Articular cartilage is the bearing surface of a joint, and is designed to provide a relatively frictionless surface to allow for smooth and painless range of motion. Articular cartilage injuries encompass a spectrum of disorders, ranging from isolated, focal cartilage defects to osteoarthrosis, which is diffuse degeneration of articular cartilage.
Articular cartilage injuries of the knee are relatively common. Generally, in younger patients, articular cartilage injuries occur as a result of trauma, often sports-related. In older patients, articular cartilage injuries are often related to degenerative conditions. When articular cartilage injuries occur as a result of trauma, there may be associated injuries to the ligamentous structures of the knee and/or the menisci. Sometimes articular cartilage injuries are incidental findings, discovered at the time of a surgery, which is being performed for another reason, such as an anterior cruciate ligament reconstruction. Some articular cartilage injuries are asymptomatic, while in other cases, articular cartilage injuries, even very small, focal defects, can be quite painful and debilitating.
Articular cartilage has a limited blood supply, and therefore, lacks intrinsic healing capacity. Therefore, articular cartilage injuries may develop into chronic problems if left untreated. Articular cartilage injuries may cause pain, mechanical symptoms, such as catching and locking, and swelling, typically after activity. Articular cartilage injuries may lead to impaired function and reduce ability to participate in sporting and recreational activities. In some cases, articular cartilage injuries cause pain even with simple activities of daily living.
The evaluation of an articular cartilage injury includes a detailed history and physical examination. X-rays, typically weightbearing x-rays, are the usually performed first. Small, focal defects will not be apparent on x-ray, but larger defects involving the underlying bone and osteoarthrosis may be readily apparent on plain x-rays. MRI is also an extremely valuable tool for evaluating articular cartilage. Newer, higher strength MRI scanners provide exquisite detail of the articular surfaces.
The treatment of articular cartilage injuries depends on multiple factors, including patient’s age, size of the defect, and concomitant injuries to the ligamentous structures or menisci. Other factors include body weight and overall alignment of the limb (knock-kneed or bow-legged). Of utmost importance is determining the individual patient’s goals, and providing realistic expectations about outcomes.
Treatment for articular cartilage injury includes both nonoperative and operative options. Nonoperative options include activity modification, physical therapy, and antiinflammatory medication. In cases of more diffuse cartilage wear, selective use of corticosteroid injections may be helpful for short term pain relief and reduction of swelling. There is also evidence that hyaluronic acid injections may be beneficial. Hyaluronic acid is a naturally occurring substance produced by the knee and can be derived synthetically and injected into the knee. This serves as a lubricating agent and may reduce pain associated with articular cartilage damage, specifically in the setting of osteoarthrosis.
There are multiple surgical options for treating articular cartilage injuries, depending on the size of the cartilage defect and its location. If a patient is experiencing primarily mechanical symptoms such as catching or locking, a simple debridement or smoothing of the cartilage surface may be helpful.
For relatively small, isolated defects, a procedure called microfracture has been shown to produce very good results. This involves creating small perforations in the underlying bone, which allow cells from the bone marrow to populate the cartilage defect and form a blood clot. Over time, this clot matures into a scar tissue, which resembles articular cartilage, although it never actually becomes truly normal articular cartilage.
Another option for small lesions involves taking plugs of cartilage from a healthy area in the knee and placing them into damaged areas. This is similar to the concept of a hair transplant. This can also be done with cartilage from cadavers, for larger defects and defects that involve bone loss.
For very large, isolated defects, cell-based treatments are available. One of these procedures, called autologous chondrocyte implantation (ACI) involves taking a tic-tac sized biopsy of cartilage, which is then sent to a laboratory facility. Cartilage cells can be isolated from the biopsy specimen and grown in culture. These cells can then be implanted back into the knee and are usually covered by a patch. This procedure can be quite effective for the treatment of large defects or when other procedures have failed.
In the setting of osteoarthrosis, joint replacement may be the best option. There are multiple different options for joint replacement, including limited resurfacing procedures, unicompartmental arthroplasty and standard total knee arthroplasty.
A substantial amount of research is currently being done in the field of articular cartilage injury. We can expect new techniques to be developed and available in the near future.
For more information please visit International Cartilage Repair Society: www.cartilage.org
Nathan K. Endres, MD, is a board-eligible orthopedic surgeon at the UVM Medical Center with fellowship training in sports medicine, shoulder surgery and orthopedic trauma. His practice expertise is in operative management of knee, shoulder and traumatic ski injuries. Dr. Endres is also an assistant professor in the Department of Orthopaedics and Rehabilitation, Division of Sports Medicine and Shoulder Surgery , McClure Musculoskeletal Research Center, at the Larner College of Medicine at UVM.