CHAPTER 8 Posterior Ankle Arthroscopy for Conditions Causing Ankle Pain

Os Trigonum, Posterior Ankle Soft Tissue Impingement, Flexor Hallucis Longus Stenosis, Haglund’s Deformity, and Other Considerations

Posterior ankle arthroscopy is an increasingly used technique that allows the orthopedic surgeon to address a number of causes of posterior ankle pain.¹^–⁴ This minimally invasive technique has several advantages over traditional open surgical approaches to the posterior ankle, which can involve extensive dissection because of the depth of the ankle from the posterior skin. Concerns for wound healing problems in this high–tensile area of skin are minimized by the use of small arthroscopy portals, which often eliminates the need for postoperative immobilization and speeding recovery. One concern with using arthroscopic techniques in the posterior ankle region is the potential for neurovascular injuries.⁵ However, with application of good anatomic knowledge of the posterior ankle region and the use of proper technique, this approach has proved to be safe and effective.³^–⁶ The magnification provided by the arthroscope allows the surgeon to work with greater precision and enhances the safety of the procedure. Several common causes of posterior ankle pain that are readily treated with posterior ankle arthroscopy are described in this chapter.

OS TRIGONUM

Os trigonum syndrome has been described in association with posterior ankle impingement in activities involving extreme plantar flexion, such as classical ballet and soccer. Also, a symptomatic os trigonum can be associated with tenosynovitis of the flexor hallucis longus (FHL) tendon.⁷^–¹⁰

Normal and Pathologic Anatomy

Symptomatic os trigonum syndrome can be caused by repetitive forced plantar flexion, as seen in ballet dancers and soccer players, although symptoms can arise in other athletes and in nonathletes after acute ankle injuries. The normal talus has a posteromedial and a posterolateral tubercle. The posterolateral tubercle provides attachment for the fibrous component of the beginning of the tunnel for the FHL tendon. An enlarged posterolateral tubercle is called a trigonal process, and one that is separated from the body of the talus is called an os trigonum. Sarrafian summarized four large series totaling 2142 talus specimens, and the incidence of os trigonum ranged from 2.2% to 7.7%.¹¹ In some cases, an apparent os trigonum may represent nonunion of a fractured trigonal process after forced plantar flexion, but this has no bearing on clinical decision making or treatment.

History and Physical Examination

Athletes with posterior ankle pain due to an os trigonum have complaints similar to those of any patient with posterior ankle impingement; pain is worsened with plantar flexion. Posterior ankle pain can be vague by patient history, and the presence of FHL tenosynovitis can further diffuse the pain sensation. The physical examination finding of tenderness anterior to the Achilles tendon and retrocalcaneal bursa is strongly suggestive of posterior ankle impingement and can be elicited from both the posterolateral and the posteromedial sides of the ankle. This is particularly true when an unstable os trigonum is present. FHL tenosynovitis adds to the posteromedial tenderness in some cases. Extreme passive plantar flexion can exacerbate the pain, but this increase in pain is not specific for os trigonum, because it can also be found in cases of posterior soft tissue impingement.

Diagnostic Imaging

Radiographs are helpful for demonstrating the presence of an os trigonum or large trigonal process. Magnetic resonance imaging (MRI) is the preferred test for assessing the pathoanatomy of the os trigonum, which is best demonstrated by bone marrow edema of the os trigonum and adjacent talus. MRI is also helpful in differentiating other causes of posterior ankle pain and impingement, such as FHL tenosynovitis, loose bodies, posterior soft tissue impingement, and occult osteochondral lesions (Fig. 8-1).¹² Fluoroscopy can be used to guide injection of the os trigonum for diagnostic purposes.¹³ Ultrasound can also be used to assess the pathoanatomy of the posterior ankle.¹⁴

FIGURE 8-1 T2 MRI sagital image shows a large trigonal process of the talus (A), which can also cause posterior impingement like an os trigonum. The posterior soft tissue impingement lesion (arrow) is the torn deep component of the posterior tibial-fibular ligament which is shown detached from the posterior tibial plafond. This transverse ligament an displace into the ankle joint.

Indications and Contraindications

Posterior ankle arthroscopy is indicated for patients with unresolved pain from os trigonum impingement. There are no notable contraindications to posterior ankle arthroscopy. The absence of a posterior tibial pulse behind the medial malleolus is an indication to review an MRI to assess the vascular anatomy.

The patient is placed in the prone position, and a thigh tourniquet is typically used to avoid tethering of the muscles of the posterior leg. The knees are padded, and a bump is placed anterior to the distal tibia, with the ankle and foot allowed to hang over the end of the table so that the ankle and hallux can be passively dorsiflexed during the procedure. Distraction is not needed, and the arthroscopist can lean against the sole of the foot to increase dorsiflexion, minimizing the need for assistance.

