Guido Wierer1,2, Danko Milinkovic3, James R Robinson4, Michael J Raschke5, Andreas Weiler6, Christian Fink7,8, Mirco Herbort7,9, Christoph Kittl5. 1. Department of Orthopedics and Traumatology, Paracelsus Medical University Salzburg, Salzburg, Austria. wierer@gmail.com. 2. Research Unit for Orthopaedic Sports Medicine and Injury Prevention (OSMI), ISAG, UMIT Hall, Hall in Tirol, Austria. wierer@gmail.com. 3. Department of Orthopedic and Trauma surgery, Arcus Sportclinic, Pforzheim, Germany. 4. Avon Orthopaedic Centre, Bristol, UK. 5. Department of Trauma, Hand and Reconstructive Surgery, Westphalian Wilhelms University Muenster, Muenster, Germany. 6. Sporthopaedicum Berlin, Berlin, Germany. 7. Research Unit for Orthopaedic Sports Medicine and Injury Prevention (OSMI), ISAG, UMIT Hall, Hall in Tirol, Austria. 8. Gelenkpunkt - Sports and Joint Surgery, Innsbruck, Austria. 9. OCM Clinic, Munich, Germany.
Abstract
PURPOSE: The purpose of the present study was to determine how the medial structures and ACL contribute to restraining anteromedial instability of the knee. METHODS: Twenty-eight paired, fresh-frozen human cadaveric knees were tested in a six-degree of freedom robotic setup. After sequentially cutting the dMCL, sMCL, POL and ACL in four different cutting orders, the following simulated clinical laxity tests were applied at 0°, 30°, 60° and 90° of knee flexion: 4 Nm external tibial rotation (ER), 4 Nm internal tibial rotation (IR), 8 Nm valgus rotation (VR) and anteromedial rotation (AMR)-combined 89 N anterior tibial translation and 4 Nm ER. Knee kinematics were recorded in the intact state and after each cut using an optical tracking system. Differences in medial compartment translation (AMT) and tibial rotation (AMR, ER, IR, VR) from the intact state were then analyzed. RESULTS: The sMCL was the most important restraint to AMR, ER and VR at all flexion angles. Release of the proximal tibial attachment of the sMCL caused no significant increase in laxity if the distal sMCL attachment remained intact. The dMCL was a minor restraint to AMT and ER. The POL controlled IR and was a minor restraint to AMT and ER near extension. The ACL contributed with the sMCL in restraining AMT and was a secondary restraint to ER and VR in the MCL deficient knee. CONCLUSION: The sMCL appears to be the most important restraint to anteromedial instability; the dMCL and POL play more minor roles. Based on the present data a new classification of anteromedial instability is proposed, which may support clinical examination and treatment decision. In higher grades of anteromedial instability an injury to the sMCL should be suspected and addressed if treated surgically.
PURPOSE: The purpose of the present study was to determine how the medial structures and ACL contribute to restraining anteromedial instability of the knee. METHODS: Twenty-eight paired, fresh-frozen human cadaveric knees were tested in a six-degree of freedom robotic setup. After sequentially cutting the dMCL, sMCL, POL and ACL in four different cutting orders, the following simulated clinical laxity tests were applied at 0°, 30°, 60° and 90° of knee flexion: 4 Nm external tibial rotation (ER), 4 Nm internal tibial rotation (IR), 8 Nm valgus rotation (VR) and anteromedial rotation (AMR)-combined 89 N anterior tibial translation and 4 Nm ER. Knee kinematics were recorded in the intact state and after each cut using an optical tracking system. Differences in medial compartment translation (AMT) and tibial rotation (AMR, ER, IR, VR) from the intact state were then analyzed. RESULTS: The sMCL was the most important restraint to AMR, ER and VR at all flexion angles. Release of the proximal tibial attachment of the sMCL caused no significant increase in laxity if the distal sMCL attachment remained intact. The dMCL was a minor restraint to AMT and ER. The POL controlled IR and was a minor restraint to AMT and ER near extension. The ACL contributed with the sMCL in restraining AMT and was a secondary restraint to ER and VR in the MCL deficient knee. CONCLUSION: The sMCL appears to be the most important restraint to anteromedial instability; the dMCL and POL play more minor roles. Based on the present data a new classification of anteromedial instability is proposed, which may support clinical examination and treatment decision. In higher grades of anteromedial instability an injury to the sMCL should be suspected and addressed if treated surgically.
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