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A New Angle on Knee Problems

X-rays are often used to identify problems in the knee and other joints. A new measurement has been introduced to help doctors evaluate knee X-rays. The measurement is called anteroposterior patellar-tilt angle. It records the angle between the top of the kneecap (patella) and the thighbone (femur).

By studying X-rays of cadavers (human bodies preserved for study), doctors have found that this angle is best observed when X-rays are taken with the knee slightly bent (30 degrees). The measurement is reliable. This means that different doctors come up with the same results.

The measurement is useful because it shows a difference between normal and problem knees. Patellar-tilt angle is less in knees that have tendinitis. Notably, even when patients only have symptoms in one knee, the angle is reduced in both knees. Doctors think that a smaller tilt between knee and thighbone puts more stress on the patellar tendon in the knee. This makes it more likely that knee pain and tenderness may develop over time. Why tendinitis sometimes shows up in one knee and not the other when both have a reduced angle is unclear.

An easy new measurement for evaluating knee X-rays has been introduced. The measurement is reproducible and may help identify who is at risk for some types of knee tendinitis.

References: Timothy F. Tyler, MS, PT, ATC, et al. Evidence of Abnormal Anteroposterior Patellar Tilt in Patients with Patellar Tendinitis with Use of a New Radiographic Measurement. In The American Journal of Sports Medicine. May/June 2002. Vol. 30. No. 3. Pp. 396-401.

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