Osteochondral Lesion of the Talus (OLT) Treated by Matrix-Based Techniques (Matrix-Induced Chondrocyte Implantation [MACI] and Autologous Matrix-Induced Chondrogenesis [AMIC])

Markus Walther

INDICATION

Matrix-induced chondrocytes implantation (MACI) and autologous matrix-induced chondrogenesis (AMIC) are surgical treatment options for symptomatic cartilage defects. MACI is a two-step procedure in which in vitro cultured chondrocytes are cultured and seeded onto an acid collagen scaffold which is transplanted to the defect and fixed in place with fibrin glue. AMIC is a one-step procedure combining microfracture of the vascular subchondral bone with the application of a bilayer collagen matrix. Microfracturing causes release of blood and bone marrow that form a super clot containing the requisite building blocks for cartilage repair: multipotent mesenchymal progenitor cells, cytokines, and growth factors. The collagen matrix secures the clot and improves its overall stability. Furthermore, it provides an environment where cells can adhere, proliferate, and produce repair tissue in a protected setting.¹

Compared to other cartilage reconstruction techniques, MACI and AMIC provide a stable cartilage rim which can be maintained at the site of the lesion. Large defects can be readily addressed with this technique. The use of the matrix makes it much easier to manage shoulder lesions of the talus (Fig. 16-1). Finally a matrix can be glued to the bone surface with fibrin glue. Gluing the matrix to the bone helps to avoid osteotomies in nearly all cases.²

MACI and AMIC are best suited for patients between 18 and 50 years of age. They are indicated for management of symptomatic osteochondral lesions failing debridement, drilling, or microfracture.³^, ⁴^, ⁵

Primary MACI or AMIC can be considered in focal cartilage defects of the talus (ICRS Grade III and IV) >1.5 cm² or in osteochondral lesions of the talus (OLT) associated with expansive subchondral cysts (Scranton Stage V lesion).⁴^, ⁶

However, there are some disadvantages of MACI for the talus. These include high cost and the need for a two-stage procedure to allow time for chondrocyte culture. Harvesting cells for culturing is considered to be a part of a drug-producing process. Therefore special permission has to be requested by the local healthcare administration. Standard operating procedures (SOPs) for harvesting and transportation of the cartilage cells are mandatory for the accreditation process.

AMIC is an off the shelf product to be used in a one-step procedure. Both, AMIC and MACI are not approved by the Food and Drug Administration (FDA) for the use in foot and ankle surgery (as of July 2012). Therefore informed consent and extended patient education are imperative.

Contraindications for MACI or AMIC include generalized degenerative changes in the joint, cartilage defects in the corresponding opposite joint surface, inflammatory joint disease, crystal arthropathy, and neuroarthropathy. Instability and axis malalignment do not represent contraindications if these can be addressed along with cartilage reconstruction.

For larger OLTs or OLTs failing prior surgical management, both techniques provide patients and their treating surgeons a potentially successful treatment avenue that did not exist prior to MACI or AMIC.

Patient Positioning to Harvest Chondrocytes (Only Indicated for MACI)

The patient position to harvest chondrocytes is that used for a standard arthroscopy of the ankle. Harvest of chondrocytes can be performed with conventional knee or ankle arthroscopy. Suitable locations for harvesting expendable articular cartilage from the knee include peripheral superomedial or superolateral femoral condyle or the intercondylar notch. Alternatively, Giannini et al.⁷ have demonstrated that the detached OLT fragment at the time of index arthroscopic debridement/drilling or microfracture may be an acceptable source of chondrocytes for MACI, however these results have not been confirmed by Candrian et al.⁸ Another possible harvest area is the anterior part of the talus.⁶

Figure 16-1. MRI (T2-weighed, coronary view) of an osteochondral defect at the medial talar shoulder.

By using a curette, two to three full-thickness articular grafts are harvested, grafts that include the superficial layer of the subchondral bone. The grafts are transferred to a sterile container with nutrient medium and transported to the laboratory. Using a patented procedure, the articular cartilage matrix is enzymatically disrupted to isolate the chondrocytes. Culturing of chondrocytes requires approximately 2 to 6 weeks; the length is dependent on the method used by the company that the performs the culture.

