Continuing Education Activity
Cartilage graft transplantation is frequently used in the treatment of chondral and osteochondral lesions, most commonly in the knee. These procedures can serve to improve the quality of life for those with pathology of the cartilage within joints and alleviate symptoms. This activity will serve to highlight the challenges of cartilage transplants, as well as illuminate the roles of various members of the interprofessional team in the successful management of such joint pathology.
- Review the anatomical structures necessary to understand cartilage graft transplantation.
- Describe the technique involved in cartilage graft transplantation.
- Summarize the indications for a cartilage graft transplantation procedure.
- Outline the role of collaboration and communication within the interprofessional team caring for patients with cartilage graft transplantation to improve clinical outcomes.
Joint pain is a complex problem facing medical practitioners that has its origin in a host of conditions, injuries, and diseases. Between 2013 and 2015 alone, an estimated 54.4 million United States (US) adults (22.7%) annually were told by a doctor that they had some form of arthritis, rheumatoid arthritis, gout, lupus, or fibromyalgia.
Physicians, researchers, and other medical providers have, for centuries, sought to understand the etiology and causes of joint pain in an effort to develop effective treatments to alleviate discomfort.
Joint pain and/or arthritis is one of the most prevalent and expensive conditions known to humankind. In 2013, the American national medical costs attributable to arthritis were $140 billion. Additionally, with the aging population of most countries, the cost of treating arthritis is expected to double if not triple in the next several decades. As such, the need to find effective treatments, both medical and surgical, for the loss of articular cartilage is both important and financially imperative.
The human knee is perhaps the most common joint to suffer the effects of articular cartilage loss. In a population of patients greater than 45-years-old, the age-standardized prevalence of radiographic osteoarthritis (OA) of the knee was reported to be between 19.2% (Framingham Study) to 27.8% (Johnston County Osteoarthritis Project). Additionally, in the Third National Health and Nutrition Examination Survey (NHANES III), nearly 37% of participants age 60 years or older had radiographic evidence of knee osteoarthritis.
Thus, much attention has been turned to finding an effective method whereby the damaged or deficient articular hyaline cartilage can be restored to the knee.
One method of surgically restoring a viable articular surface to the knee joint whose hyaline cartilage surface has been injured is through osteochondral allograft transplantation. Osteochondral allograft transplantation is an effective treatment when the source of knee pain is a large chondral defect or in the cases of post-traumatic arthritis. Ultimately, osteochondral allograft transplantation involves transferring allograft articular cartilage and subchondral bone that is appropriately size-matched to fill chondral defects with matured hyaline cartilage. Were one to describe this technique in a commonly understood metaphor, it would simulate the repair of a pot or chuckhole in the street by size match insertion of transplanted asphalt along with its attached subsurface roadbed into the defect.
Anatomy and Physiology
A basic understanding of the anatomy of articular (i.e., hyaline) cartilage is important in preparation for osteochondral allograft transplantation.
The extracellular matrix makes up approximately 65% to 80% of the total mass of cartilage and is composed of water, type II collagen, and proteoglycan.
Chondrocytes are the cells within the articular cartilage that produce collagen, proteoglycans, and enzymes. They are derived from chondroblasts and physiologically respond to mechanical loading and hydrostatic pressure changes.
Normal articular cartilage is composed of four major layers:
- The superficial zone (i.e., tangential zone) is, as the name suggests, the most superficial layer and has the highest concentration of collagen with the lowest concentration of proteoglycans. Within this zone, the collagen fibers are oriented parallel to the joint, and it is here where only articular progenitor cells are found.
- The intermediate zone is deep to the superficial zone and is the thickest layer of the four zones. Its abundant collagen with random orientation and proteoglycans sets it apart from the superficial and deep zones.
- The deep zone (i.e., basal layer) is beneath the intermediate zone. It has the highest concentration of proteoglycans and the lowest concentration of collagen, with the collagen fibers being oriented perpendicular to the joint.
- The tidemark is the deepest layer separating the articular cartilage from the subchondral bone.
Osteochondral allograft transplantation is appropriate for symptomatic chondral lesions within joints that are larger than 2 cm x 2 cm, as smaller lesions can be appropriately treated with autograft or microfracture techniques. Several studies have revealed that high-grade chondral lesions appropriate for osteochondral allograft transplantation were present in 5 to 20% of all patients who underwent arthroscopic evaluation of the joint, with 4 to 5% of which being younger than 40 years old. About half of these patients had a history of associated trauma. Many of these younger patients who have failed nonsurgical management may benefit from cartilage transplant procedures to improve their quality of life while avoiding more invasive joint replacement arthroplasty.
Patients who are at continued increased risk for osteonecrosis should not undergo osteochondral allograft transplantation. This often includes patients with chronic corticosteroid use. Additionally, cigarette smoking and a history of inflammatory arthritis would be a contraindication for the procedure. Osteochondral allograft transplantation is relatively contraindicated in the setting of meniscal deficiency, which can be diagnosed with magnetic resonance imaging (MRI) or diagnostic arthroscopy. Multiple studies have demonstrated improved graft survival after concomitant meniscal allograft transplantation.
