Issue: April 2006

ByCarol C. Frey, MD

April 01, 2006

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Subtalar arthroscopy: indications, equipment and technique

Issue: April 2006

ByCarol C. Frey, MD

Carol C. Frey, MD [photo]
Carol C. Frey

Indications for subtalar arthroscopy include the following: chondromalacia, subtalar impingement lesions, osteophytes, lysis of adhesions with post-traumatic arthrofibrosis, synovectomy and the removal of loose bodies.

Other therapeutic indications include: instability, debridement and treatment of osteochondral lesions, retrograde drilling of cystic lesions, evaluation of coalition, removal of a symptomatic os trigonum, evaluation and excision of fractures of the anterior process of the calcaneus and lateral process of the talus, and subtalar fusion.

Contraindications

Contraindications to subtalar arthroscopy include infection and advanced degenerative joint disease with deformity. Relative contraindications include severe edema, poor vascularity, and poor skin quality.

Equipment:

a 2.7-mm 30º short arthroscope;
a small joint shaver set with a 2-mm and 2.9-mm shaver blade and small abrader;
an arthroscopic pump;
normal saline and a gravity system; and
an 18-gauge spinal needle.

Distraction is obtained using normal saline and a gravity system 18-gauge spinal needle.

For arthroscopic purposes, the subtalar joint is divided into anterior (talocalcaneonavicular) and posterior (talocalcaneal) articulations. [Figs. 1A, B] The anterior and posterior articulations are separated by the tarsal canal, which has a large lateral opening called the sinus tarsi.

Within the tarsal canal and sinus tarsi, the interosseous talocalcaneal ligament, the medial and intermediate roots of the inferior extensor retinaculum, the cervical ligament, fatty tissue and blood vessels are found. The lateral ligamentous support of the subtalar joint consists of the lateral talocalcaneal ligament, the posterior talocalcaneal ligament, the lateral root of the inferior extensor retinaculum, and the calcaneofibular ligament.

The anterior subtalar joint is generally thought to be inaccessible to arthroscopic visualization because of the thick interosseous ligament that fills the tarsal canal. Because of this, the region normally has no connection with the posterior joint complex.

The posterior subtalar joint has a synovial lining. This joint has a posterior capsular pouch with small lateral, medial and anterior recesses.

Portal placement and safety

Three standard portals are recommended for visualization and instrumentation of the subtalar joint. The anatomic landmarks for lateral portal placement include the lateral malleolus, the sinus tarsi and the Achilles tendon. The anterior portal is established approximately 1 cm distal to the fibular tip and 2 cm anterior to it. [Fig. 2] The middle portal is just anterior to the tip of the fibula, directly over the sinus tarsi. The posterior portal is approximately one finger width proximal to the fibular tip and 2 cm posterior to the lateral malleolus. Careful dissection and portal placement help avoid the superficial peroneal nerve branches with placement of the anterior portal and the sural nerve and peroneal tendons with placement of the posterior portal.

Surgical technique

Local, general, spinal or epidural anaesthesia can be used for this procedure. The patient is placed in the lateral decubitis position with the operative extremity draped free. [Figure 3] Padding is placed between the lower extremities, as well as under the contralateral extremity to protect the peroneal nerve. A tourniquet is recommended.

The anterior portal is identified first with an 18-gauge spinal needle and the joint is inflated with a 20-cc syringe. A small skin incision is made and the subcutaneous tissue is gently spread using a straight mosquito clamp. A cannula with a semi-blunt trocar is then placed, followed by a 2.7-mm, 30º oblique arthroscope. The middle portal is placed under direct visualization using an 18-gauge spinal needle and outside-in technique. The posterior portal can be placed at this time using the same direct visualization technique.

The trocar is placed in an upward and slightly anterior manner. The portal is usually safe when placed behind the saphenous vein and sural nerve, and anterior to the Achilles tendon. With placement of the posterior portal, care must be taken to avoid the sural nerve.

The best portal combination for access to the posterior joint includes placement of the arthroscope through the anterior portal and instrumentation through the posterior portal. This allows direct visualization and access of nearly the entire surface of the posterior facet, posterior aspect of the ligaments in the sinus tarsi, the lateral capsule and its small recess, Steida’s process (os trigonum), and the posterior pouch of the posterior joint with its synovial lining.

The structures in the sinus tarsi, the anterior process of the calcaneus, and occasionally the anterior joint, can be visualized best by placing the arthroscope through the anterior portal and instrumentation through the middle portal. This portal combination is recommended for visualization and instrumentation of the sinus tarsi and anterior aspects of the posterior subtalar joint.

If the ligaments that insert on the floor of the sinus tarsi are torn, damaged or need debridement, the anterior joint can be visualized and accessed with this portal combination. Furthermore, this portal combination allows excellent visualization and access to the anterior process of the calcaneus.

Fig. 1: First view of sinus tarsi with posterior facet and interosseous ligaments to the right before debridement.

Fig. 2: Posterior facet to left, anterior facet to right and entrance to tarsal canal in the center.

Fig. 3: Anterior process of the calcaneus.

Fig. 4: Scope in anterior portal: view of anterior aspect of posterior subtalar joint.

Fig. 5: Lateral capsule and ligament attachments to calcaneus.

Fig. 6: Scope in anterior portal: view of medial capsule through posterior subtalar joint.

Fig. 7: Scope anterior, posterior probe: view of the posterior aspect of the posterior joint.

