The implant has to come out. It should come out quickly, and without the bone loss.

When a knee replacement fails, the old implant usually has to come out before a new one can go in. If bone cement is still holding it, surgeons work it free with thin osteotomes, saws and high-speed burrs. If a cemented stem will not come free, some also use a trephine reamer, a hollow cutter passed over the stem to clear the cement around it. Surgical reviews describe getting a well-fixed cemented stem extension out as long and difficult work, and bone can be broken or lost along the way. In one center’s first knee revisions for a loose tibial component, operations that also replaced the well-fixed femoral component took about an hour longer overall than those that revised only the tibia, and substantial bone loss was found at its removal in 7% of those knees.

The MicoCalo Implant Extraction Assist System (MIEAS) uses a low-frequency electromagnetic field to heat the metal implant so the bone cement right next to it softens. It is designed for the step after the joint is exposed and before the old component is extracted. The aim is for the implant to come free with less force and less bone lost, shortening time in the operating room and under anesthesia.

In one early bench demonstration on a cemented hip stem, in cement cured on the bench that day and with no bone, the field ran for 3 minutes 24 seconds. The stem was then clamped and the cement pulled off it by hand. Softening the cement is how the implant is released; cement left on the bone, where it has to come out, is still cleared with the usual techniques. We aim to shorten the heating time further.

Instruments and bone loss at removal: Bieganowski et al., Knee Surg Relat Res 2022;34:30, PMID 35725586. “Always long and difficult” and trephines: Pasquier et al., Orthop Traumatol Surg Res 2020;106(1S):S135–S147, PMID 31812635, on extracting cemented knee stem extensions. Hour and 7%: Martin et al., Bone Joint J 2020;102-B(6 Supple A):123–128, PMID 32475265; one center, aseptic first revisions for a loose tibial component: 76 knees with both components revised vs 88 with the tibia alone, median 204.5 vs 152 minutes for the whole operation.