Posterior Ankle Impingement Syndrome: An Operative Masterclass in Diagnosis and Surgical Management

Welcome, fellows, to the operating theater. Today, we're tackling a challenging yet rewarding condition: Posterior Ankle Impingement Syndrome (PAIS). This is a clinical disorder characterized by posterior ankle pain, typically exacerbated by forced plantarflexion – a common complaint in athletes, especially dancers. Think of it as a "nut in a nutcracker" phenomenon, where posterior structures get compressed between the tibia and calcaneus during extreme plantarflexion.

Our goal is to provide a comprehensive, step-by-step guide to both diagnosis and surgical management, focusing on the nuances that differentiate a good outcome from an excellent one.

Understanding Posterior Ankle Impingement Syndrome (PAIS)

Etiology and Pathogenesis

PAIS can stem from various pathologies. The most common include:
* Trigonal Process Pathology: This involves the posterolateral process of the talus, often called the trigonal process. Injuries here can range from acute or chronic fractures to disruption of a pre-existing synchondrosis, or direct compression. When the posterolateral process remains separated from the talus, we call it an os trigonum.
* Flexor Hallucis Longus (FHL) Tendon Dysfunction: This can manifest as stenosing tenosynovitis or impingement due to a prominent posterior talar process.
* Tibiotalar Pathology: Intrinsic ankle trauma can lead to articular chondral damage or bony injury, causing pain in extreme plantarflexion. Post-traumatic thickened, inflamed, or calcified soft tissues (capsule, synovium, ligaments) can also contribute.
* Subtalar Pathology: Osteochondritis or arthritis, especially in the posterior articular facets, can produce similar pain. Chronic PAIS with limited ankle motion can also lead to degenerative changes in the subtalar joint due to compensatory loading.
* Other Causes: Prominent calcaneal posterior process, synovial cysts, anomalous muscles, or even tumors can contribute.

It's crucial to remember that combined pathologies are common. For instance, ballet dancers frequently present with associated trigonal process injury and FHL tenosynovitis. Patients often compensate for loss of plantarflexion by adopting antalgic positions, like an inverted en pointe position in dancers, which can lead to secondary issues like anterior tibiofibular ligament sprains, calf strain, or plantar foot pain.

Comprehensive Surgical Anatomy

Let's review the critical anatomy of the posterior ankle region, fellows. This area is bounded superiorly by a horizontal line 4 cm above the lateral malleolus tip and inferiorly by a curved line 4 cm below it.

The central axis of this region is the Achilles tendon. Surrounding it, in the medial and lateral retromalleolar sulci, are crucial neurovascular and musculoskeletal structures.

Key Bony Structures:

• Posterior Talar Process: This protrudes posterior to the articular surface of the ankle joint. It extends both posteriorly and medially, comprising two projections: the posteromedial process and the posterolateral process (trigonal process).
• Groove for FHL: These two processes are divided by a distinct groove that houses the flexor hallucis longus (FHL) tendon.
• Os Trigonum: An accessory ossicle that forms when the posterolateral process fails to fuse with the talus.
• Posterior Calcaneal Process: A prominence here can also impinge on the hindfoot.

FIG 1 • Posterior talar process anatomy. Superior view of the talus shows the close relationship of the flexor hallucis longus tendon and the trigonal process.

Neurovascular and Tendinous Structures:

• Medial Retromalleolar Sulcus (from anterior to posterior):
  • Posterior Tibial Tendon: Lies immediately posterior to the medial malleolus.
  • Flexor Digitorum Longus (FDL) Tendon: Posterior to the posterior tibial tendon.
  • Posterior Tibial Artery and Veins: Located between the FDL and FHL.
  • Posterior Tibial Nerve: Most posterior of the neurovascular bundle, often immediately adjacent to the FHL tendon sheath. This is a critical structure to protect during a posteromedial approach.
  • Flexor Hallucis Longus (FHL) Tendon: This is the most posterior structure of the tarsal tunnel contents, running in its own fibro-osseous tunnel between the posteromedial and posterolateral talar processes. Its intimate relationship with the trigonal process makes it a frequent co-pathology.
• Lateral Retromalleolar Sulcus:
  • Peroneal Tendons (Longus and Brevis): Run posterior to the lateral malleolus.
  • Sural Nerve: This purely sensory nerve runs superficially in the posterolateral ankle, often lying just anterior to the Achilles tendon and posterior to the peroneal tendons. It is highly susceptible to injury during posterolateral approaches.

