Talar Dome Resurfacing with the HemiCap Prosthesis

Fig. 17.1

The osteochondral defect (arrow) is exposed through an oblique medial malleolar osteotomy. A K-wire can be inserted into the talus through one of the predrilled holes to hold the medial malleolus in place

The necrotic fragment of the defect can now be identified and debrided. Utilizing a drill guide, a guide pin is placed into the center of the defect, perpendicular to the curvature of the medial talar dome. The guide pin ensures that a perpendicular direction is maintained throughout the procedure. The titanium screw of the metal implant is inserted after drilling a pilot hole. A contact probe is used to determine the radius of curvature in the sagittal and coronal planes to allow for a precise fit of the articular component to the existing articular surface. A matching reamer prepares the site for placement of the articular component. The reamer is a cannulated instrument used over the guide pin with a diameter of 15 mm. A sizing trial with corresponding offsets allows for final verification of proper fit. The selected articular component is oriented into the correct planes and is placed on the screw. It is impacted with a gentle hammer-stroke on an instrument with a plastic tip, thereby engaging the taper interlock (Fig. 17.2). After the confirmation of slightly recessed implant edges, the osteotomy is reduced. Initially, large diameter K-wires are placed through the predrilled screw holes to confirm correct alignment. A Weber bone clamp can be placed for initial compression. Placement of the proximal leg of the Weber clamp is facilitated by creating a small hole in the distal tibial cortex proximal to the osteotomy using a 2.5-mm drill. We routinely use two 3.5-mm cancellous lag screws with a length of 40 or 45 mm. The posterior tibial tendon sheath is not repaired and the wound is closed with Ethilon 3.0 sutures using a vertical mattress (Donati) technique.

Fig. 17.2

Final view after the articular component (arrow) is oriented into the correct planes and is placed on the screw. Note that the edges of the implant are slightly recessed (approximately 0.5 mm) compared to the adjacent cartilage level

17.3 Rehabilitation

The postoperative management consists of a plaster cast for 1 week. A functional non-weight-bearing brace (Walker) or a detachable plaster cast can be applied for another 5 weeks. During this period, non-weight-bearing sagittal range of motion exercises are allowed, i.e., 15 min twice daily. After these 6 weeks, radiographs of the operated ankle are obtained to confirm consolidation of the malleolar osteotomy. Subsequently, physical therapy is prescribed to assist in functional recovery and facilitate the return to full weight bearing over approximately 1 month. Return to normal weight bearing and walking should thus be accomplished 10 weeks after surgery. Impact activities, such as running, are allowed when no signs of prosthetic loosening and migration are seen after 6 months of follow-up. Non-contact sports are allowed after 9 months of follow-up and contact sports 1 year after surgery. However, the risk of periprosthetic fracture during contact sports should be discussed with the patient. We reported the first clinical case report of the talus implant in which the patient was able to play korfball (contact sports) at the preinjury level after 1 year and continued to play at this level at 2 years follow-up [21].

17.4 Discussion

Treatment of osteochondral lesions or osteonecrosis by means of metal resurfacing implants is relatively new, and the literature is scarce. Promising clinical results have been reported for the treatment of the femoral [27] and humeral head [18], as well as the first metatarsal [10] and patellar surface [5]. Two biomechanical cadaveric studies provided foundations for use of the talus implant in the ankle joint [1, 24]. We performed a prospective case series of 15 patients with a clinical follow-up of 1 year [16]. All patients had failed prior surgical treatment of a large defect of the medial talar dome. Failed prior surgical treatments were debridement and bone marrow stimulation, cancellous bone grafting of the defect, and screw fixation. Various outcome measures were recorded prospectively, including numeric rating scales (NRS) of pain at rest, climbing stairs, and running, American Orthopaedic Foot & Ankle Society (AOFAS) Ankle and Hindfoot clinical rating System, Foot and Ankle Outcome Score (FAOS), and Short Form 36 (SF-36). After 1 year follow-up, there was significant improvement in the NRS, AOFAS, four of five subscales of the FAOS, and the SF-36 physical component scale. There were four minor complications that resolved within the study period. Three patients reported an area of numbness about the scar, which resolved within the postoperative year. Another patient had a superficial wound infection, which was effectively treated by oral antibiotics. On radiographs there were no signs of prosthetic loosening, cyst formation, or degenerative changes at 1 year follow-up (Fig. 17.3). The medial malleolar osteotomy healed in all cases.

Fig. 17.3

Mortise (a) view and lateral (b) weight-bearing radiographs of a left ankle 1 year postoperatively showing correct positioning of the implant

Alternative current treatment methods for large or secondary lesions are osteochondral autograft transfer system (OATS), cancellous bone grafting, an osteochondral allograft, ankle arthrodesis, or ankle arthroplasty. Although excellent results of OATS have been published [17], the risk of donor site morbidity in the knee is worrisome [19]. An additional disadvantage of osteochondral autografts is difficulty in matching the talar surface geometry and poor graft integration [12]. Limited availability and donor site pain are also disadvantages of cancellous bone grafting [2]. Osteochondral allografts can be used for massive defects but are not recommended for localized OCDs, based upon the gradual deterioration of the hyaline part of such grafts in the knee and resorption and fragmentation of the graft [20]. Ankle arthrodesis and prosthesis are definite solutions for a recurrent OCD but are not preferable in young patients. Should the metal implant fail in the long term, it can be removed and the ankle joint fused.

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 exposure. If the osteotomy is created too medially, i.e., in the articular facet of the malleolus, exposure of the talar dome may be insufficient for adequate treatment. Furthermore, a small distal fragment may be prone to fracture when fixed at the end of the procedure. Conversely, if the osteotomy is created too laterally, it will exit in the tibial plafond. This is undesirable because the medial tibial plafond directly articulates with the medial talar dome [11, 24], and damage to this weight-bearing area might lead to secondary osteoarthritis [7]. We therefore routinely use a probe to determine the intersection of the tibial plafond and the articular facet of the medial malleolus when performing the osteotomy [22].

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. 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 [28]. 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 [24]. When the prosthetic device is correctly implanted, excessive contact pressures of the implant on the tibial plafond are avoided [24].

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