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Mechanism of the pivot shift
1Department of Orthopaedic Surgery, Keio University, Tokyo, Japan.
The Journal of Bone and Joint Surgery. British Volume
|September 1, 1990
Summary
The pivot shift in knees is caused by a complex interaction between knee geometry and valgus torque. Division of the anterior cruciate ligament and iliotibial tract stops this abnormal knee movement.
Area of Science:
- Orthopedic Surgery
- Biomechanics
- Knee Kinematics
Background:
- The pivot shift phenomenon is a hallmark of anterior cruciate ligament (ACL) deficiency.
- Understanding the biomechanical factors contributing to the pivot shift is crucial for surgical reconstruction and rehabilitation.
Purpose of the Study:
- To investigate the mechanism of the pivot shift under valgus torque.
- To determine the role of the anterior cruciate ligament (ACL) and iliotibial tract (ITB) in the pivot shift.
Main Methods:
- Analysis of knee movements under valgus torque in 29 fresh cadaveric knees.
- Three-dimensional motion analysis using biplanar photography.
- Sequential division of knee ligaments (ACL, ITB) to assess their contribution.
Main Results:
- Sectioning the ACL alone resulted in a pivot shift in 7/20 knees and abnormal internal rotation in 13/20 knees.
- Division of both the ACL and ITB eliminated the pivot shift, maintaining internal tibial rotation.
- The medial collateral ligament (MCL) served as the axis of rotation during the pivot shift, tightened by valgus torque.
Conclusions:
- The pivot shift is a complex dynamic event resulting from the interaction between knee joint geometry and applied valgus stress.
- The ACL and ITB play critical roles in preventing abnormal tibial rotation and the pivot shift phenomenon.
- The MCL acts as a crucial rotational axis, highlighting its importance in knee stability.