Surgical Warning: Always identify the FHL tendon as your key landmark in the posterior ankle. Medial to the FHL lies the neurovascular bundle. Lateral to it lies the trigonal process. Misidentification can lead to catastrophic neurovascular injury.

Preoperative Planning: The Foundation of Success

Before we make any incisions, meticulous preoperative planning is paramount.

Patient History and Physical Examination

A thorough history is crucial. Patients typically report chronic or recurrent deep, mechanical posterior ankle pain, exacerbated by forced plantarflexion or push-off activities (e.g., dancing, kicking, downhill running, high heels). Inquire about any recent or remote ankle trauma, but always consider overuse as a primary etiology.

On physical examination:
* Range of Motion (ROM): Measure and record tibiotalar, subtalar, and hallux ROM.
* Forced Plantarflexion Test: This maneuver aims to reproduce the patient's typical pain. It also helps estimate passive ROM limitation.
* Maquirriain Test: Similar to the forced plantarflexion test, but performed in a closed kinetic chain position, which can be more provocative for some patients.
* One-Leg Hop Test: Useful for ruling out concurrent Achilles tendon pathology.
* Palpation: Localize tenderness to the posteromedial or posterolateral aspect, helping to narrow the differential.
* AOFAS Ankle-Hindfoot Score: This objective scoring system provides a baseline for functional assessment and outcome measurement.

Imaging and Other Diagnostic Studies

While history and physical exam can strongly suggest PAIS, imaging studies are essential to confirm the cause and guide treatment.
* Ankle Radiographs: Obtain routine views, especially a lateral view, which is critical for clearly defining trigonal process anatomy and measuring ankle ROM. Look for os trigonum, fracture lines (though radiographs cannot differentiate acute from chronic), or other bony abnormalities.
* Bone Scintigraphy: A helpful diagnostic tool, especially if an acute fracture or synchondrosis disruption is suspected. Increased activity is present in these cases. A normal bone scan virtually rules out trigonal process pathology.
* Magnetic Resonance Imaging (MRI): This is considered the technique of choice for PAIS.
* It allows us to determine the nature of both osseous and soft tissue lesions.
* It helps exclude other causes of posterior ankle pain.
* MRI can demonstrate bone contusions of the trigonal process (bone marrow edema on STIR sequences), which are prevalent in PAIS.
* It can identify synovial cysts or occult fractures not visible on plain radiographs.

FIG 3 • A. Parasagittal T1-weighted image showing a posterior tibia fracture, which was occult in the initial radiographs.

FIG 3 • B. Parasagittal T1-weighted image showing a synovial cyst from the tibiotalar joint causing PAIS.

Differential Diagnosis

Always consider a broad differential, as misdiagnosis is common.
* Posterolateral Pain: Achilles tendinopathy, peroneal tendinopathy or tear, retrocalcaneal bursitis, Sever’s disease, sural neuralgia.
* Posteromedial Pain: Posterior deltoid sprain, osteochondral lesion of the talus, soleus syndrome, posterior tibial tendinopathy, tarsal tunnel syndrome, posteromedial tarsal coalition.
* Systemic Causes: If bilateral PAIS is suspected, a careful workup for systemic inflammatory or rheumatologic conditions is warranted. Simultaneous bilateral posterior ankle surgery is generally not recommended.

