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Valgus Loading causes coupled Internal Rotation and significant increases in ACL strain
Author(s):
KOH J. (United States of America)
,
KOH J. (United States of America)
Affiliations:
Zhang L.
Zhang L.
Affiliations:
ESSKA Academy. KOH J. May 9, 2018; 209364; P04-1453 Topic: Biomechanics
Prof. Dr. Jason KOH
Prof. Dr. Jason KOH
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Abstract
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Objectives: Many ACL injuries occur because of noncontact mechanisms that include valgus load. ACL strain increases with anterior and internal rotation force; however, pure valgus may not load the ACL strongly. We hypothesize that valgus loading on the knee causes knee internal rotation and increased ACL strain.

Methods: 8 fresh frozen cadaver knees (63±1.1yrs) were mounted on the customized 6-DOF robot testing platform. Through a medial parapatellar arthrotomy a microstrain DVRT was attached to the anteromedial bundle of ACL while the capsular and ligamentous structures were left intact. The 6-DOF robot with JR3 force sensor was used to test 2 loading conditions (FIXED or FREE) at different flexion angles (10,20,30 deg). All the testing was repeated with an additional 100N anterior loading force on the tibia. FIXED: 10 Nm Valgus loading torque with fixed internal/external rotation. FREE: 10Nm Valgus with free internal/external rotation. Following this, the knee was alternately externally and internally rotated with 10Nm torque. Forces acting on the knee as well as ACL strain were continuously monitored.

Results: : In FIXED (Fig 1), 10 Nm valgus loading caused increased tibial internal rotation (IR) torque with knee flexion angle (p = 0.01). Additional anterior load combined with valgus force caused additional IR torque (p<0.001). In FREE valgus load caused coupled tibial IR (p<0.001) (Fig 2) and increased ACL strain(p<0.01) (Fig 3) with increasing flexion. Additional anterior load significantly increased IR and ACL strain. An IR load further increased strain; ER resulted in less strain but still higher than the unloaded condition.

Conclusions: "Valgus collapse" has been implicated as an ACL injury mechanism; however, previous studies have shown limited effect of pure valgus on ACL strain. This may have been an effect of the constraints on knee rotation in biomechanical or simulation testing. When the tibia was allowed to freely rotate, valgus load caused increased knee internal rotation and ACL strain. This is consistent with video injury analysis. Combined valgus, internal rotation, and anterior load created even higher ACL strains that could potentially lead to ACL failure.

CONCLUSION(S): Valgus load can cause coupled internal tibial rotation and increased ACL strain. This may be a contributor to ACL injury mechanisms. Avoidance of valgus may help decrease ACL strain and risk of injury.

Keywords:
ACL, strain, valfus
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