MPFL reconstruction is a surgical procedure designed to restore stability to the kneecap (patella) after it has repeatedly dislocated. The Medial Patellofemoral Ligament (MPFL) is a band of tissue on the inside of the knee that functions as the primary restraint against the kneecap slipping out of its groove. When this ligament is torn or stretched, the patella can easily slip out of position, leading to chronic instability. This surgery creates a new, functional ligament to hold the kneecap securely in place.
Understanding Patellar Instability
The kneecap normally tracks within a groove on the end of the thigh bone, called the trochlea, as the knee bends and straightens. The MPFL is responsible for providing 50–60% of the force resisting the kneecap’s movement toward the outside of the leg, especially when the knee is close to full extension (0–30 degrees of flexion). It is a static stabilizer, meaning it works independently of muscle contraction to keep the joint aligned.
Patellar instability often begins with a traumatic event, such as a sports injury, which forces the kneecap to dislocate laterally, or toward the outside of the leg. This dislocation stretches or tears the MPFL, with up to 100% of first-time dislocations resulting in MPFL rupture. Once the MPFL is damaged, it may heal in a lengthened position, leaving the kneecap without its main soft-tissue restraint.
Recurrent dislocations become more likely after the initial injury, particularly if the individual has underlying anatomical factors like a shallow trochlear groove or a kneecap that sits too high. Each subsequent dislocation further damages the joint and increases the risk of long-term cartilage damage, which is why surgical intervention is often recommended for chronic instability.
How MPFL Reconstruction is Performed
The MPFL reconstruction procedure typically involves replacing the damaged ligament with a tendon graft. The surgery is performed under anesthesia and usually begins with one or more small incisions around the knee. Surgeons often use an arthroscope, a tiny camera, to examine the inside of the joint for any additional cartilage or meniscal damage.
The new ligament is created using a tendon, which may be an autograft taken from the patient’s own body, most commonly the hamstring tendon (semitendinosus or gracilis). Alternatively, an allograft, which is tissue from a donor, can be used. The chosen tendon is prepared and folded to increase its strength before being implanted.
The surgical technique involves securing the graft to the kneecap and the thigh bone (femur) at specific anatomical points to mimic the original MPFL. On the patella, the graft is typically secured through small tunnels or with specialized anchors near the superior-medial border. At the femur, the graft is fixed at a precise location known as Schottle’s point, which is crucial for ensuring the new ligament is properly tensioned throughout the knee’s range of motion.
Specialized hardware, such as bio-absorbable screws or sutures, is used to anchor the graft securely into the bone tunnels. The surgeon carefully tensions the graft to provide stability and prevent lateral movement of the patella without pulling it too tightly toward the inside of the leg. This meticulous process ensures the kneecap tracks correctly.
The Post-Operative Recovery Timeline
Recovery from MPFL reconstruction follows a structured, phased approach, beginning immediately after the procedure. In the initial phase, which lasts about two weeks, the primary focus is managing pain and swelling, protecting the surgical site, and restoring full knee extension. Patients are often placed in a hinged knee brace, which is locked in extension for walking, and they will use crutches.
The next phase, from approximately three to six weeks, transitions into early rehabilitation with increasing range of motion and gentle strengthening exercises. Physical therapy begins shortly after surgery and focuses on regaining quadriceps control and gradually increasing the knee’s flexion. While weight-bearing is often allowed as tolerated with the brace, the weight-bearing status may be modified if additional procedures were performed concurrently.
Between two and five months, the rehabilitation progresses to advanced strengthening and functional activities. This phase includes exercises designed to improve stability, balance, and the strength of the muscles surrounding the knee. The goal during this period is to prepare the joint for a return to higher-impact activities.
A return to sport or unrestricted high-level activity typically occurs between six and twelve months after surgery. The timeline is highly dependent on meeting specific functional criteria, such as achieving a certain percentage of strength and hop-test performance compared to the uninjured leg. This final stage focuses on sport-specific training to ensure the reconstructed ligament and surrounding muscles are fully prepared for the demands of competition.
Expected Outcomes and Potential Risks
MPFL reconstruction is a highly successful procedure, with studies showing an overall rate of recurrent patellar dislocation below 2%. The primary expected outcome is a stable kneecap, which significantly reduces the apprehension and fear of re-injury that patients experience with chronic instability. Patients can also anticipate improved functional scores and a return to their desired level of activity.
Despite the high success rate, there are potential risks and complications associated with the surgery. The most common complications include persistent anterior knee pain and knee stiffness or a loss of full range of motion. Other less common, but serious, risks include:
- Re-injury or continued instability.
- Patellar fracture.
- Hardware irritation.
- Infection.
- Nerve irritation, which can cause temporary or permanent numbness around the incision sites.
- Deep vein thrombosis (blood clot).