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After reading several articles of posterior tibial tendon dysfunction, I began to get the impression that adult progressive flatfoot is due to weakness of tibialis posterior. I have always viewed this as a secondary issue, with some other factor causing excessive pronation and the PT muscle succumbing to overuse and degenerative changes (which certainly adds to the progressive deformity). I've seen clinicians treat this primarily with strengthening exercises without addressing the biomechanical issues. It seems to me that the gamut of proper treatment for this does not involve the muscle itself (orthotics, bracing, arch stabilizing sugeries, etc). Does the moniker of PTTD misguide treatment in some way? Is the PT muscle the chicken or the egg?
IMHO, PTTD is NOT due to a weak post tib muscle (I actually think the muscle is very strong).
Our work that is 'in press' has shown that the force needed to supinate the foot in those with PTTD is around 320 newtons (can't recall exact value) whereas the population normal is around 140-180 newtons.
Our published research shows that the force to supinate the foot is approx ~30% explained by variation in the transervse plane psoition of the STJ axis --> more medial axis in PTTD --> post tib muscle has very poor/short lever arm to joint axis --> appears weaker, when its not really. Strengthening the muscle is not going to do a lot of good as its probably very strong already, its just a very inefficient invertor as it has the short lever arm to the joint axis.
As we have shown the force needed to supinate the foot in those with PTTD is so high, it gives a pointer to the probable cause --- ie the muscle has spent a lifetime of working so hard, it just can't keep on doing it ---> degenerative changes in tendon.
__________________
Craig Payne
Department of Podiatry
La Trobe University
Melbourne, Australia http://www.latrobe.edu.au/podiatry
__________________________________________________ ___________________________________ God put me on this earth to accomplish a certain number of things - right now I am so far behind, I will never die.
The views expressed above are those of the author and not that of La Trobe University This is where I am, where are you?
When ever you see one of these pay particular attention to the actual track of the tendon as it descends...so many are well anterior and pass superficial to the malleollus...rather than posterior to it...very short lever.
Regards Phill
From a clinical perspective I have found this "diagnosis" an interesting area of biomechanics. To be able to reduce a patients symptoms, obviously controlling the necessary biomechanics is the first aim, and the offering a strengthening programme of the is any tendinosis present the next (ina nut shell).
But how to control this patient? One one hand I have wanted to control that excessively pronated, rearfoot collapse with a solid semi rigid device. Maybe around 14/18 deg mod root and a firm medial block in the shoe, that available in the Brook Beast or the Brooks Synergy (two examples, but there are others that are of use). But have noticed that you get them back 2-3 months later and they have compressed the shoe laterally which would happen if they are controlled too much medially/or the shoe to soft laterally which sometimes os the case.
SO, Craig suggests that the STJ is more medially deviated....so you should need more control medial to STJ axis-increase moments on this side for increase supination...BUT...this foot ends up walking out the lateral side of the shoe... I tend to agree with Craig, but still find myself a little lost. I feel that this does come back to the kinetic vs kinematics arguement, where Kirby has mentioned previously, that the kinetics may have changed slightly but the kinematics may have changed alot (correct me if I am wrong :) ). Hence visually biomechanics may have not changed, but the patients symptoms may have changed.
After reading several articles of posterior tibial tendon dysfunction, I began to get the impression that adult progressive flatfoot is due to weakness of tibialis posterior. I have always viewed this as a secondary issue, with some other factor causing excessive pronation and the PT muscle succumbing to overuse and degenerative changes (which certainly adds to the progressive deformity). I've seen clinicians treat this primarily with strengthening exercises without addressing the biomechanical issues. It seems to me that the gamut of proper treatment for this does not involve the muscle itself (orthotics, bracing, arch stabilizing sugeries, etc). Does the moniker of PTTD misguide treatment in some way? Is the PT muscle the chicken or the egg?
