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Knee News

Tapping Test Can Be Used to Diagnose Bone Marrow Edema of the Knee

Bone marrow edema (BME) of the knee is a painful, but self-limiting disease that can occasionally progress to irreversible osteonecrosis (bone cell death). Currently, other than finding presence of BME through magnetic resonance imaging (MRI), there are no tests for it.

The diagnosis of BME is important in order to be able to treat it properly, according to the type of BME. Ischemic BME, for example, can be treated with core decompression for immediate resolution of pain.

The authors of this study wanted to see if a tapping test, using a reflex hammer, would be a good indicator of the presence of BME in the knee. For the study, researchers assessed 70 patients, average age 51 years. Group 1, 44 patients (46 knees) had BME, while group 2 acted as the control group. They had knee pain but BME was not found through MRI.

The researchers used an ordinary reflex hammer to tap along the knee while the patient reported the severity of the pain using the Visual Analog Scale (VAS), a scale of 0 to 10, with 10 being the worst pain imaginable. X-rays and MRIs were performed before the tapping test, however the physician performing the tapping test was blinded to the x-ray and MRI results.

Results of the tapping showed that patients with BME reported an average VAS of 3.7 (out of 10) in affected areas of the knee and an average of 1.59 in the non-affected parts of the knee. This compared with the control group, which reported a VAS of 0.85 in their painful knees.

The authors note that there were weaknesses in the study, which include that the tap testing was done precisely the same way in all patients, with the aid of a mechanism that supported the mallet and allowed it to strike in the same place on all patients.

In conclusion, the authors write that the test is economical, easy to perform in a doctor's office, and not time-consuming. While the tapping test has its limitations as to the part of the joint and the type of patients, the authors say that the tapping test is a good screening test for diagnosis of BME in the knee.


Nicolas Aigner, MD, et al. Tapping Test in Patients with Painful Bone Marrow Edema of the Knee. In The Clinical Journal of Pain. February 2008. Vol. 24. No. 2. Pp. 131-124.

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