Nonoperative Management

Initial treatment for overuse-related PAIS is typically nonoperative:
* Rest and Activity Modification: Avoid activities requiring forced plantarflexion.
* Pharmacotherapy: Nonsteroidal anti-inflammatory drugs (NSAIDs).
* Cryotherapy: Ice application to reduce inflammation.
* Immobilization: Rarely indicated, but acute articular or bony injuries may benefit from a brief period of casting and limited weight-bearing.
* Physical Therapy: To improve ankle and subtalar ROM, as well as strength and flexibility of regional muscles.
* Corticosteroid Injections: For trigonal process pathology or other chronic causes, a diagnostic and therapeutic corticosteroid injection can provide pain relief and should be considered at least once before surgery.

Successful nonoperative treatment has been reported in about 60% of patients. Surgical intervention is indicated only after failure of non-surgical treatment and rehabilitation, and typically, a positive response to a diagnostic posterior ankle injection.

Surgical Management: Intraoperative Masterclass

Now, let's move to the operating room. We have three primary approaches for posterior ankle pathology: open posteromedial, open posterolateral, and posterior ankle endoscopy. The choice depends on the specific pathology. A posterolateral approach is preferred for isolated bony impingement, while a medial approach is indicated when both FHL tendinopathy and bony impingement are present. Endoscopy is an advanced procedure with a significant learning curve, best mastered on cadavers.

Patient Positioning and Setup

For all posterior approaches, we will position the patient in the prone position on the operating table.

1. Tourniquet Application: Apply a pneumatic tourniquet to the ipsilateral thigh.
2. Lower Extremity Suspension: Both feet are suspended off the end of the bed. This allows for free movement of the ankle and facilitates fluoroscopic examination.
3. Triangular Support: Place a small triangular support under the distal lower leg (proximal to the ankle joint) to maintain the leg's position and allow for unrestricted ankle motion.
4. Pelvic Support: A support is placed at the ipsilateral side of the pelvis. This allows for slight, controlled rotation of the operating table when needed, enhancing access and visualization.
5. Fluoroscopy: Ensure the C-arm can be easily brought into position for lateral and oblique views of the ankle without repositioning the patient.

Surgical Warning: The prone position carries inherent risks. We must be acutely aware of potential pressure points and stretch injuries. Ensure meticulous padding of the face, eyes, ears, breasts (in females), genitalia (in males), and bony prominences. Pay particular attention to the brachial plexus and ulnar nerves, which are susceptible to stretch or compression injuries. Regularly check for adequate perfusion and nerve integrity.

Intraoperative Assessment Under Anesthesia

Once the patient is positioned and prepped, but before incision, we will perform a final assessment of ankle and subtalar ROM under anesthesia. This provides an objective baseline, free from patient guarding or pain.

Approach 1: Open Posteromedial Approach

This approach is chosen when we suspect both FHL tendinopathy and bony impingement, or primarily FHL pathology.