Nick
I do believe that there are a few things happening simultaneously in posterior tibial dysfunction (PTD):
1. There is a relatively medial STJ axis location.
2. The more medial STJ axis location causes increased magnitudes of STJ pronation moment.
3. The more medial STJ axis location causes a decrease in supination moment arm for PT muscle.
As a result of these above factors, increased tensile stress occurs within the PT tendon that causes some form of tendon damage, either a partial or complete tear or a lengthening of the tendon. All of these factors will also cause some reduction in ability for contraction of the PT muscle to generate PT tendon tension which will then continue the cascade of events:
4. Decreased internal STJ supination moment (from loss of PT tendon tensile force) which, in turn, causes a net increase in STJ pronation moment.
5. Increased tensile stress on spring ligament complex.
6. Tear or lengthening of spring ligament complex.
7. Increased abduction of forefoot on rearfoot due to #6.
8. Increased medial deviation of STJ relative to forefoot due to #7.
9. Start again at #1 again. Flattening of medial longitudinal arch and abduction of forefoot relative to rearfoot will only stop when no other ligaments stretch or tear so that the foot can finally stabilize in a new, more deformed, structure.
I have reviewed these above factors in a series of newsletters I wrote in 2000 and also in an invited article I did for Podiatry Management magazine.
(Kirby KA: Conservative Treatment of Posterior Tibial Dysfunction, Podiatry Management, Vol 19, No 7, pp. 73-82, 2000, pp. 99-106.
Kirby, Kevin A.: Foot and Lower Extremity Biomechanics II: Precision Intricast Newsletters, 1997-2002. Precision Intricast, Inc., Payson, AZ, 2002.)
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
I love you Kevin Kirby! You make it so clear. I have been given an assignment on PTTD. I have so many valuable leads thanks to you.
Carole:
Because of your comments above, I am providing you with the text from my latest lecture on posterior tibial tendon dysfunction which I will give this Friday at the 2009 Squaw Valley Foot and Ankle Seminar. Hope this helps.
Quote:
Posterior Tibial Tendon Dysfunction: Biomechanics of Effective Conservative and Surgical Treatment
Kevin A. Kirby, DPM, MS
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine
Oakland, California, USA
Posterior Tibial Tendon Dysfunction
Described in 1991 by Mueller as pathology with multiple etiologies affecting the posterior tibial (PT) tendon
Can be a seriously disabling condition causing pain, weakness and progressive development of flatfoot deformity
Mueller TJ: Acquired flatfoot secondary to tibialis posterior dysfunction: biomechanical aspects. J. Foot Surgery, 30:2-11, 1991.
Also known as “tibialis posterior dysfunction”, “posterior tibial dysfunction” and “adult acquired flatfoot deformity”
Posterior Tibial Tendon Dysfunction: Staging
Multiple staging systems proposed by various authors to classify the clinical severity of PTTD
Most commonly used staging system is that proposed by Johnson and Strom in 1989 that was later modified by Myerson in 1996
Johnson KA, Strom DE: Tibialis posterior tendon dysfunction. Clinical Ortho., 239:196-206, 1989.
Myerson MS: Adult acquired flatfoot deformity: treatment of dysfunction of the posterior tibial tendon. JBJS, 78:780-792, 1996.
Functions of the Posterior Tibial Muscle
PT muscle functions to cause:
-ankle joint plantarflexion moment
-STJ supination moment
-MTJ adduction and plantarflexion moment
Functions of the Posterior Tibial Muscle
During first half of stance phase of walking gait, primary function of PT muscle is to:
Decelerate STJ pronation
Decelerate forefoot abduction at MTJ
Decelerate forefoot dorsiflexion at MTJ
Function and Dysfunction of the Posterior Tibial Muscle
During latter half of stance phase, primary function of PT muscle is to:
Accelerate STJ supination
Accelerate forefoot adduction at MTJ
Accelerate forefoot plantarflexion at MTJ
Loss of PT function results in large decrease in STJ supination moments, forefoot adduction moments and forefoot plantarflexion moments
Biomechanical Significance of STJ Axis Location in PTTD
Research with Penn State Biomechanics Lab involves using a motion based method to determine STJ axis location in both cadaver and live subjects without drilling pins into talus
Lewis GS, Kirby KA, Piazza SJ: Determination of subtalar joint axis location by restriction of talocrural joint motion. Gait and Posture. 25:63-69, 2007.
