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Orthopaedic Surgery Foot
Hyperpronation – The Role of Subtalar Arthroereisis
Michael E Graham
Center for Foot and Ankle Disorders
Abstract
Excessive foot pronation is a common condition seen in children, adults and geriatric populations. A characteristic of this pathological condition
includes the instability of the talus on the calcaneus leading to partial to full obliteration of the sinus tarsi on weight-bearing. This usually leads
to a lowering of the medial longitudinal arch, and can also be accompanied by hind-foot valgus. The ill effects of this condition lead to other
pathological conditions in the foot that can contribute to a chain reaction to the proximal musculoskeletal structures. Subtalar arthroereisis is
a minimally invasive procedure with a long evolutionary history of stabilising the subtalar joint complex in an extra-articular manner.
Arthroereisis offers many advantages compared with the traditional methods of external support or arthrodesis procedures.
Keywords
Hyperpronation, arthroereisis, overpronation, subtalar joint complex, subtalar arthroereisis
Disclosure: Michael E Graham is the inventor of the HyProCure sinus tarsi stent and the founder of GraMedica.
Received: 16 March 2010 Accepted: 8 April 2010 Citation: European Musculoskeletal Review, 2010;5(1):65–9
Correspondence: Michael E Graham, Center for Foot and Ankle Disorders, 45700 Schoenherr Road, Shelby Township, MI 48315, US. E: [email protected]
The alignment of the osseous structures of the foot determines the
stability or instability of the foundation of the body. The talus plays a
critical role in transferring the forces from the leg through the foot
and onto the weight-bearing surface below. The motion of the talus on
the calcaneus is determined by the articular facets of this complex
as well as by the supporting soft-tissue structures. Pronation and
supination are terms commonly used to describe the normal motion
between the talus and calcaneus.
Overpronation describes a pathological condition in which there is
excessive pronation. A more correct term would be hyperpronation,
meaning excessive pronatory motion. The musculoskeletal kinetic
chain is a series of links joined together as joints and, as the adage
goes, the chain is only as strong as the weakest link. Instability
of the talus on the calcaneus will lead to instability in other parts of
the kinetic chain. Hyperpronation has been named one of the most
common causes of orthopaedic pathological conditions.1
The sinus tarsi is a naturally occurring space in between the talus
and calcaneus. It is formed by a groove on the undersurface of the
talus and upper part of the calcaneus. This opening is angled from
anterior–lateral–distal to posterior–medial–proximal. There is a good
reason for this orientation, as the normal transfer of the weight of the
body starts posterior–lateral and ends anterior–medial. The sinus
tarsi serves as a fulcrum point between the transfer of the
superincumbent weight of the body posteriorly to the calcaneus and
anteriorly to the rest of the foot. In a ‘balanced’ hind-foot that has the
normal amount of pronation and supination, this transfer of forces
occurs without any excessive strain to the supporting tissues (see
Figure 1A); however, if there is an imbalance within the subtalar joint
complex, partial to full obliteration of the sinus tarsi occurs2 (see
© TOUCH BRIEFINGS 2010
Figure 1B). Finally, an excessive force will be placed on the
supporting tissues, leading to excess pronation of the foot with each
step taken.
The goal of treatment is to eliminate the cause and not just to address
the symptoms. Clark pointed out: “In seeking to correct any angle of
deformity, the logical place to make the change, from a mechanical
point of view, is as near the angle of deviation as possible”.3
Modalities to stabilise the hind-foot have included both internal and
external methods. The real aetiology is the slipping of the talus off the
calcaneus leading to partial to full obliteration of the sinus tarsi. This
is an internal deformity; therefore, external treatment methods are
less effective. Numerous techniques for stabilising the subtalar joint
complex have been introduced, many of which have not stood the
test of time and have fallen by the wayside. The traditional mainstay
of these internal stabilisation procedures primarily consisted of an
arthrodesis; however, long-term results produced mixed degrees of
satisfaction, with a high rate of arthritis in adjacent joints.4–8
Due to the limitations of external treatment modalities, such as
braces, splints, custom-moulded arch supports and the overly
aggressive osseous procedures and their negative secondary
conditions, the challenge was to develop a more reasonable
solution. The apex of deformity in an excessively pronating foot
occurs within the subtalar joint complex, specifically within the
sinus tarsi. There are also many disadvantages with osseous
arthrodesis procedures, including a long recovery time compared
with arthroereisis, potential complications such as non-union and a
prolonged period of non-weight-bearing and partial weight-bearing.
The more aggressive rear foot reconstruction is usually reserved for
extreme cases of flat foot.
