Surgical Procedure
A curved skin incision of 6-7 cm is made along the medial malleolus.
Two screw holes are predrilled from distal to proximal in the medial malleolus.
After placement of the retractors, a medial malleolar osteotomy is created to expose the osteochondral defect. To be sure of the angle of the medial malleolar osteotomy, use an arthroscopic probe to identifiable the ankle joint behind the medial malleolus.
Utilizing the drill guide, a guide pin is placed into the center of the defect, pependicalar to the medial talar curvature.
Place the cannulated drill over the guide pin and drive until the proximal shoulder of the drill is flush with the articular surface.
Tap hole to etched depth mark on Tap.
Place the taper post over the guide pin. Advance the taper post with the driver until the line on the driver is flush with the cartilage surface.
Clean the taper post with a pincet, to ensure there is no debris left. Place centering shaft into taper post and place a contact probe over the centering shaft and rotate to obtain offsets in 4 indexing points.
Remove the centering shaft and replace with guide pin and advance the circle cutter onto the articular surface by twisting.
Drive the surface reamer over guide pin and start drilling before contacting the articular surface until it contacts the top surface on taper post.
Place the trial cap into the taper post to confirm the correct depth of the fixation component. The height of the trial cap must slightly below the existing articular cartilage surface. Adjust if necessary.
Clean again and place sizing trial cap to confirm the fit. It should be congruent with the edge of the surrounding articular surface.
Place the articular component and align it. Use a slight tap on the impactor to seat it.
The osteotomy is closed by placing a bone clamp and inserting two malleolar AO screws into the predrilled holes.
Pearls & Pitfalls
Video
The second video shows a second look arthroscopy one year after placement of a hemicap. The hemicap is almost completely covered with (fibro-)cartilage
Pearls
To be sure of the angle of the medial malleolar osteotomy, use an arthroscopic probe to identify the ankle joint behind the medial malleolus. (van Bergen, Arch Orthop Trauma Surg. 2011 Jul)
Pitfalls
Make sure not to place the HemiCAP in level of the cartilage or above, to prevent contact pressure on the distal tibia.