Isolating STJ Axis in Live Subjects by Motion Restriction of Ankle Joint
Fast MRI scans performed on 4 subjects with special apparatus that rotates STJ while limiting ankle joint motion
STJ axis determined from tibia-calcaneal motion averaged only 6.00 and 2.5 mm from “true” STJ axis determined by MRI scans
Lewis GS, Cohen TL, Seisler AR, Kirby KA, Sheehan FT, Piazza SJ: In vivo tests of an improved method for functional location of the subtalar joint axis. J Biomechanics, 42:146-151, 2009.
Results of STJ Axis Determination Led to Classification System
Feet which functioned most normally had STJ axes which passed from posterior-lateral calcaneus to first intermetatarsal space
Feet which had pronation-related symptoms and pronation gait abnormalities had “medially deviated STJ axes”
Feet which had supination-related symptoms and supination gait abnormalities had “laterally deviated STJ axes”
Mechanical Effects of Medial and Lateral Deviation of STJ Axis
Medial and lateral deviation of STJ axis affects direction and magnitude of rotational forces (moments) acting across STJ axis
STJ deviation alters effects of ground reaction force (GRF), muscular contractile forces, and ligamentous tensile forces during weightbearing activities
Alteration of Rotational Effects of GRF with STJ Axis Deviation
STJ Axis Deviation Alters Rotational Effects of Muscular Forces on STJ
STJ Axis Medial Deviation Greatly Affects PT Muscle Function
Increased pronation motion of STJ will cause internal rotation and medial translation of STJ axis in relation to PT tendon
As STJ axis becomes more medially deviated, PT tendon moment arm to STJ axis becomes shorter (i.e. PT tendon has less “leverage”)
Results in PT muscle having reduced capacity to generate important STJ supination moment during weightbearing activities
Shortened PT tendon supination moment arm creates need for increased PT muscle contractile force to produce a given magnitude of STJ supination moment
Increased tensile stress on PT tendon results, causing increased likelihood of PT tendinitis/PTTD
Kirby KA: Conservative treatment of posterior tibial dysfunction, Podiatry Management, Vol 19, No 7, pp. 73-82, 2000.
Loss of Tendon Diameter Greatly Increases Tensile Stress on Tendon
Tensile stress = tensile force per cross-sectional area (F/A), measured in pascals (Pa) = N/m2
When PT tendon develops a tear, reducing cross-sectional area, tensile stress in tendon increases in area of tear
Increased tensile stress in tendon fibers increases risk of further tear or rupture
Forefoot GRF and STJ Axis Location
Increased STJ axis medial deviation also increases distance from forefoot to STJ axis which increases STJ pronation moment from GRF acting on forefoot
STJ pronation moments are, therefore, greatest in late midstance when GRF on forefoot is greatest
Effects of Decreased PT Muscle Moment Arm Across STJ Axis
Causes decreased STJ supination moment for given magnitude of PT tendon force
Increases PT tendon force required to produce given magnitude of STJ supination moment
PT muscle becomes unable to generate sufficient STJ supination moment to decelerate STJ pronation in early stance and accelerate STJ supination in late stance phase so that increased STJ pronation motion results
Increased PT Tendon Tensile Force Leads to Tendon Pathology
Chronic high tension on PT tendon increase chances of tendon inflammation, elongation or tearing
Any inability of PT tendon to transmit tensile forces may lead to PTTD since STJ pronation moments are not counterbalanced by STJ supination moments
Increased STJ Pronation Moments Lead to Ligament Pathology
Spring ligament complex may also pathologically elongate or may develop structural defects due to excessive STJ pronation moments seen in PTTD
Spring ligament complex consists of superomedial calcaneonavicular (SMCN) ligament and inferior calcaneonavicular (ICN) ligament
Davis WH, Sobel M, DiCarlo EF, et al: Gross, histological, microvascular anatomy and biomechanical testing of the spring ligament complex. Foot Ankle Int. 17:95-102, 1996.