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Orthopaedic Surgery Foot
Figure 1: Normal Foot Showing Sinus Tarsi (A) and
Foot Showing Obliteration of Sinus Tarsi (B)
A
The birth of arthroereisis occurred in Italy with a procedure to
prevent drop foot. 10 A bone graft was inserted into the back of the
calcaneus, which hit against the back of the talus, preventing the
foot from plantarflexing and therefore preventing excessive foot
drop. EFS Chambers must have had the arthroereisis procedure in
the back of his mind when he thought it might be possible to
perform a similar procedure in the sinus tarsi to prevent excessive
twisting of the talus on the calcaneus. He inserted a bone graft into
the floor of the sinus tarsi that pressed up against the lateral
process of the talus. 11 This technique was reserved for children.
Initial results were good, but long-term results were not as good as
the bone would resorb over time and could not withstand the
chronic forces acting on it due to the lateral process of the talus.
However, this extra-articular approach was an important step in the
right direction.
The Grice procedure12 was another attempt to stabilise the subtalar
joint complex without interfering with the articular surfaces. A bone
graft was taken from the tibia and inserted in an oblique fashion into
the outer portion of the sinus tarsi, acting as an extra-articular bony
fusion. This provided even greater stability with better long-term
results.13 Limitations included issues with the longevity of the bone
graft, the fact that it was mainly reserved for paediatric patients and
the fact that it involved two surgical sites and depended on bone
fusion, among others.
B
The 1970s brought a new wave of enthusiasm into the field of
subtalar stabilisation without the use of bone grafting. A new
generation of surgeons utilising the latest materials designed
specialised devices that were simply inserted into the cavity of the
sinus tarsi. These sinus tarsi devices were composed of polymers
that initially were hand-carved then placed within the sinus tarsi.
Limitations of these designs were the high extrusion rates
combined with low durability.14 These materials just could not
Figure 2: Placement of the HyProCure Stent in
Alignment with the Sinus Tarsi and Abutting the
Lateral Part of the Canalis Tarsi
Anterior calcaneal
articulating surface
HyProCure stent
Middle calcaneal
articulating surface
Posterior calcaneal
articulating surface
The term arthroereisis is not commonly known in the medical
community. It is the combination of ‘arthro-’, meaning joint, and
‘-ereisis’, which is a Greek word meaning pushing, lifting or raising up;9
when combined, arthroereisis means the pushing, lifting or raising up
of a joint. Unfortunately, many physicians have wrongly defined this
term as joint-limiting, which implies that it is a procedure that will limit
normal motion. However, the reality is that normal motion should still
occur and only the excessive motion is limited. This procedure should
be thought of as a joint-motion-restoring procedure.
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withstand the contact forces acting on them, which led to their
fragmentation and eventual removal. Even when the devices were
partially inserted into the calcaneus, over time they would usually
fragment and require removal.
The 1990s brought the next generation of sinus tarsi devices. These
were composed of titanium, an inert material that provided
durability and did not have the biocompatibility issues experienced
with the preceding devices. The overall designs were either
cylinders or conical-shaped devices. 15 Still being extra-articular,
they were inserted into the outer wider portion of the sinus tarsi in
a lateral-to-medial orientation. A few studies showed the overall
rate of removal of these devices to be 38%.16–18 An advantage of
using titanium devices was that they could be used not only in
pediatric patients but also in geriatrics.
The still unsatisfactory rate of removal led to the most unique
design. The HyProCure® (GraMedica, Macomb, MI) sinus tarsi stent
(see Figure 2) provides the most anatomical fit into both the sinus
and the canalis portions of the sinus tarsi. Furthermore, this design
parallels the overall orientation of the sinus tarsi in an oblique
fashion versus the lateral-to-medial approach of the cylindrical and
conical designs. The use of trial sizers (see Figure 3) led to a less
traumatic and more efficient method of determining which size
stent would provide the best correction for a specific foot.
Positioning of the device is also simplified with the HyProCure
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Hyperpronation – The Role of Subtalar Arthroereisis
design, lessening the likelihood of malposition of the stent within
the sinus tarsi.
Figure 3: Trial Sizers for the HyProCure Stent
HyProCure is made of titanium. It can be used in paediatric, adult
and geriatric patients exhibiting partial to full obliteration of sinus
tarsi with a flexible deformity (that is, the talus can be repositioned
to its natural anatomical position). These features have led to a
reinvigoration of subtalar stabilisation techniques via a subtalar
arthroereisis procedure.
