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

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
(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
20
15
30
25
10
5
0
FCL
PFL
PLT
0 90 30 60
Flexion angle (Degrees)
* Synergy between FCL and PLT/PFL *

Varus Moment
• Peak FCL varus is at 30 °
• Load decreases after 30 °
FCL
10
8
6
4
2
0
16
14
12
0 90 30 60
Flexion angle (Degrees)
* 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

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

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
40
35
30
25
20
15
10
5
0
FCL Cut
PFL Cut
PLTCut
Ze ro
IR
Ze ro
30
Va ru
IR s
30
Va ru s

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
10
8
6
4
2
0
PLC Cut
Intact
0 100 200
ACL Graft Tension
300

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)
50
45
40
35
30
25
20
15
10
5
0
PFL Cut
PLT Cut
ALL Cut
*
*
*
• PCL graft force increased with
Varus loading
30 60 90
Flexion Angle (Degrees)

Effect of PLC Injuries on a PCL
Reconstruction Graft
(LaPrade, 2002)
20
18
16
14
12
10
8
6
4
2
0
PFL Cut
PLT Cut
ALL Cut
*
*
*
• PCL graft force increased with PD
& ER
30 60 90
Flexion Angle (Degrees)

Effect of PLC Injuries on a PCL
Reconstruction Graft
(LaPrade , 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 ???
(LaPrade, JOR, 2004; AJSM, 2005)
• FCL and PLT ruptured in New
Zealand white rabbits
• Allowed to heal for three and six months post-op

-15 -5
1
0
-1
-2
-3
6
5
4
3
2
5
Control
Operated
Force (N)
15 25 35
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
(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
30
25
20
15
10
5
0
30 90
Knee Flexion Angle (Degrees)
Intact
PLS Cut
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
25
20
15
10
5
0
30 90
Knee Flexion Angle (Degrees)
Intact
PLS Cut
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

 intact injured recon.
20
15
10
5
0
35
30
25
0 deg.
30 deg.
60 deg.
flexion angle

p<0.05 using Student’s ttest
90 deg.
• Injured knee translation is significantly higher than that of intact knee
• No significant difference between intact and reconstructed states

PLCR Results: External Rotation intact injured recon.
25
20
15
10
5
0
0 deg.
30 deg.
60 deg.
flexion angle
90 deg.

p<0.05 using Student’s t-test
• ER in cut knee is significantly higher
• No significant difference between intact and reconstructed states

Anatomic FCL Reconstruction
(Coobs, 2007)
• Restores varus stability
14
2
0
12
10
8
6
4
* *
0°
*
* *
15°
*
*
*
30°
* *
60°
Knee Flexion Angle
* *
90°
Intact
Sectioned
Reconstructed

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

Sports Medicine Institute
University of Minnesota www.sportsdoc.umn.edu