The surgical repair of damaged joint cartilage is broadly referred to as articular cartilage restoration or chondroplasty. Articular cartilage is the smooth, white tissue covering the ends of bones in a joint, which allows them to glide against one another with minimal friction. Because this specialized tissue is avascular (lacking a direct blood supply), it has a very limited capacity to heal itself after injury or wear. Damage to this surface, often presenting as a focal defect, can lead to pain, catching, and eventually the progression of arthritis. Specialized surgical procedures are employed to either stimulate the body to grow new tissue or to replace the damaged area.
Techniques That Stimulate Cartilage Regeneration
The most common procedure used to encourage the body’s natural healing response is known as Microfracture. This technique is performed arthroscopically, using small incisions and a camera to access the joint space. The surgeon first cleans the defect, removing all damaged cartilage tissue down to the underlying bone, known as the subchondral plate.
The core of the Microfracture procedure involves using a sharp instrument to create multiple small, closely spaced holes in the exposed bone. These perforations allow blood, bone marrow cells, and growth factors to seep out of the bone and into the cartilage defect. The released elements form a blood clot, often called a “superclot,” that fills the defect.
Over several weeks, the cells and growth factors within the clot differentiate into repair tissue. The resulting tissue, however, is typically fibrocartilage, which is structurally and biomechanically inferior to the body’s native hyaline articular cartilage. Fibrocartilage is less durable and contains primarily Type I collagen, unlike the Type II collagen found in the original tissue. Despite this difference, Microfracture remains a common option for smaller, contained cartilage lesions.
Methods Using Cartilage Grafting and Implantation
For larger or more complex cartilage defects, surgeons often turn to techniques that involve transplanting tissue to restore a more durable, hyaline-like surface. The Osteochondral Autograft Transfer System (OATS), sometimes called Mosaicplasty, is one such method. This procedure involves harvesting cylindrical plugs of healthy bone and cartilage from a non-weight-bearing area of the patient’s own joint, typically the knee.
These plugs, which contain native hyaline cartilage, are then transferred and press-fit into the prepared defect site. Using multiple small plugs to fill a larger defect gives the procedure the name Mosaicplasty. This method offers the advantage of immediate structural stability and the use of the patient’s own tissue, which eliminates the risk of rejection.
Another advanced technique is Autologous Chondrocyte Implantation (ACI), now often performed as Matrix-Associated Autologous Chondrocyte Implantation (MACI). This is a two-stage procedure designed to regenerate tissue that closely resembles native hyaline cartilage. The first stage involves a small arthroscopic biopsy to harvest a few hundred thousand healthy chondrocyte cells from a low-stress area of the joint.
These cells are then sent to a laboratory where they are cultured and expanded over several weeks to a population of millions of cells. In the second stage, the expanded cells are implanted into the defect; in the MACI technique, the cells are seeded onto a biodegradable membrane or scaffold before implantation. This scaffold is secured over the defect, where the cells continue to mature, gradually forming new Type II collagen-rich cartilage.
Factors Guiding the Choice of Procedure
Selecting the appropriate cartilage repair technique depends on several clinical variables. The size and depth of the cartilage defect is the most significant factor differentiating the procedures. Microfracture is generally reserved for smaller lesions, typically less than \(2.0\) to \(2.5\) square centimeters, while ACI/MACI is the preferred choice for larger defects, often exceeding \(3.0\) square centimeters.
The patient’s age and activity level also heavily influence the surgical plan. Younger, highly active individuals or athletes are often better candidates for ACI or OATS, as these procedures aim to create or transplant more durable hyaline or hyaline-like cartilage. Microfracture is less favored for high-impact athletes due to the inherent biomechanical weakness and long-term deterioration of the resulting fibrocartilage.
The location of the lesion within the joint dictates the feasibility of certain procedures. OATS is highly effective for defects on the weight-bearing femoral condyles, while ACI has demonstrated favorable outcomes for lesions located on the patella or the trochlear groove. The overall condition of the joint, including the presence of underlying bone damage or widespread arthritis, must be assessed, as these restoration techniques are only appropriate for isolated, focal injuries.
Post-Surgical Care and Recovery Expectations
Recovery following any major cartilage restoration procedure is prolonged and requires strict adherence to a multi-phase rehabilitation protocol. Cartilage tissue heals and matures slowly, which means patients must protect the repair site from excessive load for an extended period. A mandatory non-weight-bearing period, often lasting six to twelve weeks, is common across most techniques, requiring the use of crutches.
Physical therapy is essential, beginning almost immediately with an emphasis on restoring joint motion without loading the repair. Surgeons frequently prescribe the use of a Continuous Passive Motion (CPM) machine, which gently moves the joint for several hours each day to promote cartilage health and prevent stiffness. The goal of this early motion is to encourage the cells to produce the correct type of collagen fibers.
The entire recovery process, from surgery to a safe return to full activity, can span six to twelve months or longer, depending on the complexity of the procedure and the size of the repair. Due to the biological necessity for the new tissue to mature, high-impact activities are typically restricted for at least nine to twelve months. Patient commitment to this long-term rehabilitation is a key factor in the success of the cartilage repair.