Osteochondral allografts are commercially available from tissue banks with oversight by the Food and Drug Administration. All tissue is harvested within 24 hours of donor death, with ideal donors aging from 15 to 40 years old. Chondrocytes must remain viable for there to be any chance of successful transplantation. The clinical success of transplant is dependent on several factors, which ensure an intact extracellular matrix, viable chondrocytes, and incorporation of host bone.
Allografts can be stored fresh, frozen, or cryopreserved. Each storage technique has different effects on the biomechanical and biochemical properties of the cartilage graft. Fresh storage has been shown to have the highest level of chondrocyte viability, and storage at room temperature significantly improves the viability of osteochondral grafts. Donors are tested for HIV, hepatitis B, hepatitis C, and human T-lymphotropic virus (HTLV) prior to harvesting.
The size and location of the chondral defect determine which osteochondral allograft transplantation technique is most appropriate. Small solitary defects can be filled with a single plug that is matched exactly to the size and shape of the defect, providing complete coverage of the chondral deficiency and integration with the surrounding tissues. Below is a discussion of some of the more common methods employed to address articular surface defects.
It should be noted that due to the rather soft nature of articular cartilage, transplanting the cartilage alone without some aspect of its accompanying bony support is not possible since securing it in place is problematic if not impossible without some reliable form of shear resistant fixation.
Larger lesions may require a more significant arthrotomy of the joint to fully visualize the defect to ensure that the entire zone of injury is appropriately addressed. Having a healthy rim of cartilage available along the edges of the graft is essential for appropriate integration into the patient's tissue.
The Snowman technique, or mosaicplasty technique, is one method to address larger chondral lesions, allowing for coverage of a bigger area than is allowed by single plugs. In this technique, a single plug is placed with a standard reaming technique and held in place with wire fixation. A second plug is subsequently reamed, overlapping with the first allowing for a confluence of the two plugs, covering a larger articular surface area. In this manner, the area can be filled much like abutting small round tiles into each other to cover a larger floor surface area.
The Shell technique is ideal for the treatment of asymmetrical cartilage defects and defects that are difficult to access with standard arthrotomies, such as defects of the posterior femoral condyle. In this technique, the entire affected recipient site can be removed en bloc, and a size-matched donor bone is cut and contoured to cover the recipient lesion, covering the defect as a "shell" of protection.
The small fragment allograft technique alternatively may be used in defects of the tibial plateau where the entire meniscotibial unit is replaced by a donor unit and stabilized with screw fixation.
Finally, while this article addresses the osteochondral allograft transplantation methods, there are newer technologies wherein articular cartilage scaffolds or membranes can be sewn or adhered to the articular surface defects found within the knee. Those techniques show promise in many situations and will likely, in some instances, replace the need to transplant an auto or allograft osteochondral segment.
As with any surgical procedure, pain, bleeding, damage to surrounding anatomic structures, and infection are a risk, albeit low compared to many surgeries in the hands of a skilled arthroscopist. Outside of the general complications associated with any surgical procedure, graft failure is of the greatest concern. While patients who undergo osteochondral allograft transplantation for traumatic or idiopathic injuries have a reported graft survival of 100%, cartilaginous defects caused by post-traumatic arthritis, osteonecrosis, or osteochondrosis have a lower rate of graft survival. Ultimately, the underlying cause of the index deficit should be considered. If the cause of a patient's cartilaginous defect is due to an anatomic or medical derangement, failure to address the cause of the deficiency will inevitably lead to failure of the procedure and potential exacerbation of the joint insufficiency.
Articular cartilage defects often result in pain and discomfort that seriously affect a patient's quality of life. When non-surgical management fails, osteochondral autograft or allograft transplantation is a reasonable solution to provide patients with hope for a better quality of life. With joint pain reduced or eliminated, patients may return to normal activity while avoiding more invasive or elevated risk profile procedures such as total knee arthroplasty. Prolonging an active lifestyle is important and can lead to overall better physical and mental health.
Enhancing Healthcare Team Outcomes
Management of painful joint pathology requires an interprofessional approach that includes the patient in his care and supports a return to activities that may be limited by his or her disease process. Non-surgical management is the first-line treatment for a painful joint, and physicians and therapists must communicate and work together to help patients find solutions to their pain limitations. When non-operative measures fail, surgery may be considered.
Any time surgery is undertaken, medical practitioners must have a good surgical team in place. Surgical techs, nurses, and surgeons must work together seamlessly in the operating room to provide the patient with the highest likelihood of a successful outcome. The surgeon must then communicate with the physical therapist, who is vital to providing the patient with the appropriate post-operative protocol to ensure a safe return to function post-operatively. [Level 5]