High-density implantation — what it is, and why every timeline on this site is an adaptation

ICC — Instant CEMTRO Cell — and HD-ACI are the same technique. The clinic uses the first name, the literature publishes under the second, and that gap is why a patient told they are having “ICC” can search for hours and find nothing. If you have been given the first name, the second is the one to search.

“Instant” describes when the cells meet the membrane. The collagen membrane is cut to the lesion and seeded with the cultured cells in the operating room, then implanted after a short absorption period, rather than arriving pre-seeded from a laboratory. Multiple lesions in the same joint can be treated in one operation, which is the reason the technique appears in knees like the ones this site is written for.

The density the technique is named for rests on one animal study: in a sheep model, five million chondrocytes per cm² produced hyaline-like cartilage that varied less and resembled normal cartilage more closely than one million did, while mesenchymal cells and microfracture produced fibrocartilage instead.^E41

All of it comes from one centre in Madrid, all single-arm, none with a comparison group. That is a real limitation and it is stated first here rather than last. Within it, the results are consistent.

In the first fifty consecutive knees, IKDC rose 26.3 points at twelve months and 31.0 points at twenty-four, with pain and swelling both significantly less common and flexion improved by 25.1° at two years.^E42

In a second series of forty knees, 27.5% of patients had subchondral bone oedema on the two-year MRI, and it did not correlate with how they were doing clinically.^E43

That last finding is the one worth carrying into a follow-up appointment. “Bone marrow oedema” on a two-year MRI report reads as bad news; it happened to more than a quarter of the patients in that series, and it was not associated with how they did. It is a reason to ask the question, not a reason to assume the answer.

In forty-eight knees compared with and without a concurrent ACL reconstruction, both groups improved past the threshold that counts as a meaningful change, with no significant difference in graft appearance on MRI; activity level dropped immediately after surgery and had climbed back by two years, with 70.6% and 89.5% of the two groups returning to their pre-injury level — back to where they started, not past it.^E44

This is the part that changes how you should read the rest of this site. Rehabilitation timelines come from a small number of trials, and those trials enrolled a particular kind of knee.

The randomised trial that produced the accelerated weight-bearing timeline enrolled femoral condyle lesions only — twenty-seven medial and ten lateral — averaging 3.15 cm² in one arm and 2.89 cm² in the other.^E1

The trial that established MACI against microfracture required defects of at least 3 cm² and treated a mean of 4.8 cm², in the condyle or trochlea.^E7

Against that, the Madrid series reports a mean lesion of 6.1 cm², ranging from 1.5 to 13.5 cm² in the knee — roughly twice the size of the lesions in the trials that produced the timelines. This site's research file records that figure for the series as a whole rather than for any one published paper, which is why it is stated here as the series' own number and not as a study result.

So a reader arriving here from a standard MACI protocol is reading guidance built on a smaller lesion, often in a different compartment, sometimes in a knee with one defect rather than several. The guidance is still the best available. It is not guidance about this operation, and this site says so on every page where the difference bites.

The configuration this technique is specifically indicated for — patellofemoral, multifocal, previously operated — is also the one with the thinnest rehabilitation evidence and the longest published follow-up. The long-term picture has its own page; two things belong here because they bear on the operation rather than the rehabilitation.

In a series of thirty-eight patients with large isolated or bipolar patellofemoral lesions — the bipolar ones averaging 8.8 cm² of treated surface in total — function improved by a median of 31 Lysholm points, and twenty-five of the thirty-eight went on to have thirty-two further operations, though fourteen of those were hardware removal after a previous osteotomy.^E50

Read alongside the long-term series: this configuration carries more reoperations and lower scores than an isolated femoral condyle lesion, and patients in it still overwhelmingly say it was worth having. Good but lower, not good versus hopeless. The multifocal page carries the five-year and 12.6-year figures and the decline finding that shapes the long-horizon end of this site's program.