In 2000, a two-portal posterior approach for hindfoot and subtalar arthroscopy was introduced.¹ The patient is placed in the prone position on the operating table with a tourniquet inflated around the thigh. A triangular pad is placed under the lower leg to provide unconstrained motion of the ankle joint during surgery. The foot must hang slightly over the edge of the operating table to allow dorsiflexion of the ankle joint. A lateral support is placed against the ipsilateral hip to allow tilting of the operating table (Fig. 20-1). Image intensification using a mobile C-arm is mandatory for confirmation of correct placement of the lag screws with arthroscopically assisted subtalar joint arthrodesis.

The procedure is carried out in an outpatient surgery setting under general or spinal anesthesia. The two portals that are used for subtalar joint arthroscopy are the standard posterolateral and posteromedial portals for hindfoot endoscopy.¹ Important anatomical landmarks that should be identified before making the portals are the lateral malleolus, the lateral border of the Achilles tendon at the level of the lateral malleolus, and the medial border of the Achilles tendon. First, the posterolateral portal is created at the level or slightly above the tip of the lateral malleolus, approximately 5 mm lateral to the Achilles tendon (Fig. 20-2A). It is obligatory to have the sole of the foot in the neutral position with respect to the lower leg before incising the skin. After making the longitudinal skin incision laterally, the medial skin incision is made approximately 5 mm medial to the Achilles tendon at the same height as the lateral skin incision (Fig. 20-2B). Starting laterally, a mosquito clamp is used to dissect through the subcutaneous layer. The foot is now in the relaxed (slightly plantar-flexed) position. The mosquito clamp should point anteriorly, in the direction of the web space between the first and second toe (Fig. 20-3A). When the tip of the mosquito clamp touches the bone, it is exchanged for a 4.5-mm arthroscope trocar and obturator combination. By palpating the bone in the sagittal plane with the tip of the blunt trocar, the level of the ankle joint and subtalar joint often can be identified with the prominent posterior talar process between the joints. The trocar remains extra-articular at the level of the ankle joint. The obturator is then exchanged for a 30-degree 4-mm diameter arthroscope. The direction of view is routinely to the lateral side. At this time, the arthroscope is still outside the joint with its tip in the
fatty tissue overlying the capsule. Subsequently, the posteromedial portal is created just medial to the Achilles tendon. Through the medial skin incision a mosquito clamp is inserted and contacts the arthroscope shaft just anterior to the Achilles tendon (Fig. 20-3B). When the clamp touches the shaft, the shaft is then used as a guide to slide the tip of the mosquito clamp toward the ankle joint. The tip of the mosquito clamp has to stay in contact with the arthroscope trocar all the way down to the ankle joint at which point bony resistance is encountered (Fig. 20-3C). Normal saline is used for irrigation, however, Ringer solution can also be used. The arthroscope is now pulled back a fraction and tilted slightly until the tip of the mosquito clamp comes into view of the arthroscope (Fig. 20-3D). The clamp is used to spread the extra-articular soft tissues in front of the arthroscope. The mosquito clamp is exchanged for a 4.5 mm diameter full-radius shaver through the posteromedial portal. Again, the arthroscope shaft is used to guide the shaver toward the ankle and subtalar joint. The tip of the shaver is directed in a lateral and slightly plantar direction toward the lateral aspect of the subtalar joint. Now the fatty tissue overlying the capsule of the posterior subtalar compartment is debrided using the shaver. The shaver blade should be facing toward the bony surfaces. After removal of the capsule of the subtalar joint, the posterior compartment of the subtalar joint is visualised. The shaver is then retracted and the arthroscope is moved anteriorly through the opening in the crural fascia to visualize the posterolateral aspect of the subtalar joint (Fig. 20-4A-E). Once the subtalar joint is identified, the opening in the deep crural fascia is enlarged to increase the working area in the hindfoot. At the level of the ankle joint, the posterior tibiofibular and posterior talofibular ligaments are recognized. The posterior talar process can be freed from the soft tissue using the full-radius shaver. This is followed by identification of the flexor hallucis longus (FHL) tendon medially. The FHL tendon is an important anatomic landmark in hindfoot endoscopy as the posteromedial neurovascular bundle is located medially from the FHL tendon. Therefore, the FHL tendon is always located first, before addressing any ankle or subtalar pathology. After removal of the thin joint capsule of the ankle joint, the intermalleolar and inferior transverse ligament can be lifted up to enter and inspect the ankle joint. In most cases, it is not possible to introduce the 4-mm arthroscope into the posterior subtalar joint. However, the posterior subtalar joint can be adequately visualized from its margins without entering the joint. Intra-articular pathology can be treated under direct view looking from outside-in using small arthroscopic instruments. Distraction of the subtalar joint can be accomplished during surgery using the noninvasive ankle distractor or through manual traction by the assistant. Because of potential complications (i.e., infection, nerve injury, and fractures of the talus/calcaneus) the use of the invasive joint distraction techniques is not recommended.

