Patellar Tendon Rupture Workup

Updated: Mar 30, 2021
  • Author: Christopher C Annunziata, MD; Chief Editor: Thomas M DeBerardino, MD, FAAOS, FAOA  more...
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Laboratory Studies

In the circumstance of patellar tendon rupture secondary to systemic disease, such as chronic renal failure, systemic lupus erythematosus (SLE), rheumatoid arthritis, or diabetes, the tendon rupture is rarely the harbinger or the first symptom of the disease. Therefore, although abnormal laboratory values may be found in the face of and consistent with the systemic disease, laboratory studies otherwise are rarely indicated in the workup for patellar tendon rupture.


Plain Radiography

Plain radiographs (anteroposterior [AP], lateral, and axial) should be obtained in all patients presenting with a traumatic injury to the knee or with a hemarthrosis. Contralateral films should also be obtained as a means for comparison of patellar height. Even if a palpable gap in the extensor mechanism allows easy recognition of a patellar tendon rupture, radiographs are still necessary to assess for any other concomitant abnormalities.

The lateral view is particularly helpful to determine whether a patellar rupture has occurred. The classic finding is patella alta, but one may also notice calcification indicative of chronic patellar tendinosis (see the image below). In addition, the axial view assists in determining whether any preexisting patellofemoral arthritis exists, which may impact the rehabilitative efforts and prognosis.

Patellar tendon rupture. A lateral radiograph of t Patellar tendon rupture. A lateral radiograph of the right knee from a patient with an acute patellar tendon rupture. Note the superior patellar migration as well as the calcification below the inferior pole of the patella. This represents preexisting calcification within the patellar tendon, which likely contributed to the rupture.

The so-called empty Merchant sign on the Merchant view has been suggestive as a sensitive and specific indicator of acute patellar tendon rupture, one that physicians can learn to recognize with very little training. [33]



High-resolution ultrasonography (US) can be useful in the diagnosis of acute and chronic patellar tendon ruptures. Hypoechogenicity is associated with acute tears, whereas thickening of the tendon at the rupture site and disruption of the normal echo pattern are observed with chronic tears.

Although US is widely available and does not expose the patient to radiation, many do not have the experience necessary to perform or interpret this type of study reliably. For this reason, US is not routinely employed for the diagnosis of patellar tendon rupture in the United States, though it is used quite frequently for this purpose in Europe.

Ultrasound elastography (USE), in the form of either compression elastography (CE) or shear-wave elastography (SWE), has been advocated on the grounds that in comparison with conventional US, it may yield increased sensitivity and diagnostic accuracy in tendinopathy and may be able to detect pathologic changes before they are visible on conventional US. [34] However, the procedure has several technical limitations, and standardization remains to be achieved.


Magnetic Resonance Imaging

If the diagnosis cannot be established on the basis of clinical and radiographic examination, magnetic resonance imaging (MRI) is the imaging study of choice. The typical finding is discontinuity of tendon fibers with adjacent hemorrhage or edema. [35]



No diagnostic procedure is routinely necessary to identify an acute patellar tendon rupture. If a question or concern exists of an intra-articular fracture or osteochondral injury, the joint can be aspirated to look for fat droplets. The routine use of aspiration and injection is not recommended.



Blazina, Kerlan, and Jobe described three clinical stages of patellar tendinitis (ie, jumper's knee) that culminate with patellar tendon rupture. [36]

Initially, the insidious onset of aching in the knee centers over the infrapatellar region and localizes to the inferior pole of the patella. This usually arises after the patient engages in repetitive activity such as jumping, climbing, kicking, or running.

During the first stage of the tendinitis, the pain is present only after athletic participation. The pain typically disappears after a period of rest. Sensations of weakness or "giving way" are transient and are never associated with locking or catching.

In the second stage, pain and symptoms occur at the beginning of an activity, disappear after a warmup, and then reappear after completion of the activity. The aching becomes more persistent, and eventually the discomfort persists throughout the entirety of the activity, but athletic performance is not significantly impaired.

In the third stage, the symptoms are the same but more prolonged, and performance is definitely impaired. The athlete might even become apprehensive about further participation.

Finally, if the athlete continues with intensive activity despite exacerbation of symptoms, he or she eventually may experience a sudden catastrophic "giving way," with pain and inability to actively extend the knee. This coincides with an acute and complete rupture of the patellar tendon.