The authors commence the discussion with illustrations the structure of articular cartilage, which they stress is key to developing successful treatments. There are three identifiable zones within the cartilage – Zone 1 (superficial), Zone 2 (intermediate) and Zone 3 (deep) delineated by what is called a ‘tide mark’ from the deeper zone of calcified cartilage which is itself adjacent to the bone. The bone here is called ‘the subchondral’ bone, which just means ‘the bone under the cartilage’.
Each of the three zones contain cartilage cells suspended like bubbles in a matrix containing collagen fibres and a chemical matrix containing largely water but also a number of important chemical molecules, including a group called proteoglycans. Each zone differs from one another in the ratio of these elements, and that determines the characteristic of each layer. For example, Zone 1 has a higher number of collagen fibres aligned in a manner that allows glide.
There are no blood vessels in articular cartilage and it receives its nutrition from fluids in the joint cavity by diffusion, and from the underlying subchondral bone. The lack of its own blood supply is one of the reasons that partial and full thickness cartilage lesions have a limited ability to heal.
They also discuss adjuncts to these surgical procedures such as the use of high molecular weight hyaluronic acid and the use of cellular-based treatment modalities where cells are seeded onto a matrix, for example cells from cartilage itself stem cells from fat or bone marrow (‘mesenchymal stem cells’). Of particular interest is platelet rich plasma (PRP) which contains various growth factors that stimulate cell production as well as matrix components such as proteoglycans and collagen II.
They conclude, however, that none of the current cartilage regeneration techniques are fully satisfactory. Although there may be symptom relief, it is often due to the production of inferior fibrocartilage rather than the much more durable hyaline cartilage which is the objective of all cartilage regeneration methods. It does not seem to matter where the mesenchymal stem cells are taken from, even cartilage itself, the tendency of all of them is to mature into fibrocartilage rather than hyaline cartilage. Where the cells are augmented in a laboratory and seeded onto a scaffold or matrix there is the need for two procedures – one to harvest and one to implant – and the costs are high.
What they are hoping to develop is a method of triggering the body to produce real hyaline repair cartilage via –
- a single arthroscopic procedure
- where they are able to treat large or multiple areas
- and with the procedure being scaffold free with a simple delivery, and cost effective
Their initial work was with animals, and this was published in 2011, but currently they are busy with a trial with human patients, where their method involves drilling small holes into the subchondral bone to expose the bone marrow, and then post-operatively injecting ‘peripheral blood progenitor cells’ (PBPC) derived from the patient’s own blood, into the joint which they say is better than using bone marrow cells. The procedure is then augmented with injections of high molecular weight hyaluronic acid. [The Editor points out that this drilling method is an old method – it is the combination with the delivery of the PBPC and hyaluronic acid that is new.]
During a routine arthroscopy, the cartilage lesions are identified and holes are drilled through the lesion into the subchondral bone at regular distances.
Post-operative rehabilitation routine
Cryotherapy is started immediately post-op and continued 2-3 times a day for a month. Continuous passive motion (CPM) is initiated immediately post-op and continued for four weeks, initially starting with a range of motion (ROM) of 0-30 degrees and increasing as the clinical condition improves.
If the cartilage lesions were on the weight-bearing surfaces, the patients are instructed to use crutches, partial weight bearing for four weeks, progressing to full weight bearing by eight weeks.
If the cartilage lesions were on the patello-femoral surface, full weight bearing is started immediately with some restriction on stair climbing.
Harvesting the PBPC cells
The method that they use to gather the PBPC cells is as follows, which the authors say is safe and effective. This involves -
- Stimulation of white blood cell production with subcutaneous injections of Neupogen on days 4,5 and 6 post-op.
- On day 7 a double-bore catheter is inserted on the other leg into the femoral vein and the blood is circulated through a cell separator (apheresis) to separate off the PBPC cells. During this part of the procedure cytometry is used to measure the density and type of cell being separated off. The PBPC is separated into 5 vials.
- One vial is mixed with hyaluronic acid and injected immediately into the knee joint, while the other four vials are frozen and preserved. These are kept for injection into the knee in the same way over subsequent days.
Intra-articular injection of PBPC
The authors present several detailed case studies that are interesting and informative, but we will not cover them here.
Their clinical trials were started in 2007 and when this article was written the trial had involved 205 patients with varied cartilage problems, and 155 of them had passed the two-year mark since their surgery. Only 52 had had IKDC scoring done pre-operatively, at one year and at two years.
The authors point out that their techniques are evolving, but are very encouraging, and suggest that the technique is effective in producing true apparently resilient hyaline cartilage rather than the weaker fibrocartilage.
They are currently doing a parallel trial comparing the drilling with PBPC and hyaluronic acid as described here with using drilling and hyaluronic acid alone without the PBPC.