Keys To Preventing Complications With Subtalar Joint Implants

In order to reduce the risk of potential complications with subtalar joint implants, these authors offer salient tips on the diagnostic workup, an overview of the currently available implants and how to facilitate appropriate procedure selection.

   Subtalar arthroereisis can be an excellent procedure for many patients with varying degrees of pathology. It is a viable option to correct painful flexible flatfoot when other non-surgical treatments have failed. Subtalar arthroereisis is also a great option because it avoids the aggressive bony work one has to do with procedures such as osteotomies and arthrodesis. Subtalar joint (STJ) implants still allow for some rearfoot motion while eliminating excess pronation. The procedure also helps to preserve the soft tissue, resulting in a shorter immobilization period and a quicker recovery period.

   Zaret and Myerson described flexible pes planus as “dorsal and lateral peritalar subluxation of the forefoot, calcaneal eversion, collapse of the medial arch as well as medial uncovering of the talus.”1 Christensen and colleagues concluded that subtalar joint arthroereisis did not alter the normal closed kinetic chain mechanics and was therefore an effective means of altering subtalar motion.1,2 However, it is important not to overlook other components of the pes planovalgus deformity, which could require additional procedures.

   When deciding on whether to use a subtalar joint implant, there are many considerations. One must decide what type and size of implant to use. Surgeons must also determine the appropriate procedure selection and if any adjunctive procedures are necessary. By ensuring a thorough physical examination and proper surgical planning, surgeons can minimize the risk of complications with subtalar joint implants.

A Closer Look At The Evolution Of Subtalar Joint Implants

   In 1946, Chambers had described filling the sinus tarsi with bone to prevent eversion and still allow inversion.3 LeLievre first described the term arthroereisis in 1970. He used an accessory bone graft in the sinus tarsi to decrease the motion of the rearfoot and stabilized the bone graft with a staple if necessary.4 Since that time, we have seen the evolution of numerous designs of subtalar joint implants.

   Earlier models include the Viladot, which has a stem and umbrella feature to prevent pullout, and the Valenti, a threaded polyethylene plug inserted into the sinus tarsi. The STA-Peg (Wright Medical), which Smith and Millar produced, consists of a stem that inserts into the floor of the sinus tarsi while the lateral process of the talus rests on the top of the platform surface. The Sgarlato device is a mushroom-shaped peg that inserts into the floor of the sinus tarsi and limits forward motion of the lateral process of the talus.5 Maxwell and Brancheau introduced the MBA implant.6,7 It is a threaded titanium implant, which one inserts into the sinus tarsi. It became popular due to its relative ease of insertion, minimal dissection and quick recovery period.

   The Valenti and MBA arthroereisis devices are classified as “self-locking wedges,” which are implants that separate the talus and calcaneus. These implants block eversion while preventing further anterior displacement of the talus.5 These types of implants were originally designed for adolescent and adult use because of the minimal disturbance of the sinus tarsi. However, they have become increasingly popular in pediatric use as well.8,9

   The original STA-Peg device is an example of an “axis altering arthroereisis device,” which elevates a low subtalar joint axis and reduces frontal plane motion or calcaneal eversion.5,8,9 Examples of “direct impact prostheses” are the Sgarlato and the angulated STA-Peg, which “provide an impingement force against the lateral talar process as the foot attempts to pronate, thereby limiting valgus motion.”5,8,9 Researchers have noted that all age groups tolerate direct impact protheses because they did not change the axis of motion. However, it has proven to cause strain in some adult patients, leading to fracture of the implant.5,8

   Other current subtalar joint implants include: Bioarch, a conical metal implant (Wright Medical); the Conical Subtalar Joint Implant (CSI, Tornier); Prostop, a conical implant (Arthrex); HyProCure, a sinus tarsi stent (GraMedica); and bioBlock, a bioreabsorbable implant made of poly-L-lactic acid (PLLA) (Kinetikos Medical).8

   The benefits of a conical shaped subtalar joint implant include a more accurate fit into the sinus tarsi with a narrower trailing end, which can result in less pain and irritation.10 The blunt thread design offers a softer fit into the sinus tarsi with less irritation and less chance of synovitis and inflammation postoperatively. Each of these implants works by restricting forward, downward and medial displacement of the talus.11

