PATELLAR TENDON RUPTURES

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ANATOMY & BIOMECHANICS

Figure 1: Frontal View of Normal Patellar Tendon and Extensor Mechanism.

The patellar tendon attaches to the tibial tubercle on the front of the tibia (shin bone) just below the front of the knee. It also is attached to the bottom of the patella (kneecap). At the top of the patella, the quadriceps tendon is attached. At the tope of the quadriceps tendon is the quadriceps muscle. The quadriceps muscle is the large muscle on the front of the thigh. As the quadriceps muscle contracts (shortens), it pulls on the quadriceps tendon, the patella, the patellar tendon, and the tibia to move the knee from a flexed (bent) position to an extended (straight) position. Conversely, when the quadriceps muscle relaxes, it lengthens. This allows the knee to move from a position of extension (straight) to a position of flexion (bent). (Click HERE for a computer animation of basic knee motion (mpg file) courtesy of Rob Kroeger.)

INJURY

When the patellar tendon ruptures, the patella loses its anchoring support to the tibia. Without this anchoring effect of the intact patella tendon, the patella tends to move superiorly (towards the hip) as the quadriceps muscle contracts. Without the intact patella tendon, the patient is unable to straighten the knee. If a rupture of the patella tendon occurs, and the patient tries to stand up, the knee will usually buckle and give way because the body is no longer able to hold the knee in a position of extension (straight).

DIAGNOSIS

The examination consists of palpating the patellar tendon and the patella. Usually, when the tendon ruptures, the patella moves upwards on the thigh. At the same time, the hole between the ends of the ruptured tendon is palpable on the front of the knee. X-rays of the knee reveal the abnormal position of the patella, indicating a rupture of the patella tendon.

Figure 2: Lateral View of Ruptured Patellar Tendon.

When x-rays are taken, the patella (kneecap), is seen to move away from the knee and towards the mid thigh (Figure 2) when compared to a normal knee x-ray (Figure 3).

Figure 3: Lateral View of Normal Knee with Intact Patellar Tendon.

TREATMENT

This is an injury that must be treated surgically. Since the tendon is outside of the joint, it cannot be repaired arthroscopically. Usually, the repair is done as an outpatient or overnight stay.

Figure 4: Surgical View of Ruptured Patellar Tendon (Yellow Circle).

An incision is made on the front of the knee, overlaying the tendon. The site of the tendon rupture is identified.

Figure 5: Surgical View of Ruptured Patellar Tendon (Yellow Circle) with Tendon Ends Retracted to Expose the Femur.

The tendon ends are retracted to allow inspection of the underlying joint and femur.
ANATOMY & BIOMECHANICS

Figure 6: Surgical View of Repaired Patellar Tendon (Yellow Circle) with Sutures Visible.

The tendon ends are identified and then sewn together. Afterwards, a cast or brace is often used to protect the repair. The length of time required for casting or bracing is usually a minimum of 6 weeks followed by several weeks of rehabilitation.

PROBLEMS

The usual risks of surgery are involved including: infection, stiffness, suture reaction, failure of satisfactory healing, risks of anesthesia, phlebitis, pulmonary embolus (blood clot in the lungs), and persistent pain or weakness after the injury and repair.
For a REALAUDIO/VIDEO presentation of a ruptured patellar tendon: PATELLAR TENDON RUPTURE