Biomechanics of Subtalar Joint Arthroereisis
by Kevin A. Kirby
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Oakland, California, USA
Arthroereisis:
[(Greek) arthron: joint + ereisis: a raising up] – operative limiting of the motion in a joint that is abnormally mobile from paralysis
Dorland’s Illustrated Medical Dictionary, 25th ed., W.B. Saunders, Philadelphia, 1974.
Subtalar arthroereisis:
surgical procedure to prevent excessive pronation and preserve varus range of motion within subtalar joint
Maxwell JR, Cerniglia MW:
Subtalar joint arthroereisis. In Banks AS, Downey MS, Martin DE, Miller SJ (eds):
McGlamry’s Comprehensive Textbook of Foot and Ankle Surgery, 3rd Ed, Lippincott Williams & Wilkins, 2001,
pp. 901-914.
History of STJ Arthroereisis
Over 50 years ago, Chambers was first to describe surgical procedure to elevate floor of sinus tarsi of calcaneus with bone graft to limit STJ pronation
Chambers EF:
An operation for the correction of flexible flat feet of adolescents. West J Surg Obstet Gynecol, 54, 1946.
In 1974, Subotnick described placing an inert silicone elastomer plug into sinus tarsi to limit STJ pronation
Subotnick SI: The subtalar joint lateral extra-articular arthroereisis: a preliminary report. JAPA, 64:701, 1974.
Smith first described UHMW polyethylene plug, STA-peg, with stem in 1975
Smith S:
The STA operation:
a new surgical approach for the pronated foot in childhood.
In:
Northlake Symposium, Podiatry Institute, Tucker, GA, 1975.
Valenti designed a threaded, screw-in polyethylene plug that was reported on by Langford et al in 1987
Langford J, Bozof H, Horowitz B:
Subtalar arthroereisis:
the Valenti procedure. Clin Podiatr Med Surg, 4:153-155, 1987.
Maxwell-Brancheau (MBA) titanium screw-in implant introduced in 1997
Maxwell J, Knudson W, Cerniglia M;
The MBA arthroereisis implant: early prospective results.
In:
Vickers NS, Miller SJ, Mahan KT (eds):
Reconstructive surgery of the
foot and leg:
update ‘97.
Podiatry Institute, Tucker, GA, 1997.
HyProCure threaded titanium implant introduced in 2004
Garthwait R:
Can the Hyprocure implant provide the answer for hyperpronation?
Podiatry Today, 21:84-85, 2008.
Long Term Study of STJ Arthroereisis
Recent study of 41 juvenile flatfeet that had STJ arthroereisis procedure for mean post-op follow-up time of 12.6 years showed 81% were satisfied
Normal alignment present in 14/41 patients, mild malalignment present in 26/41 patients
Koning PM, Heesterbeek PJC, Visser ED:
Subtalar arthroereisis for pediatric flexible pes planovalgus. JAPMA, 99(5):447-453, 2009.
What Mechanical Effects Do STJ Arthroereisis Procedures Cause?
Implant fills space within sinus tarsi, blocking end range of STJ pronation ROM, while maintaining full range of STJ supination ROM
Decreases pronated rotational position of STJ
Mechanically functions by making direct mechanical contact with both calcaneus and talus:
floor of sinus tarsi of calcaneus
anterior surface of lateral process of talus
Vogler’s Classification of Arthroereisis Implants
1. Stable self-locking wedge:
Forms a self-locking wedge in sinus tarsi – “does not alter STJ axis but rather restricts its range to the neutral”
2. Axis –altering:
“elevates a pathologically low STJ axis and reduces amount of frontal plane STJ motion”
3. Direct impact: “performs on impingement effect where talar body/process makes direct contact with prosthesis”
Vogler HM:
Subtalar joint blocking operations for pathological pronation syndromes.
In:
McGlamry ED (ed):
Comprehensive Textbook of
Foot Surgery, Williams & Wilkins, Baltimore, 1987, pp.447-465.
Problems with Vogler’s Classification
Since all STJ arthroereisis implants change STJ rotational position, all are “axis-altering”
Spatial location of STJ axis changes to more lateral and inclinated position after arthroereisis procedure as STJ becomes less pronated
Kirby KA:
Methods for determination of positional variations in the subtalar joint axis.
JAPMA, 77: 228-234, 1987.
Kirby KA: Subtalar joint axis location and rotational equilibrium theory of foot function. JAPMA, 91:465-488, 2001.
Regardless of design, all STJ implants are “direct impact” since all create compression force at floor of sinus tarsi of calcaneus and anterior edge of lateral process of talus
Compression force from calcaneal floor of sinus tarsi creates supination moment that limits pronation
Kirby KA:
Rotational equilibrium across the subtalar joint axis.
JAPMA, 79:1-14, 1989.
Normal Subtalar Joint Kinematics
Pronation of STJ causes lateral process of talus to slide anteriorly and inferiorly until it abuts against floor of sinus tarsi of calcaneus
Before lateral talar process contacts implant, no sinus tarsi compression force occurs
Once lateral talar process impacts implant, compression forces dramatically increase at lateral talar process, implant and floor of sinus tarsi
Implant changes rotational position of STJ where sinus tarsi compression forces are increased
Without implant, STJ axis is more medially deviated and has lower inclination angle
With implant, STJ axis is more laterally located and has higher inclination angle
By resetting maximally pronated position of STJ to less pronated position, all arthroereisis implants will change spatial location of STJ axis
As STJ rotates from supinated to maximally pronated position, STJ axis internally rotates and medially translates
Medial deviation of STJ axis causes GRF to create increased STJ pronation moment
Medially deviated STJ axis will cause CoP from GRF to be excessively lateral to STJ axis which will greatly increase STJ pronation moment
STJ arthroereisis limits STJ pronation motion, resets maximally pronated position so STJ axis is less medially deviated, decreasing STJ pronation moments
Potential STJ Arthroereisis Sequelae Over-correction with STJ implant will cause excessive GRF on lateral metatarsal heads possibly leading to lateral dorsal midfoot interosseous compression syndrome or lateral metatarsalgia
Kirby KA:
Foot and Lower Extremity Biomechanics: A Ten Year Collection of Precision Intricast Newsletters.
Precision Intricast, Inc., Payson, Arizona, 1997, pp. 165-168.
Overcorrection with arthroereisis may lead to lateral instability if STJ axis becomes so laterally deviated that GRF is too medial to STJ axis
Placement of STJ arthroereisis implant in patients that are obese, have excessively medially deviated STJ axis or have equinus deformity may lead to chronic sinus tarsi pain due to high bone pressures within sinus tarsi
Conclusion
STJ arthroereisis procedure is time-tested procedure which limits excessive pronation motion while maintaining full supination ROM
All implants are “axis-altering” and “direct impact” since all change STJ axis location by increasing talo-calcaneal compression forces in sinus tarsi before maximal pronated position is reached
Understanding biomechanics of STJ and how pronation/supination moments may be altered by arthroereisis procedures will help podiatrist avoid negative surgical sequelae
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