In order to treat OCDs of the medial talar dome after failed primary treatment, a contoured articular inlay implant (HemiCAP^®, Arthrosurface Inc., Franklin, MA, USA) with a diameter of 15 mm was developed. Fifteen articular component offset sizes are available, based on the surface anatomy of the medial talar dome. In a cadaveric study, the offset sizes were found appropriate for a variety of talar specimens. Furthermore, it was shown that a slightly recessed implantation level prevents high contact pressures [22]. Clinical goals of the implant are to offer relief of pain and swelling, return to activity, and prevent (further) cyst formation.

At presentation, the patient’s predominant symptom was pain deep in the ankle joint during and after activity. She used to play korfball at competitive level but had stopped due to the pain. Korfball is a mixed gender team ball game, similar to mixed netball and basketball, and is very popular in the Netherlands.

At physical examination, leg alignment was neutral, the range of motion was normal and symmetric, and both ankle joints were stable. There was no recognizable tenderness on palpation.

Radiographs of the right ankle revealed a large cystic osteochondral defect of the medial talar dome (Fig. 1). A computed tomography scan confirmed the osteochondral defect, measuring 17 × 8 × 8 mm, accompanied by some small subchondral cysts and a loose fragment. After informed consent was obtained, the patient was scheduled for surgery.

The ideal indications for treatment with this implant are not yet known. The authors consider its use in patients with a large OCD on the medial talar dome who have clinically significant pain more than 1 year after primary surgical treatment. The following are regarded as contraindications: age < 18 years, OCD size > 20 mm, ankle osteoarthritis grade II or III, concomitant ankle pathology, advanced osteoporosis, infection, diabetes, or a known allergy to implant material.

The surgical approach is an important part of the implantation technique because the accuracy of implantation of this device strongly depends on the approach and quality of vision. For adequate exposure, the authors make an oblique osteotomy of the medial malleolus. The osteotomy is ideally directed toward the intersection between the tibial plafond and medial malleolus at an angle of 30° relative to the long tibial axis [21]. Although there are other osteotomy options, including anterior tibial, step-cut, and inverted V or U osteotomies, the oblique osteotomy is our preferred technique because it is relatively simple, exposure of the talus is excellent, and congruent reduction is well possible [12, 17, 21].

The surface of the prosthetic device should be placed slightly recessed relative to the surrounding surface of the talar cartilage because talar cartilage deforms during weight bearing while the implant does not. Wan et al. [25] measured a peak cartilage deformation of 34.5 ± 7.3% under full body weight in persons with a medial talar dome cartilage thickness of 1.42 ± 0.31 mm. We therefore aim at an implantation level of 0.5 mm below the adjacent cartilage. This implantation level was found appropriate in a previous cadaveric study [22]. When the prosthetic device is correctly implanted, excessive contact pressures of the implant are avoided [22].

While there are various offset sizes, each articular component has a diameter of 15 mm. This is based on the finding that primary arthroscopic treatment is generally successful for lesions up to 15 mm, while this treatment is less successful for larger lesions [6]. The set diameter may be a disadvantage of the implant. In our patient, the largest defect diameter was 17 mm. The part of the OCD that was not covered by the implant is expected to be filled by fibrocartilaginous tissue.