Failed Articular Cartilage
Articular cartilage is the smooth, bearing surface covering all joints. When damaged, it usually fails to heal on its own—but with novel treatments, it can be fixed. That said, here are some of the ways that attempted repairs have gone wrong.
People take 2-3 million steps per year, impacting their joints with a force amounting to multiples of their body weight. The surface of these joints needs to be slick and smooth. For the hip, knee, and ankle, any deformity of the cartilage surface can lead to pain. Impact injuries, loss of the meniscus cartilage, and tears of the key ligaments that guide the joints are the main contributors to cartilage wear. Surgical techniques to repair the articular cartilage have improved over the years—from simply drilling holes in the surface of the bone to inducing scar tissue formation, to complete articular cartilage replacement.
Hole drilling—originally called the Pridie procedure—led to a widely used microfracture technique. This was designed to release marrow blood and cells, which formed a coating over the surface of the damaged articular cartilage. Through the use of a continuous passive motion machine (or by bicycling and/or swimming) a layer of repair tissue formed, coating the underlying bone. For many people, these procedures provided pain relief for several years before the new tissue wore back down to the bone.
Cells of articular cartilage (chondrocytes) were grown in tissue culture in the hope that when they were injected onto an articular cartilage defect they would grow cartilage. Various methods were designed to keep this cartilage in place. Originally, the tissues naturally attached to bone (periosteum) were used. Later, surgeons used various collagen and other matrices. When these worked, pain relief was obtained. Unfortunately, the most popular technique, called ACI, required two surgical procedures: the first to harvest the cartilage, the second to re-implant the grown cells. Not only was this expensive; the results were no better than other single-surgery procedures. So the ACI technique, too, fell out of favor.
Next, plugs of intact articular cartilage with underlying bone (called OATS, or Mosaicplasty) were deployed. As with a hair transplant, these plugs attempted to cover articular cartilage injuries that were often irregular in shape and size. Their advantage was having intact articular cartilage, and so relied only on the bony healing to achieve success. However, the plugs were exclusively round. The surface of the joint is rarely exactly duplicated at another area of the joint, so there were persistent mismatches between the donor and recipient sites. The gaps between the plugs failed to heal at times. And when the plugs failed, the patient was left with at least two significant defects in their knee. Additionally, harvesting them from other parts of the joint left painful lesions at the donor sites. Despite all this, plugs have been the most widely used technique for complete cartilage repair.
Our novel contribution to the cartilage repair world has been Articular Cartilage Paste Grafting. This technique involves fracturing the arthritic defects, then harvesting cartilage and bone from the intercondylar notch—a location where the donor bone and tissue are able to grow back without leaving a painful deficit. The donor cartilage and bone are then smashed into a paste and impacted into the damaged area of the joint.
Data collected since 1991 has shown superb healing of these repairs. The cartilage is indistinguishable from normal in approximately 30% of subsequent biopsies. Another 30% are a mixture of normal and fibrocartilage; the last 30% are mostly fibrous tissue. Though this is far from perfect, the results at 17 years post-procedure show that more than 80% of patients reported decreased pain and improved function. The articular paste graft technique has been used to salvage previous surgeries with negative outcomes—including failed microfractures, ACI, OATS, Mosaicplasty, and large osteochondral defects (OCD lesions).
The sad truth is that any surgical procedure can fail or can make the patient worse. Fortunately, at least with the articular cartilage in many joints, the injuries can be repaired by a range of techniques—and the failures salvaged fairly reliably. While the days of living with joint pain until you undergo an artificial joint replacement are over, we have not yet evolved to the point of re-growing our limbs the way salamanders do.