What is Cartilage?

Articular (or hyaline) cartilage is a tissue in the body that lines the ends of the bones, providing a smooth surface for movement of the joint.  It also serves as a shock absorber during activities.  When there is an injury to the cartilage in a joint, it does not heal on its own as there is no direct blood supply to aid in this process.  Instead, cartilage continues to deteriorate over time, especially with continued activity.  This leads to a disease called Osteoarthritis.  Fortunately, there are now procedures available to restore the cartilage in a joint without having to go through a joint replacement.  The most common joint for a Cartilage Restoration procedure is the knee.

Treatment Options for Cartilage Disorders

There is a spectrum of treatment options for treating cartilage disorders including palliative, reparative, resurfacing, and reconstruction.  Palliative treatment is known as Chondral Debridement, where the uneven surface of damaged cartilage is smoothed out during arthroscopic surgery.  This does not replace injured cartilage but may relieve pain as there is no longer a loose flap of tissue moving abnormally in the joint.  This may be an option for a patient with only a partial thickness cartilage injury or an older patient who does not participate in demanding activities.  The recovery time for this procedure is minimal.  The patient can be full weight bearing and does not have any range of motion restrictions after surgery.

When there is a very small, focal lesion of missing cartilage, the patient may be a candidate for a reparative procedure known as Marrow Stimulation.  This procedure is sometimes referred to as Microfracture.  With this procedure, holes are made directly into the lesion allowing bone marrow to escape into the defect.  This allows for healing of the lesion with a substance known as Fibrocartilage, which acts similarly to innate articular cartilage when in a small area.  This is a simple arthroscopic procedure but does require some restrictions during subsequent rehabilitation to allow the Fibrocartilage to develop and heal.

Cartilage Restoration for Active Individuals

When we think of true “Cartilage Restoration” procedures, there are really two different types – Resurfacing and Reconstruction.

Resurfacing: “Repaving the Street”

When the lesion is too large for microfracture but still only involves the surface of the bone, then a resurfacing procedure is warranted.  There are several ways to resurface the end of the bone with new cartilage.  One technique is to take the patient’s own unused cells out during an arthroscopic procedure and send them to a lab to be grown into new cartilage cells, which would then be placed over the lesion that is missing cartilage.  This process is known as Autologous Chondrocyte Implantation and requires two surgical procedures – one to harvest the cells and another to put them into the defect.  The benefits of this procedure are that it uses the patient’s own cells and is able to resurface a large area of damage.  The recovery depends on where in the knee these cells are placed, but generally range of motion is encouraged early as cells adhere to the bone and proliferate right away.  Patients are able to ride a bike within weeks and even start running after just a few months.

Another resurfacing technique is done by Allograft Implantation.  Rather than two separate surgeries, this can be done in one arthroscopic or minimally invasive procedure.  The defect is debrided, and the donor cells are pasted into place and fixated with a type of biologic glue.  Similarly, patients progressively return to their normal activities within several weeks as the cells grow into real articulating cartilage.

Reconstruction: “Filling the Pothole”

When a cartilage defect extends beyond the surface to involve the underlying bone, a structural graft is necessary in a reconstructive procedure to restore the cartilage.  The size of the injured cartilage determines whether the cartilage can be obtained from the patient or must come from a donor.  If it is a smaller lesion, then a cartilage plug (includes underlying bone) may be taken from a place in the joint that does not need it and placed into the defect.  This procedure is called Osteochondral Autograft Transplantation and is typically done with a minimally invasive open incision.  However, when the size of the defect is too large to take it from another place, donor tissue is required.  In this case, a plug can be made to fit the size of the void after the missing cartilage and damaged underlying bone is removed.  Even an oval shaped plug can be fashioned to fill a large, long defect over the weightbearing surface of the knee, which is termed a BioUni.  These procedures are called Osteochondral Allograft Transplantations and may be an alternative to partial or total joint replacement for the right patient.  Although they do take longer to heal compared to a cartilage resurfacing procedure, the patients generally return to activity within a few months and have excellent outcomes.