The patellar tendon is the ligament that connects the kneecap to the tibia. It is an important part of the extensor mechanism of the lower limb, which includes the quadriceps muscle, the quadriceps tendon, the patella and the patellar tendon. These structures work together, allowing the knee to extend. The extensor mechanism is critical for many physiological functions ranging from walking to running. Without an intact extensor mechanism, all of these activities may be impossible to perform.
The typical patient who suffers a patellar tendon rupture is a young, athletic individual. As more middle-aged adults remain physically active, this injury becomes more common in older populations. The injury usually involves an awkward landing from a jumping position where the quadriceps is contracted, but the knee extends dynamically. This is called eccentric contraction and puts tremendous stress on the tendon.
Typical signs of a ruptured patellar tendon include pain just below the knee, swelling and hematoma in the front of the knee, palpable gap at a point where the tendon should be tight, difficulty walking or doing sports activities. It has been found that in almost all patients suffering from a ruptured patellar tendon, chronic tendinitis is present. The patellar tendon is usually injured in the area where blood flow is poor and the tendon is weaker. In people who are not athletes and suffer a rupture of the patellar tendon, there is usually a coexisting systemic disease or previous knee surgery that weakens the tendon.
The diagnosis of a patellar tendon rupture is usually obvious on clinical examination. These patients will not be able to extend their knee against gravity. Radiographic testing is necessary to rule out a patellar fracture which can cause similar symptoms and should be ruled out as a possible diagnosis. On X-ray, the kneecap is usually higher compared to the opposite knee, as the quadriceps pulls the kneecap upwards and nothing holds it in its normal position. Although often not required, an MRI scan can confirm the diagnosis and highlight concomitant lesions.
A ruptured patellar tendon does not heal on its own, and if left untreated will lead to weakness of the quadriceps and difficulty performing daily activities, including walking. Surgery for tendon repair has associated difficulties. The cut ends of the tendon must be sewn together. The difficulty lies in the fact that it is important to restore proper tension to the tendon. Also, repair can be difficult if the tear has been made directly on the bone. In these cases, the sutures used to repair the tendon must go directly through the bone.
Repair after a rupture of the patellar tendon is difficult and takes time. One of the most important prognostic factors for recovery is the timing of surgery, as delayed surgery can limit the possibility of recovery. Early mobilisation after surgery, strengthening and protection from excessive tension in the repaired tendon speeds up recovery. Return to daily activities occurs at least 3 months after surgery and return to sports activities at 4-6 months.