Overview
The patellar tendon (sometimes called the patellar ligament) runs from the bottom of the kneecap to the front of the tibia. It carries every ounce of force made by the quadriceps muscle group. Together, the quadriceps, kneecap, and patellar tendon form the extensor mechanism. That system straightens your knee when you stand up, climb stairs, or land from a jump. A complete rupture tears through this chain, usually where the tendon meets the lower tip of the kneecap.
The typical cause is a sudden load on a muscle that is contracting hard while being stretched. A stumble, a missed step, or a hard landing from a jump can do it. The failure is often felt as a loud pop, followed at once by an inability to straighten the leg. Without surgical repair, the tendon pulls back and scars in a shortened position. That makes later reconstruction much more difficult. Early repair, done before scarring sets in, lets the tendon ends be brought back together under acceptable tension. They are held with sutures anchored through the kneecap.
How the Procedure Works
We expose the tear through an incision down the front of the knee. Heavy locking sutures are passed through the torn tendon end. Two or three bone tunnels are then drilled through the kneecap, from its lower tip to its upper edge. The sutures are pulled through and tied over the top of the kneecap, drawing the tendon back to its attachment point.
The critical check during surgery is kneecap height. We compare the repaired side to the opposite knee on a side-view X-ray (fluoroscopy). The tension is adjusted so the kneecap sits at its normal height. Too low limits bending after surgery. Too high means the repair is loose, and a lag in straightening the knee will persist. When the tendon tissue is thin or weakened, a loop of reinforcing suture is added from the kneecap down to the front of the tibia. It protects the repair during early healing. Repair within the first week or two, before the tendon pulls back for good, produces the best outcomes.
When to Consider Patellar Tendon Repair
Patellar tendon repair is usually offered when symptoms, imaging, and a trial of non-operative care all point to surgery as the next step. The typical picture includes:
Acute patellar tendon rupture
A sudden inability to straighten the knee, with a gap you can feel below the kneecap and a high-riding kneecap on X-ray.
Chronic rupture with functional loss
An older rupture that was not repaired at first and leaves the patient unable to fully straighten the knee (an extensor lag).
Treats: Patellar Tendon Ruptures
Risks & Why We Still Recommend It
Every operation carries risk. This procedure is offered because the condition, when left untreated, can cause a knee that cannot actively straighten, since walking, stairs, and standing from a chair all depend on an intact extensor mechanism. 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 patients before patellar tendon repair include:
- bleeding and infection
- anesthesia risk
- stiffness, particularly loss of flexion
- re-rupture
- the kneecap ending up too high or too low from imperfect tensioning
- suture-anchor or hardware issues
- blood clot in the leg or lung
We proceed when there is an acute rupture of the patellar tendon and the knee can no longer actively straighten. If the operation is not right for you, we will say so.
Frequently Asked
questions we hear in clinicWhy can I not straighten my knee after this injury?
The patellar tendon carries every ounce of force made by the quadriceps muscle group. Together, the quadriceps, kneecap, and patellar tendon form the extensor mechanism, the system that straightens your knee. A complete rupture tears through that chain, so the leg can no longer actively straighten.
How soon does the tendon need to be repaired?
Repair within the first week or two, before the tendon pulls back for good, produces the best outcomes. Without surgical repair the tendon retracts and scars in a shortened position, which makes later reconstruction much more difficult.
How is the tendon reattached?
Heavy locking sutures are passed through the torn tendon end, pulled through bone tunnels drilled in the kneecap, and tied over its top, drawing the tendon back to its attachment point. When the tendon tissue is thin or weakened, a loop of reinforcing suture is added from the kneecap down to the tibia to protect the repair during early healing.
How do you know the repair is set at the right tension?
The critical check during surgery is kneecap height, compared against your opposite knee on a side-view X-ray. Too low limits bending after surgery; too high means the repair is loose and a lag in straightening the knee will persist.
What happens if I skip surgery?
Left untreated, the knee cannot actively straighten. Walking, stairs, and standing from a chair all depend on an intact extensor mechanism, and the retracted tendon scars in a shortened position that makes later reconstruction much more difficult.
Further Reading
External patient-education references and related OSI pages for additional background:
