How To Perform An Isolated Subtalar Joint Arthrodesis

Isolated arthrodesis procedures for the hindfoot are an interesting and sometimes controversial topic for foot and ankle surgeons. Historically, when it came to most major rearfoot deformities and joint conditions, surgeons utilized the triple arthrodesis versus any isolated joint fusions of this complex. The thinking was that the subtalar, calcaneocuboid and talonavicular joints all function together to allow pronation and supination of the entire foot, so if one joint needed fusion, they all needed fusion.
The trend during the past decade or two has been more toward preserving mobility when possible. Isolated hindfoot arthrodesis procedures have been under investigation and can certainly provide solutions to a variety of rearfoot pathologies. Studies have demonstrated very satisfactory results with isolated subtalar arthrodesis procedures.1
One must consider the impact of an isolated rearfoot arthrodesis on the other two joints. Studies have demonstrated the effect of isolated rearfoot fusions and significant restriction of motion occurs at the remaining joints after one of the three joints has undergone fusion. An isolated subtalar joint arthrodesis limits talonavicular motion to about 26 percent and calcaneocuboid motion to about 56 percent.2,3
The percentage of restriction of motion obviously depends upon the position of the bones being fused. If the subtalar joint underwent fusion in supination, one would expect more restriction of the calcaneocuboid and talonavicular joints. Alternatively, if the subtalar joint underwent fusion in pronation, surgeons would expect more motion of the midtarsal complex.4-6
With an isolated rearfoot fusion, one must consider the condition of the remaining rearfoot joints. If either of the remaining joints has significant arthrosis, this lack of freedom to move will likely facilitate degeneration and intensify any preexisting symptoms. The position of the subtalar joint fusion in a more pronated position will allow more midtarsal motion whereas subtalar fusion in a more supinated position will restrict midtarsal motion. An understanding of the functional relationship between the subtalar joint and the midtarsal joint complex affords the surgeon the opportunity to optimize functional results for arthrodesis.

Key Considerations In Procedure Selection

Surgeons can perform isolated subtalar arthrodesis for a variety of conditions. The list of the most common indications includes: degenerative joint disease, talocalcaneal coalition, post-traumatic arthrosis, inflammatory arthropathy, valgus/varus deformity and hindfoot instability.
For an effective subtalar arthrodesis, proper alignment is essential for any of the indications.7,8 In most cases, one can achieve proper alignment by simple manipulation of the joint. Realignment of significant varus or valgus correction by manipulation alone is limited. Even with joint resection of the talocalcaneal articulation, correction of major hindfoot deformities is limited for an isolated arthrodesis. Movement of the calcaneus with respect to the talus may be the primary focus for realignment of the hindfoot but the calcaneocuboid and talonavicular relationship is affected by any change in position of the calcaneus. In cases of severe valgus or varus, triple arthrodesis would offer greater realignment potential.
Occasionally, surgeons may perform posterior calcaneal osteototmy in addition to an isolated subtalar arthrodesis to provide additional translation of the posterior calcaneus.9 Another unique situation is depression of the posterior facet of the talocalcaneal joint after an intraarticular calcaneal fracture. Hindfoot realignment often requires restoration of heel height via bone block distraction arthrodesis of the talocalcaneal joint.10,11
Preoperative evaluation must include consideration of the goals of the procedure to fuse the talocalcaneal joint. The importance of alignment cannot be overemphasized. The fusion position of the calcaneus with respect to the talus dictates function for the remainder of the foot, especially the midtarsal joint.
If the surgeon uses the procedure for controlling a valgoplanus foot, the subtalar joint would be positioned with the lateral process of the talus up and out of the floor of the sinus tarsi in a more supinated position. If you are utilizing the procedure to correct an over-supinated hindfoot, the opposite would be the case for positioning of the fusion. In the case of a fusion for a previous calcaneus fracture, the surgeon would be elevating the depressed posterior facet by an interpositional bone graft to restore a more anatomic relationship between the talus and calcaneus for the most functional fusion.10,11

A Step-By-Step Guide To Surgery
In regard to arthrodesis of the talocalcaneal joint, one should ensure supine positioning of the patient. Rotate the entire extremity internally with support at the ipsilateral hip to maintain the position, directing the toes toward the ceiling. The foot should extend beyond the operating table from about the ankle level. This positioning facilitates intraoperative fluoroscopy and alignment assessment.
A thigh tourniquet is routinely in place with this procedure but one usually only needs this to be inflated for a portion of the procedure. For most rearfoot/ankle reconstructive procedures, we inflate the tourniquet prior to preparing the joint surfaces for arthrodesis. We generally deflate the tourniquet prior to closure. The practice of not using the tourniquet during soft tissue dissection and closure encourages more meticulous hemostasis and leads to less postoperative bleeding, swelling and their associated complications. An alternative to this practice would be utilizing a postoperative drain.
The surgeon would most commonly perform the procedure for isolated subtalar arthrodesis through a lateral incision. However, in some cases such as severe valgus, a medial incision works well. When one is using the procedure to realign a medial facet subtalar coalition, a medial incision provides better opportunity to resect the coalition and provide realignment. Visualization of the posterior facet surfaces is better from a lateral incision than from a medial incision. The lateral incision allows access to the posterior talocalcaneal articulation as well as the medial talocalcaneal articulation for joint preparation.
I prefer making an incision from just distal to the lateral malleolus, extending distally along the floor of the sinus tarsi and stopping at the anterior process of the calcaneus. If one opts for a medial incision, it should be from posterior to anterior directly over the medial facet of the talocalcaneal joint, just as one would approach a medial facet coalition resection. This incision leads to retraction of the tibialis posterior tendon superiorly and the flexor hallucis longus tendon is inferior to the sustentaculum tali.
The exposure for joint preparation requires the release of the ligamentous structures about the talocalcaneal articulation. Through the lateral incision, elevate the extensor digitorum brevis from the floor of the sinus tarsi and do the same for the interosseous talocalcaneal ligament. Preserve the soft tissues attached to the plantar talar neck. Releasing the soft tissues of the sinus tarsi from the calcaneus and elevating them with the talus preserves the lateral vascular supply to the talus.
Release the calcaneofibular ligament and release the talocalcaneal capsule to gain access to the joints. If one is using a medial approach through the superficial deltoid ligament, release the same soft tissue structures with the exception of the extensor digitorum brevis and calcaneofibular ligament.
After releasing all ligamentous structures and visualizing the joints, use a lamina spreader to distract the posterior subtalar articulation. This facilitates joint surface preparation. Surgeons routinely use osteotomes and bone curettes to remove any articular cartilage down to healthy subchondral bone. At this point, irrigate the surgical site prior to preparing the subchondral bone. Proceed to fenestrate the bone surfaces aggressively with a 2-mm drill bit and score the bone surfaces with a saw or osteotome. This step must be aggressive to break up the subchondral cortical bone plates and encourage bone union across the joint.
The union occurs best through fragmented joint surfaces and cancellous debris acting as shear strain relief bone graft. With few areas of simple fenestration, one may only achieve the union with osseous “spot welds” that could more easily fracture and lead to nonunion. Resection of the subtalar joint is not routine unless the deformity warrants this to achieve the desired alignment. After preparing the bone surfaces, leave the osseous debris in the fusion site as bone graft and insert any additional grafting material. If one is performing a distraction bone block arthrodesis, insert a tricortical autograft after preparing the host site.

What You Should Know About Fixation And Closure

After the soft tissue releases have mobilized the joints and one has prepared the subchondral surfaces, the next step is positioning for fixation. Thoroughly evaluate the knee, leg, ankle and foot to determine the best position for fusion of the talus to the calcaneus.
Intraoperatively, one should study the relationship between subtalar position and midtarsal function. With the talus forced posteriorly and the lateral process out of the floor of the sinus tarsi, the midtarsal joint will be more stable. This may be desirable for correction of a valgoplanus foot while a more cavovarus foot structure may be better served by a subtalar joint fused with the talus more anterior on the calcaneus. At the level of the sinus tarsi, one can visualize manipulation of the talocalcaneal relationship by pulling the calcaneus anteriorly or pushing it posteriorly. The proper position is with the heel in line with the leg and in neutral to slight valgus. Optimize the midtarsal joint function by the subtalar joint position.
One can facilitate successful fixation of the fusion site via numerous methods. The most common method is screw fixation. Arthrodesis of the subtalar joint as part of a triple arthrodesis only requires one point of fixation. The fixation of the other joints of the hindfoot complex prevents motion of the subtalar joint so a single screw may suffice. For an isolated subtalar arthrodesis, two points of fixation are recommended.12 Use one screw to compress the posterior facet of the subtalar joint while a second point of fixation prevents rotation.
One may insert the primary fixation screw from the talar neck through the posterior facet and into the calcaneus, or from the posterior plantar calcaneus across the posterior facet and into the talar body. The disadvantage of the primary screw placement from the talar neck down into the calcaneus is potential neurovascular injury and anterior ankle impingement. It is generally not possible to orient this screw perpendicular to the posterior facet.
I prefer utilizing two large cannulated screws from the calcaneus into the talus through one incision. Insert the first screw from the posterior plantar calcaneus and direct it into the body of the talus. This screw compresses the posterior facet of the subtalar joint.
The second screw is slightly more medial and one should direct it more distally in the talar body or neck. This screw prevents any rotation about the first lag screw. Another option for a second screw is to insert it from the lateral process of the talus into the calcaneus. The fixation for a distraction bone block arthrodesis of the subtalar joint involves fully threaded screws or screws with threads that traverse the host graft interface. Do not use the lag technique as the purpose of the screws is to maintain the distraction and prevent collapse of the graft. Employ the same screw orientation from the calcaneus into the talus.
One must use intraoperative fluoroscopic imaging to demonstrate ideal alignment and the position of the fixation. Use lateral imaging of the hindfoot/ankle to assess the talocalcaneal relationship as well as the screw position and length. A dorsal to plantar view of the foot enables one to assess the talocalcaneal angle, midtarsal alignment and the talus to first metatarsal alignment. Surgeons should also obtain ankle mortise views to confirm position of the screws in the talar body and neck. Avoid a common malposition of the lateral screw into the lateral gutter of the ankle joint.
After completing fixation, close the deep tissues with absorbable sutures and deflate the tourniquet. Again assess hemostasis and utilize cautery as needed. One can typically close the skin with 4-0 nylon. Surgeons may inject a 19:1 mixture of bupivacaine and dexamethasone phosphate in the peri-incisional area to minimize postoperative pain.
Apply a dressing that incorporates a posterior or stirrup type splint, and instruct the patient to be non-weightbearing. The first dressing change is within the first week after surgery. At this time, one can replace the removable walking cast with the splint. Advise minimal weightbearing for the first six weeks. This is followed by weightbearing in the brace for two to four weeks until clinical and radiographic union are evident.

In Conclusion

An isolated subtalar joint arthrodesis can be very effective in alleviating painful conditions, malalignment or instability affecting this joint complex. This procedure does require consideration for its effect on the adjacent joints of the hindfoot and ankle. The joints’ position for fusion must be ideal to minimize the deleterious effects on the midtarsal joint and the tibiotalar joint. The position for fusion can effectively help control an unstable flatfoot and provide stability to the midtarsal joint.
However, bear in mind that this procedure does adversely affect the ankle by removing the hindfoot’s ability to compensate for variations in terrain during gait. The forces to invert or evert the foot will be much more significant at the ankle and midtarsal complex. This will ultimately lead to accelerated degeneration of these joints. One may advise the use of shoes and foot orthoses that serve as good “shock absorbers” for patients who have had a talocalcaneal arthrodesis.

Dr. Blacklidge is a Fellow of the American College of Foot and Ankle Surgeons. He practices at the American Health Network of Indiana.

References:

1. Mann RA, Beaman DN, Horton G: Isolated subtalar arthrodesis. Foot Ankle Int 19(8):511-519, 1998.
2. Elftman H: The transverse tarsal joint and its control. Clin Orthop Relat Res 16:41, 1960.
3. O’Malley MJ, Deland JT, Lee K: Selective hindfoot arthrodesis for the treatment of adult acquired flatfoot deformity: An in vitro study. Foot Ankle Int 16(7):411-417, 1995.
4. Mann RA, Beaman DN, Horton G: Isolated subtalar arthrodesis. Foot Ankle Int 19(8):511-519, 1998.
5. Sammarco V. The talonavicular and calcaneocuboid joints: anatomy, biomechanics, and clinical management of the transverse tarsal joint. Foot and Ankle Clinics of North America, 9(1):127-145.
6. Gellman H, et al. Selective tarsal arthrodesis: An in vitro analysis of the effect on foot motion. Foot and Ankle 1987; 8(3):127-133.
7. Easley ME, Trnka HJ, Shon LC, Myerson MS. Isolated Subtalar Arthrodesis. Journal of Bone and Joint Surgery 82:613, 2000.
8. Moss M, Radack J, Rockett M. Subtalar Arthrodesis. Clinics in Podiatric Medicine and Surgery 21(2):179-201.
9. Romash MM. Reconstructive Osteotomy of the calcaneus with Subtalar arthrodesis for malunited calcaneal fractures. Clin Orthop 1993; 290:157-67.
10. Hansen ST. Subtalar Joint Arthrodesis with Bone Block Distraction Functional Reconstruction of the Foot and Ankle. Philadelphia: Lippincott Williams and Wilkins; 2000:296-299.
11. Trnka HJ, Easley ME, Lam PW, Anderson CO, Shon LC, Myerson MS. Subtalar distraction bone block arthrodesis. Journal of Bone and Joint Surgery Br. 83(6):849-54, 2001.
12. Hansen ST. Arthrodesis Techniques Functional Reconstruction of the Foot and Ankle. Philadelphia: Lippincott Williams and Wilkins; 2000:293-305. For further reading, see “How To Address Subtalar Joint Instability” in the May 2007 issue of Podiatry Today.