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Emerging Insights On Arthroscopic Subtalar Fusion

Arthroscopic subtalar joint fusion can provide better visualization to prepare joint surfaces, good union rates and fewer complications in comparison to an open arthrodesis. Discussing the lateral and posterior approaches to the procedure, these authors offer a thorough review of the literature as well as pearls from their experience.

Arthrodesis of the subtalar joint is a widely accepted and well-established surgical treatment for advanced subtalar joint disease that has failed conservative treatment. Underlying pathologies often include post-traumatic or degenerative arthrosis, talocalcaneal coalition, complex hindfoot deformity, inflammatory arthropathy or advanced posterior tibial tendon dysfunction. Patients commonly present with lateral hindfoot or sinus tarsi pain and difficulty with hindfoot frontal plane motion, which becomes more evident with ambulation on uneven ground or steep inclination/declination.1,2

Conservative treatment options for subtalar joint pain include weight loss, oral analgesics, shock-absorptive shoe gear modifications and orthoses designed to limit hindfoot range of motion.1 A corticosteroid and/or local anesthetic injection into the subtalar joint may also be of diagnostic and potentially therapeutic benefit to the patient.1

While arthrodesis of the subtalar joint is the definitive surgical treatment when conservative treatments fail, it is not without risks. Complications include delayed union or non-union, painful hardware, infection, delayed wound healing or incisional dehiscence, damage to neurovasculature, under- or overcorrection of hindfoot deformity and venous thromboembolism.3,4 In general, these risks are higher in patients with obesity, diabetes, rheumatologic arthritides, neurovascular disorders, tobacco use and non-adherence with weightbearing in the postoperative period.5 Chances of clinical success are also greater in those without an associated deformity at the level of the subtalar joint. Tuijthof and colleagues reported 65 percent clinical success for arthrodesis in those with subtalar joint deformity versus 85 percent success in those without the deformity.5

The surgical approach for subtalar joint arthrodesis has been the topic of many publications and surgical technique guides. Surgeons can perform a subtalar joint arthrodesis through either an open or arthroscopic approach. The traditional open approach to the subtalar joint has been criticized for an increased risk of incision healing complications, wound infection and neurovascular damage.5

In 1985, researchers first described an arthroscopic approach to the subtalar joint in the literature and in 1994, surgeons first utilized this approach for subtalar joint arthrodesis.6,7 Since then, there have been several cadaveric studies, technique guides and small case series focused on arthroscopic subtalar joint arthrodesis. More recently, larger case series have broadened our understanding of this technique.3,8 An overall increasing body of research on this topic has demonstrated a growing interest and utilization of the arthroscopic approach to subtalar joint arthrodesis.

Comparing Open Versus Arthroscopic Approaches

Surgical outcomes following a traditional open approach to subtalar joint arthrodesis have been widely studied and reported. This approach is preferable for patients with extensive hindfoot deformity or osseous defects, which surgeons must address with a corrective osteotomy or significant bone grafting.1,2,5 Overall, there is a high rate of clinical success following subtalar joint arthrodesis but those requiring hindfoot deformity correction have experienced less favorable outcomes.5

The open approach utilizes a relatively large incision, which carries an increased risk of post-op complications, including infection, neurovascular damage and delayed wound healing.1,5 With recent trends toward minimally invasive surgery in the foot and ankle, authors have also described a minimal incision approach to subtalar arthrodesis.9 Minimal incision subtalar joint arthrodesis with a sinus tarsi and posterior incisional approach has similar union rates and clinical outcomes as the traditional open approach, and authors have proposed minimal incision for patients at risk of wound healing complications.9

Those in favor of the arthroscopic approach claim it better preserves the blood supply to the talus, reduces postoperative morbidity and decreases both the time to union and return to activities.1 However, an arthroscopic approach, either lateral or posterior, is more demanding in terms of surgical skills, and is not indicated in patients with hindfoot malalignment or significant bone loss at the site of arthrodesis.5 Authors have reported better clinical outcome measures in terms of union rate, outcome scores and complication rate for arthroscopic subtalar joint arthrodesis, but patient selection for an arthroscopic approach excludes those with significant hindfoot deformity.10

In 2016, a retrospective review by Rungprai and colleagues of 121 patients comparing an open versus a posterior arthroscopic approach found no significant difference in the groups when comparing union rate, and both groups had significant clinical improvement.8 The study researchers chose surgical technique based on surgeon skill, preference and the presence of deformity. Sural nerve injury and painful surgical scars were more frequent in the open group but the arthroscopic group was associated with a greater frequency of hardware-related symptoms. Time to union and return to work, daily living and sports were significantly shorter in the arthroscopic group.

