The most important finding of the present study is the effectiveness of the AT-AMIC® technique for the treatment of OCLTs that yields improvement of both clinical and radiologic scores, together with an improvement in quality of life over a follow-up period of 24 months.
AMIC® has been demonstrated to allow very satisfactory clinical and radiological results in knee and hip [7, 13, 21, 25] and, as recently published, comparable to other more complex and expensive cell-based cartilage repair techniques such as matrix autologous chondrocyte implantation (MACI) [8, 15].
OCLTs often lead to a degeneration of the subchondral bone, and the presence of cysts is not uncommon . For this reason, and for other technical surgical issues, AMIC® of the talus is most commonly performed and reported as an open surgical procedure.
In 2013, Walther and Martin reported the outcome of 42 patients with a minimum 2-month follow-up, showing a significant improvement of AOFAS score from 47.3 points to 88.3 points . Subsequently, Valderrabano et al.  reported the clinical and radiographic results from 26 patients presenting OCLTs at a minimum of 24-months’ follow-up who underwent a modified AMIC® technique using autologous bone grafting sealed by a collagen matrix without drilling of the subchondral bone. In 17 cases, ligament repair was associated with the cartilage repair procedure, while calcaneal osteotomy was performed in 16. The authors reported that the AMIC® procedure was a safe treatment for OCLTs of the talus, with overall good radiological and clinical results reporting a mean post-operative MOCART score of 62 points where complete filling of the defect to the level of the surrounding cartilage was found in 35 % of patients, and complete filling with a hypertrophic cartilage layer in 50 % of patients. Moreover, 16 out of 19 patients returned to their sports activity practiced before the onset of their symptoms.
Recently, Kubosch et al.  reported results in seventeen patients with an osteochondral lesion of the medial talus who underwent surgery. Clinical and radiological assessment was performed after a mean follow-up of 39.5 ± 18.4 months, including AOFAS Score, Foot Function Index (FFI), VAS, MOCART Score, and T2 mapping. As well as finding a significant improvement in clinical parameters, a significant correlation was found between MOCART Score and the AOFAS Score and (ρ = 0.57, p = 0.04) T2 relaxation time of the RT and the MOCART Score (ρ = 0.59, p = 0.03). The researchers concluded that the one-step autologous subchondral cancellous bone grafting and AMIC leads to a significant reduction in post-operative pain and satisfying post-operative functional outcome in mid-term follow-up. MRI assessment demonstrated a good quality of regenerative tissue similar to the MRI ultrastructure of the surrounding cartilage.
Such minimally invasive surgical procedures represent undeniable advantages for the patient; in fact the open AMIC® technique includes a malleolar osteotomy to achieve good talar dome exposure to successfully restore the dome anatomy for larger or more central/posterior and shoulder lesions. Possible complications of medial malleolus osteotomy are direct operative morbidity by injury to adjacent structures such as the posterior tibial tendon, the posterior tibial artery, the tibial nerve, or the healthy tibial cartilage; mid-term morbidity by malunion or nonunion of the osteotomy; and long-term morbidity by inducing or increasing the development of local cartilage degeneration and osteoarthritis and the necessity for hardware, which may also become symptomatic in an area with limited soft tissue envelope [5, 10].
The average complication rate in anterior ankle arthroscopy has been reported to be between 3.4 and 9 % [6, 24]. In our series, we had no complications related to the surgical technique, only one related to a hypertrophic reaction in a single patient that caused pain, impingement, and functional impairment, and required another arthroscopic surgery after 8 months after index procedure. In our cohort, no medial or lateral malleolar osteotomies were required, preserving the anatomy of the ankle. Moreover, the first arthroscopic step allows the status of the cartilage to be detected and accurately assessed.
In our study, CT and MRI were performed to evaluate patients at all time points. This work thus represents the first report, we are aware of, that assesses the outcome of AMIC® using MRI in addition to CT. MRI has proven to overestimate the size of the lesions due to surrounding subchondral bone edema, confirming previously published work [14, 19]. Another important finding is that in the first six months, CT examinations showed an increase of lesion area due to the debridement and microfracturing performed during the surgical procedure but at last follow up of the lesion area was significantly reduced. In contrast, MRI showed a reduction of the injury already at 6 months after surgery with continuous improvement up to 2 years. To further evaluate cartilage repair, we assessed the MOCART score, which showed significant improvement at 24 months with respect to the 12-month follow-up. Our MOCART 24-month total mean score of 50.9 was lower than others who have reported in the existing literature [11, 21]; however, clinical- and patient-reported outcomes were comparable. Such differences have been discussed by several authors who have shown the difficulty in correlating MOCART with the clinical situation [1, 12, 16].
In 2013, Wiewiorksi et al. assessed cartilage quality in the same group of patients reported by Valderrabano  using delayed gadolinium-enhanced magnetic resonance imaging (dGEMRIC) and concluded that the biochemical properties of the cartilage repair tissue after AMIC® repair of osteochondral lesions of the talus differ from normal hyaline cartilage .
The limitations of this study include the relatively small number of patients that did not allow for subpopulation analysis, and the lack of a control group, in particular with AMIC® open procedure. Another limitation is represented by the lack of a dGEMRIC assessment of the repair tissue, which could have given useful information about tissue quality. However, the combination of MRI and CT information provided a good evaluation of the neo-cartilage and subchondral bone after the AT-AMIC® surgical procedure. Another important limitation is the lack of sport activity assessment, particularly in young patients. Further studies will focus on the evaluation of the return to the sport in patients treated with AT-AMIC® technique and autologous bone graft, also considering the type of sports activity (high or low impact) and time taken to return to sports.