankle Surgery, Volume 50, Issue 6 , Pages 672-675, November 2011 Part II FindingsStrain on the Tibialis Posterior Nerve
9 Cadaver Specimens % Reduction in Elongation Strain Elongation Without With Without With HyProCure® HyProCure® HyProCure® 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®