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Friday, March 17, 2000

Study documents abnormal lateral patellar tilt

The first in vivo study to document abnormal lateral patellar tilt in anterior cruciate ligament (ACL) deficient knees with a quadriceps contraction is presented in scientific exhibit 277.

To conduct the study, the normal and ACL-deficient knees of 11 individuals with unilateral ACL tears were studied with an open configuration MRI scanner. Scans with the quadriceps relaxed were performed at 40, 25, and 10 degrees flexion. Scans with a controlled and maximum isometric quadriceps contraction were performed at 40 and 25 degrees flexion.

Standard patellofemoral indices were measured with a computerized system. Knee ratings, tangential radiographs and instrumented laxity testing were also conducted.

When the quadriceps was at rest normal, there were no statistically significant differences between nor-mal and ACL deficient knees in their patellar indices at all flexion angles tested. When an isometric quadriceps contraction was generated at 40 degrees flexion, the patellae of both normal and ACL deficient knees medialized (mean 2 mm), but only the patellae of ACL-deficient knees had a statistically significant lateral tilt (mean 3.6 degrees) relative to the resting state (p>.05).

When an isometric quadriceps contraction was generated at 25 degrees flexion, the medial-lateral patellar alignment of normal and ACL-deficient knees did not change, but the patellae of only ACL-de-ficient knees tilted laterally (mean 4. 1 degrees) relative to the quadriceps at rest state and relative to the opposite normal knee (p>.05). The increase in lateral patellar tilt in ACL-deficient knees with a quadriceps contraction correlated with the KT 1000 maximum manual difference(p>.05). Knee ratings and patellofemoral indices with the quadriceps at rest did not correlate with the lateral patellar tilt seen in ACL-deficient knees with a quadriceps contraction.

The researchers say anterior tibial translation with a quadriceps contraction is the probable mechanism that results in lateral patellar tilt. Lateral patellar tilt has been associated with patellofemoral pain and open chain exercises and other activities that produce anterior tibial translation in ACL-deficient knees may also contribute to anterior knee pain by the mechanism of lateral patellar tilt.

The study was from the New England Baptist Hospital sports medicine section and The Brigham and Women's Hospital radiology and orthopaedic departments.

Co-authors of the study are Mark E. Steiner, MD, and Michael Haymen, MD, New England Baptist Hospital, Brookline, Mass. Other co-authors, all from The Brigham and Women's Hospital, Boston, are Seppo K. Koskinen, MD; Carl S. Winalski, MD; and Scott Martin, MD.

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2000 Academy News March 17 Index A

Last modified 17/March/2000 by IS