Patient Positioning for Transplantation of MACI or AMIC

The procedure can be performed using several types of anesthesia. Homeostasis is maintained using a thigh tourniquet inflated 100 mm Hg above the systolic blood pressure. A radiation protection mat is placed from the middle of lower thigh proximally over the patient. An image intensifier is used only if an osteotomy is utilized.

Dependent on the location of the defect, the patient is positioned supine with a slightly internal or external rotated lower extremity. Lateral recumbent position is used in case of dorsomedial approach, and on the contralateral side in case of dorsolateral approach. The affected leg is positioned free to be able to flex the knee; otherwise, adequate dorsal extension of the ankle joint is not possible. If iliac crest graft is to be obtained, the pelvis needs to be prepped and draped as well and the ipsilateral pelvis supported with a bump. Alternatively, bone graft may be harvested from the calcaneus, distal tibia, or proximal tibia, all of which are locations prepped into the surgical field for ankle surgery.⁹ A vacuum mattress can be helpful to adjust the patient’s position during the procedure.

SURGICAL APPROACHES

Depending on the location of the cartilage defect, a ventromedial, ventrocentral, or ventrolateral approach is used. The ventromedial approach is carried out between the medial malleolus and the anterior tibial tendon (Fig. 16-2). The ventrocentral access is between the anterior tibial and the extensor hallucis longus tendon (Fig. 16-3). The neurovascular bundle is retracted laterally with a blunt Hohmann retractor. With that, the entire ankle joint can be visualized well. This approach is particularly useful for treating defects on the medial and lateral talus shoulder as well as for centrally located defects.

The ventrolateral approach (Ollier approach) is carried out lateral to the peroneus tertius tendon ventral to the lateral malleolus (Fig. 16-4). Lesions of the lateral
talus shoulder can be addressed well with this approach. The capsule closure can be combined with stabilization of the external ligaments.

Figure 16-2. Ventromedial approach between the medial malleolus and the anterior tibial tendon.

Figure 16-3. Ventrocentral approach between the anterior tibial and the extensor hallucis longus tendon.

Dorsal approaches are seldom necessary, since with adequate distraction of the joint with K-wire distractor, deeper-lying defects can also be accessed. The dorsolateral approach runs dorsal to the lateral malleolus, and enables medial or lateral retraction of the peroneal tendons (Fig. 16-5).

For a dorsomedial approach between the medial malleolus and the posterior tibial tendon (Fig. 16-6), the patient is positioned on the affected side. The contralateral leg is well padded, and the affected leg is positioned in a freely moveable fashion. Using a short vacuum bean-bag positioner considerably facilitates the procedure. Here too, adequate flexion of the knee is necessary.

Surgical Technique to Implant the Matrix

The further surgical steps are illustrated using the example of a case of an OLT with subchondral cyst of the medial talar shoulder using a medial approach (Fig. 16-1).

Figure 16-4. Ventrolateral approach (Ollier approach) lateral to the peroneus tertius tendon and ventral to the lateral malleolus.

The skin incision is marked medial between the medial malleolus and the anterior tibial tendon (Fig. 16-2). After dissection to the level of the joint capsule, the joint is opened by a longitudinal incision. A 2.0-mm K-wire is drilled into the distal tibia, a second one parallel to it, in the talus. Placing the wires using the K-wire distractor as drill guide facilitates precise positioning of the wires. The joint is then distracted in maximum plantar flexion (Fig. 16-7).

Unstable cartilage is debrided. A stable cartilage edge must be established adjacent to a healthy osteochondral border. Oval-shaped preparation of the defect facilitates insertion of the collagen matrix. All necrotic bone is removed and cysts curetted. The underlying sclerotic zone is perforated using multiple small drill holes (1.2-mm K-wire) with adequate cooling or with microfracture (Fig. 16-8).

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