Overview
The medial patellofemoral ligament (MPFL) is a thin band of tissue on the inner side of the knee. It runs from the inner edge of the kneecap (patella) to the inner side of the femur (femur). It is the main check that keeps the kneecap from sliding outward when the knee is nearly straight. When the kneecap dislocates, it almost always tears the MPFL. The torn ligament rarely heals with enough strength to prevent a second event.
After a first dislocation, young patients face a real risk of another one, and that risk grows with each new event. Each dislocation can chip cartilage off the back of the kneecap or off the end of the femur. Those chips become loose bodies in the joint and speed up damage to a knee that needs to last decades. The shape of the bones can raise the risk further: a shallow groove for the kneecap (trochlear dysplasia), a kneecap that sits too high (patella alta), or a kneecap tendon that anchors too far to the outside of the tibia. All three increase the outward pull on the kneecap.
MPFL reconstruction replaces the torn ligament with a graft to restore that inner tether. When the bone shape is also abnormal, we add bone procedures to fix the underlying mechanics rather than relying on a soft-tissue repair alone.
How the Procedure Works
The most exacting part of this operation is where the graft attaches to the femur. The MPFL has a natural starting point on the bone. A tunnel placed even slightly off that spot changes how the graft tightens and loosens as the knee bends. We use X-ray guidance in the operating room to find the landmark, then test the position with a trial graft before committing. The graft should hold near-even tension from a straight knee to a bent one.
The graft is then passed to the inner edge of the kneecap and anchored at two points to spread the load. We set the final tension with the kneecap seated in its groove. Too tight restricts bending and can pull the kneecap inward. Too loose lets it slide outward again. When the groove is too shallow or the tendon anchor on the tibia sits too far outward, an MPFL graft alone is not enough, and a bone procedure is added.
That bone procedure is usually a tibial tubercle osteotomy. The bony bump on the front of the shin where the kneecap tendon attaches (the tibial tubercle) is moved to a better position and held with screws so the kneecap tracks straight in its groove. When it is needed, it is done in the same operation as the MPFL reconstruction rather than as a separate surgery.
When to Consider MPFL Reconstruction
We offer MPFL reconstruction when the symptoms, the imaging, and a trial of non-operative care all point the same way. The typical picture includes:
Recurrent patellar dislocation
Two or more kneecap dislocations. That confirms a structural problem that rehab alone will not fix.
First dislocation with osteochondral injury
A loose cartilage fragment needs surgery on its own. The MPFL is often rebuilt during the same operation.
Persistent instability symptoms
The kneecap keeps slipping or giving way, enough to get in the way of daily life or sport.
Treats: Patellar Instability
Risks & Why We Still Recommend It
Every operation carries risk. This procedure is offered because the condition, when left untreated, can cause repeat kneecap dislocations that damage cartilage and leave the kneecap feeling untrustworthy. The decision to proceed weighs the risks of surgery against the limitations the condition places on daily function. Surgery does not remove risk; it addresses a problem that is otherwise progressive. Whether it is appropriate is determined for each patient in consultation with the surgeon.
The risks we discuss with you before MPFL reconstruction include:
- bleeding and infection
- anesthesia risk
- stiffness
- instability that returns if the bone shape also needs correction
- a fracture of the kneecap (rare, from the tunnel or an over-tight graft)
- loss of motion from an over-tight graft
- blood clot in the leg or lung
Surgery makes sense when the kneecap keeps giving way, imaging shows a torn MPFL, and you have a clear goal of returning to activity. If the operation is not right for you, we will say so.
Frequently Asked
questions we hear in clinicWhy won't the torn ligament heal on its own?
When the kneecap dislocates, it almost always tears the MPFL, and the torn ligament rarely heals with enough strength to prevent a second event. That is why a reconstruction with a graft, rather than waiting for the ligament to mend, is offered once the kneecap keeps giving way.
I have only dislocated my kneecap once. Do I still need surgery?
Usually not on that basis alone. We offer reconstruction after two or more dislocations, which confirm a structural problem rehab alone will not fix. After a first dislocation, surgery comes up when a loose cartilage fragment needs an operation on its own; the MPFL is often rebuilt during that same operation.
What happens if my kneecap keeps dislocating?
The risk of another event grows with each new one, and each dislocation can chip cartilage off the back of the kneecap or the end of the femur. Those chips become loose bodies in the joint and speed up damage to a knee that needs to last decades.
Will a graft alone fix the problem?
Not always. When the groove for the kneecap is too shallow, the kneecap sits too high, or its tendon anchors too far to the outside of the tibia, an MPFL graft alone is not enough. In those cases we add bone procedures to fix the underlying mechanics rather than relying on a soft-tissue repair alone.
What can go wrong with the graft?
Tension is the balance point: too tight restricts bending and can pull the kneecap inward, too loose lets it slide outward again. Other risks we discuss include stiffness, a rare fracture of the kneecap, instability that returns if the bone shape also needs correction, and the general risks of surgery.
Further Reading
External patient-education references and related OSI pages for additional background:
