Correcting Flexible Flatfoot With Subtalar Arthroereisis

In 1946, Chambers proposed a novel approach to correcting flexible flatfoot deformity by placing a wedge on the superior surface of the calcaneus to prevent anterior displacement of the talus, limiting hindfoot pronation and correcting the deformity.¹ In 1962, Haraldsson became a pioneer in the development of this procedure by inserting a cortical wedge bone graft into the sinus tarsi.¹ LeLievre coined the term “arthroereisis” in 1970, with the author detailing a bone graft insertion into the sinus tarsi fixated with a staple.¹ Subotnick’s idea of utilizing a synthetic silicone implant in the sinus tarsi emerged in 1974. This was followed by the introduction of a cup shaped implant by Viladot in 1992.¹  

Understanding the anatomy and biomechanics of the subtalar joint has influenced the modern implant designs and techniques that surgeons use today. To review, the subtalar joint is formed by the articulation of the talus and calcaneus, supported by several ligamentous structures. The joint contains 3 articular facets located on the superior aspect of the calcaneus and the inferior aspect of the talus. The space between the articular surfaces structurally creates the sinus tarsi.² In the pathologic flexible flatfoot during gait and with weight-bearing, there is medial rotation and plantarflexion of the talus, in addition to eversion of the calcaneus leading to collapse of the medial arch and abduction of the forefoot. The repetitive pronation leads to pain along the medial column and subsequent symptomatic flatfoot deformity.³

Insights on the Clinical Assessment of Flexible Flatfoot

Flexible flatfoot deformity may present differently in different age groups. Younger children often receive referrals from pediatricians or present with concerned parents who note the child’s flatfoot structure or abnormal gait pattern.⁴ In contrast, adolescents may report pain and/or difficulty with sport activities. The pathologic development of this deformity can be influenced by various factors such as equinus, compensating metatarsus adductus, internal tibial torsion, and compensations for forefoot valgus or varus.⁴

Clinical examination should include assessment of hip and knee alignment, as well as range of motion of the ankle, rearfoot, and forefoot joints. In order to delineate between a rigid and flexible pes planus deformity, the provider should assess single and double heel rise, as well as utilize the Hubscher maneuver. This is important for preoperative surgical planning, as arthroereisis is best suited for a flexible deformity. Other specific signs for pes planus evaluation include a posterior tibial tenderness, prominent navicular, equinus deformity, and “too many toes” sign, seen on standing evaluation secondary to forefoot abduction.⁴

X-rays and advanced imaging may help assess the severity, nature of the deformity, and guide surgical planning.

A Guide to the Utility of Subtalar Arthroereisis

Foot and ankle surgeons widely adopted subtalar arthroereisis in the 1970s but the procedure has since fluctuated in popularity among practitioners. A survey conducted in 2013 on a total of 572 physicians noted 273 physicians (48%) had performed a subtalar arthroereisis, and 187 (69%) out of those 273 physicians continue to perform subtalar arthroereisis today in their practice.⁵ Despite the paucity of literature on the topic, the question remains, is subtalar arthroereisis still a valuable treatment option to address flexible pes planus deformity today?

Subtalar arthroereisis is primarily indicated for patients with the goal of joint salvage, serving as a potential option not only for the pediatric population, but also in adults for correcting flexible flatfoot secondary to posterior tibial tendon dysfunction (PTTD), although the adult literature on this procedure is limited.¹ Tahririan and colleagues identified 2 subtypes of flexible pes planus in pediatric and young adult populations, recommending lateral column lengthening for individuals with forefoot abduction and arthroereisis for those presenting with limited forefoot abduction but excessive subtalar eversion.¹

Based on the literature, it is generally advised to perform arthroereisis for patients between ages 8 to 14 to achieve optimal outcomes.⁶ Subtalar arthroereisis is contraindicated in cases of rigid pes planus as these patients are often better served with joint destructive procedures. Other contraindications include a history of prior sinus tarsi surgery or subtalar joint trauma.¹

What Are the Types of Implants?

Researchers have described and developed several arthroereisis implants throughout the years. Volger initially classified the available implants into 3 different categories: axis-altering, impact-blocking, and self-locking wedges.³

The axis-altering prostheses function with a stem vertically fixed into the tarsal sinus floor and the head of the implant contacts the lateral talar process, altering subtalar joint axis and motion. Impact-blocking devices are similar, but the head of the implant is more anterior against the lateral talar process, which serves to limit anterior translation and internal rotation. One would place self-locking implants into the tarsal sinus to support the talar neck. The implant avoids contact with the lateral talar process and sinus tarsi floor. This implant type limits plantarflexion and talar adduction.^2,3,6,7

Bioabsorbable implants have also been developed to reduce the rate of potential implant removal. A review by Faldini and colleagues looked at outcomes following bioabsorbable arthroereisis implantation, which proved to be difficult to compare to nonabsorbable implants because the indications, adjunctive procedures, and follow-up periods differed between studies.⁸ Overall, bioabsorbable implants had similar mid-term clinical outcomes compared to nonabsorbable implants if the surgeon utilized the proper surgical technique. Note that a rare inflammatory reaction to the material may occur, but this typically resolves as the implant resorbs.⁸

A Guide to the Surgical Technique

The surgical technique varies and is dependent on the type of implant. The procedure is typically minimally invasive, involving a small lateral incision approximately 1 cm anterior and inferior to the tip of the lateral malleolus.

