Similarly to mosaicplasty, the best approach to large osteochondral lesions would be regeneration with hyaline cartilage, possibly avoiding the deleterious effects of donor site morbidity [7, 11, 13–15]. Some clinical and animal experiments reported encouraging results injecting cultured autologous chondrocytes into the defect under a periosteal flap, achieving defect healing with hyaline-type cartilage [13]. ACI was first described in the knee joint, with excellent intermediate results; the application was then extended to the ankle, despite the many biomechanical differences between the two joints [11, 13].

Cartilage harvesting is the first step required in ACI [13]. Using arthroscopical standard portals, a small sample of cartilage (15–25 mg cartilage tissue) is harvested from the ipsilateral knee for cell culturing. In order to minimize the harvest site pathology, after the first cases performed in this way, ankle arthroscopy was performed to identify a different cell source. The osteochondral detached fragment in the ankle was proven to be a good source of viable cells for ACI [13, 15].

Alternatively, cartilage may be harvested directly from the lesion margins of the affected ankle in the first step arthroscopy [15]. A direct evaluation and accurate measurement of the osteochondral damage is performed at the same time.

Cartilage is sent to a specialized laboratory for cell expansion, and it is available for implantation 4 weeks later [13, 15]. In the meanwhile, after few days of crutches and joint protection, patients are allowed to weight-bear progressively, basing on pain.

The possible surgical approach to the OLT is transmalleolar, medial, or lateral, depending on the location of the defect [13]. The lesion is exposed and the damaged cartilage and bone are debrided. The lesion is accurately measured, in order to shape and size the periosteal flap to be implanted. A periosteal flap is harvested either from the proximal or distal tibia and fixed over the cartilaginous gap with reabsorbable 6-0 suture threads. The suture is sealed with fibrin glue. The chondrocytes in liquid media are then transplanted through a hole deliberately left open and finally sutured and sealed with fibrin glue. The malleolar osteotomy is finally repaired [13].

The clinical results were excellent at 10-year follow-up. The MRI outcomes showed a smooth cartilaginous layer, with hyaline-like features at biochemical evaluation using T2 mapping. The procedures achieved clinical and radiological scores which were not inferior to ACI in knee defects [13]. Nevertheless, the technical difficulties of open ACI required some improvements towards a simpler procedure [11, 13, 15].

The surgical technique was deeply influenced by the introduction of tissue engineering and a specific instrumentation for an arthroscopic procedure [15, 16]. These developments allowed to perform the procedure arthroscopically, decreasing patients’ morbidity and technical drawbacks [15, 16]. The chondrocytes are harvested and loaded on a biodegradable scaffold based on the benzylic ester of hyaluronic acid (HYAFF 11, Fidia Advanced Biopolymers, Italy). The scaffold is a 3D support for cell adhesion and proliferation thanks to a network of 10–15 μm thick fibers with interstices of variable sizes. This peculiar constitution permitted an optimal physical support to allow cell-to-cell contact, cluster formation, and extracellular matrix deposition [15, 16].

The surgical technique is completely performed arthroscopically [15, 16]. In the first step, the harvesting of chondrocytes is executed, performing a standard ankle arthroscopy. Then after culturing the chondrocytes in the hyaluronic membrane, a second standard arthroscopy is performed [15, 16]. The lesion is debrided, and after sizing and shaping the biomaterial basing on the lesion, the membrane is delivered. A custom-made-specific instrumentation was developed for this purpose (CITIEFFE, Calderara di Reno, Italy) [15]. This consists of an 8 mm diameter and 111 mm-long stainless steel cannula with a window on one side and a positioner specifically designed to slide inside the cannula delivering the scaffold directly to the site of lesion [15].

In cases with an osteochondral defect deeper than 5 mm (IIA lesions), a bone graft using cancellous bone harvested from the distal tibia is performed before biomaterial positioning [15, 16].

Autologous chondrocytes implantation (ACI) has been intensively applied for OLT with successful clinical outcomes (90 %) [14–16]. Although no clear superiority has been established, ACI is considered one of the most reliable techniques in regenerative procedures [14]. The clinical results are described as excellent in many case series, at midterm and long-term follow-ups [14, 15]. The hyaline regeneration was confirmed by histological and radiological outcomes [16]. Nevertheless, the high costs, the need of a specialized laboratory phase, and most of all two surgical steps, and the lack of the bone regeneration are the most significant limits of this technique [16, 17].

Bone marrow-derived cells transplantation (BMDCT) represents the third generation of regenerative technique for bony and chondral layer, based on mesenchymal stem cells [17, 18]. This technique may be performed one step, in a same surgical session, or with more steps, with cells culture and enrichment [17]. In our experience, we have been performing the one-step technique, developed to overcome the two surgical steps and reduce the costs of ACI [17, 18]. Moreover, the osteogenic lineage differentiation of bone marrow-derived cells allows large bony lesion regeneration [18].