Microfracture is a common orthopedic surgical technique used to treat specific types of damage to the cartilage within the knee joint. This procedure harnesses the body’s healing mechanisms to stimulate the growth of new tissue where the protective layer has worn away or been injured. The goal is to reduce pain and restore function by resurfacing a focal defect in the joint’s smooth lining. This article explains the condition, details the arthroscopic technique, and outlines the lengthy recovery process.
Articular Cartilage Damage in the Knee
The knee joint relies on a specialized tissue called articular cartilage, or hyaline cartilage, which covers the ends of the femur and tibia. This tissue provides a smooth, low-friction surface, allowing the bones to glide easily against each other during movement. Articular cartilage also acts as a shock absorber, distributing forces across the joint during activities like walking or running.
A significant challenge arises when this protective layer is damaged because articular cartilage lacks a direct blood supply, which is necessary for self-repair. Injuries, whether from acute trauma or long-term wear, can lead to a condition called a chondral defect. Minor tears or softening of the cartilage do not typically require microfracture.
The primary indication for this surgery is a full-thickness chondral defect, where the cartilage has completely worn away. This exposure leaves the underlying bone unprotected. Such defects cause symptoms like intermittent swelling, pain, and a catching or locking sensation in the knee. Microfracture surgery is designed to address these specific, isolated areas of damage, rather than widespread joint degeneration like osteoarthritis.
How the Microfracture Procedure Works
Microfracture is performed as an arthroscopic surgery, using small incisions, a camera, and specialized instruments. The first step involves thoroughly cleaning the defect by removing any remaining unstable or loose cartilage around the edges. This preparation creates a stable rim around the target area, which is necessary to contain the new healing tissue.
Once the defect is prepared, the surgeon uses a sharp, pointed instrument called an awl to create multiple tiny holes in the exposed subchondral bone. These holes, or microfractures, are spaced approximately three to four millimeters apart and are just deep enough to penetrate the hard bone layer beneath the cartilage. The mechanical disruption of the bone allows blood and bone marrow elements to seep out into the cartilage defect.
This process releases cells and growth factors from the bone marrow, which combine with the blood to form what is often called a “superclot.” This clot covers the defect and acts as a scaffold for the body’s repair process. Over time, the cells within the clot mature, forming new tissue that fills in the damaged area and resurfaces the joint.
Post-Surgical Recovery and Rehabilitation
The recovery phase following a microfracture procedure is lengthy and requires strict adherence to the protocol. The newly formed blood clot is delicate and must be protected from excessive weight-bearing forces that could dislodge it. Patients are typically required to remain non-weight-bearing on the operated leg for a period of six to eight weeks, relying on crutches.
During this initial period, many protocols recommend the use of a Continuous Passive Motion (CPM) machine for several hours each day. The CPM machine gently moves the knee through a prescribed range of motion. This motion helps nourish the joint and promotes the optimal contouring of the healing tissue, encouraging the cells to form a smoother, more organized repair surface.
Physical therapy begins shortly after surgery and focuses on maintaining muscle strength and gradually increasing the knee’s range of motion without stressing the repair site. After the initial non-weight-bearing phase, a slow, progressive return to weight-bearing activities begins, often guided by the physical therapist. High-impact activities and sports are typically restricted for six to nine months to allow the repair tissue sufficient time to mature and harden.
The tissue formed from the superclot is fibrocartilage, which is a dense, fibrous scar-like tissue. This repair tissue is functionally different from the original hyaline cartilage. While fibrocartilage can significantly reduce pain and improve function, it is less durable than native hyaline cartilage and may not be as robust in the long term.