The ankle joint is marked anteriorly by placing a skin marker across the joint line of the dorsiflexed ankle. Two portals are made on either side of the Achilles tendon, 1 to 2 cm inferior to the anterior ankle joint line at approximately the level of the tip of the fibula (Fig. 8-2). This position allows adequate access to the ankle and subtalar joints. Alternatively, fluoroscopy can be used to confirm portal position. After the skin incisions are made, it is essential to use a fine, straight hemostat to spread tissues anterior to the Achilles tendon and make a puncture directly in the midline through the fascia separating the superficial and deep posterior compartments (Figs. 8-3 and 8-4). After this ventral fascia is penetrated, the hemostat is directed laterally and then advanced anteriorly in a posterolateral position behind the ankle. The hemostat can then be spread during removal to open the fascial opening. This is performed from both portals. It is important to maintain this method of placing instruments into the deep posterior compartment. Introducing instruments through this midline fascial opening from the superficial posterior compartment and initially directing instruments laterally protects the posteromedial neurovascular structures (Fig. 8-5).

FIGURE 8-2 The incision for posterior ankle arthroscopy portal is made directly next to the Achilles tendon and angled anteriorly toward the midline.

FIGURE 8-3 Axial magnetic resonance imaging the direction of the posterior ankle arthroscopy portals (white lines and arrow). D, flexor digitorum tendon; H, flexor hallucis longus tendon; L, loose body.

FIGURE 8-4 Cadaver shows a midline fascial opening from the superficial posterior compartment into the deep posterior compartment. The Achilles tendon has been removed (arrow).

FIGURE 8-5 A medial portal is used for introduction of the arthroscope. Notice that the trocar is directed toward the posterolateral ankle after it has been passed through the midline fascial opening (M) medial malleolus.

Initially, the arthroscope is placed through the medial portal and a soft tissue débrider through the lateral portal. Loose connective tissues behind the ankle joint are removed to demonstrate the superficial posterior tibiofibular ligament (PTFL) (Fig. 8-6). The ankle is dorsi and plantar flexed to identify the articular margin, and the os trigonum posterior to this point can then be cleared of lateral soft tissues. Some fibers of the posterior talofibular ligament are attached to the os trigonum, but the remainder of the PTFL attachment onto the talus should be preserved (Fig. 8-7). The subtalar joint is identified, and the clearing of soft tissues around the os trigonum continues, using the joint line of the ankle and subtalar joint as boundaries. Medially, the FHL tendon can be identified by moving the great toe into dorsiflexion. The FHL is used to mark the most medial boundary of the dissection (Fig. 8-8). The proximal attachment of the FHL tunnel is released from the os trigonum, which also serves to release the FHL, relieving any stenosis of the muscle or tendon simultaneously. At this point, the scope should be able to visualize the os trigonum well, and a freer elevator or similar blunt elevator can be used to probe the os and the fibrous junction between the os and the posterior talus (Fig. 8-9). In many cases, this junction can be loosened with a combination of the freer elevator and the shaver. Alternatively, a bipolar or unipolar cautery device may be used to strip the soft tissues, including the posterior talofibular ligament and the attachment of the FHL tendon sheath, from the os trigonum. After it is free, the os trigonum can be removed with a hemostat through either portal, although the posterolateral portal often works better (Fig. 8-10). It may be necessary to extend the portal enough to allow for the removal of a large os in some cases. Final inspection and débridement of the edges of the excision site can be performed. It is not uncommon for the calcaneal articular surface of the subtalar joint to be exposed posteriorly, because the os trigonum often has an articular surface that corresponds to the calcaneal side of the joint (Fig. 8-11).

FIGURE 8-6 Release of the fibrous tunnel of the flexor hallucis longus tendon (arrows). PTFL, posterior tibiofibular ligament; S, superficial posterior tibiofibular ligament; T, posterior talar body; Y, tibial slip or intermalleolar ligament.

FIGURE 8-7 Surface of the removed trigonal process. Notice the remaining attachment of the posterior tibiofibular ligament (PTFL). S, superficial posterior tibiofibular ligament; T, posterior talar body.

FIGURE 8-8 The arthroscopic view shows the os trigonum (A), flexor hallucis longus tendon (B), torn deep posterior tibiofibular ligament (C), and subtalar joint line (S).

FIGURE 8-9 Freer elevator is used to mobilize the fibrous junction of os trigonum.

FIGURE 8-10 The arthroscopic view shows a hemostat removing the os trigonum (A), the posterior talus exposed after removal of the os trigonum (B), and the flexor hallucis longus tendon (C).

FIGURE 8-11 The posterior talus is exposed after removal of the os trigonum (O). F, flexor hallucis longus tendon; S, calcaneal side of subtalar joint.

