Phinit Phisitkul and Annunziato Amendola
DEFINITION
Posterior ankle impingement syndrome is a clinical disorder characterized by posterior ankle pain that occurs in forced plantarflexion. It can be caused by an acute or chronic injury, with the os trigonum or trigonal process of the talus as the most offending structure.10,19
Synonyms used for posterior ankle impingement syndrome include posterior block of the ankle, posterior triangle pain, talar compression syndrome, os trigonum syndrome, os trigonum impingement, posterior tibiotalar impingement syndrome, and nutcracker-type syndrome.4,11,20,36
The os trigonum is a secondary ossification center of the talus. It mineralizes between the ages of 11 and 13 years in boys and 8 and 11 years in girls. It fuses with the posterior talus within 1 year, forming the posterolateral process, often called the Stieda or trigonal process. The os trigonum remain as a separate ossicle in 1.7% to 7% of normal feet, twice as often unilaterally as bilaterally.3,8,16,24
ANATOMY
The posterior process of the talus is composed of a smaller posteromedial process and a larger posterolateral or trigonal process flanking the sulcus for the flexor hallucis longus (FHL) tendon.
The os trigonum may be found in connection with the posterolateral tubercle (FIG 1). It is completely corticalized and has three surfaces: anterior, inferior, and posterior.
FIG 1 • Os trigonum.
The anterior surface connects to the posterolateral tubercle via fibrous, fibrocartilaginous, or cartilaginous tissue. The inferior surface forms the posterior part of the talocalcaneal joint.
The posterior surface is nonarticular and has the attachments of posterior talofibular ligament, posterior talocalcaneal ligament, deep layer of the flexor retinaculum, and the talar component of the fibuloastragalocalcaneal ligament of Rouviere and Canela Lazaro.28
The tibialis posterior tendon, the flexor digitorum longus tendon, and the flexor hallucis longus tendon situate in their own fibrous tunnels in continuity with the fascia of the deep posterior compartment.
The neurovascular bundles are just medial and posterior to the flexor hallucis longus tendon at the level of the ankle joint, with the tibial nerve as the most lateral structure (FIG 2).
In some variants, the posterior tibial artery can be thin or absent (0–2%), with the dominant peroneal artery traversing across the posterior ankle toward the tarsal tunnel.2,6
PATHOGENESIS
Most cases of posterior ankle impingement syndrome occur in athletes such as ballet dancers or soccer players who have sustained acute or repetitive injuries with the ankle in forced plantarflexion, causing the “nutcracker effect”12,20 (FIG 3). Ankle sprain may cause avulsion fracture of the posterior talofibular ligament and secondary impingement.15,21,25,34
Symptoms can be aggravated by any structures localized between the posterior tibial plafond and the calcaneal facet of the posterior subtalar joint, such as the os trigonum, long trigonal process, flexor hallucis longus tendon, posterior inferior tibiofibular ligament, intermalleolar ligament, and any osseous, articular cartilage, capsule, or synovial lesions of the posterior ankle or subtalar joint.
FHL tenosynovitis is commonly associated with posterior ankle impingement due to the intimate relationship between the tendon and the os trigonum or the trigonal process at the posterior aspect of the talus. This lesion can be an associated injury or secondary to the inflamed surrounding structures.17,26,30
FIG 2 • Neurovascular bundle posteromedial to the FHL tendon.
FIG 3 • Forced plantarflexion as a cause of the nutcracker effect in the os trigonum.
NATURAL HISTORY
The natural history of posterior ankle impingement is currently unknown. Os trigonum is a benign condition and usually is asymptomatic.
When symptomatic, nonoperative treatment has been found to be successful in 60% of cases. However, Hedrick and McBryde10 reported that only 40% of those successfully treated patients could achieve full preinjury activity levels. The prognosis with nonoperative treatment is generally poor in high-activity patients such as ballet dancers.20
PATIENT HISTORY AND PHYSICAL FINDINGS
The routine history should include sex, age, occupation, sports activities, and mechanism of the injury.
Patients should be asked for the description of pain, its location, and any aggravating positions or activities. Pain from the impingement usually is directly posterior or posterolateral to the ankle joint. Pain in the posteromedial aspect may be associated with tenosynovitis of the FHL tendon, which is usually described as pain along the tendon longitudinally. Aggravation of the symptoms with the ankle in full plantarflexion is essential to the diagnosis.
