MPFL reconstruction is a surgical procedure that replaces a torn or stretched ligament on the inner side of your knee to stop your kneecap from repeatedly sliding out of place. The medial patellofemoral ligament (MPFL) is a thin band of tissue that connects the inner edge of your kneecap to your thighbone near the inner knob of the knee. Despite being thin, it has a tensile strength of about 208 newtons and serves as the primary restraint preventing your kneecap from shifting outward. When this ligament tears, which happens in 94% to 100% of patellar dislocations, your kneecap loses its main stabilizer.
Why the MPFL Matters
Every time you bend or straighten your knee, your kneecap glides along a groove in your thighbone. The MPFL acts like a checkrein on the inner side, keeping the kneecap centered in that groove. Without it, the kneecap can drift laterally and dislocate, especially during activities that involve twisting, pivoting, or sudden changes in direction.
A torn MPFL that goes untreated leads to recurring dislocation in 14% to 44% of cases. Each subsequent dislocation can damage the cartilage on the undersurface of the kneecap and on the thighbone groove, eventually accelerating joint degeneration.
Who Needs This Surgery
The strongest indication for MPFL reconstruction is a history of two or more patellar dislocations, particularly after physical therapy, bracing, and strengthening exercises have failed to keep the kneecap stable. Surgery after a single first-time dislocation is less common but sometimes considered when there are ongoing symptoms of instability, a cartilage injury from the dislocation, or a loose fragment inside the joint.
During a physical exam, your surgeon will push your kneecap sideways. If you instinctively tense up or feel uneasy (the “apprehension sign”) and the kneecap slides more than halfway across its width without a firm stopping point, that strongly suggests the MPFL is damaged. MRI confirms the diagnosis, typically showing a characteristic bone bruise pattern on the outer side of the thighbone and the inner face of the kneecap, along with a visible tear in the ligament itself.
How the Surgery Works
MPFL reconstruction replaces the damaged ligament with a tendon graft that mimics the original structure. The most commonly used graft is the gracilis tendon, a small hamstring tendon harvested from your own knee during the same procedure. Alternatively, surgeons may use donor tissue (allograft), with semitendinosus-gracilis being the most common choice in that category.
The graft is threaded along the path of the original MPFL. On the kneecap side, it’s typically secured with small anchors drilled into the inner edge of the bone. On the thighbone side, fixation usually involves an interference screw or a suture anchor placed at the anatomic attachment point near the inner knob of the femur. The goal is to recreate the natural tension of the original ligament so the kneecap tracks properly without being over-tightened, which would restrict motion.
When Additional Procedures Are Needed
For some people, a torn MPFL isn’t the only problem. If your kneecap sits too far to the outside because of the way your bones are aligned, an isolated MPFL reconstruction may not be enough. Surgeons measure this alignment on a CT scan or MRI by checking the distance between two bony landmarks. When that distance exceeds 20 millimeters, a procedure to shift the bony bump where the patellar tendon attaches (called a tibial tubercle osteotomy) is often performed at the same time. This addresses both the soft tissue damage and the underlying skeletal malalignment in one operation.
In rare cases of extreme abnormality in the groove itself, a procedure called trochleoplasty can reshape the groove. This remains uncommon, particularly in the United States, because of concerns about long-term cartilage wear, and it’s generally reserved for severe cases where other options can’t provide stability.
Success and Complication Rates
MPFL reconstruction significantly outperforms simple repair of the torn ligament. At an average follow-up of 12 years, reconstruction produced a 14% rate of re-dislocation compared to 41% with repair alone. Reoperation rates for persistent instability were also lower: 7% after reconstruction versus 21% after repair. About 75% of patients returned to sport after reconstruction.
Complications range from 0% to 32% across published studies, though the most common issue is persistent anterior knee pain rather than a structural failure. Stiffness or loss of motion occurs in up to 20% of cases. Patellar fracture is a less frequent but more serious complication, reported in up to 8.3% of cases, and is linked to specific tunnel-drilling techniques that use larger diameter holes through the kneecap. Surgical failure, meaning recurrent instability significant enough to need revision, ranges from 0% to about 11%.
Recovery Timeline
For the first two weeks after surgery, you’ll bear about half your body weight on the operated leg using crutches and a hinged knee brace. By weeks two through four, you can progress to full weight-bearing on flat surfaces while still wearing the brace. Early range of motion is limited to 90 degrees of knee bend for the first four weeks, then gradually increases to 110 degrees by eight weeks and 120 degrees by ten weeks. Full flexion is the target from about ten weeks onward.
The later phases of rehab focus on rebuilding quad strength, balance, and movement quality. Clearance for return to sport requires your operated leg to reach at least 85% of the strength and hop distance of your healthy leg, along with no apprehension during sport-specific movements. For most people, this process takes somewhere between six and nine months, depending on the sport and individual progress. Your surgeon will make the final call on return to play based on both objective testing and clinical assessment.