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Posterolateral Knee Biomechanics and Pathobiomechanics

Posterolateral Knee Biomechanics and Pathobiomechanics. ESSKA 2000 – ISAKOS Knee Course. Robert F. LaPrade, M.D., Ph.D. Professor Department of Orthopaedic Surgery University of Minnesota. FCL PFL PLT. Overview of PLC Biomechanics.

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Posterolateral Knee Biomechanics and Pathobiomechanics

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  1. Posterolateral Knee Biomechanics and Pathobiomechanics ESSKA 2000 – ISAKOSKnee Course Robert F. LaPrade, M.D., Ph.D. Professor Department of Orthopaedic Surgery University of Minnesota

  2. FCL PFL PLT Overview of PLC Biomechanics • The importance of the posterolateral corner knee structures • Sectioning studies • Functional assessment • Effect on Orthopaedicprocedures • Healing ? • Osteoarthritis • Mechanical assessmentof treatments

  3. Varus Instability at 30° • FCL is primary restraint to varus • Cutting popliteus tendon and other PLC structures increases varus(Nielsen, 1984 & 1986; Gollehan, 1987; Grood, 1988; Veltri, 1995) • Cruciates are alsoimportant 2° stabilizers

  4. Anterior Translation at 30° • Sectioning PLC - no increase in primary anterior translation(Gollehon 1987;Grood,1988) • In ACLD knees, absent PLC results in increased translation (0°-30°) (Nielsen 1986; Wroble 1993) * Think about PLC for 3+ Lachman

  5. Posterior Translation at 90° • PCL only ligament for initial posterior restraint at all flexion angles(Bantigan and Voshell, 1941; Gollehon, 1987) • PLC minor restraint to posterior translation(Gollehon, 1987; Grood,1988; Veltri, 1995)

  6. Posterior Translation at 90°(Gollehon, 1987; Grood, 1988) • Combined PCL / PLC injuries ↑↑↑ posterior translation

  7. External Rotation (“Dial Test”) • Sectioning of PLC structures increases ER(Gollehon, 1987;Grood, 1988;Lipke, 1981; Nielsen,1984) • 30° of flexion = 13° increase ER • 90° of flexion = 5.3° increase ER • Additional section of PLC / PCL increases ER at 90° flexion(Grood, 1988)and ACL/PCL(Wroble, 1993)increases ER at 90° flexion

  8. Cruciate Ligaments and Varus • Recruited with deficient PLC to resist varus • Section of PLC increases mean force on ACL at all flexion angles(Markoff, 1993) • Section of PLC increases force on PCL at > 45°(Markoff, 1993) Varus instability: severe effect on ACLR / PCLR and ↑↑ force on medial compartment

  9. Effect of Popliteus onPosterior Translation (Harner, 1998) • Simulated popliteus contraction decreases in situ forces on PCL at 30° and 90° • Also decreases posterior translation in PCL-deficient knees

  10. Force Measurement of PLC Structures(LaPrade, 2003) • FCL and PLT / PFL act synergistically in ER • FCL main structure for varus

  11. External Rotation Torque • FCL force decreases with flexion angle • Force in the popliteus complex increases with flexion angle * Synergy between FCL and PLT/PFL *

  12. Varus Moment • Peak FCL varus is at 30° • Load decreases after 30° * No load on PLT/PFL with intact FCL *

  13. Biomechanical FailureStrengths(LaPrade, 2004) PFL 229 N FCL 295 N PLT 680 N * Gracilis / ITB grafts may not be strong enough

  14. Deficient PCL / PLC(Skylar, 1993) • ↑↑ Stress on medial compartment

  15. Effect of PLC Injuries on ACL Reconstructions(LaPrade, 1999) • Significant increase in graft force seen for varus at 0° and 30° • Repair / reconstruct PLC injuries at time of ACLR to reduce risk of ACLR failure

