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

Overview of PLC Biomechanics The importance of the posterolateral corner knee structures – Sectioning studies – Functional assessment – Effect on Orthopaedic procedures – Healing ? – Osteoarthritis Mechanical assessment of treatmentsFCL PFL PLT

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 also important 2° stabilizers

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

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)

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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)

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

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

PLC Rabbit Model Mild medial compartment OA at 6 months

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

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

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

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

The Effect of a PTO on PLCD 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.

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

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

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                

Anatomic FCL Reconstruction (Coobs, 2007) Restores varus stability

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

THANK YOU Sports Medicine Institute University of Minnesota