Examination must be performed to rule out other pathologies causing posterior ankle and hindfoot pain, such as Achilles tendinopathy, Haglund syndrome, “pump bump” syndrome, tibialis posterior tendinitis, and peroneal tendon injuries. Diligent palpation of the described structures for pain is recommended.
The physical examination should include:
Examination for retromalleolar swelling. Mild swelling occurs in posterior ankle impingement syndrome. Significant swelling should raise the suspicion of peroneal or tibialis posterior tenosynovitis.
Passive ankle plantarflexion. In a positive test, sharp pain or crepitus is produced at full plantarflexion.
In FHL tenosynovitis, pain is produced with active/passive motion of the hallux while a thumb palpates the tendon for tenderness and crepitus. The presence of FHL tenosynovitis should be documented, and it should be treated accordingly.
FIG 4 • Lateral radiograph of the ankle.
Tenderness from FHL tenosynovitis is produced with active/passive motion of the hallux while a thumb palpates the tendon for tenderness and crepitus. The presence of FHL tenosynovitis should be documented, and it should be treated accordingly.
Tenderness of other posterior ankle structures. Individual palpation of the peroneal tendons, tibialis posterior tendon, Achilles tendon, and posterior aspect of the calcaneal tuberosity is essential to exclude other pathologies. Palpation of the os trigonum itself is difficult due to its depth. Other diagnoses should be considered if there is no pain with passive ankle plantarflexion and the positive test for other possible lesions in spite of the presence of the os trigonum on radiographs.
IMAGING AND OTHER DIAGNOSTIC STUDIES
A lateral radiograph of the ankle usually demonstrates the osseous lesions sufficiently (FIG 4). Lateral radiographs can be taken in full ankle plantarflexion and slight external rotation of the limb to visualize impingement from the os trigonum.9
Bone scanning has been reported to identify the symptomatic os trigonum. It is not routinely obtained, however, and does not replace accurate history taking and physical examination (FIG 5). False-positive results in patients with high activity levels make this study less useful.29
CT scan can help clarify osseous or osteochondral lesions, especially when the posteromedial facet fracture is suspected.7
MRI is the most useful imaging examination for posterior ankle impingement syndrome (FIG 6). Anatomic variants and a range of osseous and soft tissue abnormalities have been found to be associated with this condition. Posterior tibiotalar synovitis and marrow edema within one or more of the tarsal bones were found in all cases. In contrast, os trigonum was found in only 30% of cases.5,23,26
Diagnostic injection can be helpful when the signs and symptoms are inconclusive.14,25 The postinjection symptoms have been shown to be parallel to results after surgical excision of the os trigonum. However, injection directly into the junction between the os trigonum and the talus is difficult and must be done under fluoroscopic guidance in experienced hands.
FIG 5 • Positive bone scan.
DIFFERENTIAL DIAGNOSIS
Haglund syndrome
Tendinitis (Achilles tendon, peroneal tendons, posterior tibial tendons)
Loose bodies
Ankle or subtalar arthritis
NONOPERATIVE MANAGEMENT
Nonoperative treatment is always the first approach. However, it has shown less than optimal results in the published literature, with, at best, a 60% rate of improvement plus long-term modification of activities.10
Avoidance of aggravating activities such as forced plantarflexion is the most important factor, because it will avoid impingement and aggravation of the inflammatory response. This measure may not be tolerable in athletes who routinely require this position, such as ballet dancers and soccer players.
FIG 6 • MRI examination for posterior ankle impingement syndrome.
Supportive treatments include rest, ice, anti-inflammatory medications, and immobilization in a short-leg walking cast.
One or two cortisone injections under fluoroscopic guidance have shown more than 80% response rate at 2 years.25 Its use was not routinely recommended due to the risk of FHL tendon rupture and potential disabilities especially in ballet dancers.
Physical therapy can be instituted as symptoms improve. It consists of phonophoresis, isometric exercises, heel cord stretching, and selected isometric strengthening.