An earlier comparative study by Scranton in 1999 found decreased length of hospital stay in the arthroscopic group but no difference in tourniquet time or hardware removal.11

What You Should Know About The Lateral Arthroscopic Approach

When accessing the subtalar joint from a lateral approach for arthroscopy, the patient must be in a lateral decubitus position. This position allows for forced varus of the foot to open the sinus tarsi and increase access to the lateral joint.12 This approach requires resection of the interosseous talocalcaneal ligament in order to fully access the subtalar joint.12 The main risks associated with the anatomic location of portal sites for a lateral approach include damage to the peroneal tendons and superficial peroneal or sural nerves. Authors have described both a two-portal and three-portal approach for arthroscopic subtalar arthrodesis.1,3 Surgeons have also utilized a lateral sinus tarsi approach to the subtalar joint for arthroscopic triple arthrodesis procedures.13,14

For a two-portal lateral approach, place the posterolateral portal just lateral to the Achilles tendon and place the anterolateral portal in the central sinus tarsi, 1 cm distal and 1 to 2 cm anterior to the distal fibular tip.10 In 2007, Glanzmann and Sanhueza-Hernandez reported on a series of 41 subtalar joint fusions utilizing this lateral two-portal approach.10 They reported an overall fusion rate of 100 percent at a mean of 11 weeks, significant improvement in outcome scores, one case of peroneal tendonitis and no cases of nerve injury.

Researchers have described an alternative two-portal lateral approach in which one places the middle portal just anterior and distal to the distal fibular tip, and places the anterior portal 0.5 cm above the tip of the anterior process of the calcaneus.15 In 2013, Lintz and coworkers demonstrated with a cadaveric study that this two-portal technique allows for access to more than 90 percent of the posterior facet for joint preparation while decreasing the risk of sural nerve or small saphenous vein injury associated with a posterolateral portal.15 The authors reported no nerve injuries and a 10 percent incidence of peroneus brevis tendon injury, all in cases where surgeons mistakenly placed the middle portal posterior to the distal fibular tip.

In 2018, Walter and colleagues reported on a series of 77 arthroscopic subtalar joint fusions through a similar two-portal sinus tarsi approach.3 They reported an overall fusion rate of 97 percent at a mean of 15 weeks. Complications included superficial infection in 1 percent, partial sural nerve injury in 1 percent, flexor hallucis longus tendon injury with subsequent rupture in 1 percent and deep venous thrombosis in 1 percent.
For a three-portal lateral approach, place the anterolateral portal 1 cm distal and 2 cm anterior to the distal fibular tip. Place the middle portal over the sinus tarsi 1 cm anterior to the distal fibular tip and place the posterolateral portal 0.5 cm proximal to the distal fibular tip, just lateral to the Achilles tendon.1 In 2009, Ahn and colleagues reported on 26 arthroscopic subtalar joint fusions utilizing a similar three portal lateral approach.16 They reported a 97 percent satisfaction rate, an increase in outcome scores postoperatively and no serious complications.

A Guide To The Posterior Arthroscopic Approach To Subtalar Fusion

Our preferred arthroscopic approach is posterior with the patient in prone positioning. Prone positioning allows for ankle joint and subtalar joint range of motion off the edge of the bed.1 Advantages of the posterior approach include better evaluation of the hindfoot and the opportunity to visualize the ankle joint through the same portals.8 Prone positioning also allows for better ergonomics for screw placement. However, the surgeon should take care to position and accommodate the patient properly to reduce risks, such as orbital, cervical and brachial plexus injuries that are associated with prone surgeries of any kind.12 In comparison with other approaches, while the posterior approach does allow adequate visualization of the subtalar joint, it may be necessary to resect more bone to reach the most distal aspect of the joint.

Researchers have also described two- and three-portal posterior techniques.1,8,17-19,20 For a two-portal posterior approach, place the posterolateral portal just lateral to the Achilles tendon and place the posteromedial portal just medial to the Achilles tendon, both at the level of the subtalar joint.17 For a three-portal posterior approach, place the first two portals similarly and place an additional accessory portal posterolaterally, 1 cm proximal and 1 cm posterior to the tip of the lateral malleolus.8 One can also place the accessory portal at the sinus tarsi.1

In 2011, Mouilhade and coworkers carried out a cadaveric study utilizing a two-portal posterior approach, which demonstrated complete access to the talar and calcaneal articular surfaces of the posterior facet for joint preparation.21 They noted a single incidence of partial sural nerve laceration (10 percent).

