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I was invited to lecture on the biomechanics of subtalar arthroereisis procedures (which includes the Hyprocure Implant) in October 2009 at the Podiatry Institute’s Reconstructive Surgery of the Foot and Ankle Seminar in San Diego. Since the specific biomechanics of subtalar arthroereisis implants are rarely lectured on, since there is considerable misinformation about what these implants can and cannot do, and since the topic of subtalar arthroereisis implants are becoming of greater interest worldwide, I thought it might be helpful to make my PowerPoint lecture notes available for those that are interested.
Quote:
Biomechanics of Subtalar Joint Arthroereisis
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine
Subtalar Arthroereisis
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:
at floor of sinus tarsi of calcaneus and anterior surface of lateral process of talus
Vogler’s Classification of Arthroereisis Implants
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”
Axis –altering: “elevates a pathologically low STJ axis and reduces amount of frontal plane STJ motion”
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
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Considering the common presentation and diagnosis of sinus tarsi compression syndrome (ref here http://www.podiatry-arena.com/podiat...hread.php?t=33 post 8) I would have thought that a rigid arthroereisis in the sinus tarsi would tend to instigate this problem. Do you think that it is possible that a person with such an implant would have an antalgic response to pronating the STJ and avoid excessive compression?
I can imagine that if a certain subject had a maximally pronated STJ that was mainly resisted by osseous compression at the sinus tarsi then adding a bush to separate the bony surfaces and therefore change / shorten the moment arm available to GRF relative to the STJ axis at the time when the interfaces compress would relatively reduce the interface compression forces. So where there is little supinating muscular activity e.g. post tib and plastic deformation of the medial ligaments then an arthroereisis would be a good alternative. Which seems to be pretty much what your saying in your lecture notes.
Cheers Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Considering the common presentation and diagnosis of sinus tarsi compression syndrome (ref here http://www.podiatry-arena.com/podiat...hread.php?t=33 post 8) I would have thought that a rigid arthroereisis in the sinus tarsi would tend to instigate this problem. Do you think that it is possible that a person with such an implant would have an antalgic response to pronating the STJ and avoid excessive compression?
I can imagine that if a certain subject had a maximally pronated STJ that was mainly resisted by osseous compression at the sinus tarsi then adding a bush to separate the bony surfaces and therefore change / shorten the moment arm available to GRF relative to the STJ axis at the time when the interfaces compress would relatively reduce the interface compression forces. So where there is little supinating muscular activity e.g. post tib and plastic deformation of the medial ligaments then an arthroereisis would be a good alternative. Which seems to be pretty much what your saying in your lecture notes.
Cheers Dave
Dave:
Sinus tarsi pain and extrusion of implants from the sinus tarsi are a known complication of STJ arthroereisis. Jeff Christensen, DPM, (one of my classmates from CCPM) has done some cadaver research on arthroereisis implants and has found very high contact pressures in the sinus tarsi with some of these implants which may explain some of the sinus tarsi pain in using some of these designs. However, many children do quite well with these implants and can run and play without any symptoms. This seems especially important if the children are involved in sports where proper foot orthoses can't be worn (e.g. gymnastics, ballet). Many surgeons recommend these implants only for children, but a few do them on adults also. I have only done the procedure on cadaver specimens. However, a few of my friends who have performed very many of these procedures over the years, such as Donald Green, DPM, has reported excellent results with this procedure.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
However, a few of my friends who have performed very many of these procedures over the years, such as Donald Green, DPM, has reported excellent results with this procedure.
Well the proof of the pudding is in the eating then.
Were most of these Arthroereisis implants the soft type?
Dave
__________________
Descartes seems to consider here that beliefs formed by pure reasoning are less doubtful than those formed through perception.
Well the proof of the pudding is in the eating then.
Were most of these Arthroereisis implants the soft type?
Dave
Dave:
Don performs the arthroereisis implant that has a stem and, I believe, is made of silastic. In speaking with my buddy Jeff Christensen about STJ arthroereisis biomechanics last year at our first "Biomechanics of Surgery Seminar" in Oakland, he says that he has yet to find an arthroereisis implant that reduces the talo-calcaneal contact pressures in his cadaver experiments, due probably to the implants not being custom fit to the sinus tarsi space it eventually occupies. Jeff, I believe, was using Fuji Pressure Sensive Film in his studies on these implants. Hopefully, the next generation of these implants will have better fit to the sinus tarsi than the current screw-in implants (e.g. MBA, Hyprocure) that have recently become more popular.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Sorry I missed your lecture in San Diego. What a great place to visit (or live)
Don't you think this procedure has been over utilized simply because it's so easy to perform and, when done alone, completely reversible? I'm not saying it's a bad procedure, what I'm saying is too many are done without proper preoperative evaluation.
