Introduction

With the introduction of a two-portal endoscopic hindfoot approach in 2000, access to the posterior aspect of the ankle and subtalar joint has become a save possibility. Thereby resulting in a superior approach of posterior located intra-articular pathology as well as the possible treatment of multiple extra-articular structures of the hindfoot such as the os trigonum, flexor hallucis longus and the deep portion of the deltoid ligament.

Anatomy

A detailed knowledge of the anatomy of the ankle joint, the tendineous and neurovascular structures around the ankle is important to plan and perform arthroscopic surgery. The anatomic landmarks of bone and tissue in and around the ankle joint can easily be palpated and can be marked on the patient's skin. Landmarks are important for a proper portal positioning and can assist through the course of the procedure. The following landmarks are important: both malleoli and the anterior joint line, which can palpated by dorsi- and plantarflexing the ankle. The anterior tibial tendon; peroneal tertius tendon and the Achilles tendon act as landmarks. Vascular landmarks include the great saphenous vein, and the small saphenous vein. Neural landmarks are the sural nerve, running 2 cm posterodistally to the lateral malleolus, and the superficial peroneal nerve.

Anatomy of the flexor hallucis longus

The flexor hallucis longus (FHL) is the most laterally located bipennate muscle of the human calf. It runs distally in a fibro-osseous gliding channel, located between the posteromedial and posterolateral talar process, at the ankle-subtalar joint complex level. The flexor retinaculum, situated in between both processes, keeps the tendon in place. The FHL tendon inserts in the distal phalanx of the hallux after passing distally and medially underneath the sustentaculum tali. The FHL tendon is an important landmark in hindfoot endoscopy, as the posterior tibial neurovascular bundle runs just medial from this tendon. Hence, the safe area is lateral of the FHL tendon.

Anatomy of the subtalar joint

A functional subtalar joint consists of an anterior, middle, and posterior facet. The posterior facet has both an intra-capsular and extra-capsular ligamentous support. The intra-capsular ligamentous support includes the posterior talo-calcaneal ligament, the lateral talo-calcaneal ligament and the anterior capsular ligament of the posterior subtalar joint. The extra articular ligamentous support consists of the cervical ligaments, the calcaneo-fibular ligament, superficial deltoid ligament and the interosseous talo-calcaneal ligaments.
Talo-calcaneal coalitions may occur in any of these facets. However, the middle facet is predominantly involved. A talocalcaneal coalition may be osteofibrous, cartilaginous, or osseous union of the talus and calcaneus. Some coalitions may resolve during childhood as a result of weight-bearing biomechanical activity24. Limited movement between two or more bones of the subtalar joint complex leads to excessive stresses in the hindfoot joint, thereby causing painful inflammations and premature bone degeneration.

Anatomy of the peroneal tendons

The peroneus brevis muscle is situated dorsomedially to the peroneus longus muscle from its proximal aspect up to the fibular tip. Here, the peroneal brevis tendon is still relatively flat. Proximal of the lateral malleolus tip the peroneus longus tendon is located dorsally to the peroneus brevis tendon. Distal of the lateral malleolus tip, the peroneus brevis tendon becomes rounder, and crosses the round peroneus longus tendon. The distal posterolateral part of the fibula forms a fibrocartilaginous sliding channel for the two peroneal tendons. The tendons lie constrained in the malleolar groove by the superior peroneal retinaculum and distally by the inferior peroneal retinaculum.

Diagnostic imaging

After history taking and physical examination the diagnosis can be confirmed or rejected based upon different available imaging techniques. In case history taking and physical examination do not reveal abnormalities, additional diagnostics can be used to search for a clue or to rule out pathology, i.e. medico-legal reasons. Close consultation between the orthopaedic surgeon and the radiologist is necessary to decide upon optimal radiographic diagnostics.

In patients without a history of trauma but with isolated recognizable posteromedial ankle pain during flexion of the great toe while palpating the tendon at the level of the gliding channel, no additional diagnostics are needed. In case conservative treatment options fail, the intervention will be a release regardless of the pathology. A MRI scan can be valuable to rule out tendon ruptures.

In patients with posteromedial ankle pain associated with a positive hyperplanterflexion test, standard weight-bearing radiographs in the antero-posterior and lateral direction must be made. In case of doubt for the differentiation between hypertrophy of the posterior talar process or an os trigonum, a lateral hindfoot radiograph view with the foot in 25 degrees exorotation in relation to the standard lateral ankle view is advised. In ballet dancers a lateral radiograph with the foot in maximal plantarflexion can be useful to determine whether a bony posterior ankle impingement is present. Especially in posttraumatic cases, a spiral CT scan can be important to ascertain the extent of the injury / location of the osteochondral defect and/or the exact location of calcifications or fragments.

Surgical Treatment

Indications

The indications can be categorized according to their anatomical orientation.

Articular

A subdivision is made for bony and soft tissue pathology;

• Bony pathology includes loose bodies, ossicles, posttraumatic calcifications, avulsion fragments and osteophytes. These osteophytes can be located either at the posterior tibial rim or at the level of the subtalar joint.

• Cartilage pathology includes chondromatosis, posterior located talar, tibial or calcaneal osteochondral defects, degenerative joint changes such as talar cystic lesions, osteoarthritis and intraosseous talar ganglions.

• Soft tissue pathology includes posttraumatic synovitis, villonodular synovitis and syndesmotic soft tissue impingement.

Peri-articular

• Posterior ankle impingement, based on bony and / or soft tissue impingement. Bony impingement includes a hypertropic posterior talar process, os trigonum or talus bipartita. Soft tissue impingement includes a partial rupture or fibrosis of the PTFL, intermalleolar ligament or deep portion of the posterior tibiofibular ligament.

• Avulsion fragments (Cedell fracture) and posttraumatic calcifications or ossicles in the deep portion of the deltoid ligament.

• FHL tendinopathy.

• Tarsal tunnel syndrome.

• Recurrent peroneal tendon dislocation.

Contraindications

• The absolute contraindication is a localized soft tissue infection.

• Relative contraindications are severe oedema, patients suffering from vascular diseases such as diabetes, and moderate degenerative joint disease.

Post-operative rehabilitation

The patient can be discharged the same day of surgery and weightbearing is allowed as tolerated. The patient is instructed to perform active dorsiflexion of the ankle to the neutral position (knee slightly bent). This exercise should be performed 2 or 3 days times per hour for the first days after surgery. The patient is instructed to elevate the foot when not walking to prevent edema. The dressing is removed 3 days post-operative. Normal walking without crutches at 4 - 5 days post surgery. Patients with limited range of motion are directed to a physiotherapist. Running can be started when range of motion is normal and in absence of swelling. This can on avarage be expected at 3 weeks post surgery. Sport resumption can on average be expected at 6 weeks post surgery. 

Recommended literature

Van Dijk CN, Scholten PE, Krips R. A 2-portal endoscopic approach for diagnosis and treatment of posterior ankle pathology. Arthroscopy. 2000 Nov;16(8):871-6.

Van Dijk CN, de Leeuw PA, Scholten PE. Hindfoot endoscopy for posterior ankle impingement. Surgical technique. J Bone Joint Surg Am. 2009 Oct 1;91 Suppl 2:287-98.

Van Dijk CN.Hindfoot endoscopy. Foot Ankle Clin. 2006 Jun;11(2):391-414, vii.