  16. Effects of Tensioning on an ACL Graft and Integrity of the PLC on Tibiofemoral Rotation(Wentorf, 2002) • Significant increase in ER seen with increasing ACL graft tension with PLC cut • Repair / reconstruct PLC injuries first, prior to ACL graft fixation, to reduce risk of ER deformity

  17. PLC Repairs / Reconstructions and ACLR(Kanamori, 2000) • High loads on PLC if concurrent ACLR not performed * Need to reconstruct both simultaneously

  18. PCL graft force increased with Varus loading Effect of PLC Injuries on a PCL Reconstruction Graft(LaPrade, 2002) * * *

  19. Effect of PLC Injuries on a PCL Reconstruction Graft(LaPrade, 2002) * • PCL graft force increased with PD & ER * *

  20. Effect of PLC Injuries on a PCL Reconstruction Graft(LaPrade, 2002) • Repair / reconstruct posterolateral structures at time of PCL reconstruction to decrease chance of post-reconstruction PCL graft failure • Assess for posterolateral knee injury prior to PCL graft fixation.

  21. In Vitro Forces in a PCL Graft (Markolf, 1997) • With intact posterolateral structures, no increase in PCL graft force with a varus or external rotation moment

  22. Effect of Deficient PLC on PCLR (Harner, 2000) • Forces in PCL graft significantly increased for PLS deficiency • PCL graft is ineffective and overloaded with PLS deficiency

  23. Animal Models of PLC Instability • Rabbit anatomy similar (JOR, 2003) • Rabbit instability created, mild OA(JOR, 2004; AJSM,2005) • Goat anatomy similar (JOR, 2005) • Goat instability created • Canine anatomy / biomechanics similar (JOR, 2007)

  24. Does the PLC Heal ???(LaPrade, JOR, 2004; AJSM, 2005) • FCL and PLT ruptured in New Zealand white rabbits • Allowed to heal for three and six months post-op

  25. In Vivo Rabbit Model Greatly decreased force at maximum varus angulation * PLC does not heal *

  26. PLC Rabbit Model • Mild medial compartment OAat 6 months

  27. PLC Canine Model(Griffith, 2007) • Similar anatomy / biomechanics * in vivo studies ongoing *

  28. Effect of Opening Wedge PTO on PLC Injury(LaPrade, 2007) • Chronic PLC injuries in varus stretch out with PLCR • Observation that some patients do not need PLCR post osteotomy

  29. Results - Varus Opening • Significant increase in varus opening with PLC cut at • Significant decease in varus after PTO • No statistical difference between intact and after PTO

  30. Results - External Rotation • Significant increase in ER with PLC cut • Significant decease in ER after performing the PTO • No statistical difference between intact and after PTO

  31. The Effect of a PTO onPLCD Knee • Opening wedge PTO significantly decreases varus opening & ER in a PLC deficient cadaveric knee. • Concurrent increase in MCL forces may account for increase in knee stability.

  32. Anatomic PLC Reconstruction(LaPrade, AJSM, 2004) • FCL, PLT, PFL anatomically reconstructed • Biomechanical testing intact, cut, and reconstructed PLC buckle transducers

  33.                 - p<0.05 using Student’s t-test PLCR Results: Varus • Injured knee translation is significantly higher than that of intact knee • No significant difference between intact and reconstructed states

  34.                PLCR Results: External Rotation • ER in cut knee is significantly higher • No significant difference between intact and reconstructed states  - p<0.05 using Student’s t-test

  35. Anatomic FCL Reconstruction(Coobs, 2007) • Restores varus stability

  36. Summary of Key Points in PLC Biomechanics • FCL prevents abnormal varus motion • FCL and popliteus complex prevent abnormal ER • PLC does not heal • Recognize PLC injury prior to cruciate ligament(s) reconstruction • Significant stress on medial compartment

  37. THANK YOU Sports Medicine Institute University of Minnesota www.sportsdoc.umn.edu

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