A word of caution is warranted about the use of an osteotome in cases of partially fused os trigonum or large trigonal processes. The angle achieved with an osteotome is often not steep enough to avoid penetration of the posterior talar body and can extend too far anteriorly, even with extreme dorsiflexion of the ankle joint. A curved osteotome may give a false sense of avoiding this problem. In some cases, it is best to use an arthroscopic burr to remove bony prominences rather than to perform an unintended osteotomy into the talar body. The portals can be closed with 3-0 nonabsorbable suture, and a bulky, soft dressing can be placed.

PEARLS& PITFALLS

• Patient positioning is critical to allow for adequate motion of the ankle and hallux during the procedure. This is accomplished by placing a bump beneath the anterior leg and having the patient’s ankle and foot slightly overhanging the end of the table.

• Ankle and calf tourniquets are avoided so that the posterior leg musculature is not tethered by the tourniquet.

• Because of the required precision of the procedure, it is preferable to use general anesthesia so that patient movement will not interfere with the surgery. The prone position makes it impossible to convert to a general anesthetic without repositioning.

• Portal placement and instrument passage, as described earlier, are critical to the success and safety of the procedure. Portals are made on the medial and lateral margins of the Achilles tendon. Blunt spreading though the superficial posterior compartment fascia directly anterior to the Achilles tendon allows access to the deep posterior compartment. Instruments are directed to the posterolateral ankle first, and then work can proceed toward the medial side at the level of the ankle joint.

• The FHL tendon is the medial boundary of all dissection, and motion of the hallux is helpful to locate the FHL.

• The ankle should be dorsiflexed fully if an osteotome is being used to remove an os trigonum. Even with care, it is easy to cut into the talar body. The use of fluoroscopy can help to determine whether the appropriate angle can be achieved. An arthroscopic burr is a good alternative in such cases.

• Large bone fragments may require extension of the lateral portal for removal. If further arthroscopy is needed, the incision can be sutured to maintain fluid pressure.

Postoperative Rehabilitation Protocol

The ankle is dressed with a bulky soft dressing, and weight bearing is allowed as tolerated, usually with crutches for the first week. Active and passive motion of the hallux is encouraged as tolerated. In some cases, a removable cast boot is helpful for early mobilization during the first few weeks. Sutures are usually removed 10 to 14 days after surgery, and rehabilitation is advanced with low-impact aerobic exercises and ankle and hallux dorsiflexion stretches as tolerated. Regaining full active strength of the hallux can sometimes be difficult, and formal physical therapy may be warranted for retraining.

Summary

Posterior ankle arthroscopy is an effective and minimally invasive technique for removal of an os trigonum. The magnification of the arthroscope allows for very precise surgical technique with minimal dissection. The excellent visualization of all of the posterior ankle structures also allows for related pathologies to be evaluated and treated simultaneously. As with all posterior ankle arthroscopic procedures, adhering to the basic rules of portal placement and instrument passage are key to the safety of the technique.

POSTERIOR ANKLE SOFT TISSUE IMPINGEMENT

“Posterior ankle impingement syndrome” was long used as a general phrase to describe posterior ankle pain that is worsened with plantar flexion of the ankle.¹⁵^,¹⁶ Over time, a more anatomic approach to diagnosing the cause of posterior ankle pain has evolved, and posterior ankle soft tissue impingement is now recognized as a separate, although often associated, condition resulting from posterior bony impingement. Posterior ankle soft tissue impingement results from either a tear of the deep portion of the PTFL from the posterior rim of the tibial plafond or a tear of the posterior portion of the deep deltoid ligament (DDL).¹⁷^–¹⁹

Normal and Pathologic Anatomy

The ligaments of the posterior ankle have been well described and are pictured in Figure 8-6.²⁰ The PTFL is composed of a deep and a superficial component. The superficial fibers are visible from the posterior view and fan out in a superior and medial direction from the fibular attachment to attach broadly on the tibia. The deep portion is a thick band that lies anterior to the superficial ligament and extends across the back of the ankle joint to the medial malleolus. It is not easily seen from the posterior view in an intact specimen. The deep band forms a labral rim of the posterior tibial plafond and increases the coverage of the posterior talus.

When the deep band is torn from the attachment on the tibial plafond, it becomes hypermobile and can displace into or out of the ankle joint, creating painful impingement symptoms. If the torn ligament is unstable, it usually lies in an inferior and more posterior position and can then be readily visualized from the posterior arthroscopic view (Fig. 8-12). If posterior impingement is suspected and the ligament is not visualized in this manner, a probe can be passed into the ankle joint and stability can be tested by pulling posteriorly on the ligament to determine whether it is displaced out of the joint. From the anterior arthroscopic view, posterior impingement is often not easily visualized with joint distention, but the ligament can be displaced into the ankle joint with posterior pressure, giving clear evidence of the instability and impingement.