Spring Ligament Elongation Leads to Increased Deformity
If posterior tibial tendon can not develop adequate tension during its phasic activity to intermittently reduce tensile forces on spring ligament complex, then eventual plastic deformation, elongation or failure of these ligaments may occur
Elongation or failure of spring ligament complex leads to further medial longitudinal arch collapse and further abduction of forefoot on rearfoot
Spring Ligament Elongation Leads to Increased STJ Pronation Moments
Increased abduction of forefoot increases STJ pronation moment arm for GRF (i.e. CoP) which, in turn, further increases magnitude of STJ pronation moments in late midstance in PT dysfunction
Goals for Treatment of Posterior Tibial Tendon Dysfunction
Reduce STJ pronation moments acting on foot by increasing STJ supination moments with orthoses and shoegear
Reduce inflammation, edema and pain in PT tendon to allow more normal PT muscle function and more normal gait function
Increase strength of PT muscle after inflammation has been reduced to improve ability of PT muscle to generate STJ supination moments
Typical Foot Orthoses for Mechanical Treatment of PTTD
3/16 - 4/16” polypropylene shell
4/4 degree rearfoot posts
3 mm to 6 mm medial heel skive
Heel contact points 1/8” – 3/16” thick
18 mm to 20 mm heel cup height
Minimal medial expansion on positive cast
Positive cast balanced 2 - 6 degrees inverted
Use of Medial Heel Skive in Treatment of PTTD
Medial heel skive technique is orthosis modification which allows for precise amounts of varus wedging to be added into heel cup of an orthosis in order to increase STJ supination moments acting on foot during weightbearing activities
Kirby KA: The medial heel skive technique: improving pronation control in foot orthoses, JAPMA, 82: 177-188, 1992.
Feet with PTTD Have Reduced Plantar Area Medial to STJ Axis
As STJ axis becomes medially deviated, foot orthosis has decreased surface area medial to STJ axis by which to generate STJ supination moments
Medially Deviated STJ Axis of PTTD Affects Function of Orthosis
Foot orthosis needs to have more “pronation control” features as STJ axis becomes more medially deviated in PTTD
Medial arch of foot may not be medial to STJ axis in foot with severely medially deviated STJ axis
Medial calcaneus is area of plantar foot with longest supination moment arm to STJ axis
Medial calcaneus is, therefore, a very important area on plantar foot for foot orthosis to generate STJ supination moments in PTTD
Synergy of Medial Heel Skive and Increased Orthosis Medial Arch Height
Medial heel skive without increased medial arch height causes too little medial longitudinal arch force from orthosis to optimize pronation control
Increased medial arch height without medial heel skive causes excessive medial arch force from orthosis
Combination of both medial heel skive and increased medial longitudinal arch height in orthosis will result in optimum synergistic STJ supination effect from orthosis
PTTD Orthoses Shift Reaction Forces More Medially on Plantar Foot
High Top Boots/Shoes are Needed Along With Foot Orthoses for PTTD
Very important that patient wear orthoses in high top hiking boots or high top shoes to increase orthosis efficacy
Biomechanical Effect of High Top Boots in PT Dysfunction
High top boot acts synergistically with medial heel skive orthosis to increase STJ supination moment
Boot acts both superior and inferior to STJ axis to exert STJ supination moment
Foot orthosis can only act inferior to STJ axis to exert STJ supination moment
Clinical Effect of Orthoses and Boots on PT Dysfunction
High top boots and foot orthoses work together to realign STJ axis to a more normal position
Alternatives to High Top Boots and Foot Orthoses for PT Dysfunction
Arizona Ankle Brace
Southwest Ankle Brace
Platinum Ankle Brace (PAL)
ProLab Functional AFO
Richie Brace
Ankle-Foot Orthoses in PTTD
Double steel upright hinged ankle brace with medial T-strap is also very effective at treating PTTD
Important to Reduce Local Inflammation in PTTD
Patients are started on twice daily icing therapy (20 minutes/session) in order to reduce local inflammation in PT tendon