In 2017, Oliva and colleagues published a review of 19 cases of arthroscopic subtalar arthrodesis with a two-portal posterior approach.22 They reported a fusion rate of 94 percent at a mean of nine weeks and noted a significant improvement in outcome scores. The authors noted a single case of neuropraxia to the plantar foot.

Donnenwerth and Roukis completed a systematic review of posterior two portal hindfoot endoscopy in 2013.23 The authors noted an overall incidence of complications of 3.8 percent with the most common complication involving wound healing. Secondary surgeries were required in 1.8 percent of the reviewed cases.

Other Pertinent Considerations With The Arthroscopic Subtalar Joint Arthrodesis

The most important prerequisites for arthroscopic arthrodesis of the subtalar joint are the surgeon’s comfort and skill level. While similarities exist between ankle joint arthroscopy and subtalar joint arthroscopy, a unique skill set is required to successfully perform an arthroscopic subtalar arthrodesis. The flexor hallucis longus is an important landmark in both approaches, indicating proximity to the medial ankle neurovascular bundle.1,23

Walter and colleagues reported damage to the flexor hallucis longus tendon during arthroscopic debridement through the sinus tarsi approach in their 2018 publication.3 With either the open or arthroscopic approach, the pathologic subtalar joint may be obscured by fibrosis, osteophytes and joint space narrowing. Distraction may be necessary to enter the joint. Options for distraction include manual traction, intra-articular trocar placement or external distraction devices.

Once one is within the joint, the surgeon can employ a combination of shavers, curettes, burrs and osteotomes to remove cartilage. Surgeons should remove cartilage completely to the level of subchondral bone as always indicated with arthrodesis. Several authors report the use of adjunctive biologics at the arthrodesis site to encourage successful union and fill any defects.8,10

Fixation usually includes perccutaneous insertion of one, two or three screws into the posterior plantar aspect of the calcaneus toward the talus. We recommend a two- or three-screw method to provide additional points of fixation, and limit rotational forces across the healing joint surfaces.

A recent retrospective review by Vila Y Rico and colleagues in 2018 compared three different fixation constructs for arthroscopic subtalar joint fusion: a single 6.5 mm screw, a single 7.3 mm screw and two 7.3 mm screws.24 The authors reported an overall fusion rate of 95 percent with a significantly higher rate of non-union in the group utilizing a single 6.5 mm screw for fixation. Another author began a study using two screw fixation and then switched to a single screw construct without any significant change in outcomes, and an assumed reduction in operating time and cost.3

The postoperative protocol varies with each physician’s personal preferences and the relationship with each individual patient. Our general recommendation is strict non-weightbearing until skin incisions have healed. As bone begins to fuse at six to eight weeks, the patient may begin weightbearing in a protective boot. We recommend obtaining postoperative imaging at eight weeks to assess for osseous healing and hardware integrity.

In Conclusion

Recent trends toward minimally invasive surgical techniques have contributed to a growing interest and popularity of arthroscopy in general. Researchers have shown that subtalar joint arthrodesis through an arthroscopic approach decreases rates of certain complications but the indication for this approach is somewhat limited. A traditional open approach is more appropriate and predictable in patients who require correction of significant hindfoot deformity or bone grafting.

The primary benefit of arthroscopic subtalar arthrodesis is a reduced risk of incision-related complications such as infection, delayed wound healing and incisional dehiscence. An arthroscopic approach may allow adequate visualization and preparation of the joint surfaces, and reported union rates for this approach equal those of an open approach. While there is some evidence an arthroscopic approach provides better clinical results, arthroscopic studies tend to exclude patients with deformities that put them at a higher risk of failure regardless of approach.5 In the appropriate patient population, and with adequate training and experience, an arthroscopic approach to subtalar joint arthrodesis can minimize wound complications while providing good overall clinical results.

Dr. Barton is a first-year podiatric medicine and surgery resident with the Gundersen Medical Foundation in La Crosse, Wis.

Dr. Cifaldi is a first-year podiatric medicine and surgery resident with the Gundersen Medical Foundation in La Crosse, Wis.

Dr. Roukis is attending staff in the Orthopedic Center with the Gundersen Health System in La Crosse, Wis. He is a Past President and a Fellow of the American College of Foot and Ankle Surgeons. Dr. Roukis has disclosed that is a consultant for DePuy Synthes, FH ORTHO, Integra and Novastep, and receives royalties from CrossRoads Extremity, Novastep and Stryker Orthopaedics.

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By Ellen C. Barton, DPM, Andrea J. Cifaldi, DPM, and Thomas S. Roukis, DPM, PhD, FACFAS
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