DEFINITION

Osteochondral lesion of the talus (OLT) may cause significant pain and mechanical symptoms in the involved ankle.

The talar articular surface is enclosed within the osseous structures of the ankle mortise.

Sammarco and Makwana3 described treatment of OLT through a “trap door” osteotomy with an autogenous talar autograft obtained from a non-weight-bearing portion of the talus.

Surgical reconstruction of OLT may require osteotomy of the tibia or fibula for adequate exposure. Traditionally, osteotomy of the malleoli (medial and lateral) have been described in order to obtain access for cartilage grafting of these lesions. Malleolar osteotomies are unstable and typically require an extended period of non-weight bearing for adequate osseous healing. Nonunion of malleolar osteotomies may occur and may require further surgery.

The anterior trap door osteotomy was developed as a stable alternative to malleolar osteotomies. This osteotomy is intrinsically stable and can be fixed with absorbable pins, facilitating postoperative imaging.

INDICATIONS

The anterior trap door osteotomy is indicated for exposure during surgical treatment of OLT. Typically, this type of exposure is necessary for cartilage grafting procedures such as osteochondral allograft or autograft reconstruction of a defect.

The osteotomy can be used for lesion of the anterior twothirds of the talar dome. The osteotomy can be placed medially, centrally, or laterally, depending on the location of the talus which requires exposure.

SURGICAL MANAGEMENT

Patient Positioning

The patient is positioned supine under appropriate anesthesia, with thigh tourniquet control. The patient is placed on a beanbag patient positioner to facilitate positioning of the extremity. The patient is rolled laterally toward the operative extremity for medial lesions and can be rolled medially for central and lateral lesions. The leg, ankle, and foot are prepared and draped from below the knee distally.

Approach

For a medial lesion, a 7-cm anteromedial longitudinal incision is made over the ankle joint parallel to the medial talar facet. Dissection is carried medial to the tibialis anterior tendon, taking care to identify and protect the saphenous vein and nerve.3

Central lesions use a midline incision centered over the ankle mortise. The superficial peroneal nerve is identified in the subcutaneous tissue over the anterior ankle and the extensor retinaculum is divided. The interval between the tibialis anterior and extensor hallucis longus (EHL) tendons is used, identifying the deep

peroneal nerve and anterior tibial artery which must be protected and retracted laterally with the EHL tendon.2

An anterolateral osteotomy can be used for OLT in the lateral talar dome.1 An incision is made centered over the tibiofibular joint and dissection carried out through the extensor retinaculum. The superficial peroneal nerve will be directly in the field and must be identified and protected. Dissection over the anterior tibia is done, and the anteroinferior tibiofibular ligament must be incised in its midportion to remove the tibial trapdoor fragment. This should be sutured for repair during closure.

The soft tissue is dissected to the ankle joint and a capsulotomy performed.

Enough capsule is stripped from the tibia to expose the medial half of the joint. A synovectomy is performed if needed.

P.758

TECHNIQUES

• Tibial Osteotomy Using the Trap Door

Opening the Tibial Trap Door

Strip the periosteum proximally along the distal tibial metaphysis to the upper limit of the wound.

Make a 1-cm mark on the medial tibial plafond beginning at the angle of Hardy (TECH FIG 1A). Make a second mark 3 cm above the joint line.

Drill two transverse parallel holes across the tibial metaphysis beneath the cortex where the tibial trap door is to be removed. Absorbable pins will be inserted into these predrilled holes when the trap door is replaced after the graft has been inserted in the talar dome.

Make two vertical parallel saw cuts with a Hall Micro-Oscillating Saw (Zimmer, Inc., Warsaw, IN) using a no. 64 saw blade to a depth of 2 cm at the joint surface (TECH FIG 1B).

Taper these cuts proximally and upward to the anterior tibial metaphysis 3 cm above the joint. To protect the talar surface, insert a Freer elevator between the tibia and talus.

Make a third horizontal saw cut connecting these cuts at their upper limit.

Angle the saw inferiorly and 22 degrees posteriorly from the anterior metaphysis toward the joint surface.

TECH FIG 1 • A. A 7-cm anteromedial incision exposing the medial half of the ankle joint, showing the angle of Hardy (arrow). B. Saw cuts are made 1 cm wide, 3 cm high, and 2 cm deep (not seen), creating a trap door (arrow). C. The trap door is removed and set aside to be replaced after the graft is inserted. A probe has been inserted into the lesion (arrow).

Use a thin 10-mm osteotome to mobilize the trap door. Remove the trap door and place it aside (TECH FIG 1C).

Coring Out the Lesion

Plantarflex the ankle to deliver the osteochondral lesion into view (TECH FIG 2). Probe the lesion to determine its exact location.

Select the appropriate-size coring instrument: 6, 8, or 10 mm.

Place the coring instrument at right angles to the talar dome and extract the lesion. The removed bone is to be used later.

Harvesting and Inserting the Graft

Expose the medial facet of the talar body using a mini-Hohmann retractor with the ankle in plantarflexion.

Position the harvesting instrument on the medial facet 4 mm beneath the talar dome.

Harvest the graft in such a way that when inserted into the recipient site, the slightly elevated inferior margin of the graft from the medial facet will be oriented toward the medial border of the talar dome, approximating the shape of the normal talar weight-bearing surface (TECH FIG 3A).

P.759

TECH FIG 2 • The ankle is plantarflexed to expose the lesion and a premeasured 8-mm coring device is used to remove the lesion (arrow).

TECH FIG 3 • A. The osteochondral graft is harvested from the anterior portion of the medial facet 4 mm below the articular surface of the talar dome and at least 10 mm away from the recipient site (arrow). B. The osteochondral graft has been inserted into the recipient site (upper arrow) and the bony material removed, including attached remaining cartilage from the defect that has been inserted into the donor site (lower arrow).

TECH FIG 4 • The trap door is replaced and secured with bioabsorbable pins (arrows) placed into predrilled holes.

Débride the talar recipient site and tap the osteochondral graft into place with the inferior medial facet portion oriented toward the medial border of the talus (TECH FIG 3B).

Completion

Insert the material that was removed, including the osteochondral lesion, in the donor site. This can be augmented with cancellous bone taken from the distal tibia.

Insert the tibial bone block back into its bed and insert bioabsorbable pins (Orthosorb, Biomet, Warsaw, IN) into the predrilled holes to secure the bone block in place (TECH FIG 4).

Approximate the deep tissues with 3-0 absorbable suture and close the skin with 3-0 monofilament nylon. Apply a compression dressing and posterior splint.

• Additional Technique

P.760

If the bone at the base of recipient site is excessively sclerotic, it may be drilled using a 0.045 Kirschner wire before inserting the graft in order to encourage vascular ingrowth.

For lesions on the lateral talar dome, use the same technique but make the most lateral vertical saw cut 2 mm away from the distal tibiofibular syndesmosis to avoid violating the joint.

PEARLS AND PITFALLS

This technique avoids the need for a medial malleolar osteotomy. It provides excellent visualization of and access to the lesion through a single incision while avoiding a second procedure on an asymptomatic knee to harvest the graft.

The procedure is best suited for lesions up to 10 mm in diameter and up to 10 mm deep located in the anterior two-thirds of the medial or lateral talar dome margins.

The graft can be placed just beneath the subchondral bone of the medial or lateral facet because these surfaces bear minimal weight and no complications have been noted in the medial or lateral gutters.

The surgeon should avoid making the vertical saw cuts more than 3 cm deep at the joint surface or 4 cm in height because this increases the risk of a medial malleolar stress fracture.

In harvesting the osteochondral graft, the surgeon should avoid taking the graft too near the talar surface or too near the recipient site in order to avoid a stress fracture of the talar dome.

Patients with arthritis can have progression of the condition even though the graft becomes incorporated and survives.

The most common minor complaint is occasional aching at the anteromedial joint line with activity.

POSTOPERATIVE CARE

The compression dressing and posterior splint are changed at the first follow-up visit.

Sutures are removed at 2 weeks, and a non-weight-bearing short-leg cast is used for 1 month.

A range-of-motion boot is then prescribed with 50% weight bearing for 3 weeks, after which physical therapy is instituted.

REFERENCES

1. Garras DN, Santangelo JA, Wang DW, et al. A quantitative comparison of surgical approaches for posterolateral osteochondral lesions of the talus. Foot Ankle Int 2008;29(4):415-420.

    

    

2. Kreuz PC, Lahm A, Haag M, et al. Tibial wedge osteotomy for osteochondral transplantation in talar lesions. Int J Sports Med 2008;29(7):584-589.

    

    

3. Sammarco GJ, Makwana NK. Treatment of talar osteochondral lesions using local osteochondral graft. Foot Ankle Int 2002;23(8):693-698.