MPFL Reconstruction for Patellar Instability

The patella is a floating bone inside the quadriceps tendon. As you bend the knee, it slides down a V-shaped channel at the end of the femur called the trochlear groove, which is what keeps it tracking straight.

In the first twenty or thirty degrees of bend, before the kneecap settles into that groove, bone gives it almost no protection. What holds it is the medial patellofemoral ligament, a band from the inner edge of the patella to the femur. It supplies roughly 50 to 60 percent of the restraint against the kneecap sliding outward, and tears in nearly every dislocation.

MPFL reconstruction rebuilds that torn checkrein. A thin tendon graft is anchored to the inner edge of the kneecap and fixed to a precise point on the femur, recreating the ligament that failed.

The word to notice is reconstruction. Once the ligament has stretched and the kneecap has dislocated repeatedly, tightening the remaining tissue is unreliable. Two details decide the result: the femoral fixation point must be anatomic, confirmed on X-ray, and the graft must be tensioned as a checkrein rather than pulled tight, because over-tensioning causes pain and cartilage wear on the inner kneecap.

Most dislocations happen with a twist on a planted foot rather than a direct blow. Anatomy usually explains why it happened to you and not a teammate.

• Trochlear dysplasia. A shallow or flat groove that gives the kneecap little to sit in.
• Patella alta. A kneecap that rides high and does not engage the groove until later in flexion.
• Lateralized tibial tubercle. An attachment point that pulls the kneecap outward.
• Generalized ligamentous laxity. Loose joints throughout the body.
• Rotational alignment. Inward-turned femurs, knock-knee alignment, or weak hip abductors.
• A previous dislocation that left the MPFL incompetent.

• The kneecap slipping to the outside, sometimes returning on its own as the knee straightens
• Rapid swelling after the episode
• A feeling the knee will give out when pivoting or descending stairs
• Apprehension when someone pushes the kneecap outward
• Catching or grinding, which can signal a loose cartilage fragment

Examination looks at how far the kneecap can be pushed outward, whether that reproduces apprehension, how it tracks as the knee straightens, and whether you have generally loose joints.

X-rays include a true lateral and an axial view to assess trochlear shape and patellar height and to look for a fragment knocked off during the dislocation. MRI shows the torn MPFL, the bruise pattern on the inner kneecap and outer femur that is nearly diagnostic, and any cartilage fragment. Cross-sectional imaging measures how far outward the tibial tubercle sits, because that number can change the operation.

A first-time dislocation is usually treated without surgery: bracing, a structured program for the quadriceps and hip, and a gradual return. Many people never dislocate again. The exception is a first dislocation that knocks a fragment of cartilage or bone loose, which needs prompt surgery, and the ligament is often reconstructed at the same time.

Reconstruction is recommended for recurrent dislocation or repeated slipping, and for instability that still limits you despite honest rehabilitation. Anatomy matters in planning: a high-riding kneecap or a tubercle far to the outside may need a bone realignment as well, because a graft alone cannot overcome significant malalignment.

• Strengthen the quadriceps beforehand; it shortens the recovery meaningfully.
• Stop nicotine, and hold anti-inflammatories and blood thinners as directed.
• Have a hinged brace, crutches, and ice at home before the day of surgery.
• Book physical therapy so the first visit falls within the first week.
• Arrange a driver and help at home for the first day or two.

1. Anesthesia and arthroscopy. General anesthesia with a regional block, then arthroscopy to assess cartilage, remove or fix loose fragments, and watch how the kneecap tracks.
2. Graft preparation. A hamstring tendon is harvested through a small incision, or donor tissue is prepared.
3. Patellar fixation. The graft is secured to the inner border of the kneecap with anchors or through small tunnels.
4. Femoral fixation. The graft is passed beneath the tissue layer and fixed at the anatomic origin of the ligament, a point verified on X-ray. Getting this within a few millimeters is what makes the difference between a knee that moves normally and one that is stiff or painful.
5. Tensioning. Tension is set in mid-flexion so the kneecap sits centered and still glides, then motion is checked through a full arc.
6. Additional work. A tibial tubercle osteotomy or cartilage procedure is performed when needed.

Timelines below describe an isolated MPFL reconstruction. Adding a tubercle osteotomy extends protected weight bearing to about six weeks and pushes return to sport later.

Weeks 0 to 2

Weight bearing as tolerated in a brace locked straight for walking. Therapy starts within the first week on quadriceps activation, swelling control, and gentle flexion to about ninety degrees.

Weeks 2 to 6

Flexion progresses toward full and the brace is unlocked, then weaned as quadriceps control returns.

Weeks 6 to 12

Strengthening for the quadriceps, hip abductors, and rotators, since hip control is a large part of keeping the kneecap centered.

Months 3 to 4

A graded running progression, then jumping and landing mechanics.

Months 4 to 6

Return to sport once strength is close to the other leg, hop testing is symmetric, and the knee no longer feels apprehensive with cutting.

Possible complications include infection, blood clot, stiffness or loss of flexion, and persistent pain at the front of the knee. Fracture of the patella is an uncommon but recognized risk when tunnels are made in that bone. An over-tensioned or poorly positioned graft can push the kneecap too far to the inside and cause medial pain or cartilage wear, which is why femoral position is confirmed on X-ray.

Instability can recur, particularly in patients with a very shallow groove, a high-riding kneecap, or uncorrected malalignment. In skeletally immature patients, fixation is chosen to avoid the growth plate. No surgeon can guarantee an outcome.