   One study showed that the insertion of the PLLA bioabsorbable implant was virtually complication free and did not need to be removed.10 The study included 21 children, ranging from ages 8 to 15, who had bilateral symptomatic flexible flatfoot. There was a four-year follow-up period, which showed lasting correction and complete absorption of the implant. This specific implant allowed for subtalar joint adaptation and remodeling, improving and eliminating symptoms as the child matured. The absorbable capability of the implant avoids the need for implant removal and there is no loss of hindfoot correction.

What To Look For In The Patient Exam

   The first step to preventing complications with subtalar joint arthroereisis is a thorough physical and gait examination. Clinical examination should always begin with non-weightbearing evaluation of the rearfoot and forefoot.

   Green described the foot as a tripod. If one or more aspects of the tripod are out of alignment, then there will be issues with stability.12 This tripod theory allows for evaluation of planar dominance. Do not ignore deformities in each plane when considering surgery. Correction in only one plane will not fully re-establish the stability of the tripod. Correction in only one plane could actually accentuate and further deform a second plane of deformity or cause compensation, requiring additional procedures in the future.12 It is important to remember that correction of only the heel alignment, such as with a subtalar joint implant, is not addressing all the plane deformities that can often be present with symptomatic flatfoot.

   Assessment of the flexibility of each joint and its reducibility is an important aspect of the flatfoot workup.12 Subtalar joint arthroereisis is not effective in a rigid rearfoot valgus deformity. One should test both weightbearing and non-weightbearing reducibility of rearfoot valgus.

   A heel raise test can assess whether the heels will invert as a patient stands on the ball of his or her feet. Failure of the heel to invert could be caused by posterior tibial tendon dysfunction (PTTD), a ruptured PT tendon, tarsal coalition or vertical talus, and one will need to address this accordingly.12 Additional examination should include the Silfverskiold test to assess the gastroc-soleal complex as well as assessment of the resting calcaneal stance position, the “too many toes sign” and hypermobility of the first ray. Exams should also include assessing subtalar joint range of motion and strength, and whether pain is present, and the position of the forefoot when the heel is in neutral position.

   Recognition of severe forefoot varus or fixed supinatus is essential with pre-op surgical planning. If a patient already has a supinatus of the forefoot, then preventing the subtalar joint from everting with an implant will only further accentuate the forefoot supinatus and cause further problems.12,13

   One can check reducibility of a forefoot varus with the Hubscher maneuver. Dorsiflexion of the hallux and external rotation of the leg should restore the medial longitudinal arch and realign the heel to rectus. If the forefoot varus is unable to reduce, then an adjunctive surgical procedure such as a medial column osseous procedure may be warranted.5 An example would be the Cotton procedure to plantarflex the medial cuneiform using a dorsally placed bone graft.

   Evaluate the patient’s gait for heel valgus, medial arch collapse, medial talar bulge and early heel off. If equinus is present, which is often the case, one can easily correct this with a tendo-Achilles lengthening (TAL) or gastroc recession during surgery depending on the type of deformity present. Not only is it likely for the equinus to cause the progression of the painful flatfoot, addressing it early on will help prevent breakdown of the implant. Another finding to look for when assessing equinus is a patient complaint of metatarsalgia or keratodermas on the plantar aspect of the metatarsal heads.5

   During the gait examination, one should also evaluate midstance for locking of the midtarsal joint. An inability of the midtarsal joint to lock results in continual collapse of this joint, which one sees with transverse plane dominant deformities.5,13

   One can also test this with the patient non–weightbearing. With the patient’s rearfoot in the neutral position as well as in a supinated position, one should put the midtarsal joint through range of motion in order to test for locking capability. If the patient’s midtarsal joint continues to pronate and remains unlocked with the subtalar joint in a neutral or supinated position, then the patient is a poor candidate for arthroereisis. One will not be able to correct the underlying deformity with an arthroereisis alone.

