In the physical examination, special attention is given to the range of motion (regarding dorso- and in particular plantar flexion) and laxity of the ankle joint in order to determine the accessibility of the defect. In case of a normal plantar flexion, 90–95 % of the lesions can be treated by means of anterior arthroscopy. An additional CT scan in full plantar flexion can be made to determine if the lesion is accessible by means of anterior arthroscopy without fixed distraction or if a posterior approach is indicated.

In adolescents in (sub)acute situations, or other primary cases, in which the fragment is 15 mm or larger, fixation of the fragment should be considered [10]. Preoperative planning consists of localization of the defect on CT. It is important to plan the approach and to fine-tune it to the choice of fixation technique, i.e., screw, absorbable fixation, or fibrin glue [3, 4, 8]. Most medial lesions can be approached by anterior arthrotomy. In case of doubt we advice to make a preoperative CT scan in forced plantar flexion with sagittal reconstruction. If the anterior 50 % of the lesion comes in front of the anterior distal tibia, an anterior arthrotomy can be performed. In more posterior lesions, a medial malleolar osteotomy is needed. For lateral lesions, an oblique fibular osteotomy can be necessary when the defect is located posterior. In other cases standard anterolateral incision is sufficient [5, 6]. In most patients detachment of the anterior talofibular ligament (ATFL) (and calcaneofibular ligament (CFL)) is needed in order to dislocate the talus anterior. After fixation of the fragment, the ligaments are reconstructed.

Most important in the preoperative planning is the detection of the amount of malalignment of the ankle by means of physical examination, standard weight-bearing X-rays, and alignment views. Correction of the deformity is usually between 5 and 10 mm displacement.

For preoperative planning, however, a CT scan is preferred, because it visualizes the exact location and size of the lesion [2]. A CT is required for size and location, and curvation of the talus can be checked by a 3D reconstruction. Specific for the OATS procedure, it is important to check the ipsilateral knee for any pathology. An allograft has to be matched before operation, while the exact fit of a metal implant and OATS are determined intraoperatively.

Preoperatively a CT scan is made to evaluate the size and location of the defect. The defect should be focal, contained, and preferably more than 1.5 cm in diameter or 1 cm² [7]. Preoperatively contraindications to ACI (bipolar lesions (“kissing lesions”) and diffuse degenerative joint changes) need to be diagnosed on preoperative X-ray as well as on CT scan. Skeletal malalignment and ligamentous instability should be diagnosed preoperatively with adequate physical examination. These deformities are corrected concomitantly at the time of surgery [1]. For preoperative planning, it is important to choose a donor chondrocyte site at a location with healthy cartilage and outside the articulating surface. For this technique two surgeries need to be planned: a primary arthroscopy with chondrocyte harvesting and a secondary arthrotomy to place back the cultivated cartilage.

Preoperative planning consists of adequate localization of the lesion on CT. Retrograde drilling is done for primary OCDs when there is more or less intact cartilage with a large subchondral cyst or when the defect is hard to reach via the usual anterolateral and anteromedial portals as diagnosed on preoperative CT. For medial lesions, arthroscopic drilling can take place through the sinus tarsi. For lateral lesions, the cyst is approached from anteromedial.