Arthroscopic subtalar joint arthrodesis was intended to yield less morbidity, preserve the blood supply, and
preserve proprioception and neurosensory input.² In arthroscopically assisted subtalar joint arthrodesis, the posterior subtalar joint is fused using the posterior two-portal hindfoot endoscopy technique with the patient in the prone position. The two standard posterior portals for hindfoot endoscopy are created in the same manner as described above. After local capsulotomy, the posterior subtalar joint is identified. This is followed by identification of the FHL tendon medially. Next release of the flexor retinaculum from the posterior talar process is performed using the arthroscopic punch to establish better access to the posterior subtalar joint. Via the posterior portals, the articular cartilage is removed from the posterior subtalar joint using ring curettes. To open up the posterior subtalar joint and create an increased working space, a blunt trocar is introduced in the subtalar joint through an accessory anterolateral sinus tarsi portal (Fig. 20-5). A small skin incision is made at the level of the sinus tarsi. A spinal needle is introduced and directed toward the tip of the lateral malleolus. The arthroscope is used to check the position of the needle. A large blunt trocar (4.0 mm diameter) is inserted through the sinus tarsi portal and is maneuvered toward the posterior facet of the subtalar joint (Fig. 20-6). The blunt trocar is put in the posterior subtalar joint from a lateral position. As the blunt trocar is almost parallel to the posterior subtalar joint, the sideward movement prevents the trocar of gouging the subchondral bone. With the assistant holding the blunt trocar in place, all the cartilage is removed from the posterior facet of the subtalar joint using ring curettes. The portals can be switched if necessary. After complete removal of the articular cartilage, the subchondral bone is entered to expose the vascular cancellous bone. The subchondral bone plate is partially removed with a burr. Using a small chisel, multiple 2-mm deep longitudinal grooves are made in the subchondral cancellous bone of the talus and calcaneus. A vertical skin incision is made at posterior heel for introduction of two cannulated lag screws off the weight-bearing surface of the calcaneus. Using the C-arm image intensifier 6.5-mm lag screws are placed across the posterior subtalar joint (Fig. 20-7A-D). The length of the two screws can be estimated using the preoperative weight-bearing lateral radiographs of the ankle. Before drilling, it is important to check the correct alignment of the hindfoot (approximately 5 degrees of valgus). The assessment of correct hindfoot alignment by eyeballing is facilitated by having the patient in the prone position. Biomechanical and finite element analysis of screw position in subtalar joint arthrodesis showed that a double diverging screw configuration confers the highest compression, the greatest torsional stiffness, and the least joint rotation.^{3, 4} The position of the lag screws is also important; one screw in the talar neck and the other screw in the medial dome of the talus is optimal. Countersinking the screw heads in the dorsal cortex of the calcaneus prevents posterior screw head prominence. Coaptation of the posterior subtalar surfaces can be checked arthroscopically when tightening both the screws. No bone grafting is used. The skin is closed using 3-0 nonresorbable Ethilon sutures. A plaster cast is applied to the lower leg.