The patellar tendon is a robust band of fibrous connective tissue located at the front of the knee. It functions as the lower anchor of the quadriceps muscle group, connecting the base of the kneecap (patella) to the top of the shinbone (tibial tuberosity). Working with the powerful quadriceps muscles, this structure allows the leg to straighten (knee extension), which is fundamental for walking and standing. A tear in this tendon is a serious orthopaedic injury that severely compromises the knee’s extensor mechanism, requiring prompt medical assessment.
Physical Signs and Functional Loss
A tear in the patellar tendon is often accompanied by an immediate and intense sensation described as a distinct pop or tearing sound felt within the knee. Acute, sharp pain develops rapidly at the front of the joint, often localized directly beneath the kneecap. The knee quickly exhibits significant soft tissue swelling (effusion), and bruising may spread across the joint.
The most telling visual sign of a severe tear is a pronounced deformity. When the tendon is compromised, the unrestrained quadriceps muscle contracts and pulls the kneecap upward toward the thigh. This abnormal positioning is medically termed patella alta (“high patella”) and is an externally visible marker of the damage. A noticeable, soft indentation or gap may also be revealed directly below the kneecap where the tendon has separated.
Functionally, the injury results in a significant loss of the ability to actively straighten the lower leg, known as extensor lag. The patient cannot perform a straight leg raise against gravity because the critical link in the extensor mechanism is broken. The knee will often buckle or give way when attempting to bear weight, making unassisted walking impossible.
Differentiating Partial and Complete Tears
Tears are categorized by the extent of fiber disruption, ranging from partial to complete. In a partial tear, only some fibers are damaged, while a substantial portion remains intact. Patients experience considerable pain and weakness, but they may still retain a limited capacity to extend the knee against resistance. The visual deformity of the kneecap is often minimal or absent because the remaining intact fibers maintain some tension on the patella.
A complete tear, or rupture, represents a full separation of the tendon, entirely disrupting the connection between the kneecap and the shinbone. This separation results in the total loss of the knee’s ability to extend; the leg cannot be straightened actively under any circumstances. Complete tears are associated with the most severe visual markers, including the high-riding patella (patella alta) and a distinct, palpable gap just beneath the kneecap. These severe injuries often occur during forceful quadriceps contraction against resistance, such as when landing awkwardly from a jump.
Immediate First Steps and Seeking Care
Following a suspected patellar tendon injury, the initial response should focus on minimizing pain and swelling and protecting the knee from further damage. The immediate application of the R.I.C.E. protocol is advised:
- Rest, to avoid any weight-bearing on the injured leg.
- Ice, applied for 15 to 20 minutes every couple of hours to reduce pain and internal bleeding.
- Compression, using a light elastic bandage to help limit swelling.
- Elevation, positioning the leg above the level of the heart.
It is important to keep the injured leg as straight as possible using a temporary splint or immobilizer to prevent the kneecap from shifting further upward. Avoiding any attempt to actively straighten the leg will help minimize additional strain on the compromised tendon. This injury requires immediate professional medical attention due to the high probability of a severe tear.
An urgent evaluation is necessary to determine the extent of the damage. Medical professionals typically order diagnostic imaging, such as X-rays, to assess the position of the patella and confirm the upward displacement characteristic of a tear. An MRI scan may also be utilized to visualize the soft tissue and determine the precise location and size of the tendon tear. Complete tears almost always necessitate prompt surgical intervention for repair, making a swift diagnosis a priority.