Blunt dissection should extend down into the sinus tarsi. For self-locking implants, a blunt probe can help to find the tunnel direction, and progressive size implant trials determine appropriate implant selection. After determining the appropriately sized implant, the hindfoot supinates into the corrected position, and the surgeon places the implant and checks it under fluoroscopy. For impact-blocking devices, one will then place a guidewire into the talus in a retrograde fashion, or into the calcaneus in an antegrade fashion. Next, using a drill over the guidewire will allow placement of a screw or implant device.^1,3

Typical postoperative protocol involves immediate weight-bearing if the patient has the procedure in isolation. If the surgeon is performing an adjunctive procedure, then one should utilize the standard period of non-weight-bearing for that procedure.³ Other common adjunctive soft tissue procedures include gastrocnemius recession, tendo-Achilles lengthening, posterior tibial tendon repair and flexor digitorum longus tendon transfer. One may also complete bony procedures in addition to arthroereisis implantation including accessory navicular resection, coalition resection and calcaneal osteotomies.⁸

What Are the Potential Complications?

The complications for subtalar arthroeresis fall into 4 main categories, which include inappropriate procedural selection, surgeon technical error, adaptation/irritation, and failure of the implant (Figures 1–2).³

The most common complication is persistent sinus tarsi pain, which requires implant removal in approximately 10–40% of patients.⁹ Fortunately, implant removal nearly completely alleviates the pain, and research has shown that the correction maintains over time.^3,6 Inappropriate implant sizing may also necessitate implant removal due to over- or undercorrection of the deformity.⁹ Cook and colleagues retrospectively reviewed patients requiring arthroereisis explanation, finding that removal was often associated with smaller implant sizing.⁷ The smaller implant led to undercorrection with persistent pronation and residual deformity.⁷ The literature is limited regarding complication rates, and higher quality studies are needed to determine the true risk/benefit for arthroereisis implantation.

Insights on Implant Longevity and Outcomes

In terms of implant longevity, studies show implant removal timeframe is highly variable.¹⁰ Researchers have hypothesized that retaining the implant for at least 2 years could facilitate soft tissue and bone adaptation. However, there is currently no available data supporting the optimal duration of implantation for sustaining long-term correction.³ Some authors believe the implants should be removed at skeletal maturity.¹⁰ Roth and colleagues suggest removing implants after approximately 30 months, although Konig and colleagues suggest routine implant removal at 1 year postoperative.¹⁰ Based on the literature, there is no clear consensus regarding implant removal timeframe and necessity.

There is a scarcity of high-quality prospective studies assessing arthroereisis long-term outcomes. Recently, a large systematic review by Smith and colleagues assessed 2550 feet.¹¹ This study reported radiographic, kinematic, and clinical outcomes. Radiographically, all postoperative films had notable improvement in angles including calcaneal inclination, AP talar calcaneal angle, AP talar first metatarsal angle, and lateral talar first metatarsal angle. The review only recorded patient satisfaction in 4 of the 24 included studies. Approximately 80% of patients reported excellent outcomes postoperatively, 15% reported good and 5% reported a poor outcome. Only 181 complications arose among the 2550 feet and only 29 of those 78 patients required revision surgery due to pain.¹¹

A study by García Bistolfi and colleagues looked at functional and radiographic outcomes in patients with an average 5-year follow-up.¹² The retrospective study included 14 pediatric patients treated with self-locking wedge arthroereisis implants. Radiographically, all assessed angles improved significantly; however, only the talar declination angle and Kite’s angle reached normal values. Of the 9 patients researchers followed for 5 years, none developed signs of subtalar joint osteoarthritis. VAS and AOFAS scores assessed patients’ pre- and postoperative pain and function, which revealed statistically significant improvement. In this study, no implants were removed for breakage, migration or pain.¹²

Mazzotti and colleagues assessed 34 pediatric patients at an average of 15 years postoperative and noted 70% of patients maintained a physiologic footprint and proper hindfoot alignment, and 30/34 patients reported satisfaction from the procedure.¹³ The overall heterogeneity of outcome reporting between available studies creates a challenge when attempting to demonstrate the comprehensive understanding of the procedures ability to truly treat and correct the deformity.¹³

In Conclusion

The available limited literature suggests that subtalar arthroereisis may be a good potential treatment option for addressing flexible flatfoot in the appropriately selected patient. Overall, the most common complication appears to be persistent sinus tarsi pain, which fortunately responds well to implant removal. Regarding implant longevity, the duration of implantation in relation to maintaining correction remains uncertain. Lastly, while most available literature supports the use of arthroereisis for the treatment of flexible flatfoot deformity, there is still ongoing debate regarding its outcomes and overall success.

Sara Judickas, DPM, is a third-year resident at Grant Medical Center Foot and Ankle Surgical Residency in Ohio.

Meghan Roby, DPM, is a third-year resident at Grant Medical Center Foot and Ankle Surgical Residency in Ohio.

Ian Barron, DPM, FACFAS, is an Assistant Professor in the Department of Orthopedics at UT Health Science Center San Antonio.

References

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