Anterior ankle arthroscopy represents a reliable and widely performed treatment option for a variety of indications such as bony or soft tissue impingement, osteochondral defects, loose bodies, ossicles, synovitis, and instability. With anterior arthroscopy, it is difficult to approach the posterior aspect of the ankle joint, unless distraction is used or marked laxity is present, and the subtalar joint is not visualized. For these reasons, prone arthroscopy has been developed and used more frequently for the treatment of posterior ankle joint and subtalar conditions. As described in a few anatomical studies, posterior portals to the ankle joint have shown to be safe and reliable,¹, ², ³ although potential complications related to neurovascular bundle location have been described.⁴ In addition, a prone approach allows the endoscopic visualization of some posterior structures of the hindfoot (i.e., os trigonum, flexor hallucis longus [FHL], deep portion of the deltoid ligament, retrocalcaneal bursa, Achilles tendon, etc.).

The hindfoot complex is composed of three articulations (distal tibiofibular syndesmosis, talocrural joint, subtalar joint). The major contributors to stability are (1) the congruity of the articular surfaces, (2) the static ligamentous restraints, and (3) the musculotendinous units, which allow for dynamic stabilization.

Superficially, from the lateral edge of the Achilles tendon to the posterior edge of the lateral malleolus, lies the sural nerve (˜1 cm lateral to the Achilles tendon) that heads obliquely toward the lateral portion of the foot. Lateral to the sural nerve lie the peroneal tendons, which are stabilized by the superior and inferior retinacula. The superior retinaculum is the major restraint to peroneal dislocation and runs posterior to the calcaneofibular ligament, from the tip of the lateral malleolus to the posterolateral aspect of the calcaneus (see Chap. 5).

Superficially, from the medial edge of the Achilles tendon to the posterior edge of the medial malleolus, lie the FHL tendon, the neurovascular bundle (posterior tibial artery and nerve), the flexor digitorum longus tendon, and the tibialis posterior tendon (see Chap. 5).

Deep to the distal part of the Achilles tendon lies the retrocalcaneal bursa.

The next layer is formed by the posterior joint capsule of the tibiotalar and subtalar joints.

The subtalar joint is formed by three articular surfaces: anterior, middle, and posterior (Fig. 17-1A). The middle articular surface is located medially, at the level of the sustentaculum tali of the calcaneus. The anterior and posterior surfaces are divided laterally by the tarsal canal that opens laterally into the sinus tarsi (Fig. 17-1A-D). In the tarsal canal lies the interosseous talocalcaneal ligament, one of the most important stabilizers of the subtalar joint.

Looking from behind, the body of the talus presents two processes: posterolateral and posteromedial (Fig. 17-2). These are divided by a groove, which contains the FHL tendon (Fig. 17-2). The posterolateral process is also known as trigonal or Stieda process and, when separated from the talar body, is called os trigonum.

The ligamentous structures (Fig. 17-2) of the posterior ankle include (1) the posterior inferior tibiofibular ligament (PITFL), (2) the posterior talofibular ligament (PTFL), (3) the calcaneofibular ligament (CFL), (4) the posterior talocalcaneal ligament, (5) the medial talocalcaneal ligament, (6) the posterior tibiotalar ligament (part of the deltoid ligament), and (7) the tibiocalcaneal ligament (part of the deltoid ligament).

The PITFL (part of the tibiofibular syndesmosis) is composed of a superficial and a deep (or transverse) fascicle. The superficial component originates at the posterior edge of the lateral malleolus, heads proximally and medially, and inserts into the posterior tibial tubercle. The term PITFL is usually used to refer to the superficial component. The transverse ligament originates above the digital fossa of the lateral malleolus and inserts on the lower part of the posterior border of the tibial articular surface in a superomedial direction. The transverse ligament, as a true labrum, deepens the articular tibial surface, increasing the tibial concavity.⁵

The PTFL and the CFL are part of the lateral ligamentous complex of the ankle. Posteriorly, the PTFL has a long attachment, which involves nearly the entire nonarticular portion of the posterior talus to the groove for the FHL tendon. The fibular attachment is centered an average of 10 mm proximal to the distal tip in the digital fossa. The CFL restrains subtalar inversion and thereby indirectly limits talar tilt within the ankle mortise. With the foot in plantigrade position, the CFL forms an angle of about 133° with the fibula. The CFL inserts on the anterior edge of the distal fibula, centered 9 mm from the distal tip.⁶

The posterior tibiotalar ligament and the tibiocalcaneal ligament represent the posterior part of the deltoid ligament. The deltoid ligament is composed of a superficial and a deep layer. The deep deltoid takes origin in the intercollicular groove and the posterior colliculus of the medial malleolus, and inserts into the posterior medial talus. The superficial layer takes origin from the anterior colliculus and fans out anteriorly to insert into the navicular, the spring ligament, the sustentaculum tali, and the posterior talus. The deep layer of deltoid resists external rotation of the talus and the superficial layer resists abduction of the talus.⁶

The history of patients with pain around the ankle or the hindfoot should be thoroughly evaluated in terms of previous injuries, duration of symptoms, activities eliciting the pain, and type and location of the pain. Any anatomical, axial, or gait abnormality of the foot and ankle should be evaluated. All the periarticular structures (neurovascular and musculotendinous) should be evaluated. With the patient complaining of hindfoot pain, the tibialis posterior, FHL, and peroneal tendons should be palpated at rest and against resistance, in order to reproduce the symptoms. Hyper-plantar flexion can elicit the pain in patients with posterior impingement or os trigonum syndrome. Pain, catching, snapping, grinding, swelling, and tenderness around the involved joint are typical symptoms of osteochondral lesions (OCLs) or loose bodies. Patients with tarsal tunnel syndrome typically complain of numbness in the foot, radiating to the big toe and the first three toes, pain, burning or electrical sensations, and tingling over the base of the foot and the heel. Depending on the area of entrapment, other areas can be affected.

