Posterolateral Knee Biomechanics and Pathobiomechanics ESSKA 2000 ISAKOS

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

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 treatments FCL 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 (La. Prade, 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 (La. Prade, 2004) PFL 229 N FCL 295 N PLT 680 N * Gracilis / ITB grafts may not be strong enough

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

Effect of PLC Injuries on ACL Reconstructions (La. Prade, 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 (La. Prade, 2002) * * * • PCL graft force increased with Varus loading

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

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

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)

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

In Vivo Rabbit Model Greatly decreased force at maximum varus angulation * 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 (La. Prade, 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 (La. Prade, 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 - p<0. 05 using Student’s ttest • No significant difference between intact and reconstructed states

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 www. sportsdoc. umn. edu