Icing is continued until medial ankle edema and pain has diminished
NSAIDS may also be helpful at reducing the pain and edema at the medial ankle area
Less swelling around tendon leads to better tendon function
Strengthening of Posterior Tibial Muscle
Patients are started on strengthening exercises for PT muscle once they have worn orthoses for three weeks and/or tendon has become less symptomatic
Exercises can consist of isometric exercises or concentric and eccentric adduction exercises with tire inner-tube or theraband
Biomechanics of Surgical Treatment of PTTD
Any displacement osteotomy of calcaneus or midfoot may affect STJ axis location and mechanical function of foot and lower extremity
Medial displacement osteotomies of calcaneus increase supination moment arm for GRF acting on plantar calcaneus and also increase supination moment arm for Achilles tendon
Mechanical effects of frontal and transverse plane calcaneal and midfoot osteotomies are best understood using STJ axis location/rotational equilibrium theory
Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001.
1. Posterior calcaneal displacement osteotomy causes medial shift in plantar calcaneus relative to STJ axis so STJ supination moment is increased when GRF acts plantar to calcaneus
2. Posterior calcaneal displacement osteotomy also causes a medial shift in Achilles tendon force relative to STJ axis which increases supination moment during late midstance and propulsion, when Achilles tendon tensile forces are greatest
Intraoperative Assessment of Calcaneal Osteotomy with STJ Axis Palpation
STJ axis palpation technique used during calcaneal displacement surgery in order to assess for optimum calcaneal alignment
Roukis TS, Kirby KA: A simple intraoperative technique to accurately align the rearfoot complex. JAPMA, 95:505-507, 2005.
Anterior Axial Projection of Foot
New radiographic projection, Anterior Axial Projection, invented in 1985
Kirby KA, Loendorf AJ, Gregorio R: Anterior axial projection of the foot. JAPMA, 78: 159-170, 1988.
Anterior axial projection allows reproducible method of obtaining frontal plane image of relative positions of plantar rearfoot, forefoot and ankle mortise while the patient stands in angle and base of gait
Anterior Axial Positioning Device
Made of radiolucent plastic with longitudinal bisection line on top
Has steel pin embedded within posterior edge of top surface to act as horizontal reference line
Characteristics of Anterior Axial Projection of Foot
Central beam inclinated 10 degrees from anterior to posterior with x-ray tube below level of foot
X-ray plate (i.e. film) positioned vertically and against posterior aspect of heel of foot
Patient is positioned on device with center of second digit and center of plantar calcaneus resting on longitudinal bisection line
Patient is positioned in angle and base of gait with opposite foot resting on surface of same height as positioning device
Anterior axial projection readily demonstrates plantar contours of calcaneus and its position relative to ankle mortise
Plantar contours of medial and lateral calcaneal tubercles are well visualized relative to horizontal reference marker and relative to ankle mortise
Anterior axial projection is used to document relative changes in calcaneal position with posterior displacement calcaneal osteotomies which are commonly used for posterior tibial tendon dysfunction
Posterior Displacement Osteotomies of Calcaneus
Preoperatively, plantar calcaneus is laterally positioned relative to ankle mortise
Postoperatively, plantar calcaneus is more centrally located relative to ankle mortise
Summary of Treatment Approaches for PTTD
PTTD may be successfully treated both non-surgically and surgically
Clinical decision of when to treat PTTD surgically should be based on patient response to conservative care and level of activity
Understanding the biomechanics and pathophysiology of PTTD is critical to developing an optimal treatment plan for patients with this painful and potentially disabling disorder
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Primacy of PTTD
Linear Mode