For instance, I know of a "surgeon" who has performed this many many times however has recently told me that he has never done a concomitant procedure, not even an Achilles lengthening!
Steve
__________________
DrSArbes
Fellow American College of Foot & Ankle Surgeons
Board Certified Foot & Ankle Surgery, ABPS
Adjunct Professor OCPM
Green Bay, Wisconsin, USA
Sorry I missed your lecture in San Diego. What a great place to visit (or live)
Don't you think this procedure has been over utilized simply because it's so easy to perform and, when done alone, completely reversible? I'm not saying it's a bad procedure, what I'm saying is too many are done without proper preoperative evaluation.
For instance, I know of a "surgeon" who has performed this many many times however has recently told me that he has never done a concomitant procedure, not even an Achilles lengthening!
Steve
Steve:
I believe you hit the nail squarely on the head. Podiatrists probably shouldn't be doing this procedure unless they are well trained in other flatfoot correction procedures so that the most appropriate procedures may be selected for each patient.
A good example of overuse of this procedure was the local podiatrist who did the STJ arthroereisis procedure on a 38 year old female school teacher with plantar fasciitis that didn't respond to poorly made foot orthoses. The unfortunate lady developed lateral dorsal midfoot pain within a few weeks of the arthroereisis procedure due to over-correction with the arthroereisis and another podiatrist removed the plug from her sinus tarsi which eliminated her lateral midfoot pain but this next left her with chronic sinus tarsi pain. A few months later I was referred the patient for orthoses, made her a better set of foot orthoses and this which ultimately made her sinus tarsi pain vanish within 3 weeks of receiving them. This lady only needed better foot orthoses from the start, but since the original podiatrist had determined that "the patient had failed foot orthosis therapy", she got the arthroereisis procedure and 6 months of frustration, pain and disability.
Sad story, but very true.
__________________
Sincerely,
Kevin
**************************************************
Kevin A. Kirby, DPM
Adjunct Associate Professor
Department of Applied Biomechanics
California School of Podiatric Medicine at Samuel Merritt College
Interesting discussion on what is an exciting develpment in foot surgery. Have seen quite a few patients who have undergone subtalor arthroeresis for juvenille flat foot & aquired flat foot and without exception have enjoyed good outcomes. Would be interested to hear what protocols are generally followed post operatively regarding orthotic management. Kevin wrote,
Quote:
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
If consideration is to be given to reducing these compressive forces, and it seems reasonable to suggest this would be desirable in the long term, surely orthotic management is vital to ensure stability of the implant and surrounding bone?
Interesting discussion on what is an exciting develpment in foot surgery. Have seen quite a few patients who have undergone subtalor arthroeresis for juvenille flat foot & aquired flat foot and without exception have enjoyed good outcomes. Would be interested to hear what protocols are generally followed post operatively regarding orthotic management. Kevin wrote, If consideration is to be given to reducing these compressive forces, and it seems reasonable to suggest this would be desirable in the long term, surely orthotic management is vital to ensure stability of the implant and surrounding bone?
As discussed in the Biomechancial treatment post-op Hyprocure thread Here
A case-control study was undertaken to identify differences in patients with flexible flatfoot deformity who required explantation of subtalar arthroereisis compared with those who did not. All patients who required removal of a self-locking wedge-type subtalar arthroereisis were identified between 2002 and 2008. Propensity scores matched 22 explanted subtalar arthroereises to 44 controls (nonexplanted arthroereises), resulting in a total of 66 implants that met all inclusion and exclusion criteria. Multivariate logistic regression found that patients who required explantation had a greater odds of radiographic undercorrection, determined from radiographic anteroposterior talar-first metatarsal angles postoperatively, P = .0012, odds ratio (OR) = 1.175 (95% confidence interval [CI] 1.066 to 1.295), or residual transverse plane-dominant deformities, as determined from radiographic calcaneocuboid abduction angles postoperatively, P = .05, OR = 1.096 (95% CI 1.06 to 1.203). Patients with smaller postoperative anteroposterior talocalcaneal angles had a 16.7% reduction in odds for arthroereisis explantation (P = .0019) (95% CI 6.5% to 25.8%). Age, gender, implant size, shape, duration, implant position, surgeon experience, and concomitant procedures were not statistically different between the 2 groups. This study helps identify key factors that may result in subtalar arthroereisis explantation.
I am take interest in ‘cruciate pivot point’ of Farabeuf? What is it? It's described Chambers in his article "An operation for the correction of flexible flat feet of adolescents", West J Surg Obst Gynecol, 1946;54:77–86. As I understand it's anatomical landmark on the lateral aspect of the canalis tarsi. But what is role of this point in subtalar arthroereisis?
P.S. In my country this article is not available. Anybody help me with this?
Biomechanics of Subtalar Arthroereisis
Linear Mode