Many classification schemes have been devised for sinus tarsi
devices. A simplified version consists of type I and II designs. Type I
devices are partially anchored into either the talus or calcaneus,
while type II designs are completely extraosseous and are further
divided into type IIA or IIB. Type IIA are mainly positioned in the
outer half of the sinus tarsi and typically angled lateral to medial;
these are the conical and cylinder-shaped stents. Type IIB sit much
deeper, with an extension into the canalis portion of the sinus tarsi
as well as into the sinus portion of the sinus tarsi (see Figure 2).
Additionally, type IIB devices are angled along the orientation of the
sinus tarsi, anterior–lateral–distal to proximal–medial–posterior.
Currently, the only type IIB device is the HyProCure design.
Figure 4: Before (A) and After (B) Implantation of the
HyProCure Stent
A
The primary area of stabilisation of the sinus tarsi occurs at the
‘cruciate pivot point’ of Farabeuf,11 who described an anatomical
landmark located on the lateral aspect of the canalis tarsi. This is the
area where the weight of the body passes from the posterior–lateral
aspect of the subtalar joint complex to the anterior–medial aspect of
the foot. In a hyperpronating foot, this pivot point shifts medially. The
tip of the type IIA devices enters into this area. The lateral process
of the talus will slip off the posterior facet of the calcaneus and
will rotate, pressing up against the device. The average person
takes approximately 10,000 steps a day19,20 and, after an average of
3.5 years, the removal rate of type IIA devices is 37% due to the
biomechanical forces acting on these devices.15,16,21
HyProCure, a type IIB device, also provides stability to the cruciate
pivot point. A key feature is that the talar stabilising portion is
located at the middle third of the device versus the tip of the type
IIA device. The most medial aspect of HyProCure is threaded for
tissue on-growth, medially anchoring deep into the canalis portion
of the tarsal sinus. This helps to lock the HyProCure stent within the
sinus tarsi so that the tapered portion is able to stabilise the talus
on the calcaneus. The outer third of the HyProCure device also
helps to stabilise the sinus portion of the sinus tarsi by preventing
the anterior deviation of the lateral process of the talus (see Figure
4). A very important part of the design is the tapered portion of
this stent, which abuts the lateral aspect of the canalis to prevent
over-insertion. This has been an unreported problem with the type
IIA devices in that they have been pushed right through the sinus
tarsi to end up in the medial aspect of the foot.
The HyProCure design has been used in the US since 200422 and has
been used internationally since 2006. Due to its advanced design, it
has been used in patients from three to 94 years of age. Individuals
of all activity levels, including marathon runners, triathletes,
football players and more, have benefited by having their feet
stabilised. When the subtalar joint complex is stabilised, it helps to
eliminate the secondary strains to the soft tissues and joints not
only in the foot but also in the knees, hips, back, neck, etc.
EUROPEAN MUSCULOSKELETAL REVIEW
B
There are numerous advantages of the subtalar arthroereisis
procedure over other modalities. First, it is minimally invasive, only
requiring a very small incision (usually 1.5–2.0cm) centred over the
sinus tarsi. No nerves, significant blood vessels, muscles or
tendons are encountered during the insertion of one of these
devices into the sinus tarsi. Second, the device is placed internally
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Orthopaedic Surgery Foot
right into the apex of the deformity. Unlike braces or customised
arch supports, which the patient must comply with in order for
them to work, an internal device will always work regardless of
whether the patient is wearing a shoe or not. Finally, subtalar
arthroereisis provides a definitive procedure that corrects the
excessive subtalar motion, thereby restoring balance to the
architecture of the foot structures without interfering with
subsequent growth.
Since the boundaries of the sinus tarsi are ossified by three years
of age, the subtalar arthroereisis option can be used in patients
three years of age and older,23 as long as there is a flexible
deformity. Even when the child grows, there should be no need to
revise the device due to growth of the bones. There are six different
sizes of the HyProCure device, which are all the same length but
with different diameters. The most commonly used sizes in
skeletally mature feet are 6 and 7. Therefore, if a size 6 or 7 is used
in a paediatric foot, that patient should not require revision once
skeletal maturity is achieved.
The latest generation of sinus tarsi devices are reversible, i.e. they
can be completely removed without any permanent defect to the
sinus tarsi. Unlike a joint-destructive procedure with a partial or full
replacement, where the joint is removed, subtalar arthroereisis
devices are simply inserted into the space, and the tissues adhere
to the device to hold it in place. If the device has to be removed, a
small incision is made and the stent is grasped and simply
extracted; since these devices are completely extra-articular, there
is no damage to the joint and therefore no possibility of the patient
developing joint arthritis.