1. Incision: Make a 4-cm curvilinear incision posterior to the medial malleolus, at the level of the superior border of the calcaneus. The incision should follow the anticipated course of the underlying neurovascular bundle to facilitate identification and protection.
2. Superficial Dissection: Carefully incise the skin and subcutaneous tissue. Identify and protect the lesser saphenous vein and sural nerve branches if encountered more posteriorly.
3. Deep Dissection and Neurovascular Bundle Identification: Deepen the dissection through the crural fascia. You will encounter the flexor retinaculum. Carefully incise it longitudinally. The critical step here is to identify the neurovascular bundle (posterior tibial artery, veins, and nerve) and the FHL tendon. The FHL tendon is typically the most posterior structure within the tarsal tunnel.
4. Retraction: Using a blunt retractor (e.g., a small Hohmann or a specialized vessel loop retractor), gently retract the entire neurovascular bundle and the FHL tendon posteriorly. This provides access to the posterior aspect of the talus and the tibiotalar joint.
5. Capsulotomy: Perform a careful capsulotomy of the posterior tibiotalar joint.
6. Bony Excision: Identify the symptomatic os trigonum or the prominent posterior talar process. Using a small osteotome, rongeur, or high-speed burr, meticulously excise the offending bony pathology. Ensure complete removal to prevent recurrence.
7. Smoothing and Débridement: After bony removal, use a rasp to smooth any sharp edges on the talus or tibia. Débride any hypertrophic capsulitis, inflamed synovium, or scar tissue in the posterior compartment.
8. FHL Excursion Check and Release: With the bony impingement addressed, check the excursion of the FHL tendon by passively moving the hallux. If impingement or restricted gliding persists, the fibro-osseous tunnel of the FHL needs to be released. This is performed by incising the flexor retinaculum and any constricting fascial bands from proximal to distal, extending down to the level of the sustentaculum tali. Ensure the tendon glides freely.
9. Final Assessment: Plantarflex the foot and palpate for any remaining bone-on-bone impingement or soft tissue restriction.
10. Closure: Irrigate the wound thoroughly. Close the deep fascia and subcutaneous layers with absorbable sutures. Close the skin with non-absorbable sutures or staples.

Approach 2: Open Posterolateral Approach

This approach is typically reserved for isolated bony impingement, particularly of the posterolateral talar process or os trigonum, without significant FHL pathology.

1. Incision: Begin a curvilinear incision at the posterior ankle mortise, aligning it with the posterior border of the peroneal tendons. Crucially, ensure the incision lies anterior to the sural nerve to minimize the risk of injury. The sural nerve typically runs superficially, just anterior to the Achilles tendon.
2. Superficial Dissection: Incise skin and subcutaneous tissue. Identify and protect the sural nerve and its branches.
3. Deep Dissection: Deepen the dissection, carefully retracting the peroneal tendons anteriorly. You will expose the posterior capsule of the ankle joint.
4. Capsulotomy: With the ankle in slight dorsiflexion, perform a capsulotomy to expose the lateral talar process or os trigonum.
5. Bony Excision: Using a small osteotome, rongeur, or high-speed burr, carefully remove the symptomatic lateral talar process or os trigonum.
6. Decompression Assessment: Once the bony fragment is removed, actively plantarflex the foot. Palpate the posterior ankle to ensure there is no residual bone-on-bone impingement. Adequate osseous decompression is critical.
7. Smoothing and Débridement: Use a rasp to smooth any sharp bony edges. Débride any inflamed or hypertrophic soft tissues.
8. FHL Considerations: Remember, the fibro-osseous tunnel of the FHL tendon cannot be safely released from this lateral approach due to the proximity of the neurovascular bundle medially. If FHL pathology is suspected, a posteromedial approach or endoscopic technique is preferred.
9. Closure: Irrigate the wound. Close the deep fascia, subcutaneous tissue, and skin in layers.

Approach 3: Posterior Ankle Endoscopy (van Dijk's Technique)

This is a minimally invasive approach, offering excellent visualization and reduced soft tissue trauma, but it demands precise portal placement and a thorough understanding of the posterior ankle anatomy.

Preparation and Distraction

• Manual Distraction: While the patient is prone, apply manual distraction to the os calcis (heel). This opens the posterior compartment of the ankle joint, allowing better visualization of the talar dome and tibial plafond. This is particularly useful for inspecting osteochondral defects or subchondral cystic lesions.

Portal Placement and Initial Exploration

1. Posterolateral Portal (Working Portal):
   • This is the first portal to be made.
   • Locate the level or slightly above the tip of the lateral malleolus, just lateral to the Achilles tendon.
   • Make a small skin incision.
   • Introduce a clamp (e.g., a mosquito clamp or artery forceps). Direct the clamp anteriorly, aiming towards the first interdigital space (between the first and second toes). This trajectory guides you safely into the posterior compartment.
   • Advance the clamp until it touches bone (usually the posterior talus).
   • Exchange the clamp for a 4.5-mm arthroscope shaft with a blunt trocar. Advance the blunt trocar along the same trajectory. The blunt trocar should be situated extra-articularly at the level of the ankle joint; it is not strictly necessary to enter the joint capsule at this stage.