   Always take radiographs of the foot and ankle. Always evaluate the talar-first metatarsal angle and the calcaneal inclination angle. Check for the presence of an accessory navicular, which can contribute to pain and surgical decisions. Other deformities that one should rule out for causes of flatfoot include ankle valgus, a ball and socket ankle, diastasis and subtalar joint coalition. In all these cases, an arthroereisis would be contraindicated.

   Again, it is crucial to examine the patient thoroughly and always have a high index of suspicion for other causes of the painful flatfoot deformity. Not addressing all deformities will result in lower success rates when it comes to subtalar arthroereisis.

Key Considerations With Procedure Selection

   One of the best ways to prevent complications with the use of subtalar joint implants is to avoid an improper procedure choice. This means adequately working up every aspect of the patient’s deformity and taking other deformities into account. While many patients could benefit from subtalar arthroereisis, they may benefit with it being an adjunctive procedure as opposed to a primary procedure.

   There is usually an underlying cause for a symptomatic flexible flatfoot. This cause can be PTTD, neuromuscular origin as one might detect in children, ligamentous laxity or equinus. Surgeons can greatly improve the surgical outcome by addressing these deformities at the same time, whether it is via a flexor digitorum longus (FDL) to PT transfer, PT tendon repair, a Kidner procedure and/or spring ligament repair, medial calcaneal osteotomy (MCO) or TAL or gastrocnemius recession.

   When it comes to the mild type II PTTD, Schon suggests that an arthroereisis may be enough to restore the normal function of the subtalar joint while eliminating the need for a calcaneal osteotomy.10 However, in regard to the more severe type II PTTD, he prefers to do an arthroereisis in combination with a medial calcaneal osteotomy and a FDL to PT transfer to ensure adequate correction. He will then perform heel cord lengthening or an opening wedge medial cuneiform osteotomy for residual deformity.

How To Ensure Proper Patient Selection

   Although one can use subtalar joint implants in children as well as adults, one needs to be mindful of the differences in anatomy and pathologies.

   Bones in children are much softer and will accommodate to a sinus tarsi implant easier. Their deformities are usually flexible and a bone procedure is not warranted in children. When it comes to the pediatric patient, the goal is that the subtalar joint implant will realign the talus over the calcaneus and allow for subtalar joint remodeling. This can help prevent future problems such as degenerative joint disease when these patients are adults.1

   However, joint adaptation over the years due to a neglected painful flatfoot can cause a once flexible flatfoot to become rigid in an adult. For these patients, one should avoid performing a subtalar joint arthroereisis procedure as the sole procedure. Not only will it not correct the underlying cause of the deformity but the patient will not tolerate the device well.

   Other contraindications to a subtalar arthroereisis discussed by Dockery and Crawford include: a rigid flatfoot that is irreducible; a rigid rearfoot varus; degenerative joint disease (DJD) or arthritis of the subtalar joint; poor bone stock; skewfoot; severe obesity, asymptomatic flatfoot; and patients less than 3 years old.13

   As most of us know, healing a wound in a patient with diabetes or vascular impairment can be quite the challenge. One benefit of subtalar joint implants is being able to perform the procedure through minimal incision sites. Minimal incisions facilitate a lower risk of infection and non-healing wounds. A subtalar joint implant can also be a good choice for an elderly patient because a long post-op immobilization period is not necessary. Accordingly, there is less need to worry about patient adherence or a risk of falling.

Pertinent Pointers On Surgical Technique

   When following the standard insertion protocol of a subtalar joint implant, it is important to assess the position and motion of the hindfoot after the insertion of each sizer. If excessive eversion is still present with the sizer in place, then the sizer is too small. If the sizer is too large, the heel and forefoot will be in a varus position. The correct size should limit abnormal eversion but not cause a varus position of the heel. When considering a subtalar joint implant, remember that the appropriate size should allow for about 2 to 4 degrees of subtalar joint eversion.5 This is an extremely important consideration when assessing implant sizes.

   Intraoperative fluoroscopic examination of the placement of the implant is also an essential step. A true AP X-ray is necessary to view the location of the implant. Proper placement of the subtalar joint implant should show the leading medial edge of the implant not crossing over the longitudinal bisection line of the talus.13 Reversal of the implant is advised if the implant is over this talar bisection.