The worst possible complications of the titanium subtalar
stabilisation devices include inability of the soft tissues to adjust to
the new demands placed on them, displacement of the sinus tarsi
device, a period of tissue adaptation, synovitis and altered gait. It is
a surgical procedure and is therefore also subject to the other
potential complications associated with any surgery, including
incision dehiscence, scar formation, infection, prolonged pain,
swelling and stiffness and a possible reaction to anaesthesia or
post-operative medications. Additionally, the potential complications
of subtalar arthroereisis are lower compared with arthrodesis.
There is a very long list of the ill effects of hind-foot overpronation.24
Excessive motion of the talus on the calcaneus leads to abnormal
strain not only to the involved joints of these two bones but also to
the attached soft tissues. A partial list of secondary foot deformities
as a result of hyperpronation includes posterior tibialis tendon
dysfunction, plantar fasciitis, Achilles tendinitis, tarsal tunnel
syndrome, first ray disorders, hallux abductovalgus, metatarsus
primus varus, hallux limitus/rigidus, abductory twist and contracted
toes. Since these are the ‘effects’ and the ‘cause’ is hyperpronation,
it makes sense to first control the underlying aetiology. Furthermore,
if caught early enough, the secondary symptoms might resolve
on their own.
Since the foot is the foundation of the body, the stability of the talus
on the calcaneus is crucial for proper alignment of the rest of the
musculoskeletal chain. The ankle joint is formed between the talus,
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tibia and fibula. It functions as a mortise and tenon. This allows for
pure dorsiflexion and plantarflexion. In a hyperpronating foot the
talus rotates medially, and this excessive motion has to be
compensated for. If the ankle is strong enough, the compensation
will occur in the knee joint; if the ligamentous structures of the
knee are strong enough to withstand the excessive motion, the
head of the femur will twist abnormally away from the pelvis,
leading to a pelvic tilt. This instability of the pelvis translates to
excessive strain on the vertebrae of the lower back. The very strong
muscles of the spine then contract to straighten the spine. Over
time, this strain can lead to spinal stenosis, herniation of the
intervertebral discs and the need for chiropractic care, physical
therapy, oral medications and even surgery.25
The ill effects continue up the musculoskeletal chain to involve
the upper back, and lead to a tilting of the shoulders, placing
excessive strain on the rotator cuff and, eventually, partial rupture
of these structures. Further compensation occurs in the neck,
leading to strain of the supporting tissues there. Finally, abnormal
tilting of the head can occur, leading to instability of the mandible.
The muscles supporting the normal alignment of the mandible are
then required to contract to stabilise this bone into its proper
alignment, which, if uncorrected, will lead to temporomandibular
joint disorders. 26
When comparing the possible complications of the stabilisation of
the subtalar joint complex with a sinus tarsi stent with the possible
ill effects of untreated hyperpronation, one can easily see why it is
so critical to stabilise the subtalar joint as soon as possible. Not
only can the sinus tarsi devices be used in symptomatic feet to
eliminate the cause of so many other symptoms, it can also be
used as a preventative measure to end the excessive strain and the
secondary effects of this extremely common condition.
Further research is forthcoming showing more conclusively the
functional outcomes of this extremely powerful procedure. Thanks
to the newer generation of sinus tarsi stents, many of the potential
complications caused by previous designs have been minimised or
even eliminated. This minimally invasive procedure is ideal for the
treatment of hyperpronation because it does not require prolonged
immobilisation, allows for immediate weight-bearing, can be
performed on patients as young as three years of age as long as
they have a flexible repositionable subtalar joint complex, is
reversible and does not depend on external modalities. n
Michael E Graham is in private practice at the Center
for Foot and Ankle Disorders in Shelby Township,
Michigan. He is a pioneer and innovator in the field of
subtalar arthroeresis surgery. After performing
hundreds of sinus tarsi implant procedures, he
recognised a need for improvements to the existing
implants. Using his knowledge in the area of
biomechanical foot functioning, and understanding
the ultimate need of patients, he developed the
HyProCure sinus tarsi implant. Dr Graham has lectured internationally on this
subject, and has also trained hundreds of surgeons on how to successfully perform
a subtalar arthroereisis procedure using a sinus tarsi implant in the treatment of
hyperpronation. He graduated from the Temple University School of Podiatric
Medicine in 1994, and completed a two-year surgical residency at Kern Hospital for
Special Surgery in 1996.
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Hyperpronation – The Role of Subtalar Arthroereisis
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