SURGICAL MANAGEMENT
Indications
Failure of nonoperative treatment after at least 3 months
Inability to to return to required activities after nonoperative treatment
Preoperative Planning
All imaging studies are reviewed. MRI is helpful in the evaluation of associated lesions.
All the pathologies should be carefully detected. Surgical steps with informed consent can be added accordingly, such as loose body removal, treatment for osteochondritis dissecans lesions, or an open FHL repair.
When surgery is indicated, the treatment for an os trigonum, an acute or chronic fracture of the trigonal process, or an intact large trigonal process is virtually the same. Further studies, eg, CT scan, to distinguish them may not be necessary.
If arthroscopic or open surgery is planned, the posterior tibial pulse must be palpable in the soft spot posterior to the medial malleolus, because an absence or a minor artery may be associated with a dominant peroneal artery. This artery traverses across the posterior ankle and is at high risk during arthroscopy.
Positioning
The patient is placed in the prone position with standard padding (FIGS 7 AND 8).
The patient's ankles are at the level just distal to the end of the bed to leave enough room for possible anterior or lateral arthroscopic portals.
The surgeon's body can be used to dorsiflex the ankle by leaning forward.
FIG 7 • Prone positioning.
FIG 8 • Ensure adequate padding of all surfaces.
Approach
The posterior aspect of the ankle and subtalar joints can be accessed open or arthroscopically.
Open approaches can be posteromedial or posterolateral, on either side of the Achilles tendon.
The posteromedial approach is recommended by the author. When the bony impingement is accompanied by pathologies in the neurovascular bundles or lesions in the FHL tendon that may require a repair, a posteromedial approach is advantageous.
The posterolateral approach also may be used for cases that require only excision of the os trigonum and trigonal process or release of the FHL tendon.
The arthroscopic approach has advantages over open surgeries in terms of minimizing surgical injury, postoperative pain, and early return to activities.
We prefer the prone over the supine or lateral decubitus position because it provides a more direct approach, minimizing the risk of instrument skiving off toward the neurovascular bundles.
Apart from the magnification advantage, we have found that this method also aids in visualization of intra-articular pathologies.27
This technique requires familiarity with the hindfoot anatomy and arthroscopic skills.
TECHNIQUES
ESTABLISHMENT OF PORTALS
The anatomic landmarks of the posterior ankle are drawn, including the Achilles tendon, the medial and lateral malleoli, and the superior aspect of the calcaneal tuberosity.
The posterolateral and the posteromedial portals are located 1.5 cm proximal to the superior aspect of the calcaneal tuberosity on either side of the Achilles tendon (TECH FIGS 1 AND 2).
Ankle joint injection can be performed through the posterolateral portal, but it is not necessary, because the joint will be inspected easily after the os trigonum or the trigonal process has been removed.
TECH FIG 1 • Placement of posteromedial and posterolateral portals with the patient in the prone position.
The posterolateral portal is established first with a vertical skin incision, followed by blunt dissection with a straight hemostat. The tip of the hemostat should be kept just next to the Achilles tendon laterally to minimize injury to the sural nerve.
The dissection proceeds through a fat layer directly anteriorly.
The os trigonum usually is palpable, and a blunt trocar is inserted toward its superior aspect.
A 4-mm arthroscope is inserted through the cannula.
Next, the posteromedial portal is established at the same level just medial to the Achilles tendon.
A straight hemostat is used to dissect into the same soft tissue tunnel as the arthroscope. The hemostat is advanced while it is kept in contact with the arthroscopic cannula until the tip is seen by the arthroscope.
The soft tissue is gently dilated. A full-radius 3.5-mm shaver is inserted into the posteromedial portal until the tip is seen (TECH FIGS 3 AND 4).
TECH FIG 2 • Topographical landmarks of the pertinent structures.
TECH FIG 3 • The hemostat is visualized when creating the second portal.
TECH FIG 4 • The 3.5 mm shaver is visualized through the second portal.
DÉBRIDEMENT OF THE SOFT TISSUE
The initial débridement of the fatty tissue is performed first to make room for the arthroscopic maneuvers. This step will improve visualization tremendously.
The shaver is kept deep just above or below the os trigonum, with its cutting surface turned laterally.
The shaver is gradually moved medially until the FHL tendon is seen. The FHL tendon indicates the location of the neurovascular bundles, which lie medial and superficial to it.
