What Is a Patellar Tendon Rupture, and How Is It Repaired?

Key takeaways

• A ruptured patellar tendon is an emergency. You should get urgent medical help, not book a scan.
• Surgery to reattach the tendon is usually needed within days of the injury.
• Recovery usually takes many months of structured rehabilitation.
• After repair, standing whole-body imaging can help your surgeon check the position of the kneecap (patella) and leg alignment during recovery.
• The patellar tendon is different from the quadriceps tendon. The quadriceps tendon sits above the kneecap, not below it.

What are the symptoms of a patellar tendon rupture?

The most obvious symptom is that you cannot straighten your knee after the injury. You may have felt or heard a pop at the front of the knee. The kneecap often rides higher than normal, because nothing is holding it down from below.

You may also see a gap or dent just below the kneecap, where the tendon has torn away. Walking becomes very difficult or impossible.

What causes a patellar tendon to rupture?

The most common cause is a sudden, forceful tightening of the quadriceps muscle while the knee is bent. Examples are landing from a jump or stumbling off a step. The tendon gives way under the load.

The rupture usually happens where the tendon attaches to the bottom of the kneecap. In some cases it tears away from where it attaches on the shinbone instead.

How does the extensor mechanism of the knee work?

The extensor mechanism is the chain of structures that lets you straighten your knee. The quadriceps muscle joins the top of the kneecap through the quadriceps tendon. The patellar tendon then joins the bottom of the kneecap to the tibial tuberosity, a bony bump at the top of your shinbone. If either tendon ruptures, the chain is broken and the knee cannot straighten.

A quadriceps tendon rupture breaks the chain above the kneecap. A patella ligament rupture breaks it below. Both stop you from straightening your leg, but the surgical approach is different.

How is a torn patellar tendon repaired with surgery?

Surgical repair is almost always necessary. The torn ends of the tendon cannot heal on their own, because the quadriceps muscle pulls them apart. For the best results, surgery is usually done within the first week or two after the injury.

What happens during the operation

The surgeon makes a cut over the front of the knee. They reattach the tendon to the kneecap with strong stitches passed through holes drilled in the bone. In some cases, a wire or cable is placed for a while to protect the repair as it heals. If the tendon tissue is too damaged, a graft from another tendon may be used to strengthen the repair.

The aim is to bring the patella back to its correct position, so the extensor mechanism works properly again. If the kneecap sits too high after repair, the knee may not bend or straighten normally.

What does recovery after patellar tendon repair look like?

Recovery is long and structured. Most people spend several months in a rehabilitation programme. It slowly builds quadriceps strength and brings back the knee's range of movement.

Throughout this process, your surgical team will want to check that the patella is sitting in the right position and that leg alignment is on track.

How does standing imaging help after patellar tendon repair?

Standard X-rays are usually taken lying down. That position relaxes the muscles and removes the effect of gravity. So the kneecap may look normal even when it does not sit normally under real-life load. A standing, weight-bearing image shows where the patella actually sits when you are on your feet.

ScanAlign standing EOS imaging takes a full-length image from your hips to your ankles in one single exposure, with about 90% less radiation than a standard X-ray, around ten times less. This lets your surgeon see the patella position in relation to the whole leg. That includes any changes in knee alignment or leg length that may have developed during recovery.

Your body is a connected chain. When one knee is kept still for weeks, the hip, ankle and other leg often compensate. A whole-body standing image shows these compensations, so they can be addressed during rehabilitation.

Is a standing alignment scan right for you?

ScanAlign does not assess or treat acute ruptures. Our imaging is designed for the recovery phase. This is when you and your surgeon want to understand alignment and patella position under real weight-bearing conditions.

Before you start a treatment, or change the one you are on, it is worth getting a detailed diagnosis. Knowing whether the cause sits in the pelvis, the legs or the spine changes what will actually help.

Frequently asked questions