Articular cartilage is the smooth, shiny, white tissue covering the ends of bones at the joint. Articular cartilage reduces friction when bones glide over each other, making the movements smooth and painless. It also acts as a shock absorber to help prevent traumatic injuries to the bones. When cartilage is damaged, it can cause pain with movement, limited joint mobility, and eventually progress to osteoarthritis.
Cartilage damage can occur from normal wear and tear of the body’s joints as we age, from traumatic injury, or from other disease conditions. Because of its avascular nature (absence of blood supply), cartilage cannot repair itself. In some cases, surgery may be required to restore cartilage function and prevent progression of the damage into arthritis.
Articular cartilage may be damaged with trauma, sports injuries, or progressive degeneration (wear and tear).
Dr. Driscoll will perform a physical examination to look for altered range of motion, swelling, and bone alignment. X-rays are routinely used to evaluate the joint and assess for arthritis or fracture. Often, magnetic resonance imaging (MRI), or even arthroscopy, is required to accurately evaluate cartilage damage, as it is not seen well with X-rays.
Young adults with cartilage injury are often good candidates for cartilage restoration surgery because these methods help prevent the progression of damage into osteoarthritis.
The most common joint requiring cartilage restoration is the knee joint. Others include the shoulder and ankle joints.
Surgery is often not necessary in smaller cartilage defects (<1 cm2). Defects smaller than 2 cm2 can often be treated arthroscopically and have a good prognosis. Larger defects may require more aggressive cartilage restoration techniques such as osteochondral allograft transplant or autologous cartilage implantation (ACI), as described below.
Some cartilage procedures can be performed arthroscopically, a minimally invasive surgery using arthroscope, a small flexible tube with a light and video camera at the end that enables to view inside the joints and perform surgery. Others require an “open” approach, in which a small incision is made to expose and treat the damaged area.
The surgical procedures for cartilage restoration include:
- Autologous Chondrocyte Implantation
- Osteochondral Autograft Transplantation
- Osteochondral Allograft Transplantation
Microfracture is an arthroscopic surgery that involves creating multiple small holes in the subchondral (below the cartilage) bone with a sharp tool called an awl. This stimulates the formation of a blood clot in the cartilage defect. This clot is rich in stem cells and growth factors from the adjacent bone marrow that help stimulate the formation of fibrocartilage within the defect. Young patients with a single small lesion are suitable candidates for microfracture.
Drilling is an arthroscopic procedure like microfracture in which multiple holes are made in the subchondral bone with the help of a surgical drill or wire to stimulate a healing response.
Autologous chondrocyte implantation (ACI) is accomplished in two stages. The first stage involves arthroscopic cartilage biopsy used for cartilage cell production in the lab. This is followed by the second stage, which involves implantation of these new cells into the defect.
The first step is performed arthroscopically during which healthy cartilage cells are removed from a non-weight bearing area of the joint. These cells are then cultured in a laboratory for 3-5 weeks to increase their number.
Implantation of the new cartilage cells is performed through an open surgical procedure. This involves preparation of the defect, after which a layer of the bone-lining (periosteum) is stitched over the defect and sealed with suture and fibrin glue. The cultured cells are then injected into the defect just below the cover.
Autologous chondrocyte implantation is indicated in younger patients who have a larger lesion (over 2 cm2). As the patient’s own cells are used, there is no risk of tissue rejection.
Osteochondral autograft transplantation is a procedure in which healthy cartilage tissue is taken from the non-weight bearing part of the bone and placed into the defect area creating a smoother surface on the cartilage of the joint. This procedure is often ideal for defects < 2 cm2 , particularly if the sub-chondral bone is affected.
Osteochondral allograft transplantation is performed when the cartilage defect is large and involves the bone beneath the cartilage. An osteochondral allograft is a block of bone and cartilage obtained from a deceased donor. The allograft is sterilized and prepared to fit exactly into the defect area.
Finally, knee alignment is often a critical consideration in cartilage restoration. Varus (bow-legged) or valgus (knock-kneed) knee alignment results in excess stress on the cartilage on the concave side of the joint. In some cases, alignement requires correction with a realignment osteotomy in addition to cartilage restoration surgery in order to offload the damaged cartilage and increase likelihood of long-term success.