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Graham_EU Musc 26/04/2010 11:03 Page 65 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. 65 Graham_EU Musc 26/04/2010 11:04 Page 66 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. 66 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 EUROPEAN MUSCULOSKELETAL REVIEW Graham_EU Musc 26/04/2010 11:04 Page 67 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 67 Graham_EU Musc 29/04/2010 12:01 Page 68 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, 68 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. EUROPEAN MUSCULOSKELETAL REVIEW Graham_EU Musc 26/04/2010 11:05 Page 69 Hyperpronation – The Role of Subtalar Arthroereisis 1. 2. 3. 4. 5. 6. 7. 8. 9. Soomekh D, Baravarian B, Pediatric and Adult Flatfoot Reconstruction: Subtalar Arthroereisis versus Realignment Osteotomy Surgical Options, Clin Podiatr Med Surg, 2006;23(4):695–708. Johnson KA, Stron DE, Tibialis posterior tendon dysfunction, Clin Orthop, 1989;239:196–206. Clark WA, A rebalancing operation for pronated feet, J Bone Joint Surg Am, 1931;13:867–71. 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