TECH FIG 1 • A. Cross-section of the ankle joint at level of the arthroscope. (1) The arthroscope is placed through the posterolateral portal, pointing in the direction of the webspace between the first and second toe.

1. Visualization Setup:

   • Once the blunt trocar is in place, exchange it for a 30-degree 4.0-mm arthroscope. Use a lateral view direction to prevent lens damage during insertion.
   • Pull the scope backward slightly until the tip of the clamp (which was initially used to create the portal) comes into view. This confirms your orientation.

2. Posteromedial Portal (Instrument Portal):

   • This portal is made just medial to the Achilles tendon, at the same horizontal level as the posterolateral portal.
   • Make a small skin incision.
   • Introduce a clamp through this portal, directing it towards the arthroscope shaft (which is in the posterolateral portal). Visually confirm the clamp entering the endoscopic field. This ensures safe passage and avoids neurovascular injury.

TECH FIG 1 • A. Cross-section of the ankle joint at level of the arthroscope. The arthroscope is placed through the posterolateral portal, pointing in the direction of the webspace between the first and second toe. The full-radius resector is introduced through the posteromedial until it touches the arthroscope shaft. It then glides into an anterior direction until it touches bone.

Debridement and Pathology Management

1. Clearing the Field:

   • Introduce a 3.5-mm full-radius shaver through the posteromedial portal.
   • Using the shaver, partially remove the fatty tissue and adhesions overlying the joint capsule.
   • Rouvière Ligament: Be aware that the crural fascia in the hindfoot can be quite thick, forming the Rouvière ligament. This fibrous band often needs to be partially excised or sectioned to adequately approach the posterior ankle joint.

2. Identifying Key Landmarks:

   • The FHL tendon is your most important landmark. It runs centrally.
   • Remember the anatomical pearl: the neurovascular bundle is medial to the FHL tendon, and the trigonal process is lateral to it. Always keep these relationships in mind to prevent iatrogenic injury.

TECH FIG 1 • A. Visualizing the FHL tendon and neurovascular bundle.

1. Pathology Resection:
   • Os Trigonum/Posterior Talar Process: If a symptomatic os trigonum or nonunion of a posterior talar process fracture is present, proceed with its removal.
     • This involves partial detachment of the posterior talofibular ligament and release of the flexor retinaculum, both of which attach to the posterior talar prominence.
     • Use a small arthroscopic shaver, burr, or osteotome introduced through the posteromedial portal to excise the ossicle or prominent bone. Ensure complete removal.

TECH FIG 1 • B. Posterior left ankle endoscopic view. The os trigonum synchondrosis was released, and the ossicle is ready for excision. The FHL tendon is marked.

TECH FIG 1 • C. Posterior ankle endoscopic view after trigonal process resection.

*   **FHL Release:** If FHL tenosynovitis or impingement is present, release the FHL by detaching the flexor retinaculum from the posterior talar process. Ensure free gliding of the tendon.
*   **Osteochondral Defects:** If osteochondral defects or subchondral cystic lesions are identified on the talar dome or tibial plafond, débride them using the shaver and burr, and drill microfracture holes if indicated, under direct visualization.

Final Steps

1. Irrigation and Hemostasis: Thoroughly irrigate the posterior compartment to remove debris. Control any bleeding using electrocautery or by maintaining adequate fluid pressure.
2. Range of Motion Check: Perform

REFERENCES

1. Abramowitz Y, Wollstein R, Barzilay Y, et al. Outcome of resection of a symptomatic os trigonum. J Bone Joint Surg Am 2003; 85:1051–1057.

2. Barfield WR. The biomechanics of kicking in soccer. Clin Sports Med 1998;17:711–728.