Fig. 8: Posterior capsule to the left and posterior calcaneus to right and posterior processes of talus above. The sheath of the FHL is seen between the processes.

Courtesy of Carol Frey

Subtalar joint evaluation

Diagnostic subtalar arthroscopy examination begins with the arthroscope viewing from the anterior portal. With the arthroscope in the anterior portal, [Fig. 4] the ligaments which insert on the floor of the sinus tarsi are visualized. It is easy to get disoriented, as the ligaments are closely packed and cross over one another in the sinus tarsi.

More medial, the deep interosseous ligament [Figure 5] is observed to fill the tarsal canal. The arthroscope should be now slowly withdrawn and the arthroscopic lens rotated to view the anterior process of the calcaneus [Fig. 6]. The arthroscopic lens is then rotated in the opposite direction to view the anterior aspect of the posterior talocalcaneal articulation [Fig. 7].

Next, the anterolateral corner of the posterior joint is examined and reflections of the lateral talocalcaneal ligament and the calcaneofibular ligament are observed [Fig. 8]. The lateral talocalcaneal ligament is noted anterior to the calcaneofibular ligament. The arthroscopic lens may then be rotated medially and the central articulation is observed between the talus and the calcaneus [Figure 9]. The posterolateral gutter may be seen from the anterior portal. It is often possible to advance the scope along the lateral and posterior lateral gutter, and visualize the posterior pouch and Stieda’s process (or os trigonum) [Fig. 10].

The arthroscope is then switched to the posterior portal. From this view, the interosseous ligament may be seen anteriorly in the joint.

As the arthroscopic lens is rotated laterally, the lateral talocalcaneal ligament and calcaneofibular ligament reflections again may be seen. The central talocalcaneal joint may then be seen from this posterior view and the posterolateral gutter examined [Fig. 11]. The posterolateral recess, posterior gutter and posterior-lateral corner of the talus is visualized. The posteromedial recess and posteromedial corner of the talocalcaneal joint can be seen from the posterior portal.

Fig. 9: Posterior lateral subtalar joint view through the posterior portal.

Fig. 10: Posterior medial capsule with calcaneus at right.

Fig. 11: Os trigonum.

Postoperative care

After completing the procedure, the portals are closed with sutures. A compression dressing is applied from the toes to the mid-calf. Ice and elevation are recommended until the inflammatory phase has passed. The patient is allowed to ambulate with the use of crutches, and weight-bearing is permitted as tolerated.

The sutures are removed approximately 10 days after the procedure. The patient should begin gentle active range-of-motion exercises of the foot and ankle immediately after surgery.

Once the sutures are removed, if indicated, the patient is referred to a physical therapist for supervised rehabilitation. The patient should be able to return to full activities at 6 to 12 weeks postoperatively.

Sinus tarsi pathology: The best portal combination for the evaluation and debridement of pathology in the sinus tarsi is the arthroscope in the anterior portal and the instruments placed in the middle portal. One can debride torn interosseous ligaments, synovitis, remove loose bodies, and lysis of adhesions can be undertaken. A radiofrequency wand is a useful tool to access the hard to get to spots in the sinus tarsi and subtalar joint.

Os trigonum pathology: The best portal combination for evaluation and removal of the Os Trigonum is the arthroscope in the anterior portal and the instrumentation in the posterior portal.

The os trigonum or a symptomatic Steida’s process can be debrided with a burr or shaver and removed through an arthroscopic portal using a standard arthroscopic grabber. Rarely, it is necessary to enlarge the portal for delivery of the os trigonum.

Arthroscopic subtalar arthrodesis: Both the anterior and posterior portals are used in an alternating fashion during the procedure for viewing and for instrumentation. It is important to obtain a fusion of the posterior facet. The anterior facet is generally not fused. A primary synovectomy and debridement are necessary for visualization.

Debridement and complete removal of the articular surface of the posterior facet of the subtalar joint down to subchondral bone is the next phase of the procedure. Once the articular cartilage has been resected, approximately 1 mm to 2 mm of subchondral bone is removed to expose bleeding cancellous bone.

Spot-weld holes measuring approximately 2 mm in depth are created on the surfaces of the calcaneus and talus to create vascular channels. The posteromedial corner is inspected to insure adequate debridement.

In general, no autogenous bone graft or bone substitute is needed. The guide wire for a large cannulated screw (6.5 mm to 7 mm) can be visualized as it enters the posterior facet. The foot is then put in position (about 0º to 5º of valgus), the guide wire advanced, followed by placement of the screw. Screw position and length are confirmed with fluoroscopy. Postoperative care is similar to open techniques.

Complications

Although rare, the most likely complication to occur after subtalar arthroscopy is injury to any of the neurovascular structures in the proximity of the portals, including the sural nerve and superficial peroneal nerve. Other possible complications include infection, instrument breakage and damage to the articular cartilage.

Carol C. Frey, MD, is director of the West Coast Sports Medicine Foundation Fellowship, Foot & Ankle, Manhattan Beach, Calif. She is also Editorial Board Section Editor, Foot & Ankle, for Orthopedics Today.

For more information:
Frey C, Gasser S, Feder K. Arthroscopy of the subtalar joint. Foot Ankle Int. 1994;15(8):424-428.
Frey C, Feder K, DiGiovanni C. Arthroscopic evaluation of the subtalar joint: does sinus tarsi syndrome exist? Foot Ankle Int. 1999;20(3):185-191.
Parisien JS. Current Techniques in Arthroscopy, 3rd Edition. New York: Thieme. 1998:161-168.