Injections with local anesthetics into the joints, around the nerves, and in the tendon sheaths can be helpful when clinical examination and imaging are inconclusive.

Plain weight-bearing radiographs of both ankles (anteroposterior, lateral, and mortise views) together with an oblique view of the foot are essential in the diagnosis. The rearfoot alignment (Cobey/Saltzman) view may be required to evaluate the ankle joint and identify any calcaneal-to-tibial deformities (see Chap. 2). Magnetic resonance imaging (MRI) may be indicated in case of chondral or soft tissue pathologies.

Most hindfoot pathologies can be initially managed with conservative treatment, and this includes (1) rest, (2) ice, (3) physical therapy, (4) orthoses, (5) anti-inflammatory drugs, and (6) local injections. If adequate nonoperative measures fail, surgery should be considered. The main indications to prone ankle arthroscopy include (1) OCLs (of subtalar and posterior ankle joint); (2) posterior soft tissue or bony impingement; (3) os trigonum syndrome; (4) posterior loose bodies; (5) FHL or peroneal tenosynovitis; (6) posterior synovitis; (7) subtalar (or ankle) joint arthritis; (8) posterior tibial, talar, or calcaneal fractures (for arthroscopic reduction and internal fixation or loose body removal); and (9) talocalcaneal coalition (TCC).

On the other hand, prone arthroscopy is contraindicated in case of previous posteromedial open surgery (with consequent extensive scar around the posteromedial neurovascular bundle or FHL transfer), joint or soft tissue infection, and absence of posterior tibial pulses.⁷, ⁸

General anesthesia with a regional block or spinal anesthesia is administered. Preoperative antibiotic prophylaxis is generally performed with intravenous cefazolin 2 g. Adequate gel or foam padding is positioned on the operative table to protect the patient’s head, chest, knees, elbows, and shins (Fig. 17-3). A tourniquet is positioned at the proximal thigh. The patient is then flipped into a prone position with the feet hanging off the operative table (Fig. 17-3A, B). During this phase, particular attention should be paid to protect the ventral areas of the patient (i.e., breast, abdomen, and genitals) from excessive pressure. If distraction is anticipated, the head of the operative table can be lowered to counteract the traction force. At this point, the patient is ready for prepping and draping.

The thigh tourniquet is inflated and the posteromedial (PM) and posterolateral (PL) portals are routinely used (Fig. 17-4). The Achilles tendon and the medial and lateral malleoli are marked with a surgical pen. With the ankle in the neutral position, a line is drawn from the tip of the lateral malleolus to the Achilles tendon, parallel to the sole of the foot. The PL portal should be placed above this line, tangential to the Achilles tendon (Fig. 17-4A). The PM portal is made first at the same level of the PL portal adjacent to the Achilles tendon. An 18-gauge needle is used to inject

10 mL of saline into the ankle or subtalar joint (Fig. 17-4B). Motion of the foot indicates successful joint instillation. A longitudinal skin incision is made, and a blunt instrument is used to approach the joint, pointing the posterior aspect of the tibiofibular joint, entering the subtalar joint or the ankle joint. A 2.7- or 4.0-mm 30° angle arthroscope is then inserted into the joint. The PL portal longitudinal incision is then made. A mosquito clamp is introduced and directed toward the arthroscope shaft in a 90° angle and then moved anteriorly in the direction of the ankle joint. The clamp is used to spread the extra-articular soft tissue in front of the tip of the lens (Fig. 17-4A-D).

The initial synovectomy and debridement are performed using a 4.0-mm shaver, in order to create a space in the posterior aspect of the ankle and subtalar joint from the peroneal tendon sheath to the FHL tendon and from the ankle joint superiorly to the posterior calcaneal facet of the subtalar joint inferiorly. The FHL tendon is an important landmark and should always be kept in view medially, in order to avoid damaging the neurovascular bundle during the procedure. Passive motion of the great toe and the first ray will assist in the identification of the FHL tendon and the peroneus longus tendon, respectively.

When examining the subtalar joint (Fig. 17-5A-F), a probe can be inserted between talus and calcaneus to palpate the articular cartilage. Gentle levering of the probe can distract the joint and improve visualization. Noninvasive distraction strap is usually ineffective to improve subtalar joint visualization. If subtalar joint opening is required, a transcalcaneal thin wire distraction is recommended.⁹ The posterior tuberosity of the calcaneus is palpated, and the correct wire insertion site is identified on the medial calcaneus. A 1.8-mm wire is placed on the inferior aspect of the tuberosity to avoid injuring the medial neurovascular structures. The wire is drilled parallel to the plantar aspect of the foot. The wire must be posterior and inferior to the medial neurovascular bundle. The wire is attached to a reusable triangular spatial frame foot plate.⁹ The wire is tensioned to 90 pounds, and a traction frame system is attached to the operative table and foot plate (Fig. 17-6). A 2.7-mm arthroscope can be passed beneath the CFL into the anterolateral gutter of the subtalar joint and an anterior portal can be
established if needed. Performing an anterior portal under arthroscopic guidance from prone approach is safe and reliable since the foot usually sits in slight external rotation.⁷