In Conclusion

   When it comes to subtalar joint implants, the benefits include a less invasive technique, overall ease of the procedure and the ability to allow some rearfoot motion. Minimal dissection allows for a quick recovery period and short immobilization time, speeding up healing time and reducing the chances of complications and non-adherence. The overall technical ease also makes this a good procedure choice while still providing a good reduction of eversion and pain. However, it is important to ensure a thorough history and examination, and pay sharp attention to detail during the insertion of the implant.

   Although it can be tempting to do a quick and simple surgery like an arthroereisis as the sole procedure, it may prove to be ineffective in the long run when adjunctive procedures could have facilitated a different outcome. Resisting this temptation and remembering the aforementioned steps can help prevent subtalar joint implant failure, improve postoperative success and prevent the need for further procedures in the future.

Dr. DeHeer is a Fellow of the American College of Foot and Ankle Surgeons, and is a Diplomate of the American Board of Podiatric Surgery. He is also a team podiatrist for the Indiana Pacers and the Indiana Fever. Dr. DeHeer is in private practice with various offices in Indianapolis.

Dr. Malenkos is a second-year resident at Westview Hospital in Indianapolis.

For further reading, see “Assessing The Pros And Cons Of Subtalar Implants” in the May 2006 issue of Podiatry Today and “Techniques And Experiences In Foot And Ankle Surgery,” a supplement to the August 2006 issue.

References:

1. Zaret D, Myerson M. Arthroereisis of the subtalar joint. Foot Ankle Clin 2003; 8(3):605-617. 2. Christensen JC, Campbell N, DiNucci K. Closed kinetic chain tarsal mechanics of subtalar joint arthroerisis. J Am Podiatric Med Assoc 1997; 86(10):467-73. 3. Chambers EFS. An operation for the correction of flexible flatfeet of adolescents. Surg Gynecol Obstet 1946; 54:77. 4. LeLievre J. Current concepts and correction in the valgus foot. Clin Orthop 1970; 70:43-55. 5. McGlamry ED. Subtalar joint arthroereisis. In: Banks AS, Downey MS (eds.) Comprehensive textbook of foot and ankle surgery, vol. 3, chapter 27. Lippincott, Williams and Wilkins, Philadelphia, pp. 901-14, 2001. 6. Maxwell JR, Carro A, Sun C. Use of the Maxwell-Brancheau arthroereisis implant for the correction of posterior tibial tendon dysfunction. Clin Pod Med Surg July 1999; 16(3):479-489. 7. Maxwell JR, Knudson W, Cerniglia M. The MBA arthroereisis implant: early prospective results. In Vickers NS, Miller SJ, Mahan KT, et al (eds): Reconstructive Surgery of the Foot and Leg: Update 1997. Podiatry Institute, Tucker, GA, pp. 256-64, 1997. 8. Vogler H. Subtalar joint blocking operations for pathological pronation syndromes. In: McGlamry ED (ed.) Comprehensive textbook of foot surgery. Lippincott, Williams and Wilkins, Philadelphia, pp. 466-482, 1984. 9. Yu GV. Subtalar arthroereisis. In: McGlamry ED, Banks A, Downey M. Comprehensive textbook of foot surgery, Lippincott, Williams and Wilkins, Philadelphia, pp. 818-828, 1992. 10. Schon L. Subtalar arthroereisis: a new exploration of an old concept. Foot Ankle Clin 2007; 12(2):329-339. 11. Dockery G, Crawford M. Subtalar arthroereisis: The Maxwell-Brancheau (MBA) implant. In: Chang T (ed.) Master techniques in podiatric surgery: the foot and ankle. Lippincott, Williams and Wilkins, Philadelphia, 2004. 12. Green DR, Carol A. Planal dominance. J Am Podiatry Assoc 1984; 74(2):98-103. 13. Soomekh D, Baravarian B. Pediatric and adult flatfoot reconstruction: subtalar arthroereisis versus realignment osteotomy surgical options. Clin Pod Med Surg 2006; 23(4):695-708.