The os trigonum is débrided off all the attached soft tissue circumferentially (TECH FIG 5).
TECH FIG 5 • The os trigonum is débrided of soft tissue attachments with a shaver circumferentially.
Medially, the retinaculum of the FHL is released off the os trigonum with a shaver or arthroscopic scissors (TECH FIG 6).
Tenosynovitic lesions of the FHL, if seen, may require a release and débridement further distally. Great care is taken to release the fibrous sheath from only the posterior attachment on the calcaneal wall. A partial tear of the FHL can be débrided, but a tear greater than 50% may require an open repair.
The posterior talofibular ligament attached on the lateral aspect of the os trigonum is released.
TECH FIG 6 • The FHL is visualized and released from its soft tissue attachments to the os trigonum.
RESECTION OF THE OS TRIGONUM AND TRIGONAL PROCESS
The synchondrosis is palpated by a Freer elevator coming from the superior aspect.
Next, the tip of the instrument is pushed into the synchondrosis.
Cracking of the synchondrosis is performed by levering maneuvers from either the superior or inferior surface (TECH FIG 7).
TECH FIG 7 • Lever the os trigonum loose from its talar attachments with a Freer elevator.
The os trigonum is removed as a whole using a grasper (TECH FIG 8). In the presence of an intact enlarged trigonal process it is removed entirely with a burr.
The posterior aspect of the talus is evaluated, and any sharp bony edges are rounded off (TECH FIG 9).
TECH FIG 8 • The os trigonum is removed as a whole using a grasper.
The most posterior aspect of the articular cartilage of the posterior talar facet of the subtalar joint is always removed together with the os trigonum.
TECH FIG 9 • The posterior aspect of the talus is evaluated and rounded off, particularly around the FHL tendon.
EVALUATION OF ASSOCIATED LESIONS
The posterior aspect of the ankle joint is evaluated. Synovitis or a thickened intermalleolar ligament is débrided. Stay lateral to the FHL tendon. Loose bodies are removed if present. Intra-articular views of the ankle joint are best achieved with a 2.7-mm arthroscope.
The subtalar joint is evaluated in the same manner (TECH FIG 10). The dynamic view of the hindfoot is inspected when the ankle is manipulated into full plantarflexion.
There should be no impingement at the completion of the procedure.
If arthroscopic evaluation or treatment of the anterior ankle joint is required, it can be performed in two ways.
The first way is to reposition the patient into the supine position and redrape the limb.
The second way is to bend the knee to 90 degree and perform the anterior ankle arthroscopy in the upsidedown manner. This requires experience and familiarity of the ankle anatomy.
TECH FIG 10 • Multiple views of the ankle and subtalar joint.
POSTOPERATIVE CARE
Portal incisions routinely are left unsutured.
A compressive soft dressing is applied. The patient is informed about the possibility of some drainage in the first couple of postoperative days. The dressing can be changed if necessary.
Leg elevation is encouraged.
No immobilization is required.
Patients can bear weight as tolerated in a postoperative shoe.
When acute pain subsides, usually 2 to 3 days postoperatively, patients can begin early range-of-motion and strengthening exercise.
Full activities are allowed gradually as tolerated.
OUTCOMES
Nonoperative treatment has not shown promising results, especially in high-demand athletes, but a success rate of more than 80% could be achieved when cortisone injections are routinely given under fluoroscopic guidance.10,25
When nonoperative treatment has failed, excellent outcomes have been reported with either open or arthroscopic resection of the os trigonum.1,13,18,20,22,32,33
Arthroscopic techniques can help minimize morbidities associated with open dissection, such as a painful scar, severe postoperative pain, and wound complications. It requires arthroscopic skills and familiarity with hindfoot anatomy.31,35
COMPLICATIONS
Neurovascular injuries are possible with either arthroscopic or open approaches. Neurapraxia of the tibial, peroneal, and sural nerves has been reported; most patients recovered spontaneously. Permanent sensory deficit and neuroma formation have occurred when the nerves were transected, especially the sural nerve when the open posterolateral approach is used.1
Symptoms can persist after operative treatment. Correct diagnosis and adequate treatment of all associated pathologies are the keys.
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